JAK2V617F mRNA metabolism in myeloproliferative neoplasm cell lines
Authors: P Nauroy, F Delhommeau, F Baklouti
Journal: Blood Cancer Journal (2014)

Myeloproliferative neoplasms (MPNs) are a heterogeneous group of leukemias with defective regulation of myeloid stem cell proliferation.They include four distinct diseases: chronic myeloid leukemia, polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF). 1,2In 2005, four independent studies have concurred to the identification in MPN patients of a specific mutation in the Janus kinase 2 (JAK2) protein (1849 G-T in exon 14; 617Val-Phe) in the majority of MPNs. 1,2Indeed, this JAK2V617F variant was identified in 95% of PV, 55% of ET and 65% of PMF patients.The amino-acid change triggers a constitutive activation of the JAK2 protein, independently of cytokines.Whether JAK2V617F is the initiating event in these MPNs remains under debate; however, JAK2V617F seems to drive the phenotype of the disease.JAK2 gene is located on human chromosome 9, at p24.1 locus.It is composed of 25 exons and encodes a 1132 amino-acid protein of 130.7 kDa apparent molecular weight.The gene is expressed only in blood cells, bone marrow and lymph nodes.Occurrence of JAK2V617F in association with phenotypically different classes of MPNs raised a controversy as to the real function of the mutated JAK2 and the possible involvement of additional genetic determinants in these phenotypic discrepancies.Recent whole genomic studies have identified few single-nucleotide polymorphisms (SNPs) in the vicinity of exon 14 3-5 (Figure 1a).Notably, it has been anticipated that the 46/1 haplotype predisposes to the JAK2V617F mutation. 5Other studies have suggested that several SNPs could be implicated in MPN phenotype disparity. 6The question remains as to the possible role of these SNPs in MPN phenotypic discrepancies.This 46/1 haplotype is a 280-kb-long region on chromosome 9 that includes JAK2, INSL4 and INSL6 genes.Four SNPs define the 'GGCC' part of this haplotype and are located in the JAK2 gene: rs3780367 T/G in intron 10, rs10974944 C/G in intron 12, rs12343867 T/C in intron 14 and rs1159782 T/C in intron 15 (Figure 1a).All four SNPs are in complete linkage disequilibrium. 7he 46/1 haplotype includes the sequences frequently mutated in MPNs like mutations in exons 12 and 14.On another hand, the rs10974944G minor allele was significantly more common in PV than in ET conditions. 3In addition, it was shown that other JAK2 SNPs, namely rs7046746, rs10815148 and rs12342421, were also significantly associated with PV and ET but not with PMF. 6 In this work, we hypothesized that the JAK2V617F and/or the 46/1 haplotype could have an impact on JAK2 mRNA level or/and pre-mRNA maturation.To provide new insights into the JAK2 mRNA expression and splicing, six cell lines, derived from patients with MPNs, were chosen on the basis of their JAK2 status (Figure 1b), and cultured in appropriate media (Supplementary Table 1).It has been suggested that both in human and mouse, the phenotypic expression of the disease depends on the intensity of the signaling, which is thought to be modulated only by the number of JAK2V617F copies. 8Moreover, it was recently emphasized that the number of JAK2 genes in UKE-1 cell line