Expression of the PTCH1 tumor suppressor gene is regulated by alternative promoters and a single functional Gli-binding site.
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.
Agren
Marie
M
Department of Bioscience at NOVUM, Center for Nutrition and Toxicology, Karolinska Institute, Huddinge 141 57, Sweden.
Kogerman
Priit
P
Kleman
Marika I
MI
Wessling
Martina
M
Toftgård
Rune
R
D016475:3T3 Cells; D024506:5' Flanking Region / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D024202:Electrophoretic Mobility Shift Assay; D005786:Gene Expression Regulation; D016147:Genes, Tumor Suppressor; D049452:Green Fluorescent Proteins; D053823:Hedgehog Proteins; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D000072079:Patched Receptors; D000072081:Patched-1 Receptor; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D015398:Signal Transduction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D000071676:Zinc Finger Protein GLI1
D053823:Hedgehog Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins; D008565:Membrane Proteins; D015513:Oncogene Proteins; C000606236:PTCH1 protein, human; D000072079:Patched Receptors; D000072081:Patched-1 Receptor; C000606240:Ptch1 protein, mouse; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; C509239:SHH protein, human; D015534:Trans-Activators; D014157:Transcription Factors; D000071676:Zinc Finger Protein GLI1; D049452:Green Fluorescent Proteins; D008156:Luciferases