Nuclear factor kappaB mediates the inhibitory effects of interleukin-1 on growth hormone-inducible gene expression.
BACKGROUND
Hepatic expression of growth hormone (GH)-inducible genes serine protease inhibitor (Spi 2.1) and insulin-like growth factor (IGF)-I are inhibited by interleukin (IL)-1. The current study examines the role of the nuclear factor kappaB (NFkappaB) pathway and suppressor of cytokine signaling (SOCS)-3 expression as potential mechanisms for IL-1-mediated GH resistance.


METHODS
CWSV-1 hepatocytes were cotransfected with Spi 2.1 or IGF-1 promoter luciferase constructs and empty pCMV4 vector or dominant negative inhibitor-kappaBalpha (IkappaBalpha)S/A construct. Cells were treated with or without IL-1 and then stimulated with or without recombinant human GH. Cell extracts were assayed for luciferase activity and protein, normalized and expressed as fold-induction. CWSV-1 cells transfected with pCMV4 or IkappaBalphaS/A were treated with or without IL-1 then SOCS-3 mRNA was measured. Finally, CWSV-1 cells were cotransfected with a SOCS-3 promoter construct with or without pCMV4 or IkappaBalphaS/A and then stimulated with or without IL-1 to investigate SOCS-3 promoter activity.


RESULTS
CWSV-1 cells cotransfected with pCMV4 demonstrated a three- to fivefold induction of Spi 2.1 or IGF-1 promoter activity after GH stimulation that was almost completely inhibited by IL-1. Cotransfection with IkappaBalphaS/A increased GH-inducible Spi 2.1 and IGF-1 promoter activity, but the inhibitory effects of IL-1 on both promoters were attenuated by cotransfection with IkappaBalphaS/A. IL-1 stimulated SOCS-3 mRNA expression and promoter activity. Cotransfection with IkappaBalphaS/A increased IL-1-inducible SOCS-3 promoter activity, but not SOCS-3 mRNA or protein.


CONCLUSIONS
Signaling via the NFkappaB pathway is responsible for the inhibitory effects of IL-1 on GH-inducible gene expression by a mechanism that does not seem to involve increased SOCS-3 expression.
Buzzelli
Mark D
MD
Departments of Surgery, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
Navaratnarajah
Maithili
M
Ahmed
Tamer
T
Nagarajan
Murali
M
Shumate
Margaret L
ML
Lang
Charles H
CH
Cooney
Robert N
RN
D002478:Cells, Cultured; D005786:Gene Expression Regulation / Q000187:drug effects; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D019382:Human Growth Hormone / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000494:pharmacology*; D007375:Interleukin-1 / Q000378:metabolism / Q000494:pharmacology*; D016328:NF-kappa B / Q000187:drug effects / Q000378:metabolism*; D011336:Probability; D011401:Promoter Regions, Genetic / Q000187:drug effects; D012333:RNA, Messenger / Q000032:analysis; D012680:Sensitivity and Specificity; D015398:Signal Transduction / Q000187:drug effects; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics / Q000378:metabolism*
D007375:Interleukin-1; D016328:NF-kappa B; D012333:RNA, Messenger; C106644:SOCS3 protein, human; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I