The raf proto-oncogene shows significant homologies to protein kinase-C in regions involved with ligand binding and kinase regulation (activation). More specifically, the cysteine finger which exists in a duplicated form in pk-C are present in an identical context within the raf protein and show approximately 50% sequence relatedness. Raf, when non-activated, may be seen as a diffuse cytoplasmic protein. In neuroepitheliomas, where we believe raf to be activated, the protein is found concentrated in the golgi apparatus (i.e., in the particulate fraction of the cell). To test the transforming and tumorigenic potential of the c-raf-1 proto-oncogene, retroviral recombinants were constructed using Mulligan's pLJ and pZip vectors. Injection into newborn mice of infected cells, or the G418 selected psi-am clones containing the c-raf-1 sense construct, caused tumors demonstrable within 1-2 weeks. Similar short latency periods were seen with pLJ-PDGF A chain transfected psi-am cells. It is concluded that the normal c- raf-1 gene product may act in a transforming capacity in the absence of structural modifications. Raf has been found to be related to the transformed phenotype of a chemically induced (AAF) human B-cell malignancy and a laryngeal carcinoma (SQ20B). Two additional head and neck carcinoma DNAs have also been found to transform 3T3 cells, in which we subsequently identified altered human raf loci. SQ20B cells transfected with DNA capable of anti-sense raf RNA transcription are non-tumorigenic.
