The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The gene symbol ENDOU in Homo sapiens encodes placental protein 11 (PP11), a member of the eukaryotic EndoU-family endoribonucleases. The key primary biochemical study explicitly analyzes human PP11/ENDOU (UniProt P21128) and establishes its enzymatic identity, distinguishing it from the viral nidoviral EndoU (coronavirus nsp15) that is often discussed in parallel due to homology. Throughout this report, mechanistic claims are supported only when the cited source explicitly addresses human ENDOU/PP11 rather than viral EndoU. (laneve2008thetumormarker pages 1-2, laneve2008thetumormarker pages 2-3)
Human ENDOU/PP11 is an uridylate-specific endoribonuclease (an RNase) that binds and cleaves RNA internally (endoribonucleolysis), rather than a protease. This corrected earlier annotations that had labeled PP11 as a serine protease; biochemical testing on recombinant protein found no detectable protease activity, supporting reclassification as an RNase. (laneve2008thetumormarker pages 1-2, laneve2008thetumormarker pages 7-8, laneve2008thetumormarker pages 3-5)
Laneve et al. (2008, Journal of Biological Chemistry, Dec 2008) demonstrated that recombinant human ENDOU cleaves single-stranded RNA to generate products bearing 2′,3′-cyclic phosphate termini—an important mechanistic signature shared with related EndoU-family RNases. (laneve2008thetumormarker pages 1-2, laneve2008thetumormarker pages 2-3, laneve2008thetumormarker pages 6-7)
Biochemical assays showed ENDOU is uridylate-directed (cleaves at/near uridylate residues) and is Mn²⁺-dependent under the tested in vitro conditions. In that study, activity was evaluated using defined oligoribonucleotide substrates and reaction buffers that included MnCl₂; cleavage preferences were reported around dinucleotide contexts including GU, UA, AU, CU, UU, and UC (interpretable as sequence-context preferences flanking uridylates). (laneve2008thetumormarker pages 1-2, laneve2008thetumormarker pages 6-7, laneve2008thetumormarker pages 7-8)
More recent mechanistic work (outside the requested 2023–2024 window but directly informative) supports that eukaryotic EndoU enzymes can be divalent metal–regulated, with human EndoU exhibiting calcium-dependent activation through an allosteric mechanism involving its N-terminal extension and catalytic core. (Malard et al., Nature Communications, Apr 2025; https://doi.org/10.1038/s41467-025-58462-6) (malard2025molecularbasisfor pages 1-2)
Laneve et al. combined homology modeling (using Xenopus XendoU as a template; PDB 2c1w) with site-directed mutagenesis and identified residues required for cleavage activity: E243, H244, E249, H259, and K302 (human numbering as reported). Mutants substantially lost processing activity while retaining RNA-binding in mobility-shift assays, supporting these residues as part of the functional catalytic apparatus. The authors also highlighted a flexible loop/flap (Gly248–Asn260) in the predicted RNA-binding region as a candidate determinant of binding and specificity. (Laneve et al., JBC, Dec 2008; https://doi.org/10.1074/jbc.m805759200) (laneve2008thetumormarker pages 2-3, laneve2008thetumormarker pages 6-7, laneve2008thetumormarker pages 7-8, laneve2008thetumormarker pages 3-5)
ENDOU/PP11 was initially isolated as a placenta-derived glycoprotein and is described as highly expressed in the syncytiotrophoblast. Prior localization work cited by Laneve et al. reported PP11 to be exclusively localized in the cytoplasm of syncytiotrophoblast. (laneve2008thetumormarker pages 1-2, laneve2008thetumormarker pages 2-3)
When PP11 cDNA was expressed in E. coli, two forms were reported: a ~45 kDa precursor and a ~42 kDa mature protein. Laneve et al. purified and studied a recombinant His-tagged form corresponding to the mature protein in enzymatic assays. (laneve2008thetumormarker pages 1-2, laneve2008thetumormarker pages 2-3)
Proteomics on isolated placental cytotrophoblasts found ENDOU to be upregulated in placentas complicated by preeclampsia with fetal growth restriction (PE-FGR) relative to controls, suggesting ENDOU expression changes may be a feature of placental hypoplasia/pathophysiology (study design: LC–MS/MS differential proteomics). (Nomoto et al., J Clin Biochem Nutr, Jul 2021; https://doi.org/10.3164/jcbn.21-37) (nomoto2021upregulationofendou pages 4-5, nomoto2021upregulationofendou pages 6-6)
Given its cytoplasmic localization in syncytiotrophoblast and biochemical RNase activity, Laneve et al. proposed that PP11 could contribute to placental physiology via RNA recognition and degradation, including a hypothesis that RNA binding/cleavage might help recognize viral RNAs or mRNAs (a proposed role rather than a direct demonstration of endogenous substrates). (laneve2008thetumormarker pages 8-8)
A major recent development is a 2023 Nature Communications study in Drosophila identifying an EndoU-family RNase (Arlr) as a regulator of lipid droplet homeostasis during aging. Importantly for human ENDOU annotation, the study reports that transgenic full-length human ENDOU expressed in fly fat body rescued arlr mutant phenotypes (lipid droplet size and total triacylglycerol levels) and reduced mRNA levels of candidate lipolysis genes in that mutant background, supporting conserved EndoU-family functionality in mRNA-level regulation relevant to lipid metabolism. This provides experimental evidence for a conserved capacity of human ENDOU to functionally substitute for an EndoU-family RNase in vivo (cross-species rescue), though it does not identify native human ENDOU targets in human tissues. (Sun et al., Nature Communications, Oct 2023; https://doi.org/10.1038/s41467-023-42042-7) (sun2023theendoribonucleasearlr pages 6-7, sun2023theendoribonucleasearlr pages 1-2)
An evolutionary analysis supports that EndoU-family RNases are part of an ancient RNase lineage with an evolutionary connection to RNase A-like folds, reinforcing that ENDOU is best interpreted as a conserved RNase domain protein rather than a placenta-specific oddity. (Mushegian et al., RNA, Apr 2020; https://doi.org/10.1261/rna.074385.119) (OpenTargets Search: -ENDOU)
Laneve et al. summarize prior tumor-marker reports for PP11/ENDOU and provide explicit detection frequencies:
- 66.7% of analyzed mucinous cystadenocarcinomas
- 57.1% of analyzed serous cystadenocarcinomas
- 47% of breast cancers
- 38% of testicular and gastric cancers
with absence in normal ovaries (as reported in the cited tumor-marker context). These values reflect historical tumor-marker literature summarized in the 2008 biochemical reclassification paper. (Laneve et al., J Biol Chem, Dec 2008; https://doi.org/10.1074/jbc.m805759200) (laneve2008thetumormarker pages 1-2)
Two later oncology studies (bioinformatics + experimental validation) extend biomarker applications:
- In head and neck squamous cell carcinoma (HNSCC), ENDOU was identified as an independent survival marker candidate; ENDOU overexpression reduced proliferation and migration in cell lines in that study’s model system. (Xu et al., Frontiers in Oncology, Feb 2021; https://doi.org/10.3389/fonc.2020.522332) (OpenTargets Search: -ENDOU)
- In cervical squamous cell carcinoma, a transcriptomic meta-analysis selected ENDOU as a candidate diagnostic biomarker and immunohistochemistry reported ~1% positivity in tumors vs ~40% positivity in non-tumor tissues (in the cohort examined), consistent with reduced expression in tumor. (Bašić et al., Oncology Letters, Oct 2021; https://doi.org/10.3892/ol.2021.13101) (OpenTargets Search: -ENDOU)
ENDOU’s upregulation in PE-FGR cytotrophoblasts suggests potential use as a placental pathology biomarker or mechanistic clue for disease, though causality and clinical utility require validation in larger cohorts. (Nomoto et al., Jul 2021; https://doi.org/10.3164/jcbn.21-37) (nomoto2021upregulationofendou pages 4-5, nomoto2021upregulationofendou pages 6-6)
The strongest 2023 primary evidence retrieved here is the cross-species functional study showing human ENDOU can rescue an EndoU-family lipid phenotype in vivo in flies, supporting a broader physiological scope for ENDOU-like RNases beyond placenta/tumor-marker contexts. (Sun et al., Oct 2023; https://doi.org/10.1038/s41467-023-42042-7) (sun2023theendoribonucleasearlr pages 6-7, sun2023theendoribonucleasearlr pages 1-2)
A targeted 2023–2024 literature search retrieved few directly relevant full-text ENDOU mechanistic studies for humans; therefore, 2024 ENDOU-specific advances (e.g., new human interactomes, endogenous RNA targetomes, new structures, or clinical validations) could not be comprehensively summarized from the currently retrieved corpus. This report therefore emphasizes validated mechanistic foundations (2008) plus the most relevant recent functional work available (2023). (laneve2008thetumormarker pages 1-2, sun2023theendoribonucleasearlr pages 1-2)
Open Targets lists disease associations for ENDOU with low-to-moderate scores across several conditions (e.g., cardiovascular disease, age-related macular degeneration, kidney disease, basal cell carcinoma, retinitis pigmentosa), but the evidence entries retrieved here did not include linked PubMed/PMC identifiers; therefore these should be treated as hypothesis-generating rather than definitive without underlying study inspection. (OpenTargets Search: -ENDOU)
| Study | Year/Month | Publication type | Key finding for ENDOU function | Enzymatic details (substrate/cofactor/products) | Localization/expression | Application/disease context | URL/DOI |
|---|---|---|---|---|---|---|---|
| Laneve et al., J. Biol. Chem. | 2008/Dec | Primary research | Human ENDOU/PP11 was experimentally reclassified from a putative protease to an endoribonuclease in the XendoU/EndoU family; mutagenesis supported a catalytic center involving H244, E243, E249, H259, and K302 (laneve2008thetumormarker pages 1-2, laneve2008thetumormarker pages 2-3, laneve2008thetumormarker pages 6-7, laneve2008thetumormarker pages 7-8, laneve2008thetumormarker pages 3-5) | Binds RNA and cleaves single-stranded RNA at uridylates in a Mn²⁺-dependent reaction, yielding 2′,3′-cyclic phosphate ends; cleavage preference reported around GU, UA, AU, CU, UU, and UC motifs (laneve2008thetumormarker pages 1-2, laneve2008thetumormarker pages 2-3, laneve2008thetumormarker pages 6-7, laneve2008thetumormarker pages 7-8) | High placental expression, especially syncytiotrophoblast; prior work cited in the paper reported exclusive cytoplasmic localization in syncytiotrophoblast; precursor (~45 kDa) and mature (~42 kDa) forms were described (laneve2008thetumormarker pages 1-2, laneve2008thetumormarker pages 3-5, laneve2008thetumormarker pages 2-3, laneve2008thetumormarker pages 7-8) | Tumor-marker context: reported in 66.7% of mucinous cystadenocarcinomas, 57.1% of serous cystadenocarcinomas, 47% of breast cancers, and 38% of testicular/gastric cancers; authors also proposed a possible placental antiviral role (laneve2008thetumormarker pages 1-2, laneve2008thetumormarker pages 8-8) | https://doi.org/10.1074/jbc.m805759200 |
| Mushegian et al., RNA | 2020/Apr | Evolutionary/computational primary research | Positioned EndoU-family ribonucleases, including human ENDOU, within an ancient evolutionary relationship to the RNase A-like superfamily, supporting ENDOU as part of a deeply conserved RNase lineage rather than an isolated placental protein class (OpenTargets Search: -ENDOU) | Evolution/structure focused; no new human biochemical assay details extracted here beyond EndoU-family catalytic-domain homology (OpenTargets Search: -ENDOU) | Family-level context across bacteria, archaea, eukaryotes, and viruses; not a human localization study (OpenTargets Search: -ENDOU) | Useful for functional inference and domain-based annotation of human ENDOU (OpenTargets Search: -ENDOU) | https://doi.org/10.1261/rna.074385.119 |
| Nomoto et al., J. Clin. Biochem. Nutr. | 2021/Jul | Primary research | Proteomics identified ENDOU as significantly upregulated in cytotrophoblasts from placentas with preeclampsia/fetal growth restriction (PE-FGR), reinforcing relevance in placental biology (nomoto2021upregulationofendou pages 4-5, nomoto2021upregulationofendou pages 6-6) | Described, citing prior biochemical work, as a poly(U)-specific/uridylate-cleaving endoribonuclease acting on single-stranded RNA in an Mn²⁺-dependent manner; no new catalytic chemistry defined in this study (nomoto2021upregulationofendou pages 4-5) | Increased ENDOU protein expression in PE-FGR cytotrophoblasts versus controls (nomoto2021upregulationofendou pages 4-5, nomoto2021upregulationofendou pages 6-6) | Pregnancy disease/placental pathology biomarker context; paper also discussed homology to coronavirus Nsp15 and possible relevance to stress/host-response pathways (nomoto2021upregulationofendou pages 4-5, nomoto2021upregulationofendou pages 6-6) | https://doi.org/10.3164/jcbn.21-37 |
| Xu et al., Front. Oncol. | 2021/Feb | Primary research with bioinformatics and cell assays | ENDOU emerged as an independent prognostic marker candidate in head and neck squamous cell carcinoma (HNSCC); overexpression inhibited proliferation and migration of FaDu and Cal-27 cells, consistent with a tumor-suppressive effect in that setting (OpenTargets Search: -ENDOU) | Functional cancer study; enzymatic mechanism not newly characterized, but paper identified ENDOU/PP11 as uridylate-specific endoribonuclease based on prior literature (OpenTargets Search: -ENDOU) | Reported relatively low ENDOU expression in HNSCC, especially HPV-positive samples; correlations with immune infiltrates were noted (OpenTargets Search: -ENDOU) | Prognostic biomarker and tumor-suppressor-like candidate in HNSCC (OpenTargets Search: -ENDOU) | https://doi.org/10.3389/fonc.2020.522332 |
| Bašić et al., Oncol. Lett. | 2021/Oct | Primary research/meta-analysis with immunohistochemistry | Integrative transcriptomic meta-analysis nominated ENDOU as a potential diagnostic biomarker in cervical squamous cell carcinoma (OpenTargets Search: -ENDOU) | No new enzymology; paper characterized ENDOU as a soluble poly(U)-specific endoribonuclease based on prior studies (OpenTargets Search: -ENDOU) | IHC showed ENDOU positivity in ~1% of tumors versus ~40% of non-tumor tissues in the analyzed cohort, consistent with reduced expression in cancer tissue (OpenTargets Search: -ENDOU) | Potential diagnostic biomarker for cervical squamous cell carcinoma; low ENDOU associated with inhibition of epithelial development/differentiation processes (OpenTargets Search: -ENDOU) | https://doi.org/10.3892/ol.2021.13101 |
| Sun et al., Nat. Commun. | 2023/Oct | Primary research | Drosophila Arlr was identified as an ortholog/paralog system for mammalian EndoU biology; human ENDOU rescued arlr mutant lipid-storage defects, supporting conserved ENDOU-family function in post-transcriptional control of lipid metabolism (sun2023theendoribonucleasearlr pages 6-7, sun2023theendoribonucleasearlr pages 1-2) | In the cross-species rescue experiments, human ENDOU expression restored lipid droplet size and TAG levels and reduced mRNAs of candidate lipolysis genes; study implies conserved RNase-dependent control of target mRNAs but did not provide new human biochemical reaction chemistry (sun2023theendoribonucleasearlr pages 6-7, sun2023theendoribonucleasearlr pages 1-2) | Functional rescue was achieved by transgenic human ENDOU expression in Drosophila fat body; paper notes ENDOU contains a signal peptide and EndoU domain (sun2023theendoribonucleasearlr pages 6-7) | Mechanistic relevance to lipid homeostasis/aging and evidence for conserved physiological roles beyond placenta (sun2023theendoribonucleasearlr pages 6-7, sun2023theendoribonucleasearlr pages 1-2) | https://doi.org/10.1038/s41467-023-42042-7 |
| Malard et al., Nat. Commun. | 2025/Apr | Primary structural/biophysical research | Although outside 2023–2024, this mechanistically important study showed that eukaryotic/human EndoU is activated allosterically by Ca²⁺ binding remote from the catalytic triad, linking its N-terminal extension to catalytic control (malard2025molecularbasisfor pages 1-2) | Crystal structure and biophysical assays supported calcium-dependent activation; calcium binding triggers structural rearrangements and water-mediated signaling to the catalytic core; study builds on prior knowledge that human ENDOU cleaves ssRNA 5′ of uridylates (malard2025molecularbasisfor pages 1-2) | Reported expression in placenta and stratified squamous epithelia; cited as a biomarker in several cancers (squamous cell carcinoma, ovarian adenocarcinoma, non-trophoblastic tumors, breast cancer) (malard2025molecularbasisfor pages 1-2) | Mechanistic clarification of ENDOU regulation and renewed biomarker relevance; not within requested date priority window but highly informative for annotation (malard2025molecularbasisfor pages 1-2) | https://doi.org/10.1038/s41467-025-58462-6 |
Table: This table compiles the most relevant evidence for human ENDOU/PP11 across foundational biochemistry, placental pathology, cancer biomarker studies, evolutionary inference, and recent cross-species functional work. It emphasizes experimentally supported claims and separates mechanistic human ENDOU findings from broader EndoU-family context.
References
(laneve2008thetumormarker pages 1-2): Pietro Laneve, Ubaldo Gioia, Rino Ragno, Fabio Altieri, Carmen Di Franco, Tiziana Santini, Massimo Arceci, Irene Bozzoni, and Elisa Caffarelli. The tumor marker human placental protein 11 is an endoribonuclease*. Journal of Biological Chemistry, 283:34712-34719, Dec 2008. URL: https://doi.org/10.1074/jbc.m805759200, doi:10.1074/jbc.m805759200. This article has 65 citations and is from a domain leading peer-reviewed journal.
(laneve2008thetumormarker pages 2-3): Pietro Laneve, Ubaldo Gioia, Rino Ragno, Fabio Altieri, Carmen Di Franco, Tiziana Santini, Massimo Arceci, Irene Bozzoni, and Elisa Caffarelli. The tumor marker human placental protein 11 is an endoribonuclease*. Journal of Biological Chemistry, 283:34712-34719, Dec 2008. URL: https://doi.org/10.1074/jbc.m805759200, doi:10.1074/jbc.m805759200. This article has 65 citations and is from a domain leading peer-reviewed journal.
(laneve2008thetumormarker pages 7-8): Pietro Laneve, Ubaldo Gioia, Rino Ragno, Fabio Altieri, Carmen Di Franco, Tiziana Santini, Massimo Arceci, Irene Bozzoni, and Elisa Caffarelli. The tumor marker human placental protein 11 is an endoribonuclease*. Journal of Biological Chemistry, 283:34712-34719, Dec 2008. URL: https://doi.org/10.1074/jbc.m805759200, doi:10.1074/jbc.m805759200. This article has 65 citations and is from a domain leading peer-reviewed journal.
(laneve2008thetumormarker pages 3-5): Pietro Laneve, Ubaldo Gioia, Rino Ragno, Fabio Altieri, Carmen Di Franco, Tiziana Santini, Massimo Arceci, Irene Bozzoni, and Elisa Caffarelli. The tumor marker human placental protein 11 is an endoribonuclease*. Journal of Biological Chemistry, 283:34712-34719, Dec 2008. URL: https://doi.org/10.1074/jbc.m805759200, doi:10.1074/jbc.m805759200. This article has 65 citations and is from a domain leading peer-reviewed journal.
(laneve2008thetumormarker pages 6-7): Pietro Laneve, Ubaldo Gioia, Rino Ragno, Fabio Altieri, Carmen Di Franco, Tiziana Santini, Massimo Arceci, Irene Bozzoni, and Elisa Caffarelli. The tumor marker human placental protein 11 is an endoribonuclease*. Journal of Biological Chemistry, 283:34712-34719, Dec 2008. URL: https://doi.org/10.1074/jbc.m805759200, doi:10.1074/jbc.m805759200. This article has 65 citations and is from a domain leading peer-reviewed journal.
(malard2025molecularbasisfor pages 1-2): Florian Malard, Kristen Dias, Margaux Baudy, Stéphane Thore, Brune Vialet, Philippe Barthélémy, Sébastien Fribourg, Fedor Karginov, and Sebastien Campagne. Molecular basis for the calcium-dependent activation of the ribonuclease endou. Nature Communications, Apr 2025. URL: https://doi.org/10.1038/s41467-025-58462-6, doi:10.1038/s41467-025-58462-6. This article has 7 citations and is from a highest quality peer-reviewed journal.
(nomoto2021upregulationofendou pages 4-5): Masataka Nomoto, Tomomi Kotani, Rika Miki, Takafumi Ushida, Kenji Imai, Yukako Iitani, Sho Tano, Jingwen Wang, Yoshinori Moriyama, Tomoko Kobayashi, Nobuko Mimura, Takayuki Iriyama, Fumitaka Kikkawa, and Hiroaki Kajiyama. Upregulation of endou in cytotrophoblasts from placenta complicated with preeclampsia and fetal growth restriction. Journal of Clinical Biochemistry and Nutrition, 69:280-285, Jul 2021. URL: https://doi.org/10.3164/jcbn.21-37, doi:10.3164/jcbn.21-37. This article has 0 citations and is from a peer-reviewed journal.
(nomoto2021upregulationofendou pages 6-6): Masataka Nomoto, Tomomi Kotani, Rika Miki, Takafumi Ushida, Kenji Imai, Yukako Iitani, Sho Tano, Jingwen Wang, Yoshinori Moriyama, Tomoko Kobayashi, Nobuko Mimura, Takayuki Iriyama, Fumitaka Kikkawa, and Hiroaki Kajiyama. Upregulation of endou in cytotrophoblasts from placenta complicated with preeclampsia and fetal growth restriction. Journal of Clinical Biochemistry and Nutrition, 69:280-285, Jul 2021. URL: https://doi.org/10.3164/jcbn.21-37, doi:10.3164/jcbn.21-37. This article has 0 citations and is from a peer-reviewed journal.
(laneve2008thetumormarker pages 8-8): Pietro Laneve, Ubaldo Gioia, Rino Ragno, Fabio Altieri, Carmen Di Franco, Tiziana Santini, Massimo Arceci, Irene Bozzoni, and Elisa Caffarelli. The tumor marker human placental protein 11 is an endoribonuclease*. Journal of Biological Chemistry, 283:34712-34719, Dec 2008. URL: https://doi.org/10.1074/jbc.m805759200, doi:10.1074/jbc.m805759200. This article has 65 citations and is from a domain leading peer-reviewed journal.
(sun2023theendoribonucleasearlr pages 6-7): Xiaowei Sun, Jie Shen, Norbert Perrimon, Xue Kong, and Dan Wang. The endoribonuclease arlr is required to maintain lipid homeostasis by downregulating lipolytic genes during aging. Nature Communications, Oct 2023. URL: https://doi.org/10.1038/s41467-023-42042-7, doi:10.1038/s41467-023-42042-7. This article has 13 citations and is from a highest quality peer-reviewed journal.
(sun2023theendoribonucleasearlr pages 1-2): Xiaowei Sun, Jie Shen, Norbert Perrimon, Xue Kong, and Dan Wang. The endoribonuclease arlr is required to maintain lipid homeostasis by downregulating lipolytic genes during aging. Nature Communications, Oct 2023. URL: https://doi.org/10.1038/s41467-023-42042-7, doi:10.1038/s41467-023-42042-7. This article has 13 citations and is from a highest quality peer-reviewed journal.
(OpenTargets Search: -ENDOU): Open Targets Query (-ENDOU, 5 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.