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L-NAME-induced dispersion of melanosomes in melanophores activates PKC, MEK and ERK1.

Melanosome movement represents a good model of cytoskeleton-mediated transport of organelles in eukaryotic cells. We recently observed that inhibiting nitric oxide synthase (NOS) with Nomega-nitro-L-arginine methyl ester (L-NAME) induced dispersion in melanophores pre-aggregated with melatonin. Activation of cyclic adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase (PKA) or calcium-dependent protein kinase (PKC) is known to cause dispersion. Also, PKC and NO have been shown to regulate the mitogen/extracellular signal-regulated kinase (MEK)-ERK pathway. Accordingly, our objective was to further characterize the signaling pathway of L-NAME-induced dispersion. We found that the dispersion was decreased by staurosporine and PD98059, which respectively inhibit PKC and MEK, but not by the PKA inhibitor H89. Furthermore, Western blotting revealed that ERK1 kinase was phosphorylated in L-NAME-dispersed melanophores. L-NAME also caused dispersion in latrunculin-B-treated cells, suggesting that this effect is not due to inhibition of the melatonin signaling pathway. Summarizing, we observed that PKC and MEK inhibitors decreased the L-NAME-induced dispersion, which caused phosphorylation of ERK1. Our results also suggest that NO is a negative regulator of phosphorylations that leads to organelle transport.