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Human melanocortin 1 receptor variants, receptor function and melanocyte response to UV radiation

M. Cathy Scott1, Kazumasa Wakamatsu2, Shosuke Ito2, Ana Luisa Kadekaro1, Nobuhiko Kobayashi3, Joanna Groden4, Renny Kavanagh1, Takako Takakuwa5, Victoria Virador6, Vincent J. Hearing6 and Zalfa A. Abdel-Malek1,*

1 Department of Dermatology, University of Cincinnati College of Medicine, PO Box 670592, Cincinnati, Ohio 45267-0592, USA
2 Fujita Health University School of Health Sciences, Toyoake, Aichi 470-1192, Japan
3 Department of Dermatology, Nara Medical University, Kashihara, Nara 634-8522, Japan
4 Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, PO Box 670524, Cincinnati, Ohio 45267-0524, USA
5 POLA Laboratories, 560 Kashio-cho, Totsuka-ku, Yokohama 244-0812, Japan
6 Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD 20892, USA



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  		Fig. 1. Dose-responses of various melanocyte cultures to {alpha}-MSH. The responses of NHM 753-c, 830-c, 849-b and 755-c, homozygous or compound heterozygous for MC1R variants, and NHM 747-c, 729-c and 751-b, homozygous for the consensus MC1R were compared. The response of NHM 765-c, heterozygous for Val92Met substitution, is also presented, since it is comparable to NHM 753-c and 830-c in the ratio of eumelanin to pheomelanin. The responses to {alpha}-MSH were tested as described in the Materials and Methods. The effects of increasing doses of {alpha}-MSH on cAMP formation, tyrosinase activity and cell proliferation are presented in A, B and C, respectively. Basal levels of cAMP (Pmole/106 cells) in the cultures tested were as follows: 753-c=2.176±0.134; 830-c=1.451; 849-b=1.172±0.0219; 755-c=2.193±0.206; 765-c=1.675±0.137; 747-c=1.074±0.098; 729-b=2.007±0.128; 751-b=0.84±0.103. In A and B, each value represents the mean percent of control of six determinations±s.e. In C, each value is the mean percent of control of three determinations±s.e.

 


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  		Fig. 2. Cytotoxic effects of UVBR on melanocytes with different MC1R genotypes. We compared the response to UVBR of NHM 753-c, 830-c and 849-b homozygous or heterozygous for loss-of-function mutations in MC1R to that of NHM 765-c and NHM 755-c, heterozygous or homozygous for Val92Met substitution, respectively. All melanocyte cultures were irradiated a single time with UVBR and cell number and viability were determined on days 2 and 4 after irradiation, as described in Materials and Methods. Each value represents the mean percent cell death of three determinations±s.e.

 




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