N-Methyl-D-aspartate receptor stimulation activates tyrosinase and promotes melanin synthesis in the ink gland of the cuttlefish Sepia officinalis through the nitric Oxide/cGMP signal transduction pathway. A novel possible role for glutamate as physiologic activator of melanogenesis.
The tyrosinase-catalyzed conversion of l-tyrosine to melanin represents the most distinctive biochemical pathway in the ink gland of the cuttlefish Sepia officinalis; however, the molecular mechanisms underlying its activation have remained so far largely uncharted. In this paper we demonstrate for the first time that l-glutamate can stimulate tyrosinase activity and promote melanin synthesis in Sepia ink gland via the N-methyl-d-aspartate (NMDA) receptor/NO/cGMP signal transduction pathway. Incubation of intact ink glands with either l-glutamate or NMDA resulted in an up to 18-fold increase of tyrosinase activity and a more than 6-fold elevation of cGMP levels. Comparable stimulation of tyrosinase was induced by an NO donor and by 8-bromo-cGMP. An NMDA receptor antagonist, NO synthase (NOS) inhibitors, and a guanylate cyclase blocker suppressed NMDA-induced effects. Immunohistochemical evidence indicated that enhanced cGMP production was localized largely in the mature part of the ink gland. Increased de novo synthesis of melanin was demonstrated in NMDA- and NO-stimulated ink glands by a combined microanalytical approach based on spectrophotometric determination of pigment levels and high performance liquid chromatography quantitation of pyrrole-2,3, 5-tricarboxylic acid, a specific melanin marker, in melanosome-containing fractions. These results fill a longstanding gap in the understanding of the complex biochemical mechanisms underlying activation of melanogenesis in the mature ink gland cells of S. officinalis and disclose a novel physiologic role of the excitatory neurotransmitter glutamate mediated by the NMDA receptor/NO/cGMP signaling pathway.
Palumbo
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Zoological Station "Anton Dohrn," Villa Communale, 80121 Naples and the Departments of Zoology and Organic and Biological Chemistry, University of Naples Federico II, 80134 Naples, Italy.
Poli
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Di Cosmo
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d'Ischia
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M
D000818:Animals; D006152:Cyclic GMP / Q000378:metabolism*; D004789:Enzyme Activation; D018698:Glutamic Acid / Q000378:metabolism*; D008543:Melanins / Q000096:biosynthesis*; D008974:Mollusca / Q000378:metabolism*; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists*; D015398:Signal Transduction
D008543:Melanins; D016194:Receptors, N-Methyl-D-Aspartate; D009569:Nitric Oxide; D018698:Glutamic Acid; D014442:Monophenol Monooxygenase; D006152:Cyclic GMP