Induction of SOCS-3 is insufficient to confer IRS-1 protein degradation in 3T3-L1 adipocytes.
Insulin receptor substrate (IRS)-1 is a key protein in insulin signaling. Several studies have shown that the expression of IRS-1 can be modulated by protein degradation via the proteasome and the degradation of IRS-1 can be related to insulin-resistant states. The degradation of IRS-1 has been shown to be induced by SOCS-1 and SOCS-3 via the ubiquitin pathway. The goal of our study was to determine if the induction of SOCS-3 correlated with increased IRS-1 degradation in cultured 3T3-L1 adipocytes. Interestingly, our studies have shown that there is little correlation between the induction in SOCS-3 expression and the degradation of IRS-1 in mature 3T3-L1 adipocytes. Our results clearly demonstrate that treatment with leukemia inhibitory factor (LIF) or cardiotrophin (CT)-1 strongly induces the expression of SOCS-3 in mature 3T3-L1 adipocytes, but does not affect the degradation of IRS-1. On the contrary, tumor necrosis factor (TNF) alpha and insulin, which very weakly induce SOCS-3 expression, have profound effects on IRS-1 degradation. In summary, our results indicate that the expression of SOCS-3 does not correlate with the degradation of IRS-1 proteins in fat cells.
He
Fang
F
Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA.
Stephens
Jacqueline M
JM
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D016207:Cytokines / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D015850:Interleukin-6 / Q000494:pharmacology; D053605:Leukemia Inhibitory Factor; D051379:Mice; D010750:Phosphoproteins / Q000378:metabolism*; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000096:biosynthesis*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D016207:Cytokines; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D015850:Interleukin-6; C526295:Irs1 protein, mouse; D053605:Leukemia Inhibitory Factor; C507838:Lif protein, mouse; D010750:Phosphoproteins; C491411:Socs3 protein, mouse; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D014409:Tumor Necrosis Factor-alpha; C092073:cardiotrophin 1