Interleukin-6 inhibits hepatic growth hormone signaling via upregulation of Cis and Socs-3.
Cytokines may cause an acquired growth hormone (GH) resistance in patients with inflammatory diseases. Anabolic effects of GH are mediated through activation of STAT5 transcription factors. We have reported that TNF-alpha suppresses hepatic GH receptor (GHR) gene expression, whereas the cytokine-inducible SH2-containing protein 1 (Cis)/suppressors of cytokine signaling (Socs) genes are upregulated by TNF-alpha and IL-6 and inhibit GH activation of STAT5. However, the relative importance of these mechanisms in inflammatory GH resistance was not known. We hypothesized that IL-6 would prevent GH activation of STAT5 and that this would involve Cis/Socs protein upregulation. GH +/- LPS was administered to TNF receptor 1 (TNFR1) or IL-6 null mice and wild-type (WT) controls. STAT5, STAT3, GHR, Socs 1-3, and Cis phosphorylation and abundance were assessed by using immunoblots, EMSA, and/or real time RT-PCR. TNF-alpha and IL-6 abundance were assessed by using ELISA. GH activated STAT5 in WT and TNFR1 or IL-6 null mice. LPS pretreatment prevented STAT5 activation in WT and TNFR1 null mice; however, STAT5 activation was preserved in IL-6 null mice. GHR abundance did not change with LPS administration. Inhibition of STAT5 activation by LPS was temporally associated with phosphorylation of STAT3 and upregulation of Cis and Socs-3 protein in WT and TNFR1 null mice; STAT3, Cis, and Socs-3 were not induced in IL-6 null mice. IL-6 inhibits hepatic GH signaling by upregulating Cis and Socs-3, which may involve activation of STAT3. Therapies that block IL-6 may enhance GH signaling in inflammatory diseases.
Denson
Lee A
LA
The Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut, USA. lee.denson@yale.edu
Held
Matthew A
MA
Menon
Ram K
RK
Frank
Stuart J
SJ
Parlow
Albert F
AF
Arnold
Dodie L
DL
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology; D013006:Growth Hormone / Q000494:pharmacology*; D017874:Immediate-Early Proteins / Q000235:genetics*; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008099:Liver / Q000254:growth & development / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D008894:Milk Proteins; D011506:Proteins / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D047888:Receptors, Tumor Necrosis Factor, Type I; D012097:Repressor Proteins; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D015854:Up-Regulation / Q000502:physiology
D015703:Antigens, CD; D004268:DNA-Binding Proteins; D013006:Growth Hormone; D017874:Immediate-Early Proteins; D015850:Interleukin-6; D008070:Lipopolysaccharides; D008894:Milk Proteins; D011506:Proteins; D012333:RNA, Messenger; D018124:Receptors, Tumor Necrosis Factor; D047888:Receptors, Tumor Necrosis Factor, Type I; D012097:Repressor Proteins; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; C491411:Socs3 protein, mouse; C494087:Stat3 protein, mouse