NEOPLASTIC TRANSFORMATION AND CHARACTERIZATION OF HUMAN FIBROBLASTS BY TREATMENT WITH CO-60 GAMMA-RAYS AND THE HUMAN C-HA-RAS ONCOGENE

Human fibroblasts (KMST-6) immortalized by treatment with Co-60 gamma rays were further neoplastically transformed by transfection of the c- Ha-ras oncogene from human lung cancer. The ras-transfected cells form ed undifferentiated fibrosarcoma in nude mice. One of the tumors was r ecultured and a neoplastic human fibroblast line, KMST-6/RAS, was esta blished. To analyze multistep carcinogenesis of human cells, the cellu lar characteristics of these genetically matched immortalized (KMST-6) and neoplastic (KMST-6/RAS) cell lines were studied in detail. KMST-6 /RAS cells showed an increased saturation density, colony formation on confluent monolayers of normal human fibroblasts, proliferation in ne omycin-containing medium, anchorage-independent growth, and enhanced e xpression of the transfected c-Ha-ras oncogene, whereas the immortaliz ed cells did not demonstrate these characteristics. Unexpectedly, grow th of KMST-6/RAS cells was serum-dependent, although they were neoplas tic. Interestingly, the neoplastic cells did not show the criss-crossi ng or piling up growth pattern characteristic of transformed rodent fi broblasts.