Mitf dosage as a primary determinant of melanocyte survival after ultraviolet irradiation

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Abstract

Microphthalmia-associated transcription factor (Mitf) is essential for melanocyte development and function and regulates anti-apoptoticBcl2expression. We hypothesized that cellular deficiency ofMitfcan influence melanocyte survival in response to ultraviolet (UV) radiation. Primary melanocyte cultures were prepared from neonatal wild-type mice and congenic animals heterozygous forMitfmutationsMitfmi-vga9/+andMitfMi-wh/+and exposed to UV irradiation. Wild-type melanocytes were more resistant to UV-induced apoptosis than melanocytes partially deficient in Mitf activity, as determined by relative levels of intracellular melanin and relative activation of Mitf target genesTyr, Tyrp1, Dct,andCdk2.Comparative experiments with wild-type cells and congenic albino melanocytes demonstrated that these differences are not due to differences in melanin content, implicating Mitf as a primary determinant of UV-dependent melanocyte survival.Mitfactivity correlated directly with resistance to UV-induced apoptosis in melanocytes. Mitf was important not only for regulating the expression of anti-apoptotic Bcl-2 following UV irradiation, but also the expression of the pro-apoptotic BH3-only Bad protein and activation of the extrinsic apoptotic pathway. Hence, Mitf is a multifaceted regulator of UV-induced apoptosis in melanocytes.

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