Prognostic role of BRAF in human cutaneous melanoma : gene versus protein expression

Melanoma is the deadliest type of skin cancer with an increasing incidence for past two decades. Once melanoma is metastasized (cancer cells are spread out through the body) there is no effective treatment available and 84% of the patients die within 5 years. However, the discovery of braf mutation in melanoma increased the hope for developing new treatments. We first evaluated the effect of braf V600E mutation on melanoma patient survival. In a systematic review we revealed that patients with braf V600E mutation have almost two times more risk of death compared with patients with wild type braf. Next we evaluated the correlation of brafV600E mutation with protein expression. We found that compared with nevi samples, BRAF protein expression was remarkably increased in primary melanomas and further increased in metastatic melanoma patients. Higher BRAF protein expression was significantly correlated with other poor prognosis factors and lead to a significant worse five-year survival. However, we did not find a significant correlation between BRAF protein expression and braf V600E mutation. In our attempt to investigate the cause of induced BRAF protein, we found novel expression of BRAF splice variants (BRAFsv) in both melanoma patients and cell lines. We identified new kinase-dead BRAFsv, which have a dominant negative effect on full-length BRAF and are able to suppress downstream signaling and reduce melanoma cell proliferation. These variants were highly expressed in primary melanoma compared to normal samples, while the expression was decreased in metastatic and more aggressive types of melanoma. In addition, kinase-dead BRAFsv showed a protective effect on patient survival, which remained significant at the presence of full-length BRAF. Thus, patients who expressed the kinase-dead variant and had lower levels of full-length BRAF expression showed the best survival rate in 5 years. Our invitro analysis also indicates that over expression of kinase-dead BRAFsv in melanoma cell lines enhances the effect of BRAF inhibitor treatment. All in all, the data presented in this thesis elucidated a new era in the evaluation of melanoma patient prognosis and revealed new possibilities for more effective melanoma treatments.Medicine, Faculty ofMedicine, Department ofExperimental Medicine, Division ofGraduat