Different impact of calreticulin mutations on human hematopoiesis in myeloproliferative neoplasms


Mutations of calreticulin (CALRm) define a subtype of myeloproliferative neoplasms (MPN). We studied the biological and genetic features of CALR-mutated essential thrombocythemia and myelofibrosis patients. In most cases, CALRm were found in granulocytes, monocytes, B and NK cells, but also in T cells. However, the type 1 CALRm spreads more easily than the type 2 CALRm in lymphoid cells. The CALRm were also associated with an early clonal dominance at the level of hematopoietic stem and progenitor cells (HSPC) with no significant increase during granulo/monocytic differentiation in most cases. Moreover, we found that half of type 2 CALRm patients harbors some homozygous progenitors. Those patients were associated with a higher clonal dominance during granulo/monocytic differentiation than patients with only heterozygous type 2 CALRm progenitors. When associated mutations were present, CALRm were the first genetic event suggesting that they are both the initiating and phenotypic event. In blood, type 1 CALRm led to a greater increased number of all types of progenitors compared with the type 2 CALRm. However, both types of CALRm induced an increase in megakaryocytic progenitors associated with a ruxolitinib-sensitive independent growth and with a mild constitutive signaling in megakaryocytes. At the transcriptional level, type 1 CALRm seems to deregulate more pathways than the type 2 CALRm in megakaryocytes. Altogether, our results show that CALRm modify both the HSPC and megakaryocyte biology with a stronger effect for type 1 than for type 2 CALRm.

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Fig. 1: CALRm are present in all hematopoietic cells.
Fig. 2: CALRm harbor a high clonal dominance at the progenitor cell level.
Fig. 3: CALRm are present at similar VAF in progenitors and mature cells.
Fig. 4: CALRm is the first event in hematopoiesis.
Fig. 5: CALRm induce a spontaneous growth of megakaryocytic progenitors dependent on JAK2 and PI3K.
Fig. 6: CALR type 1 mutation induces constitutive signaling.
Fig. 7: CALR type 1 and type 2 mutations induce mild gene expression deregulation in megakaryocytes.


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This work was funded by grants from the Agence Nationale pour la Recherche (Thrombocytosis, WV), the Ligue Nationale contre le Cancer (équipe labellelisée HR 2016, 2019), the Fondation Laurette Fugain (WV, IP), INCA PLBIO 2016 (IP), by grant “ Taxe d’apprentissage” Gustave Roussy—2016 (LS and MEK) and from the INSERM. Labex GR-Ex (IP, WV) is funded by the program “Investissements d’avenir.” Support to SNC was from Fondation contre le cancer, Salus Sanguinis Action de recherché concertée (ARC) 16/21-073 and WelBio F 44/8/5—MCF/UIG—10955. MEK was supported by the SFH (Société française d’hématologie), XC and AT were supported by the university Paris-Diderot (MENRT grant), MM by la Ligue Nationale contre le Cancer, Gustave Roussy Foundation and SFH. GRM was a recipient from allocations doctorales sur domaines cibles (ARDoc, Ile-de-France region). GV was supported by a PhD aspirant fellowship of the Fonds Nationals de la Recherche Scientifique, Belgium. We want to thank the platforms of bioinformatic (Khadija M Diop, Guillaume Meurice and Marc Deloger) and flow cytometry and Edwige Leclercq, Marie-Hélène Courtier for CALR sizing analysis.

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El-Khoury, M., Cabagnols, X., Mosca, M. et al. Different impact of calreticulin mutations on human hematopoiesis in myeloproliferative neoplasms. Oncogene 39, 5323–5337 (2020). https://doi.org/10.1038/s41388-020-1368-3

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