Focal adhesion kinase (FAK) phosphorylation is not required for genistein-induced FAK-beta-1-integrin complex formation

It has previously been shown that changes in the activity of focal adhesion kinase (FAK), and its binding to beta -1-integrin, accompany genistein-ind uced adhesion of prostate cells. Consumption of genistein world wide is ass ociated with a lower incidence of metastatic prostate cancer. Early human c linical trials of genistein are under way to evaluate genistein's potential causal role in this regard. Though an important cell adhesion-associated s ignaling molecule, FAK's role in regulating prostate cell adhesion was not clear. Elucidation of this process would provide important information rela ting to both biology and potential clinical endpoints. It was hypothesized that FAK activation and complex formation are temporally related in prostat e cells, and can thus be separated. Significant activation of FAK was demon strated when cells adhered to fibronectin, as compared to poly-l-lysine, th us demonstrating that beta -1-integrin plays a significant role in activati ng FAK. Neither FAK activation, nor FAK-integrin complex formation, require d beta -1-integrin ligand. However, disruption of the cellular cytoskeleton by cytochalasin D prevented FAK activation, but did not block genistein-in duced complex formation. In the face of a disrupted cytoskeleton, signaling through FAK could not be restored through either integrin cross linking, o r re-establishment of tensile forces via attachment to solid matrix. These studies demonstrate that FAK-beta -1-integrin complex formation does not re quire FAK activation, suggesting that it is an early event in prostate cell adhesion. An intact cytoskeleton is necessary for FAK activation. The func tional importance of beta -1-integrin in prostate cells is demonstrated. Cu rrent findings support plans to test genistein in prostate cancer.