Role of TGF-β in Melanoma

Human malignant melanoma is highly resistant to chemotherapy and current immunotherapeutic approaches induce long term remission only in the minority of patients. The transforming growth factor-β (TGF-β) has attracted much attention as a therapeutic target because it plays an important and pleiotropic role in melanoma progression. TGF-β is a multifunctional cytokine involved in the regulation of many cellular processes including cell proliferation, differentiation and survival. Resistance to the growth inhibitory effects of TGF-β without alterations of TGF-β signaling molecules is characteristic of cutaneous melanoma. Melanoma produces increasing amounts of TGF-βwith disease progression, inhibiting immune responses and providing an optimal microenvironment for undisturbed tumor growth. In addition, TGF-β exerts its tumor promoting functions via direct effects on tumor cell motility and invasiveness and indirectly by modulating tumor stroma and extracellular matrix, supporting angiogenesis and inhibiting immune surveillance. TGF-β acts through multiple intracellular signaling pathways and the outcome of TGF-β signaling is context-dependent. Defining the impact of the different TGF-β signaling pathways on melanoma progression will help to identify suitable therapeutic targets. Here we review the current knowledge of TGF-β in melanoma and discuss recent therapeutic approaches targeting the TGF-β pathway.