Iterative chromosome mutation and selection as a mechanism of complete transformation of human diploid fibroblasts by SV40 T antigen.

Abstract

The acquisition of an extended lifespan and of neoplastic properties, including anchorage independence, ability to grow in low serum-containing media, morphological transformation, immortalization and tumorigenicity in nude mice were studied in 31 human fibroblast lineages transfected with plasmids containing the SV40 early genes. Plasmids were used that contained sequences for large T alone, or large T plus small t or large T plus small t plus the SV40 origin. Cells expressing large T antigen gradually acquired the ability to form colonies in low serum or to form anchorage-independent colonies. Large T antigen was sufficient to cause complete transformation to tumorigenicity if multi-step lineage evolution was obtained by prolonged serial passage and if in vivo progression was assisted by means of a gelatin sponge implantation technique. Cells derived from progressive tumors initiated in sponges showed enhanced tumorigenicity as measured by ability to obtain tumors without using sponges and with reduced latent period, higher incidence and with fewer cells inoculated. Multiple lineages of human fibroblasts have been converted to tumorigenicity without additional treatments such as transfection with activated oncogenes or exposure to carcinogens. These data, taken in conjunction with earlier studies showing that T antigen causes chromosome mutation preceding and accompanying the accumulation of the neoplastic phenotype, suggests that the T protein drives the transformation process by acting as a mutagen and cells with growth advantages were selected for in vitro and in vivo. With the possible exception of morphological transformation, the presence or absence of genes for small t and the SV40 origin were not critical for the process.