Light modulates the melanophore response to alpha-MSH in Xenopus laevis: An analysis of the signal transduction crosstalk mechanisms involved

Autor(es)

Isoldi, Mauro Cesar ^{[1, 2]} ; Provencio, Ignacio ^[1] ; de Lauro Castrucci, Ana Maria ^[3]

Afiliação do(s) autor(es)

^[1] Univ Virginia, Dept Biol, Charlottesville, VA 22904 - USA

^[2] Univ Fed Ouro Preto, Dept Ciencias Biol, DECBI NUPEB, BR-35400000 Ouro Preto, MG - Brazil

^[3] Univ Sao Paulo, Dept Fisiol, Inst Biociencias, BR-05508900 Sao Paulo - Brazil

• Tipo de documento: Artigo Científico
• Fonte: General and Comparative Endocrinology; v. 165, n. 1, p. 104-110, JAN 1 2010.
• Citações Web of Science: 8

Resumo

Melanin granule (melanosome) dispersion within Xenopus laevis melanophores is evoked either by light or alpha-MSH. We have previously demonstrated that the initial biochemical steps of light and alpha-MSH signaling are distinct, since the increase in cAMP observed in response to alpha-MSH was not seen after light exposure. cAMP concentrations in response to alpha-MSH were significantly lower in cells pre-exposed to light as compared to the levels in dark-adapted melanophores. Here we demonstrate the presence of an adenylyl cyclase (AC) in the Xenopus melanophore, similar to the mammalian type IX which is inhibited by Ca(2+)-calmodulin-activated phosphatase. This finding supports the hypothesis that the cyclase could be negatively modulated by a light-promoted Ca(2+) increase. In fact, the activity of calcineurin PP2B phosphatase was increased by light, which could result in AC IX inhibition, thus decreasing the response to alpha-MSH. St-Ht31, a disrupting agent of protein kinase A (PKA)-anchoring kinase A protein (AKAP) complex totally blocked the melanosome dispersing response to alpha-MSH, but did not impair the photo-response in Xenopus melanophores. Sequence comparison of a melanophore AKAP partial clone with GenBank sequences showed that the anchoring protein was a gravin-like adaptor previously sequenced from Xenopus non-pigmentary tissues. Co-immunoprecipitation of Xenopus AKAP and the catalytic subunit of PKA demonstrated that PKA is associated with AKAP and it is released in the presence of alpha-MSH. We conclude that in X laevis melanophores, AKAP12 (gravin-like) contains a site for binding the inactive PKA thus compartmentalizing PKA signaling and also possesses binding sites for PKC. Light diminishes alpha-MSH-induced increase of cAMP by increasing calcineurin (PP2B) activity, which in turn inhibits adenylyl cyclase type IX, and/or by activating PKC, which phosphorylates the gravin-like molecule, thus destabilizing its binding to the cell membrane. (C) 2009 Elsevier Inc. All rights reserved. (AU)

• Processo FAPESP: 01/02460-1 - Melanopsina: fisiologia comparativa do gene e da transdução do sinal luminoso em células pigmentares de peixes, anfíbios e mamíferos
• Beneficiário: Ana Maria de Lauro Castrucci
• Linha de fomento: Auxílio à Pesquisa - Temático
• Processo FAPESP: 06/03381-1 - Fisiologia comparativa de relógios periféricos: genes de relógio (CLOCK, PER1, PER2, CRY1 e BMAL 1) e sua modulação por luz e hormônios em peixes, anfíbios e mamíferos
• Beneficiário: Ana Maria de Lauro Castrucci
• Linha de fomento: Auxílio à Pesquisa - Temático