Increased sensitivity of melanocytes to oxidative stress and abnormal expression of tyrosinase-related protein in vitiligo

BACKGROUND: Vitiligo is a depigmenting disease of the skin, which may derive from programmed melanocyte death or destruction due to inherent sensitivity to oxidative stress arising from either toxic intermediates of melanin, a melanocyte-specific protein, or other sources. Tyrosinase-related protein (TRP) -1 has been shown to be involved not only in melanin biosynthesis but also in the prevention of premature melanocyte death in animals. OBJECTIVES: To clarify the biological role of human TRP-1 in melanocyte survival. METHODS: Cultured melanocyte strains from an active advancing border of vitiligo were established and studied. RESULTS: The established 'vitiligo melanocytes' showed large perikaryon and stubby dendrites. They showed early cell death when exposed to oxidative stress (ultraviolet B) and increased and abnormal immunostaining and immunoprecipitation by antibodies against human and mouse TRP-1, indicating an altered synthesis and processing of TRP-1. In pulse-chase and sequential immunoprecipitation experiments, vitiligo melanocytes revealed abnormal protein-protein interaction with calnexin, a melanogenesis-associated chaperone, suggesting altered folding and maturation of nascent TRP-1 polypeptides. Northern blot analysis indicated a decreased expression of TRP-1 mRNA, but heteroduplex analysis and verification of the mutation at the carboxy terminus of TRP-1 by restriction enzyme analysis did not show any abnormality. CONCLUSIONS: Our study suggests that the early cell death of vitiligo melanocytes is related to their increased sensitivity to oxidative stress, which may arise from complex processes of abnormal synthesis and processing of TRP-1 and its interaction with calnexin.