| First Author | Ferris LA | Year | 2021 |
| Journal | Mol Cell Biochem | Volume | 476 |
| Issue | 8 | Pages | 2899-2916 |
| PubMed ID | 33743134 | Mgi Jnum | J:343405 |
| Mgi Id | MGI:7565912 | Doi | 10.1007/s11010-021-04117-1 |
| Citation | Ferris LA, et al. (2021) Purine-rich element binding protein B attenuates the coactivator function of myocardin by a novel molecular mechanism of smooth muscle gene repression. Mol Cell Biochem 476(8):2899-2916 |
| abstractText | Myocardin is a potent transcriptional coactivator protein, which functions as the master regulator of vascular smooth muscle cell differentiation. The cofactor activity of myocardin is mediated by its physical interaction with serum response factor, a ubiquitously expressed transactivator that binds to CArG boxes in genes encoding smooth muscle-restricted proteins. Purine-rich element binding protein B (Purbeta) represses the transcription of the smooth muscle alpha-actin gene (Acta2) in fibroblasts and smooth muscle cells by interacting with single-stranded DNA sequences flanking two 5' CArG boxes in the Acta2 promoter. In this study, the ability of Purbeta to modulate the cofactor activity of myocardin was investigated using a combination of cellular and biochemical approaches. Results of smooth muscle gene promoter-reporter assays indicated that Purbeta specifically inhibits the coactivator function of myocardin in a manner requiring the presence of all three single-stranded DNA binding domains in the Purbeta homodimer. DNA binding analyses demonstrated that Purbeta interacts with CArG-containing DNA elements with a much lower affinity compared to other purine-rich target sequences present in the Acta2 promoter. Co-immunoprecipitation and DNA pull-down assays revealed that Purbeta associates with myocardin and serum response factor when free or bound to duplex DNA containing one or more CArG boxes. Functional analysis of engineered Purbeta point mutants identified several amino acid residues essential for suppression of myocardin activity. Collectively, these findings suggest an inhibitory mechanism involving direct protein-protein interaction between the homodimeric Purbeta repressor and the myocardin-serum response factor-CArG complex. |
