bcl-2 over-expression enhances NF-κB activity and induces mmp-9 transcription in human MCF7(ADR) breast-cancer cells

Abstract

bcl-2 expression is often associated with poor prognosis in several types of tumors; however, the role of this molecule in breast cancer is still controversial. We found earlier that over-expression of bcl-2 in a human breast-cancer cell line (MCF7(ADR)) enhances its tumorigenicity and metastatic potential by inducing metastasis-associated properties such as increased secretion of the matrix metalloproteinase-9 (mmp-9). In the present study, we investigated the effect of bcl-2 over-expression on the activity of the transcription factor NF-κB, an important regulator of genes involved in tumor progression and invasion. Transient transfection experiments indicate that over-expression of bcl-2 in the MCF7(ADR) cell line, enhances NF-κB-de pendent transcriptional activity. Mobility-shift analysis revealed an increase of NF-κB DNA-binding in bcl-2-over-expressing clones that correlated with lower levels of the NF-κB cytoplasmic inhibitor IκBα. Moreover, point mutations of 2 highly conserved residues within the BH1 and BH2 domains that abrogate the interaction of bcl-2 with bax, or deletion of the N-terminal BH4 domain, completely eliminate the ability of this molecule to up-regulate NF-κB-dependent transactivation. Since mmp-9 is a NFκB- regulated gene, we also investigated whether bcl-2 overexpression up- regulated mmp-9 transcription. We found that induction of mmp-9 mRNA correlates with the activation of an mmp-9-promoter-reporter-gene construct in transient transfection assay, and a mutation of the (-600)mmp-9-NF-κB binding element abolishes this effect. The overall data indicate that bcl-2- mediated regulation of NF-κB-transcription-factor activity may represent an important mechanism for the promotion of malignant behavior in MCF-7(ADR) cells. (C) 2000 Wiley-Liss Inc.