A critical player in each of these processes is the p53 tumor MLN0128 concentration suppressor, which provides surveillance against cellular insults of many types and may induce G1 arrest and cellular senescence in response to tetraploidy or missegregated chromosomes.9, 10 p53 and its close relative, p73, are also linked to the mitotic spindle assembly checkpoint, as both proteins interact with kinetochore and spindle checkpoint proteins.7, 11, 12 In fact, combined loss

of p53 and p73 leads to increased polyploidy and aneuploidy in primary cultured cells9 and results in a higher incidence of tumor development in mouse liver.13 The striking tolerance of the liver for altered ploidy leads to consideration of whether a tetraploid checkpoint exists in hepatocytes. We addressed this question by analysis of checkpoint mediator p53, and characterized the synchronized

process of cellular proliferation and growth that AZD2014 occurs to regenerate the liver in response to PH in both WT and p53-null mice. Our results reveal that p53 alters levels of hepatocyte ploidy during liver regeneration and aging. Although chromosome segregation errors are common in WT hepatocytes expressing p53, these errors (e.g., abnormal mitotic figures and lagging chromosomes) are even more frequent in hepatocytes deficient for p53. Since p53′s effects may be mediated by context-specific, mitotic regulators,14 we examined whether p53 regulated expression of mediators of hepatic cell division in normal and regenerating liver. We identified Aurora kinase A (Aurka), Forkhead-box transcription factor Foxm1, regulator of cytokinesis Lats2, and Polo-like kinases (Plk2 and Plk4) as directly regulated by p53 in quiescent liver, a mitotic transcription program that is altered during liver regeneration. Thus, our findings suggest that p53 plays a role in controlling

levels of hepatic polyploidy/aneuploidy by direct transcription regulation of multiple downstream effectors. ChIP, chromatin immunoprecipitation; p53RE, p53 response element; PCR, polymerase else chain reaction; PH, partial hepatectomy; WT, wild-type. PH to remove 70% of total liver tissue, or Sham surgery was performed using isoflurane anesthesia, as described.15 5-7 C57Bl6/Sv129 F1 mice, WT or p53−/−, 2 months of age, were used for each experimental condition according to The University of Texas MD Anderson Cancer Center Institutional Animal Care and Use Committee guidelines. p53 knockout mice were sacrificed 0.5, 1, 1.5, 2, 3, 3.5, 4, or 7 days following PH and sham surgery; remnant liver tissue was harvested, flash-frozen, and processed for RNA, immunoblot, and chromatin immunoprecipitation (ChIP) analyses. Liver/body weight ratios were calculated to determine the recovery of liver mass. ChIP analyses were performed as described.