Menin builds bone early and blocks it late: two opposite jobs in the same lineage
also called menin osteoblast commitment · menin Smad1/5 Runx2 · menin JunD osteoblast
In bone-forming cells, menin is needed at the start to make a stem cell become a bone cell at all - but later, once the cell is committed, menin holds back the final maturation step. So blocking menin does opposite things depending on which stage the cell is at.
The same thing, for a scientist
Menin's role in the osteoblast lineage is stage-dependent and sign-flipping, which makes the effect of a menin inhibitor on a growing skeleton genuinely unpredictable rather than merely unknown. In C3H10T1/2 multipotential mesenchymal stem cells, menin knockdown **blocks** BMP-2-induced commitment to osteoblast (ALP, type I collagen, Runx2, osteocalcin all reduced); menin co-immunoprecipitates with Smad1 and Smad5 and is required for BMP-2-induced Smad1/5 transcriptional activity; adipogenic and chondrogenic markers are unaffected [E1]. In already-committed MC3T3-E1 osteoblasts the same knockdown does the **opposite** - stable menin inactivation increases ALP activity, mineralisation, type I collagen and osteocalcin [E1]. The late-stage suppression is mediated at least in part through JunD: JunD promotes osteoblast differentiation, menin binds it and inhibits its AP-1 transcriptional activity and the ALP activity it induces [E2].
The stage dependence, in one table
| Cell stage | Manipulation | Direction | Mechanism [E1][E2] |
|---|---|---|---|
| Multipotential MSC (C3H10T1/2) | Menin antisense | Commitment to osteoblast blocked | Menin-Smad1/5, BMP-2 signalling |
| Same cells, adipogenic and chondrogenic markers | Menin antisense | Unaffected | - |
| Committed osteoblast (MC3T3-E1) | Menin antisense, transient | No effect on BMP-2-stimulated ALP/Runx2/OCN | - |
| Committed osteoblast (MC3T3-E1) | Stable menin inactivation | Maturation accelerated: ALP, mineralisation, COL1, OCN all up | JunD de-repression 2 |
Endogenous menin rises to day 14 of differentiation culture and falls thereafter 1 - again a protein the tissue regulates on its own schedule, as in the beta cell.
What this predicts for a menin inhibitor in a child
A systemic menin inhibitor hits both compartments at once. In the mesenchymal progenitor pool it would be predicted to reduce recruitment of new osteoblasts; in already-committed osteoblasts it would be predicted to accelerate maturation and mineralisation. An acceleration of terminal osteoblast maturation with a depleted progenitor pool is, in outline, a description of premature skeletal maturation with reduced long-term bone accrual - and the revumenib label independently reports irreversible increased femoral growth-plate closure in 6-7-week-old rats at ~2x human AUC, with the instruction to monitor bone growth and development in paediatric patients 3. The two have never been connected in the literature, and this entry is the connection, offered as a mechanistic hypothesis rather than a demonstrated chain.
The honest caveat is large: growth-plate closure is driven by the chondrocyte, and 1 found chondrogenic markers unaffected by menin knockdown in the one system where it looked. So the most obvious mechanistic route to the label finding is the one that has the least support.
Raised alkaline phosphatase on both labels
Alkaline phosphatase increased in 33% of revumenib-treated patients and in 41% of ziftomenib-treated patients 34 - the one bone-related laboratory abnormality present on both labels, and higher on the drug with no parathyroid signal. ALP is also exactly the osteoblast maturation marker that goes up when menin is stably inactivated in committed osteoblasts 12. This is a concrete, checkable prediction that has never been tested: if the ALP rise is bone-derived and on-target, bone-specific ALP should rise while liver ALP does not. The labels report total ALP only, and both labels also report transaminase elevations, so a hepatic origin is at least as likely. Isoenzyme fractionation on stored samples would settle it.
| lineage | mesenchymal stem cell -> committed osteoblast -> osteocyte |
|---|---|
| early role | required for BMP-2/Smad1/5 commitment |
| late role | suppresses maturation, via JunD |
| chondrocyte evidence | chondrogenic markers unaffected by menin knockdown in BMP-2-treated 10T1/2 cells; no growth-plate chondrocyte study exists |
label signals
{
"revumenib_ALP_pct": 33,
"ziftomenib_ALP_pct": 41,
"growth_plate": "irreversible closure in juvenile rat at ~2x human AUC"
}- Menin's role in bone flips sign with cell stage, so the effect of a menin inhibitor on a growing skeleton cannot be predicted from the direction of the effect in any single assay.
- A drug that simultaneously depletes osteoprogenitors and accelerates terminal osteoblast maturation would cost a child peak bone mass in a way that only shows up decades later.
- The one bone laboratory abnormality present on both labels - raised ALP - has never been fractionated, so the most basic question about the skeletal signal is unanswered by choice, not by difficulty.
- Is the alkaline phosphatase rise on both menin inhibitors bone-derived or hepatic? Isoenzyme fractionation of stored samples would answer it and has never been done.
- Does a menin inhibitor accelerate mineralisation in human osteoblasts and deplete the osteoprogenitor pool, as the stage-dependent model predicts?
- Does menin do anything in the growth-plate chondrocyte? The one relevant experiment found chondrogenic markers unaffected, and no study has looked directly.
- E1moderate confidence 3 of 5: One strong study, or several smaller consistent ones.paper
Menin is required for BMP-2/Smad1/5-driven commitment of mesenchymal stem cells to the osteoblast lineage but suppresses later osteoblast maturation; chondrogenic markers were unaffected by menin knockdown.
Inactivation of menin, the product of the multiple endocrine neoplasia type 1 gene, inhibits the commitment of multipotential mesenchymal stem cells into the osteoblast lineage. · Sowa H, Kaji H, Canaff L, Hendy GN, Tsukamoto T, Yamaguchi T, et al. · Journal of Biological Chemistry 2003What this evidence cannot show
Immortalised murine cell lines (C3H10T1/2, MC3T3-E1) and antisense oligonucleotide knockdown, 2003 methodology; no in-vivo arm; the chondrogenic null is from BMP-2-treated 10T1/2 cells, not from growth-plate chondrocytes.
Evidence that argues against this (1)
- In vivo, conditional Men1 deletion in mature osteoblasts reduces bone mineral density, trabecular volume and cortical thickness - i.e. the net skeletal outcome of menin loss in the committed compartment is less bone, not more, despite the in-vitro maturation acceleration. Kanazawa I et al. 2015
- E2moderate confidence 3 of 5: One strong study, or several smaller consistent ones.paper
Menin suppresses late osteoblast differentiation by binding JunD and inhibiting its AP-1 transcriptional activity and the alkaline phosphatase activity it induces.
Menin suppresses osteoblast differentiation by antagonizing the AP-1 factor, JunD. · Naito J, Kaji H, Sowa H, Hendy GN, Sugimoto T, Chihara K · Journal of Biological Chemistry 2005What this evidence cannot show
MC3T3-E1 cells with stable transfection and co-transfection reporters; JunD levels rose when menin was knocked down, so the effect is partly abundance and partly activity; no in-vivo confirmation in this paper.
Evidence that argues against this (1)
- JunD in osteoblasts promotes differentiation, whereas in the beta cell and in fibroblasts released JunD is growth-promoting; the sign of JunD release is tissue-specific and cannot be generalised from one tissue to another. Naito J et al. 2005
- E3established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.database
Revumenib caused irreversible increased femoral growth-plate closure in juvenile rats at ~2x human AUC, with a label instruction to monitor bone growth in paediatric patients; alkaline phosphatase increased in 33% of patients.
REVUFORJ (revumenib) tablets, for oral use - US Prescribing Information (SPL version 5, published 20 Feb 2026) · Syndax Pharmaceuticals, Inc. · DailyMed / FDA Structured Product Label, setid 6eb3cdbc-0e74-477d-82d6-3bb172d3f63f 2026What this evidence cannot show
Label summary of a 13-week juvenile rat study; no incidence, no severity grading, no histomorphometry, and no human bone-age or height-velocity data anywhere.
Evidence that argues against this (1)
- The ziftomenib label reports no growth-plate finding, and its paediatric section states that safety and effectiveness in children have not been established, so the growth-plate signal is currently single-compound. Kura Oncology et al. 2025
- E4established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.database
Alkaline phosphatase increased in 41% of ziftomenib-treated patients, a higher rate than revumenib's 33%.
KOMZIFTI (ziftomenib) capsules, for oral use - US Prescribing Information (SPL version 1, published 16 Dec 2025) · Kura Oncology, Inc. · DailyMed / FDA Structured Product Label, setid b650f696-3391-4274-8b55-a5f5e9d04769 2025What this evidence cannot show
Total ALP only; no isoenzyme fractionation; both labels also report hepatic transaminase elevations, so origin is unresolved.
Evidence that argues against this (1)
- The ziftomenib label carries no calcium, phosphate or PTH row, so its ALP rise has no accompanying mineral-axis context and is at least as consistent with hepatic as with skeletal origin. Kura Oncology et al. 2025
- ← related toOsteoblast — the bone-building niche cell whose expansion suppresses CML and makes MLL-AF9 AML worse
menin acts cell-intrinsically in this cell; this entry covers its niche function instead
Offers the first mechanistic hypothesis for the label's growth-plate finding - accelerated terminal osteoblast maturation plus depleted osteoprogenitor commitment - while noting the chondrocyte route it would actually require has a negative result behind it
Late-stage osteoblast suppression by menin runs through JunD, which in bone PROMOTES differentiation - so the sign of JunD release is tissue-specific and opposite to its sign in fibroblasts and beta cells
- ← refutesIn a live mouse, losing menin in bone cells means less bone - and menin overexpression means more
In vivo, osteoblast Men1 deletion gives DEFICIENT mineral apposition and low ALP, the opposite of the in-vitro maturation acceleration; the conflict is recorded, not resolved
the osteoblast master gene of that mechanism; this entry adds that the leukaemia bin is at P2 and the osteoblast COMPASS literature is at P1