Prostate apoptosis response 4 (Par4) is a 38kD protein originally identified as the product of a gene that is upregulated in prostate tumor cells undergoing apoptosis. It is a leucine zipper and death domain containing protein whose levels increase in neurons undergoing apoptosis as a result of trophic factor withdrawal or exposure to oxidative and metabolic insults. Par4 levels are reported to be increased in their lumbar spinal cord specimens further suggesting a role in neuronal degeneration. The tumor suppressor WT1 represses and activates transcription. The loss and/or imbalance of the dual transcriptional activity of WT1 may contribute to Wilms tumor. Par4 is a WT1 interacting protein that also functions as a transcriptional repressor.