Enhanced expression of alpha-fetoprotein gene in cultured rat liver epithelial cells treated with N-methyl-N'-nitro-N-nitrosoguanidine.

The expression of alpha-fetoprotein (AFP) gene in a cultured normal rat liver epithelial cell line (WB-F344) and its chemical carcinogen-treated clonal derivatives was examined. WB-F344 cells expressed low levels of AFP and albumin mRNAs. Clonal cell strains and tumor cell lines derived from WB-F344 cells which had been treated multiple times with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) showed heterogeneous levels of expression of AFP mRNA. Enhanced expression was seen in 8 of 18 (44%) cell strains/lines which expressed high gamma-glutamyltranspeptidase (GGT) activity, and in 4 of 6 (67%) of GGT-negative cell strains/lines. Southern blot analyses of DNAs after digestion by HpaII endonuclease indicated that MNNG-treated cells frequently showed hypomethylation of the AFP gene. Tumor cell lines derived from WB-F344 cells which were transformed by a single treatment with MNNG consistently expressed higher levels of AFP mRNA than tumor cell lines derived from spontaneously transformed WB-F344 cells. These results suggest that enhanced expression of AFP in MNNG-treated cultured rat liver epithelial cells may be related to the effect of treatment with this carcinogen, which is known to induce DNA hypomethylation.