Figure 1.

Schematic presentation of the melanocortin system in human. The melanocortins (ACTH, α-, β- and γ-MSHs) are peptide hormones derived from the proopiomelanocortin (POMC) prohormone through tissue-dependent post-translational modification by two convertases: PC1/3 (encoded by PCSK1) cleaves the prohormone to obtain ACTH and β-LPH, and cleavage of ACTH by PC2 (encoded by PCSK2) gives α-MSH. β- and γ-MSH are also obtained by PC2 cleavage of POMC. Together with the antagonists, agouti-signalling protein (ASIP) and agouti-related protein (AgRP), the melanocortins bind to five melanocortin receptors MC1-5Rs with various affinities. MC1R mainly regulates melanogenesis, whereas the specific ACTH-receptor MC2R is essential for the regulation of glucocorticoidogenesis. MC3-5Rs are involved in the regulation of energy homeostasis (food intake, energy storage, lipolysis), autoimmune response, anti-inflammatory, cardiovascular and natriuretic processes, sexuality and social behavior. See references in the main text. In the figure, only the main tissues and functions in human were noted for simplification.