Macromolecular changes accompanying immortalization and tumorigenic conversion in a human fibroblast model system.

Mutagenesis of a diploid human fibroblast strain, KD, with the chemical carcinogen 4 nitroquinolin-1-oxide led to the isolation of stably immortalized neoplastic substrains. Four of these transformed strains, HuT-11, -12, -13, and -14, have been characterized in great detail with regard to morphology and changes in gene expression from the parental KD strain. The HuT-11, -12 and -13 substrains are immortalized and non-tumorigenic, in contrast to HuT-14 which is both immortalized and tumorigenic. The HuT-14 substrain expresses a defective beta-actin as a consequence of a point mutation in 1 of the 2 functional beta-actin alleles. All 4 HuT strains have induced expression of the phosphoprotein plastin and 2 EGF-related polypeptides, and down-regulated expression of the transformation-sensitive tropomyosin isoforms. KD and HuT cells expressing high levels of exogenous mutant beta-actin after gene transfection show morphological alterations. HuT-12 transfectants with excessive mutant beta-actin expression exhibit an elevated tumorigenic potential and tropomyosin-isoform switching characteristic of the tumorigenic HuT-14 strain.