Review Papers Claim by Claim

Key claims (visual-first)

• RAD18 is overexpressed in GBM and glioblastoma stem cells (GSCs) and correlates with poor prognosis in TCGA data Preprint clinical/TCGA analysis
• RAD18 depletion (multiple si/sh) causes growth arrest (G1), loss of BrdU incorporation, reduction of gliomasphere formation, decreased Sox2/Oct4, and reduced tumor growth in xenografts Preprint functional assays
• Rescue experiments with catalytically‑dead RAD18 restore proliferation, implying a non‑enzymatic (scaffolding/regulatory) role Preprint rescue data
• RAD18 appears to regulate YAP/Hippo signaling: RAD18 loss reduces nuclear YAP and leads to YAP phosphorylation/retention in cytoplasm; YAP overexpression rescues proliferation Preprint YAP/Hippo link
• Ectopic RAD18 increases proliferation and features of transformation in NIH3T3 (soft agar, colony formation) Preprint NIH3T3 assay

Strengths — why the dataset is persuasive

1. Multiple independent perturbations: siRNA and inducible shRNA sequences, plus rescue with differently mutated RAD18 constructs, reduce off‑target concerns Preprint methods robustness
2. Concordant in vitro and in vivo phenotypes: G1 arrest, stemness loss, and smaller orthotopic tumors align across assays, strengthening biological relevance Preprint phenotypic consistency
3. Clinical correlation: TCGA/IHC analysis suggests clinical relevance and prognostic association, supporting translational value Preprint clinical link

Major weaknesses, uncertainties, and blind spots

• Mechanistic gap: the molecular link between RAD18 and YAP nuclear retention remains unproven. The work shows correlation + genetic epistasis (YAP rescue), but lacks biochemical evidence (e.g., co‑IP, proximity ligation, mapping of interacting domains or post‑translational modifications) to explain how RAD18 controls YAP localization or stability Preprint mechanistic gap
• Non-catalytic claim needs broader mechanistic corroboration: other groups have shown RAD18 catalytic roles (PCNA mono-ubiquitination, TLS) are central to DDR and replication stress responses RAD18 canonical roles
• Lack of deposited raw data / full blots: the paper states that data are available on request. Public deposition of uncropped blots, raw flow cytometry FCS files, and xenograft measurement tables is needed to maximize reproducibility and allow reanalysis Preprint data availability
• Cell-line generalizability & heterogeneity: experiments were done in several GBM lines and two primary GSCs (Gb4, Gb7) but GBM inter-patient heterogeneity is high; TCGA analyses are helpful but functional studies across more patient-derived GSCs and molecular subtypes (classical/proneural/mesenchymal) would strengthen generality Preprint cohort limits
• Potential compensatory pathways and redundancy: RAD18 interfaces with multiple DDR proteins (RAD6, RNF8/RNF168, PCNA/Polκ). The authors show Rad6 unchanged, and Polκ not phenocopying RAD18 depletion in proliferation, but systematic interrogation of interacting partners (co-IP/MS) was not shown — leaving open network compensation possibilities Prior RAD18-GBM functional studies

Context with prior literature (concise)

1. RAD18 canonical role: TLS/PCNA mono‑ubiquitination and replication damage tolerance is well established; RAD18 also participates in DSB repair and chromatin ubiquitin signaling (UBZ domain) — the present paper adds an apparent TLS‑independent pro‑proliferative function in GBM, echoing recent reports linking RAD18 to cancer progression and therapy resistance Preprint & prior work
2. Related cancer work: RAD18 has been implicated in supporting oncogenic replication stress tolerance and mutagenesis in other cancers; a RAD18–YAP link was recently reported in triple‑negative breast cancer, consistent with the present GMB observations but requiring cross‑validation of mechanisms across tumor types Molecular RAD18 context
3. Cell-type specificity of RAD18 phenotypes: other studies show RAD18 loss phenotypes vary by cell type (e.g., hyper-recombination in HCT116 but not RPE-1) — consistent with the present claim that RAD18's role in proliferation could be context dependent and may exploit GBM-specific network wiring Cell-type specificity of RAD18

Practical reproducibility checklist (what I would want to see to accept claims)

1. Public deposition of raw data: uncropped Western blots, raw flow cytometry FCS files, ELDA raw well-by-well counts, xenograft tumor measurements and randomization records, and statistical scripts (GraphPad/linear mixed model code). The authors currently state data are available on request — this is insufficient for community reproducibility Preprint data statement
2. Biochemical interaction evidence: co-immunoprecipitation or proximity ligation showing physical/or indirect complexing between RAD18 and YAP regulators (e.g., LATS1/2, MOB1, AMOT, or YAP itself), or mass‑spec of RAD18 interactome in GBM cells to identify effectors that influence YAP localization.
3. Mapping of RAD18 domain(s) responsible for the non‑catalytic effect: truncation/mapping experiments (e.g., UBZ, SAP, RAD6-binding) to locate the scaffolding interface would clarify mechanism and therapeutic targeting strategy.
4. Rescue with mutants that separate catalytic vs non‑catalytic functions while controlling expression level: expression levels of rescue constructs should be shown to match endogenous RAD18 to avoid artefactual overexpression effects (NIH3T3 oncogenicity results may be expression-level dependent).
5. Broaden GSCs tested to multiple patient-derived lines across GBM subtypes and rigorously annotate genetic drivers (EGFR amplification/PTEN status/IDH1), to test generality.

Suggested targeted experiments (high value, doable)

1. RAD18 interactome in GBM: IP-MS of endogenous RAD18 in Gb4/Gb7 with crosslinking to identify associated proteins; focus on Hippo pathway components and nuclear transport machinery — would identify direct effectors.
2. Test whether RAD18 affects YAP phosphorylation by LATS: measure LATS1/2 activity, YAP S127 phosphorylation kinetics, and proteasome dependence of YAP degradation after RAD18 KD; rescue with phosphorylation-resistant YAP-S127A to see if nuclear retention is sufficient.
3. Domain swap and mapping: generate RAD18 truncations/mutants to define the minimal non-catalytic domain that rescues proliferation — critical to design inhibitors that block scaffolding rather than catalytic site.
4. CRISPR RAD18 knockout vs inducible knockdown: compare acute depletion to chronic KO to detect compensation/adaptive changes; perform RNA-seq after acute KD to identify transcriptional programs downstream of RAD18 loss (Hippo/YAP targets expected to change).
5. Pharmacologic modulation: combine RAD18 depletion with YAP inhibitors (e.g., verteporfin or TEAD inhibitors) in GBM models to test for synthetic interactions (authors suggest combination therapy).

Conclusion and confidence

The manuscript provides multi-layered evidence that RAD18 supports GBM proliferation and GSC maintenance by a mechanism that appears independent of canonical E3 catalytic activity and is linked to regulation of the Hippo/YAP pathway. Evidence is consistent and biologically plausible, but key mechanistic steps (how RAD18 controls YAP nuclear retention) are not established and raw data are not publicly deposited. The work is promising and of moderate-to-high quality, but further biochemical mapping, broader patient‑derived model testing, and open data would substantially raise confidence.

Confidence (subjective): moderate (6/10) — claims well-supported phenotypically, mechanistic inference currently moderate due to missing biochemical proof and open data.

Actionable next steps for authors (short)

• Deposit uncropped blots, FCS files, ELDA raw counts, and xenograft measurement tables to a public repository (e.g., FigShare / Mendeley / GEO where appropriate).
• Provide RAD18 IP-MS and co-IP data testing YAP/Hippo interactors; add domain mapping of RAD18 non-catalytic function.
• Expand to 3–5 additional patient-derived GSCs across molecular subtypes and show consistent phenotypes.