title: Synergy of leptin/STAT3 with HER2 receptor induces tamoxifen resistance in breast cancer cells through regulation of apoptosis-related genes.
abstract: OBJECTIVE
  Tamoxifen is a major treatment modality for estrogen receptor positive breast cancer, but the occurrence of resistance remains a problem. Recently, obesity-related leptin has been found to interfere with tamoxifen in breast cancer MCF-7 cells. In the present study we investigated the effect of leptin on three tamoxifen-treated breast cancer cell types (i.e., MDA-MB-231, MCF-7 and MCF-7/HER2).
  
  
  METHODS
  The effect of tamoxifen/leptin treatment was evaluated using a MTT cell viability assay. mRNA expression was assessed by real time PCR and protein expression by Western blotting. WWOX, Survivin and BCL2 gene promoter activities were evaluated by chromatin immunoprecipitation.
  
  
  RESULTS
  Cell viability assays revealed that estrogen receptor negative MDA-MB-231 cells were resistant, that estrogen receptor positive MCF-7 cells were sensitive and that MCF-7/HER2 cells were relatively resistant to tamoxifen, while leptin co-administration 'rescued' MCF-7 and, especially, MCF-7/HER2 cells from the anti-proliferative effect of tamoxifen. The cell lines also exhibited a different phosphorylation status of STAT3, a transcription factor that is activated by the obesity related leptin receptor b (Ob-Rb). Most importantly, chromatin immunoprecipitation assays revealed differential STAT3 binding to the anti-apoptotic BCL2 and pro-apoptotic WWOX gene promoters in MCF-7 and MCF-7/HER2 cells, leading to concomitant modifications of its mRNA/protein expression levels, thus providing a selective advantage to HER2 over-expressing MCF-7/HER2 cells after treatment with tamoxifen and tamoxifen plus leptin.
  
  
  CONCLUSIONS
  Our study provides novel evidence indicating that synergy between the leptin/Ob-Rb/STAT3 signalling pathway and the HER2 receptor protects tamoxifen-treated HER2 over-expressing cells from the inhibitory effect of tamoxifen through differential regulation of apoptosis-related genes.
authors.affiliation: Department of Biomedical Research and Technology, Institute for Research and Technology-Thessaly (I.RE.TE.TH), Centre for Research and Technology-Hellas (CE.R.T.H.), Larissa, 41222, Greece.
authors.forename: Vassilis
authors.initials: V
authors.lastname: Papanikolaou
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Stefanou
authors.forename: Stephanie
authors.initials: S
authors.lastname: Dubos
authors.forename: Ioanna
authors.initials: I
authors.lastname: Papathanasiou
authors.forename: Maria
authors.initials: M
authors.lastname: Palianopoulou
authors.forename: Vaia
authors.initials: V
authors.lastname: Valiakou
authors.forename: Aspasia
authors.initials: A
authors.lastname: Tsezou
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000502:physiology; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D020738:Leptin / Q000378:metabolism* / Q000494:pharmacology; D060888:Real-Time Polymerase Chain Reaction; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D050796:STAT3 Transcription Factor / Q000378:metabolism; D020845:Selective Estrogen Receptor Modulators / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013629:Tamoxifen / Q000494:pharmacology
chemical_list: D020738:Leptin; D018719:Erb-b2 Receptor Tyrosine Kinases; D050796:STAT3 Transcription Factor; D020845:Selective Estrogen Receptor Modulators; D013629:Tamoxifen; C494086:STAT3 protein, human; C508053:ERBB2 protein, human