12 Another important finding of our study is the discovery of JNK inhibitors originated from licorice as the regulators of miR-122 for PTP1B repression; decreased levels of PTP1B allowed cells to maintain the phosphorylation of IRβ and IRS1 at tyrosine residues with the inhibition of IRS1/2 serine

phosphorylation. IsoLQ or LQ treatment caused 50%-60% inhibition of JNK1 in a cell model exposed to TNF-α (15 minutes), being consistent with our previous report.12 More important, IsoLQ treatment at 10 and 30 mg/kg inhibited HFD-induced JNK1 activation by 50% and 100%, respectively,12 which matches the repression of PTP1B shown in the Inhibitor Library mouse present study. IR sensitization was further supported by not only the inhibition of glucose production in hepatocytes, but the increase in glucose uptake by myotubes or adipocytes. The improved glucose homeostasis was strengthened by the glucose-lowering effect shown in an animal model. Our results that IsoLQ treatment decreased body weight and liver weight gains and the plasma triacylglycerol contents in HFD-fed mice also support their beneficial effects on metabolic syndrome.12 SIRT1 levels are decreased in insulin-resistant CX-4945 cells or tissues. The effect of SIRT1 on insulin resistance is also affected by the repression

of PTP1B transcription at the chromatin level.40 The agents used in the present study had the capability to activate SIRT1, which may be associated with the regulation of glucose metabolism. However, PTP1B inhibition by IsoLQ seems to be independent of SIRT1, as supported in part by our finding that IsoLQ treatment inhibited PTP1B expression even after SIRT1 inhibition using sirtinol and nicotinamide

(data not shown). Nrf2 contributes to the inhibition of LXRα-dependent lipogenesis,41 whereas AMPK activation of SIRT1 inhibits gluconeogenesis and increases energy expenditure.42 Although the enhanced energy metabolism by IsoLQ may PRKACG involve Nrf2 and/or AMPK, PTP1B repression by IsoLQ seems to be irrelevant to the molecules. This possibility is supported by the finding that the agent decreased PTP1B levels in hepatocytes deficient in Nrf2 or those treated with compound C (an AMPK inhibitor) (data not shown). In conclusion, the present study identified miR-122 dysregulation as a cause of hepatic insulin resistance, which may depend on the posttranscriptional induction of PTP1B, as mediated by JNK1-dependent inactive phosphorylation of HNF4α. Our finding that PTP1B induction can be overcome by the pharmacological inhibitors of JNK provides key information in understanding liver pathobiology and designing a therapeutic strategy for hepatic insulin resistance. The authors thank Dr. Young Woo Kim (Daegu Haany University) for the kind additional supply of IsoLQ. Additional Supporting Information may be found in the online version of this article.