| THAP 1 is a nuclear proapoptotic factor that links prostate apoptosis response 4 ( Par 4 ) to PML nuclear bodies . ^^^ Here , we report that THAP 1 is a novel nuclear proapoptotic factor associated with PML NBs , which potentiates both serum withdrawal and TNF alpha induced apoptosis , and interacts with prostate apoptosis response 4 ( Par 4 ) , a well characterized proapoptotic factor , previously linked to prostate cancer and neurodegenerative diseases . ^^^ We show that endogenous Par 4 colocalizes with ectopic THAP 1 within PML NBs in primary endothelial cells and fibroblasts . ^^^ In addition , we found that Par 4 is a component of PML NBs in blood vessels , a major site of PML expression in vivo . ^^^ Finally , we investigated the role of the THAP domain in THAP 1 activities and found that this putative DNA binding domain is not required for Par 4 binding and localization within PML NBs , but is essential for THAP 1 proapoptotic activity . ^^^ |