Nuclear localization of the serine/threonine kinase DRAK2 is involved in UV-induced apoptosis

DAP kinase-related apoptosis-inducing kinase 2 (DRAK2), a member of the DAP kinase family, is a serine/threonine kinase capable of inducing apoptosis. Here we studied the relationship between DRAK2 intracellular localization and apoptosis, and found that UV light acts as a stimulus for apoptosis induced by DRAK2. The intracellular location of DRAK2 depended on the cell line: DRAK2 was found primarily in the nuclei of NRK, NIH3T3, and Caco-2 cells while it was present primarily in the cytoplasm of ACL-15, HeLa, and WI-38 cells. Overexpression of Myc-tagged DRAK2 led to apoptosis-like cell death in NRK cells, but not in ACL-15 cells. A GFP fusion protein of DRAK2 was spontaneously localized to the nucleus of ACL-15 cells and resulted in cell death. Nuclear localization and cell death were also observed with DRAK2(1-293) fused to the NLS of SV40 but not with DRAK2(1-293) alone. These results suggested that nuclear accumulation of DRAK2 and the resulting increase in the endogenous level of its kinase activity are required for cell death. UV irradiation caused nuclear accumulation of endogenous DRAK2 in ACL-15 cells, which was followed by apoptosis-like cell death. Knockdown of DRAK2 expression by siRNA partially suppressed UV-induced apoptosis. These results suggest that DRAK2 plays a role in UV induced apoptosis.