Regulation by phytoestrogens of migration, actin cytoskeleton, and signaling cascades relevant to cancer cell motility
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Genistein, daidzein, and resveratrol are polyphenolic plant compounds called phytoestrogens (PEs) because they are capable of binding and activating estrogen receptor (ER) isoforms due to structural similarity to estrogen (E2). The central hypothesis governing these investigations is that PEs can bind to plasmamembrane ERs, cross-talk with epidermal growth factor receptor (EGFR), and signal downstream to an array of molecular pathways including those involved in cell motility. This is relevant to breast cancer metastasis as PEs have been shown to have both preventative and promotional effects on breast cancer cells. The data herein investigates the role of E2, genistein, daidzein, and resveratrol in cell migration, actin cytoskeleton organization, focal adhesion assembly, as well as EGFR, focal adhesion kinase (FAK), and Rho family GTPase activation in ER (+/-) human breast cancer cells. We report that E2 and EGF increase cell migration, induce Rac-dependent lamellipodia formation, increase focal adhesion assembly, and increase EGFR, FAK, and Rac activity in ER[beta] (+) cells. We report that genistein and daidzein also increase cell migration, Rac-dependent lamellipodia formation, focal adhesion assembly, and FAK activity in ER[beta] (+) cells. Resveratrol demonstrates a biphasic concentration-dependent effect on the same signaling pathways. Resveratrol at 5 [micromolar] increases cell migration, lamellipodia formation, and increases FAK and Rac activity in ER[beta] (+) cells similar to E2. Conversely, resveratrol at 50 [micromolar] inhibits cell migration/invasion, blocks E2/EGFinduced migration, induces sustained and unpolarized filopodia, decreases focal adhesion assembly, increases EGFR activity, and decreases FAK, Cdc42, and Rac activity in ER[beta] (+) cells. The induction of filopodia by 50 [micromolar] resveratrol is partially Rho GTPaseindependent and can be observed in serum and on extracellular matrices. The induction by 50 [micromolar] resveratrol of a global, sustained extension of filopodia in conjunction with inhibition of focal adhesion assembly, as well as FAK, Cdc42, and Rac activity is hypothesized to negatively affect breast cancer cell motility. Ultimately, the elucidation of these cell structures and signaling mechanisms in response to PEs will help to determine a preventive or promotional role for plant compound-based therapies in breast cancer metastasis.