Scrable, Heidi

Abstract A p53-dependent mouse spindle checkpoint has been reported since 1995. However the underlying mechanism is still unknown. Here, we found that p53 formed complexes with CHAMP and MAD2L2. Immunofluorescence analysis revealed that p53, CHAMP and MAD2L2 colocalized at spindle fibres from pro-metaphase to anaphase. CHAMP binds MAD2L2 and antagonizes its inhibition function on APC/C. We discovered that p53 enhanced the inhibition of MAD2L2 by CHAMP. P53 knock-down decreased M-phase index. Exogenous expression of p53 increased M-phase index and extended remarkable length of time in M phase. Notably, the regulation of p53 on M phase index was completely abrogated by either CHAMP or MAD2l2 knock-down, suggesting that the regulation of p53 on spindle assembly checkpoint pathway is dependent on CHAMP and MAD2L2. These results demonstrate that p53 participates in a mitotic checkpoint that ensures the maintenance of genetic fidelity during development. Citation Format: Piyan Zhang, Erica Ungewitter, Ettore Appella, Heidi Scrable. Tumor suppressor p53 is involved in a CHAMP-dependent spindle assembly checkpoint pathway. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-121. doi:10.1158/1538-7445.AM2013-LB-121

Abstract Δ40p53, an N-terminally truncated p53 isoform, is predominantly expressed in embryonic stem cells (ESCs) and during early post-implantation embryogenesis in the mouse. We have discovered that Δ40p53 controls the switch from pluripotency to differentiation by regulating IGF signaling in ESCs. Our studies revealed this isoform of p53 inhibits retinoic acid-induced differentiation and subsequent epithelial-mesenchymal transition (EMT). As ESCs differentiate, Δ40p53 cannot activate the expression of some important developmental genes, such as p21, FGF10, DKK1, lamin A and ZO-1, coincident with decreasing Erk signaling and an enhanced Wnt/β-catenin pathway. ChIP assays suggested that p21, FGF10 and ZO-1 are inhibited at the elongation step. To distinguish between the transcription regulation functions of full-length p53 and Δ40p53, we generated stable HeLa cell lines transfected with Flag-tagged p53 and Δ40p53. qPCR and ChIP assays confirmed that Δ40p53, but not full-length p53, represses gene elongation, with a concomitant decrease in acetylation of histone H4 and H3 in the promoter region. Our studies reveal that Δ40p53, but not p53, is able to block ESC differentiation by regulation of specific gene expression at the elongation step during mouse development. Citation Format: Piyan Zhang, Heidi Scrable. Developmental checkpoint function of Δ40p53. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5439. doi:10.1158/1538-7445.AM2013-5439

Summaryp44 is a short isoform of p53 with ‘longevity‐assurance’ activity. Overexpression of p44 in the mouse (p44+/+ transgenic mice) causes a progeroid phenotype that mimics an accelerated form of aging. The phenotype includes abnormal phosphorylation of the microtubule‐binding protein tau, synaptic deficits, and cognitive decline. Genetic engineering demonstrated that the phosphorylation status of tau acts upstream of the synaptic deficits. Here, we provide evidence that p44 promotes the phosphorylation of tau in the mouse. Specifically, we show that p44 binds to the promoter of tau kinases Dyrk1A, GSK3β, Cdk5, p35, and p39 and activates their transcription. The upregulation of the above kinases is followed by increased phosphorylation of tau. Finally, we show that p44 is preferentially found in the nucleus and that its levels increase with age in the mouse brain. Taken together, these results suggest that an imbalance in the p53:p44 ratio might be involved with the altered tau metabolism that characterizes aging.

SummaryOxidative stress is a determining factor of cellular senescence and aging and a potent inducer of the tumour‐suppressor p53. Resistance to oxidative stress correlates with delayed aging in mammals, in the absence of accelerated tumorigenesis, suggesting inactivation of selected p53‐downstream pathways. We investigated p53 regulation in mice carrying deletion of p66, a mutation that retards aging and confers cellular resistance and systemic resistance to oxidative stress. We identified a transcriptional network of ~200 genes that are repressed by p53 and encode for determinants of progression through mitosis or suppression of senescence. They are selectively down‐regulated in cultured fibroblasts after oxidative stress, and, in vivo, in proliferating tissues and during physiological aging. Selectivity is imposed by p66 expression and activation of p44/p53 (also named Delta40p53), a p53 isoform that accelerates aging and prevents mitosis after protein damage. p66 deletion retards aging and increases longevity of p44/p53 transgenic mice. Thus, oxidative stress activates a specific p53 transcriptional response, mediated by p44/p53 and p66, which regulates cellular senescence and aging.

Fasting simultaneously enhances normal cell function and potentiates the effects of conventional chemotherapeutic agents on tumor growth, metastasis, and long-term survival.

OBJECTIVE Investigating the dynamics of pancreatic β-cell mass is critical for developing strategies to treat both type 1 and type 2 diabetes. p53, a key regulator of the cell cycle and apoptosis, has mostly been a focus of investigation as a tumor suppressor. Although p53 alternative transcripts can modulate p53 activity, their functions are not fully understood. We hypothesized that β-cell proliferation and glucose homeostasis were controlled by Δ40p53, a p53 isoform lacking the transactivation domain of the full-length protein that modulates total p53 activity and regulates organ size and life span in mice. RESEARCH DESIGN AND METHODS We phenotyped metabolic parameters in Δ40p53 transgenic (p44tg) mice and used quantitative RT-PCR, Western blotting, and immunohistochemistry to examine β-cell proliferation. RESULTS Transgenic mice with an ectopic p53 gene encoding Δ40p53 developed hypoinsulinemia and glucose intolerance by 3 months of age, which worsened in older mice and led to overt diabetes and premature death from ∼14 months of age. Consistent with a dramatic decrease in β-cell mass and reduced β-cell proliferation, lower expression of cyclin D2 and pancreatic duodenal homeobox-1, two key regulators of proliferation, was observed, whereas expression of the cell cycle inhibitor p21, a p53 target gene, was increased. CONCLUSIONS These data indicate a significant and novel role for Δ40p53 in β-cell proliferation with implications for the development of age-dependent diabetes.