TP53INP1 (tumor protein p53-inducible nuclear protein 1), also known as p53DINP1, SIP or Teap, is a 240 amino acid protein that localizes to nuclear bodies and exists as two alternatively spliced isoforms, designated p53DINP1a and p53DINP1b. Expressed ubiquitously with higher expression in testis, pancreas and spleen tissue, TP53INP1 functions in response to double-stranded DNA breaks and regulates p53-mediated apoptosis, specifically by phosphorylating human p53 at Ser 46, an event that leads to cell death. Additionally, TP53INP1 is thought to interact with p73 and may be involved in the regulation of p73-controlled cell cycle progression. TP53INP1 expression is downregulated in pancreatic ductal adenocarcinomas, suggesting that, via its ability to induce cell death, TP53INP1 plays a role in tumor suppression.