Epigallocathechin-3 Gallate Selectively Inhibits the PDGF-BB–induced Intracellular Signaling Transduction Pathway in Vascular Smooth Muscle Cells and Inhibits Transformation ofsis-transfected NIH 3T3 Fibroblasts and Human Glioblastoma Cells (A172)

Abstract

Enhanced activity of receptor tyrosine kinases such as the PDGF ␤-receptor and EGF receptor has been implicated as a contributing factor in the development of malignant and nonmalignant proliferative diseases such as cancer and atherosclerosis. Several epidemiological studies suggest that green tea may prevent the development of cancer and atherosclerosis. One of the major constituents of green tea is the polyphenol epigallocathechin-3 gallate (EGCG). In an attempt to offer a possible explanation for the anti-cancer and anti-atherosclerotic activity of EGCG, we examined the effect of EGCG on the PDGF-BB-, EGF-, angiotensin II-, and FCS-induced activation of the 44 kDa and 42 kDa mitogen-activated protein (MAP) kinase isoforms (p44 mapk / p42 mapk ) in cultured vascular smooth muscle cells (VSMCs) from rat aorta. VSMCs were treated with EGCG (1-100 M) for 24 h and stimulated with the above mentioned agonists for different time periods. Stimulation of the p44 mapk /p42 mapk was detected by the enhanced Western blotting method using phospho-specific MAP kinase antibodies that recognized the Tyr204-phosphorylated (active) isoforms. Treatment of VSMCs with 10 and 50 M EGCG resulted in an 80% and a complete inhibition of the PDGF-BB-induced activation of MAP kinase isoforms, respectively. In striking contrast, EGCG (1-100 M) did not influence MAP kinase activation by EGF, angiotensin II, and FCS. Similarly, the maximal effect of PDGF-BB on the c-fos and egr-1 mRNA expression as well as on intracellular free Ca 2ϩ concentration was completely inhibited in EGCG-treated VSMCs, whereas the effect of EGF was not affected. Quantification of the immunoprecipitated tyrosine-phosphorylated PDGF-R␤, phosphatidylinositol 3Ј-kinase, and phospholipase C-␥1 by the enhanced Western blotting method revealed that EGCG treatment effectively inhibits tyrosine phosphorylation of these kinases in VSMCs. Furthermore, we show that spheroid formation of human glioblastoma cells (A172) and colony formation of sis-transfected NIH 3T3 cells in semisolid agar are completely inhibited by 20-50 M EGCG. Our findings demonstrate that EGCG is a selective inhibitor of the tyrosine phosphorylation of PDGF-R␤ and its downstream signaling pathway. The present findings may partly explain the anti-cancer and anti-atherosclerotic activity of green tea.

Baicalin inhibits PDGF-BB-stimulated vascular smooth muscle cell proliferation through suppressing PDGFRβ-ERK signaling and increase in p27 accumulation and prevents injury-induced neointimal hyperplasia

“…Baicalin belongs to a class of polyphenols. Previous studies have shown that polyphenols inhibit PDGFRβ autophosphorylation [19][20][21][22]. Although the mechanisms underlying the inhibitory effect of these polyphenols remain to be established, previous studies suggested that some of these molecules may inhibit the activation of receptor tyrosine kinase by competing with adenosine triphosphate for binding to the kinase domain of the receptor, resulting in impaired activation of key signaling intermediates [23,24].…”

Epigallocatechin Gallate Suppresses Lung Cancer Cell Growth through Ras–GTPase-Activating Protein SH3 Domain-Binding Protein 1

“…EGCG is reported to affect many different signal transduction pathways, including inhibition of various protein kinases, suppression of the activation of transcription factors such as AP-1 and NFκB, blockade of growth receptormediated pathways, and induction of cell cycle arrest or apoptosis (15)(16)(17)(18). EGCG was also found to attenuate growth factor-mediated proliferation, inhibit cell transformation, and repress angiogenesis in various cancer models (19)(20)(21).…”

EGCG, a major component of green tea, inhibits tumour growth by inhibiting VEGF induction in human colon carcinoma cells

“…EGCG, the most abundant polyphenol in green tea, has been shown to inhibit cell proliferation (Asano et al, 1997) and induce apoptosis (Hibasami et al, 1998;Paschka et al, 1998) in tumour cells. Other means by which EGCG may prevent cancer include its inhibition of urokinase activity (Jankun et al, 1997), mitogen-activated protein kinases (MAPKs) activation (Jankun et al, 1997;Ahn et al, 1999), lipooxygenase and cyclooxygenase activities (Stoner and Mukhtar, 1995), and arrest of the cell cycle (Ahmad et al, 1997;Fujiki et al, 1998) in tumour cells.…”