TY - JOUR
T1 - Evidence for serum response factor-mediated regulatory networks governing SM22α transcription in smooth, skeletal, and cardiac muscle cells
AU - Li, Li
AU - Liu, Zheng Chang
AU - Mercer, Brian
AU - Overbeek, Paul
AU - Olson, Eric N.
N1 - Funding Information:
We are grateful to M. Parmacek for sharing unpublished results, to R. Schwartz and S. Schwartz for valuble reagents, to T. L'Ecuyer and H. Maisel for helpful discussion, to A. Tizenor for assistance with graphics, and to members of the Olson lab for helpful comments. Portions of this work were performed while L.L was at the University of Texas Southwestern. Work was supported by grants from the National Institutes of Health, the Human Frontiers Sciences Program, and the American Heart Association to E.N.O.
PY - 1997/7/15
Y1 - 1997/7/15
N2 - SM22α is an adult smooth muscle-specific protein that is expressed in the smooth, cardiac, and skeletal muscle lineages during early embryogenesis before becoming restricted specifically to all vascular and visceral smooth muscle cells (SMC) in late fetal development and adulthood. We have used the SM22α gene as a marker to define the regulatory mechanisms that control muscle-specific gene expression in SMCs. Previously, we reported that the 445-base-pair promoter of SM22α was sufficient to direct transcription of a lacZ reporter gene in early cardiac and skeletal muscle cell lineages and in a subset of arterial SMCs, but not in venous nor visceral SMCs in transgenic mice. Here we describe two evolutionarily conserved CArG (CC(A/T)6GG) boxes in the SM22α promoter, both of which are essential for full promoter activity in cultured SMCs. In contrast, only the promoter-proximal CArG box is essential for specific expression in developing smooth, skeletal, and cardiac muscle lineages in transgenic mice. Both CArG boxes bind serum response factor (SRF), but SRF binding is not sufficient for SM22α promoter activity, since overexpression of SRF in the embryonal teratocarcinoma cell line F9, which normally expresses low levels of SRF, fails to activate the promoter. However, a chimeric protein in which SRF was fused to the transcription activation domain of the viral coactivator VP16 is able to activate the SM22α promoter in F9 cells. These results demonstrate the SM22α promoter-proximal CArG box is a target for the regulatory programs that confer smooth, skeletal, and cardiac muscle specificity to the SM22α promoter and they suggest that SRF activates SM22α transcription in conjunction with additional regulatory factors that are cell type-restricted.
AB - SM22α is an adult smooth muscle-specific protein that is expressed in the smooth, cardiac, and skeletal muscle lineages during early embryogenesis before becoming restricted specifically to all vascular and visceral smooth muscle cells (SMC) in late fetal development and adulthood. We have used the SM22α gene as a marker to define the regulatory mechanisms that control muscle-specific gene expression in SMCs. Previously, we reported that the 445-base-pair promoter of SM22α was sufficient to direct transcription of a lacZ reporter gene in early cardiac and skeletal muscle cell lineages and in a subset of arterial SMCs, but not in venous nor visceral SMCs in transgenic mice. Here we describe two evolutionarily conserved CArG (CC(A/T)6GG) boxes in the SM22α promoter, both of which are essential for full promoter activity in cultured SMCs. In contrast, only the promoter-proximal CArG box is essential for specific expression in developing smooth, skeletal, and cardiac muscle lineages in transgenic mice. Both CArG boxes bind serum response factor (SRF), but SRF binding is not sufficient for SM22α promoter activity, since overexpression of SRF in the embryonal teratocarcinoma cell line F9, which normally expresses low levels of SRF, fails to activate the promoter. However, a chimeric protein in which SRF was fused to the transcription activation domain of the viral coactivator VP16 is able to activate the SM22α promoter in F9 cells. These results demonstrate the SM22α promoter-proximal CArG box is a target for the regulatory programs that confer smooth, skeletal, and cardiac muscle specificity to the SM22α promoter and they suggest that SRF activates SM22α transcription in conjunction with additional regulatory factors that are cell type-restricted.
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U2 - 10.1006/dbio.1997.8621
DO - 10.1006/dbio.1997.8621
M3 - Article
C2 - 9242426
AN - SCOPUS:0030851947
SN - 0012-1606
VL - 187
SP - 311
EP - 321
JO - Developmental Biology
JF - Developmental Biology
IS - 2
ER -