Mechanism of cAMP-induced Ca2+ influx in Dictyostelium: role of phospholipase A2.
cAMP-induced Ca2+ influx in Dictyostelium follows two pathways: a G-protein-dependent pathway where influx is reduced by 50-70% in Galpha2 and Gbeta-negative strains and a heterotrimeric G-protein-independent pathway. Using a pharmacological approach, we found that phospholipase A2 (PLA2) is the target of both pathways. The products of PLA2 activity, arachidonic acid (AA) and palmitic acid, induced Ca2+ influx to a similar extent as cAMP. Half-maximal activation occurred at 3 microM AA and saturation at 10 microM AA. The response to AA was quantitatively similar throughout early differentiation and thus independent of cAMP-receptor concentration. Synergy experiments revealed that cAMP and AA acted through identical pathways. The PLA2-activating peptide, a peptide with sequence similarity to the G-protein beta-subunit, activated Ca2+ influx. The G-protein-independent pathway was sensitive to genistein but not to blockers of protein kinase C and other kinases, suggesting that tyrosine kinase may directly or indirectly activate PLA2 in this case.
Schaloske
R
R
Faculty of Biology, University of Konstanz, D-78457 Konstanz, Germany.
Malchow
D
D
D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology*; D004023:Dictyostelium / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D019833:Genistein / Q000494:pharmacology; D017136:Ion Transport; D008071:Lipoprotein Lipase / Q000037:antagonists & inhibitors; D019308:Palmitic Acid / Q000494:pharmacology; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011506:Proteins / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology
D004791:Enzyme Inhibitors; D011506:Proteins; C055324:phospholipase A2-activating protein; D016718:Arachidonic Acid; D019308:Palmitic Acid; D019833:Genistein; D000242:Cyclic AMP; D011493:Protein Kinase C; D010741:Phospholipases A; D008071:Lipoprotein Lipase; D054467:Phospholipases A2; D019204:GTP-Binding Proteins; D002118:Calcium