MALIGNANT TRANSFORMATION OF HUMAN FIBROBLAST STRAIN MSU-1.1 BY V-FES REQUIRES AN ADDITIONAL GENETIC CHANGE

To determine whether the v-fes oncogene can malignantly transform huma n fibroblasts that have acquired an infinite life span and are partial ly growth-factor-independent, we transfected cell strain MSU-1.1 with a plasmid containing the v-fes oncogene and a bacterial histidinol deh ydrogenase gene. Of the 60 independent histidinol-resistant clones iso lated and assayed for v-fes expression using a fes-specific monoclonal antibody, 6 were found to express the v-fes protein at a detectable l evel. When progeny cells from these 6 clones were further characterize d, 3 of the 6 clonal populations exhibited a significant increase in t he ability to form medium-sized colonies in agarose, but none were tum origenic in athymic mice. However, when the 6 populations were propaga ted for many generations, the same 3 populations acquired the ability to form very large colonies in agarose (greater than or equal to 100 m u m in diameter) at a frequency of 2% to 17%, and formed malignant tum ors in athymic mice. This suggests that an additional genetic change r equired for malignant transformation had been spontaneously acquired i n 3 of the v-fes -transformed cell strains. To determine whether the c hange or changes were the equivalent of an activated sis or ras proto- oncogene, we transfected the v-fes oncogene into derivative strains of MSU-1.1 that express a transfected v-sis, c-H-ros or c-N-ras oncogene , but that do not form tumors, and assayed the v-fes-expressing transf ectants for tumorigenicity. The results showed that when complemented either by a ros oncogene expressed at a somewhat enhanced level or by the v-sis oncogene, v-fes can supply the additional change required fo r malignant transformation. (C) 1995 Wiley-Liss, Inc.