Prostaglandin E2 Induces interleukin-6 Expression in Human Chondrocytes via cAMP/protein Kinase A- And Phosphatidylinositol 3-kinase-dependent NF-kappaB Activation

Am J Physiol Cell Physiol. 2010 Jun;298(6):C1445-56. doi: 10.1152/ajpcell.00508.2009. Epub 2010 Mar 24.

Abstract

Elevated levels of prostaglandin (PG)E(2) and interleukin (IL)-6 have been reported in the cartilage and synovial fluid from patients with arthritic disorders. PGE(2) regulates IL-6 production in numerous different cells including macrophages and synovial fibroblasts. Although PGE(2) stimulates IL-6 expression in human chondrocytes, the underlying signaling pathway of this process has yet to be delineated. Here, we investigate the mechanism of IL-6 induction in human T/C-28a2 chondrocytes treated with exogenously added PGE(2). PGE(2) induces IL-6 mRNA and protein expression via a cAMP-dependent pathway, reaching maximal levels after 60 min of stimulation before declining to baseline levels at 6 h. Forskolin, an adenylyl cyclase activator, also stimulates IL-6 expression in human chondrocytes in a dose- and time-dependent fashion. Inhibition of downstream effectors of cAMP activity such as protein kinase A (PKA) or phosphatidylinositol 3 kinase (PI3K) blocks PGE(2)- and forskolin-induced IL-6 upregulation. Simultaneous inhibition of PKA and PI3K reduces IL-6 expression in stimulated chondrocytes well below the basal levels of untreated cells. Gel shift, supershift, and chromatin immunoprecipitation assays reveal the activation and binding of the nuclear factor (NF)-kappaB p65 subunit to the IL-6 promoter, which is markedly suppressed by selective PI3K or PKA pharmacological inhibitors. p65 knockdown completely abrogates IL-6 mRNA synthesis in PGE(2)- and forskolin-primed chondrocytes. Cumulatively, our data show that PGE(2) and forskolin induce IL-6 expression in human chondrocytes via cAMP/PKA and PI3K-dependent pathways, which in turn regulate the activation and binding of p65 to the IL-6 promoter.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adenylyl Cyclases / metabolism
  • Androstadienes / pharmacology
  • Binding Sites
  • Cells, Cultured
  • Chondrocytes / drug effects
  • Chondrocytes / enzymology*
  • Chondrocytes / immunology
  • Chromones / pharmacology
  • Colforsin / pharmacology
  • Cyclic AMP / metabolism*
  • Cyclic AMP Response Element-Binding Protein / metabolism
  • Cyclic AMP-Dependent Protein Kinases / antagonists & inhibitors
  • Cyclic AMP-Dependent Protein Kinases / metabolism*
  • Dinoprostone / metabolism*
  • Enzyme Activation
  • Enzyme Activators / pharmacology
  • Humans
  • Interleukin-6 / biosynthesis*
  • Interleukin-6 / genetics
  • Morpholines / pharmacology
  • NF-kappa B / genetics
  • NF-kappa B / metabolism*
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphoinositide-3 Kinase Inhibitors
  • Promoter Regions, Genetic
  • Protein Kinase Inhibitors / pharmacology
  • RNA Interference
  • RNA, Messenger / biosynthesis
  • Signal Transduction* / drug effects
  • Time Factors
  • Transcription Factor RelA / metabolism
  • Transcriptional Activation
  • Up-Regulation
  • Wortmannin

Substances

  • Androstadienes
  • CREB1 protein, human
  • Chromones
  • Cyclic AMP Response Element-Binding Protein
  • Enzyme Activators
  • IL6 protein, human
  • Interleukin-6
  • Morpholines
  • NF-kappa B
  • Phosphoinositide-3 Kinase Inhibitors
  • Protein Kinase Inhibitors
  • RELA protein, human
  • RNA, Messenger
  • Transcription Factor RelA
  • Colforsin
  • 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
  • Cyclic AMP
  • Cyclic AMP-Dependent Protein Kinases
  • Adenylyl Cyclases
  • Dinoprostone
  • Wortmannin