2-hydroxyglutarate competitively inhibits the alpha-KG dioxygenases - and it hits the TET demethylases AND the KDM histone demethylases, which is why its net effect on a CXXC reader is not predictable
also called 2-HG · D-2-hydroxyglutarate · oncometabolite · IDH hypermethylator phenotype
Mutant IDH enzymes make a molecule that looks enough like the fuel used by a whole family of enzymes to jam them. Two of the jammed families matter here: the ones that remove methyl marks from DNA, and the ones that remove them from histones - and the KMT2A fusion's competitors sit in the second family.
The same thing, for a scientist
**Mutant IDH1 and IDH2 lose their normal activity and gain a neomorphic one, reducing alpha-ketoglutarate to D-2-hydroxyglutarate, which is a structural mimic of alpha-KG and a competitive inhibitor of multiple alpha-KG-dependent dioxygenases** - demonstrated to occupy the same active-site space as alpha-KG in histone demethylases, and to inhibit both the KDM histone demethylases and the TET family of 5-methylcytosine hydroxylases [E1]. The cellular consequence in leukaemia is a hypermethylation phenotype: IDH1/2-mutant AMLs show global DNA hypermethylation and a specific hypermethylation signature, expression of 2-HG-producing IDH alleles induces global hypermethylation, and mutant IDH impairs TET2 catalytic function in cells [E2]. **The part this graph needs and does not currently hold is that the inhibition is not selective for DNA demethylases.** 2-HG inhibits the JmjC KDM family too - and **KDM2A and KDM2B are two of the twelve human CXXC proteins**, both of which read unmethylated CpG and both of which are candidate competitors of the KMT2A fusion at that address [E1][E3]. **So a 2-HG-high cell is simultaneously raising 5mC at CpG islands, which should hinder a CXXC reader, and impairing two of that reader's rivals, which should help it. The net direction is not derivable from the biochemistry and has never been measured in any KMT2A-fusion system.** That ambiguity is the honest state of the methylome-axis argument, and it is why this mechanism is written as its own entry rather than folded into `gene-idh2`: the same molecule points two ways and only an experiment separates them.
What is actually inhibited, and what is inferred
| target class | evidence | strength |
|---|---|---|
| histone demethylases (JmjC/KDM) | 2-HG occupies the same active-site space as alpha-KG; ectopic mutant IDH1/2 inhibits histone demethylation | direct structural and cellular 1 |
| TET 5mC hydroxylases | competitive inhibition demonstrated; ectopic mutant IDH inhibits 5mC hydroxylation; decreased 5hmC in IDH1-mutant glioma | direct biochemical and cellular 1 |
| TET2 specifically, in leukaemia | mutant IDH impairs TET2 catalytic function in cells; IDH1/2 and TET2 mutations mutually exclusive in AML | cellular plus genetic epistasis 2 |
| KDM2A and KDM2B specifically | inferred from class membership - both are alpha-KG-dependent JmjC demethylases | inference, not measured 3 |
| net effect on a KMT2A fusion | nothing | never measured in any system |
The fourth row is the one to be careful with. Neither cited paper names KDM2A or KDM2B. The inference runs through enzyme class, and it is a good inference, but inhibition constants differ greatly between dioxygenases and neither paper ranks them, so 'KDM2B is inhibited in an IDH2-mutant cell to a degree that matters for CpG-island occupancy' is a hypothesis with no number attached.
Why this cuts both ways for the address argument
The lab's hypothesis is that the KMT2A fusion's address is supplied by the menin interface rather than by the CXXC-DNA contact. A hypermethylating co-mutation bears on that in two opposite ways:
Against the fusion. The CXXC domain is blocked by 5-methyl-CpG on either strand. More 5mC at CpG islands means fewer readable sites. In SEM cells every MLL-AF4 peak sits on unmethylated CpG, so the contact is real and the substrate is methylation-sensitive.
For the fusion. KDM2B occupies 89% of unmethylated CpG sites in those same cells and CXXC1 occupies 50%, against the fusion's 20%. If 2-HG impairs KDM2A and KDM2B, the crowd at the address thins.
And a third possibility that is probably the real one. The fusion uses only a fifth of the available unmethylated CpG and its site selection tracks menin at r2 = 0.96, not uCpG availability. On that picture, moderate hypermethylation changes neither the fusion's occupancy nor its competitors' relevance, and the co-mutation is epiphenomenal. This is the prediction hyp-a-hypermethylating-comutation-should-antagonise-the-unmethylated-cpg-address is built to falsify.
| oncometabolite | D-2-hydroxyglutarate |
|---|---|
| net effect on kmt2a fusion | UNKNOWN and not derivable: raises 5mC (should hinder a CXXC reader) while impairing two of that reader's CXXC-family rivals (should help it). Never measured in any KMT2A-fusion system. |
| system | Biochemistry and ectopic expression; cellular validation in glioma (Xu 2011) and adult AML cohorts (Figueroa 2010). Nothing in any KMT2A-rearranged system. |
produced by
[ "gene-idh1", "gene-idh2" ]
inhibits directly demonstrated
[ "TET family 5mC hydroxylases", "JmjC histone demethylases (class)" ]
inhibits by class inference only
[ "gene-kdm2a", "gene-kdm2b" ]
reversed by
[ "drug-enasidenib", "drug-ivosidenib" ]
- IDH inhibitors are approved and act by lowering 2-HG, which restores TET activity and lowers CpG methylation. On this graph's own address model that RESTORES the fusion's substrate. An approved drug that plausibly helps the fusion is the sharpest unexamined interaction in this beat and nobody has looked for it.
- The class breadth of 2-HG inhibition means any therapeutic reasoning built on 'IDH mutation raises DNA methylation' has skipped over sixty other dioxygenases including the prolyl hydroxylases. A combination designed around the methylation arm could be dominated by an unrelated arm.
- What is the 2-HG inhibition constant for KDM2B and KDM2A specifically, and is it reached at the intracellular 2-HG concentrations found in IDH2-mutant AML blasts? Without that number the reader-competition half of this mechanism is unquantified.
- Does 2-HG inhibition of KDM2B change KDM2B's CHROMATIN OCCUPANCY, or only its catalytic output? CXXC binding may be catalysis-independent, in which case occupancy does not move at all.
- In an isogenic IDH2-R140Q versus wild-type pair, does the unmethylated-CpG landscape measured by Bio-CAP-seq shrink, and does it shrink preferentially at menin-bound promoters? That single experiment would settle the direction.
- Does relieving 2-HG with enasidenib EXPAND the unmethylated-CpG pool and therefore the fusion's potential address space? If so, an IDH2 inhibitor in a KMT2A-rearranged patient may be the wrong direction, and nobody has considered it.
- E1established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.paper
2-hydroxyglutarate, accumulated by tumour-derived IDH1 and IDH2 mutants, is a competitive inhibitor of multiple alpha-ketoglutarate-dependent dioxygenases including histone demethylases and the TET family of 5-methylcytosine hydroxylases, occupying the same active-site space as alpha-KG; ectopic expression of tumour-derived IDH1 and IDH2 mutants inhibits histone demethylation and 5mC hydroxylation, and IDH1 mutation in glioma is associated with increased histone methylation and decreased 5-hydroxymethylcytosine.
Oncometabolite 2-hydroxyglutarate is a competitive inhibitor of alpha-ketoglutarate-dependent dioxygenases. · Xu W, Yang H, Liu Y, et al. · Cancer Cell 2011What this evidence cannot show
Biochemistry plus ectopic expression; the cellular correlation is in glioma, not leukaemia, and nothing is in a KMT2A-rearranged system. Read from abstract only in this beat. The abstract does not name KDM2A or KDM2B, does not give inhibition constants for individual dioxygenases, and does not rank TET against KDM inhibition - so the relative potency against the enzymes this graph cares about is unknown. 'Multiple dioxygenases' is a class statement and the class has more than sixty members with very different sensitivities.
Evidence that argues against this (1)
- Because the inhibition is a class effect with unranked potencies, a cell with high 2-HG may be dominated by effects on prolyl hydroxylases, collagen modification or hypoxia signalling rather than by anything chromatin-related, and attributing a leukaemic phenotype to the TET arm specifically is an assumption this paper does not license. Figueroa ME et al. 2010
- E2established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.paper
In adult AML, IDH1/2-mutant cases display global DNA hypermethylation and a specific hypermethylation signature, expression of 2-HG-producing IDH alleles induces global hypermethylation in cells, IDH1/2 mutations are mutually exclusive with TET2 mutations, TET2 loss-of-function produces similar epigenetic defects, mutant IDH impairs TET2 catalytic function, and either mutant IDH expression or Tet2 depletion impairs haematopoietic differentiation and raises stem/progenitor marker expression.
Leukemic IDH1 and IDH2 mutations result in a hypermethylation phenotype, disrupt TET2 function, and impair hematopoietic differentiation. · Figueroa ME, Abdel-Wahab O, Lu C, et al. · Cancer Cell 2010What this evidence cannot show
Adult AML, 2010; methylation measured by HELP, an enrichment assay with a different dynamic range from bisulfite sequencing, so 'global hypermethylation' is an enrichment-relative statement. No KMT2A-rearranged subgroup is analysed. Mutual exclusivity is reported without an exclusivity test statistic in the abstract. Read from abstract only in this beat. The differentiation phenotype is in mouse and cell systems.
Evidence that argues against this (1)
- If the IDH and TET2 routes to hypermethylation are genuinely equivalent, then a cohort in which IDH2 is enriched and TET2 depleted has not acquired a novel co-mutation pattern at all - it has redistributed one, and the two rows of that table are one observation rather than two. Batayneh O et al. 2026
- E3strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
In SEM cells (human t(4;11) KMT2A::AFF1 B-ALL), KDM2B occupies 89% and CFP1/CXXC1 50% of unmethylated-CpG sites against the fusion's 20%, so the JmjC demethylase KDM2B - an alpha-KG-dependent enzyme and therefore a 2-HG target by class - is the most widely distributed reader at the fusion's own address.
MLL-AF4 Spreading Identifies Binding Sites that Are Distinct from Super-Enhancers and that Govern Sensitivity to DOT1L Inhibition in Leukemia. · Kerry J, Godfrey L, Repapi E, et al. · Cell Rep 2017What this evidence cannot show
Read in full text from PMC5263239 on 2026-09-21; the percentages are in the running text and Figure S1F and not in the abstract. One cell line. This paper contains no 2-HG, no IDH and no methylation-perturbation experiment - the link from 'KDM2B is a JmjC demethylase' to '2-HG inhibits it' is an inference from enzyme class made in this entry and not a result of either paper cited here.
Evidence that argues against this (1)
- KDM2B's CXXC-mediated CpG-island binding is not obviously dependent on its demethylase activity, so inhibiting the catalytic site with 2-HG may leave its occupancy of 89% of unmethylated CpG sites entirely intact - in which case the 'thins the crowd' argument fails at its first step. Kerry J et al. 2017
The neomorphic activity that produces the oncometabolite.
The paralogue route to the same oncometabolite, and the reason the mechanism alone cannot explain the KMT2A asymmetry.
Competitive inhibition of the TET 5mC hydroxylases; mutant IDH impairs TET2 catalytic function in cells.
CLASS INFERENCE ONLY, not measured: KDM2B is an alpha-KG-dependent JmjC demethylase and occupies 89% of unmethylated CpG sites in SEM.
Points two ways at once: raises 5mC (hinders the CXXC contact) while impairing the fusion's CXXC-family rivals (helps it). Net direction unmeasured.
A genetic route to the hypermethylation the signature entry describes, which that entry does not currently consider.
The mechanistic cause of the exclusivity: both lesions converge on impaired TET output, so the second adds nothing.
The mechanism that makes the direction ambiguous: 2-HG raises 5mC and impairs the fusion's CXXC rivals at the same time.
Mutant IDH2 is the source of the oncometabolite.
Mutant IDH1 is the other source of the same oncometabolite, and the reason the mechanism cannot explain the KMT2A asymmetry.