Green tea polyphenols inhibit HGF induced Met signaling, mobility and invasion in breast epithelial cells Free

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Phytochemicals have become widely recognized as potential chemopreventative and therapeutic agents against a variety of malignancies. EGCG, a catechin found in green tea, has been shown to inhibit proliferation and induce apoptosis in many cell lines. EGCG is also capable of blocking growth factor signaling, including EGF and PDGF. We assessed the ability of EGCG to inhibit Hepatocyte Growth Factor (HGF) signaling in breast epithelial cells. The HGF receptor, Met, is a strong prognostic indicator of breast cancer patient outcome and survival, suggesting that therapies targeting Met may have beneficial outcomes in the clinic. We have previously demonstrated that EGCG is capable of blocking HGF induced signaling in the non-tumorigenic cell line MCF10A. Concentrations of EGCG as low as 0.6 μM were able to inhibit HGF induced Met phosphorylation and downstream activation of AKT and ERK, and pretreatment of MCF10A cells with 5.0 μM EGCG was able to block the ability of HGF to induce cell motility. In order to assess if EGCG would have similar inhibitory effects towards HGF/Met signaling in other models, we used the highly tumorigenic cell line, MDA-MB-231. Similar to MCF10A cells, HGF treatment of MDA-MB-231 cells induced rapid auto-phosphorylation of the Met receptor and activation of the downstream kinases AKT and ERK, which were sustained for approximately 2 hours. Pretreatment of MDA-MB-231 cells for half an hour with EGCG was able to inhibit HGF induced Met signaling at concentrations as low as 0.6 μM up to 30 μM. Modified Boyden Chamber assays were used to demonstrate that EGCG was capable of inhibiting HGF induced invasion of MDA-MB-231 cells at 5 μM. In vitro kinase assays demonstrated that EGCG does not directly inhibit the Met receptor. Finally, we assessed the ability of other green tea catechins on their ability to inhibit HGF induced signaling and motility. ECG blocked cell motility and signaling similar to EGCG, whereas, EGC was partially able to inhibit HGF induced motility compared to EGCG and ECG. EC was not able to inhibit HGF induced signaling or motility. These observations suggest that the R1 galloyl and the R2 hydroxyl groups are important in mediating the green tea catechins’ inhibitory effect towards HGF/Met signaling. These combined in vitro studies reveal the potential benefits of green tea polyphenols as cancer therapeutic agents that inhibit Met signaling and may block invasive cancer growth.