Molecular and functional analysis of tumor-suppressor genes by transfection.

The transformed and tumorigenic phenotype of H-ras transfected rat FE-8 cells can be suppressed by cell fusion with normal rat embryo fibroblasts. Transfection into FE-8 cells of DNA prepared from normal human placenta followed by selective elimination of tumorigenic transfected cell clones resulted in the isolation of phenotypically normal revertants. These cells exhibited a fibroblastlike, normal morphology; were anchorage-dependent; and were unable to proliferate in medium with reduced serum concentrations. Their tumorigenicity was also reduced. The suppressed phenotype has been transferred in a second transfection cycle. Human repetitive DNA sequences were detected in secondary transfectant DNA. A putative human suppressor gene, designated NTS-1, has been molecularly cloned. Reintroduction of cloned NTS-1 sequences into FE-8 cells resulted in suppression of the neoplastic phenotype in spite of a high ras expression.