Loss of AP-2 results in downregulation of c-KIT and enhancement of melanoma tumorigenicity and metastasis.
Expression of the tyrosine kinase receptor, c-KIT, progressively decreases during local tumor growth and invasion of human melanomas. We have previously shown that enforced c-KIT expression in highly metastatic cells inhibited tumor growth and metastasis in nude mice. Furthermore, the ligand for c-KIT, SCF, induces apoptosis in human melanoma cells expressing c-KIT under both in vitro and in vivo conditions. Here we show that loss of c-KIT expression in highly metastatic cells correlates with loss of expression of the transcription factor AP-2. The c-KIT promoter contains three binding sites for AP-2 and EMSA gels demonstrated that AP-2 protein binds directly to the c-KIT promoter. Transfection of wild-type AP-2 into c-KIT-negative A375SM melanoma cells activated a c-KIT promoter-driven luciferase reporter gene, while expression of a dominant-negative AP-2B in c-KIT-positive Mel-501 cells inhibited its activation. Endogenous c-KIT mRNA and expression of proteins were upregulated in AP-2-transfected cells, but not in control cells. In addition, re-expression of AP-2 in A375SM cells suppressed their tumorigenicity and metastatic potential in nude mice. These results indicate that the expression of c-KIT is highly regulated by AP-2 and that enforced AP-2 expression suppresses tumorigenicity and metastatic potential of human melanoma cells, possibly through c-KIT transactivation and SCF-induced apoptosis. Therefore, loss of AP-2 expression might be a crucial event in the development of malignant melanoma.
Department of Cell Biology, The University of Texas, M.D. Anderson Cancer Center, Houston 77030. USA.
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Huang
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Jean
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Luca
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Tainsky
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Bar-Eli
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D015536:Down-Regulation / Q000235:genetics / Q000502:physiology*; D005786:Gene Expression Regulation; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics / Q000556:secondary; D008297:Male; D008545:Melanoma / Q000209:etiology* / Q000235:genetics / Q000556:secondary*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D011401:Promoter Regions, Genetic; D019009:Proto-Oncogene Proteins c-kit / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics; D019089:Stem Cell Factor / Q000494:pharmacology; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D015533:Transcriptional Activation; D014162:Transfection / Q000235:genetics; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000235:genetics
D004268:DNA-Binding Proteins; D012097:Repressor Proteins; D019089:Stem Cell Factor; D050656:Transcription Factor AP-2; D014157:Transcription Factors; D019009:Proto-Oncogene Proteins c-kit