Impaired BAX protein expression in breast cancer: Mutational analysis of the BAX and the p53 gene

We have previously shown that the pro-apoptotic BAX protein is differential ly expressed in breast cancer and in other epithelial tumors. In this line, a reduced BAX protein expression is a negative prognostic factor in variou s carcinomas including breast cancer. For p53, a trancriptional activator o f BAX in apoptosis, mutations in the coding sequence were shown to modulate BAX protein expression in cell line models on the transcriptional level. W e therefore investigated the BAX gene in 68 breast cancer specimens for the presence of mutations in the coding sequence by single-strand conformation polymorphism (SSCP)-PCR and direct sequencing. The expression of BAX prote in was assessed by immunohistochemistry. In addition, we screened for mutat ions in the exons 5-8 of the p53 gene by SSCP-PCR to assess whether mutatio ns in the DNA-binding domain of this upstream regulator of BAX gene transcr iption are responsible for differences in BAX protein expression. As previo usly observed, BAX was differentially expressed in the breast cancer sample s, but no mutations in the coding sequence of the BAX gene were found besid es a polymorphism in exon 6 at the position 552 (G->A) and additional intro nic polymorphisms. In contrast, we identified 16 of 68 (23.5%) tumors to be ar mutations in the p53 gene. In the subset of BAX-expressing tumors, the m utational inactivation of p53 did result in a reduced BAX protein expressio n (Fisher exact test, p = 0.047). Nevertheless, we identified a subset of F AX-negative tumors lacking BAX or p53 mutations. Thus, additional, not yet identified regulators, apart from p53, appear to be involved in the regulat ion of BAX protein expression. Int. J. Cancer 87:517-521, 2000. (C) 2000 Wi ley-Liss, Inc.