Interaction of BAG-1 with Retinoic Acid Receptor and Its Inhibition of Retinoic Acid-induced Apoptosis in Cancer Cells*
- Ru Liu,
- Shinichi Takayama,
- Yun Zheng,
- Barbara Froesch,
- Guo-quan Chen,
- Xin Zhang,
- John C. Reed and
- Xiao-kun Zhang‡
Abstract
BAG-1 (also known as RAP46) is an anti-apoptotic protein, which has been shown previously to interact with a number of nuclear hormone receptors, including receptors for glucocorticoid, estrogen, and thyroid hormone. We show here that BAG-1 also interacts with retinoic acid receptor (RAR). Gel retardation assays demonstrated that in vitro translated BAG-1 protein could effectively inhibit the binding of RAR but not retinoid X receptor (RXR) to a number of retinoic acid (RA) response elements (RAREs). A glutathioneS-transferase-BAG-1 fusion protein also specifically bound RAR but not RXR. Interaction of BAG-1 and RAR could also be demonstrated by yeast two-hybrid assays. In transient transfection assays, co-transfection of BAG-1 expression plasmid inhibited the transactivation activity of RAR/RXR heterodimers but not RXR/RXR homodimers. When stably expressed in breast cancer cell lines, BAG-1 inhibited binding of RAR/RXR heterodimer to a number of RAREs and suppressed RA-induced growth inhibition and apoptosis. In addition, RA-induced suppression of Bcl-2 expression was abrogated by overexpression of BAG-1. These results demonstrate that BAG-1 can regulate retinoid activities through its interaction with RAR and suggest that elevated levels of BAG-1 protein could potentially contribute to retinoid resistance in cancer cells.
Footnotes
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↵* This work was supported in part by National Institutes of Health Grant CA60988 and CA67329, the United States Army Medical Research Program Grant DAMD17-4440, the California Breast Cancer Research Program Grant 3BP-0018, and the California Tobacco-related Disease Research Program Grant 6RT-0168.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed: The Burnham Institute, Cancer Research Center, 10901 N. Torrey Pines Rd., La Jolla, CA 92037. Tel.: 619-646-3141; Fax: 619-646-3195; E-mail: xzhang{at}ljcrf.edu.
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↵1 The abbreviations used are: RAR, retinoic acid receptor; RXR, retinoid X receptor; RARE, retinoic acid response elements; TR, thyroid hormone receptor; MTT, 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide; GST, glutathioneS-transferase; tk, thymidine kinase; MHC, myosin heavy chain; CAT, chloramphenicol acetyl- transferase.
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- Received November 24, 1997.
- Revision received April 24, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
