Background: The bcl-2 gene encodes a protein that blocks apoptosis and might help to promote tumor development. It is expressed in a high percentage of breast tumors and is associated with good prognostic features. However, the mechanisms that regulate bcl-2 expression in breast carcinoma are unknown. Moreover, immunohistochemical detection of bcl-2 is related inversely to p53 expression. This notwithstanding, the immunohistochemical detection of p53 does not always correlate with the detection of p53 gene mutations. The authors studied the molecular organization of bcl-2 as well as the methylation status of its CpG island and analyzed the correlation between bcl-2 expression and p53 gene mutations.
Methods: The molecular organization of the bcl-2 gene and the methylation pattern of its CpG island were analyzed by Southern blot analysis. In addition, immunohistochemical analysis of bcl-2 and p53 protein expression was performed. Finally, the presence of mutations at exons 5-9 of the p53 gene were analyzed by polymerase chain reaction and single-strand conformation polymorphism.
Results: No molecular abnormality was found at the bcl-2 locus in cases of sporadic breast carcinoma. Moreover, loss of heterozygosity analysis failed to detect any allelic loss in the study cases. It also was found that the bcl-2 CpG island was demethylated in all cases. These results point to a lack of correlation between bcl-2 protein expression and the presence of p53 gene mutations.
Conclusions: The level of bcl-2 expression in breast carcinoma is not associated with any somatic abnormality or epigenetic change at the bcl-2 locus. Conversely, although bcl-2 expression is related inversely to p53 protein expression, the analysis of p53 mutations (limited to exons 5-9) failed to demonstrate any relationship between p53 mutations and bcl-2 protein expression.