Mechanism of diepoxybutane‐induced p53 regulation in human cells

Diepoxybutane (DEB) is the most potent active metabolite of the environmental chemical 1,3‐butadiene (BD). BD is a known mutagen and human carcinogen and possesses multisystems organ toxicity. We previously reported the elevation of p53 in human TK6 lymphoblasts undergoing DEB‐induced apoptosis. In this study, we have characterized the DEB‐induced p53 accumulation and investigated the mechanisms by which DEB regulates this p53 accumulation. The elevation of p53 levels in DEB‐exposed TK6 lymphoblasts and human embryonic lung (HEL) human fibroblasts was found to be largely due to the stabilization of the p53 protein. DEB increased the acetylation of p53 at lys‐382, dramatically reduced complex formation between p53 and its regulator protein mdm2 and induced the phosphorylation of p53 at serines 15, 20, 37, 46, and 392 in human lymphoblasts. A dramatic increase in phosphorylation of p53 at serine 15 in correlation to total p53 levels was observed in DEB‐exposed Ataxia Telangiectasia Mutated (ATM) proficient human lymphoblasts as compared to DEB‐exposed ATM‐deficient human lymphoblasts; this implicates the ATM kinase in the elevation of p53 levels in DEB‐exposed cells. Collectively, these findings explain for the first time the mechanism by which p53 accumulates in DEB‐exposed cells and contributes to the understanding of the molecular toxicity of DEB and BD. © 2009 Wiley Periodicals, Inc. J Biochem Mol Toxicol 23:373–386, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jbt.20300     

p53过表达抑制同源盒基因NKX3.1启动子活性

NKX3.1是前列腺特异表达的同源盒基因,在前列腺癌的发生发展中起重要作用,而在前列腺癌进展中常会发生p53的基因突变.为研究两者之间的关系,构建NKX-3.1启动子(1 040bp)-荧光素酶报告基因重组质粒（pGL3-1040）及其缺失突变体,瞬时转染前列腺癌细胞LNCaP.通过荧光素酶表达活性分析,检测p53过表达对NKX3.1启动子活性的影响.结果表明：p53在LNCaP细胞中过表达可明显抑制NKX3.1启动子活性;RT-PCR及Western印迹检测p53过表达对NKX3.1表达的影响.结果表明,p53过表达可以明显抑制同源盒基因NKX3.1的表达.通过TRANSFAC软件分析,在NKX3.1基因上游-526至-507区存在一个p53反应元件的5′核心序列.缺失pGL3-1040中的p53反应元件核心序列并不能消除p53对NKX3.1启动子的抑制作用,表明p53不是通过p53反应元件直接抑制NKX3.1启动子活性.进一步通过5′缺失突变分析,发现NKX3.1启动子-140～+8 bp区仍受p53负调控.此148 bp区域中含有一个Sp1和一个CREB元件,瞬时共转染Sp1表达载体或CREB表达载体的结果表明,p53并不是通过与Sp1或CREB相互作用对NKX3.1启动子发挥抑制作用的.上述结果表明,p53过表达可以抑制同源盒基因NKX3.1启动子活性,下调NKX3.1基因的转录,其调控机制有待进一步研究.     

Spodoptera frugiperda FKBP‐46 is a consensus p53 motif binding protein

p53 protein, the central molecule of the apoptosis pathway, is mutated in 50% of the human cancers. Of late, p53 homologues have been identified from different invertebrates including Drosophila melanogaster, Caenorhabditis elegans, Squid, and Clams. We report the identification of a p53‐like protein in Spodoptera frugiperda (Sf9) insect cells, which is activated during oxidative stress, caused by exposure to UV‐B or H₂O₂, and binds to p53 consensus DNA binding motifs as well as other p53 cognate motifs. Sf9 p53 motif‐binding protein is similar to murine and Drosophila p53 in terms of molecular size, which is around 50–60 kDa, as evident from UV cross‐linking, and displays DNA binding characteristics similar to both insect and vertebrate p53 as seen from electrophoretic mobility shift assays. The N‐terminal sequencing of the purified Sf9 p53 motif‐binding protein reveals extensive homology to the pro‐apoptotic FK‐506 binding protein (FKBP‐46), earlier identified in Sf9 cells as a factor which interacts with murine casein kinase. FKBP, an evolutionarily conserved protein of mammalian origin functions as a pro‐apoptotic factor. Identification of FKBP‐46 as a novel p53 motif‐binding protein in insect cells adds a new facet to our understanding of the mechanisms of apoptosis under oxidative stress in the absence of a typical p53 homologue. J. Cell. Biochem. 114: 899–907, 2013. © 2012 Wiley Periodicals, Inc.     

Mechanisms of ceramide‐induced COX‐2‐dependent apoptosis in human ovarian cancer OVCAR‐3 cells partially overlapped with resveratrol

Ceramide is a member of the sphingolipid family of bioactive molecules demonstrated to have profound, diverse biological activities. Ceramide is a potential chemotherapeutic agent via the induction of apoptosis. Exposure to ceramide activates extracellular‐signal‐regulated kinases (ERK)1/2‐ and p38 kinase‐dependent apoptosis in human ovarian cancer OVCAR‐3 cells, concomitant with an increase in the expression of COX‐2 and p53 phosphorylation. Blockade of cyclooxygenase‐2 (COX‐2) activity by siRNA or NS398 correspondingly inhibited ceramide‐induced p53 Ser‐15 phosphorylation and apoptosis; thus COX‐2 appears at the apex of the p38 kinase‐mediated signaling cascade induced by ceramide. Induction of apoptosis by ceramide or resveratrol was inhibited by the endocytosis inhibitor, cytochalasin D (CytD); however, cells exposed to resveratrol showed greater sensitivity than ceramide‐treated cells. Ceramide‐treated cells underwent a dose‐dependent reduction in trans‐membrane potential. Although both ceramide and resveratrol induced the expressions of caspase‐3 and ‐7, the effect of inducible COX‐2 was different in caspase‐7 expression induced by ceramide compared to resveratrol. In summary, resveratrol and ceramide converge on an endocytosis‐requiring, ERK1/2‐dependent signal transduction pathway and induction of COX‐expression as an essential molecular antecedent for subsequent p53‐dependent apoptosis. In addition, expressions of caspase‐3 and ‐7 are observed. However, a p38 kinase‐dependent signal transduction pathway and change in mitochondrial potential are also involved in ceramide‐induced apoptosis. J. Cell. Biochem. 114: 1940–1954, 2013. © 2013 Wiley Periodicals, Inc.