Evidence against ras activation in human ovarian carcinomas

Activation of ras genes in human ovarian carcinomas and ovarian carcinoma cell lines was tested by transfection of NIH 3T3 cells with high molecular weight DNA extracted from fresh tumors or from cell lines. Of 18 ovarian tumors and tumor cell lines that were exhaustively tested, only one yielded DNA active in focus-induction in this assay. Southern blot analysis of DNA in serially transformed NIH 3T3 foci revealed restriction fragments that hybridized with a probe specific for the human N-ras oncogene and with human repetitive (Alu) sequences. Individually transformed foci contained N-ras hybridizing fragments of different sizes. Northern blots of RNA extracted from different transformants revealed the expression of different transcripts hybridizing with the N-ras probe. The transformants also expressed a 700 base RNA that hybridized with a human B-lym probe. The low prevalence of ras activation in ovarian tumors as measured by transforming capability suggests that ras activation does not play an important role in the development of most human ovarian tumors.