Calcium Plays a Complex Role in the Regulation of Melanogenesis in Murine B16 Melanoma Cells

Abstract

To learn more of the role of calcium in the regulation of melanogenesis, we have used direct manipulation of medium calcium and pharmacological modulation of intracellular calcium to examine the consequences on unstimulated and cyclic AMP elevated tyrosinase activity and melanin synthesis and distribution in B16 melanoma cells. In unstimulated cells, calcium is clearly inhibitory to tyrosinase activity. However, in cells stimulated with cAMP-elevating agents the requirement for extracellular calcium was changed such that cells required a minimum of 0.4-0.6 mmol medium calcium for maximum tyrosinase response to these agents. Paradoxically, pharmacologically increasing intracellular calcium in cAMP-stimulated cells with ionophore inhibited tyrosinase activity, and the calcium-lowering agent TMB8 and the calcium channel blocker verapamil both stimulated tyrosinase activity. When melanin synthesis was measured in cAMP-stimulated cells, TMB8 was found to significantly increase the sensitivity and the maximum melanogenic response to alpha-MSH, suggesting the presence of at least one level of endogenous calcium inhibitory control operative in these cells. In addition, TMB8 changed the distribution of melanin between the cell and the medium such that, in the presence of alpha-MSH and TMB8, significantly more melanin was secreted into the medium. These data suggest that calcium is required for several steps in melanogenesis, having an apparently inhibitory effect on pre-tyrosinase activity in unstimulated cells, but also showing evidence of a positive role in cyclic AMP-stimulated tyrosinase activity, as well as a further possible inhibitory role in melanin movement or secretion.

Endothelin-B receptor-mediated Ca2+ signaling in human melanocytes

“…These results indicate that the loss of Ca 2+ signaling in these cells is associated with an absence of proliferation. The effects of Ca 2+ on melanogenesis and proliferation in murine melanoma cells have been studied [3]. The decrease in [Ca 2+ ] i caused by 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB8) increased melanin production and tyrosinase activity, and the increase in [Ca 2+ ] i caused by A23187 decreased tyrosinase activity in these cells.…”

“…The decrease in [Ca 2+ ] i caused by 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB8) increased melanin production and tyrosinase activity, and the increase in [Ca 2+ ] i caused by A23187 decreased tyrosinase activity in these cells. Cell proliferation was increased as extracellular Ca 2+ was increased to 0.6 mM and remained increased with higher concentrations of Ca 2+ [3]. In our laboratory the effects of ET-1, BQ788 and U73122 on melanocyte proliferation and dendricity were tested.…”

Dietary flavonoids advance timing of moult but do not affect redox status of juvenile blackbirds (Turdus merula)

“…Melanin biosynthesis by melanocytes critically depends on limiting mineral elements, including calcium. For instance, calcium may upregulate the activity of tyrosinase (Buffey et al, 1993), a fundamental enzyme in the melanin biosynthesis pathway (McGraw, 2007), thus promoting melanogenesis and possibly triggering the onset of moult. A further hypothesized mechanism linking development of melanized feathers to flavonoids, namely the buffering of the low GSH levels required for melanogenesis by the antioxidant properties of flavonoids, seems less likely to apply because of the absence of detectable effects of flavonoids on antioxidant defences.…”

Expression and function of ryanodine receptors in human melanocytes

“…The importance of Ca 2ϩ signaling for proliferation and melanogenesis has also been demonstrated in the melanocytes (Yada et al, 1991;Buffey et al, 1993). In murine melanoma cells, cell proliferation increased as the extracellular Ca 2ϩ increased from 0.1 to 0.6 mM.…”

“…In murine melanoma cells, cell proliferation increased as the extracellular Ca 2ϩ increased from 0.1 to 0.6 mM. Ca 2ϩ is required for melanogenesis, having an appar- ently inhibitory effect on pretyrosinase activity in unstimulated cells, but also showing evidence of a positive role in cyclic AMP-stimulated tyrosinase activity (Buffey et al, 1993). In melanocytes, the addition of endothelin-1, an important cytokine of UV-induced melanogenesis, increased the [Ca 2ϩ ] i and stimulated DNA and melanin syntheses (Yada et al, 1991).…”