Daisuke Umeda

Green tea polyphenol epigallocatechin-3-gallate signaling pathway through 67-kDa laminin receptor.

(–)-Epigallocatechin-3-gallate (EGCG), the principal polyphenol in green tea, has been shown to be a potent chemopreventive agent. Recently, 67-kDa laminin receptor (67LR) has been identified as a cell surface receptor for EGCG that mediates the anticancer activity of EGCG. Indeed, expression of 67LR confers EGCG responsiveness to tumor cells; however, the molecular basis for the anticancer activity of EGCG in vivo is not entirely understood. Here we show that (i) using a direct genetic screen, eukaryotic translation elongation factor 1A (eEF1A) is identified as a component responsible for the anticancer activity of EGCG; (ii) through both eEF1A and 67LR, EGCG induces the dephosphorylation of myosin phosphatase targeting subunit 1 (MYPT1) at Thr-696 and activates myosin phosphatase; and (iii) silencing of 67LR, eEF1A, or MYPT1 in tumor cells results in abrogation of EGCG-induced tumor growth inhibition in vivo. Additionally, we found that eEF1A is up-regulated by EGCG through 67LR. Overall, these findings implicate both eEF1A and MYPT1 in EGCG signaling for cancer prevention through 67LR.

The impact of the 67 kDa laminin receptor on both cell-surface binding and anti-allergic action of tea catechins

Here, we investigated the structure-activity relationship of major green tea catechins and their corresponding epimers on cell-surface binding and inhibitory effect on histamine release. Galloylated catechins; (-)-epigallocatechin-3-O-gallate (EGCG), (-)-gallocatechin-3-O-gallate (GCG), (-)-epicatechin-3-O-gallate (ECG), and (-)-catechin-3-O-gallate (CG) showed the cell-surface binding to the human basophilic KU812 cells by surface plasmon resonance analysis, but their non-galloylated forms did not. Binding activities of pyrogallol-type catechins (EGCG and GCG) were higher than those of catechol-type catechins (ECG and CG). These patterns were also observed in their inhibitory effects on histamine release. Previously, we have reported that biological activities of EGCG are mediated through the binding to the cell-surface 67kDa laminin receptor (67LR). Downregulation of 67LR expression caused a reduction of both activities of galloylated catechins. These results suggest that both the galloyl moiety and the B-ring hydroxylation pattern contribute to the exertion of biological activities of tea catechins and their 67LR-dependencies.

Involvement of 67-kDa laminin receptor-mediated myosin phosphatase activation in antiproliferative effect of epigallocatechin-3-O-gallate at a physiological concentration on Caco-2 colon cancer cells

Previously we reported that 67-kDa laminin receptor (67LR) mediates epigallocatechin-3-O-gallate (EGCG)-induced cell growth inhibition and reduction of myosin regulatory light chain (MRLC) phosphorylation at Thr-18/Ser-19, which is important for cytokinesis. Here, we found that human colon adenocarcinoma Caco-2 cells exhibited higher expression level of 67LR and EGCG at a physiologically achievable concentration (1 microM) significantly accumulated the cells in G(2)/M phase without affecting expression of Wnt-signaling components. We also found that myosin phosphatase targeting subunit 1 (MYPT1) phosphorylation at Thr-696, which inhibits myosin phosphatase and promotes MRLC phosphorylation, was reduced in response to 1 microM EGCG. 67LR knockdown by RNA interference abolished the inhibitory effects of 1 microM EGCG on cell cycle progression and the phosphorylation of MRLC and MYPT1. These results suggest that through 67LR, EGCG at a physiological concentration can activate myosin phosphatase by reducing MYPT1 phosphorylation and that may be involved in EGCG-induced cell growth inhibition.

Dietary apigenin attenuates the development of atopic dermatitis-like skin lesions in NC/Nga mice.

One of the flavones, apigenin has various physiological functions including anti-inflammatory activities. Atopic dermatitis (AD) is a chronically relapsing inflammatory disorder that is characterized by pruritic and eczematous skin lesions. To evaluate the anti-allergic effect of apigenin in vivo, we examined the effect of dietary apigenin on picrylchloride (PiCl)-induced AD-like pathology in NC/Nga mice. NC/Nga mice were fed experimental diets containing apigenin from Day 18 after sensitized with PiCl for 4 weeks. Dietary apigenin significantly alleviated the development of skin lesions, accompanied by lower serum immunoglobulin (Ig) G1 and IgE levels in NC/Nga mice. Interferon (IFN)-gamma mRNA expression level in spleen cells from NC/Nga mice was reduced by apigenin feeding. Moreover, interleukin 4-induced signal transducers and activators of transcription 6 phosphorylation in primary spleen cells from BALB/c mice was inhibited by treatment with apigenin. These results suggest that apigenin attenuates exacerbation of AD-like symptoms in part through the reduction of serum IgE level and IFN-gamma expression in NC/Nga mice.

67-kDa Laminin Receptor-dependent Protein Phosphatase 2A (PP2A) Activation Elicits Melanoma-specific Antitumor Activity Overcoming Drug Resistance

Background: Green tea polyphenol (−)-epigallocatechin-3-O-gallate (EGCG) inhibits melanoma proliferation in a cancer-specific manner through 67-kDa laminin receptor (67LR). Results: Identified protein phosphatase 2A (PP2A) as a critical downstream factor of 67LR. Conclusion: Targeting 67LR/PP2A elicits activation of tumor suppressor Merlin and inhibition of mTOR pathway overcoming drug resistance. Significance: 67LR/PP2A may be a promising therapeutic target for melanomas. The Ras/Raf/MEK/ERK pathway has been identified as a major, druggable regulator of melanoma. Mutational activation of BRAF is the most prevalent genetic alteration in human melanoma, resulting in constitutive melanoma hyperproliferation. A selective BRAF inhibitor showed remarkable clinical activity in patients with mutated BRAF. Unfortunately, most patients acquire resistance to the BRAF inhibitor, highlighting the urgent need for new melanoma treatment strategies. Green tea polyphenol (−)-epigallocatechin-3-O-gallate (EGCG) inhibits cell proliferation independently of BRAF inhibitor sensitivity, suggesting that increased understanding of the anti-melanoma activity of EGCG may provide a novel therapeutic target. Here, by performing functional genetic screening, we identified protein phosphatase 2A (PP2A) as a critical factor in the suppression of melanoma cell proliferation. We demonstrated that tumor-overexpressed 67-kDa laminin receptor (67LR) activates PP2A through adenylate cyclase/cAMP pathway eliciting inhibitions of oncoproteins and activation of tumor suppressor Merlin. Activating 67LR/PP2A pathway leading to melanoma-specific mTOR inhibition shows strong synergy with the BRAF inhibitor PLX4720 in the drug-resistant melanoma. Moreover, SET, a potent inhibitor of PP2A, is overexpressed on malignant melanoma. Silencing of SET enhances 67LR/PP2A signaling. Collectively, activation of 67LR/PP2A signaling may thus be a novel rational strategy for melanoma-specific treatment.

H89 (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide) induces reduction of myosin regulatory light chain phosphorylation and inhibits cell proliferation.

H89 (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide) is a compound characterized in vitro as a potent and selective inhibitor of protein kinase A (PKA). In this study, we found that H89 reduced the phosphorylation of the myosin regulatory light chain (MRLC) at Thr-18/Ser-19 and induced disassembly of stress fibers in HeLa cells. In addition, we found that H89 induced not only reduction of the MRLC phosphorylation but also cell growth inhibition in several human cancer cell lines. Recently H89 has been found to inhibit Rho-kinase with potency similar to or greater than that for inhibition of PKA. Indeed, the effects of H89 on both the MRLC phosphorylation and actin cytoskeleton organization were nearly identical to those of Rho-kinase inhibitor Y-27632. However, unlike H89, Y-27632 did not affect cell growth of HeLa cells. Further, when the myosin phosphatase targeting subunit 1 (MYPT1) expression was silenced by RNA interference in HeLa cells, the suppressive effect of H89 on the MRLC phosphorylation was not affected, while H89-induced cell growth inhibition was blocked. These results suggest that H89-induced reduction of the MRLC phosphorylation results from inhibition of Rho-kinase and that H89-induced cell growth inhibition is independent of reduction of the MRLC phosphorylation.

Involvement of Myosin Light Chain in Suppressive Effect of Epigallocatechin-3- O -Gallate on Histamine Release from the Human Basophilic KU812 Cells

Allergy is a hyperimmune response, and histamine release from basophils and mast cells plays crucial role in the IgE-mediated allergic response. Epigallocatechin-3-O-gallate (EGCg) is a major polyphenolic compound of green tea and has various physiological functions. We have previously reported that EGCg has an inhibitory effect on histamine release from the human basophilic KU812 cells. Although the mechanism that regulates histamine release remains to be clarified, it has been reported that the 20 kDa myosin light chains (MLC20) are involved in the cytoskeletal rearrangements associated with histamine release from mast cells. The MLC20 has been reported to be phosphorylated by protein kinases such as myosin light chain kinase (MLCK) and Rho kinase (ROCK). To clarify this inhibitory mechanism, we examined the effect of EGCg on MLC20 phosphorylation. KU812 cells were stimulated with calcium ionophore A23187 in the presence of various concentrations of EGCg. Immunoblot analysis showed that EGCg reduced the level of MLC20 phosphorylation in a dose-dependent manner. Without A23187 stimulation, EGCg also reduced the level of MLC20 phosphorylation. These results suggest that EGCg may inhibit histamine release through a potent reduction of phosphorylated MLC20.