Regulation of expression of the rat SOCS-3 gene in hepatocytes by growth hormone, interleukin-6 and glucocorticoids mRNA analysis and promoter characterization.
Suppressors of cytokine signalling (SOCS) represent a newly discovered family of molecules that seem to play an important role in the shutting off of cytokine and possibly peptide hormone action. Thus, understanding the mechanisms controlling their expression is of cardinal importance. In the present study, we have cloned the rat SOCS-3 gene and analyzed its expression and the functioning of its promoter in hepatocytes. Expression of SOCS-3 mRNA, which is very weak in freshly isolated cells, tended to increase when hepatocytes were incubated without hormones. Growth hormone (GH) and, to a much larger extent, interleukin-6 (IL-6) rapidly activated mRNA synthesis whereas glucocorticoids (GC) strongly inhibited both basal and hormone-dependent expressions. A short promoter fragment (-137/+35) responded maximally to GH and IL-6 (a threefold stimulation for each effector) and to GC (a 70-80% inhibition), whereas longer promoter sequences supported higher basal activity and lower positive hormonal responses. Deletion and mutation analyses indicated that all hormonal responses were dependent on two cis-acting sequences termed the G-rich and the A/T-rich elements. Only the A/T-rich element was active in a heterologous context, thus behaving as a typical enhancer. Unexpectedly, the two signal transducer and activator of transcription (STAT) binding sites found immediately upstream of the G-rich motif didn't seem to participate in either GH or IL-6 effect, despite the fact that one of them strongly responded to IL-6 when placed in front of a heterologous promoter. Finally, the negative regulation of SOCS-3 promoter by GC that may contribute to gene silencing in vivo, appeared to involve interactions of the GC receptor with other transcription factors and not direct binding to DNA, as no GC-response element was found in the sequence.
Paul
C
C
INSERM U-376, Hôpital Arnaud de Villeneuve, Montpellier, France; Nutrition and Diabetes Unit, School of Medicine, The University of Louvain, Brussels, Belgium.
Seiliez
I
I
Thissen
J P
JP
Le Cam
A
A
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D003001:Cloning, Molecular; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism; D003907:Dexamethasone / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D015723:Gene Library; D013006:Growth Hormone / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D006727:Hormone Antagonists / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology*; D051379:Mice; D015735:Mifepristone / Q000494:pharmacology; D008969:Molecular Sequence Data; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D011506:Proteins / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology; D012097:Repressor Proteins; D050794:STAT1 Transcription Factor; D017384:Sequence Deletion; D015398:Signal Transduction / Q000187:drug effects; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000502:physiology; D014158:Transcription, Genetic
D016895:Culture Media, Serum-Free; D004268:DNA-Binding Proteins; D006727:Hormone Antagonists; D015850:Interleukin-6; D011506:Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D012097:Repressor Proteins; D050794:STAT1 Transcription Factor; C491411:Socs3 protein, mouse; C491410:Socs3 protein, rat; C494080:Stat1 protein, mouse; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D015735:Mifepristone; D003907:Dexamethasone; D013006:Growth Hormone; D011505:Protein-Tyrosine Kinases