Neuropeptide-induced inhibition of steroidogenesis in crab molting glands: involvement of cGMP-dependent protein kinase.
In crustaceans, ecdysteroid production by the molting glands (Y-organs) is negatively regulated by a neuropeptide, molt-inhibiting hormone (MIH). The involvement of cyclic nucleotide-dependent kinases in the mechanism of action of this neuropeptide was investigated with regard to the steroidogenic activity of Carcinus maenas Y-organs. Regardless of the activity level, the major phosphotransferase activity measured in cytosolic fraction was cGMP-dependent, indicating a relatively high cytosolic concentration of cGMP-kinase in these cells. Phosphotransferase activity was nearly twofold higher in the intermolt (low steroidogenic activity) than in premolt (high steroidogenic activity) animals. In vitro incubation of premolt Y-organs with MIH for 1 hr increased by 3.7-fold the cGMP-kinase activity ratio (-cGMP/ +cGMP). Numerous endogenous protein substrates were predominantly phosphorylated in a cGMP-dependent manner in cytosolic, particulate, and membrane fractions. Similar phosphoprotein patterns were observed in both molting stages. By contrast, cAMP-kinase activity, which was low in intermolt Y-organs, increased significantly in the active steroidogenic premolt Y-organs. The increase in cAMP-kinase activity was accompanied by a cAMP-dependent phosphorylation of several specific endogenous proteins. Taken together these results strongly suggest that activation of cGMP-kinase and subsequent phosphorylation of an endogenous protein(s) may be responsible, at least in part, for the MIH-induced inhibition of steroidogenesis. By contrast, it is most unlikely that cAMP-kinase is involved in these processes.
Baghdassarian
D
D
Départment de Biologie, Laboratoire de Biochimie et Physiologie du Développement, CNRS ER 100, Ecole Normale Supérieure, Paris, France.
de Bessé
N
N
Saïdi
B
B
Sommé
G
G
Lachaise
F
F
D000818:Animals; D001345:Autoradiography; D003386:Brachyura / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004702:Endocrine Glands / Q000187:drug effects / Q000201:enzymology*; D006657:Histones / Q000494:pharmacology; D066298:In Vitro Techniques; D007447:Invertebrate Hormones / Q000494:pharmacology*; D008274:Magnesium / Q000494:pharmacology; D018978:Molting / Q000502:physiology*; D010766:Phosphorylation; D010770:Phosphotransferases / Q000187:drug effects / Q000378:metabolism*
D006657:Histones; D007447:Invertebrate Hormones; C012445:molt-inhibiting hormone; D010770:Phosphotransferases; D017868:Cyclic AMP-Dependent Protein Kinases; D017869:Cyclic GMP-Dependent Protein Kinases; D008274:Magnesium