IDENTIFICATION OF GENES THAT EXHIBIT INCREASED EXPRESSION AFTER FLAT REVERSION OF NIH/3T3 CELLS TRANSFORMED BY HUMAN ACTIVATED HA-RAS ONCOGENE

By differential hybridization, we have isolated 14 cDNA clones corresponding to genes that are more highly expressed in the flat revertant cell line R1 than in the parental human Ha-ras oncogene-transformed NIH/3T3 cell line (EJ-NIH/3T3). From cross-hybridization experiments, we determined that 5 sequence families accounted for the 14 clones. DNA sequencing revealed that four out of five selected cDNA clones represented mitochondrial genes (cytochrome b, cytochrome c oxidase subunit II, NADH dehydrogenase subunits 1 and 4, respectively), whereas one cDNA clone was homologous to the alpha-2 (type I collagen gene. Although a Southern blot analysis of the studied cell lines showed similar copy numbers of mitochondrial genomes, the transcript levels of the mitochondrial genes were high in R1, intermediate in NIH/3T3 and low in EJ-NIH/3T3 and partially revertant R2 cell lines. Alpha-2 (type I) collagen mRNA levels were high in R1 and NIH/3T3, intermediate in R2 and low in EJ-NIH/3T3 cells. hese results suggest that a complex alteration of the expression of mitochondrial and extracellular matrix components may be closely associated with the flat reversion of the transformed cells.