ABSTRACT
The intermediate filament protein, vimentin, is differentially expressed in various tissues and stages of development and in metastatic versus nonmetastatic breast cancer cell lines. Previously, we have shown vimentin expression to be regulated at least in part by a silencer element which binds a M(r) 95,000 protein and an overriding, antisilencer element which binds a M(r) 140,000 protein. Southwestern blot (DNA-protein) analyses indicate that silencer protein binding activity is missing in the metastatic breast cancer cell line (MDA-MB-231), where vimentin is highly expressed, but is present in the nonmetastatic breast cancer cell line, MCF-7, where vimentin is not expressed. This suggests that the absence of a functional silencer protein may lead to expression of vimentin as well as other genes which contribute to the metastatic state.
Subject(s)
Breast Neoplasms/genetics , Breast Neoplasms/pathology , DNA-Binding Proteins/genetics , Gene Expression Regulation, Neoplastic , Genes, Regulator , Regulatory Sequences, Nucleic Acid , Vimentin/genetics , Animals , Base Sequence , Chloramphenicol O-Acetyltransferase/genetics , DNA, Neoplasm/genetics , Female , Gene Deletion , Humans , Mice , Molecular Sequence Data , Neoplasm Metastasis , Polymerase Chain Reaction , Promoter Regions, Genetic , Transfection , Tumor Cells, CulturedABSTRACT
Vimentin, a member of the intermediate filament protein family, exhibits tissue- as well as development-specific expression. Transcription factors that are involved in expression of the chicken vimentin gene have been described and include a cis-acting silencer element (SE3) that is involved in the down-regulation of this gene (F. X. Farrell, C. M. Sax, and Z. E. Zehner, Mol. Cell. Biol. 10:2349-2358, 1990). In this study, we report the identification of two additional silencer elements (SE1 and SE2). We show by transfection analysis that all three silencer elements are functionally active and that optimal silencing occurs when multiple (at least two) silencer elements are present. In addition, the previously identified SE3 can be divided into three subregions, each of which is moderately active alone. By gel mobility shift assays, all three silencer elements plus SE3 subregions bind a protein which by Southwestern (DNA-protein) blot analysis is identical in molecular mass (approximately 95 kDa). DNase I footprinting experiments indicate that this protein binds to purine-rich sites. Therefore, multiple elements appear to be involved in the negative regulation of the chicken vimentin gene, which may be important in the regulation of other genes as well.
