Characterization of a cis-acting element required for efficient transcriptional activation of the collagen IV enhancer.

Two regulatory regions in the murine collagen IV enhancer were identified. Transient transfection assays delimited a 210-base pair fragment within the first intron of the alpha 1(IV) collagen gene that had significant transcriptional enhancer activity. DNase I protection and gel mobility shift confirmed that two regions, designated footprints A and B, within this fragment bound nuclear factors. Gel shift studies suggested that the CCTTATCTCTGATGG motif (A-34) in the footprint A region was important for specific nuclear factor binding. Mutations in the A-34 motif abolished factor binding as detected by gel shift and resulted in a significant decrease in enhancer activity in transient transfection assays of F9 teratocarcinoma cells. Two putative transcription factors of Mr = 37,000 and Mr = 94,000, which interact with the A-34 motif, were purified from Engelbreth-Holm-Swarm tumor tissue using DEAE-Sephacel, heparin-Sepharose, salmon sperm DNA-Sepharose, and specific A-34 oligonucleotide affinity chromatography. Southwestern analysis revealed that both of these factors were capable of binding the A-34 oligonucleotide directly and did not require additional subunits for binding. These data suggest that positively acting transcription factor(s) interact with the A-34 site in the enhancer and are required for efficient transcription of the alpha 1 and alpha 2(IV) collagen chain genes.