A NEGATIVE ELEMENT INVOLVED IN VIMENTIN GENE-EXPRESSION

Vimentin is one member of the intermediate filament multigene family which exhibits both tissue- and developmental stage-specific expression. In vivo, vimentin is expressed in cells of mesenchymal origin. Previously, we identified both enhancer and promoter elements in the chicken vimentin gene which regulate gene expression in a positive manner. In this report, we have identified a 40-base-pair region at -568 base pairs between the proximal and distal enhancer elements which represses transcriptional activity. This silencer region can also repress the heterologous herpes simplex virus thymidine kinase promoter, which is comparable to the vimentin promoter. In addition, the element is able to function in a position- and orientation-independent manner, and the amount of repression is increased by multiple copies. Here we show by gel retardation assays and DNase I footprinting that this region binds a protein in nuclear extracts from HeLa cells. Southwestern (DNA-protein) blot analysis indicates this protein is approximately 95 kilodaltons in size. Moreover, protein distribution and activity mimic the expression pattern of vimentin during myogenesis, i.e., protein binding increases as vimentin gene expression decreases. The silencer region shares strong sequence similarity with 5'-flanking sequences found in both the human and hamster vimentin genes and with other characterized silencer elements, including the human immunodeficiency virus long terminal repeat, rat growth hormone, chicken lysozyme, and rat insulin genes. Thus, a negative element appears to bind a 95-kilodalton protein involved in regulating the tissue-specific expression of the chicken vimentin gene.