Institute of Pathology, Molecular Pathology, University of Regensburg, Regensburg, Germany.
Lab Invest. 2012 Dec;92(12):1788-800. doi: 10.1038/labinvest.2012.140. Epub 2012 Oct 15.
T-cadherin (cadherin 13, H-cadherin, gene name CDH13) has been proposed to act as a tumor-suppressor gene as its expression is significantly diminished in several types of carcinomas, including melanomas. Allelic loss and promoter hypermethylation have been proposed as mechanisms for silencing of CDH13. However, they do not account for loss of T-cadherin expression in all carcinomas, and other genetic or epigenetic alterations can be presumed. The present study investigated transcriptional regulation of CDH13 in melanoma. Bioinformatical analysis pointed to the presence of known BRN2 (also known as POU3F2 and N-Oct-3)-binding motifs in the CDH13 promoter sequence. We found an inverse correlation between BRN2 and T-cadherin protein and transcript expression. Reporter gene analysis and electrophoretic mobility shift assays in melanoma cells demonstrated that CDH13 is a direct target of BRN2 and that BRN2 is a functional transcriptional repressor of CDH13 promoter activity. The regulatory binding element of BRN2 was located -219 bp of the CDH13 promoter proximal to the start codon and was identified as 5'-CATGCAAAA-3'. Ectopic expression of BRN2 in BRN2-negative/T-cadherin-positive melanoma cells resulted in suppression of CDH13 promoter activity, whereas BRN2 knockdown in BRN2-positive/T-cadherin-negative melanoma cells resulted in re-expression of T-cadherin transcripts and protein. Transcriptional repression of CDH13 by BRN2 may participate in malignant transformation of melanoma by increasing invasion and migration potentials of melanoma cells. The study has identified CDH13 as a novel direct BRN2 transcriptional target gene and has advanced knowledge of mechanisms underlying loss of T-cadherin expression in melanoma.
T-钙黏蛋白（钙黏蛋白 13、H-钙黏蛋白，基因名称 CDH13）被认为是一种肿瘤抑制基因，因为其在几种类型的癌中，包括黑色素瘤中的表达显著降低。等位基因缺失和启动子超甲基化被认为是 CDH13 沉默的机制。然而，它们并不能解释所有癌中 T-钙黏蛋白表达的缺失，并且可以假定存在其他遗传或表观遗传改变。本研究调查了黑色素瘤中 CDH13 的转录调控。生物信息学分析指出 CDH13 启动子序列中存在已知的 BRN2（也称为 POU3F2 和 N-Oct-3）结合基序。我们发现 BRN2 与 T-钙黏蛋白蛋白和转录本表达之间存在反比关系。黑色素瘤细胞中的报告基因分析和电泳迁移率变动分析表明，CDH13 是 BRN2 的直接靶标，BRN2 是 CDH13 启动子活性的功能性转录抑制因子。BRN2 的调节结合元件位于 CDH13 启动子的-219bp 处，靠近起始密码子，被鉴定为 5'-CATGCAAAA-3'。在 BRN2 阴性/T-钙黏蛋白阳性黑色素瘤细胞中异位表达 BRN2 导致 CDH13 启动子活性抑制，而在 BRN2 阳性/T-钙黏蛋白阴性黑色素瘤细胞中 BRN2 敲低导致 T-钙黏蛋白转录本和蛋白的重新表达。BRN2 对 CDH13 的转录抑制可能通过增加黑色素瘤细胞的侵袭和迁移潜力参与黑色素瘤的恶性转化。该研究鉴定了 CDH13 作为 BRN2 的一种新的直接转录靶基因，并提高了对黑色素瘤中 T-钙黏蛋白表达缺失机制的认识。
