Prostaglandin production by melanocytic cells and the effect of a-melanocyte stimulating hormone

NoProstaglandins are potent mediators of the inflam-matory response and are also involved in cancer development. In this study, we show that human melanocytes and FM55 melanoma cells express cyclooxygenase-1 and -2 (COX-1 and-2) and thus have the capability to produce prostaglandins. TheFM55 cells produced predominantly PGE2and PGF2a, whereas the HaCaT keratinocyte cell line produced mainly PGE2. The anti-inflammatory peptide, a-melanocyte stimulating hormone(a-MSH), reduced prostaglandin production in FM55 and HaCaT cells and reversed the effect of the pro-inflammatory cytokine TNF-a in the former. These results indicate that melanocytes produce prostaglandins and that a-MSH, by inhibiting this response, may play an important role in regulating inflammatory responses in the skin

α-Melanocyte-Stimulating Hormone Modulates Nitric Oxide Production in Melanocytes1

We have previously observed that melanocytes produce nitric oxide in response to ultraviolet radiation and lipopolysaccharide and in this study have examined how these responses are affected by α-melanocyte-stimulating hormone. Nitric oxide production by cultured cells was measured electrochemically in real time using an ISO-nitric oxide sensor probe. B16 mouse melanoma cells released nitric oxide in response to lipopolysaccharide and the effects were enhanced in cells that had been grown in the presence of 10­11-10­9 M α-melanocyte-stimulating hormone prior to stimulation. At concentrations in excess of 10­9 M α-melanocyte-stimulating hormone decreased nitric oxide production. Preincubation with lipopolysaccharide, a well-known inducer of inducible nitric oxide synthase, also increased nitric oxide production but this response was reduced by α-melanocyte-stimulating hormone. α-Melanocyte-stimulating hormone also increased the levels of nitric oxide produced in response to ultraviolet radiation (20–100 mJ per cm2) in B16 cells. The same effect was seen in human melanocytes and as this was inhibited by aminoguanidine would appear to involve an induction of inducible nitric oxide synthase. Reverse transcription–polymerase chain reaction showed that melanocytic cells express inducible nitric oxide synthase mRNA. Western blotting analysis and immunocytochemistry confirmed the presence of inducible nitric oxide synthase protein in B16 cells and FM55 human melanoma cells and that the levels were increased in response to α-melanocyte-stimulating hormone. α-Melanocyte-stimulating hormone, however, decreased inducible nitric oxide synthase protein expression, which occurred in response to lipopolysaccharide. These results suggest that α-melanocyte-stimulating hormone regulates nitric oxide production in melanocytic cells by modulating the induction of inducible nitric oxide synthase. Additional experiments showed that nitric oxide increased melanin production by B16 cells and human melanocytes. This is in keeping with a melanogenic role for nitric oxide but whether its production by melanocytes in response to α-melanocyte-stimulating hormone is associated with such a role or whether it has some other significance relating to melanocyte differentiation or in mediating immunomodulatory actions of α-melanocyte-stimulating hormone remains to be seen