Oncogenic BRAFV600E promotes anchorage-independent survival of human melanocytes

Normal cells are dependent upon integrin-mediated adhesion to the extracellular matrix for cell proliferation and survival. A trait of malignant cells is their ability to undergo anchorage-independent growth. Here, we demonstrate that the constitutively active B-RAFV600E present in a significant number of melanomas protects primary human melanocytes from anoikis, a form of apoptosis induced by lack of adhesion to an extracellular matrix. Moreover, expression of B-RAFV600E, but not wild type B-RAF induced dramatic morphological changes in primary human melanocytes. In particular, BRAFV600E expressing melanocytes displayed fewer dendrites, appeared rounded and the majority detached from the culture flask. Importantly, the loss of adhesion induced by BRAFV600E did not induce anoikis, with 80–90% of suspension melanocytes remaining viable after transduction. Our findings demonstrate that constitutively active B-RAFV600E promotes anchorage-independent growth of primary human melanocytes. The impact B-RAFV600E on melanocyte adhesion and survival could conceivably increase cell motility and may account for the unique histopathological characteristics of B-RAFV600E melanomas, including upward migration of cells into the epidermal layer and intraepidermal 'nest' formation. Taken together, our data highlight that activated B-RAF regulates the adhesion and survival of human epidermal melanocytes.1 page(s