Immunosuppression by Mutated Calreticulin Released from Malignant Cells

• DOI: 10.1016/j.molcel.2019.11.004
• Publication Date: 2019-11-27T15:37:38Z
• Authors: Peng Liu; Liwei Zhao; Friedemann Loos; Caroline Marty; Wei Xie; Isabelle Martins; Sylvie Lachkar; Bo Qu; Emmanuelle Waecke...; Isabelle Plo; William Vainchenker; Franck Perez; David Rodriguez; Carlos López-Otin; Peter van Endert; Laurence Zitvogel; Oliver Kepp; Guido Kroemer
• Keywords: Mice, Inbred C57BL; Mice; Phagocytosis; Cell Line, Tumor; Neoplasms; Mutation; Immune Tolerance; Animals; Humans; Calreticulin; 3. Good health

Mutations affecting exon 9 of the CALR gene lead to the generation of a C-terminally modified calreticulin (CALR) protein that lacks the KDEL endoplasmic reticulum (ER) retention signal and consequently mislocalizes outside of the ER where it activates the thrombopoietin receptor in a cell-autonomous fashion, thus driving myeloproliferative diseases. Here, we used the retention using selective hooks (RUSH) assay to monitor the trafficking of CALR. We found that exon-9-mutated CALR was released from cells in response to the biotin-mediated detachment from its ER-localized hook, in vitro and in vivo. Cellular CALR release was confirmed in suitable mouse models bearing exon-9-mutated hematopoietic systems or tumors. Extracellular CALR mediated immunomodulatory effects and inhibited the phagocytosis of dying cancer cells by dendritic cells (DC), thereby suppressing antineoplastic immune responses elicited by chemotherapeutic agents or by PD-1 blockade. Altogether, our results demonstrate paracrine immunosuppressive effects for exon-9-mutated CALR.