Silymarin Suppresses the PGE(2)-Induced Cell Migration Through Inhibition of EP2 Activation; G Protein-Dependent PKA-CREB and G Protein-Independent Src-STAT3 Signal Pathways

摘要

Silymarin has been known as a chemopreventive agent, and possesses multiple anti-cancer activities including induction of apoptosis, inhibition of proliferation and growth, and blockade of migration and invasion. However, whether silymarin could inhibit prostaglandin (PG) E-2-induced renal cell carcinoma (RCC) migration and what are the underlying mechanisms are not well elucidated. Here, we found that silymarin markedly inhibited PGE(2)-stimulated migration. PGE(2) induced G protein-dependent CREB phosphorylation via protein kinase A (PKA) signaling, and PKA inhibitor (H89) inhibited PGE(2)-mediated migration. Silymarin reduced PGE(2)-induced CREB phosphorylation and CRE-promoter activity. PGE(2) also activated G protien-independent signaling pathways (Src and STAT3) and silymarin reduced PGE(2)-induced phosphorylation of Src and STAT3. Inhibitor of Src (Saracatinib) markedly reduced PGE(2)-mediated migration. We found that EP2, a PGE(2) receptor, is involved in PGE(2)-mediated cell migration. Down regulation of EP2 by EP2 siRNA and EP2 antagonist (AH6809) reduced PGE(2)-inudced migration. In contrast, EP2 agonist (Butaprost) increased cell migration and silymarin effectively reduced butaprost-mediated cell migration. Moreover, PGE(2) increased EP2 expression through activation of positive feedback mechanism, and PGE(2)-induced EP2 expression, as well as basal EP2 levels, were reduced in silymarin-treated cells. Taken together, our study demonstrates that silymarin inhibited PGE(2)-induced cell migration through inhibition of EP2 signaling pathways (G protein dependent PKA-CREB and G protein-independent Src-STAT3). (c) 2013 Wiley Periodicals, Inc.