Tamoxifen treatment promotes phosphorylation of the adhesion molecules, p130Cas/BCAR1, FAK and Src, via an adhesion-dependent pathway.
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.
Cowell
L N
LN
Focal Adhesion Biology Group, The Oncology Research Unit, The Children's Hospital at Westmead, and Discipline of Paediatrics and Child Health, University of Sydney, Westmead, New South Wales, Australia.
Graham
J D
JD
Bouton
A H
AH
Clarke
C L
CL
O'Neill
G M
GM
D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D050719:Crk-Associated Substrate Protein / Q000378:metabolism*; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism*; D006801:Humans; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013629:Tamoxifen / Q000494:pharmacology*; D019061:src-Family Kinases / Q000378:metabolism*
D018931:Antineoplastic Agents, Hormonal; C493841:BCAR1 protein, human; D015815:Cell Adhesion Molecules; D050719:Crk-Associated Substrate Protein; D011960:Receptors, Estrogen; D013629:Tamoxifen; D051416:Focal Adhesion Protein-Tyrosine Kinases; D016392:Proto-Oncogene Proteins pp60(c-src); D019061:src-Family Kinases; D051057:Proto-Oncogene Proteins c-akt