SPECIFIC-INHIBITION OF C-FOS PROTOONCOGENE EXPRESSION BY TRIPLE-HELIX-FORMING OLIGONUCLEOTIDES

The promoter region of the c-fos oncogene 5' flanking sequence contain s enhancer elements crucial for binding nuclear factors that regulate transcription following cell proliferation and differentiation. Single -stranded deoxyoligonucleotides were chosen for modulation of c-fos pr otooncogene expression because of their high-affinity binding to speci fic nucleotide sequences. We designed two oligonucleotides that form a triple-helix complex on the retinoblastoma gene product-responsible e lement of the c-fos oncogene. Modification of the DNA tripler with dim ethyl sulfate and affinity cleaving assays demonstrate that the predic ted oligonucleotides form a DNA tripler structure with the c-fos promo ter in a sequence-specific manner. Tumorigenic and non-tumorigenic fib roblasts were transiently transfected with fos-CAT plasmid modified wi th alkylating tripler-forming oligonucleotide reagents. A dramatic dep ression of CAT activity was found when the cross-linked triple helix c omplex at the retinoblastoma gene product-related site of the c-fos pr omoter was used.These experiments suggest that transcription of indivi dual genes can be selectively modulated in cell culture by sequence sp ecific tripler formation in regulatory enhancer sequences. (C) 1996 Wi ley-Liss, Inc.