bcl-2 gene hypomethylation and high-level expression in B-cell chronic lymphocytic leukemia

Blood. 1993 Sep 15;82(6):1820-8.


The bcl-2 gene becomes transcriptionally deregulated in the majority of low-grade non-Hodgkin lymphomas as a result of t(14;18) translocations that place the bcl-2 gene at 18q21 into juxtaposition with the Ig heavy-chain locus at 14q32. This chromosomal translocation or similar bcl-2 gene rearrangements involving the Ig light-chain genes have been reported to occur in some cases of B-cell chronic lymphocytic leukemia (B-CLL). We analyzed the structure, methylation, and expression of the bcl-2 gene in 20 cases of B-CLL or closely related variants of this lymphoproliferative disorder, including at least 16 typical examples of CD5+ B-CLL. None of the 20 specimens had evidence of bcl-2 gene rearrangements, based on Southern blot analysis using three different bcl-2 probes. However, immunoblot analysis using antibodies specific for the Bcl-2 protein showed that 14 of 20 cases (70%) contained levels of p26-Bcl-2 that were equal to or greater than those found in a t(14;18)-bearing lymphoma cell line. Furthermore, in 19 of 20 cases (95%), the Bcl-2 protein was present at levels that were 1.7- to 25-fold higher than in normal peripheral blood lymphocytes. These differences in the relative levels of Bcl-2 protein among cases of B-CLL appeared to be functionally significant, in that a preliminary analysis of 3 representative cases showed that CLL cells with higher levels of Bcl-2 protein survived longer in culture and were delayed in their onset of DNA degradation relative to CLL cells with lower Bcl-2 protein levels. Evaluation of the methylation status of the bcl-2 gene using the isoschizomers Msp I and Hpa II, and a probe corresponding to the first major exon of the gene showed complete demethylation of both copies of the bcl-2 gene in a region corresponding to a 2.4-kb Msp I fragment in all 20 cases of B-CLL. In contrast, analysis of 6 of 6 B-cell lines that harbor a t(14;18) was consistent with hypomethylation of only one of the two bcl-2 alleles. Neither copy of the bcl-2 gene was demethylated in this region in 5 of 5 lymphoid cell lines that lack this translocation. However, hypomethylation of the bcl-2 gene did not necessarily correlate with the relative levels of Bcl-2 protein present in the B-CLL cells, suggesting that additional mechanisms for regulating bcl-2 expression are involved.(ABSTRACT TRUNCATED AT 400 WORDS)

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biomarkers, Tumor / analysis*
  • Chromosome Mapping
  • Chromosomes, Human, Pair 14*
  • Chromosomes, Human, Pair 18*
  • DNA, Neoplasm / analysis
  • DNA, Neoplasm / genetics
  • DNA, Neoplasm / isolation & purification
  • DNA, Neoplasm / metabolism*
  • Gene Expression*
  • Genes, Immunoglobulin
  • Humans
  • Immunoblotting
  • Immunoglobulin Heavy Chains / genetics
  • Immunoglobulin Light Chains / genetics
  • Leukemia, Lymphocytic, Chronic, B-Cell / genetics*
  • Methylation
  • Nuclear Proteins / analysis
  • Proliferating Cell Nuclear Antigen
  • Protein-Tyrosine Kinases / biosynthesis
  • Protein-Tyrosine Kinases / genetics
  • Proto-Oncogene Proteins / analysis
  • Proto-Oncogene Proteins / biosynthesis*
  • Proto-Oncogene Proteins / genetics*
  • Proto-Oncogene Proteins c-bcl-2
  • Proto-Oncogenes*
  • Restriction Mapping
  • Translocation, Genetic*
  • Tumor Cells, Cultured


  • Biomarkers, Tumor
  • DNA, Neoplasm
  • Immunoglobulin Heavy Chains
  • Immunoglobulin Light Chains
  • Nuclear Proteins
  • Proliferating Cell Nuclear Antigen
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • Protein-Tyrosine Kinases