Death-Associated Protein Kinase-2 (DAPK2) Potentiates Erythroid Progenitor Cell Apoptosis in Response to Cisplatin, and Cytokine Withdrawal.

DAPK2 is a Ca⁺⁺/CAM-regulated S/T kinase which when ectopically over-expressed in 293 cells, can induce membrane blebbing and apoptosis. In contrast to DAPK1 (its tumor-suppressor orthologue), DAPK2’s expression is tissue- restricted, and presently is shown to be markedly up-regulated in developing primary erythroblasts. To assess DAPK2 function in erythroid progenitor cells, wild-type and kinase-inactive K52A forms were expressed in UT7epo cells, and an siRNA lentivirus also was developed. In this Epo-dependent human erythroid progenitor cell model, wt-DAPK2 did not significantly induce apoptosis. Sensitivity to cell death due to exposure to cisplatin, however, was markedly potentiated, and altered cell morphologies were observed. These effects depended upon DAPK2’s kinase activity, and were not mediated by DAPK2-K52A. Furthermore, siRNA-mediated knock-down of DAPK2 proved to protect UT7epo erythroid progenitor cells from apoptosis due to cytokine-withdrawal. Knock-downs were confirmed at the protein level, and no such effects were exerted by negative control siRNA constructs. Within erythroid progenitor cells, DAPK2’s pro-apoptotic effects appear to be regulated by two clinically relevant cues - cisplatin exposure, and Epo deprivation. Mechanisms that regulate DAPK2, and its proposed caspase-independent apoptotic actions, presently are under investigation in primary erythroblast systems.