Interleukin-6 inhibits growth hormone-mediated gene expression in hepatocytes.
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.
Ahmed
Tamer A
TA
Dept. of Surgery, H070, Pennsylvania State Univ, College of Medicine, Hershey, PA 17033, USA.
Buzzelli
Mark D
MD
Lang
Charles H
CH
Capen
John B
JB
Shumate
Margaret L
ML
Navaratnarajah
Maithili
M
Nagarajan
Murali
M
Cooney
Robert N
RN
D000818:Animals; D002460:Cell Line; D002843:Chromatin / Q000378:metabolism; D017930:Genes, Reporter; 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 / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism* / Q000494:pharmacology; D008156:Luciferases; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011981:Receptors, Prolactin / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D050799:STAT5 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
D002843:Chromatin; D015850:Interleukin-6; C091103:LOC299282 protein, rat; D009687:Nuclear Proteins; D012333:RNA, Messenger; D011981:Receptors, Prolactin; D011994:Recombinant Proteins; D050799:STAT5 Transcription Factor; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D008156:Luciferases