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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.

During systemic inflammation, the liver becomes unresponsive to growth hormone (GH), resulting in decreased plasma insulin-like growth factor-I (IGF-I) with concomitant reductions in lean body mass. Transgenic mice that overexpress IL-6 also demonstrate impaired growth and decreased IGF-I. To determine whether IL-6 directly inhibits GH-inducible gene expression, CWSV-1 hepatocytes were incubated with IL-6 (10 ng/ml), then stimulated with recombinant human GH (500 ng/ml, 18 h). The increase in IGF-I and serine protease inhibitor 2.1 (Spi 2.1) mRNA in GH-treated cells was inhibited by treatment with IL-6 for 24 h. To investigate potential mechanisms, we examined the effects of IL-6 on GH receptor (GHR) expression and GH signaling via the JAK/signal transducer and activator of transcription (STAT) and MAP kinase pathways. Incubation of cells with IL-6 (10 ng/ml, 24 h) had no effect on GHR abundance or signaling proteins JAK2, STAT5b, and ERK1/2. Although GH transiently increased (2- to 5-fold) the tyrosine phosphorylation of GHR, JAK2, STAT5b, and ERK1/2, IL-6 did not alter these phosphorylation events. However, nuclear protein from IL-6-treated cells demonstrated reduced STAT5 DNA binding (by EMSA) at 15 min (-20%) and 60 min (-43%) after GH stimulation. To determine whether IL-6 inhibits GH-inducible promoter activity, CWSV-1 cells were transfected with Spi 2.1 or prolactin receptor promoter luciferase vectors, incubated with or without IL-6, then stimulated with GH. The induction of both Spi 2.1 (7.5-fold) and prolactin receptor (4-fold) promoter activity by GH was inhibited by IL-6. In summary, IL-6 mediates hepatic GH resistance by a time-dependent inhibition of GH-inducible promoter activity that is associated with reductions in STAT5 DNA binding.