Regulator that plays a central role in regulation of apoptosis and cell growth via its interactions with proteins such as TP53 (By similarity). Regulates p53/TP53 by enhancing the DNA binding and transactivation function of p53/TP53 on the promoters of proapoptotic genes in vivo. Inhibits the ability of APPBP1 to conjugate NEDD8 to CUL1, and thereby decreases APPBP1 ability to induce apoptosis. Impedes cell cycle progression at G2/M. Its apoptosis-stimulating activity is inhibited by its interaction with DDX42 (By similarity). Interacts with P53/TP53; the interaction promotes pro-apoptotic activity (By similarity). Interacts with BCL2 (By similarity). Interacts with protein phosphatase 1. Interacts with RELA NF-kappa-B subunit. This interaction probably prevents the activation of apoptosis, possibly by preventing its interaction with p53/TP53. Interacts with APC2 and APPBP1. Interacts with DDX42 (via the C-terminus); the interaction is not inhibited by TP53BP2 ubiquitination and is independent of p53/TP53 (By similarity). Predominantly found in the perinuclear region. Some small fraction is nuclear. The ankyrin repeats and the SH3 domain are required for a specific interactions with p53/TP53. Belongs to the ASPP family.