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Platelet-derived growth factor-induced destabilization of smooth muscle alpha-actin mRNA
M H Corjay1, R S Blank, G K Owens
1Department of Physiology, University of Virginia School of Medicine, Charlottesville 22908.
Abstract:
We have previously shown that treatment of postconfluent, quiescent rat vascular smooth muscle cells (SMC) with platelet-derived growth factor (PDGF) dramatically reduced smooth muscle (SM) alpha-actin synthesis and SM alpha-actin mRNA abundance, suggesting a role for this mitogen in the control of SMC differentiation. In the present studies, we explored the molecular mechanisms whereby PDGF decreases SM alpha-actin mRNA levels. Treatment of postconfluent SMC with both platelet PDGF and recombinant PDGF-BB resulted in a dramatic and concentration-dependent decrease in SM alpha-actin mRNA levels. We observed no differences in efficacy between platelet PDGF and PDGF-BB, indicating that the PDGF-A chain is not required for the effect. The rate of decrease in SM alpha-actin mRNA abundance in PDGF-treated SMC was greater than that observed in cells treated with the transcriptional inhibitor, actinomycin D, with or without PDGF, indicating that PDGF induced a transcriptionally dependent destabilization of the cytosolic SM alpha-actin mRNA pool. This effect appeared selective for SM alpha-actin, in that there was no evidence of a similar change in non-muscle (NM) beta-actin mRNA stability following PDGF treatment. Results of nuclear run-on analyses showed no differences in SM alpha-actin transcription between PDGF- and vehicle-treated SMC at either 4 or 24 hours following treatment, demonstrating that decreases in transcription of the SM alpha-actin gene did not contribute to PDGF-induced changes in SM alpha-actin mRNA abundance. Results of these studies support a possible role for PDGF in regulation of SMC differentiation via a post-transcriptional control mechanism.
Insights
Platelet-derived growth factor (PDGF) reduces smooth muscle alpha-actin mRNA by destabilizing existing mRNA, not by altering gene transcription. This suggests PDGF regulates smooth muscle cell differentiation through post-transcriptional mechanisms.
Area of Science:
- Cell Biology
- Molecular Biology
- Cardiovascular Research
Background:
- Platelet-derived growth factor (PDGF) is known to influence vascular smooth muscle cell (SMC) proliferation and differentiation.
- Previous studies indicated PDGF reduces smooth muscle (SM) alpha-actin synthesis and mRNA levels in SMCs.
Purpose of the Study:
- To elucidate the molecular mechanisms by which PDGF decreases SM alpha-actin mRNA levels in quiescent SMCs.
- To determine if PDGF affects SM alpha-actin gene transcription or mRNA stability.
Main Methods:
- Treatment of postconfluent rat SMCs with platelet PDGF and recombinant PDGF-BB.
- Measurement of SM alpha-actin and non-muscle beta-actin mRNA levels.
- Assessment of mRNA decay rates using actinomycin D.
- Nuclear run-on analyses to evaluate gene transcription.
Main Results:
- PDGF treatment caused a concentration-dependent decrease in SM alpha-actin mRNA levels.
- PDGF accelerated the decay of SM alpha-actin mRNA, indicating destabilization.
- This destabilization effect was specific to SM alpha-actin and not observed for non-muscle beta-actin.
- No significant changes in SM alpha-actin gene transcription were detected between PDGF-treated and control cells.
Conclusions:
- PDGF regulates SM alpha-actin mRNA abundance through a post-transcriptional mechanism, specifically by enhancing mRNA destabilization.
- PDGF's role in controlling SMC differentiation appears to be mediated by post-transcriptional regulation of key differentiation markers like SM alpha-actin.