title: PGE2 induces IL-6 in orbital fibroblasts through EP2 receptors and increased gene promoter activity: implications to thyroid-associated ophthalmopathy.
abstract: BACKGROUND
  IL-6 plays an important role in the pathogenesis of Graves' disease and its orbital component, thyroid-associated ophthalmopathy (TAO). Orbital tissues become inflamed in TAO, a process in which prostanoids have been implicated. Orbital fibroblasts both generate and respond to PGE(2), underlying the inflammatory phenotype of these cells.
  
  
  RESULTS
  Using cultured orbital and dermal fibroblasts, we characterized the effects of PGE(2) on IL-6 expression. We found that the prostanoid provokes substantially greater cytokine synthesis in orbital fibroblasts, effects that are mediated through cell-surface EP(2) receptors and increased steady-state IL-6 mRNA levels. The pre-translational up-regulation of IL-6 results from increased gene promoter activity and can be reproduced with the PKA agonist, Sp-cAMP and blocked by interrupting the PKA pathway. PGE(2)-induced production of cAMP in orbital fibroblasts was far greater than that in dermal fibroblasts, resulting from higher levels of adenylate cyclase. PGE(2) provokes CREB phosphorylation, increases the pCREB/CREB ratio, and initiates nuclear localization of the pCREB/CREB binding protein/p300 complex (CBP) preferentially in orbital fibroblasts. Transfection with siRNAs targeting either CREB or CBP blunts the induction of IL-6 gene expression. PGE(2) promotes the binding of pCREB to its target DNA sequence which is substantially greater in orbital fibroblasts.
  
  
  CONCLUSIONS
  These results identify the mechanism underlying the exaggerated induction of IL-6 in orbital fibroblasts and tie together two proinflammatory pathways involved in the pathogenesis of TAO. Moreover, they might therefore define an attractive therapeutic target for the treatment of TAO.
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.
authors.forename: Nupur
authors.initials: N
authors.lastname: Raychaudhuri
authors.forename: Raymond S
authors.initials: RS
authors.lastname: Douglas
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Smith
mesh_terms: D000242:Cyclic AMP / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D015232:Dinoprostone / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000378:metabolism; D006111:Graves Disease / Q000378:metabolism*; D049970:Graves Ophthalmopathy / Q000378:metabolism*; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism*; D010641:Phenotype; D010766:Phosphorylation; D011453:Prostaglandins / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D058307:Receptors, Prostaglandin E, EP2 Subtype / Q000378:metabolism*; D050880:p300-CBP Transcription Factors / Q000378:metabolism
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D015850:Interleukin-6; D011453:Prostaglandins; D034741:RNA, Small Interfering; D058307:Receptors, Prostaglandin E, EP2 Subtype; D000242:Cyclic AMP; D050880:p300-CBP Transcription Factors; D015232:Dinoprostone