UV radiation (UV) is classified as a “complete carcinogen” because it is both a mutagen and a non-specific damaging agent and has properties of both a tumor initiator and a tumor promoter.,In environmental abundance, UV is the most important modifiable risk factor for skin cancer and many other environmentally-influenced skin disorders.,However, UV also benefits human health by mediating natural synthesis of vitamin D and endorphins in the skin, therefore UV has complex and mixed effects on human health.,Nonetheless, excessive exposure to UV carries profound health risks, including atrophy, pigmentary changes, wrinkling and malignancy.,UV is epidemiologically and molecularly linked to the three most common types of skin cancer, basal cell carcinoma, squamous cell carcinoma and malignant melanoma, which together affect more than a million Americans annually.,Genetic factors also influence risk of UV-mediated skin disease.,Polymorphisms of the melanocortin 1 receptor (MC1R) gene, in particular, correlate with fairness of skin, UV sensitivity, and enhanced cancer risk.,We are interested in developing UV-protective approaches based on a detailed understanding of molecular events that occur after UV exposure, focusing particularly on epidermal melanization and the role of the MC1R in genome maintenance.
We describe a mechanism of tumorigenesis mediated by kinase-dead BRAF in the presence of oncogenic RAS.,We show that drugs that selectively inhibit BRAF drive RAS-dependent BRAF binding to CRAF, CRAF activation, and MEK-ERK signaling.,This does not occur when oncogenic BRAF is inhibited, demonstrating that BRAF inhibition per se does not drive pathway activation; it only occurs when BRAF is inhibited in the presence of oncogenic RAS.,Kinase-dead BRAF mimics the effects of the BRAF-selective drugs and kinase-dead Braf and oncogenic Ras cooperate to induce melanoma in mice.,Our data reveal another paradigm of BRAF-mediated signaling that promotes tumor progression.,They highlight the importance of understanding pathway signaling in clinical practice and of genotyping tumors prior to administering BRAF-selective drugs, to identify patients who are likely to respond and also to identify patients who may experience adverse effects.,► BRAF activates ERK but in some circumstances BRAF inhibitors can induce tumor growth ► BRAF inhibitors drive BRAF-CRAF binding, activating ERK in cells with oncogenic RAS ► Kinase-dead mutants of BRAF have the same effect as BRAF inhibitors ► Oncogenic RAS and kinase-dead BRAF cooperate to induce melanoma in mice