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
- 358 Downloads
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 (ERα) 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.
KeywordsCaveolin Tamoxifen Breast cancer Resistance Hormone-dependent EGFR ERK1/2 Phosphorylated-caveolin mTOR Oestrogen receptor ERα
The authors would like to thank Carol Dutkowski and Denise Barrow for their excellent technical assistance. To Dr. Andrew Hollins for construction of the recombinant caveolin-1 construct and Dr. Arwyn T. Jones for advice on subcellular fractionation. This research was generously supported by the Tenovus organisation and a Welsh School of Pharmacy studentship to NBPT. ‘Iressa’ and ‘Faslodex’ are trademarks of the AstraZeneca group of companies.
- 5.Nicholson R, Hutcheson I, Hiscox S et al (2005) Growth factor signalling and resistance to selective oestrogen receptor modulators and pure anti-oestrogens: the use of anti-growth factor therapies to treat or delay endocrine resistance in breast cancer. Endocr Relat Cancer 12:S29–S36. doi: 10.1677/erc.1.00991 CrossRefPubMedGoogle Scholar
- 9.Gee J, Robertson J, Ellis I et al (2001) Phosphorylation of ERK1/2 mitogen-activated protein kinase is associated with poor response to anti-hormonal therapy and decreased patient survival in clinical breast cancer. Int J Cancer 95:247–254. doi: 10.1002/1097-0215(20010720)95:4≤247::AID-IJC1042≥3.0.CO;2-S CrossRefPubMedGoogle Scholar
- 10.McClelland R, Barrow D, Madden T et al (2001) Enhanced epidermal growth factor receptor signalling in MCF7 breast cancer cells following long-term culture in the presence of the pure antioestrogen ICI 182, 780 (Faslodex). Endocrinology 142:2776–2788. doi: 10.1210/en.142.7.2776 CrossRefPubMedGoogle Scholar
- 14.Li S, Couet J, Lisanti M (1996) Src tyrosine kinases, Galpha subunits, and H-Ras share a common membrane-anchored scaffolding domain, caveolin. Caveolin binding negatively regulates the auto-activation of Src tyrosine kinases. J Biol Chem 271:29182–29190. doi: 10.1074/jbc.271.46.29182 CrossRefPubMedGoogle Scholar
- 19.Engelman J, Zhang X, Razani B et al (1999) p42/44 MAP kinase-dependent and -independent signaling pathways regulate caveolin-1 gene expression. Activation of Ras-MAP kinase and protein kinase a signaling cascades transcriptionally down-regulates caveolin-1 promoter activity. J Biol Chem 274:32333–32341. doi: 10.1074/jbc.274.45.32333 CrossRefPubMedGoogle Scholar
- 52.Jiang X, Yeung S (2006) Regulation of microtubule-dependent protein transport by the TSC2/mammalian target of rapamycin pathway. Cancer Res 66:2006Google Scholar