Expression of non‐hepatic‐type S‐adenosylmethionine synthetase isozyme in rat hepatomas induced by 3′‐methyl‐4‐dimethylaminoazobenzene

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Abstract
It is known that a high incidence of hepatocellular carcinoma in rat liver can be induced by such azo dye carcinogens as 3′‐methyl‐4‐dimethylaminoazobenzene (3′‐MeDAB). Mammalian S‐adenosylmethionine (AdoMet) synthetase exists as two isozymes, non‐hepatic‐type and liver‐type enzymes, which are the products of two different genes. We have examined the expression of two AdoMet synthetase isozyme proteins and mRNAs in rat hepatomas induced by 3′‐Me‐DAB. The levels of non‐hepatic‐type enzyme protein and mRNA are clearly induced by 3′‐Me‐DAB feeding. On the other hand, the levels of liver‐type enzyme protein and mRNA are nearly the same or slightly decreased during hepatocarcinogenesis. These results indicate that the expression of the non‐hepatic‐type isozyme gene is obviously influenced with the progression of carcinogenesis and that the non‐hepatic‐type isozyme is useful as a oncodevelopmental marker in the liver.