Protein tyrosine phosphatase 1B (PTP1B), which can directly dephosphorylate both the insulin receptor and insulin receptor substrate 1 (IRS-1), thereby terminating insulin signaling, reportedly plays an important role in insulin resistance. Accumulating evidence has demonstrated that O-GlcNAc modification regulates functions of several important components of insulin signal pathway. In this study, we identified that PTP1B is modified by O-GlcNAcylation at three O-GlcNAc sites (Ser104, Ser201, and Ser386). Palmitate acid (PA) impaired the insulin signaling, indicated by decreased phosphorylation of both serine/threonine-protein kinase B (Akt) and glycogen synthase kinase 3 beta (GSK3β) following insulin administration, and upregulated PTP1B O-GlcNAcylation in HepG2 cells. Compared with the wild-type, intervention PTP1B O-GlcNAcylation by site-directed gene mutation inhibited PTP1B phosphatase activity, resulted in a higher level of phosphorylated Akt and GSK3β, recovered insulin sensitivity, and improved lipid deposition in HepG2 cells. Taken together, our research showed that O-GlcNAcylation of PTP1B can influence insulin signal transduction by modulating its own phosphatase activity, which participates in the process of hepatic insulin resistance.

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It has been intensively studied that inflammation contributes to the insulin resistance development in obesity-induced type 2 diabetes mellitus (T2DM). In this study, we assessed the effect of karyopherin β1 (KPNβ1) in hepatic insulin resistance and the underlying mechanisms using high-fat diet (HFD) fed mice and palmitate (PA)-stimulated hepatocytes (HepG2). KPNβ1 expression is increased in the HFD fed mice liver. PA upregulated KPNβ1 expression in HepG2 cells in a time-dependent manner. PA also increased pro-inflammatory cytokines expression, including tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), and interleukin 1β (IL-1β). KPNβ1 knockdown reversed PA-induced pro-inflammatory cytokines expression and insulin-stimulated glucose uptake in HepG2 cells. In addition, KPNβ1 knockdown reduced intracellular lipid accumulation. Mechanistically, KPNβ1 transports nuclear factor kB (NF-κB) p65 from the cytoplasm to the nucleus to increase pro-inflammatory genes expression. In summary, KPNβ1 acts as a positive regulator in the NF-κB pathway to enhance palmitate-induced inflammation response and insulin resistance in HepG2 cells.

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