Myeloproliferative neoplasms (MPN) are clonal hematopoietic stem cell neoplasms including polycythemia vera (PV), essential thrombocytemia (ET) and primary myelofibrosis (PMF), spontaneously evolving in leukemia. MPN are driven by somatic mutations of JAK2, calreticulin (CALR) and MPL genes, all activating the JAK2/STAT signaling pathway and uncontrolled production of myeloid cells. JAK2 and MPL mutations insist directly to essential pathways of myelopoiesis. In contrast, CALR mutations, exclusively found in ET or PMF, affect a multifunctional protein, apparently not connected with hematopoiesis. CALR mutations consist in various CALR exon 9 deletions and/or insertions, all causing a 1-bp frameshift, removing the ER retrieval motif KDEL and converting into coding sequence the first 31 bases of 3¿UTR mRNA. The biological consequences of the conversion of noncoding mRNA into coding region have not been investigated so far in MPNs. Recently, we detected a novel CALR deletion (c.1254+10_+33del24,) in two siblings diagnosed with JAK2 V617F-negative PV. CALRdel24 is located 10 bp downstream the stop codon in a highly conserved region of 3¿UTR mRNA. It does not alter the coding sequence, but leads to CALR overexpression and biological features of JAK2-driven PV, including erythrocytosis. This project is aimed at identifying, in normal myelopoiesis and MPNs, the epigenetic interactors acting on this CALR 3'UTR mRNA region and the biological role of consequent RNA modifications. We plan to identify RNA binding proteins and miRNAs targeting this CALR 3'UTR site and their relevance in complex regulative functions including mRNA modification, translation efficiency and protein localization, to be studied in relation to CALR hematopoietic functions. By exploring these new aspects of MPNs in primary samples from normal donors and MPN patients, we may identify new physiological mechanisms of hematopoiesis, which are deregulated in MPNs and that can be targeted by treatments.
