Expression and roles of claudin-3 and claudin-4 in ovarian cancer

Claudin-3和-4在包括卵巢癌在内的几种恶性肿瘤中经常过表达。有趣的是，我们还发现这些基因倾向于在正常和恶性组织中协调表达，这表明了一种共同的调节机制。为了更好地理解转录调控的机制，我们系统地研究了这些基因的启动子。我们发现CLDN3和CLDN4都需要SP1位点才能完全激活（CLDN4中有两个关键的SP1位点，CLDN3中有一个）。此外，我们发现这两个启动子都是通过表观遗传过程调节的。表达高水平CLDN3和/或CLDN4的细胞具有低DNA甲基化和相应启动子的高组蛋白乙酰化。有趣的是，在CLDN3的情况下，启动子的甲基化阻止SP1结合，这为非表达细胞中的CLDN3沉默提供了一种机制。由于CLDN3和CLDN4在大部分卵巢癌中均升高，导致其失调的机制可能代表了卵巢肿瘤发生的一般途径。

Claudin-3 and -4 are frequently overexpressed in several malignancies, including ovarian cancer. Interestingly, we also found that these genes tended to be coordinately expressed in both normal and malignant tissues, suggesting a common mechanism of regulation. In order to better understand the mechanisms of transcriptional regulation, we systematically studied the promoters of these genes. We have found that both CLDN3 and CLDN4 require SP1 sites for full activation (there are two crucial SP1 sites in CLDN4 and one in CLDN3). In addition, we have found that both promoters are regulated through epigenetic processes. Cells that express high levels of CLDN3 and/or CLDN4 have low DNA methylation and high histone acetylation of the corresponding promoter(s). Interestingly, in the case of CLDN3, methylation of the promoter prevented SP1 binding, providing a mechanism for CLDN3 silencing in non-expressing cells. Because both CLDN3 and CLDN4 are elevated in a large fraction of ovarian cancer, the mechanisms leading to their deregulation may represent a general pathway in ovarian tumorigenesis. In an attempt to characterize the roles on claudin-3 and -4 in ovarian cancer, we have used Illumina oligonucleotide arrays. We have identified genes that are altered by expression of claudins and observed several genes known to be involved in angiogenesis such as IL-8, MMP1, and several chemokines. Functional assays have confirmed that cells expressing claudin-3 and claudin-4 induce angiogenesis of co-cultivated cells in vitro. These findings have been validated in an in vivo mouse dorsal skinfold assay. We are planning to extend these findings by inhibiting putative downstream targets such as IL-8 and other chemokines to verify their roles in ovarian angiogenesis.