title: Constitutively active ErbB2 regulates cisplatin-induced cell death in breast cancer cells via pro- and antiapoptotic mechanisms.
abstract: Despite the frequent expression of N-terminally truncated ErbB2 (ΔNErbB2/p95HER2) in breast cancer and its association with Herceptin resistance and poor prognosis, it remains poorly understood how ΔNErbB2 affects chemotherapy-induced cell death. Previously it was shown that ΔNErbB2 upregulates acid extrusion from MCF-7 breast cancer cells and that inhibition of the Na(+)/H(+) exchanger (SLC9A1/NHE1) strongly sensitizes ΔNErbB2-expressing MCF-7 cells to cisplatin chemotherapy. The aim of this study was to identify the mechanism through which ΔNErbB2 regulates cisplatin-induced breast cancer cell death, and determine how NHE1 regulates this process. Cisplatin treatment elicited apoptosis, ATM phosphorylation, upregulation of p53, Noxa (PMAIP1), and PUMA (BBC3), and cleavage of caspase-9, -7, fodrin, and PARP-1 in MCF-7 cells. Inducible ΔNErbB2 expression strongly reduced cisplatin-induced ATM- and p53-phosphorylation, augmented Noxa upregulation and caspase-9 and -7 cleavage, doubled p21(WAF1/Cip1) (CDKN1A) expression, and nearly abolished Bcl-2 expression. LC3-GFP analysis demonstrated that autophagic flux was reduced by cisplatin in a manner augmented by ΔNErbB2, yet did not contribute to cisplatin-induced death. Using knockdown approaches, it was shown that cisplatin-induced caspase-7 cleavage in ΔNErbB2-MCF-7 cells was Noxa- and caspase-9 dependent. This pathway was augmented by NHE1 inhibition, while the Na(+)/HCO3 (-) cotransporter (SLC4A7/NBCn1) was internalized following cisplatin exposure.
  
  
  CONCLUSIONS
  This work reveals that ΔNErbB2 strongly affects several major pro- and antiapoptotic pathways and provides mechanistic insight into the role of NHE1 in chemotherapy resistance. These findings have relevance for defining therapy regimens in breast cancers with ΔNErbB2 and/or NHE1 overexpression.
authors.affiliation: Department of Biology, Section for Cell and Developmental Biology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Haraldur H
authors.initials: HH
authors.lastname: Sigurðsson
authors.affiliation: Department of Biology, Section for Cell and Developmental Biology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Christina W
authors.initials: CW
authors.lastname: Olesen
authors.affiliation: Department of Biology, Section for Cell and Developmental Biology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Rie
authors.initials: R
authors.lastname: Dybboe
authors.affiliation: Department of Biology, Section for Cell and Developmental Biology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Gitte
authors.initials: G
authors.lastname: Lauritzen
authors.affiliation: Department of Biology, Section for Cell and Developmental Biology, University of Copenhagen, Copenhagen, Denmark. sfpedersen@bio.ku.dk.
authors.forename: Stine F
authors.initials: SF
authors.lastname: Pedersen
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000473:pathology; D027682:Cation Transport Proteins / Q000096:biosynthesis; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002945:Cisplatin / Q000008:administration & dosage*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D061986:MCF-7 Cells; D010766:Phosphorylation; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis* / Q000235:genetics; D027982:Sodium-Bicarbonate Symporters / Q000096:biosynthesis; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000096:biosynthesis / Q000235:genetics
chemical_list: D027682:Cation Transport Proteins; D002945:Cisplatin; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018719:Erb-b2 Receptor Tyrosine Kinases; D027982:Sodium-Bicarbonate Symporters; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; C422022:SLC4A7 protein, human; C490998:SLC9A1 protein, human; C508053:ERBB2 protein, human