From the Department of Medical Science, Graduate School of Medicine, University of Hiroshima, 1-2-3 Kasumi, Minami-ku, Hiroshima City, Hiroshima 734-8553, Japan.
J Biol Chem. 2011 Jun 10;286(23):20812-22. doi: 10.1074/jbc.M110.206904. Epub 2011 Mar 17.
Peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 (Pin1) is a unique enzyme that associates with the pSer/Thr-Pro motif and catalyzes cis-trans isomerization. We identified Pin1 in the immunoprecipitates of overexpressed IRS-1 with myc and FLAG tags in mouse livers and confirmed the association between IRS-1 and Pin1 by not only overexpression experiments but also endogenously in the mouse liver. The analysis using deletion- and point-mutated Pin1 and IRS-1 constructs revealed the WW domain located in the N terminus of Pin1 and Ser-434 in the SAIN (Shc and IRS-1 NPXY binding) domain of IRS-1 to be involved in their association. Subsequently, we investigated the role of Pin1 in IRS-1 mediation of insulin signaling. The overexpression of Pin1 in HepG2 cells markedly enhanced insulin-induced IRS-1 phosphorylation and its downstream events: phosphatidylinositol 3-kinase binding with IRS-1 and Akt phosphorylation. In contrast, the treatment of HepG2 cells with Pin1 siRNA or the Pin1 inhibitor Juglone suppressed these events. In good agreement with these in vitro data, Pin1 knock-out mice exhibited impaired insulin signaling with glucose intolerance, whereas adenoviral gene transfer of Pin1 into the ob/ob mouse liver mostly normalized insulin signaling and restored glucose tolerance. In addition, it was also demonstrated that Pin1 plays a critical role in adipose differentiation, making Pin1 knock-out mice resistant to diet-induced obesity. Importantly, Pin1 expression was shown to be up-regulated in accordance with nutrient conditions such as food intake or a high-fat diet. Taken together, these observations indicate that Pin1 binds to IRS-1 and thereby markedly enhances insulin action, essential for adipogenesis.
肽基脯氨酰顺/反异构酶 NIMA 相互作用蛋白 1（Pin1）是一种与 pSer/Thr-Pro 基序结合并催化顺反异构化的独特酶。我们在过表达 myc 和 FLAG 标签的 IRS-1 的小鼠肝脏免疫沉淀物中鉴定出 Pin1，并通过过表达实验和内源性实验证实了 IRS-1 与 Pin1 之间的关联。使用缺失和点突变的 Pin1 和 IRS-1 构建体进行的分析表明，Pin1 的 N 端的 WW 结构域和 IRS-1 的 SAIN（Shc 和 IRS-1 NPXY 结合）结构域中的 Ser-434 参与了它们的结合。随后，我们研究了 Pin1 在 IRS-1 介导的胰岛素信号中的作用。在 HepG2 细胞中过表达 Pin1 可显著增强胰岛素诱导的 IRS-1 磷酸化及其下游事件：PI3K 与 IRS-1 结合和 Akt 磷酸化。相反，用 Pin1 siRNA 或 Pin1 抑制剂 Juglone 处理 HepG2 细胞可抑制这些事件。与这些体外数据非常吻合的是，Pin1 敲除小鼠表现出葡萄糖耐量受损的胰岛素信号受损，而将 Pin1 腺病毒基因转移到 ob/ob 小鼠肝脏中则可使胰岛素信号基本正常化并恢复葡萄糖耐量。此外，还证明了 Pin1 在脂肪分化中起关键作用，使 Pin1 敲除小鼠对饮食诱导的肥胖具有抗性。重要的是，Pin1 的表达显示出与营养条件（如进食或高脂肪饮食）相适应的上调。综上所述，这些观察结果表明 Pin1 与 IRS-1 结合，从而显著增强胰岛素作用，这对于脂肪生成至关重要。
