BINDING OF WILD-TYPE AND MUTANT FORMS OF P53 PROTEIN FROM HUMAN TUMORS TO A SPECIFIC DNA-SEQUENCE OF THE FIRST INTRON OF THE H-RAS ONCOGENE

p53 is the most frequent target for genetic alterations in a wide vari ety of human cancers. The product of the p53 tumor suppressor gene bin ds to DNA and activates transcription from promoters containing its co nsensus binding site. In the accompanying paper we have found that P53 tumor suppressor protein recognizes specifically a transcriptional el ement within the human H-ras protooncogene (Spandidos DA, et al, Int J Oncol 7: 1029-1034, 1995). We transfected Saos-2 cells, which are p53 -null cells, with plasmids encoding for the wild type (wt) and for one 'hot spot' mutant (mt) of the p53 gene (H 273). Using the resulted nu clear extracts for gel retardation assays, we showed binding of both t he wild-type and the mutant form of p53 to the H-ras DNA. Furthermore, using nuclear extracts from head and neck tumors and from adjacent no rmal tissues in gel retardation assays, we found binding of both the w ild-type and the p53 mutant in the same responsive element of the H-ra s oncogene. These experimental results suggest a direct role of p53 in regulation of H-ras. Identification of cellular proto-oncogenes as me diators of the transcriptional effects of wild-type and mutant forms o f p53 gene, will be a step towards a better understanding of the role of oncogenes and once-suppressor genes in tumor promotion.