A ten-residue export signal is the 5' partner's whole contribution - and the field disagrees about which direction it pushes
also called CALM NES · CRM1-dependent CALM-AF10 transformation
The only part of PICALM that the leukaemia actually needs is a short tag telling the cell to pump the protein out of the nucleus. Swapping that tag for the same tag taken from unrelated proteins works just as well - but one influential paper argues the opposite, that keeping the fusion IN the nucleus is what matters.
The same thing, for a scientist
**The result.** CALM residues **544-553** form a leucine-rich NES recognised by CRM1/XPO1. In murine bone-marrow assays, mutating it abolishes transformation; fusing **CALM 540-557 alone**, or NES motifs taken from **ABL1, Rev, PKIA or APC**, to AF10 is sufficient to immortalise cells; and the same element controls HOXA overexpression and focal H3K79 hypermethylation [E1]. An independent group reached the same conclusion in a separate system [E2]. Replacing CALM entirely with **CRM1** gives a CRM1-AF10 chimera that causes leukaemia with HOXA activation, and mutating the CRM1 residues that contact NUP214 abolishes self-renewal and leukaemogenesis [E3]. **The disagreement, stated rather than smoothed.** Okada et al. report that hDOT1L contributes to CALM-AF10 transformation by **preventing** nuclear export of the fusion, i.e. by making it more nuclear [E4]; Klein et al. report that restoring the AF10 PZP domain **promotes nuclear localisation** of CALM-AF10 and **abolishes** transformation [E5]. Both of those align a *more nuclear* fusion with *less* transformation in Conway's frame and with *more* transformation in Okada's. **This graph does not resolve it**; the contradiction is recorded because it is load-bearing for any intervention aimed at the shuttling step.
Export signal or chromatin docking signal?
Conway et al.'s later work found that CRM1 binds HOXA chromatin in a pattern resembling CALM-AF10's, including in cells that do not express CALM-AF10 3, which makes a second reading available: the NES is not primarily an export signal here but a docking signal onto chromatin-prebound CRM1, the architecture reported for NUP98-HoxA9. The two readings make opposite predictions about nuclear-export inhibition:
- Export model: blocking CRM1 traps the fusion in the nucleus and should be protective - and CALM-AF10 cells are reported selectively sensitive to leptomycin B 1.
- Docking model: blocking CRM1 removes the chromatin anchor, which should also be protective, but for a different reason and with a different expected effect on H3K79 methylation.
A locus-resolved H3K79me2 measurement under an XPO1 inhibitor would separate them, and has not been reported.
Why this matters to the menin question
In a KMT2A fusion the 5' partner supplies the chromatin address through CXXC and menin. In CALM-AF10 the 5' partner supplies a transport motif that any protein could carry, and the address appears to be supplied by CRM1, by the MOZ/ENL complex, or by both. That is a mechanistically different way of arriving at the same output genes, and it is the concrete reason to expect menin independence.
| mechanism class | nucleocytoplasmic transport |
|---|---|
| motif | CALM NES, Q13492-1 residues 544-553; sufficient construct 540-557 |
| receptor | CRM1 / XPO1 |
| necessity | demonstrated in two independent laboratories |
| sufficiency | heterologous NES motifs from ABL1, Rev, PKIA and APC substitute for the CALM NES |
| orthogonal chimera | CRM1-AF10 causes leukaemia with HOXA activation; NUP214-contact mutants do not |
| unresolved contradiction | Okada et al. place DOT1L as an inhibitor of CALM-AF10 export and treat nuclear retention as pro-oncogenic; Conway et al. and Suzuki et al. find nuclear retention abolishes transformation; Klein et al. find PZP-driven nuclear localisation also abolishes it. No experiment in this beat's reading reconciles them. |
| menin involvement | none reported |
- CRM1 exports hundreds of cargoes including several tumour suppressors; an XPO1 inhibitor buys no selectivity from this rationale and carries selinexor's known toxicity.
- If the docking model is right, an export inhibitor might stabilise the fusion on chromatin rather than displace it, and the intervention could point the wrong way.
- The 5' partner's contribution is a generic motif that hundreds of proteins carry, so there is no CALM-AF10-selective surface here to design against.
- Export or chromatin docking? A locus-resolved H3K79me2 measurement under an XPO1 inhibitor would separate the two models, and has not been reported.
- Why does making CALM-AF10 nuclear abolish transformation in three papers while a fourth treats nuclear retention as the oncogenic state? Either the systems differ in a way nobody has identified or one reading is wrong.
- Is selinexor active in CALM-AF10 leukaemia? Leptomycin B sensitivity is reported, XPO1 is highly expressed in patient samples, and no clinical XPO1-inhibitor result in this fusion was found on 2026-09-20.
- E1strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
In murine bone-marrow clonogenic and transplantation assays, CALM residues 544-553 form a CRM1-recognised NES necessary for CALM-AF10 transformation; CALM 540-557 alone or heterologous NES motifs from ABL1, Rev, PKIA or APC fused to AF10 are sufficient to immortalise cells; the NES also controls HOXA overexpression and focal H3K79 hypermethylation; and CALM-AF10 leukaemia cells are selectively sensitive to leptomycin B.
A CALM-derived nuclear export signal is essential for CALM-AF10-mediated leukemogenesis. · Conway AE, et al. · Blood 2013What this evidence cannot show
Murine bone marrow plus HEK293 imaging. Leptomycin B is a covalent CRM1 inhibitor and a tool compound, not a clinical agent. Numbering frame stated by the authors (NP_009097.2 / Q13492-1).
Evidence that argues against this (1)
- Okada et al. report the opposite polarity - that hDOT1L contributes to transformation by PREVENTING nuclear export of CALM-AF10. The two papers use different systems but the disagreement is about the sign of the same phenomenon. Okada Y et al. 2006
- E2strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
An independent group found that a nuclear export signal within CALM is necessary for CALM-AF10-induced leukaemia, with CALM-AF10 NES mutants localising to the nucleus in COS-7 cells.
Nuclear export signal within CALM is necessary for CALM-AF10-induced leukemia. · Suzuki M, et al. · Cancer Sci 2014What this evidence cannot show
Separate laboratory, separate system (COS-7 imaging plus murine leukaemia). Independent replication of the necessity claim is the reason this mechanism is graded strong.
Evidence that argues against this (1)
- PUBLISHED CONFLICTING RESULT on what the NES requirement is a requirement FOR. In a mouse model of CALM-AF10 leukaemia, full-length CALM-AF10 in LEUKAEMIA CELLS localised to the NUCLEUS, and the authors propose that the contribution of endocytic 5' partners is HOMO-OLIGOMERISATION - measured by fluorescence resonance energy transfer - rather than any effect on internalisation or transport. If the fusion is nuclear in the cell type that matters, then 'the NES is necessary for leukaemogenesis' and 'the NES is necessary because it exports the fusion' are two claims, and the COS-7 imaging tests only the export half in a cell where the fusion is not oncogenic. Stoddart A et al. 2012
- E3strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
Fusing the CRM1 nuclear export receptor to AF10 in place of CALM causes leukaemia with transcriptional activation of HOXA genes; CRM1 binds HOXA chromatin in a pattern resembling CALM-AF10 binding even without CALM-AF10; and mutating the CRM1 motifs that contact NUP214 abolishes self-renewal in colony assays and prevents leukaemia over 300 days.
Fusion of the CRM1 nuclear export receptor to AF10 causes leukemia and transcriptional activation of HOXA genes. · Aumann WK, et al. · Leukemia 2021What this evidence cannot show
Murine fetal-liver haematopoietic cells and transplantation. A chimera is a strong argument about sufficiency and a weak one about what the natural fusion does.
Evidence that argues against this (1)
- PUBLISHED CONFLICTING RESULT about what the substituted region contains. A CRM1-AF10 chimera replaces the whole CALM moiety at once, and the CALM span that carries the NES also carries the clathrin-binding region - and that region independently selects the disease: excluding the C-terminal portion of CALM required for optimal clathrin binding gives a myeloproliferative disease in mice, including it gives acute myeloid leukaemia with Pim1 and Crebbp changes. So the chimera's success shows a CRM1 moiety can substitute for everything CALM contributes, not that export is the contribution; and the one experiment that dissects the region attributes the phenotype difference to something other than endocytosis, which leaves oligomerisation and the NES both unexcluded. Stoddart A et al. 2012
- E4moderate confidence 3 of 5: One strong study, or several smaller consistent ones.paper
hDOT1L contributes to CALM-AF10-mediated leukaemic transformation by preventing nuclear export of CALM-AF10 and by upregulating Hoxa5 through H3K79 methylation.
Leukaemic transformation by CALM-AF10 involves upregulation of Hoxa5 by hDOT1L. · Okada Y, et al. · Nat Cell Biol 2006What this evidence cannot show
Murine bone marrow plus U2OS imaging. Recorded here as the dissenting reading, not as the consensus. It predates the NES mapping and the heterologous-NES substitution experiments.
Evidence that argues against this (1)
- Two later studies from two laboratories find that NES mutation, which makes the fusion nuclear, ABOLISHES transformation - the opposite direction from 'preventing export contributes to transformation'. Suzuki M et al. 2014
- E5strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
Restoring a functional AF10 PZP domain to CALM-AF10 promotes nuclear localisation of the fusion, is required for its chromatin association, downregulates Hoxa genes and abolishes transformation and leukaemogenesis.
The role of the PZP domain of AF10 in acute leukemia driven by AF10 translocations. · Klein BJ, et al. · Nat Commun 2021What this evidence cannot show
Murine HSPCs. Note the apparent paradox this creates and which the entry does not resolve: PZP restoration makes the fusion MORE nuclear and MORE chromatin-associated while making it LESS transforming, which is hard to reconcile with a simple 'nuclear equals oncogenic' model in either direction.
Evidence that argues against this (1)
- PUBLISHED ALTERNATIVE MODEL that predicts the paradox this item ends on. If nuclear-and-chromatin-associated were the oncogenic state, restoring the PZP domain would not abolish transformation. A model in which the axis is not nuclear-versus-cytoplasmic but WHERE on chromatin the complex is retained does predict it: the MOZ/ENL complex recruits the DOT1L/AF10 fusion complex and maintains its chromatin retention through MOZ/MORF acetyltransferase activity, with ENL's YEATS-domain interaction with MOZ critical for CALM-AF10 transformation, and combined MOZ/MORF plus DOT1L inhibition cooperatively inducing differentiation. Under that account a PZP-restored fusion is redirected to unmodified-H3K27 chromatin and away from the MOZ/ENL-marked sites that matter - which resolves the paradox without an export term, and makes the NES model's explanatory role smaller than this entry gives it. Komata Y et al. 2023
the 5' partner's mechanistic contribution
NES at Q13492-1 residues 544-553
NES mutation abolishes focal H3K79 gain and HOXA expression
leptomycin B produces complete nuclear accumulation
CRM1 is the shared element, and NUP214 is CRM1's docking nucleoporin
the receptor the CALM NES is recognised by
NES instance of the route; the CRM1-AF10 chimera is the reciprocal proof
separates the export model from the docking model
both are 5-prime partners that set the fusion address -- but in OPPOSITE directions: SFPQ-ABL1 is nuclear, CALM-AF10 requires nuclear export
Dot1a export is leptomycin-B sensitive, so DOT1L itself is a CRM1 cargo when a partner supplies the signal
the NES/clathrin-binding/oligomerisation claims all concern one CALM span and no experiment separates them; the fusion is nuclear in leukaemia cells
the tethering model has the fusion capturing XPO1 and decreasing export; Conway et al. (PMID 25027513) have CRM1 pre-localised at HOXA and RECRUITING the NES-bearing fusion. Both cannot be the general rule, and this entry cites tethering as the prior that makes the 2025 CUT&RUN unsurprising
if CRM1 is itself a chromatin-binding factor at HOXA (PMID 25027513), a CRM1-AF10 chimera supplies the chromatin anchor directly and cannot discriminate 'CRM1 as pre-existing address' from 'CRM1 as the chromatin-binding moiety inside the fusion' - the same distinction this experiment exists to make
- ← related toAF10/MLLT10 fusions drive aberrant self-renewal of non-stem progenitors — found only by opening the paper
a second maintenance result for this fusion exists and is reachable only through CRM1 and CALM: disrupting the CALM-CRM1 interaction prevents CALM-AF10 enrichment at HOXA chromatin with IMMEDIATE loss of transcription (PMID 25027513), so '29 records, one on topic' is a floor and not a measurement of the literature
- ← analogous toSET::NUP214 has no address of its own: chromatin-bound CRM1 is already at HOX, and the fusion's FG repeats dock onto it
the two lesions touch the same CRM1-NUP214 contact from opposite sides