Editing MC1R in human melanoma cells by CRISPR/Cas9 and functional analysis

MC1R (melanocortin 1 receptor) encodes the melanocortin-1 receptor, which can activate intracellular cAMP synthesis under the stimulation of the α-melanocyte stimulating hormone (α-MSH) ligand. Increased cAMP then activates the protein kinase A (PKA) pathway, resulting in the up-regulation of the expression of the microphthalmia-associated transcription factor (MITF) which is a critical regulatory factor of melanin synthesis, and tyrosinase (TYR), the rate-limiting enzyme of melanin synthesis tyrosinase (TYR), and ultimately affects production of eumelanin and pheomelanin, and the coat color phenotype of mammalian species. Previous reports have indicated that the mutation A243T in the transmembrane domain 6 (TM6) of MC1R protein might disrupt the function of MC1R, contributing to the red phenotype in Duroc pig. However, functional analysis of the A243T mutation in MC1R has not yet been carried out. In this study, we attempted to used single-stranded oligo-deoxyribonucleotides (ssODN) as donor templates to introduce the c.727G>A (A243T) mutation into MC1R in human melanoma cell line SK-MEL-2 by CRISPR/Cas9 to analyze its effects on MC1R functions. We found the occurrence of ssODN recombination reached to 10%. Unfortunately, Sanger sequencing MC1R in six single-cell clones revealed that none carried the c.727G>A mutation, but all carried undesired mutations surrounding the target site. Cells transfected with CRISPR/Cas9 plasmids and ssODN presented significantly attenuated cAMP activation, and down-regulated MITF and TYR expression, indicating that the editing MC1R could affect the melanin synthesis function in cells. This study provides a basis for further investigation the mechanism of MC1R mutation on animal coat color.