Studies have previously shown that mutant calreticulin (CALR), found in a subset of patients with myeloproliferative neoplasms (MPNs), interacts with and subsequently promotes the activation of the thrombopoietin receptor (MPL). However, the molecular mechanism behind the activity of mutant CALR remains unknown. Here we show that mutant, but not wild-type, CALR interacts to form a homomultimeric complex. This intermolecular interaction among mutant CALR proteins depends on their carboxyl-terminal domain, which is generated by a unique frameshift mutation found in patients with MPN. With a competition assay, we demonstrated that the formation of mutant CALR homomultimers is required for the binding and activation of MPL. Since association with MPL is required for the oncogenicity of mutant CALR, we propose a model in which the constitutive activation of the MPL downstream pathway by mutant CALR multimers induces the development of MPN. This study provides a potential novel therapeutic strategy against mutant CALR-dependent tumorigenesis via targeting the intermolecular interaction among mutant CALR proteins.
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This work was funded in part by the Ministry of Education, Culture, Sports, Science and Technology (MEXT)-Supported Program for the Strategic Research Foundation at Private Universities; MEXT’s Promotion Plan for the Platform of Human Resource Development for Cancer project; Japan Society for the Promotion of Science’s KAKENHI Grants #15K15368, #16K09859, #17K16195, #17H04211, #18K16098, #18K16127, #18K16126, and #18K08372; and grants from the Takeda Science Foundation, SENSHIN Medical Research Foundation, and Japan Leukemia Research Fund. The funders had no role in manuscript preparation. We are grateful to Dr Hitoshi Kiyoi for providing Marimo cell line, to Shing Leng Chan for her critical reading of the manuscript, and to members of the Department of Hematology for supporting this study. We would like to acknowledge the Laboratory of Molecular and Biochemical Research, Laboratory of Morphological Analysis and Imaging, and the Division of Cell Biology at the Research Support Center of Juntendo University.
Conflict of interest
MA, YY and NK have submitted a patent application related to this study. The remaining authors declare that they have no conflict of interest.
About this article
Calreticulin mutants as oncogenic rogue chaperones for TpoR and traffic-defective pathogenic TpoR mutants
The role of the thrombopoietin receptor MPL in myeloproliferative neoplasms: recent findings and potential therapeutic applications
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