title: Regulation of melanosome movement by MAP kinase.
abstract: Our objectives were to further characterize the signaling pathways in melatonin-induced aggregation in Xenopus melanophores, specifically to investigate a possible role of mitogen-activated protein kinase (MAPK). By Western blotting we found that melatonin activates MAPK, which precedes melanosome aggregation measured in a microplate reader. Activation of MAPK, tyrosine phosphorylation of a previously described 280-kDa protein, and melanosome aggregation are sensitive to PD98059, a selective inhibitor of MAPK kinase. The MAPK activation is also decreased by the adenylate cyclase stimulant forskolin. In summary, we found that MAPK is activated during melatonin-induced melanosome aggregation. Activation was decreased by an inhibitor of MAPK kinase, and by forskolin. In addition to inhibition of cyclic adenosine 3',5'-monophosphate (cAMP), reduction in protein kinase A activity (PKA), and activation of protein phosphatase 2A, we suggest that melatonin receptors activate the MAPK cascade and tyrosine phosphorylation of the 280-kDa protein. Although the cAMP/PKA signaling pathway is the most prominent, our data suggest that simultaneous activation of the MAPK cascade is of importance to obtain a completely aggregated state. This new regulatory mechanism of organelle transport by the MAPK cascade might be important in other eukaryotic cells.
authors.affiliation: Department of Medicine and Care, Division of Pharmacology, Faculty of Health Sciences, Linköping University, Linköping, Sweden.
authors.forename: Tony P M
authors.initials: TP
authors.lastname: Andersson
authors.forename: Samuel P S
authors.initials: SP
authors.lastname: Svensson
authors.forename: Annika M
authors.initials: AM
authors.lastname: Karlsson
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002465:Cell Movement; D005576:Colforsin / Q000378:metabolism / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D007700:Kinetics; D020935:MAP Kinase Signaling System; D008547:Melanophores / Q000378:metabolism; D020460:Melanosomes / Q000378:metabolism* / Q000502:physiology; D008858:Microscopy, Phase-Contrast; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D008954:Models, Biological; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D005576:Colforsin; D014443:Tyrosine; D000242:Cyclic AMP; D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one