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ABSTRACT: TNFα is a pleiotropic cytokine that signals for both survival and apoptotic cell fates. It is still unclear that the dual role of TNFα can be regulated in cancer cells. We previously described an apoptotic pathway involving p53→CDIP→TNFα that was activated in response to genotoxic stress. This pathway operated in the presence of JNK activation; therefore, we postulated that CDIP itself could sensitize cells to a TNFα apoptotic cell fate, survival, or death. We show that CDIP mediates sensitivity to TNFα-induced apoptosis and that cancer cells with endogenous CDIP expression are inherently sensitive to the growth-suppressive effects of TNFα in vitro and in vivo. Thus, CDIP expression correlates with sensitivity of cancer cells with TNFα, and CDIP seems to be a regulator of the p53-mediated death versus survival response of cells to TNFα. This CDIP-mediated sensitivity to TNFα-induced apoptosis favors pro- over antiapoptotic program in cancer cells, and CDIP may serve as a predictive biomarker for such sensitivity.
Cancer Research 05/2012; 72(9):2373-82. · 7.86 Impact Factor
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ABSTRACT: The p53 protein is activated by stress signals and exhibits both protective and death-promoting functions that are considered important for its tumor suppressor function. Emerging evidence points toward an additional role for p53 in metabolism. Here, we identify Lpin1 as a p53-responsive gene that is induced in response to DNA damage and glucose deprivation. Lpin1 is essential for adipocyte development and fat metabolism, and mutation in this gene is responsible for the lypodystrophy phenotype in fld mice. We show that p53 and Lpin1 regulate fatty acid oxidation in mouse C2C12 myoblasts. p53 phosphorylation on Ser18 in response to low glucose is ROS and ATM dependent. Lpin1 expression in response to nutritional stress is controlled through the ROS-ATM-p53 pathway and is conserved in human cells. Lpin1 provides a critical link between p53 and metabolism that may be an important component in mediating the tumor suppressor function of p53.
Molecular cell 11/2011; 44(3):491-501. · 14.61 Impact Factor
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ABSTRACT: The p53 tumor suppressor protein has a well-established role in cell-fate decision-making processes. However, recent discoveries indicate that p53 has a non-tumor-suppressive role. Here we identify guanidinoacetate methyltransferase (GAMT), an enzyme involved in creatine synthesis, as a p53 target gene and a key downstream effector of adaptive response to nutrient stress. We show that GAMT is not only involved in p53-dependent apoptosis in response to genotoxic stress but is important for apoptosis induced by glucose deprivation. Additionally, p53-->GAMT upregulates fatty acid oxidation (FAO) induced by glucose starvation, utilizing this pathway as an alternate ATP-generating energy source. These results highlight that p53-dependent regulation of GAMT allows cells to maintain energy levels sufficient to undergo apoptosis or survival under conditions of nutrient stress. The p53-->GAMT pathway represents a new link between cellular stress responses and processes of creatine synthesis and FAO, demonstrating a further role of p53 in cellular metabolism.
Molecular cell 11/2009; 36(3):379-92. · 14.61 Impact Factor
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ABSTRACT: The small heat shock protein alphaB-crystallin is a molecular chaperone that is induced by stress and protects cells by inhibiting protein aggregation and apoptosis. To identify novel transcriptional regulators of the alphaB-crystallin gene, we examined the alphaB-crystallin promoter for conserved transcription factor DNA-binding elements and identified a putative response element for the p53 tumor suppressor protein. Ectopic expression of wild-type p53 induced alphaB-crystallin mRNA and protein with delayed kinetics compared to p21. Additionally, the induction of alphaB-crystallin by genotoxic stress was inhibited by siRNAs targeting p53. Although the p53-dependent transactivation of an alphaB-crystallin promoter luciferase reporter required the putative p53RE, chromatin immunoprecipitation failed to detect p53 binding to the alphaB-crystallin promoter. These results suggested an indirect mechanism of transactivation involving p53 family members p63 or p73. DeltaNp73 was dramatically induced by p53 in a TAp73-dependent manner, and silencing p73 suppressed the transcriptional activation of alphaB-crystallin by p53. Moreover, ectopic expression of DeltaNp73alpha (but not other p73 isoforms) increased alphaB-crystallin mRNA levels in the absence of p53. Collectively, our results link the molecular chaperone alphaB-crystallin to the cellular genotoxic stress response via a novel mechanism of transcriptional regulation by p53 and p73.
Breast Cancer Research and Treatment 09/2009; 122(1):159-68. · 4.43 Impact Factor
