JAK2-V617F is activated constitutively and stimulates the various signaling pathways downstream of JAK2 in cytokine-stimulated cells, thus leading to cytokine-independent cell survival and proliferation when expressed in cytokine-dependent hematopoietic cell lines and causing phenotypes similar to PV in various murine models [1, 2, 4]. Here, JAK2 is linked to acquired polycythemia vera.