title: Sphingosine activates protein kinase A type II by a novel cAMP-independent mechanism.
abstract: Protein kinase A (PKA) has long been recognized as playing a major role in many regulatory processes in cells through its activation by the ubiquitous second messenger cAMP. We show here a novel mode of activation of PKA type II that is independent of cAMP and is, instead, dependent on sphingosine. PKA type II is specifically activated by sphingosine and its analog, dimethylsphingosine, but not by sphingosine-1-phosphate or other lipids. Like cAMP, sphingosine activates PKA holoenzyme but not the catalytic subunit alone, suggesting that the activation is mediated by the regulatory subunits. However, sphingosine-activated PKA, but not cAMP-activated PKA, is inhibited by phosphatidylserine, suggesting a distinct mechanism of activation. Furthermore, unlike cAMP, sphingosine does not induce the dissociation of PKA holoenzyme into catalytic and regulatory subunits. Modulation of sphingosine levels in vivo results in alteration in basal membrane-associated PKA activity consistent with a direct effect of membrane sphingosine on PKA type II. Importantly, sphingosine-dependent but not cAMP-dependent activation of PKA specifically phosphorylates Ser58 of the multifunctional adapter protein 14-3-3zeta, promoting the conversion of dimeric 14-3-3 to a monomeric state, thus potentially modulating several biological functions. These results define a new mode of PKA activation that is sphingosine-dependent and mechanistically different from the classical cAMP-dependent activation of PKA. Furthermore, they suggest that stimuli that induce sphingosine accumulation and modulate phospholipid content at the cell membrane have the potential to activate PKA, thereby inducing the phosphorylation of distinct substrates and biological activities.
authors.affiliation: Cytokine Receptor Laboratory, Division of Human Immunology, Hanson Institute, G.P.O. Box 14 Rundle Mall, Adelaide SA 5000, Australia.
authors.forename: Yuefang
authors.initials: Y
authors.lastname: Ma
authors.forename: Stuart
authors.initials: S
authors.lastname: Pitson
authors.forename: Timothy
authors.initials: T
authors.lastname: Hercus
authors.forename: Jane
authors.initials: J
authors.lastname: Murphy
authors.forename: Angel
authors.initials: A
authors.lastname: Lopez
authors.forename: Joanna
authors.initials: J
authors.lastname: Woodcock
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D020134:Catalytic Domain; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002852:Chromatography, Ion Exchange; D000242:Cyclic AMP / Q000378:metabolism*; D054754:Cyclic AMP-Dependent Protein Kinase RIIalpha Subunit; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D004983:Ethanolamines / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D015151:Immunoblotting; D007700:Kinetics; D050356:Lipid Metabolism; D008246:Lysophospholipids / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D009206:Myocardium / Q000201:enzymology; D041681:NIH 3T3 Cells; D010718:Phosphatidylserines / Q000737:chemistry; D010743:Phospholipids / Q000378:metabolism; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D013110:Sphingosine / Q000031:analogs & derivatives / Q000378:metabolism*; D013379:Substrate Specificity; D000099157:Sphingosine Kinase
chemical_list: D048948:14-3-3 Proteins; D000242:Cyclic AMP; D054754:Cyclic AMP-Dependent Protein Kinase RIIalpha Subunit; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases; D004983:Ethanolamines; D008246:Lysophospholipids; D010718:Phosphatidylserines; D010743:Phospholipids; D017853:Phosphotransferases (Alcohol Group Acceptor); D012694:Serine; D013110:Sphingosine; D000099157:Sphingosine Kinase; C517821:Prkar2a protein, mouse; C060506:sphingosine 1-phosphate; C005448:phosphorylethanolamine