Requirement for c-ras proteins during viral oncogene transformation

Many retroviral oncogenes have been classified into one of several categories based on structure, enzymology and cellular localization(1). These genes originated from host cells and are probably derived from genes normally involved in the control of cell proliferation(2). The cellular counterparts of three oncogenes have been identified as a growth factor or growth factor receptor(3–6); related oncogenes include receptor-like membrane proteins which often express tyrosine kinase activity. These growth factor-related oncogenes are structurally and biochemically distinct from the membrane-associated ras gene family, which bind and hydrolyse GTP(7–9). Oncogenes localized primarily in the cytoplasm which probably have serine kinase activity, have also been identified(10–12). Although the structure and biochemistry of many oncogenes have been extensively studied, relatively little is known about the functional relationships of oncogene proteins within the cell. An opportunity to study such interaction is provided by the identification of a monoclonal antibody that neutralizes cellular ras proteins when microinjected into cells(13). It has been shown previously that the injected antibody inhibits the initiation of S-phase in NIH 3T3 cells(14). In the present study we injected this monoclonal antibody into NIH 3T3 cells transformed by a variety of oncogenes. The results show that transformation by three growth factor receptor-like oncogenes depends on c-ras proteins, while transformation by two cytoplasmic oncogenes appears to be independent of c-ras protein.