SKI activates Wnt/beta-catenin signaling in human melanoma.
Overexpression of the oncoprotein SKI correlates with the progression of human melanoma in vivo. SKI is known to curtail the growth inhibitory activity of tumor growth factor beta through the formation of repressive transcriptional complexes with Smad2 and Smad3 at the p21(Waf-1) promoter. Here, we show that SKI also stimulates growth by activating the Wnt signaling pathway. From a yeast two-hybrid screen and immunoprecipitation studies, we identified the protein FHL2/DRAL as a novel SKI binding partner. FHL2, a LIM-only protein, binds beta-catenin and can function as either a transcriptional repressor or activator of the Wnt signaling pathway. SKI enhanced the activation of FHL2 and/or beta-catenin- regulated gene promoters in melanoma cells. Among the SKI targets were microphthalmia-associated transcription factor and Nr-CAM, two proteins associated with melanoma cell survival, growth, motility, and transformation. Transient overexpression of SKI and FHL2 in ski(-/-) melanocytes synergistically enhanced cell growth, and stable overexpression of SKI in a poorly clonogenic human melanoma cell line was sufficient to stimulate rapid proliferation, decreasing the number of cells in the G(1) phase of the cell cycle, and dramatically increasing clonogenicity, colony size and motility. Taken together, these results suggest that by targeting members of the tumor growth factor beta and beta-catenin pathways, SKI regulates crucial events required for melanoma growth, survival, and invasion.
Chen
Dahu
D
Huffington Center on Aging and Departments of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
Xu
Weidong
W
Bales
Elise
E
Colmenares
Clemencia
C
Conacci-Sorrell
Maralice
M
Ishii
Shunsuke
S
Stavnezer
Ed
E
Campisi
Judith
J
Fisher
David E
DE
Ben-Ze'ev
Avri
A
Medrano
Estela E
EE
D000818:Animals; D016466:CHO Cells; D015815:Cell Adhesion Molecules / Q000096:biosynthesis / Q000235:genetics; D002455:Cell Division / Q000502:physiology; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000502:physiology; D006224:Cricetinae; D003598:Cytoskeletal Proteins / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic; D006367:HeLa Cells; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D060850:LIM-Homeodomain Proteins; D008545:Melanoma / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D051739:Microphthalmia-Associated Transcription Factor; D009124:Muscle Proteins; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D015534:Trans-Activators / Q000502:physiology*; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin
C495270:CTNNB1 protein, human; C495267:CTNNB1 protein, mouse; D015815:Cell Adhesion Molecules; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; C105987:FHL2 protein, human; C491382:Fhl2 protein, mouse; D018398:Homeodomain Proteins; D060850:LIM-Homeodomain Proteins; C497234:MITF protein, human; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; D009124:Muscle Proteins; C491152:NRCAM protein, human; C491151:Nrcam protein, mouse; D011518:Proto-Oncogene Proteins; C512653:Ski protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin; C060614:SKI protein, human