Prostate apoptosis response-4 (Par-4) is a human gene coding for a tumor-suppressor protein that induces apoptosis in cancer cells, but not in normal cells. The tumor suppressor PAR-4 represses and activates transcription. The protein encoded by this gene is a PAR-4-interacting protein that itself functions as a transcriptional repressor. It contains a putative leucine zipper domain that interacts with the zinc finger DNA binding domain of PAR-4. This protein is specifically upregulated during apoptosis of prostate cells [1].

The active domain of the Par-4 protein has been found to confer cancer resistance in transgenic mice without compromising normal viability or aging and may have therapeutic significance [2].