Silymarin suppresses the PGE2 -induced cell migration through inhibition of EP2 activation; G protein-dependent PKA-CREB and G protein-independent Src-STAT3 signal pathways

Mol Carcinog. 2015 Mar;54(3):216-28. doi: 10.1002/mc.22092. Epub 2013 Oct 11.

Abstract

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) E2 -induced renal cell carcinoma (RCC) migration and what are the underlying mechanisms are not well elucidated. Here, we found that silymarin markedly inhibited PGE2 -stimulated migration. PGE2 induced G protein-dependent CREB phosphorylation via protein kinase A (PKA) signaling, and PKA inhibitor (H89) inhibited PGE2 -mediated migration. Silymarin reduced PGE2 -induced CREB phosphorylation and CRE-promoter activity. PGE2 also activated G protien-independent signaling pathways (Src and STAT3) and silymarin reduced PGE2 -induced phosphorylation of Src and STAT3. Inhibitor of Src (Saracatinib) markedly reduced PGE2 -mediated migration. We found that EP2, a PGE2 receptor, is involved in PGE2 -mediated cell migration. Down regulation of EP2 by EP2 siRNA and EP2 antagonist (AH6809) reduced PGE2 -inudced migration. In contrast, EP2 agonist (Butaprost) increased cell migration and silymarin effectively reduced butaprost-mediated cell migration. Moreover, PGE2 increased EP2 expression through activation of positive feedback mechanism, and PGE2 -induced EP2 expression, as well as basal EP2 levels, were reduced in silymarin-treated cells. Taken together, our study demonstrates that silymarin inhibited PGE2 -induced cell migration through inhibition of EP2 signaling pathways (G protein dependent PKA-CREB and G protein-independent Src-STAT3).

Keywords: EP2; PGE2; migration; renal carcinoma; silymarin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alprostadil / analogs & derivatives
  • Alprostadil / pharmacology
  • Antioxidants / pharmacology*
  • Benzodioxoles / pharmacology
  • Carcinoma, Renal Cell / metabolism
  • Carcinoma, Renal Cell / pathology*
  • Cell Line, Tumor
  • Cell Movement / drug effects*
  • Cell Movement / genetics
  • Cyclic AMP Response Element-Binding Protein / metabolism
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • Dinoprostone / antagonists & inhibitors*
  • Dinoprostone / metabolism
  • Down-Regulation
  • Enzyme Activation
  • Enzyme Inhibitors / pharmacology
  • GTP-Binding Proteins / metabolism
  • HCT116 Cells
  • HT29 Cells
  • Humans
  • Integrases / genetics
  • Kidney Neoplasms / metabolism
  • Kidney Neoplasms / pathology*
  • Phosphorylation
  • Prostaglandin Antagonists / pharmacology
  • Quinazolines / pharmacology
  • RNA Interference
  • RNA, Small Interfering
  • Receptors, Prostaglandin E, EP2 Subtype / antagonists & inhibitors
  • Receptors, Prostaglandin E, EP2 Subtype / biosynthesis
  • Receptors, Prostaglandin E, EP2 Subtype / genetics
  • Receptors, Prostaglandin E, EP2 Subtype / metabolism*
  • STAT3 Transcription Factor / metabolism
  • Signal Transduction / drug effects
  • Silymarin / pharmacology*
  • Wound Healing
  • Xanthones / pharmacology
  • src-Family Kinases / antagonists & inhibitors
  • src-Family Kinases / metabolism

Substances

  • Antioxidants
  • Benzodioxoles
  • CREB1 protein, human
  • Cyclic AMP Response Element-Binding Protein
  • Enzyme Inhibitors
  • PTGER2 protein, human
  • Prostaglandin Antagonists
  • Quinazolines
  • RNA, Small Interfering
  • Receptors, Prostaglandin E, EP2 Subtype
  • STAT3 Transcription Factor
  • STAT3 protein, human
  • Silymarin
  • Xanthones
  • 6-isopropoxy-9-oxoxanthene-2-carboxylic acid
  • saracatinib
  • src-Family Kinases
  • Cyclic AMP-Dependent Protein Kinases
  • Cre recombinase
  • Integrases
  • GTP-Binding Proteins
  • Alprostadil
  • butaprost
  • Dinoprostone