Molecular basis of reduced albumin gene expression in hepatoma cell lines with different growth rates.

To study the relationship between expression of a differentiated function and cellular proliferation we analyzed the molecular mechanisms controlling albumin gene expression in rat liver and in rat hepatoma cell lines of different growth rates: low (MH1C1), intermediate (FAO), and high (3924A), as evaluated by both cell doubling time and histone H3 gene expression. In comparison with the liver, albumin accumulation was reduced in FAO cells and absent in MH1C1 and 3924A cells. Thus, these hepatoma cell lines do not show the inverse relationship between cellular growth rate and expression of a differentiation marker that has been often described in several hepatic and nonhepatic cellular systems. This conclusion is further reinforced by the finding that all cell lines, irrespective of their growth rate, failed to express alpha-fetoprotein mRNA, a dedifferentiation marker, and that two other liver-abundant genes, transferrin and apolipoprotein A-1, are regulated in a way similar to that of albumin. The defect in albumin accumulation was due to decreased or lacking synthesis which, in turn, was accompanied by reduction or absence of albumin mRNA. Run-on transcription assays provided evidence for diminished or absent albumin gene transcription. Southern blot analysis revealed that the structure of the albumin gene is preserved in all the tumor cell lines; however, we found a different methylation state of the albumin gene that correlated well with albumin expression.