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Activated RhoA stimulates c-fos gene expression in myocardial cells
T Ueyama1, T Sakoda, S Kawashima
1First Department of Internal Medicine, Kobe University School of Medicine, Japan.
Abstract:
Rho regulates various cell functions, including cell morphology and motility. However, the functional role of Rho on the signaling pathway in myocardial cells (MCs) is unknown. In the present study, we attempted to explore the mode of Rho action for c-fos gene expression in MCs. Expression of the c-fos promoter/enhancer linked to the luciferase reporter gene (c-fos luciferase) was stimulated by the wild type of RhoA and the point-mutated active form of RhoA (RhoA Val14) but not the biologically inactive effector domain mutant of RhoA. Rho GDP dissociation inhibitor inhibited the action of RhoA on c-fos luciferase expression. The deletion analysis revealed that the c-fos serum response element (SRE) and the 12-O-tetradecanoylphorbol-13-acetate response element (TRE) mainly account for c-fos luciferase expression by RhoA Val14. The c-fos SRE mutant, which contains an intact binding site for the serum response factor but lacks the ternary complex factor binding site, was activated by RhoA Val14. The action of RhoA Val14 on c-fos luciferase expression was not inhibited by downregulation of protein kinase C, protein kinase C inhibitors, or tyrosine kinase inhibitors. These results indicate that activated RhoA stimulates c-fos gene expression through the c-fos SRE and TRE and that the signaling pathway from activated RhoA to the c-fos promoter/enhancer is independent of these inhibitor-sensitive pathways in MCs.
Insights
Activated RhoA stimulates c-fos gene expression in myocardial cells via the c-fos serum response element and TRE. This pathway is independent of protein kinase C and tyrosine kinase signaling.
Area of Science:
- Molecular Biology
- Cell Signaling
- Cardiology
Background:
- Rho GTPases regulate fundamental cell processes like morphology and motility.
- The specific role of Rho in myocardial cell (MC) signaling pathways, particularly for gene expression, remains largely uncharacterized.
Purpose of the Study:
- To elucidate the mechanism by which RhoA influences c-fos gene expression in myocardial cells.
- To identify the specific regulatory elements and signaling cascades involved in RhoA-mediated c-fos activation.
Main Methods:
- Utilized a luciferase reporter assay system with a c-fos promoter construct in myocardial cells.
- Employed RhoA wild-type and mutant forms, Rho GDP dissociation inhibitor, and analyzed promoter deletion mutants (SRE and TRE regions).
- Investigated the involvement of protein kinase C and tyrosine kinase pathways.
Main Results:
- Activated RhoA (RhoA Val14) significantly stimulated c-fos promoter activity.
- The serum response element (SRE) and 12-O-tetradecanoylphorbol-13-acetate response element (TRE) within the c-fos promoter were identified as key mediators.
- RhoA-mediated c-fos activation was independent of protein kinase C and tyrosine kinase signaling pathways.
Conclusions:
- Activated RhoA directly stimulates c-fos gene expression in myocardial cells.
- The c-fos SRE and TRE are critical for mediating RhoA's effect on transcription.
- The signaling pathway linking activated RhoA to the c-fos promoter in MCs operates independently of common kinase pathways.