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Antiproliferative action of protein kinase C in cultured rabbit aortic smooth muscle cells
K Kariya1, Y Fukumoto, T Tsuda
1Department of Internal Medicine, Kobe University School of Medicine, Japan.
Abstract:
In rabbit aortic smooth muscle cells (SMC), protein kinase C-activating 12-O-tetradecanoylphorbol-13-acetate (TPA) inhibited the whole blood serum (WBS)-induced DNA synthesis. The inhibitory action of TPA was mimicked by another protein kinase C-activating phorbol ester, phorbol-12,13-dibutyrate (PDBu), but not by 4 alpha-phorbol-12,13- didecanoate known to be inactive for this enzyme. Prolonged treatment of the cells with PDBu caused the down-regulation of protein kinase C. In these cells, WBS still induced DNA synthesis but the inhibitory action of TPA was abolished. DNA synthesis started at 18 h and reached a maximal level 24 h after the addition of WBS. TPA inhibited the WBS-induced DNA synthesis even when added 12 h after the addition of WBS. These results suggest that protein kinase C has an antiproliferative action in rabbit aortic SMC and that this action is attributed to the inhibition of the progression from the late G1 into S phase of the cell cycle. TPA also inhibited the phospholipase C-mediated hydrolysis of phosphoinositides which was induced by WBS within several minutes, but the relevance of this effect on the antiproliferative action of TPA is uncertain.
Insights
Protein kinase C activation inhibits DNA synthesis in rabbit aortic smooth muscle cells by blocking cell cycle progression. This antiproliferative effect is linked to inhibiting the transition from G1 to S phase.
Area of Science:
- Cell Biology
- Biochemistry
- Physiology
Background:
- Protein kinase C (PKC) plays a role in cellular signaling pathways.
- The regulation of smooth muscle cell proliferation is crucial for vascular health.
- Whole blood serum (WBS) can induce DNA synthesis in aortic smooth muscle cells.
Purpose of the Study:
- To investigate the role of PKC in regulating DNA synthesis in rabbit aortic smooth muscle cells (SMC).
- To determine the effect of PKC activation on WBS-induced proliferation.
- To elucidate the phase of the cell cycle affected by PKC activation.
Main Methods:
- Treatment of rabbit aortic SMC with phorbol esters (TPA, PDBu) to activate PKC.
- Assessment of DNA synthesis following WBS stimulation.
- Down-regulation of PKC by prolonged phorbol ester treatment.
- Analysis of cell cycle progression.
Main Results:
- PKC activators (TPA, PDBu) inhibited WBS-induced DNA synthesis in SMC.
- Inactive phorbol ester did not inhibit DNA synthesis, confirming PKC involvement.
- Prolonged PDBu treatment led to PKC down-regulation and abolished TPA's inhibitory effect.
- TPA inhibited WBS-induced DNA synthesis even when added late in the G1 phase, suggesting a late G1 block.
- PKC activation also inhibited WBS-induced phospholipase C activity, though its relevance is unclear.
Conclusions:
- PKC activation exerts an antiproliferative effect on rabbit aortic SMC.
- The antiproliferative action of PKC is mediated by inhibiting the cell cycle transition from late G1 to S phase.
- These findings highlight PKC as a potential regulator of vascular smooth muscle cell proliferation.