The bioactive phospholipid, lysophosphatidylcholine, induces cellular effects via G-protein-dependent activation of adenylyl cyclase.
The naturally occurring phospholipid, lysophosphatidylcholine (lyso-PC), regulates a broad range of cell processes, including gene transcription, mitogenesis, monocyte chemotaxis, smooth muscle relaxation, and platelet activation. Despite the growing list of cellular effects attributable to lyso-PC, the mechanism(s) by which it alters cell function have not been elucidated. In this report, we have examined the effects of exogenous lyso-PC on signal transduction processes within a variety of lyso-PC-responsive cells, including human platelets, monocyte-like THP-1 cells, and the megakaryoblastic cell line, MEG-01. Pretreatment of each of these cells with increasing concentrations of lyso-PC (25-150 microg/ml) was associated with a progressive increase in the cytosolic concentration of cAMP. The accumulation of cAMP in platelets correlated closely with the ability of lyso-PC to inhibit multiple platelet processes, including platelet aggregation, agonist-induced protein kinase C activation, thromboxane A2 generation, and the tyrosine phosphorylation of platelet proteins. In each of the cell types examined, the ability of lyso-PC to increase the cellular levels of cAMP was synergistically enhanced by pretreating the cells with the cAMP phosphodiesterase inhibitor, theophylline (5 mM), and was specifically inhibited by the P-site inhibitor of adenylyl cyclase, 2,5-dideoxyadenosine. A role for the stimulatory G-protein, Gs, in the lyso-PC-induced activation of adenylyl cyclase was suggested by the ability of the GTPase inhibitor, guanylyl 5'-thiophosphate (0.2 mM), to inhibit the lyso-PC-stimulated increase in cAMP, and also by the ability of cholera toxin to inhibit increases in membrane GTPase activity in response to lyso-PC. The functional significance of lyso-PC-induced activation of adenylyl cyclase was investigated in MEG-01 cells. Treatment of these cells with either lyso-PC or dibutyryl cAMP for 36-40 h resulted in a 3-5-fold increase in the surface expression of the natural anticoagulant protein, thrombomodulin (TM). The ability of lyso-PC to increase TM expression was abolished by pretreating these cells with the adenylyl cyclase inhibitor, 2,5-dideoxyadenosine, whereas the dibutyryl cAMP-induced increase in TM remained insensitive to adenylyl cyclase inhibition. These studies define an important role for the adenylyl cyclase signaling system in mediating cellular effects induced by lyso-PC.
Yuan
Y
Y
Department of Medicine, Monash Medical School, Box Hill Hospital, Victoria, Australia 3128.
Schoenwaelder
S M
SM
Salem
H H
HH
Jackson
S P
SP
D000262:Adenylyl Cyclases / Q000378:metabolism*; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D001798:Blood Proteins / Q000378:metabolism; D000242:Cyclic AMP / Q000096:biosynthesis; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D008244:Lysophosphatidylcholines / Q000494:pharmacology*; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects; D010974:Platelet Aggregation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D015398:Signal Transduction; D013928:Thromboxane A2 / Q000096:biosynthesis; D014443:Tyrosine / Q000378:metabolism
D001798:Blood Proteins; D008244:Lysophosphatidylcholines; D014443:Tyrosine; D013928:Thromboxane A2; D000242:Cyclic AMP; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases