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Mechanismmoderate confidence 3 of 5: One strong study, or several smaller consistent ones.Q32-brca1-hr-licensing

The CTCF licensing cascade: CTCF recruits HP1-gamma, KAP1, SUV39H1, SETDB1 and KDM5A to a break, that repressive chromatin licenses EARLY BRCA1/BARD1, and early BRCA1/BARD1 licenses EXO1/DNA2 long-range resection - measured entirely in U2OS and HEK-293T, with engineered breaks and one etoposide arm

also called CTCF hierarchical recruitment cascade in HR · repressive chromatin priming of BRCA1/BARD1 · HP1-gamma-BARD1 licensing · early BRCA1 pathway

When DNA breaks, the loop protein CTCF calls in the machinery that normally silences genes, and that silencing machinery is what lets the BRCA1 repair complex arrive and start trimming the broken ends. Everything known about this was measured in a bone-cancer cell line and a kidney cell line with artificially cut DNA, never in a blood cell.

The same thing, for a scientist

**The cascade, in the order the source paper establishes it** [E1]: 1. **CTCF at the break.** CTCF is recruited to DSBs through its zinc-finger region, independently of PARylation [E2]. It associates with **BARD1** even in undamaged cells and rarely with BRCA1; 50 microM etoposide for 1 h augments the BARD1 contact and additionally enables a weak BRCA1 contact [E1]. 2. **CTCF recruits the repressive assembly.** HP1-gamma, KAP1, SUV39H1, SETDB1 and KDM5A. CTCF interacts preferentially with **HP1-gamma**, modestly with HP1-alpha, weakly with HP1-beta, tested both endogenously and with tagged constructs at matched-or-lower gamma expression. The zinc fingers that bind HP1-gamma are not the ones that bind BARD1 directly [E1]. 3. **The chromatin change is a PAIR, not a single mark.** H3K9 methylation is written (SUV39H1, SETDB1, scaffolded by KAP1) **and H3K4 methylation is removed** (KDM5A). CTCF depletion loses both. Deprivation of any one component compromises the immediate accumulation of the others [E1]. 4. **BRCA1/BARD1 is licensed, through HP1.** HP1-gamma's chromoshadow domain binds the BARD1 PxVxL motif at **569-573** (PLVLI, confirmed against Q99728 in this beat); the PEELI mutant of it loses HP1 binding and is not rescued [E1]. 5. **Early versus late BRCA1.** The CTCF/HP1 route gives an **early** pool; the ATM/RNF8/RNF168/RAP80/ABRAXAS1 route gives a **late** pool. ATM inhibition alone removes late BRCA1, does **not** affect end resection, and yet markedly reduces HR efficiency. Co-depleting CTCF or HP1-gamma with ATM inhibition adds nothing further [E1]. 6. **Resection, in two consecutive stages.** CtIP does short-range initiation; early BRCA1/BARD1 recruits SMARCAD1 and **EXO1/DNA2** for long-range extension; BRCA2 loads RAD51. Double and triple co-depletions of CtIP, HP1-gamma, BRCA1 and BRCA2 are non-additive. The authors describe recruitment as parallel and function as sequential [E1]. 7. **Pharmacology, in a supplementary panel and load-bearing for this graph.** *'Inhibitors blocking H3K9 methylation, including **UNC-0638**, chaetocin, and **Bix-01294**, disturbed the immediate accumulation of H3K9me3, HP1-gamma, and BRCA1/BARD1 but not CTCF at the DSBs'* [E1, Supplementary Fig. S5E-G]. **SYSTEM BOUNDS, stated in the claim and not only the caveat.** Every experiment is in **U2OS osteosarcoma** reporter lines - AsiSI-ER, ER-mCherry-LacI-FokI-DD, DR-GFP and EJ5-GFP - or in **HEK-293T**. Damage is delivered by **FokI nuclease at a Lac operator array, AsiSI restriction, laser micro-irradiation, phleomycin, and etoposide at 50 microM for 1 h**. So the brief's premise that the breaks were purely enzyme-induced is **partly wrong**: a TOP2 poison is used, but only for the co-immunoprecipitations, not for the recruitment imaging or the HR reporters. **There is no haematopoietic cell, no fusion protein, no primary cell, no in vivo work, and no measurement at the *KMT2A* locus anywhere in this paper.** **The published disagreement.** The founding CTCF-HR paper put CTCF **downstream** of BRCA1 and showed it associating with BRCA2 PARylation-dependently [E2]. The early/late split in [E1] is the reconciliation, offered by the party that needs it. **An independent, older line agrees about direction at the H3K9 step and disagrees about mechanism.** G9a is phosphorylated at Ser211 by CK2 on DSB induction, recruited to chromatin, interacts directly with **RPA**, and promotes RPA and RAD51 loading; loss of G9a impairs DNA damage repair and sensitises cancer cells to radiation and chemotherapeutics [E3]. That is a second, RPA-based route from the same enzyme family to the same outcome, and it does not run through HP1 or BRCA1.

Go deeper
Why the two-mark switch matters more than the H3K9 half alone

Every argument this graph has run about H3K9 at the KMT2A locus has been about the level of one mark. This cascade's licence is a coordinated pair: H3K9 methylation up, H3K4 methylation down, at the same chromatin, at the same time.

That has a direct methodological consequence for the experiments this graph has already run and proposed. ana-q108-h3k9me3-at-the-kmt2a-bcr-measured and ana-q111-cd34-h3k9me2-over-the-kmt2a-locus-measured measure one mark in unperturbed cells. Under this model neither could detect the licence, for two independent reasons: the licence is damage-conditional, and it is a ratio rather than a level.

And there is a third reason, which Q110's hypothesis already names: the H3K9me3 domain formed at a break spreads tens of kilobases, so a design that normalises the breakpoint cluster region against its own 20 kb flanks would cancel the signal it is looking for.

The pharmacology is the part that reaches this graph's clinic

One sentence in Supplementary Fig. S5E-G is the most consequential thing in this paper for the Iqbal Lab's purposes:

'Consistently, inhibitors blocking H3K9 methylation, including UNC-0638, chaetocin, and Bix-01294, disturbed the immediate accumulation of H3K9me3, HP1-gamma, and BRCA1/BARD1 but not CTCF at the DSBs.'

drug-unc0642 is in this graph as a proposed prophylactic co-administration with anthracycline or etoposide. UNC-0638 is its immediate chemical sibling - the same G9a/GLP quinazoline series from the same programme. So the proposal's mechanism of action is measured, in this paper, to block BRCA1/BARD1 arrival at a break.

Three honest limits on reading that as a clinical warning, all stated in risk-an-h3k9-axis-inhibitor-given-with-a-top2-poison-removes-a-repair-licence: it is U2OS; it is an imaging readout of immediate accumulation rather than a repair-outcome measurement under drug; and chaetocin's inclusion in the same sentence weakens the trio, since chaetocin is nonspecific and a thioredoxin-reductase inhibitor. UNC-0638 and BIX-01294 are the two interpretable arms, and they are both G9a-directed, so the sentence establishes that blocking G9a blocks BRCA1/BARD1 loading - not that blocking SUV39H1 does.

What would have to be true for this to apply to infant t(4;11), and none of it is established
  1. The cascade runs in a haematopoietic cell. Not shown anywhere.
  2. It runs in the cell of origin, which is a fetal progenitor whose cycling state is unmeasured; the cascade's output is S/G2-restricted HR.
  3. It runs at a TOP2-poison-induced break, not only at a nuclease-induced one. Partly addressed - etoposide augments the CTCF-BARD1 interaction - but recruitment and repair outcome under etoposide were not measured.
  4. It runs at this locus, chr11q23.3. No member of the cascade has ever been localised at the KMT2A locus in any cell type; see absence-no-resection-factor-localised-at-the-kmt2a-locus and, for the writers and HP1-alpha, absence-no-h3k9-writer-or-reader-localised-at-the-kmt2a-locus.
  5. The HP1 paralogue present at that locus in that cell is HP1-gamma. Unmeasured.

Five conditions, zero established. That is why the confidence on this entry is moderate for the mechanism as published and why every entry built on it in this beat carries a prior well below 0.5.

Facts and figures
mechanism classdamage-conditional chromatin licensing of a repair-factor recruitment step (as opposed to a steady-state chromatin state)
stage of diseaseNONE established. This is general DSB biology. Its possible relevance to this graph is at GENESIS - the moment a TOP2 break is made at the KMT2A locus - and that relevance is entirely hypothetical; see `hyp-the-writer-reaches-the-kmt2a-anchor-only-through-ctcf-and-only-after-the-break` and `hyp-the-menin-arm-and-the-ctcf-arm-license-consecutive-steps-of-one-resection-reaction`.
epigenetic readoutH3K9me2/me3 GAINED and H3K4me2/me3 LOST at the break, as a pair. This is the point at which this cascade differs from every H3K9 argument already in this graph: the licence is a coordinated switch of two marks in opposite directions, not the level of one mark. A measurement of H3K9me3 alone at a locus cannot distinguish 'the licence was granted' from 'the licence was not granted but H3K9me3 happens to be high here'.
cell typeU2OS and HEK-293T only. NO haematopoietic cell anywhere in the source paper.
cell stateDNA DAMAGE, minutes-scale and transient, in cycling cells. The cascade's output is homologous recombination, which requires a sister chromatid and is therefore S/G2-restricted; U2OS and HEK-293T are both rapidly cycling transformed lines. Nothing in the paper addresses quiescence, and a G0/G1 progenitor may not run this cascade at all.
subcellular localizationnucleus; chromatin flanking a double-strand break
subnuclear localizationthe break-proximal chromatin domain itself - defined operationally in this paper by laser micro-irradiation strips, by proximity ligation against gammaH2AX, and by ChIP at the FokI/LacO array. No compartment claim (lamina, speckle, nucleolus) is made or tested, and the older literature holds that the H3K9me3 domain formed at a break spreads tens of kilobases, which means the relevant object is a domain and not a point.
shown for fusionNO - nobody has looked, in any fusion. The source paper contains no fusion protein, no leukaemia cell and no KMT2A locus measurement, and no other published work applies this cascade to a fusion.
absence classnever-measured
the chain
[
  "CTCF is recruited to a DSB through its zinc-finger region, PARylation-independently",
  "CTCF recruits HP1-gamma (preferentially over HP1-alpha and HP1-beta), KAP1, SUV39H1, SETDB1 and KDM5A",
  "SUV39H1/SETDB1 write H3K9me2/me3 and KDM5A removes H3K4me2/me3 at the break chromatin",
  "HP1-gamma binds the H3K9 methylation through its chromo domain and BARD1 through its chromoshadow domain contacting the PxVxL motif at BARD1 569-573",
  "EARLY BRCA1/BARD1 accumulates within minutes - a pool distinct from the ATM/RNF8/RAP80/ABRAXAS1-dependent LATE pool",
  "early BRCA1/BARD1 recruits SMARCAD1 and the exonucleases EXO1/DNA2",
  "EXO1/DNA2 perform long-range resection, following CtIP-dependent short-range initiation; BRCA2 then loads RAD51",
  "removing any one repressive component, or blocking H3K9 methylation pharmacologically, collapses the steps below it but NOT CTCF itself"
]
system bounds
{
  "cell_lines": [
    "U2OS (osteosarcoma) reporter derivatives",
    "HEK-293T"
  ],
  "u2os_reporters": [
    "AsiSI-ER-U2OS (gift of G. Legube)",
    "ER-mCherry-LacI-FokI-DD U2OS (gift of R. Greenberg)",
    "U2OS DR-GFP (HR reporter)",
    "U2OS EJ5-GFP (NHEJ reporter)"
  ],
  "damage_modalities": [
    "FokI nuclease at an integrated Lac operator array - clustered, site-specific",
    "AsiSI restriction after 4-hydroxytamoxifen",
    "laser micro-irradiation",
    "phleomycin - random whole-genome",
    "etoposide 50 micromolar for 1 h - used for co-immunoprecipitation only"
  ],
  "were_the_breaks_top2_poison_induced": "PARTLY, and this corrects a premise in the dispatch brief. Etoposide IS used and is a TOP2 poison, but it appears in the reagent list and in the co-IP experiments (Fig 2A, Fig 3A/B, Fig 3G, Fig 5F), not in the recruitment imaging, the ChIP at the FokI site, or the DR-GFP/EJ5-GFP functional assays. So the INTERACTIONS were shown to be TOP2-poison-responsive; the RECRUITMENT and REPAIR-EFFICIENCY results rest on nuclease, laser and radiomimetic damage.",
  "not_present": [
    "any haematopoietic cell",
    "any primary cell",
    "any fusion protein",
    "any in vivo experiment",
    "any measurement at the KMT2A locus or at 11q23",
    "any paediatric or fetal context"
  ],
  "inhibitors_used": {
    "Ku-55933": "ATM inhibitor - used to separate early from late BRCA1",
    "UNC0638": "G9a/GLP inhibitor - blocks immediate H3K9me3, HP1-gamma and BRCA1/BARD1 accumulation at DSBs",
    "Bix 01294": "G9a inhibitor - same result",
    "Chaetocin": "nonspecific histone lysine methyltransferase inhibitor and thioredoxin-reductase-1 inhibitor - same result, but see the caveat, it contributes little independent evidence",
    "CPI-455": "pan-KDM5 inhibitor"
  },
  "key_separation_of_function_reagent": "BARD1 PEELI - the PxVxL motif at 569-573 (PLVLI in Q99728) substituted to PEELI, which loses binding to the chromoshadow domain of ALL HP1 subtypes",
  "ctcf_fragment_boundaries_as_used": "GST-CTCF N 1-267, ZF 246-588, C 578-727",
  "timeline": "received 2025-04-29, revised 2026-06-14, accepted 2026-06-29, collection date 2026-08-12"
}
what this graph already held and what is new
{
  "already_held": "gene-suv39h1 E6 and gene-setdb1 cite this paper for the recruitment list, and `hyp-the-writer-reaches-the-kmt2a-anchor-only-through-ctcf-and-only-after-the-break` (Q110) states the topology that CTCF is upstream of the H3K9 writers and that the mark at the KMT2A anchor may be break-triggered. That hypothesis is the graph's existing statement of the 'one arm' position and this entry does not restate it.",
  "new_here": "(1) the full cascade below the writers - early-versus-late BRCA1, the HP1-gamma/BARD1 PxVxL interface, SMARCAD1, EXO1/DNA2, the CtIP short-range / EXO1-DNA2 long-range split; (2) the SYSTEM BOUNDS read off the methods rather than the abstract, including that etoposide is used and where; (3) the pharmacology - UNC-0638 and BIX-01294 blocking BRCA1/BARD1 accumulation, which is in a supplementary figure and reachable by no literature query; (4) the paralogue discrimination across all three HP1s; (5) the published contradiction with the founding CTCF-HR paper."
}
How this could bite us back
  • The cascade's top node, CTCF, is a near-total pan-essential in DepMap (mean -1.826, 99.76% of 1,258 lines below -0.5), so nothing at the top of this mechanism is druggable for benefit. Every therapeutic touch-point in it is a way of damaging repair, not of improving it.
  • The one pharmacological result in the paper - UNC-0638 and BIX-01294 blocking BRCA1/BARD1 accumulation - is the mechanism of a drug this graph proposes giving prophylactically with etoposide to children. That inverts the sign of the proposal and is the whole content of `risk-an-h3k9-axis-inhibitor-given-with-a-top2-poison-removes-a-repair-licence`.
  • If a future beat proposes ENHANCING this cascade at the KMT2A locus to protect it, note that the BRCA1-A complex restricts resection precisely to prevent over-resection, and that hyper-resection is itself a driver of mutagenic repair. The cascade has an optimum, not a direction.
  • The KDM5A limb means a pan-KDM5 inhibitor is also a repair-licence inhibitor, which adds a drug class this graph has never counted as genotoxic-combination-relevant.
Still open
  1. Does this cascade operate in any haematopoietic cell? Every experiment is U2OS or HEK-293T, and the single most valuable replication would be the DR-GFP arm plus HP1-gamma depletion in a B-lineage progenitor or a KMT2A-rearranged line.
  2. Does it operate at a TOP2-poison-induced break? Etoposide augments the CTCF-BARD1 interaction, but no recruitment or repair-outcome experiment in the paper uses etoposide as the damaging agent - and TOP2 breaks are the ones this disease is about.
  3. Is the early/late BRCA1 split real outside this group? It is the load-bearing reconciliation with the 2017 paper's opposite topology and rests on non-additivity of co-depletions.
  4. Do UNC-0638 and BIX-01294 block BRCA1/BARD1 loading through G9a's catalytic activity, or through the G9a-RPA contact that [E3] describes? The two would predict different behaviour for a catalytically dead G9a and the experiment has not been done.
Every source behind this entry (4)
  1. E1strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper

    CTCF establishes a hierarchical recruitment cascade in homologous recombination. In U2OS and HEK-293T cells, CTCF recruits the repressive chromatin proteins HP1-gamma, KAP1, SUV39H1, SETDB1 and KDM5A, enabling rapid accumulation of BRCA1/BARD1 at DSBs; CTCF depletion abrogates their enrichment with loss of H3K9 methylation and H3K4 demethylation at DSBs and defective rapid BRCA1/BARD1 recruitment; deprivation of one repressive component, or deregulation of H3K9 methylation/H3K4 demethylation, compromises the immediate accumulation of the others and of BRCA1/BARD1; consequently EXO1/DNA2 recruitment is abrogated, causally linked to defective end resection and dysfunctional HR; and the authors identify a critical role for CTCF in coupling BRCA1/BARD1 with the HR licensing point, the DNA end resection step. Read in the full text: CTCF associates with BARD1 but rarely BRCA1 without damage and 50 microM etoposide for 1 h increases both; CTCF interacts preferentially with HP1-gamma, modestly with HP1-alpha, weakly with HP1-beta, confirmed with tagged constructs where HP1-gamma bound robustly at the lowest expression of the three; HP1-gamma pulls down full-length CTCF and the ZF fragment 246-588 but not N 1-267 or C 578-727; the BARD1 PxVxL motif is at 569-573 and the PEELI mutant loses binding to the chromoshadow domain of all HP1 subtypes and is not rescued in CTCF-depleted cells; UNC-0638, chaetocin and Bix-01294 disturb the immediate accumulation of H3K9me3, HP1-gamma and BRCA1/BARD1 but not CTCF at DSBs; ATM inhibition with Ku-55933 alone has no effect on end resection while markedly reducing HR efficiency, and combining it with CTCF or HP1-gamma depletion does not further aggravate either; depletion of HP1-gamma, SUV39H1, SETDB1, KAP1, KDM5A, BRCA1/BARD1, EXO1/DNA2 or CtIP had little effect on HR activity in already CTCF-deficient cells; and the pathway spans CtIP-dependent short-range resection and subsequent EXO1/DNA2-dependent long-range resection with BRCA2 mediating RAD51 loading.

    CTCF primes repressive chromatin for rapid BRCA1/BARD1 recruitment to drive homologous recombination repair of DNA double-strand breaks. · Hwang SY, Choi D, Choi MJ, Jo HR, Jeong JH, Kang MA, Lee JS · Nucleic Acids Research 2026
    PMID 42475683DOI
    What this evidence cannot show

    U2OS osteosarcoma reporter derivatives and HEK-293T only; no haematopoietic cell, no primary cell, no fusion, no in vivo work, no KMT2A locus. A large part of the epistasis argument rests on NON-ADDITIVITY of co-depletions (Supplementary Figs S8-S10), which is weaker than an ordered rescue - non-additivity is also produced by a shared ceiling or by incomplete knockdown. Several load-bearing results, including the entire inhibitor panel, are in supplementary figures and are therefore unreachable by any title or abstract query (rule 80 in the positive direction). Chaetocin, one of the three H3K9 inhibitors, is a nonspecific KMT inhibitor and a thioredoxin-reductase-1 inhibitor, so the pharmacological trio is effectively two G9a-directed compounds plus one uninterpretable one. The interaction mapping uses over-expressed tagged constructs and whole-cell-extract co-IP. DOI taken from PubmedData/ArticleIdList inside PubmedData only - the record carries 191 ArticleId elements in total, most from its reference list.

    Evidence that argues against this (1)
    • The founding paper of the CTCF-HR link places CTCF DOWNSTREAM of BRCA1 and has it acting through BRCA2 in a PARylation-dependent manner - the opposite ordering. The early/late BRCA1 split that reconciles the two is proposed by this paper and has not been independently replicated. Hilmi K et al. 2017
  2. E2strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper

    CTCF is recruited to double-strand breaks through its zinc finger domain independently of PARP-1-catalysed PARylation, ensures proper DSB repair kinetics after gamma-irradiation, and its loss compromises HR-mediated repair with hypersensitivity to DNA-damaging agents and PARP inhibitors; the authors place CTCF DOWNSTREAM of BRCA1 in the HR pathway and show it associates with BRCA2 in a PARylation-dependent manner, enhancing BRCA2 recruitment to DSBs, while not influencing recruitment of 53BP1 or LIGIV.

    CTCF facilitates DNA double-strand break repair by enhancing homologous recombination repair. · Hilmi K, Jangal M, Marques M, Zhao T, Saad A, et al. · Science Advances 2017
    PMID 28560323DOI
    What this evidence cannot show

    Abstract read; full text not fetched in this beat, so the cell systems are not stated here and no methods claim is made about it. Its stated topology conflicts with [E1]'s. Neither paper is in a haematopoietic cell; neither touches the KMT2A locus.

    Evidence that argues against this (1)
    • [E1] reports the opposite ordering and offers the early/late BRCA1 distinction to absorb the conflict. A reader should treat the direction of the CTCF-BRCA1 arrow as contested rather than settled, and any experiment this graph designs should be able to distinguish the two orderings rather than assuming one. Hwang SY et al. 2026
  3. E3strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper

    An independent and earlier line reaches the same directional conclusion about the H3K9 methyltransferase step by a different mechanism: loss of G9a impairs DNA damage repair and enhances the sensitivity of cancer cells to radiation and chemotherapeutics; in response to double-strand breaks G9a is phosphorylated at serine 211 by casein kinase 2 and recruited to chromatin; chromatin-enriched G9a directly interacts with replication protein A and promotes loading of RPA and the RAD51 recombinase onto DSBs, facilitating homologous recombination and cell survival; and the RPA-G9a interaction was confirmed to be critical for RPA foci formation and HR upon DNA damage. The authors present this as a rationale for using G9a inhibitors as cancer therapeutics.

    G9a coordinates with the RPA complex to promote DNA damage repair and cell survival. · Yang Q, Zhu Q, Lu X, Du Y, Cao L, et al. · Proceedings of the National Academy of Sciences 2017
    PMID 28698370DOI
    What this evidence cannot show

    Abstract read; full text not fetched. The systems are unnamed 'cancer cells' in the abstract, so this inherits the same non-haematopoietic uncertainty. Crucially, the MECHANISM is different from [E1]'s: G9a-RPA is a direct protein contact, not a histone-mark licence, and G9a's methyltransferase activity is not shown by the abstract to be required for the RPA interaction. So this is convergent on DIRECTION - G9a loss impairs HR and sensitises to chemotherapeutics - and not confirmatory of [E1]'s mechanism. It also involves CK2, which this graph already holds as the kinase of the LEDGF phospho-switch.

    Evidence that argues against this (1)
    • If G9a promotes HR through a direct RPA contact rather than through H3K9 methylation, then UNC-0638 and BIX-01294 - which inhibit the catalytic SET domain - might not reproduce a G9a-knockdown phenotype, and the shared direction between this paper and [E1] would be coincidental rather than mechanistic. Neither paper tests whether catalytic activity is required for the other's readout. Yang Q et al. 2017
  4. E4strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper

    A third independent line gives the G9a/GLP axis a FUNCTIONAL repair phenotype, and it is broader than HR: EHMT1/2 (GLP/G9A) catalyse H3K9me2 and have direct roles in DNA repair; PARP-inhibitor-resistant high-grade serous ovarian carcinoma cells display a global increase in H3K9me2 with over-expression of EHMT1/2, reproduced in a PARPi-resistant patient-derived xenograft; genetic or pharmacologic disruption of EHMT1/2 sensitises those cells to PARPi; and functional DNA repair assays show that disruption of EHMT1/2 ABLATES BOTH homologous recombination AND non-homologous end joining, with immunofluorescence for phosphorylated H2AX showing large increases in DNA damage. Cell-cycle analysis shows EHMT1/2-inhibitor-treated cells remain in G1 while PARPi increases the S and G2 fraction.

    Histone methyltransferases EHMT1 and EHMT2 (GLP/G9A) maintain PARP inhibitor resistance in high-grade serous ovarian carcinoma. · Watson ZL, Yamamoto TM, McMellen A, Kim H, Hughes CJ, Wheeler LJ, et al. · Clinical Epigenetics 2019
    PMID 31775874DOI
    What this evidence cannot show

    Abstract read in full and the record fetched from efetch in this beat; full text not read. IDENTIFIER CORRECTION MADE IN-RUN: this citation was first drafted with the DOI 10.1186/s13148-019-0764-4 written from recall, which is WRONG - the record's own PubmedData/ArticleIdList gives 10.1186/s13148-019-0758-2. The error was caught by re-fetching before hand-back and is recorded here rather than silently fixed, because it is the exact failure mode the standing brief documents. System: high-grade serous OVARIAN carcinoma cell lines and one PDX, adult, not haematopoietic, and the damaging agent is a PARP inhibitor rather than a TOP2 poison. The mechanism is NOT shown to be the HP1/BRCA1 licence of [E1] - the paper attributes sensitisation to DNA damage plus cell-cycle dysregulation and reports PI3K/AKT/mTOR transcriptional changes as well.

    Evidence that argues against this (1)
    • That EHMT1/2 disruption ablates NHEJ as well as HR argues AGAINST reading this as support for a specific HR-licensing mechanism - a perturbation that removes both major repair pathways plus arrests cells in G1 is a broad phenotype with several possible causes, and the authors themselves offer cell-cycle dysregulation as a mechanism alongside DNA damage. For the risk argument, however, the broadness makes the concern worse rather than better, which is the honest reading in both directions. Watson ZL et al. 2019
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