In vitro Progression‐associated c‐H‐ras Activation in Neoplastic Hepatocyte Lines Established from SV40‐T Antigen Gene‐harboring Transgenic Mice

In order to investigate the molecular mechanisms of multistep hepatocarcinogenesis in SV40‐T antigen gene‐harboring transgenic mice, 9 hepatocellular carcinoma (HCC) lines and 10 “preneoplastic” hepatocyte lines were established from the animals and their biological and molecular changes during culture were investigated. Three of the 9 HCC lines showed progression during culture in terms of growth rate and growth capability in soft agar and in nude mice. This progression was associated with the appearance of activated c‐H‐ras oncogene. Including these 3 lines, H‐ras activation was observed in a total of 7 of the 9 HCC lines (78%), whereas it was found only in 1 of 10 (10%) “preneoplastic” hepatocyte lines. These data thus indicate that H‐ras activation may be an event occurring at a relatively late stage of hepatocarcinogenesis in this transgenic mouse system and that it may serve towards completion of the carcinogenic process together with the T‐antigen.