TRANSCRIPTION FACTORS NUCLEAR FACTOR-I AND SP1 INTERACT WITH THE MURINE COLLAGEN ALPHA-1(I) PROMOTER

The collagen alpha-1(I) promoter, which is efficiently transcribed in NIH 3T3 fibroblasts, contains four binding sites for trans-acting factors, as demonstrated by DNase I protection assays (D. A. Brenner, R. A. Rippe, and L. Veloz, Nucleic Acids Res. 17:6055-6064, 1989). This study characterizes the DNA-binding proteins that interact with the two proximal footprinted regions, both of which contain a reverse CCAAT box and a G + C-rich 12-bp direct repeat. Analysis by DNase I protection assays, mobility shift assays, competition with specific oligonucleotides, binding with recombinant proteins, and reactions with specific antisera showed that the transcriptional factors nuclear factor I (NF-I) and Sp1 bind to these two footprinted regions. Because of overlapping binding sites, NF-I binding and Sp1 binding appear to be mutually exclusive. Overexpression of NF-I in cotransfection experiments with the alpha-1(I) promoter in NIH 3T3 fibroblasts increased alpha-1(I) expression, while Sp1 overexpression reduced this effect, as well as basal promoter activity. The herpes simplex virus thymidine kinase promoter, which contains independent NF-I- and Sp1-binding sites, was stimulated by both factors. Therefore, expression of the collagen alpha-1(I) gene may depend on the relative activities of NF-I and Sp1.