title: NBCn1 and NHE1 expression and activity in DeltaNErbB2 receptor-expressing MCF-7 breast cancer cells: contributions to pHi regulation and chemotherapy resistance.
abstract: Altered pH-regulatory ion transport is characteristic of many cancers; however, the mechanisms and consequences are poorly understood. Here, we investigate how a truncated, constitutively active ErbB2 receptor (DeltaNErbB2) common in breast cancer impacts on the Na(+)/H(+)-exchanger NHE1 and the Na(+),HCO(3)(-)-cotransporter NBCn1 in MCF-7 human breast cancer cells and address the roles of these transporters in chemotherapy resistance. Upon DeltaNErbB2 expression, mRNA and protein levels of NBCn1, yet not of NHE1, increased several-fold, and the localization of both transporters was altered paralleling extensive morphological changes. The rate of pH(i) recovery after acid loading increased by 50% upon DeltaNErbB2 expression. Knockdown and pharmacological inhibition confirmed the involvement of both NHE1 and NBCn1 in acid extrusion. NHE1 inhibition or knockdown sensitized DeltaNErbB2-expressing cells to cisplatin-induced programmed cell death (PCD) in a caspase-, cathepsin-, and reactive oxygen species-dependent manner. NHE1 inhibition augmented cisplatin-induced caspase activity and lysosomal membrane permeability followed by cysteine cathepsin release. In contrast, NBCn1 inhibition attenuated cathepsin release and had no net effect on viability. These findings warrant studies of NHE1 as a potential target in breast cancer and demonstrate that in spite of their similar transport functions, NHE1 and NBCn1 serve different functions in MCF-7 cells.
authors.affiliation: Section for Cell and Developmental Biology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen O, Denmark. glauritzen@bio.ku.dk
authors.forename: G
authors.initials: G
authors.lastname: Lauritzen
authors.forename: M B F
authors.initials: MB
authors.lastname: Jensen
authors.forename: E
authors.initials: E
authors.lastname: Boedtkjer
authors.forename: R
authors.initials: R
authors.lastname: Dybboe
authors.forename: C
authors.initials: C
authors.lastname: Aalkjaer
authors.forename: J
authors.initials: J
authors.lastname: Nylandsted
authors.forename: S F
authors.initials: SF
authors.lastname: Pedersen
mesh_terms: D000136:Acid-Base Equilibrium / Q000235:genetics*; D000970:Antineoplastic Agents / Q000627:therapeutic use; D001692:Biological Transport / Q000235:genetics / Q000502:physiology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002403:Cathepsins / Q000378:metabolism; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D027982:Sodium-Bicarbonate Symporters / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D000970:Antineoplastic Agents; D002403:Cathepsins; D027682:Cation Transport Proteins; D050505:Mutant Proteins; D034741:RNA, Small Interfering; 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