RAD18: E3 Ubiquitin-Protein Ligase in DNA Damage Tolerance

Introduction

RAD18 (also known as RNF73, RING finger protein 73) is an E3 ubiquitin-protein ligase that plays a central role in the cellular response to DNA damage, particularly in the DNA damage tolerance (DDT) pathway that allows cells to complete replication despite the presence of DNA lesions [hedglin-2015-regulation-abstract]. The human RAD18 gene was first identified as a homolog of the yeast RAD18, mapping to chromosome 3p24-25, a region frequently deleted in various cancers including lung, breast, ovary, and testis malignancies [tateishi-2000-dysfunction-abstract]. RAD18 functions primarily by catalyzing the monoubiquitination of proliferating cell nuclear antigen (PCNA) at lysine 164, a modification that serves as a molecular switch to recruit specialized translesion synthesis (TLS) polymerases capable of bypassing DNA lesions that would otherwise stall replicative polymerases [watanabe-2004-poleta-abstract].

The protein operates as part of an E2-E3 complex with the ubiquitin-conjugating enzyme RAD6 (also called UBE2A/UBE2B or hHR6), and this partnership is essential for its function in postreplication repair [tateishi-2000-dysfunction-abstract]. Beyond its canonical role in TLS, RAD18 has been implicated in additional DNA repair processes including homologous recombination, double-strand break repair, and the Fanconi anemia pathway, establishing it as a multifunctional coordinator of genome maintenance [huang-2009-hrrrepair-abstract; geng-2010-fanconianemia-abstract]. The enzymatic activity of RAD18 (EC 2.3.2.27) classifies it as a RING-type E3 ubiquitin transferase, and the protein belongs to the RAD18 family of ubiquitin ligases that is conserved across eukaryotes.

Enzymatic Activity and Substrate Specificity

RAD18 functions as an E3 ubiquitin-protein ligase that catalyzes the transfer of ubiquitin from an E2 ubiquitin-conjugating enzyme to specific substrate proteins. The primary and best-characterized substrate of RAD18 is PCNA, specifically at lysine 164 [watanabe-2004-poleta-abstract]. This monoubiquitination event is critical for initiating translesion DNA synthesis in response to replication fork stalling at DNA lesions.

A key mechanistic insight into RAD18 function was provided by structural and biochemical studies demonstrating that the RAD6/RAD18 complex specifically promotes monoubiquitination rather than polyubiquitin chain formation [hibbert-2011-monoubiquitination-abstract]. The E2 enzyme RAD6, when functioning alone, possesses an intrinsic capability for ubiquitin chain synthesis through a noncovalent interaction between ubiquitin and a "backside" binding site on RAD6. However, when RAD6 associates with RAD18, the C-terminal RAD6-binding domain (R6BD) of RAD18 competitively occupies this backside binding site, thereby preventing ubiquitin from binding there and blocking chain formation [hibbert-2011-monoubiquitination-abstract]. This elegant mechanism ensures that PCNA receives only a single ubiquitin moiety, which is the specific signal for TLS polymerase recruitment.

The substrate specificity of RAD18 extends beyond PCNA. Studies have identified 53BP1 as an additional direct substrate of RAD18-mediated ubiquitination [watanabe-2009-53bp1-abstract]. RAD18 monoubiquitinates the kinetochore-binding domain of 53BP1 at lysine 1268, and this modification enhances the chromatin retention of 53BP1 at sites of DNA double-strand breaks during G1 phase. RFC2, a subunit of the replication factor C complex, has also been reported as a RAD18 substrate [hedglin-2015-regulation-abstract]. The identification of multiple substrates indicates that RAD18 coordinates several aspects of the DNA damage response through its ubiquitination activity.

The complex stoichiometry of functional RAD18 has been elucidated through detailed structural analysis. The active complex consists of one RAD6 molecule bound to a RAD18 homodimer, forming a RAD6A-(RAD18)₂ ternary complex [masuda-2012-asymmetric-abstract]. Interestingly, only one of the two RAD6-binding domains in the RAD18 dimer is necessary for complex formation and ligase activity, revealing an asymmetric functional architecture. Similarly, while inactivating mutations in the RING or SAP domains of both RAD18 subunits strongly reduces activity, inactivation in only one subunit has no effect, further supporting the asymmetric model.

Role in Translesion Synthesis and DNA Damage Tolerance

Translesion synthesis represents one of the two major DNA damage tolerance pathways that allow cells to complete DNA replication despite the presence of template lesions. When replicative polymerases encounter DNA damage, they stall, leading to uncoupling between the replicative helicase and polymerase activities. This uncoupling generates extended stretches of single-stranded DNA (ssDNA) that become coated with replication protein A (RPA) [hedglin-2015-regulation-abstract]. The RPA-ssDNA complex serves as the primary signal for RAD18 recruitment to stalled replication forks.

Upon recruitment, RAD18 together with RAD6 catalyzes the monoubiquitination of PCNA at K164. This modified form of PCNA (monoUb-PCNA) has substantially increased affinity for Y-family TLS polymerases, particularly DNA polymerase eta (Polη), compared to unmodified PCNA [watanabe-2004-poleta-abstract]. The enhanced affinity facilitates polymerase exchange at the stalled fork, allowing TLS polymerases to incorporate nucleotides opposite damaged template bases. Although TLS polymerases can replicate past lesions, they lack the proofreading activity of replicative polymerases and are often error-prone, which explains why TLS is associated with damage-induced mutagenesis.

RAD18 participates in TLS polymerase recruitment through two complementary mechanisms [watanabe-2004-poleta-abstract]. First, monoubiquitinated PCNA provides a binding platform for Polη through the polymerase's ubiquitin-binding zinc finger (UBZ) domain. Second, RAD18 directly interacts with Polη through physical protein-protein contact, providing an additional layer of polymerase recruitment that is independent of PCNA modification. Cells lacking RAD18 fail to form Polη nuclear foci following UV irradiation, demonstrating the essential nature of this E3 ligase for TLS initiation.

The regulation of RAD18-dependent TLS is tightly integrated with cell cycle progression through phosphorylation-dependent mechanisms [day-2010-phosphorylation-abstract]. The kinase Cdc7/DDK (Dbf4/Drf1-dependent Cdc7 kinase) phosphorylates RAD18 at a serine-rich "S box" region within its C-terminal domain, with S434 identified as a primary target. This phosphorylation is essential for efficient RAD18-Polη association and the subsequent formation of Polη foci at sites of replication fork stalling. The Cdc7-RAD18 regulatory axis provides a mechanism for coordinating DNA replication progression with postreplication repair.

Beyond TLS, DNA damage tolerance also operates through template switching (TS), an error-free pathway that uses the undamaged sister chromatid as a template for bypass synthesis. While RAD18-dependent PCNA monoubiquitination initiates TLS, this modification can be extended to K63-linked polyubiquitin chains by the Ubc13-Mms2/RAD5 (HLTF and SHPRH in humans) complex, which routes DDT toward the template switching pathway [hedglin-2015-regulation-abstract]. Thus, RAD18 functions at a critical decision point in choosing between error-prone and error-free damage tolerance mechanisms.

It is important to note that while Polη is the most extensively studied TLS polymerase in the context of RAD18, monoubiquitinated PCNA also recruits other Y-family polymerases including Polκ, Polι, and Rev1. Each TLS polymerase exhibits preference for bypass of specific types of DNA damage; for example, Polη is specialized for bypass of UV-induced cyclobutane pyrimidine dimers (CPDs), while Polκ preferentially bypasses benzo[a]pyrene adducts. These polymerases contain ubiquitin-binding domains—UBZ domains in Polη and Polκ, and UBM domains in Polι and Rev1—that mediate their interaction with monoubiquitinated PCNA [yang-2018-tumorigenesis-abstract].

Intriguingly, Polη plays a unique non-catalytic role in promoting PCNA monoubiquitination itself [durando-2013-noncatalytic-abstract]. Polη physically bridges RAD18 and PCNA through its C-terminal domain, facilitating their interaction independently of polymerase catalytic activity. Catalytically inactive Polη mutants can still stimulate PCNA monoubiquitination to levels comparable to wild-type protein. This scaffolding function is specific to Polη among Y-family polymerases, as Polκ and Polι lack this capability. This non-catalytic role has important implications for understanding why xeroderma pigmentosum variant (XPV) patients, who carry mutations in Polη, experience increased mutagenesis—catalytically inactive Polη can still promote recruitment of alternative, more error-prone TLS polymerases.

Domain Structure and Function

RAD18 is a 495 amino acid protein (in humans) containing several functionally distinct domains that coordinate its various activities in DNA damage response. The domain architecture includes an N-terminal RING finger domain, a ubiquitin-binding zinc finger (UBZ4) domain, a SAP (SAF-A/B, Acinus and PIAS) domain, and a C-terminal RAD6-binding domain (R6BD).

The RING finger domain (IPR001841) located at the N-terminus is the catalytic domain responsible for E3 ubiquitin ligase activity. This domain mediates the interaction with the E2 ubiquitin-conjugating enzyme RAD6 and facilitates ubiquitin transfer to substrates [notenboom-2007-domains-abstract]. Structural studies have determined the crystal structure of the homodimeric RAD18 RING domain (PDB: 2Y43), revealing a classical RING-RING dimer that dimerizes through helices adjacent to the RING domains. The RING domain can theoretically recruit two RAD6 molecules, but the full-length RAD18 homodimer binds only a single RAD6 molecule due to constraints imposed by other domains.

The UBZ4 domain (IPR006642) is a C2HC-type zinc finger that functions as a ubiquitin-binding module rather than a DNA-binding domain as initially proposed [notenboom-2007-domains-abstract]. NMR structural studies have determined the structure of the RAD18-UBZ domain both alone (PDB: 2MRF) and in complex with ubiquitin (PDB: 2MRE), revealing that it adopts a β1-β2-α fold and binds ubiquitin with micromolar affinity (Kd approximately 42 μM) [rizzo-2014-ubzstructure-abstract]. The RAD18-UBZ4 interacts with ubiquitin through both its α-helix and β1 strand, distinguishing it from the Polη-UBZ3 domain that uses only the α-helix for binding. This ubiquitin-binding activity is critical for RAD18 accumulation at DNA damage sites, particularly through recognition of RNF8-generated ubiquitin chains at double-strand breaks [huang-2009-hrrrepair-abstract].

The SAP domain (IPR003034) provides DNA-binding activity, with preferential affinity for single-stranded DNA over double-stranded DNA (affinity approximately 1 μM for ssDNA) [notenboom-2007-domains-abstract]. Despite its DNA-binding capability, the SAP domain is not absolutely required for RAD18 accumulation at damage sites but appears crucial for PCNA ubiquitination and Polη focus formation [nakajima-2006-replication-dependent-abstract]. The SAP domain may function by positioning the RAD18 complex appropriately at stalled replication forks where ssDNA is exposed.

The C-terminal RAD6-binding domain (R6BD) provides a second interaction interface with RAD6, distinct from the RING domain interaction [notenboom-2007-domains-abstract]. Importantly, this domain competes with ubiquitin for the backside binding site on RAD6, thereby suppressing polyubiquitin chain formation and ensuring monoubiquitination specificity [hibbert-2011-monoubiquitination-abstract].

Cellular Localization

RAD18 is predominantly a nuclear protein that displays dynamic localization patterns depending on cell cycle phase and DNA damage status. Under normal conditions, RAD18 shows diffuse nuclear distribution, but upon DNA damage, it rapidly accumulates at sites of DNA lesions, forming distinct nuclear foci [nakajima-2006-replication-dependent-abstract].

Following UV irradiation, RAD18 forms numerous nuclear foci (typically >80 per cell) that colocalize extensively with PCNA, consistent with its role at stalled replication forks [nakajima-2006-replication-dependent-abstract]. This UV-induced pattern is replication-dependent and relies on the SAP domain of RAD18. The colocalization with PCNA reflects RAD18's function in monoubiquitinating this replication clamp to initiate translesion synthesis.

In contrast, ionizing radiation (IR) induces a distinct pattern of RAD18 localization. X-ray-induced RAD18 foci are fewer in number (approximately 50 per cell) but larger than UV-induced foci, and they colocalize with γ-H2AX rather than PCNA [nakajima-2006-replication-dependent-abstract]. This pattern reflects RAD18's replication-independent role in double-strand break repair. The IR-induced recruitment depends on the zinc finger domain and occurs through recognition of ubiquitin chains generated by the RNF8/UBC13 system at break sites [huang-2009-hrrrepair-abstract].

The mechanism of RAD18 recruitment differs between these two types of DNA damage. At stalled replication forks, RPA-coated single-stranded DNA serves as the recruitment signal, while at double-strand breaks, RAD18 is recruited through a signaling cascade involving H2AX phosphorylation, MDC1, RNF8, and ubiquitin chain formation. RAD18 colocalizes with chromatin-associated conjugated ubiquitin and ubiquitylated H2A throughout the cell cycle and following irradiation, indicating constitutive association with ubiquitin-modified chromatin.

Cell cycle-specific patterns have also been observed. RAD18 shows distinct localization during G1 phase when it participates in 53BP1-dependent DSB repair, and during S phase when it functions in replication-coupled DNA damage tolerance [watanabe-2009-53bp1-abstract]. Accumulation of RAD18 in nucleoli has been observed in late G2, dependent on its zinc finger domain.

Regulatory Mechanisms

The activity and localization of RAD18 are tightly controlled through multiple regulatory mechanisms including post-translational modifications, protein-protein interactions, and transcriptional regulation.

Phosphorylation represents a key regulatory mechanism for RAD18 function. Cdc7/DDK kinase phosphorylates RAD18 at serine residues within the S box region, with S434 being a major target [day-2010-phosphorylation-abstract]. This phosphorylation enhances RAD18's interaction with Polη and is essential for efficient Polη recruitment to stalled replication forks. The phosphorylation occurs both during normal S phase and is enhanced following UV damage through a Chk1-dependent pathway, integrating RAD18 function with DNA damage checkpoint signaling. Additionally, SLF1 recognizes RAD18 phosphorylated at S442 and S444 through its tandem BRCT domain, facilitating RAD18 accumulation at DNA breaks in post-replicative chromatin.

More recently, O-GlcNAcylation has emerged as another important modification regulating RAD18 function. This modification promotes both translesion DNA synthesis and homologous recombination repair. Importantly, abrogation of RAD18 O-GlcNAcylation limits Cdc7-dependent RAD18 phosphorylation at S434, establishing crosstalk between these two modifications. Reduced O-GlcNAcylation significantly decreases damage-induced PCNA monoubiquitination, impairs Polη focus formation, and enhances UV sensitivity.

RAD18 is also subject to autoubiquitination at multiple lysine residues (K161, K261, K309, K318 in mouse RAD18), which regulates its stability and activity [notenboom-2007-domains-abstract]. Auto-ubiquitination mediated by RAD6 inhibits RAD18 recruitment to DNA breaks, providing a negative feedback mechanism.

Several accessory proteins regulate RAD18 activity at damaged sites. SIVA1 functions as a critical adaptor protein that constitutively interacts with PCNA and directs RAD18 to its substrate [han-2014-siva1-abstract]. SIVA1 binds RAD18 through domains separate from those used to bind PCNA, creating a bridging complex. Cells lacking SIVA1 phenocopy RAD18 deficiency with compromised PCNA monoubiquitination, defective Polη recruitment, increased UV sensitivity, and elevated mutation frequencies.

Other proteins that regulate RAD18 function include NBS1 (mutated in Nijmegen breakage syndrome), which recruits RAD18 to sites of DNA damage through direct binding; Claspin and CHK1, which participate in checkpoint-dependent RAD18 regulation; and chromatin remodeling complexes including Ino80, RSC, and NuRD that modulate chromatin accessibility at damage sites [hedglin-2015-regulation-abstract].

Roles Beyond Translesion Synthesis

While RAD18 is best characterized for its function in translesion synthesis, accumulating evidence demonstrates its participation in additional DNA repair pathways, establishing it as a multifunctional coordinator of genome maintenance.

In double-strand break (DSB) repair, RAD18 plays distinct roles depending on cell cycle phase. During G1, RAD18 promotes DSB repair through a 53BP1-dependent mechanism [watanabe-2009-53bp1-abstract]. RAD18 directly associates with 53BP1 via its zinc finger domain and monoubiquitinates 53BP1 at K1268, enhancing 53BP1 chromatin retention at break sites. Rad18-null cells exhibit impaired DSB repair efficiency and reduced post-irradiation viability. This function appears to promote non-homologous end joining (NHEJ) repair.

During S and G2 phases, RAD18 participates in homologous recombination (HR) repair through a mechanism that involves direct interaction with RAD51C [huang-2009-hrrrepair-abstract]. Importantly, this HR function is independent of RAD18's E3 ligase activity and depends solely on its recruitment to damage sites. RAD18 localizes to DSBs through its zinc finger domain, which binds ubiquitin chains created by the RNF8/UBC13 complex, while the RING domain mediates RAD51C interaction. This reveals how RAD18 functions as a molecular bridge connecting DNA damage checkpoint signaling with repair processes.

RAD18 also plays a significant role in the Fanconi anemia (FA) pathway, which is essential for interstrand crosslink (ICL) repair [geng-2010-fanconianemia-abstract]. RAD18-mediated PCNA ubiquitination recruits FANCL, the E3 ligase of the FA core complex, to chromatin. Monoubiquitinated PCNA then stimulates FANCL-catalyzed monoubiquitination of the FANCI-FANCD2 complex, which is the critical activation step for ICL repair. This establishes PCNA as a regulatory hub coordinating TLS and FA pathway responses to DNA damage.

Beyond these pathway connections, RAD18 directly interacts with FANCD2 independently of the FA core complex and is required for efficient FANCD2 and FANCI chromatin loading [williams-2011-fancd2-abstract]. The E3 ligase activity of RAD18 is necessary for FANCD2 chromatin loading through a mechanism that appears independent of PCNA modification, suggesting additional direct roles for RAD18 in FA pathway regulation. RAD18-deficient cells show increased sensitivity to DNA crosslinking agents including mitomycin C and cisplatin.

Recent work has also implicated RAD18 in suppressing R-loop-mediated genome instability by promoting FANCD2 recruitment to difficult-to-replicate and R-loop-prone genomic sites. This function helps prevent transcription-replication conflicts, expanding RAD18's role as a guardian of genome stability.

Evolutionary Conservation

The RAD6-RAD18 pathway for PCNA modification represents an evolutionarily ancient DNA damage tolerance mechanism that is highly conserved across eukaryotes. The human RAD18 gene was identified through its homology to the Saccharomyces cerevisiae RAD18 gene, and the yeast pathway has served as a foundational model for understanding mammalian DNA damage tolerance [tateishi-2000-dysfunction-abstract].

Human RAD18 encodes a 495-amino acid protein that shares 20% sequence identity and 42% similarity with yeast Rad18, with particularly strong conservation in the functional domains including the RING finger and zinc finger motifs. The mouse ortholog (mRAD18Sc) is 509 amino acids and shows strong conservation with both yeast and human homologs, demonstrating preserved domain architecture across mammals [vanderlaan-2000-mrad18-abstract]. The conservation of the RING-zinc-finger structure and the interaction with RAD6 homologs indicates that the core biochemical mechanism of PCNA monoubiquitination has been maintained throughout eukaryotic evolution.

Functionally orthologous genes have been identified in diverse fungi including Neurospora crassa (uvs-2) and Aspergillus nidulans (nuvA), all sharing the characteristic zinc finger motifs and involvement in DNA repair. Notably, the Schizosaccharomyces pombe rad18 gene is not a true ortholog of S. cerevisiae RAD18 but instead belongs to the SMC family of proteins (the true ortholog is RHC18), illustrating the importance of functional rather than nomenclature-based comparisons.

The conservation of the RAD6-RAD18 pathway extends to the downstream signaling as well. PCNA monoubiquitination at K164, the recruitment of Y-family TLS polymerases, and the extension to K63-linked polyubiquitin chains for template switching are all conserved from yeast to humans, underscoring the fundamental importance of this pathway in maintaining genome stability across evolution.

Clinical Relevance and Role in Cancer

RAD18 has emerged as a significant factor in cancer biology through multiple mechanisms, reflecting its dual nature as both a genome maintenance factor and a potential contributor to mutagenesis [yang-2018-tumorigenesis-abstract]. The human RAD18 gene maps to chromosome 3p24-25, a region frequently deleted in lung, breast, ovarian, and testicular cancers, initially suggesting a tumor suppressor role [tateishi-2000-dysfunction-abstract].

However, the relationship between RAD18 and cancer is complex. RAD18 and the downstream Y-family TLS polymerases confer DNA damage tolerance at the expense of DNA replication fidelity, making them attractive candidate mediators of mutagenesis and carcinogenesis. Consistent with this, RAD18 is pathologically overexpressed in many cancer types including colorectal cancer, triple-negative breast cancer, and lung adenocarcinoma [yang-2018-tumorigenesis-abstract]. One mechanism of RAD18 overexpression involves increased protein stability through binding to MAGE-A4, a cancer/testis antigen that is normally absent in somatic cells but is aberrantly expressed in tumors.

Studies of RAD18 in colorectal cancer (CRC) have demonstrated that high RAD18 expression correlates with lymph node metastasis and poor prognosis. RAD18 overexpression increases the metastatic potential of CRC cells through activation of the epithelial-mesenchymal transition (EMT) pathway. In triple-negative breast cancer (TNBC), RAD18 is highly expressed and inversely related to patient prognosis, promoting cancer stem cell characteristics through the Hippo/YAP signaling pathway.

In vivo studies using mouse models have provided mechanistic insights into RAD18's role in shaping mutational landscapes [lou-2021-mutational-signatures-abstract]. Analysis of carcinogen-induced tumors revealed that Rad18-proficient tumors predominantly display COSMIC mutational signature 22, while Rad18-deficient tumors show features associated with homologous recombination defects (signature 3). Analysis of The Cancer Genome Atlas (TCGA) data demonstrates that RAD18 expression is strongly associated with high single nucleotide variant burdens across multiple human cancer types, suggesting RAD18 promotes mutagenesis in human cancers.

The role of RAD18 in drug resistance has also been documented. In osteosarcoma, RAD18 was identified as a determinant of doxorubicin sensitivity through genome-wide CRISPR screening. Rad18 knockout increased sensitivity to doxorubicin, while overexpression led to resistance, highlighting RAD18 as a potential therapeutic target for overcoming chemoresistance.

Paradoxically, RAD18 can also act as a tumor suppressor in specific contexts. In carcinogen-induced oral cancer models, Rad18 deficiency accelerated tumor onset, with Rad18-null tumors showing increased genomic instability and characteristic mutational patterns. This context-dependent activity reflects the balance between RAD18's role in maintaining genome stability through proper TLS and its contribution to mutagenesis through error-prone polymerase activity.

Open Questions

Despite substantial progress in understanding RAD18 function, several important questions remain:

1. Substrate specificity determinants: While PCNA, 53BP1, and RFC2 have been identified as RAD18 substrates, the full spectrum of RAD18 targets remains incompletely characterized. Understanding how RAD18 achieves substrate selectivity in different cellular contexts requires further investigation.

2. Coordination between pathways: RAD18 participates in TLS, HR, NHEJ, and FA pathways. How the cell coordinates these different activities of RAD18 and directs it toward specific pathways depending on damage type and cell cycle phase remains unclear.

3. Regulatory integration: Multiple modifications regulate RAD18 (phosphorylation, O-GlcNAcylation, auto-ubiquitination), but how these modifications are integrated to produce context-appropriate responses is not fully understood.

4. Tissue-specific functions: The observation that RAD18 maps to a region frequently deleted in various cancers raises questions about potential tissue-specific roles that may be relevant to tumor suppression.

5. Structure of full-length complex: While structures of individual domains are available, a complete structural understanding of the RAD6-(RAD18)₂-PCNA complex and how it achieves substrate monoubiquitination is lacking.

6. Template switching coordination: How RAD18-dependent monoubiquitination is extended to polyubiquitin chains that promote template switching, and how the choice between TLS and TS is made, requires further mechanistic characterization.

7. Alternative E3 ligases: CRL4-Cdt2 can also monoubiquitinate PCNA independently of RAD18 in proliferating cells. The relative contributions and coordination of these alternative pathways in different contexts remains to be determined.

References

• [tateishi-2000-dysfunction-abstract] Tateishi S, Sakuraba Y, Masuyama S, Inoue H, Yamaizumi M. Dysfunction of human Rad18 results in defective postreplication repair and hypersensitivity to multiple mutagens. Proc Natl Acad Sci USA. 2000;97(14):7927-7932. PMID: 10884424. DOI: 10.1073/pnas.97.14.7927

• [watanabe-2004-poleta-abstract] Watanabe K, Tateishi S, Kawasuji M, Tsurimoto T, Inoue H, Yamaizumi M. Rad18 guides poleta to replication stalling sites through physical interaction and PCNA monoubiquitination. EMBO J. 2004;23(19):3886-3896. PMID: 15359278. DOI: 10.1038/sj.emboj.7600383

• [nakajima-2006-replication-dependent-abstract] Nakajima S, Lan L, Kanno S, Usami N, Kobayashi K, Mori M, Shiomi T, Yasui A. Replication-dependent and -independent responses of RAD18 to DNA damage in human cells. J Biol Chem. 2006;281(45):34687-34695. PMID: 16980296. DOI: 10.1074/jbc.M605545200

• [notenboom-2007-domains-abstract] Notenboom V, Hibbert RG, van Rossum-Fikkert SE, Olsen JV, Mann M, Sixma TK. Functional characterization of Rad18 domains for Rad6, ubiquitin, DNA binding and PCNA modification. Nucleic Acids Res. 2007;35(17):5819-5830. PMID: 17720710. DOI: 10.1093/nar/gkm615

• [watanabe-2009-53bp1-abstract] Watanabe K, Iwabuchi K, Sun J, Tsuji Y, Tani T, Tokunaga K, Date T, Hashimoto M, Yamaizumi M, Tateishi S. RAD18 promotes DNA double-strand break repair during G1 phase through chromatin retention of 53BP1. Nucleic Acids Res. 2009;37(7):2176-2193. PMID: 19228710. DOI: 10.1093/nar/gkp082

• [huang-2009-hrrrepair-abstract] Huang J, Huen MSY, Kim H, Leung CCY, Glover JNM, Yu X, Chen J. RAD18 transmits DNA damage signaling to elicit homologous recombination repair. Nat Cell Biol. 2009;11(5):592-603. PMID: 19396164. DOI: 10.1038/ncb1865

• [geng-2010-fanconianemia-abstract] Geng L, Huntoon CJ, Karnitz LM. RAD18-mediated ubiquitination of PCNA activates the Fanconi anemia DNA repair network. J Cell Biol. 2010;191(2):249-257. PMID: 20937699. DOI: 10.1083/jcb.201005101

• [day-2010-phosphorylation-abstract] Day TA, Palle K, Barkley LR, Kakusho N, Zou Y, Tateishi S, Verreault A, Masai H, Vaziri C. Phosphorylated Rad18 directs DNA Polymerase η to sites of stalled replication. J Cell Biol. 2010;191(5):953-966. PMID: 21098111. DOI: 10.1083/jcb.201006043

• [hibbert-2011-monoubiquitination-abstract] Hibbert RG, Huang A, Boelens R, Sixma TK. E3 ligase Rad18 promotes monoubiquitination rather than ubiquitin chain formation by E2 enzyme Rad6. Proc Natl Acad Sci USA. 2011;108(14):5590-5595. PMID: 21422291. DOI: 10.1073/pnas.1017516108

• [williams-2011-fancd2-abstract] Williams SA, Longerich S, Sung P, Vaziri C, Kupfer GM. The E3 ubiquitin ligase RAD18 regulates ubiquitylation and chromatin loading of FANCD2 and FANCI. Blood. 2011;117(19):5078-5087. PMID: 21355096. DOI: 10.1182/blood-2010-10-311761

• [masuda-2012-asymmetric-abstract] Masuda Y, Suzuki M, Kawai H, Suzuki F, Kamiya K. Asymmetric nature of two subunits of RAD18, a RING-type ubiquitin ligase E3, in the human RAD6A-RAD18 ternary complex. Nucleic Acids Res. 2012;40(3):1065-1076. PMID: 21967848. DOI: 10.1093/nar/gkr805

• [rizzo-2014-ubzstructure-abstract] Rizzo AA, Salerno PE, Bezsonova I, Korzhnev DM. NMR structure of the human Rad18 zinc finger in complex with ubiquitin defines a class of UBZ domains in proteins linked to the DNA damage response. Biochemistry. 2014;53(37):5895-5906. PMID: 25162118. DOI: 10.1021/bi500823h

• [han-2014-siva1-abstract] Han J, Liu T, Huen MSY, Hu L, Chen Z, Huang J. SIVA1 directs the E3 ubiquitin ligase RAD18 for PCNA monoubiquitination. J Cell Biol. 2014;205(6):811-827. PMID: 24958773. DOI: 10.1083/jcb.201311007

• [hedglin-2015-regulation-abstract] Hedglin M, Benkovic SJ. Regulation of Rad6/Rad18 Activity During DNA Damage Tolerance. Annu Rev Biophys. 2015;44:207-228. PMID: 26098514. DOI: 10.1146/annurev-biophys-060414-033841

• [vanderlaan-2000-mrad18-abstract] van der Laan R, Roest HP, Hoogerbrugge JW, Smit EM, Slater R, Baarends WM, Hoeijmakers JH, Grootegoed JA. Characterization of mRAD18Sc, a mouse homolog of the yeast postreplication repair gene RAD18. Genomics. 2000;69(1):86-94. PMID: 11013078. DOI: 10.1006/geno.2000.6220

• [durando-2013-noncatalytic-abstract] Durando M, Tateishi S, Vaziri C. A non-catalytic role of DNA polymerase η in recruiting Rad18 and promoting PCNA monoubiquitination at stalled replication forks. Nucleic Acids Res. 2013;41(5):3079-3093. PMID: 23345618. DOI: 10.1093/nar/gkt016

• [yang-2018-tumorigenesis-abstract] Yang Y, Gao Y, Zlatanou A, Tateishi S, Yurchenko V, Rogozin IB, Vaziri C. Diverse roles of RAD18 and Y-family DNA polymerases in tumorigenesis. Cell Cycle. 2018;17(7):833-843. PMID: 29683380. DOI: 10.1080/15384101.2018.1456296

• [lou-2021-mutational-signatures-abstract] Lou J, Yang Y, Gu Q, Price BA, Qiu Y, Fedoriw Y, Desai S, Mose LE, Chen B, Tateishi S, Parker JS, Vaziri C, Wu D. Rad18 mediates specific mutational signatures and shapes the genomic landscape of carcinogen-induced tumors in vivo. NAR Cancer. 2021;3(1):zcaa037. PMID: 33447826. DOI: 10.1093/narcan/zcaa037

Citations

1. day-2010-phosphorylation-abstract.md
2. durando-2013-noncatalytic-abstract.md
3. geng-2010-fanconianemia-abstract.md
4. han-2014-siva1-abstract.md
5. hedglin-2015-regulation-abstract.md
6. hibbert-2011-monoubiquitination-abstract.md
7. huang-2009-hrrrepair-abstract.md
8. lou-2021-mutational-signatures-abstract.md
9. masuda-2012-asymmetric-abstract.md
10. nakajima-2006-replication-dependent-abstract.md
11. notenboom-2007-domains-abstract.md
12. rizzo-2014-ubzstructure-abstract.md
13. tateishi-2000-dysfunction-abstract.md
14. vanderlaan-2000-mrad18-abstract.md
15. watanabe-2004-poleta-abstract.md
16. watanabe-2009-53bp1-abstract.md
17. williams-2011-fancd2-abstract.md
18. yang-2018-tumorigenesis-abstract.md

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Comprehensive research report: Human RAD18 (UniProt Q9NS91)

Verification and identity
- Gene/protein: RAD18 (RNF73), human E3 ubiquitin-protein ligase; UniProt Q9NS91. Recent human studies consistently examine RAD18 as the principal E3 ligase catalyzing PCNA Lys164 monoubiquitination in DNA damage tolerance pathways, matching the UniProt description and domain architecture, with no conflicting gene symbol usage detected (ma2024rad18oglcnacylationpromotes pages 1-2, chen2024atrlimitsrad18mediated pages 1-2, khatib2024parp10promotesthe pages 1-2).

Key concepts and definitions
- Primary biochemical function: RAD18 is a RING-type E3 ubiquitin ligase that, with its E2 partner RAD6, catalyzes monoubiquitination of the replication clamp PCNA at Lys164, initiating translesion DNA synthesis (TLS) and coordinating downstream damage tolerance decisions. This modification recruits TLS polymerases (e.g., REV1/Polη) and can be extended to K63-linked chains for template switching, linking to recombination-based bypass and fork protection (Oct 2023; Bioscience Reports; Jul 2024; Nature Communications) (xia2023implicationsofubiquitination pages 10-11, khatib2024parp10promotesthe pages 1-2). URLS: https://doi.org/10.1042/bsr20222591; https://doi.org/10.1038/s41467-024-50429-3.
- Core domains and roles: RAD18 contains a catalytic RING domain (E3 function), a UBZ domain that binds ubiquitin and contributes to damage-site targeting, a SAP domain implicated in DNA/chromatin binding, and a PCNA-interacting motif (PIP) recently mapped adjacent to Ser403; the PIP-like region mediates RAD18–PCNA interaction and is subject to regulation (May 2024; Cell Death & Disease; Mar 2024; EMBO Journal) (ma2024rad18oglcnacylationpromotes pages 1-2, chen2024atrlimitsrad18mediated pages 1-2). URLS: https://doi.org/10.1038/s41419-024-06700-y; https://doi.org/10.1038/s44318-024-00066-9.

Localization and pathway context
- Cellular localization: RAD18 accumulates at stalled replication forks and at RPA-coated ssDNA regions during replication stress; it is also recruited to nascent strand gaps where it ubiquitinates PCNA to enable TLS-mediated gap filling. RAD18’s activity influences replication fork stability, and at telomeres (ALT cells), ATR-modulated RAD18 activity controls PCNA ubiquitination to preserve telomere integrity (Mar 2024; EMBO Journal; Jul 2024; Nature Communications; Oct 2023; Bioscience Reports) (chen2024atrlimitsrad18mediated pages 1-2, khatib2024parp10promotesthe pages 1-2, xia2023implicationsofubiquitination pages 5-7). URLS: https://doi.org/10.1038/s44318-024-00066-9; https://doi.org/10.1038/s41467-024-50429-3; https://doi.org/10.1042/bsr20222591.
- Pathway roles: RAD18 is central to DNA damage tolerance (DDT). PCNA K164 monoubiquitination triggers TLS polymerase engagement; subsequent K63-linked polyubiquitination coordinates template switching and fork remodeling, which support fork stability and damage bypass. RAD18 also participates in crosstalk with the Fanconi anemia (FA) pathway (FANCD2/FANCI ubiquitination and chromatin loading) and HR-associated mechanisms, thereby shaping repair pathway choice during replication stress (Oct 2023; Bioscience Reports; Mar 2024; EMBO Journal; May 2024; Cell Death & Disease) (xia2023implicationsofubiquitination pages 10-11, chen2024atrlimitsrad18mediated pages 1-2, ma2024rad18oglcnacylationpromotes pages 1-2). URLS: https://doi.org/10.1042/bsr20222591; https://doi.org/10.1038/s44318-024-00066-9; https://doi.org/10.1038/s41419-024-06700-y.

Recent developments and latest research (priority 2023–2024)
- ATR constrains RAD18 activity at forks and telomeres: ATR phosphorylates RAD18 at Ser403 adjacent to a PIP motif, weakening RAD18–PCNA interaction and limiting PCNA monoubiquitination. This prevents excessive SLX4 accumulation at stalled forks and protects fork integrity; in ALT cells, this preserves telomere stability. ATR inhibition (VE‑821) or knockdown increases PCNA monoubiquitination after HU, aphidicolin, or UV (Mar 2024; EMBO Journal) (chen2024atrlimitsrad18mediated pages 1-2). URL: https://doi.org/10.1038/s44318-024-00066-9.
- O-GlcNAcylation tunes RAD18’s recruitment and activity: Human RAD18 is O-GlcNAcylated at Ser130/Ser164/Thr468. These modifications promote RAD18 accumulation at damage sites and enable CDC7-dependent RAD18 Ser434 phosphorylation, which supports damage-induced PCNA monoubiquitination, Polη focus formation, and TLS efficiency. Mutating these sites (S130A/S164A/T468A) reduces PCNA monoubiquitination, impairs Polη foci, and increases UV sensitivity; O-GlcNAcylation also enhances RAD18’s contribution to HR through RAD51C/ubiquitin interactions and RAD51 loading, reducing CPT hypersensitivity (May 2024; Cell Death & Disease) (ma2024rad18oglcnacylationpromotes pages 1-2). URL: https://doi.org/10.1038/s41419-024-06700-y.
- PARP10 recruits RAD18 to gaps for REV1-dependent filling: PARP10 interacts with RAD18 and recruits it to nascent ssDNA gaps, leading to PCNA monoubiquitination and REV1 recruitment for gap filling in G2. PARP10’s catalytic activity and PIP-box-mediated interaction with PCNA are required; in BRCA-deficient cells, PARP10 is hyperactive, and its inactivation increases gap accumulation and cytotoxicity (Jul 2024; Nature Communications) (khatib2024parp10promotesthe pages 1-2). URL: https://doi.org/10.1038/s41467-024-50429-3.
- Alternative E3 for PCNA in unperturbed replication: BRCA1/BARD1 ubiquitinates PCNA independently of RAD18 under unperturbed conditions to prevent ssDNA gaps and promote continuous DNA synthesis, indicating PCNA ubiquitination control extends beyond the canonical RAD18–RAD6 axis (May 2024; Nature Communications) (salaslloret2024brca1bard1ubiquitinatespcna pages 1-2). URL: https://doi.org/10.1038/s41467-024-48427-6.

Current applications and real-world implementations
- Therapeutic targeting of RAD18/RAD6 axis and associated regulators: Reviews highlight the RAD18–RAD6 pathway as a tractable therapeutic target for modulating DDT and replication fork stability. Overexpression of RAD18 is reported across several cancers and is linked to therapy resistance phenotypes; efforts include targeting E2/E3 interfaces and deubiquitinases such as USP1 that counteract PCNA-Ub (Oct 2023; Bioscience Reports) (xia2023implicationsofubiquitination pages 10-11, xia2023implicationsofubiquitination pages 18-19). URL: https://doi.org/10.1042/bsr20222591.
- Vulnerabilities in BRCA-deficient settings: The RAD18-dependent gap-filling axis (via PARP10→RAD18→PCNA-Ub→REV1) mitigates nascent strand gaps in BRCA-deficient cells; inhibition of PARP10 or disruption of RAD18 recruitment sensitizes these cells, suggesting combination strategies with DNA damaging agents (Jul 2024; Nature Communications) (khatib2024parp10promotesthe pages 1-2). URL: https://doi.org/10.1038/s41467-024-50429-3.

Expert opinions and authoritative analyses
- A 2023 expert review synthesizes how ubiquitination, including RAD18-mediated PCNA modification, orchestrates replication fork stabilization and DDT signaling, emphasizing translational opportunities in oncology by modulating E2/E3/DUB activities and repair-pathway crosstalk (Oct 2023; Bioscience Reports) (xia2023implicationsofubiquitination pages 10-11, xia2023implicationsofubiquitination pages 5-7, xia2023implicationsofubiquitination pages 18-19). URL: https://doi.org/10.1042/bsr20222591.
- Primary 2024 studies deliver mechanistic consensus: ATR acts as a brake on RAD18 at stalled forks and ALT telomeres; O-GlcNAc/PTM crosstalk tunes RAD18’s recruitment and function; and PCNA ubiquitination can be executed by BRCA1/BARD1 in the absence of stress, refocusing the field on the context-specific regulation of PCNA-Ub beyond the canonical RAD18 pathway (Mar–Jul 2024; EMBO Journal; Cell Death & Disease; Nature Communications) (chen2024atrlimitsrad18mediated pages 1-2, ma2024rad18oglcnacylationpromotes pages 1-2, khatib2024parp10promotesthe pages 1-2, salaslloret2024brca1bard1ubiquitinatespcna pages 1-2). URLS: https://doi.org/10.1038/s44318-024-00066-9; https://doi.org/10.1038/s41419-024-06700-y; https://doi.org/10.1038/s41467-024-50429-3; https://doi.org/10.1038/s41467-024-48427-6.

Relevant statistics and data from recent studies
- ATR inhibition elevates PCNA K164 monoubiquitination in multiple stress contexts (HU, aphidicolin, UV), consistent with ATR’s S403 phosphorylation limiting RAD18–PCNA binding (Mar 2024; EMBO Journal) (chen2024atrlimitsrad18mediated pages 1-2). URL: https://doi.org/10.1038/s44318-024-00066-9.
- Defined genotoxic conditions used for gap-induction and repair: PARP10→RAD18 axis tested under 0.4 mM hydroxyurea and 150 μM cisplatin; PARP10 catalytic activity and PCNA interaction are required for REV1 recruitment and gap filling (Jul 2024; Nature Communications) (khatib2024parp10promotesthe pages 1-2). URL: https://doi.org/10.1038/s41467-024-50429-3.
- RAD18 PTM mutants alter sensitivity and repair outputs: An O-GlcNAc-deficient RAD18 mutant (S130A/S164A/T468A) reduces damage-induced PCNA monoubiquitination, impairs Polη focus formation, and increases cellular sensitivity to UV; O-GlcNAcylation promotes RAD18’s contribution to HR, lowering CPT hypersensitivity via improved RAD51 loading (May 2024; Cell Death & Disease) (ma2024rad18oglcnacylationpromotes pages 1-2). URL: https://doi.org/10.1038/s41419-024-06700-y.
- Cell-type specific roles in recombination control: RAD18 loss elevates hyper-recombination phenotypes (sister chromatid exchange, gene conversion) in some human cell lines (e.g., HCT116) and these effects are linked to defective PCNA K164 ubiquitination, underscoring context-specific RAD18 functions (Jan 2025; Biomolecules) (rogers2025celltypespecific pages 1-2). URL: https://doi.org/10.3390/biom15010150.

Mechanistic synthesis: substrate specificity and reaction
- Enzymatic reaction: RAD18 transfers ubiquitin from E2 RAD6 to PCNA (Lys164), predominantly forming mono-ubiquitinated PCNA (mUb-PCNA) that acts as a platform for TLS polymerases; RAD18 thereby controls the switch from replicative to specialized polymerases at damaged templates and in post-replicative gap filling (Oct 2023; Bioscience Reports; Jul 2024; Nature Communications) (xia2023implicationsofubiquitination pages 10-11, khatib2024parp10promotesthe pages 1-2). URLS: https://doi.org/10.1042/bsr20222591; https://doi.org/10.1038/s41467-024-50429-3.
- Recruitment logic: RAD18 is targeted to sites of replication stress by RPA-coated ssDNA and by adapter/regulator proteins such as PARP10. ATR signaling modulates RAD18–PCNA interaction via S403 phosphorylation to prevent over-ubiquitination and excessive SLX4 accumulation, preserving fork/telomere integrity in ALT contexts (Mar 2024; EMBO Journal; Jul 2024; Nature Communications) (chen2024atrlimitsrad18mediated pages 1-2, khatib2024parp10promotesthe pages 1-2). URLS: https://doi.org/10.1038/s44318-024-00066-9; https://doi.org/10.1038/s41467-024-50429-3.
- PTM crosstalk: O-GlcNAcylation of RAD18 (S130/S164/T468) facilitates subsequent CDC7-dependent S434 phosphorylation, supporting optimal PCNA monoubiquitination and efficient TLS/HR (May 2024; Cell Death & Disease) (ma2024rad18oglcnacylationpromotes pages 1-2). URL: https://doi.org/10.1038/s41419-024-06700-y.
- Alternative E3 activity on PCNA: In unperturbed replication, BRCA1/BARD1 can ubiquitinate PCNA independently of RAD18 to prevent replication-associated ssDNA gaps, indicating layered control of PCNA ubiquitination in different cellular contexts (May 2024; Nature Communications) (salaslloret2024brca1bard1ubiquitinatespcna pages 1-2). URL: https://doi.org/10.1038/s41467-024-48427-6.

Embedding: Evidence map
| Aspect | Key finding / definition | Mechanism / details | Evidence (Year; Journal) | URL |
|---|---|---:|---|---|
| Identity / organism | Human RAD18 (UniProt Q9NS91), E3 ubiquitin ligase involved in DNA damage tolerance | Member of RAD18 family; RING-type E3 ligase annotation (EC 2.3.2.27) | 2024; Cell Death & Disease; 2024; EMBO J (ma2024rad18oglcnacylationpromotes pages 1-2, chen2024atrlimitsrad18mediated pages 1-2) | https://doi.org/10.1038/s41419-024-06700-y, https://doi.org/10.1038/s44318-024-00066-9 |
| Domains (RING, UBZ, SAP, PIP) & roles | RING = catalytic E3 activity; UBZ = ubiquitin-binding/targeting to lesions; SAP = DNA/chromatin interactions; PIP-like motif adjacent to Ser403 mediates PCNA contact | Domain architecture guides recruitment to damage, ubiquitin recognition, and PCNA engagement (PIP adjacent to ATR-phosphorylated S403) | 2024; Cell Death & Disease; 2024; EMBO J (ma2024rad18oglcnacylationpromotes pages 1-2, chen2024atrlimitsrad18mediated pages 1-2) | https://doi.org/10.1038/s41419-024-06700-y, https://doi.org/10.1038/s44318-024-00066-9 |
| Enzymatic function | Catalyzes monoubiquitination of PCNA at Lys164 (with E2 RAD6) to initiate TLS; can influence FANCI/FANCD2 signalling | RAD18–RAD6 conjugates single ubiquitin onto PCNA K164 → recruits Y-family TLS polymerases or supports extension to K63-linked chains for template switching | 2024; Nat Commun; 2023; Biosci Reports (khatib2024parp10promotesthe pages 1-2, xia2023implicationsofubiquitination pages 10-11) | https://doi.org/10.1038/s41467-024-50429-3, https://doi.org/10.1042/bsr20222591 |
| Recruitment / localization | Localizes to stalled forks and ssDNA regions coated by RPA; recruited to nascent-gap structures by adapter factors | Recruitment aided by adapter proteins (e.g., PARP10 recruits RAD18 to gaps); interplay with PCNA, RPA, and upstream sensors at forks; RAD18 activity regulated at telomeres/ALT | 2024; Nat Commun; 2024; EMBO J (khatib2024parp10promotesthe pages 1-2, chen2024atrlimitsrad18mediated pages 1-2) | https://doi.org/10.1038/s41467-024-50429-3, https://doi.org/10.1038/s44318-024-00066-9 |
| Pathway roles | Central regulator of DNA damage tolerance: TLS initiation, template switching, crosstalk with HR and fork stability mechanisms | mUb-PCNA (K164) promotes TLS polymerase recruitment; K63 extension/template switching connects to fork reversal and recombination-based bypass; RAD18 also impacts FA pathway ubiquitination and fork protection | 2023-2024; Biosci Reports; EMBO J; Cell Death & Disease (xia2023implicationsofubiquitination pages 10-11, chen2024atrlimitsrad18mediated pages 1-2, ma2024rad18oglcnacylationpromotes pages 1-2) | https://doi.org/10.1042/bsr20222591, https://doi.org/10.1038/s44318-024-00066-9, https://doi.org/10.1038/s41419-024-06700-y |
| Recent regulation (2023–2024) | Multiple PTMs and alternative E3s modulate PCNA ubiquitination and RAD18 activity: ATR phosphorylation (S403) limits RAD18–PCNA binding; O-GlcNAcylation (S130/S164/T468) promotes RAD18 accumulation; PARP10 recruits RAD18 to gaps; BRCA1/BARD1 can ubiquitinate PCNA in unperturbed replication independently of RAD18 | ATR phosphorylates S403 adjacent to a PIP motif to restrict RAD18–PCNA interaction; O-GlcNAcylation enables CDC7-dependent S434 phosphorylation → supports PCNA mUb; PARP10→RAD18 recruits REV1 for gap-filling; BRCA1/BARD1 adds another layer of PCNA ubiquitination control | 2024; EMBO J; 2024; Cell Death & Disease; 2024; Nat Commun; 2024; Nat Commun (chen2024atrlimitsrad18mediated pages 1-2, ma2024rad18oglcnacylationpromotes pages 1-2, khatib2024parp10promotesthe pages 1-2, salaslloret2024brca1bard1ubiquitinatespcna pages 1-2) | https://doi.org/10.1038/s44318-024-00066-9, https://doi.org/10.1038/s41419-024-06700-y, https://doi.org/10.1038/s41467-024-50429-3, https://doi.org/10.1038/s41467-024-48427-6 |
| Disease / therapy relevance | RAD18 is frequently overexpressed in diverse cancers and implicated in chemoresistance; RAD18/RAD6 axis is a therapeutic target to sensitize tumours; BRCA-deficient contexts depend on gap-filling pathways involving RAD18 | Overexpression correlates with progression and therapy resistance (e.g., cisplatin resistance, TNBC RAD6/RAD18 signalling); PARP10 inhibition or RAD6/RAD18 targeting sensitizes BRCA-deficient or gap-prone tumours | 2023-2024; Biosci Reports; 2024; Nat Commun (xia2023implicationsofubiquitination pages 10-11, khatib2024parp10promotesthe pages 1-2, salaslloret2024brca1bard1ubiquitinatespcna pages 1-2) | https://doi.org/10.1042/bsr20222591, https://doi.org/10.1038/s41467-024-50429-3, https://doi.org/10.1038/s41467-024-48427-6 |
| Quantitative / experimental highlights | ATR inhibition increases PCNA monoubiquitination; RAD18 PTM mutants reduce damage-induced PCNA mUb and increase UV/CPT sensitivity; PARP10→RAD18 recruitment increases REV1-dependent gap filling under cisplatin/HU | Chen 2024: ATR inhibition (VE-821) or knockdown → elevated PCNA-Ub after HU/APH/UV; Ma 2024: RAD18 (3A) PTM mutant → reduced PCNA mUb, impaired Polη foci, increased UV sensitivity; Khatib 2024: PARP10 catalytic requirement for REV1 recruitment and gap filling under defined genotoxin doses (cisplatin, HU) | 2024; EMBO J; 2024; Cell Death & Disease; 2024; Nat Commun (chen2024atrlimitsrad18mediated pages 1-2, ma2024rad18oglcnacylationpromotes pages 1-2, khatib2024parp10promotesthe pages 1-2) | https://doi.org/10.1038/s44318-024-00066-9, https://doi.org/10.1038/s41419-024-06700-y, https://doi.org/10.1038/s41467-024-50429-3 |

Table: A compact evidence map (2023–2024) summarizing RAD18 identity, domains, enzymatic activity, recruitment, pathway roles, recent regulatory mechanisms, disease relevance, and key experimental highlights with source links for rapid reference.

Notes on ambiguity and domain alignment
- The literature surveyed explicitly studies human RAD18 and is consistent with the UniProt entry (RING-type E3 ligase; UBZ, SAP domains; and a functional PIP motif proximal to S403). No conflicting gene symbol usage or organism mismatch was found in recent sources (ma2024rad18oglcnacylationpromotes pages 1-2, chen2024atrlimitsrad18mediated pages 1-2, khatib2024parp10promotesthe pages 1-2).

References (URLs and dates)
- Ma et al., Cell Death & Disease, May 2024. RAD18 O-GlcNAcylation promotes TLS and HR. https://doi.org/10.1038/s41419-024-06700-y (ma2024rad18oglcnacylationpromotes pages 1-2).
- Xia et al., Bioscience Reports, Oct 2023. Ubiquitination and replication fork stability in cancer therapy; RAD18–RAD6 axis overview, cancer relevance. https://doi.org/10.1042/bsr20222591 (xia2023implicationsofubiquitination pages 10-11, xia2023implicationsofubiquitination pages 5-7, xia2023implicationsofubiquitination pages 18-19).
- Chen et al., EMBO Journal, Mar 2024. ATR limits RAD18-mediated PCNA monoubiquitination; S403 phosphorylation near PIP. https://doi.org/10.1038/s44318-024-00066-9 (chen2024atrlimitsrad18mediated pages 1-2).
- Khatib et al., Nature Communications, Jul 2024. PARP10 recruits RAD18 to nascent gaps → PCNA-Ub → REV1. https://doi.org/10.1038/s41467-024-50429-3 (khatib2024parp10promotesthe pages 1-2).
- Salas-Lloret et al., Nature Communications, May 2024. BRCA1/BARD1 ubiquitinates PCNA independently of RAD18 in unperturbed replication. https://doi.org/10.1038/s41467-024-48427-6 (salaslloret2024brca1bard1ubiquitinatespcna pages 1-2).
- Rogers et al., Biomolecules, Jan 2025. Cell type-specific suppression of hyper-recombination by RAD18 linked to PCNA K164 ubiquitination. https://doi.org/10.3390/biom15010150 (rogers2025celltypespecific pages 1-2).

References

1. (ma2024rad18oglcnacylationpromotes pages 1-2): Xiaolu Ma, Hui Fu, Chenyi Sun, Wei Wu, Wenya Hou, Zibin Zhou, Hui Zheng, Yifei Gong, Honglin Wu, Junying Qin, Huiqiang Lou, Jing Li, Tie-Shan Tang, and Caixia Guo. Rad18 o-glcnacylation promotes translesion dna synthesis and homologous recombination repair. Cell Death & Disease, May 2024. URL: https://doi.org/10.1038/s41419-024-06700-y, doi:10.1038/s41419-024-06700-y. This article has 9 citations and is from a peer-reviewed journal.

2. (chen2024atrlimitsrad18mediated pages 1-2): Siyuan Chen, Chen Pan, Jun Huang, and Tingting Liu. Atr limits rad18-mediated pcna monoubiquitination to preserve replication fork and telomerase-independent telomere stability. The EMBO Journal, 43:1301-1324, Mar 2024. URL: https://doi.org/10.1038/s44318-024-00066-9, doi:10.1038/s44318-024-00066-9. This article has 12 citations.

3. (khatib2024parp10promotesthe pages 1-2): Jude B. Khatib, Ashna Dhoonmoon, George-Lucian Moldovan, and Claudia M. Nicolae. Parp10 promotes the repair of nascent strand dna gaps through rad18 mediated translesion synthesis. Nature Communications, Jul 2024. URL: https://doi.org/10.1038/s41467-024-50429-3, doi:10.1038/s41467-024-50429-3. This article has 14 citations and is from a highest quality peer-reviewed journal.

4. (xia2023implicationsofubiquitination pages 10-11): Donghui Xia, Xuefei Zhu, Ying Wang, Peng Gong, Hong-Shu Su, and Xingzhi Xu. Implications of ubiquitination and the maintenance of replication fork stability in cancer therapy. Bioscience Reports, Oct 2023. URL: https://doi.org/10.1042/bsr20222591, doi:10.1042/bsr20222591. This article has 2 citations and is from a peer-reviewed journal.

5. (xia2023implicationsofubiquitination pages 5-7): Donghui Xia, Xuefei Zhu, Ying Wang, Peng Gong, Hong-Shu Su, and Xingzhi Xu. Implications of ubiquitination and the maintenance of replication fork stability in cancer therapy. Bioscience Reports, Oct 2023. URL: https://doi.org/10.1042/bsr20222591, doi:10.1042/bsr20222591. This article has 2 citations and is from a peer-reviewed journal.

6. (salaslloret2024brca1bard1ubiquitinatespcna pages 1-2): Daniel Salas-Lloret, Néstor García-Rodríguez, Emily Soto-Hidalgo, Lourdes González-Vinceiro, Carmen Espejo-Serrano, Lisanne Giebel, María Luisa Mateos-Martín, Arnoud H. de Ru, Peter A. van Veelen, Pablo Huertas, Alfred C. O. Vertegaal, and Román González-Prieto. Brca1/bard1 ubiquitinates pcna in unperturbed conditions to promote continuous dna synthesis. Nature Communications, May 2024. URL: https://doi.org/10.1038/s41467-024-48427-6, doi:10.1038/s41467-024-48427-6. This article has 14 citations and is from a highest quality peer-reviewed journal.

7. (xia2023implicationsofubiquitination pages 18-19): Donghui Xia, Xuefei Zhu, Ying Wang, Peng Gong, Hong-Shu Su, and Xingzhi Xu. Implications of ubiquitination and the maintenance of replication fork stability in cancer therapy. Bioscience Reports, Oct 2023. URL: https://doi.org/10.1042/bsr20222591, doi:10.1042/bsr20222591. This article has 2 citations and is from a peer-reviewed journal.

8. (rogers2025celltypespecific pages 1-2): Colette B. Rogers, Wendy Leung, Ryan M. Baxley, Rachel E. Kram, Liangjun Wang, Joseph P. Buytendorp, Khoi Le, David A. Largaespada, Eric A. Hendrickson, and Anja-Katrin Bielinsky. Cell type specific suppression of hyper-recombination by human rad18 is linked to proliferating cell nuclear antigen k164 ubiquitination. Biomolecules, 15:150, Jan 2025. URL: https://doi.org/10.3390/biom15010150, doi:10.3390/biom15010150. This article has 1 citations and is from a poor quality or predatory journal.

Citations

1. rogers2025celltypespecific pages 1-2
2. xia2023implicationsofubiquitination pages 10-11
3. xia2023implicationsofubiquitination pages 5-7
4. xia2023implicationsofubiquitination pages 18-19
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6. https://doi.org/10.1038/s41467-024-50429-3.
7. https://doi.org/10.1038/s41419-024-06700-y;
8. https://doi.org/10.1038/s44318-024-00066-9.
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RAD18 – Overview and Key Functions

RAD18 is a human gene encoding an E3 ubiquitin-protein ligase critical for DNA damage tolerance and repair. The RAD18 protein (UniProt Q9NS91) contains a RING-finger domain that confers E3 ligase activity, a SAP domain for DNA binding, and a ubiquitin-binding zinc-finger (UBZ) domain (www.nature.com) (pmc.ncbi.nlm.nih.gov). These domains enable RAD18 to recognize stalled DNA replication sites and coordinate the post-replication repair (PRR) pathway. RAD18 is conserved from yeast to humans and interacts with the E2 ubiquitin-conjugating enzyme RAD6 (also known as UBE2A/B in humans) (www.ncbi.nlm.nih.gov). Together, the RAD18–RAD6 complex monoubiquitinates proliferating cell nuclear antigen (PCNA) on Lysine-164 of PCNA (www.nature.com). PCNA is a DNA-sliding clamp and a master coordinator of replication and repair proteins at replication forks (pmc.ncbi.nlm.nih.gov). By tagging PCNA with ubiquitin, RAD18 acts as a molecular switch that prevents replication fork collapse, allowing cells to tolerate DNA damage during S phase (pmc.ncbi.nlm.nih.gov). This post-replication “damage tolerance” mechanism is distinct from direct DNA repair: rather than immediately fixing a DNA lesion, RAD18-mediated PCNA ubiquitination permits DNA synthesis to continue past the lesion, avoiding deadly fork stalling (pmc.ncbi.nlm.nih.gov).

Role in DNA Damage Tolerance – Translesion Synthesis and Template Switching

Translesion DNA Synthesis (TLS): The primary function of RAD18 is to trigger TLS, a process by which specialized DNA polymerases replicate across damaged DNA templates. Upon DNA damage (e.g. UV-induced lesions), RAD18-RAD6 adds a single ubiquitin to PCNA (monoubiquitination), which creates a docking signal for Y-family TLS polymerases such as Polη (eta) and Polκ (kappa) (www.nature.com) (www.nature.com). These polymerases have low-fidelity but can accommodate distorted DNA bases, allowing replication to bypass lesions (www.nature.com). TLS is error-prone, often introducing mutations, but it is vital for avoiding acute replication failure. For example, cells lacking RAD18 cannot ubiquitinate PCNA after UV damage and fail to recruit Polη, leading to stalled replication and hypersensitivity to UV (www.ncbi.nlm.nih.gov) (www.nature.com). A landmark study in yeast first linked RAD6–RAD18 to PCNA ubiquitination as the key step in DNA damage tolerance (pmc.ncbi.nlm.nih.gov), a finding later confirmed in human cells (www.nature.com). In human fibroblasts, RAD18 knockouts display defective replication on UV-damaged templates and increased chromosomal breaks, underscoring RAD18’s role in maintaining fork progression (www.ncbi.nlm.nih.gov). Consistently, RAD18-deficient mouse cells show elevated genomic instability and mutagen sensitivity (pmc.ncbi.nlm.nih.gov).

Template Switching (Error-Free PRR): In addition to TLS, RAD18-initiated PCNA ubiquitination can be channeled into an error-free damage bypass pathway. Monoubiquitin on PCNA can be extended into a Lys-63–linked polyubiquitin chain by other E3 ligases (in yeast, Rad5; in human, HLTF and SHPRH) (www.nature.com). This polyubiquitinated PCNA promotes a template switching mechanism, where the replication machinery bypasses the lesion by using the newly synthesized sister chromatid as a template instead of the damaged strand. Template switching avoids mutations and complements the TLS pathway. RAD18 is required for this process as the initiator of PCNA ubiquitination, even though the extension to polyubiquitin involves additional factors (www.nature.com). Through TLS and template switching, RAD18 safeguards replication: it allows cells to tolerate DNA lesions during S phase, deferring repair to after replication. A 2024 report in Nucleic Acids Research succinctly stated that RAD18 “prevents replication fork collapse by promoting DNA translesion synthesis and template switching,” highlighting its dual role in these tolerance pathways (pmc.ncbi.nlm.nih.gov).

Molecular Mechanism and Interactions

PCNA Ubiquitination Reaction: RAD18 functions as a RING-type E3 ligase that works with the E2 enzyme RAD6. RAD18 directly binds RAD6 via a conserved RING/Rad6-binding domain and facilitates transfer of ubiquitin from RAD6 to PCNA (pubmed.ncbi.nlm.nih.gov). Notably, human RAD18 specifically ubiquitinates PCNA at K164, and this modification is absolutely dependent on RAD18-RAD6 in vivo (www.nature.com). In biochemical assays, the RAD18/RAD6 complex predominantly catalyzes monoubiquitination rather than polyubiquitin chain formation (pubmed.ncbi.nlm.nih.gov). Structural studies indicate RAD18 likely forms a homo-dimer and encircles DNA together with PCNA and RAD6, ensuring ubiquitin is attached to PCNA’s DNA-bound form (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). RAD18 contains a SAP domain (a DNA-binding motif) that preferentially binds single-stranded DNA, helping target the ligase to stalled replication forks where stretches of single-stranded DNA accumulate (pmc.ncbi.nlm.nih.gov). This targeting is enhanced by RAD18’s UBZ domain, which can bind ubiquitin — a recent study showed RAD18’s UBZ domain recognizes ubiquitinated chromatin marks at damage sites (pmc.ncbi.nlm.nih.gov). Indeed, recruitment of RAD18 to sites of stalled replication involves RPA-coated ssDNA and possibly pre-existing ubiquitinated proteins. For example, both ATR kinase activation and RAD18 loading are triggered by RPA-ssDNA, suggesting RAD18 scans replication protein A filaments for fork distress signals (www.embopress.org). Once localized, RAD18 ubiquitinates PCNA, which in turn attracts TLS polymerases that also carry ubiquitin-binding motifs (UBM/UBZ in Polη, Polκ) (www.nature.com).

Key Interactions: Beyond PCNA and RAD6, RAD18 interacts with multiple genome maintenance proteins. It physically associates with REV1/Polη in cells to facilitate polymerase switch during TLS (www.nature.com). Intriguingly, RAD18 also binds the recombination factor RAD51C, a paralog of RAD51, and helps localize RAD51C to DNA breaks (www.nature.com) (www.nature.com). This suggests RAD18 serves as a hub connecting replication stress tolerance to homologous recombination (HR) repair. Regulatory proteins modulate RAD18’s activity via binding: for instance, the MAGEA4 oncoprotein (a cancer-testis antigen) binds directly to RAD18’s C-terminal domain. A 2024 EMBO Journal study reported that MAGEA4 docking on RAD18 partially displaces RAD6 and inhibits RAD18’s auto-ubiquitination, thereby stabilizing the RAD18 protein (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Normally, RAD18 can undergo autoubiquitination (tags itself for degradation to turn off its signal), but MAGEA4 binding protects RAD18 from self-degradation (pmc.ncbi.nlm.nih.gov). This interaction enhances RAD18’s TLS activity and is thought to encourage error-prone DNA synthesis in cancer cells overexpressing MAGEA4 (pmc.ncbi.nlm.nih.gov). In healthy tissue, RAD18 and MAGEA4 are both highly expressed in testes and during spermatogenesis (pmc.ncbi.nlm.nih.gov), hinting that this regulatory mechanism may operate in germ cells. Aberrant MAGEA4 expression in tumors effectively “hijacks” RAD18, keeping it active even without exogenous DNA damage, which can exacerbate genomic instability (pmc.ncbi.nlm.nih.gov). The RAD18–MAGEA4 interface is now being explored as a potential drug target to block TLS in cancers (pmc.ncbi.nlm.nih.gov).

Subcellular Localization and Regulation

Localization: Consistent with its role in DNA replication and repair, RAD18 is predominantly a nuclear protein. Immunohistochemistry data show RAD18 has selective nuclear expression in proliferating cell types – for example, in germinal center B-cells and spermatogonia in testis, RAD18 is strongly nuclear (www.proteinatlas.org). In cell culture, RAD18 relocalizes to nuclear foci upon DNA damage. These foci often colocalize with replication fork markers such as PCNA. A study of gastric cancer tissues confirmed that RAD18 protein is mainly detected in the nucleus of tumor cells (pubmed.ncbi.nlm.nih.gov). RAD18 does not have a classic nuclear localization sequence, but its binding partners (PCNA, RPA, etc.) and DNA-binding SAP domain concentrate it in the nucleus. Notably, RAD18 can shuttle to sites of double-strand breaks and stalled forks as needed. For example, after UV irradiation or replication stress, RAD18 accumulates at damage sites in an RPA- and PCNA-dependent manner (www.embopress.org). RAD18’s PIP motif (PCNA-interacting peptide) near its C-terminus also contributes to binding PCNA directly (www.embopress.org). Recent research (EMBO J, 2024) identified that the ATR kinase phosphorylates RAD18 at Ser403, adjacent to this PIP motif, which weakens RAD18’s interaction with PCNA (www.embopress.org). This phosphorylation by ATR is a key regulatory mechanism to restrict RAD18 activity during replication stress (www.embopress.org). By limiting how tightly RAD18 binds PCNA, ATR prevents excessive PCNA ubiquitination. This is physiologically important, as unchecked RAD18 activity can lead to aberrant processing of replication forks (discussed below). In summary, RAD18 is constitutively nuclear in cycling cells and dynamically enriched at DNA lesions, with its localization and activity finely tuned by cell-cycle checkpoints.

Post-translational Regulation: Cells tightly regulate RAD18 through modifications to ensure it acts at the right time and place. ATR-mediated phosphorylation is one such control: upon replication stress, ATR phosphorylates RAD18 (Ser403), causing RAD18 to release PCNA and thus limiting PCNA monoubiquitination (www.embopress.org). Functionally, this prevents an overactivation of the TLS pathway. A 2024 study demonstrated that inhibiting ATR led to excessive RAD18-dependent PCNA ubiquitination and consequent replication fork breakage – an outcome that could be rescued by RAD18 knockdown or a PCNA-K164R (non-ubiquitinable) mutant (www.embopress.org) (www.embopress.org). Thus, ATR acts as a brake on RAD18 to preserve replication fork stability (www.embopress.org) (www.embopress.org). Another layer of regulation is O-GlcNAcylation (O-linked N-acetylglucosamine modification) of RAD18. Emerging evidence (Cell Death & Disease, 2024) indicates RAD18 is modified by O-GlcNAc at multiple residues (Ser130, Ser164, Thr468), mediated by the OGT enzyme that localizes to DNA damage sites (www.nature.com) (www.nature.com). Loss of RAD18’s O-GlcNAc modification (by mutating those sites) impairs its recruitment to damaged DNA and reduces its ability to ubiquitinate PCNA (www.nature.com). Mechanistically, O-GlcNAcylation of RAD18 was required for efficient RAD18 phosphorylation at Ser434 by CDC7 kinase, which in turn promotes PCNA ubiquitination and Polη focus formation (www.nature.com). Cells expressing an O-GlcNAc-deficient RAD18 mutant showed reduced HR repair and heightened sensitivity to DNA damage (www.nature.com). Therefore, O-GlcNAcylation positively regulates RAD18, enhancing both TLS and homologous recombination functions. RAD18 is also subject to autoubiquitination, as mentioned earlier. Autoubiquitination typically targets RAD18 for proteasomal degradation, serving as a negative feedback to turn off PRR once lesions are bypassed (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Interactions with proteins like MAGEA4 that suppress autoubiquitination will prolong RAD18’s half-life. In summary, phosphorylation (ATR), glycosylation (O-GlcNAc), and self-ubiquitination of RAD18 all integrate to modulate the timing and intensity of RAD18’s activity in the DNA damage response.

Biological Processes and Pathways Involving RAD18

Post-Replication Repair (PRR) Pathway: RAD18 is a central player in the PRR pathway, also known as the DNA damage tolerance pathway. This pathway comes into play when replication forks encounter DNA lesions that cannot be immediately repaired. Rather than stalling indefinitely, PRR allows forks to bypass lesions, and repair is handled after DNA replication. RAD18’s ubiquitination of PCNA is the molecular trigger for PRR (pmc.ncbi.nlm.nih.gov). Depending on context, RAD18-mediated PCNA ubiquitination can initiate error-prone TLS or be coupled to error-free template switching. The importance of RAD18 in PRR is illustrated by the Rad18 knockout phenotype: RAD18-null mouse embryonic stem cells and knockout mice exhibit defective post-replication repair, evidenced by accumulation of daughter-strand gaps behind replication forks and elevated sensitivity to UV, methylating agents, and other mutagens (pmc.ncbi.nlm.nih.gov). In S. cerevisiae, rad18 mutants were first discovered for their inability to survive DNA damage despite intact excision repair, defining the post-replication repair pathway. Human RAD18 restores post-replication repair when expressed in rad18-deficient yeast (pmc.ncbi.nlm.nih.gov), highlighting the pathway’s conservation. RAD18 also interacts with the Fanconi Anemia (FA) pathway, which is another post-replication repair mechanism especially for DNA interstrand crosslinks. A recent study (PLoS Genetics, 2022) found that RAD18 helps recruit the Fanconi anemia protein FANCD2 to sites of transcription-replication conflicts (pmc.ncbi.nlm.nih.gov). In RAD18-deficient human cells, R-loop structures (RNA–DNA hybrids) accumulate, leading to replication stress and double-strand breaks, partly because FANCD2 fails to localize to resolve these R-loops (pmc.ncbi.nlm.nih.gov). RAD18 activity was shown to be critical for activating FANCD2 under replication stress caused by either transcription blockage or mild replication inhibitors (pmc.ncbi.nlm.nih.gov). Thus, RAD18 links standard PRR (PCNA ubiquitination) with the FA pathway to protect stalled forks from transcriptional interference. This underscores a broader role for RAD18: it’s not only guarding against exogenous DNA damage like UV, but also against endogenous stresses such as hard-to-replicate sequences and R-loops (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

Homologous Recombination (HR) and Double-Strand Break Repair: Although traditionally associated with replication lesions, RAD18 has emerging roles in double-strand break (DSB) repair, particularly in promoting HR. In the context of a one-ended DSB arising at a collapsed replication fork, RAD18 appears to channel repair toward HR (error-free repair using a sister chromatid) rather than non-homologous end joining (NHEJ). In mid-2024, Palek et al. reported that RAD18 is actively recruited to DSBs in post-replicative chromatin by recognizing ubiquitylated histone H2A marks (pmc.ncbi.nlm.nih.gov). Specifically, ubiquitination of histone H2A at K15 (placed by upstream DNA damage response E3s like RNF168) creates a binding site for RAD18’s UBZ domain (pmc.ncbi.nlm.nih.gov). RAD18’s presence at breaks then antagonizes 53BP1 loading (pmc.ncbi.nlm.nih.gov). 53BP1 is a factor that favors NHEJ and blocks DNA end resection; by limiting 53BP1 accumulation, RAD18 tilts the balance toward resection and homologous recombination. Using super-resolution microscopy, RAD18 was seen localizing adjacent to DSB sites and confining 53BP1 to peripheral chromatin domains around the break (pmc.ncbi.nlm.nih.gov). Mechanistically, RAD18’s effect required cooperation with SLF1 (SCAF-like factor 1), which helps target RAD18 to newly replicated chromatin marked by unmethylated H4K20 (H4K20me0 is a signature of post-replicative chromatin) (pubmed.ncbi.nlm.nih.gov) (pubmed.ncbi.nlm.nih.gov). Intriguingly, RAD18’s own ubiquitin ligase activity is auto-regulated at DSBs: if RAD18 autoubiquitinates itself (with RAD6’s help), its recruitment to breaks is inhibited (pmc.ncbi.nlm.nih.gov). By preventing self-ubiquitination (for example, via SLF1 or MAGEA4 as discussed), RAD18 can persist at damage sites and promote HR repair. Supporting this model, mutations in RAD18 found in some cancer patients impaired RAD18’s recruitment to DSBs and were associated with genomic instability (www.sciencedirect.com) (pubmed.ncbi.nlm.nih.gov). In summary, RAD18 extends its influence beyond replication forks to the realm of DSB repair: it helps decide the repair pathway choice by favoring homologous recombination in replicating cells, thereby preventing toxic misrepair.

Replication Stress and Fork Rescue: Oncogene activation and other intrinsic stressors often cause replication fork stalling or slowing, known as replication stress. RAD18 has been identified as a key factor that cancer cells exploit to survive high levels of replication stress. A notable study (J. Cell Biol., 2017) showed that RAD18 and Polκ enable tolerance of oncogene-induced replication stress, such as that caused by Cyclin E overexpression (pmc.ncbi.nlm.nih.gov). RAD18-deficient cells fail to resolve stalled forks efficiently and undergo lethal fork collapse when driven into unscheduled replication by oncogenic signals (pmc.ncbi.nlm.nih.gov). In line with this, cells require RAD18 to recover from prolonged S-phase checkpoint arrest (pmc.ncbi.nlm.nih.gov). Recent evidence also points to RAD18’s role in alternative replication rescue pathways like break-induced replication (BIR) (pmc.ncbi.nlm.nih.gov), a process to restart broken forks. These diverse functions position RAD18 as a central responder to replication impediments, whether they are DNA lesions, difficult-to-replicate DNA structures, or collisions between replication and transcription machineries (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). By catalyzing PCNA ubiquitination and cooperating with multiple repair pathways, RAD18 coordinates a network of responses that preserve genome integrity during DNA synthesis.

RAD18 in Health and Disease

Cancer Genomics and Mutagenesis: Given its role in tolerating DNA damage (often at the cost of introducing mutations), RAD18 has a complex relationship with cancer. On one hand, RAD18 is protective against acute DNA damage and genomic instability; on the other, its error-prone bypass of lesions can contribute to mutagenesis. High levels of RAD18 have been observed in many cancers, and this is often associated with aggressive disease. For instance, a 2020 clinical study of 96 gastric cancer patients found that tumors with strong RAD18 expression had significantly higher rates of lymph node metastasis and vascular invasion, and patients with RAD18-high tumors had markedly shorter overall survival (pubmed.ncbi.nlm.nih.gov). Specifically, high nuclear RAD18 in gastric tumors correlated with advanced stage (p = 0.0253) and poor prognosis (p = 0.0061 for overall survival) (pubmed.ncbi.nlm.nih.gov). Similarly, in triple-negative breast cancer (TNBC), RAD18 was shown to be overexpressed in high-grade tumors and to correlate inversely with patient survival (pmc.ncbi.nlm.nih.gov). Experimental models have elucidated how RAD18 may drive cancer progression: RAD18’s TLS activity can generate mutations that fuel tumor evolution (pmc.ncbi.nlm.nih.gov). In TNBC cells, RAD18 was found to promote a cancer stem cell-like phenotype via interaction with the Hippo/YAP signaling pathway (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). RAD18 also engages in a positive feedback loop with tumor-associated macrophages: tumor-secreted factors induce macrophages to produce TGF-β, which in turn activates RAD18 and YAP in cancer cells, sustaining stemness and therapy resistance (pmc.ncbi.nlm.nih.gov). These findings underscore that RAD18 is not simply a repair protein but can be co-opted by tumors to enhance malignant traits (metastasis, stemness, mutational adaptability).

Therapeutic Resistance: Cancer cells often rely on RAD18 to survive DNA-damaging treatments, making it a factor in chemo- and radio-resistance. Overexpression of RAD18 has been linked to resistance to platinum chemotherapy in colorectal cancer and to radiotherapy in glioblastoma and lung cancers (www.nature.com) (www.nature.com). For example, knocking down RAD18 in glioma models increased their sensitivity to ionizing radiation, indicating RAD18 normally helps repair or tolerate radiation-induced DNA damage (www.nature.com). Mechanistically, RAD18 can modulate the repair of therapy-induced DNA lesions: one study showed RAD18 overexpression in esophageal carcinoma enhanced repair of radiation damage by regulating DNA-PKcs (a key NHEJ factor) (pmc.ncbi.nlm.nih.gov). Another report described RAD18 promoting epithelial–mesenchymal transition (EMT) and metastasis in colorectal cancer, suggesting RAD18’s activity may extend to altering gene expression programs via DNA damage signals (pmc.ncbi.nlm.nih.gov). These insights have motivated efforts to target RAD18 or its partners pharmacologically. Small-molecule inhibitors of the RAD18 pathway are being explored as adjuvants to cancer therapy. In 2022, researchers discovered a series of xanthene compounds (e.g., “TZ9”) that disrupt RAD6–RAD18 function, thereby blocking PCNA ubiquitination (pmc.ncbi.nlm.nih.gov) (pubmed.ncbi.nlm.nih.gov). These compounds inhibit the RAD6~Ub thioester formation and the RAD6–RAD18 interaction, effectively shutting down TLS (pmc.ncbi.nlm.nih.gov). Notably, treating cells with a RAD6/RAD18 inhibitor (like TZ9) phenocopies RAD18 loss: it prevented NiV virus protein ubiquitination (as discussed below) and also impaired post-replication repair (pubmed.ncbi.nlm.nih.gov). Patent literature in 2021–2023 reflects active interest in RAD18 inhibitors for cancer treatment, indicating preclinical development of molecules aiming to block RAD18-mediated tolerance in tumors (patents.google.com) (patents.justia.com). The rationale is that disabling RAD18 will render cancer cells less able to cope with therapy-induced DNA damage or replication stress, thereby enhancing the efficacy of chemo/radiation. However, this strategy must balance the potential for increased normal tissue toxicity and genomic instability.

Viral Exploitation of RAD18: In an interesting twist, viruses can hijack the RAD18 pathway for their own life cycle. A recent study (Cell Reports, 2023) on Nipah virus (NiV) – a highly pathogenic paramyxovirus – revealed that NiV usurps the RAD6–RAD18 ubiquitin complex to modify its matrix (M) protein (pubmed.ncbi.nlm.nih.gov). The NiV M protein must shuttle from the nucleus (where virions assemble) to the cytoplasm for viral budding. RAD18 was found to directly ubiquitinate NiV M at Lys258 via K63-linked polyubiquitin chains, using RAD6A as the E2 enzyme (pubmed.ncbi.nlm.nih.gov). This ubiquitination of M is crucial for its nuclear export: ubiquitinated M relocalizes to the cytoplasm and reaches the plasma membrane for virion release (pubmed.ncbi.nlm.nih.gov). Disrupting the RAD18–RAD6A complex, either by mutating RAD18’s RING domain or applying the RAD6 inhibitor TZ9, blocked M’s ubiquitination and trapped the M protein in the nucleus (pubmed.ncbi.nlm.nih.gov). As a result, NiV and the related Hendra virus were unable to efficiently bud from infected cells, greatly attenuating infection (pubmed.ncbi.nlm.nih.gov). This finding identifies RAD18 as a host factor essential for NiV egress. It suggests that RAD18 inhibitors might serve as antivirals against certain viruses, although host DNA repair would concurrently be affected. Nonetheless, the NiV example highlights RAD18’s versatile enzymatic activity – extending beyond PCNA to ubiquitinate other proteins (here a viral protein) when recruited to them. It also provides a “real-world” demonstration that small molecules targeting the RAD18/RAD6 pathway (like TZ9) can have tangible biological effects (e.g. blocking a lethal virus) (pubmed.ncbi.nlm.nih.gov).

Expert Perspectives and Current Research Frontiers

RAD18 is widely regarded by experts as a master regulator of replication stress responses. As an authoritative review noted, RAD18 “coordinates multiple DNA repair and damage tolerance pathways including post-replication repair, homologous recombination, Fanconi anemia, and break-induced replication” (pmc.ncbi.nlm.nih.gov). By modifying the key sliding clamp PCNA, RAD18 orchestrates the switch between high-fidelity replication and specialized rescue pathways (pmc.ncbi.nlm.nih.gov). This central role has made RAD18 a focal point in understanding how cells maintain genome stability. Recent research (2022–2024) has significantly expanded our understanding of RAD18’s functions:
- Transcription-Associated Damage: Wells et al. (PLoS Genet, Dec 2022) demonstrated that RAD18 prevents transcription-replication conflicts from turning into DNA breaks by recruiting FANCD2 to resolve R-loops (pmc.ncbi.nlm.nih.gov). This indicates RAD18 is active at common fragile sites and conflict-prone genes, not just at exogenous damage sites.
- DSB Repair Choice: Palek et al. (Nucleic Acids Res, July 2024) showed RAD18 is a novel factor in DSB repair pathway choice – promoting HR by excluding 53BP1 in the context of newly replicated chromatin (pmc.ncbi.nlm.nih.gov). This was a surprising new role, hinting that RAD18 links the replication-coupled repair of one-ended breaks to the classical HR machinery.
- Regulatory Modifications: Zhang et al. (Cell Death Dis., 2024) uncovered the O-GlcNAc modification of RAD18 as a key enhancer of its activity in both TLS and HR, connecting cellular metabolic status (glucose levels) to DNA repair capacity (www.nature.com) (www.nature.com). In parallel, Okano et al. (EMBO J., 2024) identified ATR kinase as a checkpoint that restrains RAD18, thereby protecting replication forks and telomeres from excessive processing (www.embopress.org) (www.embopress.org). This kind of crosstalk between checkpoint signaling and RAD18 ensures a balance between damage bypass and fork stability.
- Structural Insights: Griffith-Jones et al. (EMBO J., 2024) provided high-resolution insight into RAD18’s regulation by cancer-testis antigens (MAGE proteins). Their work solved how MAGEA4 binds RAD18’s RING domain and RAD6-binding domain, stabilizing the ligase and enhancing its activity (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). This not only explained one mechanism of chemoresistance in MAGEA4-positive tumors, but also suggested a new therapeutic angle: disrupting the RAD18–MAGEA4 interaction may selectively sensitize cancer cells (pmc.ncbi.nlm.nih.gov).
- Disease Models: Recent in vivo studies have examined RAD18 in disease contexts. For example, a 2024 Scientific Reports study tested RAD18’s role in B cell lymphomas using Rad18-knockout mice. Spontaneously, Rad18-deficient mice had increased B-cell malignancies after carcinogen exposure (www.nature.com), but in an aggressive Myc-driven lymphoma model, loss of Rad18 did not significantly alter tumor onset (www.nature.com) (www.nature.com). These results imply that RAD18’s role in cancer can be context-dependent and potentially compensated by parallel pathways in some cell types (www.nature.com).

Overall, current expert consensus portrays RAD18 as a guardian of replication that, if dysregulated, can become a double-edged sword – preventing catastrophic genome damage on one hand, but enabling genome instability and therapy resistance on the other (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Its importance is underscored by the breadth of processes it touches: from ensuring fertility (spermatogenesis requires RAD18 for meiotic DNA repair (www.nature.com)) to influencing the outcomes of cancer therapy. As of 2024, RAD18 remains an active research focus. Key open questions include how RAD18 selects its substrates (beyond PCNA and the few known targets), how it is coordinated with polymerase choice in different lesions, and whether transient RAD18 inhibition can be a safe and effective strategy to augment cancer treatments. Ongoing clinical interest is evident – RAD18 expression is being evaluated as a prognostic biomarker, and preclinical trials of RAD18-pathway inhibitors are likely on the horizon (patents.google.com) (patents.justia.com).

In summary, RAD18 is a pivotal E3 ligase in human cells with a well-established role in monoubiquitinating PCNA to promote DNA damage tolerance. It operates at the crossroads of DNA replication, repair, and checkpoint signaling, ensuring that cells can bypass DNA lesions and recover from replication stress. Cutting-edge studies in 2023–2024 have expanded its known functions to include aiding homologous recombination and preventing transcription-associated genome instability, as well as illuminating mechanisms of its regulation. Clinically, while essential for genome stability, RAD18’s activity can be a liability when hijacked by cancer cells or viruses – making it an attractive, if challenging, target for therapeutic intervention. As one research group aptly summarized, “RAD18 plays numerous roles in genome instability, driven mostly through regulated ubiquitination of [its] primary substrate, PCNA” (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Understanding and modulating those roles continues to be critical in the quest to maintain genomic integrity and improve disease outcomes.

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11. AnnotationURLCitation(end_index=3435, start_index=3315, title='RAD18 RAD18 E3 ubiquitin protein ligase [Homo sapiens (human)] - Gene - NCBI', type='url_citation', url='https://www.ncbi.nlm.nih.gov/gene/56852#:~:text=The%20protein%20encoded%20by%20this,Expression')
12. AnnotationURLCitation(end_index=3567, start_index=3436, title='RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair | Cell Death & Disease', type='url_citation', url='https://www.nature.com/articles/s41419-024-06700-y#:~:text=damage%20sites,and%20RAD51C%20binding%20ability%20of')
13. AnnotationURLCitation(end_index=3850, start_index=3682, title='A series of xanthenes inhibiting Rad6 function and Rad6-Rad18 interaction in the PCNA ubiquitination cascade - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8958325/#:~:text=The%20ubiquitination%20of%20PCNA%20on,and%20other%20replication%2C%20repair%2C%20and')
14. AnnotationURLCitation(end_index=3987, start_index=3893, title='RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair | Cell Death & Disease', type='url_citation', url='https://www.nature.com/articles/s41419-024-06700-y#:~:text=,binding%20zinc')
15. AnnotationURLCitation(end_index=4297, start_index=4177, title='RAD18 RAD18 E3 ubiquitin protein ligase [Homo sapiens (human)] - Gene - NCBI', type='url_citation', url='https://www.ncbi.nlm.nih.gov/gene/56852#:~:text=The%20protein%20encoded%20by%20this,Expression')
16. AnnotationURLCitation(end_index=4534, start_index=4399, title='Enhanced Genomic Instability and Defective Postreplication Repair in RAD18 Knockout Mouse Embryonic Stem Cells - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC151530/#:~:text=Enhanced%20Genomic%20Instability%20and%20Defective,2')
17. AnnotationURLCitation(end_index=4960, start_index=4835, title='Role of Rad18 in B cell activation and lymphomagenesis | Scientific Reports', type='url_citation', url='https://www.nature.com/articles/s41598-024-57018-w#:~:text=PCNA%2C%20mediated%20by%20Rad6%20together,free')
18. AnnotationURLCitation(end_index=5521, start_index=5396, title='Role of Rad18 in B cell activation and lymphomagenesis | Scientific Reports', type='url_citation', url='https://www.nature.com/articles/s41598-024-57018-w#:~:text=PCNA%2C%20mediated%20by%20Rad6%20together,free')
19. AnnotationURLCitation(end_index=6070, start_index=5914, title='RAD18 directs DNA\xa0double-strand break repair by homologous recombination to post-replicative chromatin - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11260465/#:~:text=RAD18%20is%20an%20E3%20ubiquitin,and%20limits%20the%20distribution%20of')
20. AnnotationURLCitation(end_index=6506, start_index=6348, title='The E3 ligase RAD18-mediated ubiquitination of henipavirus matrix protein promotes its nuclear-cytoplasmic trafficking and viral egress - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/39628457/#:~:text=novel%20mechanism%20by%20which%20Nipah,the%20cytoplasm%2C%20directing%20it%20to')
21. AnnotationURLCitation(end_index=6736, start_index=6642, title='RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair | Cell Death & Disease', type='url_citation', url='https://www.nature.com/articles/s41419-024-06700-y#:~:text=,binding%20zinc')
22. AnnotationURLCitation(end_index=7040, start_index=6871, title='E3 ligase Rad18 promotes monoubiquitination rather than ubiquitin chain formation by E2 enzyme Rad6 - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/21422291/#:~:text=E3%20ligase%20Rad18%20promotes%20monoubiquitination,The%20E2%2FE3%20complex%20Rad6%2FRad18')
23. AnnotationURLCitation(end_index=7390, start_index=7205, title='Asymmetric nature of two subunits of RAD18, a RING-type ubiquitin ligase E3, in the human RAD6A–RAD18 ternary complex - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3273806/#:~:text=E3%2C%20in%20the%20human%20RAD6A%E2%80%93RAD18,human%20RAD6A%E2%80%93RAD18%20ternary%20complex%20Yuji')
24. AnnotationURLCitation(end_index=7542, start_index=7391, title='Functional characterization of Rad18 domains for Rad6, ubiquitin, DNA binding and PCNA modification - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2034485/#:~:text=Functional%20characterization%20of%20Rad18%20domains,stranded%20DNA')
25. AnnotationURLCitation(end_index=7901, start_index=7750, title='Functional characterization of Rad18 domains for Rad6, ubiquitin, DNA binding and PCNA modification - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2034485/#:~:text=Functional%20characterization%20of%20Rad18%20domains,stranded%20DNA')
26. AnnotationURLCitation(end_index=8242, start_index=8078, title='RAD18 directs DNA\xa0double-strand break repair by homologous recombination to post-replicative chromatin - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11260465/#:~:text=classical%20role%2C%20RAD18%20has%20been,and%20limits%20the%20distribution%20of')
27. AnnotationURLCitation(end_index=8695, start_index=8552, title='ATR limits Rad18-mediated PCNA monoubiquitination to preserve replication fork and telomerase-independent telomere stability | The EMBO Journal', type='url_citation', url='https://www.embopress.org/doi/10.1038/s44318-024-00066-9#:~:text=2005%29,the%20precise%20molecular%20crosstalk%20between')
28. AnnotationURLCitation(end_index=8963, start_index=8843, title='RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair | Cell Death & Disease', type='url_citation', url='https://www.nature.com/articles/s41419-024-06700-y#:~:text=The%20E3%20ubiquitin%20ligase%20RAD18,mUb')
29. AnnotationURLCitation(end_index=9288, start_index=9165, title='Role of Rad18 in B cell activation and lymphomagenesis | Scientific Reports', type='url_citation', url='https://www.nature.com/articles/s41598-024-57018-w#:~:text=match%20at%20L77%20Several%20studies,induced')
30. AnnotationURLCitation(end_index=9559, start_index=9418, title='RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair | Cell Death & Disease', type='url_citation', url='https://www.nature.com/articles/s41419-024-06700-y#:~:text=conjugase%20RAD6%20is%20specifically%20required,binding%20zinc')
31. AnnotationURLCitation(end_index=9704, start_index=9560, title='RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair | Cell Death & Disease', type='url_citation', url='https://www.nature.com/articles/s41419-024-06700-y#:~:text=RAD18%20at%20DNA%20double,establishing%20a%20new%20rationale%20to')
32. AnnotationURLCitation(end_index=10315, start_index=10167, title='Structural basis for RAD18 regulation by MAGEA4 and its implications for RING ubiquitin ligase binding by MAGE family proteins - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10987633/#:~:text=,inhibits%20degradative%20RAD18%20autoubiquitination%2C%20which')
33. AnnotationURLCitation(end_index=10434, start_index=10316, title='Structural basis for RAD18 regulation by MAGEA4 and its implications for RING ubiquitin ligase binding by MAGE family proteins - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10987633/#:~:text=,degradative%20autoubiquitination')
34. AnnotationURLCitation(end_index=10730, start_index=10593, title='Structural basis for RAD18 regulation by MAGEA4 and its implications for RING ubiquitin ligase binding by MAGE family proteins - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10987633/#:~:text=match%20at%20L191%20MAGEA4%20MHD,We%20also%20defined')
35. AnnotationURLCitation(end_index=11027, start_index=10875, title='Structural basis for RAD18 regulation by MAGEA4 and its implications for RING ubiquitin ligase binding by MAGE family proteins - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10987633/#:~:text=match%20at%20L173%20,damage%2C%20through%20the%20stabilisation%20of')
36. AnnotationURLCitation(end_index=11289, start_index=11128, title='Structural basis for RAD18 regulation by MAGEA4 and its implications for RING ubiquitin ligase binding by MAGE family proteins - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10987633/#:~:text=highly%20specific%20to%20MAGEA4%20,term%20maintenance%20of%20spermatogenesis')
37. AnnotationURLCitation(end_index=11669, start_index=11517, title='Structural basis for RAD18 regulation by MAGEA4 and its implications for RING ubiquitin ligase binding by MAGE family proteins - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10987633/#:~:text=match%20at%20L173%20,damage%2C%20through%20the%20stabilisation%20of')
38. AnnotationURLCitation(end_index=11928, start_index=11771, title='Structural basis for RAD18 regulation by MAGEA4 and its implications for RING ubiquitin ligase binding by MAGE family proteins - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10987633/#:~:text=match%20at%20L186%20MAGEA4%20in,drug%20target%20for%20cancer%20therapies')
39. AnnotationURLCitation(end_index=12462, start_index=12292, title='Expression of RAD18 in cancer - Summary - The Human Protein Atlas', type='url_citation', url='https://www.proteinatlas.org/ENSG00000070950-RAD18/cancer#:~:text=normal%20tissue,IMMUNOHISTOCHEMISTRY%20DATA%20RELIABILITY%20Data%20reliability')
40. AnnotationURLCitation(end_index=12862, start_index=12716, title='High RAD18 Expression is Associated with Disease Progression and Poor Prognosis in Patients with Gastric Cancer - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/32356270/#:~:text=Results%3A%20RAD18%20expression%20was%20predominantly,0061%29%20and')
41. AnnotationURLCitation(end_index=13386, start_index=13243, title='ATR limits Rad18-mediated PCNA monoubiquitination to preserve replication fork and telomerase-independent telomere stability | The EMBO Journal', type='url_citation', url='https://www.embopress.org/doi/10.1038/s44318-024-00066-9#:~:text=2005%29,the%20precise%20molecular%20crosstalk%20between')
42. AnnotationURLCitation(end_index=13687, start_index=13499, title='ATR limits Rad18-mediated PCNA monoubiquitination to preserve replication fork and telomerase-independent telomere stability | The EMBO Journal', type='url_citation', url='https://www.embopress.org/doi/10.1038/s44318-024-00066-9#:~:text=phosphorylates%20human%20Rad18%20at%20Ser403%2C,mediated%20PCNA%20monoubiquitination.%20Consequently')
43. AnnotationURLCitation(end_index=14045, start_index=13857, title='ATR limits Rad18-mediated PCNA monoubiquitination to preserve replication fork and telomerase-independent telomere stability | The EMBO Journal', type='url_citation', url='https://www.embopress.org/doi/10.1038/s44318-024-00066-9#:~:text=phosphorylates%20human%20Rad18%20at%20Ser403%2C,mediated%20PCNA%20monoubiquitination.%20Consequently')
44. AnnotationURLCitation(end_index=14327, start_index=14162, title='ATR limits Rad18-mediated PCNA monoubiquitination to preserve replication fork and telomerase-independent telomere stability | The EMBO Journal', type='url_citation', url='https://www.embopress.org/doi/10.1038/s44318-024-00066-9#:~:text=ATR%20activation%20and%20Rad18,of%20this%20interplay%2C%20remain%20unresolved')
45. AnnotationURLCitation(end_index=15212, start_index=15047, title='ATR limits Rad18-mediated PCNA monoubiquitination to preserve replication fork and telomerase-independent telomere stability | The EMBO Journal', type='url_citation', url='https://www.embopress.org/doi/10.1038/s44318-024-00066-9#:~:text=ATR%20activation%20and%20Rad18,of%20this%20interplay%2C%20remain%20unresolved')
46. AnnotationURLCitation(end_index=15678, start_index=15517, title='ATR limits Rad18-mediated PCNA monoubiquitination to preserve replication fork and telomerase-independent telomere stability | The EMBO Journal', type='url_citation', url='https://www.embopress.org/doi/10.1038/s44318-024-00066-9#:~:text=ultraviolet%20%28UV%29%20radiation,suggest%20that%20ATR%20may%20constrain')
47. AnnotationURLCitation(end_index=15827, start_index=15679, title='ATR limits Rad18-mediated PCNA monoubiquitination to preserve replication fork and telomerase-independent telomere stability | The EMBO Journal', type='url_citation', url='https://www.embopress.org/doi/10.1038/s44318-024-00066-9#:~:text=%28Fig,detrimental%20consequence%20of%20replication%20stress')
48. AnnotationURLCitation(end_index=16081, start_index=15907, title='ATR limits Rad18-mediated PCNA monoubiquitination to preserve replication fork and telomerase-independent telomere stability | The EMBO Journal', type='url_citation', url='https://www.embopress.org/doi/10.1038/s44318-024-00066-9#:~:text=The%20exact%20molecular%20interplay%20between,to%20maintain%20replication%20fork%20and')
49. AnnotationURLCitation(end_index=16262, start_index=16082, title='ATR limits Rad18-mediated PCNA monoubiquitination to preserve replication fork and telomerase-independent telomere stability | The EMBO Journal', type='url_citation', url='https://www.embopress.org/doi/10.1038/s44318-024-00066-9#:~:text=Rad18%20at%20Ser403%20during%20replication,ATR%E2%80%99s%20role%20extends%20to%20maintaining')
50. AnnotationURLCitation(end_index=16725, start_index=16565, title='RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair | Cell Death & Disease', type='url_citation', url='https://www.nature.com/articles/s41419-024-06700-y#:~:text=how%20the%20regulatory%20mechanism%20of,optimal%20RAD18%20accumulation%20at%20DNA')
51. AnnotationURLCitation(end_index=16870, start_index=16726, title='RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair | Cell Death & Disease', type='url_citation', url='https://www.nature.com/articles/s41419-024-06700-y#:~:text=RAD18%20at%20DNA%20double,establishing%20a%20new%20rationale%20to')
52. AnnotationURLCitation(end_index=17151, start_index=17020, title='RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair | Cell Death & Disease', type='url_citation', url='https://www.nature.com/articles/s41419-024-06700-y#:~:text=damage%20sites,and%20RAD51C%20binding%20ability%20of')
53. AnnotationURLCitation(end_index=17498, start_index=17338, title='RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair | Cell Death & Disease', type='url_citation', url='https://www.nature.com/articles/s41419-024-06700-y#:~:text=how%20the%20regulatory%20mechanism%20of,optimal%20RAD18%20accumulation%20at%20DNA')
54. AnnotationURLCitation(end_index=17762, start_index=17618, title='RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair | Cell Death & Disease', type='url_citation', url='https://www.nature.com/articles/s41419-024-06700-y#:~:text=RAD18%20at%20DNA%20double,establishing%20a%20new%20rationale%20to')
55. AnnotationURLCitation(end_index=18246, start_index=18098, title='Structural basis for RAD18 regulation by MAGEA4 and its implications for RING ubiquitin ligase binding by MAGE family proteins - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10987633/#:~:text=,inhibits%20degradative%20RAD18%20autoubiquitination%2C%20which')
56. AnnotationURLCitation(end_index=18365, start_index=18247, title='Structural basis for RAD18 regulation by MAGEA4 and its implications for RING ubiquitin ligase binding by MAGE family proteins - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10987633/#:~:text=,degradative%20autoubiquitination')
57. AnnotationURLCitation(end_index=19304, start_index=19147, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=RAD18%20is%20a%20conserved%20E3,conductor%20at%20the%20replication%20fork')
58. AnnotationURLCitation(end_index=19903, start_index=19768, title='Enhanced Genomic Instability and Defective Postreplication Repair in RAD18 Knockout Mouse Embryonic Stem Cells - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC151530/#:~:text=Enhanced%20Genomic%20Instability%20and%20Defective,2')
59. AnnotationURLCitation(end_index=20312, start_index=20168, title='Dysfunction of human Rad18 results in defective postreplication repair and hypersensitivity to multiple mutagens - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC16647/#:~:text=hypersensitivity%20to%20multiple%20mutagens%20,Oligonucleotide')
60. AnnotationURLCitation(end_index=20819, start_index=20666, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=pathways%20to%20preserve%20genome%20stability,replication%20conflicts')
61. AnnotationURLCitation(end_index=21175, start_index=21022, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=pathways%20to%20preserve%20genome%20stability,replication%20conflicts')
62. AnnotationURLCitation(end_index=21497, start_index=21339, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=conflicts%20and%20accumulate%20DNA%3ARNA%20hybrids,replication%20conflicts')
63. AnnotationURLCitation(end_index=21982, start_index=21821, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=DNA%20replication%20is%20a%20vulnerable,at%20difficult%20to%20replicate%20and')
64. AnnotationURLCitation(end_index=22128, start_index=21983, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=to%20recruit%20the%20Fanconi%20Anemia,replication%20conflicts')
65. AnnotationURLCitation(end_index=22881, start_index=22717, title='RAD18 directs DNA\xa0double-strand break repair by homologous recombination to post-replicative chromatin - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11260465/#:~:text=classical%20role%2C%20RAD18%20has%20been,and%20limits%20the%20distribution%20of')
66. AnnotationURLCitation(end_index=23201, start_index=23037, title='RAD18 directs DNA\xa0double-strand break repair by homologous recombination to post-replicative chromatin - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11260465/#:~:text=classical%20role%2C%20RAD18%20has%20been,and%20limits%20the%20distribution%20of')
67. AnnotationURLCitation(end_index=23429, start_index=23265, title='RAD18 directs DNA\xa0double-strand break repair by homologous recombination to post-replicative chromatin - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11260465/#:~:text=classical%20role%2C%20RAD18%20has%20been,and%20limits%20the%20distribution%20of')
68. AnnotationURLCitation(end_index=23915, start_index=23751, title='RAD18 directs DNA\xa0double-strand break repair by homologous recombination to post-replicative chromatin - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11260465/#:~:text=classical%20role%2C%20RAD18%20has%20been,and%20limits%20the%20distribution%20of')
69. AnnotationURLCitation(end_index=24299, start_index=24146, title='RAD18 directs DNA double-strand break repair by homologous recombination to post-replicative chromatin - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/38884202/#:~:text=RAD18%20is%20an%20E3%20ubiquitin,to%20DNA%20breaks%2C%20interaction%20with')
70. AnnotationURLCitation(end_index=24477, start_index=24300, title='RAD18 directs DNA double-strand break repair by homologous recombination to post-replicative chromatin - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/38884202/#:~:text=to%20DNA%20lesions%20by%20monoubiquitination,Surprisingly%2C%20suppression%20of%2053BP1%20function')
71. AnnotationURLCitation(end_index=24815, start_index=24651, title='RAD18 directs DNA\xa0double-strand break repair by homologous recombination to post-replicative chromatin - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11260465/#:~:text=classical%20role%2C%20RAD18%20has%20been,and%20limits%20the%20distribution%20of')
72. AnnotationURLCitation(end_index=25263, start_index=25114, title='Exploring RAD18-dependent replication of damaged DNA and discontinuities: A collection of advanced tools - ScienceDirect', type='url_citation', url='https://www.sciencedirect.com/science/article/pii/S0168165623002122#:~:text=Exploring%20RAD18,Exploring%20the%20role%20and')
73. AnnotationURLCitation(end_index=25413, start_index=25264, title='DNA repair factor RAD18 and DNA polymerase Polκ confer tolerance of oncogenic DNA replication stress - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/28835467/#:~:text=DNA%20repair%20factor%20RAD18%20and,h%2C%20and%20cell%20lysates%20were')
74. AnnotationURLCitation(end_index=26265, start_index=26102, title='DNA repair factor RAD18 and DNA polymerase Polκ confer tolerance of oncogenic DNA replication stress - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5626543/#:~:text=Skip%20to%20main%20content%20J,Rottmayer%20%5E%7B1%7D%2C%20Anastasia%20Zlatanou')
75. AnnotationURLCitation(end_index=26589, start_index=26426, title='DNA repair factor RAD18 and DNA polymerase Polκ confer tolerance of oncogenic DNA replication stress - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5626543/#:~:text=Skip%20to%20main%20content%20J,Rottmayer%20%5E%7B1%7D%2C%20Anastasia%20Zlatanou')
76. AnnotationURLCitation(end_index=26855, start_index=26684, title='Rad18 guides polη to replication stalling sites through physical interaction and PCNA monoubiquitination - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC522788/#:~:text=Rad18%20guides%20pol%CE%B7%20to%20replication,detectable%20levels%20of%20Rad18%20protein')
77. AnnotationURLCitation(end_index=27142, start_index=26985, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=RAD18%20is%20a%20conserved%20E3,conductor%20at%20the%20replication%20fork')
78. AnnotationURLCitation(end_index=27563, start_index=27402, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=DNA%20replication%20is%20a%20vulnerable,at%20difficult%20to%20replicate%20and')
79. AnnotationURLCitation(end_index=27717, start_index=27564, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=pathways%20to%20preserve%20genome%20stability,replication%20conflicts')
80. AnnotationURLCitation(end_index=28789, start_index=28643, title='High RAD18 Expression is Associated with Disease Progression and Poor Prognosis in Patients with Gastric Cancer - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/32356270/#:~:text=Results%3A%20RAD18%20expression%20was%20predominantly,0061%29%20and')
81. AnnotationURLCitation(end_index=29085, start_index=28939, title='High RAD18 Expression is Associated with Disease Progression and Poor Prognosis in Patients with Gastric Cancer - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/32356270/#:~:text=Results%3A%20RAD18%20expression%20was%20predominantly,0061%29%20and')
82. AnnotationURLCitation(end_index=29425, start_index=29245, title='A positive feedback loop: RAD18-YAP-TGF-β between triple-negative breast cancer and macrophages regulates cancer stemness and progression - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9005530/#:~:text=tumor%20microenvironment%2C%20remains%20elusive,nude%20mice%2C%20RAD18%20promoted%20subcutaneous')
83. AnnotationURLCitation(end_index=29726, start_index=29573, title='A positive feedback loop: RAD18-YAP-TGF-β between triple-negative breast cancer and macrophages regulates cancer stemness and progression - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9005530/#:~:text=As%20a%20key%20regulator%20of,RAD18%20facilitated%20a%20highly%20stem')
84. AnnotationURLCitation(end_index=30041, start_index=29861, title='A positive feedback loop: RAD18-YAP-TGF-β between triple-negative breast cancer and macrophages regulates cancer stemness and progression - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9005530/#:~:text=tumor%20microenvironment%2C%20remains%20elusive,nude%20mice%2C%20RAD18%20promoted%20subcutaneous')
85. AnnotationURLCitation(end_index=30192, start_index=30042, title='A positive feedback loop: RAD18-YAP-TGF-β between triple-negative breast cancer and macrophages regulates cancer stemness and progression - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9005530/#:~:text=correlated%20with%20prognosis,of%20the%20stemness%20phenotype%20by')
86. AnnotationURLCitation(end_index=30584, start_index=30434, title='A positive feedback loop: RAD18-YAP-TGF-β between triple-negative breast cancer and macrophages regulates cancer stemness and progression - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9005530/#:~:text=correlated%20with%20prognosis,of%20the%20stemness%20phenotype%20by')
87. AnnotationURLCitation(end_index=31192, start_index=31063, title='Role of Rad18 in B cell activation and lymphomagenesis | Scientific Reports', type='url_citation', url='https://www.nature.com/articles/s41598-024-57018-w#:~:text=Several%20studies%20have%20addressed%20the,induced')
88. AnnotationURLCitation(end_index=31338, start_index=31193, title='Role of Rad18 in B cell activation and lymphomagenesis | Scientific Reports', type='url_citation', url='https://www.nature.com/articles/s41598-024-57018-w#:~:text=cooperates%20with%20MAGE,affects%20migration%20and%20invasion%20of')
89. AnnotationURLCitation(end_index=31666, start_index=31521, title='Role of Rad18 in B cell activation and lymphomagenesis | Scientific Reports', type='url_citation', url='https://www.nature.com/articles/s41598-024-57018-w#:~:text=cooperates%20with%20MAGE,affects%20migration%20and%20invasion%20of')
90. AnnotationURLCitation(end_index=32068, start_index=31888, title='RAD18 confers radioresistance of esophagus squamous cell carcinoma through regulating p‐DNA‐PKcs - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9582675/#:~:text=RAD18%20confers%20radioresistance%20of%20esophagus,in%20Dulbecco%27s%20Modified%20Eagle%20Medium')
91. AnnotationURLCitation(end_index=32440, start_index=32287, title='RAD18 promotes colorectal cancer metastasis by activating the epithelial-mesenchymal transition pathway - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC7251712/#:~:text=RAD18%20promotes%20colorectal%20cancer%20metastasis,4%7D%2C%20Jundong')
92. AnnotationURLCitation(end_index=32970, start_index=32785, title='A series of xanthenes inhibiting Rad6 function and Rad6-Rad18 interaction in the PCNA ubiquitination cascade - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8958325/#:~:text=Ubiquitination%20of%20proliferating%20cell%20nuclear,important%20for%20different%20activities%20along')
93. AnnotationURLCitation(end_index=33108, start_index=32971, title='The E3 ligase RAD18-mediated ubiquitination of henipavirus matrix protein promotes its nuclear-cytoplasmic trafficking and viral egress - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/39628457/#:~:text=through%20a%20K63,infection%20is%20attenuated%20in%20RAD18')
94. AnnotationURLCitation(end_index=33413, start_index=33228, title='A series of xanthenes inhibiting Rad6 function and Rad6-Rad18 interaction in the PCNA ubiquitination cascade - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8958325/#:~:text=Ubiquitination%20of%20proliferating%20cell%20nuclear,important%20for%20different%20activities%20along')
95. AnnotationURLCitation(end_index=33748, start_index=33611, title='The E3 ligase RAD18-mediated ubiquitination of henipavirus matrix protein promotes its nuclear-cytoplasmic trafficking and viral egress - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/39628457/#:~:text=through%20a%20K63,infection%20is%20attenuated%20in%20RAD18')
96. AnnotationURLCitation(end_index=34117, start_index=33951, title='EP3237444A1 - Use of rad18 inhibitors in the treatment of tumors - Google Patents', type='url_citation', url='https://patents.google.com/patent/EP3237444A1/en#:~:text=Patents%20patents.google.com%20%20EP3237444A1%20,A1%20EP3237444%20A1%20EP%203237444A1')
97. AnnotationURLCitation(end_index=34198, start_index=34118, title='U.S. Patent for Use of Rad18 inhibitors in the treatment of tumors Patent (Patent # 11,203,757 issued December 21, 2021) - Justia Patents Search', type='url_citation', url='https://patents.justia.com/patent/11203757#:~:text=U,The')
98. AnnotationURLCitation(end_index=34990, start_index=34811, title='The E3 ligase RAD18-mediated ubiquitination of henipavirus matrix protein promotes its nuclear-cytoplasmic trafficking and viral egress - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/39628457/#:~:text=ubiquitination%20cascade%20have%20remained%20elusive,modification%20crucial%20for%20M%27s%20function')
99. AnnotationURLCitation(end_index=35387, start_index=35224, title='The E3 ligase RAD18-mediated ubiquitination of henipavirus matrix protein promotes its nuclear-cytoplasmic trafficking and viral egress - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/39628457/#:~:text=utilizes%20a%20ubiquitination%20complex%20involving,Conversely%2C%20disrupting%20the')
100. AnnotationURLCitation(end_index=35672, start_index=35547, title='The E3 ligase RAD18-mediated ubiquitination of henipavirus matrix protein promotes its nuclear-cytoplasmic trafficking and viral egress - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/39628457/#:~:text=RAD18,infection%20is%20attenuated%20in%20RAD18')
101. AnnotationURLCitation(end_index=35990, start_index=35853, title='The E3 ligase RAD18-mediated ubiquitination of henipavirus matrix protein promotes its nuclear-cytoplasmic trafficking and viral egress - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/39628457/#:~:text=through%20a%20K63,infection%20is%20attenuated%20in%20RAD18')
102. AnnotationURLCitation(end_index=36257, start_index=36120, title='The E3 ligase RAD18-mediated ubiquitination of henipavirus matrix protein promotes its nuclear-cytoplasmic trafficking and viral egress - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/39628457/#:~:text=through%20a%20K63,infection%20is%20attenuated%20in%20RAD18')
103. AnnotationURLCitation(end_index=37000, start_index=36836, title='The E3 ligase RAD18-mediated ubiquitination of henipavirus matrix protein promotes its nuclear-cytoplasmic trafficking and viral egress - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/39628457/#:~:text=plasma%20membranes%20for%20effective%20viral,infection%20is%20attenuated%20in%20RAD18')
104. AnnotationURLCitation(end_index=37521, start_index=37364, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=RAD18%20is%20a%20conserved%20E3,conductor%20at%20the%20replication%20fork')
105. AnnotationURLCitation(end_index=37773, start_index=37660, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=replication%20%28BIR%29%20,12')
106. AnnotationURLCitation(end_index=38339, start_index=38186, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=pathways%20to%20preserve%20genome%20stability,replication%20conflicts')
107. AnnotationURLCitation(end_index=38824, start_index=38668, title='RAD18 directs DNA\xa0double-strand break repair by homologous recombination to post-replicative chromatin - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11260465/#:~:text=RAD18%20is%20an%20E3%20ubiquitin,and%20limits%20the%20distribution%20of')
108. AnnotationURLCitation(end_index=39356, start_index=39212, title='RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair | Cell Death & Disease', type='url_citation', url='https://www.nature.com/articles/s41419-024-06700-y#:~:text=RAD18%20at%20DNA%20double,establishing%20a%20new%20rationale%20to')
109. AnnotationURLCitation(end_index=39515, start_index=39357, title='RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair | Cell Death & Disease', type='url_citation', url='https://www.nature.com/articles/s41419-024-06700-y#:~:text=In%20this%20study%2C%20we%20identified,Although%20S130A%2FS164A%2FT468A%20%283A')
110. AnnotationURLCitation(end_index=39863, start_index=39698, title='ATR limits Rad18-mediated PCNA monoubiquitination to preserve replication fork and telomerase-independent telomere stability | The EMBO Journal', type='url_citation', url='https://www.embopress.org/doi/10.1038/s44318-024-00066-9#:~:text=ATR%20activation%20and%20Rad18,of%20this%20interplay%2C%20remain%20unresolved')
111. AnnotationURLCitation(end_index=40044, start_index=39864, title='ATR limits Rad18-mediated PCNA monoubiquitination to preserve replication fork and telomerase-independent telomere stability | The EMBO Journal', type='url_citation', url='https://www.embopress.org/doi/10.1038/s44318-024-00066-9#:~:text=Rad18%20at%20Ser403%20during%20replication,ATR%E2%80%99s%20role%20extends%20to%20maintaining')
112. AnnotationURLCitation(end_index=40613, start_index=40465, title='Structural basis for RAD18 regulation by MAGEA4 and its implications for RING ubiquitin ligase binding by MAGE family proteins - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10987633/#:~:text=,inhibits%20degradative%20RAD18%20autoubiquitination%2C%20which')
113. AnnotationURLCitation(end_index=40732, start_index=40614, title='Structural basis for RAD18 regulation by MAGEA4 and its implications for RING ubiquitin ligase binding by MAGE family proteins - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10987633/#:~:text=,degradative%20autoubiquitination')
114. AnnotationURLCitation(end_index=41098, start_index=40941, title='Structural basis for RAD18 regulation by MAGEA4 and its implications for RING ubiquitin ligase binding by MAGE family proteins - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10987633/#:~:text=match%20at%20L186%20MAGEA4%20in,drug%20target%20for%20cancer%20therapies')
115. AnnotationURLCitation(end_index=41544, start_index=41398, title='Role of Rad18 in B cell activation and lymphomagenesis | Scientific Reports', type='url_citation', url='https://www.nature.com/articles/s41598-024-57018-w#:~:text=A%20recent%20study%20analysed%20the,of%20generation%20of%20B%20cell')
116. AnnotationURLCitation(end_index=41797, start_index=41648, title='Role of Rad18 in B cell activation and lymphomagenesis | Scientific Reports', type='url_citation', url='https://www.nature.com/articles/s41598-024-57018-w#:~:text=studies%20have%20shown%20different%20roles,We%20find%20no%20activation')
117. AnnotationURLCitation(end_index=41927, start_index=41798, title='Role of Rad18 in B cell activation and lymphomagenesis | Scientific Reports', type='url_citation', url='https://www.nature.com/articles/s41598-024-57018-w#:~:text=Several%20studies%20have%20addressed%20the,induced')
118. AnnotationURLCitation(end_index=42230, start_index=42070, title='Role of Rad18 in B cell activation and lymphomagenesis | Scientific Reports', type='url_citation', url='https://www.nature.com/articles/s41598-024-57018-w#:~:text=defects%20or%20survival%20differences%20between,other%20pathways%20in%20B%20cells')
119. AnnotationURLCitation(end_index=42645, start_index=42492, title='A positive feedback loop: RAD18-YAP-TGF-β between triple-negative breast cancer and macrophages regulates cancer stemness and progression - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9005530/#:~:text=As%20a%20key%20regulator%20of,RAD18%20facilitated%20a%20highly%20stem')
120. AnnotationURLCitation(end_index=42817, start_index=42646, title='A positive feedback loop: RAD18-YAP-TGF-β between triple-negative breast cancer and macrophages regulates cancer stemness and progression - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9005530/#:~:text=tumor%20microenvironment%2C%20remains%20elusive,this%20loop%20and%20suppresses%20cancer')
121. AnnotationURLCitation(end_index=43118, start_index=42968, title='Role of Rad18 in B cell activation and lymphomagenesis | Scientific Reports', type='url_citation', url='https://www.nature.com/articles/s41598-024-57018-w#:~:text=of%20the%20Fanconi%20anaemia%20pathway,play%20a%20role%20during%20viral')
122. AnnotationURLCitation(end_index=43842, start_index=43676, title='EP3237444A1 - Use of rad18 inhibitors in the treatment of tumors - Google Patents', type='url_citation', url='https://patents.google.com/patent/EP3237444A1/en#:~:text=Patents%20patents.google.com%20%20EP3237444A1%20,A1%20EP3237444%20A1%20EP%203237444A1')
123. AnnotationURLCitation(end_index=43923, start_index=43843, title='U.S. Patent for Use of Rad18 inhibitors in the treatment of tumors Patent (Patent # 11,203,757 issued December 21, 2021) - Justia Patents Search', type='url_citation', url='https://patents.justia.com/patent/11203757#:~:text=U,The')
124. AnnotationURLCitation(end_index=45002, start_index=44845, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=RAD18%20is%20a%20conserved%20E3,conductor%20at%20the%20replication%20fork')
125. AnnotationURLCitation(end_index=45116, start_index=45003, title='RAD18 opposes transcription-associated genome instability through FANCD2 recruitment - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC9767342/#:~:text=replication%20%28BIR%29%20,12')