Activation of melanogenesis by vacuolar type H+-ATPase inhibitors in amelanotic, tyrosinase positive human and mouse melanoma cells

AbstractIn this study, we describe the activation of melanogenesis by selective vacuolar type H+-ATPase inhibitors (bafilomycin A1 and concanamycin A) in amelanotic human and mouse melanoma cells which express tyrosinase but show no melanogenesis. Addition of the inhibitors activated tyrosinase within 4 h, and by 24 h the cells contained measurable amounts of melanin. These effects were not inhibited by cycloheximide (2 μg/ml) which is consistent with a post-translational mechanism of activation. Our findings suggest that melanosomal pH could be an important and dynamic factor in the control of melanogenesis in mammalian cells

Nle4DPhe7α-Melanocyte-Stimulating Hormone Increases the Eumelanin:Phaeomelanin Ratio in Cultured Human Melanocytes

In mammals, melanin exists in two chemically distinct forms: the red-yellow phaeomelanin and the brown-black eumelanin. Although administration of the pigmentary hormone α-melanocyte-stimulating hormone (αMSH) and its synthetic analogue Nle4DPhe7αMSH induces skin darkening in man, the increases in melanogenesis in cultured human melanocytes in response to these peptides are relatively small, However, it is possible that MSH affects the eumelanin:phaeomelanin ratio rather titan total cellular melanin. Thus, this study examined the specific effects of Nle4DPhe7αMSH on the two melanins in cultured human melanocytes, quantifying eumelanin and phaeomelanin by hign performance liquid chromatography. Nle4DPhe7αMSH induced significant increases in the eumelanin content of these cells while having lesser and varied effects on the levels of phaeomelanin. As a consequences the eumelanin: phaeomelanin ratio was increased in every culture. These results demonstrate that Nle4DPhe7αMSH affects melanin type in human melanocytes and suggest a possible mechanism by which this peptide induces skin darkening in man

The sunburn response in human skin is characterized by sequential eicosanoid profiles that may mediate its early and late phases.

yesSunburn is a commonly occurring acute inflammatory process, with dermal vasodilatation and leukocyte infiltration as central features. Ultraviolet (UV) B-induced hydrolysis of membrane phospholipids releases polyunsaturated fatty acids and their subsequent metabolism by cyclooxygenases (COX) and lipoxygenases (LOX) may produce potent eicosanoid mediators modulating different stages of the inflammation. Our objective was to identify candidate eicosanoids formed during the sunburn reaction in relation to its clinical and histological course. We exposed skin of healthy humans (n=32) to UVB and for 72h examined (i) expression of pro- and anti-inflammatory eicosanoids using LC/ESI-MS/MS and (ii) immunohistochemical expression of COX-2, 12-LOX, 15-LOX and leucocyte markers, while (iii) quantifying clinical erythema. We show that vasodilatory prostaglandins (PG)E2, PGF2¿ and PGE3 accompany the erythema in the first 24-48h, associated with increased COX-2 expression at 24h. Novel, potent leukocyte chemoattractants 11-, 12- and 8-monohydroxy-eicosatetraenoic acid (-HETE) are elevated from 4-72h, in association with peak dermal neutrophil influx at 24h, and increased dermal CD3+ lymphocytes and 12- and 15-LOX expression from 24-72h. Anti-inflammatory metabolite 15-HETE shows later expression, peaking at 72h. Sunburn is characterized by overlapping phases of increases in COX products followed by LOX products that may regulate subsequent events and ultimately its resolution.The Wellcome Trus

Tyrosinase Synthesis in Different Skin Types and the Effects of α-Melanocyte-Stimulating Hormone and Cyclic AMP

Tyrosinase synthesis and its regulation in human melanocytes was studied by measuring the incorporation of [35S] methionine into incubated skin biopsies. Tyrosinase was detected in all skin samples with the highest levels in skin type IV and the lowest levels in skin type I. Following psoralen ultraviolet A (PUVA) therapy for several weeks, significant increases in the amounts of tyrosinase were found in skin types III and IV. The presence of α-melanocyte-stimulating hormone (α-MSH) (100 μmol/l) or the long-acting analogue [Nle4, DPhe7] α-MSH (1 – 10 μmol/l) in the incubation medium failed to alter tyrosinase levels in the skin biopsies taken from patients both before and after receiving PUVA therapy. Bromo-adenosine 3,5-cyclic monophosphate sodium salt (8-bromo-cAMP) (10 mmol/l), on the other hand, increased the amounts of tyrosinase both before and after PUVA, but these effects were only seen in biopsies of type III and IV skin. These results indicate that MSH fails to stimulate tyrosinase synthesis in human melanocytes. Nevertheless, tyrosinase synthesis and its regulation by cyclic AMP-dependent mechanisms could be important control points in the pigmentary response

Melanin-concentrating hormone and its receptor are expressed and functional in human skin

In this study, we have demonstrated the presence of melanin-concentrating hormone (MCH) and melanin-concentrating hormone receptor (MCHR1) transcripts in human skin. Sequence analysis confirmed that the transcripts of both genes were identical to those previously found in human brain. In culture, endothelial cells showed pro-MCH expression whereas no signal was found in keratinocytes, melanocytes, and fibroblasts. MCHR1 expression was restricted to melanocytes and melanoma cells. Stimulation of cultured human melanocytes with MCH reduced the α-MSH-induced increase in cAMP production. Furthermore, the melanogenic actions of α-MSH were inhibited by MCH. We propose that the MCH/MCHR1 signalling system is present in human skin and may have a role with the melanocortins in regulating the melanocyte