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Anti-apoptotic protein BRE/BRCC45 attenuates apoptosis through maintaining the expression of caspase inhibitor XIAP in mouse Lewis lung carcinoma D122 cells
Authors:Yiu-Loon Chui  Chun-Hung Ma  Wei Li  Zhenyu Xu  Yao Yao  Frances Ka-Yin Lin  John Yeuk-Hon Chan  Kenneth Ka-Ho Lee
Affiliation:1. Department of Chemical Pathology, Sir Y.K. Pao Centre for Cancer, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China
2. The Clinical Laboratory of Maternity and Child Healthcare Hospital of Nanshan District, Shenzhen, 518052, China
3. School of Biomedical Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China
4. Key Lab of Regenerative Medicine, Ministry of Education, Jinan University, Guang Zhou, Guang Dong, China
Abstract:Brain and Reproductive Organ Expressed (BRE), or BRCC45, is a death receptor-associated antiapoptotic protein, which is also involved in DNA-damage repair, and K63-specific deubiquitination. BRE overexpression attenuates both death receptor- and stress-induced apoptosis, promotes experimental tumor growth, and is associated with human hepatocellular and esophageal carcinoma. How BRE mediates its antiapoptotic function is unknown. Here we report based on the use of a mouse Lewis lung carcinoma cell line D122 that BRE has an essential role in maintaining the cellular protein level of XIAP, which is the most potent endogenous inhibitor of the caspases functioning in both extrinsic and intrinsic apoptosis. shRNA-mediated exhaustive depletion of BRE sensitized D122 cells to apoptosis induced not only by etopoxide, but also by TNF-α even in the absence of cycloheximide, which blocks the synthesis of antiapoptotic proteins by TNF-α-activated NF-κB pathway. In BRE-depleted cells, protein level of XIAP was downregulated, but not the levels of other antiapoptotic proteins, cIAP-1, 2, and cFLIP, regulated by the same NF-κB pathway. Reconstitution of BRE restored XIAP levels and increased resistance to apoptosis. XIAP mRNA level was also reduced in the BRE-depleted cells, but the level of reduction was less profound than that of the protein level. However, BRE could not delay protein turnover of XIAP. Depletion of BRE also increased tumor cell apoptosis, and decreased both local and metastatic tumor growth. Taken together, these findings indicate that BRE and its XIAP-sustaining mechanism could represent novel targets for anti-cancer therapy.
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