Okadaic acid stimulates osteopontin expression through de novo induction of AP-1

Osteopontin, a major non-collagenous bone matrix protein, is strikingly upregulated in various tissues under certain pathologic conditions, including cancer. However, the mechanism of upregulation of the osteopontin gene in tumor cells remains unclear. Okadaic acid, a strong non-phorbol ester tumor promoter, is known to stimulate the expression of osteopontin. The aim of the present study was to understand the mechanism by which okadaic acid regulates osteopontin gene expression. Okadaic acid stimulated osteopontin mRNA expression in several cell lines within 3 h, and the increase in osteopontin mRNA was sustained for 24 h. New protein synthesis was required for the okadaic acid-elicited increase in osteopontin mRNA expression. A serial promoter deletion study showed that the okadaic acid-response element is located between positions -265 and -73, a sequence that includes the Runx2, Ets-1, and AP-1 binding sequences. Okadaic acid increased the mRNA expression of AP-1 components but not of Runx2 or Ets-1. Site-directed mutagenesis and electrophoretic mobility shift assays confirmed that protein binding of the AP-1 consensus sequence is necessary for the okadaic acid-mediated osteopontin gene upregulation. These results indicate that de novo induction of the oncoprotein AP-1 is required for okadaic acid-stimulated osteopontin gene upregulation.     

佛波酯诱导内皮素和FOS／JUN基因在血管内皮细胞中的表达及AP－1结合活性

佛波酯诱导内皮素和ＦＯＳ／ＪＵＮ基因在血管内皮细胞中的表达及ＡＰ－１结合活性温进坤,魏素珍（河北医学院生化教研室,石家庄０５００１７）张晨晖,姚阿卿,周爱儒,汤健（北京医科大学心血管基础研究所,北京,１０００８３）关键词内皮素基因表达;ＡＰ－１转录因...     

Identification of phorbol ester response elements in the promoter of Epstein-Barr virus putative lytic switch gene BZLF1

The product of the Epstein-Barr virus BZLF1 gene encodes a protein which is related to c-fos, it has been shown to bind specifically to a consensus AP-1 site, and its expression in latently Epstein-Barr virus-infected lymphocytes is sufficient to trigger the viral lytic cycle. We identified several elements within the BZLF1 promoter (Zp) which are responsive to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), an inducer of the viral lytic cycle. These elements fall into two classes based on the factors which bind to these sequences and their resulting functional behavior. Four of the elements are homologous (ZI elements) and share homology to a protein-binding domain in the promoter region of the coordinately expressed BRLF1 gene. When cloned upstream of heterologous promoters, the ZI elements function as silencers which exhibit TPA-inducible enhancer activity. A distinct TPA-responsive element (ZII) is located near the TATA box and shares homology with the AP-1-binding site in the c-jun promoter. A synthetic oligonucleotide with a sequence corresponding to the ZII element effectively competes for binding of nuclear factors to the c-jun AP-1 site. Furthermore, we found that a complex of c-jun and c-fos bound to the ZII domain.     

FOS／JUN介导佛波酯对内皮素基因表达的诱导作用

利用凝胶电泳迁移率改变实验、RNA印迹和蛋白质印迹分析分别检查了c-jun抗体对内皮素-1(ET-1)基因AP-1位点与核蛋白结合的影响及肿瘤促进剂佛波酯(TPA)对c-fos/c-jun基因表达的作用.结果发现,c-jun抗体可使AP-1位点-核蛋白复合物的电泳迁移率发生改变,TPA显著促进c-fos/c-jun基因表达和血管内皮细胞的AP-1结合活性.实验表明,TPA对ET-1基因表达的诱导作用是通过促进AP-1转录因子c-fos/c-jun合成来介导的.