Melanocortin-1 and melanocortin-5 receptors are expressed in cultured mouse peritoneal macrophages

Adrenocorticotropic hormone (ACTH) belongs to the melanocortin group of related peptides which share a common precursor, pro-opiomelanocortin (POMC). Melanocortin expresses its functional effects by the stimulation of specific seven transmembrane G-protein linked receptors. To date, five melanocortin receptors have been cloned. In the immune system, the production of ACTH in immuno-competent cells has been reported. Because of various physiological effects of ACTH on immuno-competent cells, the hormone might be an intercellular messenger in the immune system. In this study, we report the expression of melanocortin-1 and melanocortin-5 receptors (MC1 and MC5) in cultured mouse peritoneal macrophages. By using a sensitive reverse transcription-polymerase chain reaction (RT-PCR), we demonstrate that these two receptors are specifically expressed in macrophages, whereas expression of other members of the melanocortin receptor family (MC2, MC3 and MC4) was not detected. The sizes of the MC1 and MC5 receptor reverse transcription-polymerase chain reaction (RT-PCR) products are identical to the MC1 receptor RT-PCR product in mouse skin and MC5 receptor RT-PCR product in mouse skeletal muscle. The present data suggest that ACTH may modulate macrophage function by activating MC1 and/or MC5 receptors.