Agren Marie, Kogerman Priit, Kleman Marika I, Wessling Martina, Toftgård Rune
Department of Bioscience at NOVUM, Center for Nutrition and Toxicology, Karolinska Institute, Huddinge 141 57, Sweden.
Gene. 2004 Apr 14;330:101-14. doi: 10.1016/j.gene.2004.01.010.
The PTCH1 tumor suppressor gene encodes a receptor for secreted hedgehog (HH) ligands and is important for proper proliferation, differentiation and patterning in almost every tissue and organ during embryogenesis. The PTCH1 protein works as a negative regulator of the HH-signaling pathway by repressing downstream signaling by the coreceptor smoothened (SMOH). Mutations in PTCH1 lead to constitutive expression of HH target genes and a relationship between mutated PTCH1 and the most common tumor form in the Western world, Basal Cell Carcinoma (BCC) has been clearly established. We here show that PTCH1 is transcriptionally regulated by three independent promoters generating transcripts with alternative first exons. We demonstrate that only one of two putative Gli-binding sites that were identified in the promoter region of PTCH1 is functional, and that the transactivating Gli proteins, GLI1, Gli2 and GLI3, bind and enhance transcription through this site. Moreover, a strong repression of both basal and induced PTCH1 transcription was observed following expression of a truncated version of GLI3. Most interestingly, the upstream components in the HH-signaling cascade, Sonic HH (SHH) and SMOH, solely operate through the functional Gli-binding site because mutation of the Gli-binding site resulted in the disappearance of the enhanced transcription induced by the Gli proteins, as well as by SHH or SMOH. This finding suggests that transcriptional activation of the PTCH1 gene mediated via the HH-signaling pathway is dependent on the single functional Gli-binding site.
PTCH1肿瘤抑制基因编码一种分泌型刺猬蛋白（HH）配体的受体，对胚胎发育过程中几乎每个组织和器官的正常增殖、分化和模式形成都很重要。PTCH1蛋白通过抑制共受体平滑蛋白（SMOH）的下游信号传导，作为HH信号通路的负调节因子。PTCH1的突变导致HH靶基因的组成性表达，并且已明确建立了突变的PTCH1与西方世界最常见的肿瘤形式基底细胞癌（BCC）之间的关系。我们在此表明，PTCH1由三个独立的启动子转录调控，产生具有可变第一外显子的转录本。我们证明，在PTCH1启动子区域鉴定出的两个假定的Gli结合位点中只有一个具有功能，并且反式激活的Gli蛋白GLI1、Gli2和GLI3通过该位点结合并增强转录。此外，在表达截短版本的GLI3后，观察到基础和诱导的PTCH1转录均受到强烈抑制。最有趣的是，HH信号级联反应中的上游成分，声波刺猬蛋白（SHH）和SMOH，仅通过功能性Gli结合位点起作用，因为Gli结合位点的突变导致Gli蛋白以及SHH或SMOH诱导的增强转录消失。这一发现表明，通过HH信号通路介导的PTCH1基因的转录激活依赖于单个功能性Gli结合位点。
