Our results revealed a transient, low-level caspase-3 activation downstream of disrupted Dsg3 cis- or trans-adhesion [21,22], which occurs early in PV acantholysis, is uncoupled from apoptosis or classical apoptotic pathways and, as judged from caspase-3 inhibitor treatments, contributes to major events in PV pathogenesis; these are increased expression of proliferation markers including Myc family members, p38MAPK activation, cleavage of Dsg3, keratin retraction as well as loss of intercellular adhesion. This evidence concerns the gene CASP3 and acquired polycythemia vera.