Antimitogenic Effects of Trapidil In Coronary Artery Smooth Muscle Cells by Direct Activation of Protein Kinase A
Abstract
The triazolopyrimidine trapidil has been found in controlled clinical trials to prevent restenosis after vascular injury. Although trapidil is widely regarded as a platelet-derived growth factor receptor (PDGF) antagonist, its precise mode of action is still unknown. This study was designed to investigate the inhibition of mitogenesis by trapidil in cultured bovine coronary artery smooth muscle cells (SMC) and to identify major signal transduction pathways involved. Trapidil inhibited PDGF-BB-induced mitogenesis in SMC in a concentration-dependent manner. Comparable inhibitory effects were obtained after stimulation of smooth muscle cells by phorbol ester, which suggests that the action of trapidil was not restricted to PDGF receptor-mediated mechanisms. Trapidil also inhibited PDGF- and phorbol ester-induced mitogen-activated protein kinase as well as Raf-1 kinase activity. As a possible target of trapidil, stimulation of cellular protein kinase A (PKA) activity was detected. Trapidil also induced the phosphorylation of vasodilator-stimulated phosphoprotein in SMC. Antimitogenic effects of trapidil were completely abolished by PKA inhibitors. Neither a direct stimulation of cAMP formation nor a phosphodiesterase inhibition was observed at antimitogenic concentrations of trapidil. However, trapidil directly activated purified PKA holoenzyme in a cAMP-independent manner. In conclusion, trapidil exerts its antimitogenic effects on SMC by direct activation of PKA. Thus, PKA-mediated inhibition of the Raf-1/MAP kinase pathway may be involved in the antimitogenic actions of the compound.
Footnotes
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Send reprint requests to: Karsten Schrör, M.D., Institut für Pharmakologie, Heinrich-Heine-Universität Düsseldorf, Moorenstraße 5, D-40225 Düsseldorf, Germany. E-mail: schroer{at}pharma.uni-duesseldorf.de
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This study was supported in part by the Deutsche Forschungsgemeinschaft (SFB 351, D7) and the Forschungsgruppe Herz-Kreislauf e.V., Düsseldorf, Germany.
- Abbreviations:
- SMC
- smooth muscle cells
- HEPES
- 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- IBMX
- isobutylmethylxanthine
- PAGE
- polyacrylamide gel electrophoresis
- PBS
- phosphate buffered saline
- PBS-TT
- phosphate buffered saline/Triton X-100/Tween 20
- PDGF
- platelet-derived growth factor
- PGE1
- prostaglandin E1
- PKA
- cAMP-dependent protein kinase
- PKC
- protein kinase C
- PMA
- phorbol-12-myristate-13-acetate
- PTCA
- percutaneous transluminal coronary angioplasty
- SDS
- sodium dodecyl sulfate
- VASP
- vasodilator-stimulated phosphoprotein
- PDGF-BB
- platelet-derived growth factor, isoform BB
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- Received December 12, 1997.
- Accepted April 14, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
