Cyclic AMP agonists induce the phosphorylation of phospholipase C-tau and of a 76 kDa protein co-precipitated by anti-(phospholipase C-tau) monoclonal antibodies in BALB/c-3T3 cells. Relationship to inositol phosphate formation.
Previous studies have demonstrated enhanced phosphorylation of phospholipase C-tau (PLC-tau), a key regulatory enzyme in phosphoinositide metabolism, in cells treated with platelet-derived growth factor (PDGF) and epidermal growth factor, both of which act via specific receptor tyrosine kinases. Our studies on BALB/c-3T3 cells show that agents that promote cellular cyclic AMP accumulation also increase the phosphorylation, specifically the serine phosphorylation, of this enzyme. Increased phosphorylation of PLC-t (2-3-fold) was evident within 5-10 min of addition of isobutylmethylxanthine (IBMX) and either cholera toxin or forskolin to cells, and persisted for at least 3 h. Treatment of cells with cyclic AMP agonists also enhanced, with similar kinetics, the phosphorylation of a 76 kDa protein co-precipitated by anti-PLC-tau monoclonal antibodies. Brief exposure of cells to cholera toxin/IBMX or forskolin/IBMX decreased inositol phosphate formation induced by the GTP-binding protein (G-protein) activator aluminium fluoride by approx. 50%, but was without effect on PDGF-stimulated inositol phosphate formation. These findings suggest that PLC-tau, and perhaps the 76 kDa co-precipitated protein, are substrates of cyclic AMP-dependent protein kinase in BALB/c-3T3 cells: however, the lack of effect of cyclic AMP elevation on PDGF-stimulated inositol phosphate formation indicates that the intrinsic activity of PLC-tau is unaltered by cyclic AMP-mediated phosphorylation.
Department of Cell Biology, Vanderbilt University School of Medicine, Nashville, TN 37232.
N E
NE
Olashaw
S G
SG
Rhee
W J
WJ
Pledger
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology*; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D000911:Antibodies, Monoclonal; D002460:Cell Line; D002772:Cholera Toxin / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D008970:Molecular Weight; D010750:Phosphoproteins / Q000302:isolation & purification*; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism*
D000596:Amino Acids; D000911:Antibodies, Monoclonal; D007295:Inositol Phosphates; D010750:Phosphoproteins; D010982:Platelet-Derived Growth Factor; D005576:Colforsin; D002772:Cholera Toxin; D000242:Cyclic AMP; D010738:Type C Phospholipases; D015056:1-Methyl-3-isobutylxanthine