JAK2 stimulates homologous recombination and genetic instability: Potential implication in the heterogeneity of myeloproliferative disorders

The JAK2^V617F mutation is frequently observed in classical myeloproliferative disorders, and disease progression is associated with a biallelic acquisition of the mutation occurring by mitotic recombination. In this study, we examined whether JAK2 activation could lead to increased homologous recombination (HR) and genetic instability. In a Ba/F3 cell line expressing the erythropoietin (EPO) receptor, mutant JAK2^V617F and, to a lesser extent, wild-type (wt) JAK2 induced anincrease in HR activity in the presence of EPO without modifying nonhomologous end-joining efficiency. Moreover, a marked augmentation in HR activity was found in CD34 ⁺-derived cells isolated from patients with polycythemia vera or primitive myelofibrosis compared with control samples. This increase was associated with a spontaneous RAD51 foci formation. As a result, sister chromatid exchange was 50% augmented in JAK2^V617F Ba/F3 cells compared with JAK2wt cells.Moreover, JAK2 activation increased centrosome and ploidyabnormalities. Finally, in JAK2^V617F Ba/F3 cells, we found a 100-fold and 10-fold increase in mutagenesis at the HPRT and Na/K ATPase loci, respectively. Together, this work highlights a new molecular mechanism for HR regulation mediated by JAK2 and more efficiently by JAK2^V617F. Our study might provide some keys to understand how a single mutation can give rise to different pathologies.