Novel mechanisms of the regulation of protein kinase B in adipocytes; implications for protein kinase A, Epac, phosphodiesterases 3 and 4.
Crosstalk between insulin and cAMP signalling pathways has a great impact on adipocyte metabolism. Whilst Protein kinase B (PKB) is a pivotal mediator of insulin action, in some cells regulation of PKB by cAMP has also been demonstrated. Here we provide evidence that, in a phosphatidyl inositol 3-kinase dependent manner, beta3-adrenergic stimulation (using CL316243) in adipocytes induces PKB phosphorylation in the absence of insulin and also potentiates insulin-induced phosphorylation of PKB. Interestingly, insulin- and CL316243-induced PKB phosphorylation was found to be inhibited by pools of cAMP controlled by PDE3B and PDE4 (mainly in the context of insulin), whereas a cAMP pool controlling protein kinase A appeared to mediate stimulation of PKB phosphorylation (mainly in the context of CL316243). Furthermore, an Epac (exchange protein directly activated by cAMP) agonist (8-pCPT-2'-O-Me-cAMP) mimicked the effect of the PDE inhibitors, giving evidence that Epac has an inhibitory effect on PKB phosphorylation in adipocytes. Further, we put the results obtained at the level of PKB in the context of possible downstream signalling components in the regulation of adipocyte metabolism. Thus, we found that overexpression of PKB induced lipogenesis in a PDE3B-dependent manner. Furthermore, overexpression or inhibition of PDE3B was associated with reduced or increased phosphorylation of the key lipogenic enzyme acetyl-CoA carboxylase (ACC), respectively. These PDE3B-dependent effects on ACC correlated with changes in lipogenesis. The Epac agonist, 8-pCPT-2'-O-Me-cAMP, mimicked the effect of PDE3B inhibition on ACC phosphorylation and lipogenesis.
Zmuda-Trzebiatowska
Emilia
E
Biomedical Center, C11, Department of Experimental Medical Science, 221 84 Lund, Sweden. emilia.zmuda-trzebiatowska@med.lu.se
Manganiello
Vincent
V
Degerman
Eva
E
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism*; D000103:Acetyl-CoA Carboxylase / Q000378:metabolism; D017667:Adipocytes / Q000201:enzymology*; D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; D004149:Dioxoles / Q000494:pharmacology; D004789:Enzyme Activation; D020662:Guanine Nucleotide Exchange Factors / Q000819:agonists / Q000378:metabolism*; D050155:Lipogenesis; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction
C473217:8-(4-chloro-phenylthio)-2'-O-methyladenosine-3'-5'-cyclic monophosphate; D004149:Dioxoles; C482601:Epac protein, mouse; D020662:Guanine Nucleotide Exchange Factors; C076126:disodium (R,R)-5-(2-((2-(3-chlorophenyl)-2-hydroxyethyl)-amino)propyl)-1,3-benzodioxole-2,3-dicarboxylate; D000242:Cyclic AMP; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D017868:Cyclic AMP-Dependent Protein Kinases; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; C517293:Pde3b protein, mouse; C517294:Pde3b protein, rat; D000103:Acetyl-CoA Carboxylase