Thyroid-Stimulating Hormone Inhibits Insulin Receptor Substrate-1 Expression and Tyrosyl Phosphorylation in 3T3-L1 Adipocytes by Increasing NF-κB DNA-Binding Activity

Figure 4

TSH decreased tyrosine phosphorylation of IRS-1 in 3T3-L1 adipocytes. Cells were pretreated with 100 nM insulin for 10 min and then treated with different concentrations of TSH (0.01, 0.1, and 1 mIU/ml) for 24 h. IRS-1 levels in adipocytes were quantified by Western blotting, and tyrosine phosphorylation was measured by immunoprecipitation. The relative expression levels of IRS-1 and IRS-1-tyr in each treatment group were calculated using β-tubulin as the standard. Treatment with various concentrations of bovine TSH (0.01, 0.1, and 1 mIU/ml) increased the ratio of phosphorylated IRS-1 to total IRS-1 in a dose-dependent manner in 3T3-L1 adipocytes. These data indicated that TSH suppressed IRS-1 tyrosyl phosphorylation in 3T3-L1 adipocytes ( for all comparisons).