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Destabilization of natriuretic peptide C-receptor mRNA by phorbol myristate acetate
R V Paul1, P S Wackym, M N Budisavljevic
1Medical Service, Ralph H. Johnson Department of Veterans Affairs Medical Center, Charleston, South Carolina, USA.
Abstract:
Natriuretic peptide C receptor (NPR-C) expression in rat mesangial cells is downregulated by platelet-derived growth factor (PDGF) and the protein kinase C agonist phorbol myristate acetate (PMA). This study shows that PDGF and PMA diminish NPR-C mRNA abundance and that PMA does so by accelerating the degradation of the transcript. Exposure to PMA (0.1 microM) decreased mesangial cell NPR-C mRNA levels by more than 50% within 3 h and 125I-atrial natriuretic peptide binding by approximately 50% within 6 h. Disappearance of NPR-C transcripts after PMA treatment was more than twice as rapid as that seen after inhibition of RNA transcription with actinomycin D. Treatment with PDGF A/B (10 ng/ml) also produced downregulation of NPR-C mRNA, but the rate of transcript disappearance was similar to that seen after actinomycin D. Coincubation with actinomycin D inhibited the rapid disappearance of NPR-C mRNA with PMA. NPR-C mRNA levels increased four- to eightfold within 6 h after treatment with the protein synthesis inhibitor cycloheximide, but simultaneous treatment with PMA or PDGF still decreased the level of NPR-C mRNA despite the presence of cycloheximide. These results indicate that NPR-C expression is rapidly regulated by changes in the rate of catabolism of its mRNA through a protein kinase C-activated mechanism that depends on transcription. Treatment with cycloheximide induces NPR-C mRNA, but downregulation of this mRNA by either PDGF or PMA does not depend on synthesis of new protein.
Insights
Platelet-derived growth factor (PDGF) and phorbol myristate acetate (PMA) reduce natriuretic peptide C receptor (NPR-C) expression by increasing mRNA degradation. This protein kinase C-activated mechanism regulates NPR-C levels rapidly.
Area of Science:
- Molecular Biology
- Cell Signaling
- Renal Physiology
Background:
- Natriuretic peptide C receptor (NPR-C) plays a role in regulating cardiovascular and renal functions.
- Platelet-derived growth factor (PDGF) and protein kinase C (PKC) activators are implicated in cellular processes.
- Understanding the regulation of NPR-C expression is crucial for cellular function.
Purpose of the Study:
- To investigate the molecular mechanisms by which PDGF and PMA downregulate NPR-C expression in rat mesangial cells.
- To determine the role of mRNA stability and protein synthesis in this regulatory process.
Main Methods:
- Treatment of rat mesangial cells with PDGF, PMA, actinomycin D (transcription inhibitor), and cycloheximide (protein synthesis inhibitor).
- Quantification of NPR-C mRNA levels using Northern blotting or similar techniques.
- Measurement of 125I-atrial natriuretic peptide binding to assess NPR-C receptor levels.
Main Results:
- PDGF and PMA significantly decreased NPR-C mRNA abundance in mesangial cells.
- PMA accelerated NPR-C mRNA degradation, indicating regulation at the post-transcriptional level.
- Downregulation by PDGF and PMA did not depend on new protein synthesis but required transcription.
Conclusions:
- NPR-C expression is rapidly regulated via changes in mRNA catabolism through a PKC-activated, transcription-dependent mechanism.
- PDGF and PMA downregulate NPR-C mRNA stability, independent of de novo protein synthesis.
- These findings elucidate a novel pathway for controlling NPR-C receptor levels in renal cells.