The fact that disruption of
integrin-extracellular matrix contacts leads to cell death, has converted cell adhesion into a potential target for the control of invasive
cancer. In this work, we studied the functional consequences of the interference with the activity of the very late activation
antigen (VLA) family of
integrins in human
breast cancer cell lines of distinct
malignancy. The alpha2beta1-mediated adhesion reduced the entry of highly malignant,
hormone-independent
breast cancer cells into apoptosis. Adhesion of
breast cancer cells through the VLA
integrins alpha2beta1 and alpha5beta1 was significantly reduced by an apoptosis-inducing natural
triterpenoid,
dehydrothyrsiferol (DT), when studied on low amounts of extracellular matrix. This effect was dose-dependent, not related to cell toxicity and not shared with apoptosis-inducing standard chemotherapeutics, such as
doxorubicin and
taxol. The compound did not affect either the cell surface expression level of VLA
integrins or cell distribution of
vinculin and actin during cell spreading. In addition, neither phosphorylation of the
focal adhesion kinase pp125FAK on Tyr397 nor the
protein kinase B (Akt/PKB) on Ser473 was significantly altered by DT. The
integrin activation level, assessed by binding of soluble
collagen to the
alpha2beta1 integrin, was reduced upon cell treatment with DT. Importantly, the TS2/16, an anti-beta1 activating
monoclonal antibody was able to rescue DT-treated cells from apoptosis. Since the activation state of
integrins is increasingly recognized as an essential factor in
metastasis formation, findings presented herein reveal that the chemical regulation of
integrin affinity may be a potential therapeutic strategy in
cancer therapy.