Palmitoylation-dependent activation of MC1R prevents melanomagenesis

The protein modification palmitoylation increases the ability of variant forms of the melanocortin-1 receptor (MC1R) to induce pigmentation, and this is linked to reduced development of melanomas. People with red hair, fair skin and poor tanning ability have a higher risk of developing melanoma. They often carry variants of the melanocortin-1 receptor (MC1R), which has a reduced capacity to induce pigmentation compared with the more common MCR1 forms. Rutao Cui and colleagues show how a modification called protein palmitoylation increases the ability of variant MCR1 to induce pigmentation in mice, and this is linked to reduced melanoma development. These findings may point to strategies for melanoma prevention, although it remains to be seen whether such an approach is practical. The melanocortin-1 receptor (MC1R), a G-protein-coupled receptor, has a crucial role in human and mouse pigmentation1,2,3,4,5,6,7,8. Activation of MC1R in melanocytes by α-melanocyte-stimulating hormone (α-MSH)9 stimulates cAMP signalling and melanin production and enhances DNA repair after ultraviolet irradiation10,11,12,13,14,15,16. Individuals carrying MC1R variants, especially those associated with red hair colour, fair skin and poor tanning ability (denoted as RHC variants), are associated with higher risk of melanoma5,17,18,19,20. However, how MC1R activity is modulated by ultraviolet irradiation, why individuals with red hair are more prone to developing melanoma, and whether the activity of RHC variants might be restored for therapeutic benefit are unknown. Here we demonstrate a potential MC1R-targeted intervention strategy in mice to rescue loss-of-function MC1R in MC1R RHC variants for therapeutic benefit by activating MC1R protein palmitoylation. MC1R palmitoylation, primarily mediated by the protein-acyl transferase ZDHHC13, is essential for activating MC1R signalling, which triggers increased pigmentation, ultraviolet-B-induced G1-like cell cycle arrest and control of senescence and melanomagenesis in vitro and in vivo. Using C57BL/6J-Mc1re/eJ mice, in which endogenous MC1R is prematurely terminated, expressing Mc1r RHC variants, we show that pharmacological activation of palmitoylation rescues the defects of Mc1r RHC variants and prevents melanomagenesis. The results highlight a central role for MC1R palmitoylation in pigmentation and protection against melanoma.