title: Synergistic induction of interleukin-6 expression by endothelin-1 and cyclic AMP in adipocytes.
abstract: BACKGROUND
  We have demonstrated previously that endothelin-1 (ET-1) may stimulate interleukin-6 (IL-6) release from 3T3-L1 adipocytes. In this study, we further examined the combined effect of ET-1 and cyclic adenosine monophosphate (cAMP) on IL-6 release.
  
  
  METHODS
  IL-6 release was measured by enzyme-linked immuosorbent assay. Reverse transcriptase-PCR and real-time PCR analyses were used to determine cellular mRNA levels. A luciferase reporter driven by promoter (-1310/+198) of mouse IL-6 gene was transfected into 3T3-L1 adipocytes to monitor IL-6 transcription.
  
  
  RESULTS
  ET-1 and cAMP induced IL-6 release in a synergistic manner that can be attributed to their synergistic induction of IL-6 gene expression, as evidenced by IL-6 mRNA analysis and the IL-6 promoter reporter assay. Both ET(A) and ET(B) receptors seem to be involved. In addition, enhanced IL-6 promoter activity can be similarly induced by ET-1 and catecholamines (epinephrine and norepinephrine). The cooperative interaction between ET-1 and cAMP on IL-6 expression seems distinctive, as no other proinflammatory cytokines, such as tumor necrosis factor-α (TNF-α) and IL-1β, are similarly affected. In fact, cAMP inhibited ET-1-stimulated TNF-α and IL-1β expressions in adipocytes. Furthermore, injection of mice with epinephrine and ET-1 induced a tremendously synergistic increase in serum IL-6 levels. Nevertheless, whereas cAMP induced IL-6 expression in RAW264.7 mouse macrophages, ET-1 had no effect on either the basal or the cAMP-induced IL-6 expression.
  
  
  CONCLUSIONS
  ET-1 and epinephrine may boost plasma IL-6 levels in mice in a synergistic manner, probably through their synergistic induction of IL-6 expression in adipocytes.
  
  
  CONCLUSIONS
  This study should provide a new perspective for treating IL-6-related diseases, especially those accompanied with elevated ET-1 and catecholamine levels.
authors.affiliation: Institute of Biochemistry and Molecular Biology, National Yang-Ming University, Taipei, Taiwan, ROC.
authors.forename: S-P
authors.initials: SP
authors.lastname: Chai
authors.forename: C-C
authors.initials: CC
authors.lastname: Juan
authors.forename: P-H
authors.initials: PH
authors.lastname: Kao
authors.forename: D-H
authors.initials: DH
authors.lastname: Wang
authors.forename: J C
authors.initials: JC
authors.lastname: Fong
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002395:Catecholamines / Q000378:metabolism; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D019332:Endothelin-1 / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005786:Gene Expression Regulation; D015850:Interleukin-6 / Q000378:metabolism*; D008156:Luciferases / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009638:Norepinephrine / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D002395:Catecholamines; D019332:Endothelin-1; D015850:Interleukin-6; D012333:RNA, Messenger; D000242:Cyclic AMP; D008156:Luciferases; D009638:Norepinephrine