Transcriptional regulation of bcl-2 mediated by the sonic hedgehog signaling pathway through gli-1.
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.
Bigelow
Rebecca L H
RL
Department of Molecular Pathology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
Chari
Nikhil S
NS
Unden
Anne Birgitte
AB
Spurgers
Kevin B
KB
Lee
Sangjun
S
Roop
Dennis R
DR
Toftgard
Rune
R
McDonnell
Timothy J
TJ
D016475:3T3 Cells; D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D002478:Cells, Cultured; D018920:Coculture Techniques; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005091:Exons; D053823:Hedgehog Proteins; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D015603:Keratinocytes / Q000378:metabolism; D051741:Kruppel-Like Transcription Factors; D008156:Luciferases / Q000378:metabolism; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D015735:Mifepristone / Q000494:pharmacology; D008957:Models, Genetic; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D000090063:Proto-Oncogene Mas; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis* / Q000235:genetics*; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D019076:Transgenes; D015854:Up-Regulation; D000071676:Zinc Finger Protein GLI1
D018076:DNA, Complementary; C400551:GLI1 protein, human; C498520:Gli1 protein, mouse; D053823:Hedgehog Proteins; D051741:Kruppel-Like Transcription Factors; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D019253:Proto-Oncogene Proteins c-bcl-2; C509239:SHH protein, human; D015534:Trans-Activators; D014157:Transcription Factors; D000071676:Zinc Finger Protein GLI1; D015735:Mifepristone; D008156:Luciferases