MC4R is a receptor specific to the heptapeptide core common to adrenocorticotropic hormone and alpha-, beta-, and gamma-MSH. It plays a central role in energy homeostasis and somatic growth. This receptor is mediated by G proteins that stimulate adenylate cyclase (cAMP). SNPs in MC4R (such as rs17782313) are linked with obesity, and additionally are correlated with risk for breast cancer. In immunohistochemistry, MC4R has membranous and cytoplasmic positivity in most tissues throughout the body. References: Mol Biol Rep. 2013 Dec;40(12):6657-64, PMID: 24091943