Rabbit Anti-Human F2RL3 polyclonal antibody for IHC-P. Prostate apoptosis response-4 (Par-4) is a 38kDa 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. Par-4 levels are reported to be increased in their lumbar spinal cord specimens further suggesting a role in neuronal degeneration.