α-Melanocyte-Stimulating Hormone, MSH 11–13 KPV and Adrenocorticotropic Hormone Signalling in Human Keratinocyte Cells

α-MSH signals by binding to the melanocortin-1 receptor (MC-1R) and elevating cyclic AMP in several different cells. The anti-inflammatory properties of this peptide are also believed to be cyclic AMP dependent. The carboxyl terminal tripeptides of α-MSH (KPV / KP-D-V) are the smallest minimal sequences reported to prevent inflammation but it is not known if they operate via MC-1R or cyclic AMP. The aim of this study was to examine the intracellular signalling of key MSH and ACTH peptides in human keratinotocytes. No elevation in cyclic AMP was detected in either HaCaT or normal human keratinocytes in response to α-MSH, KPV or ACTH peptides. Rapid and acute intracellular calcium, however, were observed in HaCaT keratinocytes in response to α-MSH (10−15–10−7 M), KPV (10−15–10−7 M), KP-D-V (10−15-10−7 M) and ACTH (10−15–10−7 M), but only in the presence of PIA, an adenosine agonist that inhibits the cyclic AMP pathway. Normal keratinocytes responded to all the above peptides but in addition responded to ACTH 1–17 (10−13–10−7 M) in contrast to the HaCaT keratinocytes. Stable transfection of Chinese hamster ovary cells with the MC-1 receptor showed that α-MSH and the KPV peptides elevated intracellular calcium