Transcriptional Regulation of bcl-2 Mediated by the Sonic Hedgehog Signaling Pathway through gli-1

• Published in: The Journal of biological chemistry Vol. 279; no. 2; pp. 1197 - 1205
• Main Authors: Bigelow, Rebecca L.H., Chari, Nikhil S., Undén, Anne Birgitte, Spurgers, Kevin B., Lee, Sangjun, Roop, Dennis R., Toftgård, Rune, McDonnell, Timothy J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 09.01.2004; American Society for Biochemistry and Molecular Biology
• Subjects: 3T3 Cells; Animals; Basal cell carcinoma; bcl-2 gene; Binding Sites; Blotting, Western; Cells, Cultured; Coculture Techniques; DNA, Complementary - metabolism; Dose-Response Relationship, Drug; Exons; gli-1 gene; gli-3 gene; Hedgehog Proteins; Humans; Immunoblotting; Immunohistochemistry; Keratinocytes - metabolism; Kruppel-Like Transcription Factors; Luciferases - metabolism; Male; Medicin och hälsovetenskap; Mice; Mice, Transgenic; Mifepristone - pharmacology; Models, Genetic; Promoter Regions, Genetic; Protein Structure, Tertiary; Proto-Oncogene Proteins c-bcl-2 - biosynthesis; Proto-Oncogene Proteins c-bcl-2 - genetics; Signal Transduction; Sonic hedgehog protein; Trans-Activators - metabolism; Transcription Factors - metabolism; Transcription, Genetic; Transcriptional Activation; Transfection; Transgenes; Up-Regulation; Zinc Finger Protein GLI1
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M310589200

Basal cell carcinomas (BCCs) express high levels of the antiapoptotic proto-oncogene, bcl-2, and we have shown that bcl-2 contributes to the malignant phenotype in a transgenic mouse model. The basis of bcl-2 transcriptional regulation in keratinocytes is unknown. The sonic hedgehog (SHH) signaling pathway is frequently altered in BCCs. Mediators of shh signaling include the downstream transactivator, gli-1, and transrepressor, gli-3. Seven candidate gli binding sites were identified in the bcl-2 promoter. Cotransfection of increasing amounts of gli-1 in keratinoycytes resulted in a corresponding dose-dependent increase in bcl-2 promoter luciferase activity. Gli-1 was also able to up-regulate endogenous bcl-2. Gli-3 cotransfection resulted in no significant changes in bcl-2 promoter activity compared with control. Gli-3 has been demonstrated to be proteolytically processed into an N-terminal repressive form that can inhibit downstream transactivation by gli-1. Gli-3 mutants possessing only the N-terminal region or the C-terminal region were made and used in luciferase assays. The N terminus of gli-3 inhibited gli-1 transactivation of the bcl-2 promoter. Gel shift analysis and luciferase assays demonstrated that gli binding site 4 (-428 to -420), is important for gli transcriptional regulation. Skin samples from transgenic mice expressing an RU486 gli-1 transgene exhibited significantly higher levels of endogenous bcl-2 protein in epidermal keratinocytes as assessed by immunoblotting and immunohistochemistry. Together, these findings provide consistent evidence that gli proteins can transcriptionally regulate the bcl-2 promoter and that gli-3 can inhibit transactivation by gli-1. These studies further suggest that one consequence of the deregulation of shh signaling in BCC is the up-regulation of bcl-2.