B-RAF and PI-3 kinase signaling protect melanoma cells from anoikis.
A hallmark feature of cancer is resistance to anoikis, apoptosis induced when cells either lose contact with or encounter an inappropriate extracellular matrix. Melanoma is inherently associated with a high degree of resistance to apoptosis. Mutations in B-RAF are prevalent in melanoma and promote constitutive MEK-ERK1/2 signaling and cell transformation. Acquisition of B-RAF mutations correlates with vertical phase growth when melanoma cells invade into the dermis, a collagen-rich environment that also contains fibronectin matrix. In addition, alterations in phosphoinositide-3 kinase (PI-3 kinase) signaling that lead to activation of AKT are detected in advanced melanomas. Here we show that knockdown of B-RAF expression by siRNA or pharmacological inhibition of MEK rendered melanoma cells susceptible to anoikis. Furthermore, adhesion to fibronectin but not collagen protected melanoma cells from anoikis through a PI-3 kinase-dependent pathway. Therefore, melanoma cells require either B-RAF or PI-3 kinase activation for protection from anoikis. Notably, AKT signaling in melanoma cells is substrate specific. These findings demonstrate that melanoma cells utilize multiple signaling pathways to provide resistance to apoptosis.
Boisvert-Adamo
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Center for Cell Biology and Cancer Research, Albany Medical College, Albany, NY 12208, USA.
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D023102:Anoikis / Q000502:physiology*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D006801:Humans; D008545:Melanoma / Q000201:enzymology* / Q000473:pathology*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D048493:Proto-Oncogene Proteins B-raf / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
D019869:Phosphatidylinositol 3-Kinases; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf