Cell surface expression of melanocortin-1 receptor on HaCaT keratinocytes and α-melanocortin stimulation do not affect the formation and repair of UVB-induced DNA photoproducts

Ultraviolet (UV) exposure induces an up-regulation of melanocortin-1 receptor (MC1R) expression in human skin and the α-melanocyte-stimulating hormone (α-MSH) may reduce UVB-induced DNA damage in normal human melanocytes. Using high-performance liquid chromatography coupled to tandem mass spectrometry, we investigated the formation and repair of DNA lesions in UVB-irradiated HaCaT cells stably transfected with the wild type MC1R gene (HaCaT-MC1R). Similar levels of 8 bipyrimidine photoproducts including cyclobutanepyrimidine dimers (CPDs) (T T, T C, C T), (6-4) photoproducts ((6-4)PPs) (TT-(6-4)PPs, TC-(6-4)PPs) and their Dewar valence isomers together with 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo) were found to be generated in both non-transfected and HaCaT-MC1R cells after UVB exposure. Time-course studies of DNA photoproduct yields indicated that the DNA repair ability depended upon radiation doses. It was shown that (6-4)PPs were removed from the DNA of UVB-irradiated cells much more efficiently than CPDs. The repair efficiency of 8-oxodGuo, CPDs and (6-4)PPs was relatively similar in both cell lines and was not modified by stimulation with α-MSH before UVB-exposure. In conclusion, cell surface-enforced expression of MC1Rs on HaCaT keratinocytes and α-MSH stimulation do not affect the formation of UVB-induced DNA photoproducts and their subsequent repair.