Does KMT2A::AFF1 bind the histone chaperone SET/TAF-I beta, and does that contact overlap the menin-binding motifs? A co-IP and a peptide competition
also called the twenty-year-old result nobody followed up · SET as a menin-independent route to HOXA
In 2005 somebody showed that the front end of the MLL protein - the piece every fusion keeps - sticks to a histone chaperone called SET, and that the two together switch on HOXA9. Nobody checked whether an actual fusion protein does the same, or whether the drug this project cares about would break that contact.
The same thing, for a scientist
**Premise.** The amino-terminal region of MLL binds TAF-I beta/SET through SET's acidic region; GST-MLLN pulls down TAF-I beta and histones; and the two synergistically upregulate Hoxa9 and co-immunoprecipitate on chromatin containing the Hoxa9 promoter (`gene-set` E1, PMID 15670842). Separately, SET-NUP214 binds MLL via the same SET acidic region and cooperatively enhances the HOXA10 promoter (`gene-set` E3), and SET-NUP214 recruits DOT1L and CRM1 to HOXA promoters in T-ALL (`gene-set` E2). **Nothing in that literature uses a KMT2A fusion protein.** MLLN is the wild-type N-terminal fragment. The retained portion of KMT2A in a fusion is that same region, so the obvious question has a twenty-year-old answer waiting for it and nobody has asked it. **Two experiments, both cheap, in order.** 1. **Co-IP.** Endogenous KMT2A::AFF1 in SEM or RS4;11, immunoprecipitated with an N-terminal KMT2A antibody, blotted for SET; reciprocal with anti-SET. Controls: a KMT2A-wild-type B-ALL line, and an IgG control, and blotting for menin and LEDGF on the same membranes so the positive control for the complex is internal. 2. **Epitope competition.** If the co-IP is positive, ask whether the contacts overlap: does a menin inhibitor (revumenib) at a concentration that displaces menin from chromatin also reduce SET co-IP? And does an MBM1/MBM2 peptide compete SET off the N-terminus in vitro? **The result changes a therapeutic argument, not just a mechanism.** If SET binds the fusion through a surface a menin inhibitor does not touch, then SET is a menin-inhibitor-independent contributor to HOXA activation, which is a resistance hypothesis this graph currently does not hold.
Why this is worth doing before anything else in the beat
Every other candidate experiment in this beat needs a knock-in line, a degron, or a turnover assay. This one needs two antibodies and a lysate.
It also has an unusually clean set of outcomes:
| result | what follows |
|---|---|
| no co-IP | the 2005 result does not transfer to a fusion; close the line of enquiry and record it |
| co-IP, abolished by menin inhibitor | SET rides on the menin-LEDGF complex; not an independent route, and menin inhibition covers it |
| co-IP, NOT abolished by menin inhibitor | SET is a menin-independent contact at the fusion's N-terminus; a resistance hypothesis with a mechanism, and the first such in this graph from the chaperone layer |
The third outcome is the one worth the effort, and its prior is genuinely uncertain because the SET contact is mapped only to 'MLLN' while the menin motifs sit in roughly the first 45 residues.
| design | Step 1: reciprocal endogenous co-immunoprecipitation of KMT2A::AFF1 (N-terminal KMT2A antibody) and SET/TAF-I beta in SEM and RS4;11, with a KMT2A-wild-type B-ALL comparator, IgG control, and menin and LEDGF blotted on the same membranes as an internal positive control for the N-terminal complex. Step 2 (only if step 1 is positive): does revumenib at a chromatin-displacing concentration reduce the SET co-IP, and does an MBM1/MBM2 peptide compete SET off the N-terminus in vitro? |
|---|---|
| readout | presence and menin-dependence of a KMT2A::AFF1-SET interaction |
| controls | IgG; KMT2A-wild-type B-ALL line; menin and LEDGF as internal positive controls; for step 2 a scrambled peptide and a vehicle arm, plus confirmation that the revumenib concentration actually displaces menin in the same lysate |
| cost tier | low |
| timeline | 6-10 weeks |
| why now | closes a twenty-year-old unfollowed result with two antibodies and a lysate, and its third possible outcome is a menin-inhibitor resistance hypothesis this graph does not currently hold |
tests
[ "gene-set", "hyp-kmt2a-aff1-alters-h3-3-deposition-at-fusion-targets" ]
- A positive, menin-independent result would identify a resistance route for the drug class this project's therapeutic argument rests on - a finding against interest, and the reason to run it.
- SET is also a PP2A inhibitor and an INHAT component, so even a clean co-IP would not license a chaperone interpretation without further work.
- A negative co-IP does not refute the 2005 result; it would show only that the interaction does not survive the conditions used, which for a charge-driven contact is a real possibility.
- Where exactly on the KMT2A N-terminus does SET bind? The 2005 paper maps SET's side of the interface (the acidic region) and not MLL's, so the overlap with MBM1/MBM2 cannot be predicted from the literature.
- Is there a commercially validated antibody that immunoprecipitates endogenous KMT2A::AFF1 N-terminus in SEM? This graph should check before commissioning.
- If SET does bind the fusion, does it bring H2A-H2B with it? SET is an H2A-H2B chaperone and this graph's H2B ubiquitination entries would then connect to it.
- E1moderate confidence 3 of 5: One strong study, or several smaller consistent ones.paper
The amino-terminal region of MLL interacts with TAF-I beta/SET, the acidic region of TAF-I beta is essential for that binding, GST-MLLN pulls down TAF-I beta and histones, and MLLN and TAF-I beta synergistically upregulate Hoxa9 transcription and co-immunoprecipitate in chromatin containing the Hoxa9 promoter region.
Synergistic action of MLL, a TRX protein with template activating factor-I, a histone chaperone. · Shimoyama T, Kato K, Miyaji-Yamaguchi M, Nagata K · FEBS Letters 2005What this evidence cannot show
Abstract read from efetch 2026-09-20; full text not read (no PMCID). A 2005 short report using yeast two-hybrid, GST pull-down and a transcription assay, whose own conclusion is 'these results suggest'. **The MLL fragment is wild type, not a fusion**, and the interaction maps to an acidic region, the domain class most prone to charge-driven pull-down artefacts. This is the premise of the experiment, not evidence that the experiment will be positive.
Evidence that argues against this (1)
- Twenty years without a follow-up in a KMT2A-rearranged system is itself weak evidence that the result did not replicate or did not lead anywhere - although this beat found no published refutation and an absence of follow-up is not a negative result. Cigdem S et al. 2021
- E2moderate confidence 3 of 5: One strong study, or several smaller consistent ones.paper
SET-NUP214 interacts with MLL via the SET acidic region and the two cooperatively enhance the promoter activity of HOXA10; neither the SET region alone nor the NUP214 region alone is sufficient.
SET-NUP214 and MLL cooperatively regulate the promoter activity of the HoxA10 gene. · Cigdem S, Saito S, Nishikata D, et al. · Genes to Cells 2021What this evidence cannot show
Abstract read from efetch 2026-09-20; full text not read (no PMCID). Promoter-reporter activity in transfected cells, not endogenous transcription; interaction mapping on fragments. Same laboratory lineage as E1, so the two are not independent confirmations - which is part of why the experiment is worth running in a third hand.
Evidence that argues against this (1)
- A reporter assay measures a plasmid promoter, and the 2008 Blood study found SET-NUP214 dependence of HOXA expression in exactly one of several T-ALL lines, so even the endogenous version of this effect is context-restricted. Van Vlierberghe P et al. 2008
- E3established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.paper
SET-NUP214 binds in the promoter regions of specific HOXA genes where it interacts with CRM1 and DOT1L, and siRNA against SET-NUP214 abolished HOXA expression, inhibited proliferation and induced differentiation in the LOUCY T-ALL line.
The recurrent SET-NUP214 fusion as a new HOXA activation mechanism in pediatric T-cell acute lymphoblastic leukemia. · Van Vlierberghe P, van Grotel M, Tchinda J, et al. · Blood 2008What this evidence cannot show
Abstract read from efetch 2026-09-20; full text not read (PMC2343598 exists). Established within the reported cohort and cell line; the functional arm is one line and the authors note the effect was not seen in other T-ALL lines. T-ALL, not B-ALL, and the fusion is SET-NUP214, not KMT2A::AFF1. Cited here because it establishes that a SET-containing fusion can recruit DOT1L to HOXA, which is the reason to ask whether SET does anything comparable alongside a KMT2A fusion.
Evidence that argues against this (1)
- DOT1L is recruited to KMT2A-fusion targets through AF9/ENL and AF4-family partners, a well-mapped route that needs no chaperone. A second recruitment mechanism is not required to explain anything currently observed in KMT2A-rearranged leukaemia, so the prior that SET matters here is low. Kuntimaddi A et al. 2015
co-IP of endogenous KMT2A::AFF1 with SET, then menin-inhibitor competition
whether the fusion retains the 2005 MLL N-terminus/TAF-I beta contact