Abstract
Objective: Smoothelin-A and -B isoforms are highly restricted to contractile smooth muscle cells (SMCs). Serum response factor (SRF) and myocardin are essential for contractile SMC differentiation. We evaluated the contribution of SRF/myocardin to transcriptional regulation of smoothelins. Methods: Rat vascular SMCs were transfected with smoothelin-A and smoothelin-B promoter reporter constructs and promoter activity was analyzed. The effects of mutations in the smoothelin-A promoter CArG-boxes and co-transfections with a myocardin expression plasmid were assessed. Electrophoretic mobility shift assays and chromatin immunoprecipitations were performed to investigate SRF-binding to the smoothelin-A CArG-boxes. Results: Smoothelin promoter activity was detected in vascular SMCs. Comparative sequence analysis revealed two conserved CArG elements in the smoothelin-A promoter that bind SRF as shown by chromatin immunoprecipitation. The proximal CArG-near bound SRF stronger than CArG-far in gel shift assays. Mutagenesis studies also indicated that CArG-near is more important than CArG-far in regulating smoothelin-A promoter activity. Myocardin augmented smoothelin-A promoter activity 2.5-fold in a CArG-near-dependent manner. In contrast, myocardin had little effect on the smoothelin-B promoter. Conclusion: Smoothelin-A expression is controlled by an intragenic promoter whose activity is, in part, dependent on two CArG boxes that bind SRF. Our data show a role for SRF/myocardin in regulating smoothelin-A whereas the higher smoothelin-B expression appears to be SRF/myocardin- independent.
Original language | English (US) |
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Pages (from-to) | 136-145 |
Number of pages | 10 |
Journal | Cardiovascular Research |
Volume | 70 |
Issue number | 1 |
DOIs | |
State | Published - Apr 1 2006 |
Externally published | Yes |
Keywords
- Gene expression
- Myocardin
- Serum response factor
- Smooth muscle cell differentiation
- Smoothelins
ASJC Scopus subject areas
- Physiology
- Cardiology and Cardiovascular Medicine
- Physiology (medical)