Regulated Expression of the Human Mutant ras Gene After Transfection of BALB/c Mouse Embryo Fibroblast Cells

Abstract

Four continuous cell lines constructed by transfecting BALB/c mouse fibroblast cells with an expression system that has the mutant c-Ha-ras gene under control of a truncated version of the mouse metallothionein-1 (mt-1) promoter were characterized for zinc-induced phenotype switching. These cells were selected for transformation in the presence of zinc, a known in ducer of the mt-1 promoter. When the transfected cells were grown in medium depleted of zinc, there was a dramatic reduction in their soft agar cloning efficiency. Adding zinc back to the medium restored the transformed phenotype in a dose-dependent manner. Analysis of the intracellular p21 levels of induced and uninduced cells showed that zinc was modulating the expression of the transfected ras gene. In vivo studies done with syngeneic mice showed that zinc-induced cells were tumorigenic and formed metastatic lesions in the lungs of the inoculated animals.