Mechanisms of cross talk between insulin and adiponectin signaling pathways

描述(申请人提供)：脂联素是一种主要由脂肪细胞产生的多肽激素，目前被广泛认为是一种具有抗糖尿病、抗炎和心脏保护作用的胰岛素增敏剂。然而，脂联素增敏胰岛素信号和作用的分子机制在很大程度上仍不清楚。我们最近发现了一个含有PLECKstrin同源(PH)和磷酸酪氨酸结合(PTB)结构域的蛋白APPL1，它直接与脂联素受体AdipoR1和AdipoR2相互作用。RNAi抑制APPL1不仅抑制脂联素信号转导，而且还抑制胰岛素刺激的Akt磷酸化，提示APPL1可能在脂联素和胰岛素信号转导通路之间的串扰中发挥重要作用(Mao等，2006，NAT。细胞生物，8,516-523)。与这一观点一致，我们的初步数据显示APPL1与胰岛素受体直接相互作用，更有趣的是，这种相互作用被脂联素刺激增强。此外，我们还发现APPL1在Ser430处经历了脂联素刺激的磷酸化，这提示了脂联素调节APPL1与胰岛素受体之间相互作用的潜在机制。此外，我们还发现APPL1亚型APPL2与APPL1在蛋白质序列上有54%的同源性，当在细胞中过表达时，APPL2与APPL1二聚体并抑制脂联素信号。基于这些新的发现，我们推测APPL异构体与脂联素和胰岛素信号通路中的信号分子之间的相互作用可能在这两个重要信号通路之间的串扰中发挥关键作用。为了验证这一假说，我们将：1)表征APPL1与胰岛素受体(IR)信号通路中的信号分子之间的相互作用，以及这种相互作用在胰岛素信号转导中的作用；2)阐明APPL2在调节脂联素和胰岛素信号和功能中的作用；3)确定APPL1是否在胰岛素信号转导中发挥作用以及脂联素在体内的胰岛素增敏作用。公共卫生相关性：我们认为，拟议的研究结果将提供脂联素胰岛素增敏作用的分子机制的关键信息，这将对开发治疗肥胖症、胰岛素抵抗和2型糖尿病的新药具有重要意义。

DESCRIPTION (provided by applicant): Adiponectin, a peptide hormone mainly produced by adipocytes, is now widely recognized as an insulin sensitizer that possesses anti-diabetic, anti-inflammatory and cardioprotective properties. However, the molecular mechanisms by which adiponectin sensitizes insulin signaling and action remain largely unknown. We have recently identified a pleckstrin homology (PH) and phosphotyrosine binding (PTB) domain- containing protein, APPL1 that interacts directly with the adiponectin receptors AdipoR1 and AdipoR2. Suppression of APPL1 by RNAi not only inhibits adiponectin signaling but also insulin-stimulated Akt phosphorylation, suggesting that APPL1 may play an essential role in the crosstalk between the adiponectin and insulin signaling pathways (Mao et al, 2006, Nat. Cell Biol, 8, 516-523). Consistent with this view, our preliminary data have shown that APPL1 interacts directly with the insulin receptor and more interestingly, this interaction is enhanced by adiponectin stimulation. In addition, we have found that APPL1 undergoes adiponectin-stimulated phosphorylation at Ser430; this suggests a potential mechanism by which adiponectin regulates the interaction between APPL1 and the insulin receptor. Furthermore, we have found that APPL2, an APPL1 isoform which shares 54% identity in protein sequence with APPL1, dimerizes with APPL1 and inhibits adiponectin signaling when overexpressed in cells. Based on these novel findings, we hypothesize that the interaction between APPL isoforms and signaling molecules in the adiponectin and insulin signaling pathways may play a key role in the crosstalk between these two important signaling pathways. To test this hypothesis, we will: 1) Characterize the interaction between APPL1 and signaling molecules in the insulin receptor (IR) signaling pathway and the roles of the interaction in insulin signaling; 2) Elucidate the roles of APPL2 in regulating adiponectin and insulin signaling and function; and 3) Determine whether APPL1 plays a role in insulin signaling and the insulin sensitizing effect of adiponectin in vivo. PUBLIC HEALTH RELEVANCE: We believe that results from the proposed study will provide critical information on the molecular mechanism underlying the insulin sensitizing effect of adiponectin, which should have significant implications in the development of new therapeutic drugs for the treatment of obesity, insulin resistance, and type 2 diabetes.