Effect of insulin-like growth factor binding protein-1 on integrin signalling and the induction of apoptosis in human breast cancer cells

Interaction of epithelial cells with the extracellular matrix is mediated t hrough integrin receptors, which transmit signals regulating cell growth, d ifferentiation and death. Occupation of these receptors, via Arg-Gly-Asp (R GD) recognition sequences, leads to activation of focal adhesion kinase (FA K). We treated human breast cancer cell lines with RGD-containing peptides, whi ch can disrupt integrin attachment, and investigated alterations in FAK; ph osphorylation, cell detachment and death. Cells grown in vitro were treated with insulin-like growth factor-binding protein-1 (IGFBP-1) and a small, s ynthetic RGD-containing peptide (Gly-Arg-Gly-Asp-Thr-Pro) and its negative control peptide RGE (Arg-Gly-Glu-Ser) for either 30 min followed by immunop recipitation of cell lysates with anti-phosphotyrosine and Western immunobl otting with anti-FAK or for 24h followed by cell counting, immunocytochemis try and flow cytometry. Both IGFBP-1 (0-800 ng/ml) and the synthetic RGD-containing peptide (1-100 mu g/ml) caused significant dephosphorylation of FAK. Furthermore, after 24 h h both peptides caused detachment from the matrix and the induction of ap optosis. We conclude from these data that IGFBP-1 can interact with integrin recepto rs to induce FAK dephosphorylation and subsequently influence attachment an d cell death.