| Abstract: |
The expression of Id1, a helix-loop-helix protein which inhibits the activity of basic helix-loop-helix transcription factors, is down-regulated during cellular differentiation and cell cycle withdrawal both in tissue culture models and in mouse embryos. In order to study the mechanism of control of Id1 expression, we have isolated a 210-bp enhancer clement in the upstream region of the Id1 gene whose activity recapitulates Id1 expression in C2C12 muscle cells and C3H10T1/2 fibroblasts: i.e., this element is active in proliferating cells in the presence of serum and completely inactivated upon mitogen depletion, cell cycle withdrawal, and (in the case of C2C12) induced myoblast differentiation. Using linker-scanning mutations and site- directed mutagenesis in transient transfection experiments, we have identified two functional elements within the 210-bp enhancer which are required for proper serum responsiveness. One element (A) contains a consensus Egr-1 binding site and additional flanking sequences required for optimal activity, and the other element (B) fits no known consensus. Gel shift experiments demonstrate that the protein complex binding to the A site contains Egr-1 and other proteins. This complex as well as a protein complex that binds to the B site is lost within 24 h of serum depletion, correlating with the down-regulation of id1 expression. On the basis of these findings, we propose that the regulation of the Id1 response to serum is mediated in part by the early response gene Egr-1 and as such provides a signaling link between the early-growth-response transcription factors and dominant-negative helix-loop-helix proteins. |
| Keywords: |
dna-binding proteins; nonhuman; polymerase chain reaction; protein domain; animal cell; animals; mice; complex formation; embryo; cell line; genetic transcription; cell differentiation; transcription, genetic; transfection; animalia; transcription factors; gene expression regulation; transcription regulation; molecular sequence data; fibroblasts; base sequence; dna sequence; mutagenesis, site-directed; inhibitor of differentiation protein 1; dna primers; sequence homology, nucleic acid; site directed mutagenesis; repressor proteins; immediate-early proteins; mutagenesis, insertional; muscle, skeletal; enhancer region; mice, inbred c3h; genetic regulation; zinc fingers; consensus sequence; dna protein complex; enhancer elements (genetics); promoter regions (genetics); early growth response protein 1; helix-loop-helix motifs; early response gene; priority journal; article; immediate early gene; genes, immediate-early
|
