Fetched human ASCC2 with just fetch-gene human ASCC2; GOA seeded 38 review
annotations from 39 GOA rows. Refreshed PMID caching successfully. Falcon deep
research was attempted with perplexity-lite fallback; Falcon timed out after
600 seconds and the fallback failed with a Perplexity API quota 401, so no
provider deep-research file was created. This review therefore uses the cached
primary literature, UniProt, Reactome, and the PN projection report directly.
Core synthesis: ASCC2 is a CUE-domain ubiquitin-binding subunit used in two
well-supported ASCC contexts. In the nucleus, ASCC2 recognizes K63-linked
polyubiquitin signals during alkylation damage and helps recruit ASCC repair
machinery PMID:29144457. Loss of ASCC2 impairs
repair kinetics PMID:29144457.
In the proteostasis/RQC context, ASCC2 works with ASCC3 and TRIP4 as the human
RQC-trigger complex. Hashimoto et al. identify the trimeric hRQT complex
PMID:32099016.
Juszkiewicz et al. show ASCC disassembles collided ribosomes PMID:32579943. Narita et al.
connect this to K63-polyubiquitinated uS10 and ASCC2 ubiquitin binding
PMID:36302773.
PN projection decision: the PN report projects ASCC2 to GO:0072344 rescue of
stalled cytosolic ribosome as already present, and to GO:0006515 protein
quality control for misfolded or incompletely synthesized proteins as a
candidate new-to-GOA group-level RQC annotation
[file:projects/PROTEOSTASIS/reports/pn_projection/pn_projected_annotations.tsv
"ASCC2 Translation|Cytosolic translation|Ribosome-associated QC|Ribosomal
rescue"]. I treated the projection conservatively: keep and support the specific
RQC annotations (GO:0072344, GO:0032790, GO:1990116, GO:0180022,
GO:0070530), but do not propose adding broad GO:0006515 because the existing
specific GO annotations already capture ASCC2's proteostasis role.
Annotation decisions:
GO:0043130 ubiquitin binding: MODIFY to GO:0070530 K63-linked
polyubiquitin modification-dependent protein binding.GO:0005515 protein binding: remove or mark over-annotated depending onGO:0006260 DNA replication: REMOVE; the cited evidence supports DNAA Falcon (Edison Scientific) deep-research report was generated on 2026-06-07
(the 2026-06-03 attempt had failed). It does not overturn any existing
annotation decision; it adds mechanistic depth and several primary references
that strengthen the two established core functions. Distinguishing
CONFIRMS / NEW / PROVISIONAL below.
CONFIRMS (molecular function / CUE specificity): The K63-linkage preference of
the ASCC2 CUE domain is now backed by quantitative structural/biophysical work
beyond the references already cited. Lombardi et al. show the CUE domain binds
K63-linked diUb by contacting BOTH distal and proximal ubiquitin, with strong
linkage preference (ITC: monoUb Kd ~57 uM; K63Ub2 ~8.7-10.4 uM; K48Ub2 ~98 uM;
M1/linear diUb ~400 uM), and N-terminal alpha1-helix residues (E467, S470)
are required for recruitment to alkylation-damage foci
[PMID:34971705 (Lombardi 2022) "recognizes adjacent ubiquitins in K63-linked
polyubiquitin"]. Supports the existing GO:0070530 MODIFY/ACCEPT decisions; no
change needed, but adds a primary structural reference.
NEW (ASCC2-ASCC3 scaffold interface; disease principle): A dedicated
structural study maps the ASCC2 N-terminal region (~aa 1-434) as the
high-affinity (Kd ~3.5 nM) ASCC3-binding module, clasped by the ASCC3
N-terminal arms, and shows somatic cancer mutations at this evolutionarily
conserved interface reduce ASCC2-ASCC3 affinity -- a "loss of scaffold
coupling" disease principle rather than loss of helicase catalysis
[PMID:33139697 (Jia 2020) "interaction of DNA repair factors ASCC2 and ASCC3
is affected by somatic cancer mutations"]. This is mechanistic context for the
ASCC2-ASCC3 interaction (relevant to the GO:0005515 MARK_AS_OVER_ANNOTATED
decision on PMID:29997253) and to GO:1990391 DNA repair complex. Does not
change actions; supports representing the interaction via complex/process
terms rather than generic protein binding.
NEW (pathway selection / complex modularity): TRIP4 and ALKBH3 bind ASCC3
mutually exclusively, so the ASCC3 motor is directed either to RQC (TRIP4 /
RQT complex) or to DNA alkylation repair (ALKBH3 complex); ASCC2 is shared by
both assemblies as the K63-Ub reader [PMID:37019967 (Jia 2023) "TRIP4 binds
ASCC3 mutually exclusively with the DNA/RNA dealkylase, ALKBH3"]. This
reinforces, with a mechanistic basis, why ASCC2 has dual nuclear-repair and
cytosolic-RQC roles in the review.
NEW (RQC mechanism refinement): In vitro reconstitution shows ribosomal
collision is NOT strictly required for ZNF598 ubiquitination or ASCC-mediated
disassembly; ASCC can split monosomes, polysome queues, and even 48S
complexes given (i) >=30-35 nt of 3' mRNA downstream of the P site and (ii)
sufficiently long K63-linked ubiquitin chains on uS10/eS10
[PMID:38366554 (Miscicka 2024) "Ribosomal collision is not a prerequisite for
ZNF598-mediated ribosome ubiquitination and disassembly of ribosomal complexes
by ASCC"]. Consistent with existing GO:0032790 / GO:0072344 / GO:0070530
decisions; sharpens the mechanism but does not change any action.
CONFIRMS (RQC synthesis / in vivo vs in vitro tension): A 2024 review
reiterates ASCC2 CUE-mediated K63-Ub recognition as the recruitment step for
ASCC ribosome splitting, and notes context-dependence between strong in vitro
requirement and partial in vivo dispensability of ASCC2 ubiquitin binding
[PMID:39661518 (Ford 2024) "Ubiquitin-dependent translation control
mechanisms: Degradation and beyond"]. Supports the existing suggested question
about whether CUE binding is required under endogenous conditions.
PROVISIONAL / LOW-CONFIDENCE (disease associations, NOT used to change
annotations): A pan-cancer analysis reports ASCC2 altered in ~1.8% of 10,967
tumors with tumor-type enrichments and survival associations
[PMID(unresolved): Pan et al. 2025, Sci Rep, doi:10.1038/s41598-025-03946-0];
a prostate-cancer lncRNA/miRNA ceRNA axis (TCONS_00027385/miR-874-5p/ASCC2) is
preprint-level (doi:10.21203/rs.3.rs-728951/v1) and treated as
hypothesis-generating only. Open Targets neurodegeneration/diabetes
associations are GWAS/credible-set level. None of these are used to alter GO
annotations.
References added to ASCC2-ai-review.yaml (statement-only findings, full text not
fetched): PMID:33139697, PMID:34971705, PMID:37019967, PMID:38366554,
PMID:39661518, PMID:36902118. The Brickner 2019 and Soll 2019 ArXiv/thesis items
and the Soll 2018 JBC paper (already represented as ASCC1 work via PMID:29997253)
were left in notes only. PMIDs for Pan 2025 and the Han 2021 preprint were not
reliably resolved to PubMed IDs and are kept in notes only.