Forced expression of myocardin is not sufficient for induction of smooth muscle differentiation in multipotential embryonic cells.
OBJECTIVE
Myocardin, a coactivator of serum response factor, has been shown to be required for expression of multiple CArG-dependent smooth muscle cell (SMC) marker genes. The aim of the present study was to determine whether myocardin alone is sufficient to induce SMC lineage in multipotential stem cells as evidenced by activation of the entire SMC differentiation program.


RESULTS
Overexpression of myocardin induced only a subset of SMC marker genes, including smooth muscle (SM) alpha-actin, SM-myosin heavy chain (MHC), SM22alpha, calponin, and desmin in A404 SMC precursor cells, whereas expression of smoothelin-B, aortic carboxypeptidase-like protein, and focal adhesion kinase-related nonkinase, whose promoters lack efficacious CArG elements, was not induced. Similar results were obtained in cultured SMCs, 10T1/2 cells, and embryonic stem cells. Moreover, myocardin inappropriately induced expression of skeletal and cardiac CArG-dependent genes in cultured SMCs. Stable overexpression of dominant-negative myocardin in A404 cells resulted in impaired induction of SM alpha-actin and SM-MHC by all trans-retinoic acid but had no effect on induction of smoothelin-B and aortic carboxypeptidase-like protein expression.


CONCLUSIONS
Taken together with previous studies, results demonstrate that myocardin is required for the induction of CArG-dependent SMC marker genes but is not sufficient to initiate the complete SMC differentiation program. We examined whether myocardin induces the entire smooth muscle cell (SMC) differentiation program. Results of the present study showed that myocardin knockdown or overexpression affected only a subset of SMC marker genes in multipotential cells, indicating that myocardin is required but not sufficient to induce SMC lineage.
Yoshida
Tadashi
T
Department of Molecular Physiology and Biological Physics, University of Virginia, MR5 Room 1220, 415 Lane Road, PO Box 801394, Charlottesville, VA 22908, USA.
Kawai-Kowase
Keiko
K
Owens
Gary K
GK
D000199:Actins / Q000096:biosynthesis / Q000235:genetics; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001011:Aorta / Q000166:cytology; D002417:Cattle; D002454:Cell Differentiation; D002478:Cells, Cultured / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D005799:Genes, Dominant; D017930:Genes, Reporter; D005822:Genetic Vectors / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D032383:Myocytes, Cardiac / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D009928:Organ Specificity; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000502:physiology; D027602:Serum Response Element; D026362:Serum Response Factor / Q000502:physiology; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology*; D015533:Transcriptional Activation; D014162:Transfection; D000099251:Myocardin
D000199:Actins; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; D026362:Serum Response Factor; D015534:Trans-Activators; D000099251:Myocardin