Guanosine 5'-O-(3-thiotrisphosphate) potentiates both thrombin- and platelet-derived growth factor-induced inositol phosphate release in permeabilized vascular smooth muscle cells. Signaling mechanisms distinguished by sensitivity to pertussis toxin and phorbol esters.
We compared the mechanisms by which thrombin and platelet-derived growth factor (PDGF) activate phospholipase C in cultured vascular smooth muscle cells. Thrombin caused a transient (less than 5 min) increase in inositol trisphosphate (IP3) while PDGF caused a sustained (greater than 10 min) increase. Both pertussis toxin and phorbol 12-myristate 13-acetate (PMA) inhibited the thrombin-induced increase in IP3 but neither agent affected the PDGF-induced increase in IP3. To examine the role of GTP binding (G) proteins in the activation of phospholipase C by these two hormones, GTP analogues were introduced into saponin-permeabilized cells. In the absence of hormones, guanosine 5'-O-(3-thiotrisphosphate) (GTP gamma S) caused a progressive increase in IP3 release which was inhibited 55% by PMA (200 ng/ml). In the presence of thrombin, GTP gamma S caused synergistic increase in IP3 release. The synergism between GTP gamma S and thrombin was virtually eliminated by 10 min prior exposure to PMA (200 ng/ml). When PDGF was the hormonal agonist, GTP gamma S also caused synergistic increase in IP3 release and guanosine 5'-O-(2-thiodiphosphate) blunted PDGF-induced IP3 release. However, in contrast to thrombin, the synergism between GTP gamma S and PDGF was unaffected by PMA. Thus, thrombin and PDGF activate phospholipase C by signal transduction systems which differ in kinetic properties and in sensitivity to PMA and pertussis toxin. Despite these differences, both systems appear to involve GTP binding proteins at some step.
Huang
C L
CL
Cardiovascular Research Institute, University of California, San Francisco 94143.
Ives
H E
HE
D000818:Animals; D002463:Cell Membrane Permeability; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000502:physiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D037342:Pertussis Toxin; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D051381:Rats; D015398:Signal Transduction; D013403:Sugar Phosphates / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology*; D013917:Thrombin / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D007295:Inositol Phosphates; D010982:Platelet-Derived Growth Factor; D013403:Sugar Phosphates; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D015544:Inositol 1,4,5-Trisphosphate; D006160:Guanosine Triphosphate; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D013917:Thrombin; D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate