JAK2^V617F induces resistance toward genotoxic agents. Cells were treated for 1-hour exposure with various concentrations of (A) MMC or (B) bleomycin, and cell viability was assessed by trypan blue exclusion 48 hours later. *Statistical significance (P < .05) using Student t test. Error bars represent SD. (C) Morphologic features were analyzed after 4,6 diamidino-2-phenylindole staining either in untreated cells or in 1-hour-treated cells to identify potentially apoptotic cells. Continuous MMC treatment for 48 hours was used as a positive control (percentage of apoptotic cells > 0% is indicated in the images). (D) Cleavage of caspase 3 was analyzed by Western blotting using an anti–caspase 3 antibody 48 hours after treatment.