Acta Pharmacologica Sinica (2009) 30: 235-241; doi: 10.1038/aps.2008.21; published online 19th January 2009

Aim: BAG-1 is a multifunctional anti-apoptotic gene with four isoforms, and different BAG-1 isoforms have different anti-apoptotic functions.  In this study, we transfected BAG-1 isoforms into the human breast cancer cell lines Hs578T (ER negative) and MCF-7 (ER positive) to study their effect on apoptosis with or without estrogens.    

Methods: The constructed recombinant expression vectors carrying individual BAG-1 isoforms was used to transfect human breast cancer cell lines Hs578T (ER negative) and MCF-7 (ER positive).  After stable cell lines were made, a variety of apoptosis-inducing agents, including doxorubicin, docetaxel, and 5-FU, was used to treat these cell lines with or without estrogen to test the role of BAG-1.  The mechanism by which BAG-1 affected the function of Bcl-2 was exploredby using the cycloheximide chase assay.

Results: The BAG-1 p50 and p46 isoforms significantly enhanced the resistance to apoptosis in both cell lines according to flow cytometry analysis.  BAG-1 p33 and p29 failed to protect the transfected cells from apoptosis.  The cell viability assay showed that only BAG-1 p50, but not p46, p33, or p29, increased estrogen-dependent function in ER-positive cell line MCF-7.  Only BAG-1 p50 dramatically increased its anti-apoptotic ability in the presence of estrogen, while estrogen has very little effect on the anti-apoptotic ability of other BAG-1 isoforms.  In the detection of the expression of K-ras, Hsp70, cytochrome c, Raf-1, ER-α, and Bcl-2 in MCF-7 cells by Western blot, only Bcl-2 protein expression was significantly increased in MCF-7 cells transfected with BAG-1 p50 and p46, respectively.  Furthermore, the cycloheximide chase assay indicated that the degradation of Bcl-2 protein was extended in the BAG-1 p50 and p46 transfected MCF-7 cells. 

Conclusion: Distinct isoforms of BAG-1 have different anti-apoptotic functions in breast cancer cells, and that the BAG-1 p50 isoform can potentiate the role of estrogen in ER-positive breast cancer. cells in vitro and induces apoptosis by the suppression of NF-κB activation.