The Interaction of Akt with APPL1 Is Required for Insulin-stimulated Glut4 Translocation

Department of Biochemistry , Boston University, Boston, Massachusetts, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 12/2007; 282(44):32280-7. DOI: 10.1074/jbc.M704150200
Source: PubMed


APPL1 (adaptor protein containing PH domain, PTB domain, and leucine zipper motif 1) is an Akt/protein kinase B-binding protein involved in signal transduction and membrane trafficking pathways for various receptors, including receptor tyrosine kinases. Here, we establish a role for APPL1 in insulin signaling in which we demonstrate its interaction with Akt2 by co-immunoprecipitation and pulldown assays. In primary rat adipocytes and skeletal muscle, APPL1 and Akt2 formed a complex that was dissociated upon insulin stimulation in both tissues. To investigate possible APPL1 function in adipocytes, we analyzed Akt phosphorylation, 2-deoxyglucose uptake, and Glut4 translocation by immunofluorescence following APPL1 knockdown by small interfering and short hairpin RNAs. We show that APPL1 knockdown suppressed Akt phosphorylation, glucose uptake, and Glut4 translocation. We also tested the effect in 3T3-L1 adipocytes of expressing full-length APPL1 or an N- or a C-terminal APPL1 construct. Interestingly, expression of full-length APPL1 and its N terminus suppressed insulin-stimulated 2-deoxyglucose uptake and Glut4 translocation to roughly the same extent (40-60%). We confirmed by cellular fractionation that Glut4 translocation was substantially blocked in 3T3-L1 adipocytes transfected with full-length APPL1. By cellular fractionation, APPL1 was localized mainly in the cytosol, and it showed a small degree of re-localization to the light microsomes and nucleus in response to insulin. By immunofluorescence, we also show that APPL1 partially co-localized with Glut4. These data suggest that APPL1 plays an important role in insulin-stimulated Glut4 translocation in muscle and adipose tissues and that its N-terminal portion may be critical for APPL1 function.

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    • "Depending on the cell type, adiponectin was shown to either suppress NF-κB activity, like in endothelial cells and adipocytes (Ajuwon and Spurlock, 2005; Ouchi et al., 2000) or to activate the NF-κB pathway in synovial or cardiac fibroblasts (Hattori et al., 2007; Tang et al., 2007). By interacting with adiponectin receptors, APPL1 mediates activation of the downstream kinases, including Akt, LKB1 and AMPK (Mao et al., 2006; Saito et al., 2007). Moreover, APPL1 directly interacts with Akt and LKB1 (Cheng et al., 2009; Mitsuuchi et al., 1999; Tan et al., 2010; Zhou et al., 2009). "
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    ABSTRACT: APPL1 is a multifunctional adaptor protein that binds membrane receptors, signaling proteins and nuclear factors, thereby acting in endosomal trafficking and in different signaling pathways. Here we uncover a novel role of APPL1 as a positive regulator of transcriptional activity of NF-κB under basal but not TNFα-stimulated conditions. APPL1 was found to directly interact with TRAF2, an adaptor protein known to activate the canonical NF-κB signaling. APPL1 synergized with TRAF2 to induce NF-κB activation and both proteins were necessary for this process by functioning upstream of the IKK complex. Although TRAF2 was not detectable on APPL endosomes, endosomal recruitment of APPL1 was required for its function in the NF-κB pathway. Importantly, in the canonical pathway APPL1 appeared to regulate the proper spatial distribution of p65 in the absence of cytokine stimulation, since its overexpression enhanced and its depletion reduced the nuclear accumulation of p65. Analyzing the patterns of gene transcription upon APPL1 overproduction or depletion we found altered expression of NF-κB target genes encoding cytokines. At the molecular level, overexpressed APPL1 markedly increased the level of NIK, the key component of the noncanonical NF-κB pathway, by reducing its association with the degradative complex containing TRAF2, TRAF3 and cIAP1. In turn, high levels of NIK triggered nuclear translocation of p65. Collectively, we propose that APPL1 regulates basal NF-κB activity by modulating the stability of NIK, which affects the activation of p65. This places APPL1 as a novel link between the canonical and noncanonical machineries of NF-κB activation.
    Full-text · Article · Jun 2012 · Journal of Cell Science
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    • "The interaction of APPL1 with adiponectin receptors is essential in mediating the insulin-sensitizing actions of the adipokine in skeletal muscle (12) and endothelial cells (14). Furthermore, APPL1 potentiates insulin-induced Akt activation in its several metabolic targets, including adipocytes (29), muscle cells (12), and hepatocytes (13). In hepatocytes, APPL1 potentiates insulin-induced Akt activation by competing with the intracellular pseudokinase TRB3 for binding to Akt (13). "
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    ABSTRACT: Insulin stimulates both nitric oxide (NO)-dependent vasodilation and endothelin-1 (ET-1)-dependent vasoconstriction. However, the cellular mechanisms that control the dual vascular effects of insulin remain unclear. This study aimed to investigate the roles of the multidomain adaptor protein APPL1 in modulating vascular actions of insulin in mice and in endothelial cells. Both APPL1 knockout mice and APPL1 transgenic mice were generated to evaluate APPL1's physiological roles in regulating vascular reactivity and insulin signaling in endothelial cells. Insulin potently induced NO-dependent relaxations in mesenteric arteries of 8-week-old mice, whereas this effect of insulin was progressively impaired with ageing or upon development of obesity induced by high-fat diet. Transgenic expression of APPL1 prevented age- and obesity-induced impairment in insulin-induced vasodilation and reversed obesity-induced augmentation in insulin-evoked ET-1-dependent vasoconstriction. By contrast, genetic disruption of APPL1 shifted the effects of insulin from vasodilation to vasoconstriction. At the molecular level, insulin-elicited activation of protein kinase B (Akt) and endothelial NO synthase and production of NO were enhanced in APPL1 transgenic mice but were abrogated in APPL1 knockout mice. Conversely, insulin-induced extracellular signal-related kinase (ERK)1/2 phosphorylation and ET-1 expression was augmented in APPL1 knockout mice but was diminished in APPL1 transgenic mice. In endothelial cells, APPL1 potentiated insulin-stimulated Akt activation by competing with the Akt inhibitor Tribbles 3 (TRB3) and suppressed ERK1/2 signaling by altering the phosphorylation status of its upstream kinase Raf-1. APPL1 plays a key role in coordinating the vasodilator and vasoconstrictor effects of insulin by modulating Akt-dependent NO production and ERK1/2-mediated ET-1 secretion in the endothelium.
    Full-text · Article · Sep 2011 · Diabetes
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    • "However, a significant potential risk in targeting this molecule therapeutically is likely to be its relative promiscuity in phosphoinositide and protein binding partners and the as yet poorly characterised cellular implications of its activation. Indeed, APPL1 has been shown to interact with APPL2 (Chial et al. 2008), Rab5 (Miaczynska et al. 2004), histone deacetylases (Miaczynska et al. 2004, Rashid et al. 2009), AKT2 (Mitsuuchi et al. 1999, Saito et al. 2007), AdipoRs (Mao et al. 2006) and TrkA and GIPC1 (Lin et al. 2006), thus being implicated in cellular growth and proliferation, in addition to metabolism. "
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    ABSTRACT: APPL1 is an adaptor protein that binds to both AKT and adiponectin receptors and is hypothesised to mediate the effects of adiponectin in activating downstream effectors such as AMP-activated protein kinase (AMPK). We aimed to establish whether APPL1 plays a physiological role in mediating glycogen accumulation and insulin sensitivity in muscle and the signalling pathways involved. In vivo electrotransfer of cDNA- and shRNA-expressing constructs was used to over-express or silence APPL1 for 1 week in single tibialis cranialis muscles of rats. Resulting changes in glucose and lipid metabolism and signalling pathway activation were investigated under basal conditions and in high-fat diet (HFD)- or chow-fed rats under hyperinsulinaemic-euglycaemic clamp conditions. APPL1 over-expression (OE) caused an increase in glycogen storage and insulin-stimulated glycogen synthesis in muscle, accompanied by a modest increase in glucose uptake. Glycogen synthesis during the clamp was reduced by HFD but normalised by APPL1 OE. These effects are likely explained by APPL1 OE-induced increase in basal and insulin-stimulated phosphorylation of IRS1, AKT, GSK3β and TBC1D4. On the contrary, APPL1 OE, such as HFD, reduced AMPK and acetyl-CoA carboxylase phosphorylation and PPARγ coactivator-1α and uncoupling protein 3 expression. Furthermore, APPL1 silencing caused complementary changes in glycogen storage and phosphorylation of AMPK and PI3-kinase pathway intermediates. Thus, APPL1 may provide a means for crosstalk between adiponectin and insulin signalling pathways, mediating the insulin-sensitising effects of adiponectin on muscle glucose disposal. These effects do not appear to require AMPK. Activation of signalling mediated via APPL1 may be beneficial in overcoming muscle insulin resistance.
    Full-text · Article · Jul 2011 · Journal of Endocrinology
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