title: Growth of hormone-dependent MCF-7 breast cancer cells is promoted by constitutive caveolin-1 whose expression is lost in an EGF-R-mediated manner during development of tamoxifen resistance.
abstract: Caveolin-1 displays both tumour-suppressor and tumour-promoter properties in breast cancer. Using characterised preclinical cell models for the transition of oestrogen-sensitive (WT-MCF-7 cells) to a tamoxifen-resistant (TAM-R cells) phenotype we examined the role caveolin-1 in the development of hormone-resistant breast cancer. The WT-MCF-7 cells showed abundant expression of caveolin-1 which potentiated oestrogen-receptor (ERalpha) signalling and promoted cell growth despite caveolin-1 mediating inhibition of ERK signalling. In TAM-R cells caveolin-1 expression was negligible, repressed by EGF-R/ERK signalling. Pharmacological inhibition of EGFR/ERK in TAM-R cells restored caveolin-1 and also resulted in the emergence of pools of phosphorylated caveolin-1. WT-MCF-7 cells exposed to tamoxifen for upto 12 weeks displayed increased caveolin-1 (peaking by week 2) followed (after week 8) by a marked decrease as the cells progress to develop a stable tamoxifen-resistant phenotype. The targeted down-regulation (siRNA) of caveolin-1 in WT-MCF-7 cells reduced growth but did not affect their sensitivity to tamoxifen, suggesting loss of caveolin-1 alone is not sufficient to confer tamoxifen-resistance. Hyperactivation of EGFR/ERK is a feature of tamoxifen-resistant breast cancer cells, a principal driver of cell growth. Recombinant expression of caveolin-1 in TAM-R cells did not affect EGFR/ERK activity, potentially due to mislocalisation of caveolin-1 through hyperactivation of the mTOR pathway or altered caveolin-1 phosphorylation. This work defines a novel role for caveolin-1 with implications for the clinical course of breast cancer and identifies caveolin-1 as a potential drug target for the treatment of early oestrogen-dependent breast cancers. Further, the loss of caveolin-1 may have benefit as a molecular signature for tamoxifen resistance.
authors.affiliation: Experimental Therapeutics, Welsh School of Pharmacy, Cardiff University, Redwood Building, King Edward VII Avenue, Cardiff CF10 3XF, UK.
authors.forename: Nicholas B P
authors.initials: NB
authors.lastname: Thomas
authors.forename: Iain R
authors.initials: IR
authors.lastname: Hutcheson
authors.forename: Lee
authors.initials: L
authors.lastname: Campbell
authors.forename: Julia
authors.initials: J
authors.lastname: Gee
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Taylor
authors.forename: Robert I
authors.initials: RI
authors.lastname: Nicholson
authors.forename: Mark
authors.initials: M
authors.lastname: Gumbleton
mesh_terms: D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D051242:Caveolin 1 / Q000096:biosynthesis* / Q000235:genetics; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020845:Selective Estrogen Receptor Modulators / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013629:Tamoxifen / Q000494:pharmacology*; D014162:Transfection
chemical_list: D051242:Caveolin 1; D034741:RNA, Small Interfering; D020845:Selective Estrogen Receptor Modulators; D013629:Tamoxifen; D066246:ErbB Receptors; D048049:Extracellular Signal-Regulated MAP Kinases