title: Clusterin confers resistance to TNF-alpha-induced apoptosis in breast cancer cells through NF-kappaB activation and Bcl-2 overexpression.
abstract: Secretory clusterin (sClu) is an anti-apoptotic protein that plays a role in protecting cells from Tumour-necrosis factor (TNF)-alpha-induced apoptosis. The aim of the present study was to investigate the molecular mechanisms underlying the effect of sClu on TNF-alpha-induced apoptosis  in breast cancer cells. The wild-type p53 expressing MCF-7 cell line was engineered to overexpress sClu (MCF-7/sClu), whereas the MDA-MB-231 cell line with mutant p53 was transfected with a sClu silencing siRNA (MDA-MB-231/sClu siRNA). The effects of clusterin overexpression and downregulation  on apoptosis and sensitivity to TNF-alpha were examined in vitro. Our results showed that TNF-alpha treatment increased Bcl-2 mRNA and protein levels in breast cancer cells, suggesting that Bcl-2 is directly regulated by nuclear factor-kappaB (NF-kappaB) in response to TNF-alpha. The  induction of Bcl-2 was mediated by the p65 subunit of NF-kappaB. siRNA-mediated silencing of Bcl-2 led to a significant increase in TNF-alpha-induced apoptosis. Silencing of sClu in MDA-MB-231/sClu siRNA cells abrogated TNF-alpha-mediated NF-kappaB activation and Bcl-2 overexpression, and  rendered the MDA-MB-231/sClu siRNA cells significantly more sensitive to TNF-alpha-mediated apoptosis than the parental cells. Furthermore, overexpression of sClu in MCF-7/sClu cells promoted TNF-alpha-mediated NF-kappaB activity and Bcl-2 overexpression, and rendered the MCF-7/Clu cells significantly  more resistant to TNF-alpha-mediated apoptosis. Inhibition of NF-kappaB activity or p65 and Bcl-2 expression reversed these effects. The present results suggested that sClu confers breast cancer cells resistance to TNF-alpha-induced apoptosis through NF-kappaB activation and Bcl-2 overexpression.
authors.affiliation: Department of Breast Surgery, the Affiliated Hospital of Medical College, Qingdao University, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Xingang
authors.initials: X
authors.lastname: Wang
authors.forename: Hui
authors.initials: H
authors.lastname: Zhao
authors.forename: Bo
authors.initials: B
authors.lastname: Liang
authors.forename: Qihang
authors.initials: Q
authors.lastname: Du
mesh_terms: D017209:Apoptosis; D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D051152:Clusterin / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D005260:Female; D020868:Gene Silencing; D006801:Humans; D061986:MCF-7 Cells; D050505:Mutant Proteins / Q000378:metabolism; D016328:NF-kappa B / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D051996:Transcription Factor RelA / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation
chemical_list: C495242:CLU protein, human; D051152:Clusterin; D050505:Mutant Proteins; D016328:NF-kappa B; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; C498143:RELA protein, human; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; C495901:TP53 protein, human; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha; D016159:Tumor Suppressor Protein p53