Releasing JunD does not merely de-repress it: JunD without menin becomes a growth promoter
also called JunD sign inversion · JunD growth suppressor to promoter switch · menin-free JunD
JunD normally slows cells down, but only while menin is attached. When menin is removed, the same protein starts speeding cells up instead - the effect flips sign rather than simply disappearing.
The same thing, for a scientist
In immortalised fibroblasts, stable overexpression of wild-type JunD in JunD-null cells inhibited proliferation and reverted the transformed-like phenotype, while a JunD missense mutant (G42E) with disabled menin binding had the **opposite**, growth-promoting effect; and wild-type JunD overexpressed in **Men1-null** fibroblasts enhanced their already transformed-like characteristics rather than suppressing them [E1]. The authors' conclusion is the one that matters for this beat: JunD changes from growth suppressor to growth promoter when its binding to menin is prevented, whether by a JunD mutation or by a menin-null background [E1]. This is why the endocrine question cannot be framed as simple loss of a brake. Removing menin from JunD converts a brake into an accelerator, which is a strictly worse failure mode and is the mechanistic reason menin is a tumour suppressor in endocrine tissue rather than merely a growth modulator.
The four comparisons
| Construct | Background | Effect on proliferation |
|---|---|---|
| wild-type JunD | JunD-null fibroblasts | inhibited; reverted transformed-like phenotype |
| JunD G42E (cannot bind menin) | JunD-null fibroblasts | opposite / growth-promoting |
| wild-type JunD | wild-type fibroblasts | inhibited growth |
| wild-type JunD | Men1-null fibroblasts | enhanced transformed-like characteristics |
Source: Agarwal et al., PNAS 2003 1.
The last row is the important one, because it is the genetic equivalent of the drug scenario: JunD present and normal, menin unavailable. The result was not neutrality. It was enhancement of transformation.
Why sign inversion changes the risk calculation
A common intuition about tumour-suppressor inhibition is that partial, reversible loss buys proportionally little harm - half the brake for a tenth of the time is a small effect. Sign inversion breaks that intuition. If the released partner actively promotes growth rather than merely failing to suppress it, then the harm is not proportional to how much suppression was lost; it is proportional to how much promotion was gained, and those can have different dose-response curves.
Three honest limits on how far this can be pushed:
- Wrong cells. Immortalised mouse fibroblasts, already transformed-like, are not parathyroid chief cells or islet beta cells 1.
- Overexpression. The experiments use stable overexpression of JunD, not endogenous levels.
- Genetic, not pharmacological. A Men1-null background is total and permanent. A drug occupies a pocket partially and reversibly, and may not even displace JunD (see
interface-menin-jund-pocket).
What survives those limits is a direction, not a magnitude: menin-free JunD is not inert.
| actor | gene-jund |
|---|---|
| regulator | gene-men1 |
| phenotype with menin | growth suppression; reversion of transformed-like phenotype |
| phenotype without menin | growth promotion; enhancement of transformed-like characteristics |
| mutant used | JunD missense mutant with disabled menin binding |
| endocrine tissue tested | false |
| implication | the harm from releasing JunD is not proportional to suppression lost but to promotion gained, which can follow a different dose-response |
evidence systems
[ "JunD-null immortalised mouse fibroblasts", "Men1-null immortalised mouse fibroblasts" ]
readouts
[ "proliferation", "morphology", "cyclin D1" ]
- The counter-argument at full strength: a single 2003 paper in immortalised mouse fibroblasts with overexpressed constructs, reporting an effect its own authors called unexpected, for which no independent replication in endocrine tissue was found. That is thin ground for a clinical inference.
- A Men1-null background is not a drug. Whether partial, reversible pocket occupancy releases enough JunD to invert its sign is unknown and may well be no.
- If the sign inversion is real and requires only partial menin unavailability, it would also predict a dose-dependent endocrine effect in treated patients - which is testable against the twofold exposure difference already built into the revumenib dosing arms.
- Does the sign inversion reproduce in a parathyroid, islet or pituitary cell at endogenous JunD levels? Everything rests on immortalised fibroblasts with overexpression.
- Is the inversion dose-dependent in menin availability, or does it require complete menin absence? A menin knockdown titration would answer whether partial pharmacological occupancy is enough.
- What transcriptional programme does menin-free JunD drive? Identifying it would give a biomarker that could be measured in blood or tissue from treated patients.
- Has this result been independently replicated in the twenty-plus years since? No replication in an endocrine cell type was located for this entry.
- E1strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
Stable overexpression of wild-type mouse JunD in JunD-null immortalised fibroblasts inhibited proliferation and reverted their transformed-like phenotype, whereas a JunD missense mutant with disabled menin binding had opposite, growth-promoting effects; wild-type JunD inhibited growth in wild-type fibroblasts but enhanced transformed-like characteristics when overexpressed in Men1-null fibroblasts, so JunD changes from growth suppressor to growth promoter when its binding to menin is prevented.
Transcription factor JunD, deprived of menin, switches from growth suppressor to growth promoter · Agarwal SK, Novotny EA, Crabtree JS, Weitzman JB, Yaniv M, Burns AL, Chandrasekharappa SC, Collins FS, Spiegel AM, Marx SJ · Proc Natl Acad Sci U S A 100:10770-5 2003What this evidence cannot show
Read as abstract. Immortalised mouse fibroblasts with stable overexpression; proliferation, morphology and cyclin D1 readouts. Not endocrine tissue, not endogenous expression, not pharmacological. The abstract reports direction of effect without effect sizes or replicate numbers.
Evidence that argues against this (1)
- The prior expectation the same authors set out was that JunD achieves all or most of its unique growth-inhibitory properties through binding menin. The result that menin-free JunD actively promotes growth was described as unexpected, which is a reason to want independent replication before building on it - and no independent replication in an endocrine cell type has been located. Agarwal SK et al. 2003
- E2established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.paper
Menin binds JunD directly and represses JunD-activated transcription, and MEN1 missense mutations found in patients disrupt that interaction, tying the menin-JunD interaction to menin tumour suppression.
Menin interacts with the AP1 transcription factor JunD and represses JunD-activated transcription · Agarwal SK, Guru SC, Heppner C, Erdos MR, Collins RM, Park SY, Saggar S, Chandrasekharappa SC, Collins FS, Spiegel AM, Marx SJ, Burns AL · Cell 96:143-52 1999What this evidence cannot show
Read as abstract. Establishes the interaction and its clinical relevance but not the sign inversion, which comes from the later paper.
Evidence that argues against this (1)
- Patient MEN1 missense mutations disrupting the menin-JunD interaction is weaker support than it appears, because MEN1 missense mutations are predominantly destabilising and reduce menin protein levels broadly. A mutation that unfolds menin disrupts JunD binding along with every other interaction, so loss of this one does not single JunD out as the critical partner. Nature 2012
- E3established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.paper
Menin represses JunD-induced transcription by blocking JNK-mediated JunD phosphorylation, and binds MLL1 and JUND in the same pocket with opposite transcriptional consequences.
The same pocket in menin binds both MLL and JUND but has opposite effects on transcription · Huang J, Gurung B, Wan B, Matkar S, Veniaminova NA, Wan K, Merchant JL, Hua X, Lei M · Nature 482:542-6 2012What this evidence cannot show
Read as abstract. Provides the structural setting in which JunD release by a pocket ligand becomes conceivable; says nothing about the downstream growth phenotype.
Evidence that argues against this (1)
- 'Opposite transcriptional effects' compares two different readouts in two different settings rather than one system in which both are measured, and the inversion claim in this entry requires the JunD arm to dominate once menin is displaced. The structural work shows a shared pocket; it does not rank the two. Nature 2012
what happens after the repression described there is lifted
JunD switches from growth suppressor to growth promoter when menin binding is prevented
- supports →The same pocket suppresses JUND: menin inhibition's unmeasured endocrine liability in infants
releasing JunD is not simple de-repression; the brake becomes an accelerator
a candidate mechanism for the proliferative findings seen in three species across two menin inhibitors
- ← related toJUND liberation — the drug's mechanism of action and one of its mechanisms of resistance are the same event
same molecular event, recorded in this graph as an endocrine concern; this entry records the leukaemia resistance consequence