Protein Phosphatase 1, Regulatory Subunit 13B (PPP1R13B)

PPP1R13B contains four ankyrin repeats and an SH3 domain involved in protein-protein interactions. ASPP proteins are required for the induction of apoptosis by p53-family proteins.  Expression of this gene is regulated by the E2F transcription factor. Inhibition of endogenous ASPP function suppressed the apoptotic function of endogenous p53 in response to apoptotic stimuli. ASPPs enhanced the DNA binding and transactivation function of p53 on the promoters of proapoptotic genes in vivo. Two tumor-derived p53 mutants with reduced apoptotic function were defective in cooperating with ASPP in apoptosis induction. Expression of the ASPPs was frequently downregulated in human breast carcinomas expressing wildtype p53 but not in those expressing mutant p53.