title: Targeting YB-1 in HER-2 overexpressing breast cancer cells induces apoptosis via the mTOR/STAT3 pathway and suppresses tumor growth in mice.
abstract: The Y-box binding protein-1 (YB-1) is a transcription/translation factor that is highly expressed in primary breast tumors where it is consistently associated with poor survival. It induces human epidermal growth factor receptor (her-2) along with its dimerization partner egfr by directly binding to their promoters. In addition to promoting growth by inducing receptor tyrosine kinases, YB-1 also protects cells against apoptosis through mechanisms that have not been fully revealed. Given this, we addressed whether YB-1 might be an eventual therapeutic target for breast cancer by inhibiting it with small interfering RNAs in vitro and in vivo. Inhibiting YB-1 suppressed the growth of six of seven breast cancer cell lines that had amplified her-2 or were triple negative. Importantly, targeting YB-1 induced apoptosis in BT474-m1 and Au565 breast cancer cells known to have her-2 amplifications. The potential role of signal transducers and activators of transcription 3 (STAT3) was pursued to address the underlying mechanism for YB-1-mediated survival. Inhibition of YB-1 decreased P-STAT3(S727) but not P-STAT3(Y705) or total STAT3. This was accompanied by decreased P-ERK1/2(T202/Y204), P-mTOR(S2448), and total mammalian target of rapamycin mTOR. Furthering the role of STAT3 in these cells, we show that knocking it down recapitulated the induction of apoptosis. Alternatively, constitutively active P-STAT3 rescued YB-1-induced apoptosis. Finally, targeting YB-1 with 2 different siRNAs remarkably suppressed tumor cell growth in soft agar by >90% and delayed tumorigenesis in nude mice. We conclude that HER-2 overexpressing as well as triple-negative breast cancer cells are YB-1 dependent, suggesting it may be a good therapeutic target for these exceptionally aggressive tumors.
authors.affiliation: Department of Pediatrics and Experimental Medicine, University of British Columbia, British Columbia Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: Cathy
authors.initials: C
authors.lastname: Lee
authors.forename: Jaspreet
authors.initials: J
authors.lastname: Dhillon
authors.forename: Michelle Y C
authors.initials: MY
authors.lastname: Wang
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Gao
authors.forename: Kaiji
authors.initials: K
authors.lastname: Hu
authors.forename: Eugene
authors.initials: E
authors.lastname: Park
authors.forename: Arezoo
authors.initials: A
authors.lastname: Astanehe
authors.forename: Mien-Chie
authors.initials: MC
authors.lastname: Hung
authors.forename: Peter
authors.initials: P
authors.lastname: Eirew
authors.forename: Connie J
authors.initials: CJ
authors.lastname: Eaves
authors.forename: Sandra E
authors.initials: SE
authors.lastname: Dunn
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D001483:Base Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D002455:Cell Division / Q000235:genetics*; D045744:Cell Line, Tumor; D018734:Genes, erbB-2; D008325:Mammary Neoplasms, Experimental / Q000235:genetics / Q000473:pathology*; D051379:Mice; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D034741:RNA, Small Interfering; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases
chemical_list: D002352:Carrier Proteins; D034741:RNA, Small Interfering; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; D017853:Phosphotransferases (Alcohol Group Acceptor); C546842:MTOR protein, human; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases