1. Tamoxifen treatment promotes phosphorylation of the adhesion molecules, p130Cas/BCAR1, FAK and Src, via an adhesion-dependent pathway.
- Author
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Cowell, L. N., Graham, J. D., Bouton, A. H., Clarke, C. L., and O'Neill, G. M.
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TAMOXIFEN , *PHOSPHORYLATION , *CELL adhesion molecules , *CELLULAR signal transduction , *ESTROGEN receptors , *FOCAL adhesion kinase , *PHARMACOKINETICS , *CELL migration , *PHENOTYPES - Abstract
Reports that the adhesion-associated molecule p130Cas/BCAR1 promotes resistance to tamoxifen suggested that adhesion-mediated signalling may be altered by tamoxifen treatment. We find that p130Cas/BCAR1 phosphorylation is enhanced in tamoxifen-treated estrogen receptor (ER)-positive MCF-7 breast cancer cells. The effects of estrogen and tamoxifen were assessed independently and in combination, and the results demonstrate that tamoxifen antagonizes estrogen regulation of p130Cas/BCAR1 phosphorylation. Phosphorylation correlates with tamoxifen ER antagonist effects, as phosphorylation effects are replicated by the pure antiestrogen ICI 182, 780. Correspondingly, phosphorylation is not changed in ER-negative cells exposed to tamoxifen. We show that deletion of the p130Cas/BCAR1 substrate domain substantially reduces tamoxifen-induced phosphorylation of p130Cas/BCAR1 and confers enhanced sensitivity to tamoxifen. P130Cas/BCAR1 forms a phosphorylation-dependent signalling complex with focal adhesion kinase (FAK) and Src kinase that promotes adhesion-mediated cell survival. Therefore, we examined the kinetics of p130Cas/BCAR1, Src and FAK phosphorylation over a 14-day time course and find sustained phosphorylation of these molecules after 7 days exposure to tamoxifen. Inhibition of Src kinase is shown to reduce tamoxifen-promoted p130Cas/BCAR1 phosphorylation and reduce cell viability. Stimulation of the Src/FAK/p130Cas/BCAR1 adhesion signalling pathway in tamoxifen-treated MCF-7 cells does not cause increased migration; however, there is Src-dependent phosphorylation of the cell survival molecule Akt. Correspondingly, Akt inhibition reduces cell viability in cells treated with tamoxifen. We propose that prolonged activation of adhesion-dependent signalling may confer a survival advantage in response to additional cellular insults or alternatively, may poise cells to develop a migratory phenotype in response to additional cellular cues.Oncogene (2006) 25, 7597–7607. doi:10.1038/sj.onc.1209747; published online 26 June 2006 [ABSTRACT FROM AUTHOR]
- Published
- 2006
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