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Abstract Myeloproliferative neoplasms (MPNs) are cancers involving dysregulated production and function of myeloid lineage hematopoietic cells. Among MPNs, Essential thrombocythemia (ET), Polycythemia Vera (PV) and Myelofibrosis (MF), are driven by mutations that activate the JAK–STAT signalling pathway. Somatic mutations of calreticulin (CRT), an endoplasmic reticulum (ER)‐localized lectin chaperone, are driver mutations in approximately 25% of ET and 35% of MF patients. The MPN‐linked mutant CRT proteins have novel frameshifted carboxy‐domain sequences and lack an ER retention motif, resulting in their secretion. Wild type CRT is a regulator of ER calcium homeostasis and plays a key role in the assembly of major histocompatibility complex (MHC) class I molecules, which are the ligands for antigen receptors of CD8+T cells. Mutant CRT‐linked oncogenesis results from the dysregulation of calcium signalling in cells and the formation of stable complexes of mutant CRT with myeloproliferative leukemia (MPL) protein, followed by downstream activation of the JAK–STAT signalling pathway. The intricate participation of CRT in ER protein folding, calcium homeostasis and immunity suggests the involvement of multiple mechanisms of mutant CRT‐linked oncogenesis. In this review, we highlight recent findings related to the role of MPN‐linked CRT mutations in the dysregulation of calcium homeostasis, MPL activation and immunity.
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Mechanism of mutant calreticulin-mediated activation of the thrombopoietin receptor in cancers
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.
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- Award ID(s):
- 1855425
- PAR ID:
- 10224058
- Publisher / Repository:
- DOI PREFIX: 10.1083
- Date Published:
- Journal Name:
- Journal of Cell Biology
- Volume:
- 220
- Issue:
- 7
- ISSN:
- 0021-9525
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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