Albumin and alpha-fetoprotein gene expression and DNA methylation in rat hepatoma cell lines

To define systems for the study of gene control and differentiation in vitro, we analyzed albumin and alpha-fetoprotein (AFP) gene expression and gene methylation in a series of rat hepatoma-derived cell lines and controls. These cell lines had several specific phenotypes: adult (high albumin and low AFP mRNA), fetal (high albumin, high AFP), embryonic (low albumin, high AFP), or undifferentiated (no albumin or AFP). The adult hepatocyte phenotype is marked by a novel 2.2-kb AFP gene transcript and high DNA methylation. In general, tumor cell lines had higher albumin and AFP gene methylation than hepatocytes in vivo. Levels of total DNA methylation did not determine the methylation patterns of specific genes, except for one cell line with hypermethylated and one with hypomethylated DNA. 5'-Hypomethylation of the AFP gene correlated with gene activity in all cases; the albumin gene showed a similar relationship, but with some exceptions. Only adult hepatocytes, not cell lines, have a unique 3'-region of AFP gene demethylation.