Insulin resistance-inducing cytokines differentially regulate SOCS mRNA expression via growth factor- and Jak/Stat-signaling pathways in 3T3-L1 adipocytes.
Various cytokines, including tumor necrosis factor (TNF) alpha, growth hormone (GH) and interleukin (IL)-6, induce insulin resistance. Recently, it was demonstrated that induction of suppressor of cytokine signaling (SOCS)-3 by TNFalpha and GH is an important mechanism by which these cytokines impair insulin sensitivity. The current study investigated in 3T3-L1 adipocytes whether TNFalpha and GH also upregulate SOCS-1 and SOCS-6, which have both been shown to inhibit insulin signaling potently, and whether IL-6 might alter synthesis of SOCS-1, -3 and -6. Interestingly, 10 ng/ml TNFalpha, 500 ng/ml GH and 30 ng/ml IL-6 induced SOCS-1 mRNA time-dependently with maximal stimulation detectable after 8 h of TNFalpha and 1 h of GH and IL-6 addition respectively. Furthermore, TNFalpha and GH caused sustained upregulation of SOCS-1 for up to 24 h, whereas stimulation by IL-6 was only transient, with SOCS-1 mRNA returning to basal levels 2 h after effector addition. Induction of SOCS-1 was dose-dependent, and significant stimulation was detectable at concentrations as low as 3 ng/ml TNFalpha, 50 ng/ml GH and 10 ng/ml IL-6. Furthermore, stimulation experiments and studies using pharmacologic inhibitors suggested that the positive effect of TNFalpha, GH and IL-6 on SOCS-1 mRNA is, at least in part, mediated by Janus kinase (Jak) 2. Finally, SOCS-3 expression was dose- and time-dependently induced by IL-6, at least in part via Jak2, but none of the cytokines affected SOCS-6 expression. Taken together, our results show a differential regulation of SOCS mRNA by insulin resistance-inducing hormones, and suggest that SOCS-1, as well as SOCS-3, may be an important intracellular mediator of insulin resistance in fat cells and a potential pharmacologic target for the treatment of impaired insulin sensitivity.
Fasshauer
M
M
University of Leipzig, Department of Internal Medicine III, 04103 Leipzig, Germany.
Kralisch
S
S
Klier
M
M
Lossner
U
U
Bluher
M
M
Klein
J
J
Paschke
R
R
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western / Q000379:methods; D002352:Carrier Proteins / Q000235:genetics*; D016207:Cytokines / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects*; D013006:Growth Hormone / Q000494:pharmacology; D007333:Insulin Resistance; D015850:Interleukin-6 / Q000494:pharmacology; D053614:Janus Kinase 2; D051379:Mice; D011233:Precipitin Tests / Q000379:methods; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000235:genetics; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics*; D013268:Stimulation, Chemical; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D002352:Carrier Proteins; D016207:Cytokines; D015850:Interleukin-6; D011506:Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; C106644:SOCS3 protein, human; C473085:SOCS6 protein, human; C491590:Socs1 protein, mouse; C491411:Socs3 protein, mouse; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D013006:Growth Hormone; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2