Encyclopedia
Melanocortin 1 receptor
- genes
1. Introduction
The MC1R gene provides instructions for making a protein called the melanocortin 1 receptor. This receptor plays an important role in normal pigmentation. The receptor is primarily located on the surface of melanocytes, which are specialized cells that produce a pigment called melanin. Melanin is the substance that gives skin, hair, and eyes their color. Melanin is also found in the light-sensitive tissue at the back of the eye (the retina), where it plays a role in normal vision.
Melanocytes make two forms of melanin, eumelanin and pheomelanin. The relative amounts of these two pigments help determine the color of a person's hair and skin. People who produce mostly eumelanin tend to have brown or black hair and dark skin that tans easily. Eumelanin also protects skin from damage caused by ultraviolet (UV) radiation in sunlight. People who produce mostly pheomelanin tend to have red or blond hair, freckles, and light-colored skin that tans poorly. Because pheomelanin does not protect skin from UV radiation, people with more pheomelanin have an increased risk of skin damage caused by sun exposure.
The melanocortin 1 receptor controls which type of melanin is produced by melanocytes. When the receptor is activated, it triggers a series of chemical reactions inside melanocytes that stimulate these cells to make eumelanin. If the receptor is not activated or is blocked, melanocytes make pheomelanin instead of eumelanin.
Common variations (polymorphisms) in the MC1R gene are associated with normal differences in skin and hair color. Certain genetic variations are most common in people with red hair, fair skin, freckles, and an increased sensitivity to sun exposure. These MC1R polymorphisms reduce the ability of the melanocortin 1 receptor to stimulate eumelanin production, causing melanocytes to make mostly pheomelanin. Although MC1R is a key gene in normal human pigmentation, researchers believe that the effects of other genes also contribute to a person's hair and skin coloring.
The melanocortin 1 receptor is also active in cells other than melanocytes, including cells involved in the body's immune and inflammatory responses. The receptor's function in these cells is unknown.
2. Health Conditions Related to Genetic Changes
2.1. Melanoma
Certain variations in the MC1R gene increase the risk of developing melanoma, a type of skin cancer that begins in melanocytes. These variations reduce the ability of the melanocortin 1 receptor to stimulate eumelanin production in melanocytes, resulting in fair skin. Because eumelanin normally protects skin from the harmful effects of UV radiation, a lack of this pigment leaves skin more vulnerable to damage from sun exposure. Skin damage caused by UV radiation from the sun is a major risk factor for developing melanoma.
Studies suggest that other variations in the MC1R gene may also increase the risk of developing melanoma in the absence of UV radiation-related skin damage. In these cases, melanomas can occur in people of dark or light skin coloring. These cancers are often associated with mutations in additional genes related to melanoma risk, such as the BRAF and CDKN2A genes. Researchers are working to explain the complex relationship among MC1R variations, other genetic and environmental factors, and melanoma risk.
2.2. Oculocutaneous Albinism
Certain genetic changes in the MC1R gene modify the appearance of people with oculocutaneous albinism type 2. This form of albinism, which is caused by mutations in the OCA2 gene, is characterized by fair hair, light-colored eyes, creamy white skin, and vision problems. People with genetic changes in both the OCA2 and MC1R genes have many of the usual features of oculocutaneous albinism type 2; however, they typically have red hair instead of the usual yellow, blond, or light brown hair seen with this condition.
3. Other Names for This Gene
-
MC1-R
-
melanocortin 1 receptor (alpha melanocyte stimulating hormone receptor)
-
Melanocortin-1 receptor
-
melanocyte stimulating hormone receptor
-
melanotropin receptor
-
MSH-R
-
MSHR_HUMAN
This entry is adapted from the peer-reviewed paper https://medlineplus.gov/genetics/gene/mc1r
References
- Duffy DL, Box NF, Chen W, Palmer JS, Montgomery GW, James MR, Hayward NK,Martin NG, Sturm RA. Interactive effects of MC1R and OCA2 on melanoma riskphenotypes. Hum Mol Genet. 2004 Feb 15;13(4):447-61.
- García-Borrón JC, Sánchez-Laorden BL, Jiménez-Cervantes C. Melanocortin-1receptor structure and functional regulation. Pigment Cell Res. 2005Dec;18(6):393-410. Review.
- Ha T, Naysmith L, Waterston K, Oh C, Weller R, Rees JL. Defining thequantitative contribution of the melanocortin 1 receptor (MC1R) to variation inpigmentary phenotype. Ann N Y Acad Sci. 2003 Jun;994:339-47. Review.
- Healy E. Melanocortin 1 receptor variants, pigmentation, and skin cancersusceptibility. Photodermatol Photoimmunol Photomed. 2004 Dec;20(6):283-8.Review.
- Kanetsky PA, Rebbeck TR, Hummer AJ, Panossian S, Armstrong BK, Kricker A,Marrett LD, Millikan RC, Gruber SB, Culver HA, Zanetti R, Gallagher RP, Dwyer T, Busam K, From L, Mujumdar U, Wilcox H, Begg CB, Berwick M. Population-based studyof natural variation in the melanocortin-1 receptor gene and melanoma. CancerRes. 2006 Sep 15;66(18):9330-7.
- King RA, Willaert RK, Schmidt RM, Pietsch J, Savage S, Brott MJ, Fryer JP,Summers CG, Oetting WS. MC1R mutations modify the classic phenotype ofoculocutaneous albinism type 2 (OCA2). Am J Hum Genet. 2003 Sep;73(3):638-45.
- Landi MT, Bauer J, Pfeiffer RM, Elder DE, Hulley B, Minghetti P, Calista D,Kanetsky PA, Pinkel D, Bastian BC. MC1R germline variants confer risk forBRAF-mutant melanoma. Science. 2006 Jul 28;313(5786):521-2.
- Mumm CD, Draznin M. Melanocortin-1 receptor: loss of function mutations andskin cancer. Dermatol Online J. 2006 Sep 8;12(5):13. Review.
- Rees JL. Genetics of hair and skin color. Annu Rev Genet. 2003;37:67-90.Review.
- Rees JL. The genetics of sun sensitivity in humans. Am J Hum Genet. 2004Nov;75(5):739-51.
- Rouzaud F, Kadekaro AL, Abdel-Malek ZA, Hearing VJ. MC1R and the response ofmelanocytes to ultraviolet radiation. Mutat Res. 2005 Apr 1;571(1-2):133-52.
- Sturm RA. Skin colour and skin cancer - MC1R, the genetic link. Melanoma Res. 2002 Oct;12(5):405-16. Review.
