g., cancer, cell death, and cell proliferation). Other TA-p73–bound genes, associated with inflammatory response and development, are supported by the phenotype of p73−/− mice, which display severe developmental and inflammatory defects and die soon after birth.18 Our work identifies the Foxo3 gene as a new target Talazoparib datasheet of p53 and TA-p73 in the quiescent mouse liver. Loss of FoxO3-mediated regulation of transcription is directly linked to increased proliferation and tumorigenesis in human cancers8, 37; however, mechanisms that control Foxo3 itself

remain poorly defined. We suggest that p53, p73, and FoxO3 function along the same axis in a tumor suppressor network because many target genes of FoxO3 are also known p53/p73 targets [e.g., Cdkn1a (p21), Cdkn1b (p27), and growth arrest and DNA-damage-inducible alpha]. In turn, functions of FoxO3 as a transcription factor augment p53 proapoptotic activity.38 Previous studies have suggested that p53 and FOXO3 proteins interact as a protein complex.39

Whether feed-forward regulation of antiproliferative genes by a p53-FoxO3 complex in the quiescent liver is disrupted during regeneration because of decreased levels of FoxO3 protein and a loss of p53–target gene interactions requires further study. Overall, our results establish a direct, linear pathway between p53 family members and FoxO tumor suppressors in normal tissues. Despite selleck chemicals llc many studies of p53/p73 target genes, mechanisms of endogenous p53 and TA-p73–mediated transcriptional regulation are understood for a very limited number of target genes in vivo. In

quiescent liver cells, we found p53-dependent recruitment of histone acetyltransferase p300 at the Foxo3 p53RE to be a mechanism of histone modification and gene activation in vivo, and this was in agreement with the direct interaction of p53/p73 with p300 observed in cultured cells.33, 34 Binding of p300 at the Foxo3 p53RE is decreased but not lost in the livers of p53−/− mice, and this suggests that endogenous p73, independently of p53, relies on similar coregulators of transcription and partially compensates for a loss of p53. Recruitment medchemexpress of p300 and activation of Foxo3 expression significantly decrease during day 1 of liver regeneration when both p53 and p73 show a loss of binding to the Foxo3 p53RE; this provides additional evidence for p53/p73-mediated recruitment of p300 as a critical mechanism to activate expression of the Foxo3 gene in the quiescent liver. Thus, we conclude that both p53 and TA-p73 lose the ability to bind and regulate expression of specific hepatic genes during the G0-G1-S transition. Importantly, p53/p73 binding to the Foxo3 p53RE is restored when liver regeneration is complete, and this leads to activation of Foxo3 expression as hepatocytes reenter G0. Similarly, p53 binding to Afp is restored 7 days after PH,5 but transcriptional activity of p53 is not required for termination of liver regeneration.