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-actin promoter function
differentially in SM vs. non-SM cells
Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, Virginia 22906
Transcriptional
activity of the smooth muscle (SM)
-actin gene is differentially
regulated in SM vs. non-SM cells. Contained within the rat SM
-actin
promoter are two MCAT motifs, binding sites for transcription enhancer
factor 1 (TEF-1) transcriptional factors implicated in the regulation
of many muscle-specific genes. Transfections of SM
-actin
promoter-CAT constructs containing wild-type or mutagenized MCAT
elements were performed to evaluate their functional significance.
Mutation of the MCAT elements resulted in increased transcriptional
activity in SM cells, whereas these mutations either had no effect or
decreased activity in L6 myotubes or endothelial cells. High-resolution
gel shift assays resolved several complexes of different mobilities
that were formed between MCAT oligonucleotides and nuclear extracts
from the different cell types, although no single band was unique to
SM. Western blot analysis of nuclear extracts with polyclonal
antibodies to conserved domains of the TEF-1 gene family revealed
multiple reactive bands, some that were similar and others that
differed between SM and non-SM. Supershift assays with a polyclonal
antibody to the TEF-related protein family demonstrated that TEF-1 or
TEF-1-related proteins were contained in the shifted complexes. Results
suggest that the MCAT elements may contribute to cell type-specific
regulation of the SM
-actin gene. However, it remains to be
determined whether the differential transcriptional activity of MCAT
elements in SM vs. non-SM is due to differences in expression of TEF-1
or TEF-1-related proteins or to unique (cell type specific)
combinatorial interactions of the MCAT elements with other
cis-elements and trans-factors.
vascular smooth muscle cells; transcription enhancer factor 1; transcriptional regulation
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