Myeloproliferative neoplasms (MPNs) are frequently driven by mutations within the C-terminal domain (C-domain) of calreticulin (CRT). CRTDel52 and CRTIns5 are recurrent mutations. Oncogenic transformation requires both mutated CRT and the thrombopoietin receptor (Mpl), but the molecular mechanism of CRT-mediated constitutive activation of Mpl is unknown. We show that the acquired C-domain of CRTDel52 mediates both Mpl binding and disulfide-linked CRTDel52 dimerization. Cysteine mutations within the novel C-domain (C400A and C404A) and the conserved N-terminal domain (N-domain; C163A) of CRTDel52 are required to reduce disulfide-mediated dimers and multimers of CRTDel52. Based on these data and published structures of CRT oligomers, we identify an N-domain dimerization interface relevant to both WT CRT and CRTDel52. Elimination of disulfide bonds and ionic interactions at both N-domain and C-domain dimerization interfaces is required to abrogate the ability of CRTDel52 to mediate cell proliferation via Mpl. Thus, MPNs exploit a natural dimerization interface of CRT combined with C-domain gain of function to achieve cell transformation.
Mechanism of mutant calreticulin-mediated activation of the thrombopoietin receptor in cancers
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Arunkumar Venkatesan, Jie Geng, Malathi Kandarpa, Sanjeeva Joseph Wijeyesakere, Ashwini Bhide, Moshe Talpaz, Irina D. Pogozheva, Malini Raghavan; Mechanism of mutant calreticulin-mediated activation of the thrombopoietin receptor in cancers. J Cell Biol 5 July 2021; 220 (7): e202009179. doi: https://doi.org/10.1083/jcb.202009179
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