Modifications in alpha 2u globulin gene structure, transcription, and mRNA translation in hepatomas.

alpha 2u globulin synthesis ceases when a liver cell becomes malignant. We have compared the structure and transcription of the alpha 2u globulin genes in Morris hepatomas 5123D and 7793 with that of normal hepatic genes using alpha 2u globulin cDNA as a hybridization probe. No alpha 2u globulin mRNA was detected in hepatoma 7793 by cell-free translation, Northern blot, or R0t analysis. In hepatoma 5123D, however, a small number of alpha 2u globulin RNA sequences were detected by Northern blot and R0t analysis, but this RNA was not detectably translationally active either in vivo or in an in vitro cell-free translational system. No structural differences between normal liver and the hepatoma alpha 2u globulin genes were observed by Southern blot analysis of genomic DNA digested with restriction endonucleases Pst I, Bam HI, or Ava I. However, a general demethylation of cytosine residues in the alpha 2u globulin genes of hepatomas has been found using the restriction enzyme Hha I and the isoschizomeric pair of restriction enzymes Msp I and Hpa II. Therefore, loss of the alpha 2u globulin phenotype in these hepatomas is accompanied by extensive demethylation of DNA sequences within and/or immediately flanking the alpha 2u globulin genes.