Similarities and differences in smooth muscle alpha-actin induction by TGF-beta in smooth muscle versus non-smooth muscle cells.
Transforming growth factor-beta (TGF-beta) has been shown to stimulate smooth muscle (SM) alpha-actin expression in smooth muscle cells (SMCs) and non-SMCs. We previously demonstrated that the 2 CArG boxes A and B and a novel TGF-beta control element (TCE) located within the first 125 bp of the SM alpha-actin promoter were required for TGF-beta inducibility of SM alpha-actin in SMCs. The aims of the present study were (1) to determine whether the TCE exhibits SMC specificity or contributes to TGF-beta induction of SM alpha-actin expression in non-SMCs (ie, endothelial cells and fibroblasts) and (2) to determine whether TGF-beta can induce expression of multiple TCE-containing SMC differentiation marker genes, such as SM22alpha, h(1) calponin, and SM myosin heavy chain (SM MHC) in non-SMCs. Results of transient transfection assays demonstrated that mutation of CArG A, CArG B, or the TCE within a 125-bp promoter context completely abolished TGF-beta inducibility of SM alpha-actin in endothelial cells and fibroblasts. However, in contrast to observations in SMCs, inclusion of regions upstream from (-155) completely repressed TGF-beta responsiveness in non-SMCs. Electrophoretic mobility shift assays showed that TGF-beta enhanced binding of a serum response factor to the CArG elements and the binding of an as-yet-unidentified factor to the TCE in endothelial cells and fibroblasts, but to a much lesser extent compared with SMCs. TGF-beta also stimulated expression of the SMC differentiation marker SM22alpha in non-SMCs. However, in contrast to SMCs, TGF-beta did not induce expression of h(1) calponin and SM MHC in non-SMCs. In summary, these results suggest a conserved role for CArG A, CArG B, and the TCE in TGF-beta-induced expression of SM alpha-actin in SMCs and non-SMCs that is modified by a complex interplay of positive- and negative-acting cis elements in a cell-specific manner. Furthermore, observations that TGF-beta stimulated expression of several early but not late differentiation markers in non-SMCs indicate that TGF-beta alone is not sufficient to induce transdifferentiation of non-SMCs into SMCs.
Hautmann
M B
MB
Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, Charlottesville 22908, USA.
Adam
P J
PJ
Owens
G K
GK
D000199:Actins / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D002135:Calcium-Binding Proteins / Q000235:genetics; D002417:Cattle; D002478:Cells, Cultured; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism*; D008840:Microfilament Proteins / Q000235:genetics; D009124:Muscle Proteins / Q000235:genetics; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000235:genetics; D009687:Nuclear Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D026362:Serum Response Factor; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D000096985:Calponins
D000199:Actins; D002135:Calcium-Binding Proteins; D004268:DNA-Binding Proteins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D018995:Myosin Heavy Chains; D009687:Nuclear Proteins; D012333:RNA, Messenger; D026362:Serum Response Factor; D016212:Transforming Growth Factor beta; D000096985:Calponins; C058992:Tagln protein, mouse; C051615:transgelin