Division of Applied Biological Chemistry, Department of Bioscience and Biotechnology, Faculty of Agriculture, Kyushu University, Fukuoka 819-0395, Japan.
Molecules. 2020 Nov 23;25(22):5481. doi: 10.3390/molecules25225481.
Epigallocatechin-3--gallate (EGCG) is one of the major bioactive compounds known to be present in green tea. We previously reported that EGCG shows selective toxicity through activation of the protein kinase B (Akt)/cyclic guanosine monophosphate (cGMP)/acid sphingomyelinase (ASM) axis via targeting its receptor 67-kDa laminin receptor (67LR), which is overexpressed in cancer. However, little is known about upstream mechanisms of EGCG-elicited ASM activation. In this study we show that the proto-oncogene tyrosine-protein kinase Src, also known as c-src, plays a crucial role in the anticancer effect of EGCG. We showed that EGCG elicits phosphorylation of Src at Tyr 416, a crucial phosphorylation site for its activity, and that the pharmacological inhibition of Src impedes the upstream events in EGCG-induced cell death signaling including upregulation of Akt activity, increase in cGMP levels, and activation of ASM. Moreover, focal adhesion kinase (FAK), which is involved in the phosphorylation of Src, is colocalized with 67LR. EGCG treatment enhanced interaction of FAK and 67LR. Consistent with these findings, pharmacological inhibition of FAK significantly neutralized EGCG-induced upregulation of Akt activity and activation of ASM. Taken together, FAK/Src play crucial roles in the upstream signaling of EGCG.
表没食子儿茶素没食子酸酯 (EGCG) 是一种主要的生物活性化合物，已知存在于绿茶中。我们之前的报告表明，EGCG 通过靶向其受体 67kDa 层粘连蛋白受体 (67LR) 激活蛋白激酶 B (Akt)/环鸟苷酸 (cGMP)/酸性鞘磷脂酶 (ASM) 轴，表现出选择性毒性，67LR 在癌症中过表达。然而，对于 EGCG 诱导的 ASM 激活的上游机制知之甚少。在这项研究中，我们表明原癌基因酪氨酸蛋白激酶Src，也称为 c-src，在 EGCG 的抗癌作用中起着至关重要的作用。我们表明 EGCG 引发Src 的 Tyr 416 磷酸化，这是其活性的关键磷酸化位点，Src 的药理抑制阻碍了 EGCG 诱导的细胞死亡信号转导中的上游事件，包括 Akt 活性的上调、cGMP 水平的增加和 ASM 的激活。此外，参与Src 磷酸化的粘着斑激酶 (FAK) 与 67LR 共定位。EGCG 处理增强了 FAK 和 67LR 的相互作用。与这些发现一致，FAK 的药理抑制显著中和了 EGCG 诱导的 Akt 活性上调和 ASM 的激活。总之，FAK/Src 在 EGCG 的上游信号转导中起着至关重要的作用。
