Tissue- and cell-specific casein gene expression. II. Relationship to site-specific DNA methylation

J Biol Chem. 1983 Sep 10;258(17):10805-11.


The relationship between DNA methylation and the expression of the gamma- and beta-casein genes was investigated in both expressing and nonexpressing tissues and in isolated tumor cell subpopulations displaying differential casein gene expression. MspI/HpaII digestions of DNA isolated from liver, a totally nonexpressing tissue, indicated that specific sites of hypermethylation existed in these genes as compared to the DNA isolated from casein-producing lactating mammary gland. The positions of these sites were mapped in the gamma-casein gene by comparing total genomic DNA Southern blots to the restriction digests of several overlapping phage clones constituting the gamma-casein gene. In contrast, the methylation status of the HhaI sites in the gamma-casein gene was found to be invariant regardless of the expression status of the gene. The inverse correlation between the hypermethylation of certain MspI/HpaII restriction sites in the casein genes and their potential expressibility was further substantiated by studies in 7,12-dimethylbenz(a)anthracene- and N-nitrosomethylurea-induced mammary carcinomas, which have an attenuated casein gene expression, and in cell subpopulations isolated from the 7,12-dimethylbenz(a)-anthracene tumor which were either depleted or enriched in casein-producing cells. Analysis of total tumor DNAs indicated that the casein genes were hypermethylated at the same sites observed in liver. However, a very faint hybridization signal was observed in the HpaII digests, suggesting cell-specific methylation differences. We have confirmed the hypomethylation of at least two of these MspI/HpaII sites within the subpopulation containing the casein-producing cells at a level consistent with the relative enrichment in that fraction. These results demonstrate differential site-specific casein gene methylation not only between tissues but also between cell subpopulations within a single tissue.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 9,10-Dimethyl-1,2-benzanthracene
  • Animals
  • Base Sequence
  • Caseins / genetics*
  • Cell Separation
  • DNA (Cytosine-5-)-Methyltransferases / metabolism
  • DNA / metabolism*
  • Female
  • Gene Expression Regulation*
  • Mammary Neoplasms, Experimental / genetics
  • Mammary Neoplasms, Experimental / pathology
  • Rats
  • Rats, Inbred Strains
  • Substrate Specificity


  • Caseins
  • 9,10-Dimethyl-1,2-benzanthracene
  • DNA
  • DNA (Cytosine-5-)-Methyltransferases