Further characterization of a thermosensitive transformation variant of mouse fibroblasts

Temperature-sensitive (ts) variants that express phenotype at low (33 degrees) but not at high (38.5 degrees) temperature were isolated from a mouse fibroblast strain C3H2K cells. Among these variants, cloned ts-12B cells showed at 38.5 degrees a density-dependent inhibition of growth typical of normal fibroblasts cultured in vitro. However, at low temperature they lost this capacity and grew to a higher saturation density. The ts variant was also temperature-sensitive as regards serum requirement: it required a higher concentration of serum for growth at 38.5 degrees than at 33 degrees. However, the cells behaved at both temperatures like the parent strain, possessing anchorage-dependence for growth and fibronectin, whereas they were like transformed cells with respect to release of high fibrinolytic activity. No type-C virus core protein p30 was detected at either temperature. Thus, various parameters of transformation in vitro were independently regulated in these variant cells.