Deletion of Nck1 attenuates hepatic ER stress signaling and improves glucose tolerance and insulin signaling in liver of obese mice

Abstract

Obesity has been shown to create stress in the endoplasmic reticulum (ER), and that initiates the activation of the unfolded protein response (UPR). This has been reported to cause insulin resistance in selective tissues through activation of the inositol-requiring enzyme 1α (IRE1α)-c-Jun NH2-terminal kinase (JNK) pathway, which results in the phosphorylation of the insulin receptor substrate-1 (IRS-1) at an inhibitory site and blocks insulin receptor signaling. In this study, we report that the Src homology domain-containing adaptor protein Nck1, previously shown to modulate the UPR, is of functional importance in obesity-induced ER stress signaling and inhibition of insulin actions. We have examined obese Nck1−/− and Nck1 +/+ mice for glucose tolerance, insulin sensitivity, and signaling as well as for ER stress markers and IRS-1 phosphorylation at Ser307. Our findings show that obese Nck1-deficient mice display improved glucose disposal accompanied by enhanced insulin signaling in liver. This correlates with attenuated IRE1α and JNK activation and IRS-1 phosphorylation at Ser307 compared with obese wild-type mice. Consistent with our in vivo data, we report that downregulation of Nck1 using siRNA in HepG2 cells results in decreased thapsigargin-induced IRE1α activation and signaling and IRS-1 phosphorylation at Ser307, whereas it markedly enhances insulin signaling. Overall, in liver and in cultured cells, we show that depletion of Nck1 attenuates the UPR signal and its inhibitory action on insulin signaling. Taken all together, our findings implicate Nck1 in regulating the UPR, which secondary to obesity impairs glucose homeostasis and insulin actions.

Nck2 Deficiency in Mice Results in Increased Adiposity Associated With Adipocyte Hypertrophy and Enhanced Adipogenesis

“…We and others implicated Nck in regulating the UPR through its interaction with the b-subunit of the eukaryotic initiation factor 2 (eIF2b) (8,10,11), Ser/Thr phosphatase PP1 (8,12), PERK (13,14), and IRE1a (7). We demonstrated that Nck1 is essential for sustained hepatic activation of the IRE1a-JNK pathway associated with impaired glucose homeostasis secondary to obesity in mice (15). We also have showed that Nck1 modulates PERK-dependent regulation of insulin biosynthesis and survival in pancreatic b-cells (13,14).…”

“…The antibodies used were as follows: Hsp90 (4877S) (44728G) from Invitrogen; Flag (3165) from Sigma; and Nck1 and panNck as previously described (10,15). The 3T3-L1 cell line from ATCC was cultured as recommended by the manufacturer.…”

“…Tissues and cell extracts were prepared as previously reported (15). Total proteins (20-50 mg) were resolved by SDS-PAGE, transferred onto polyvinylidene fluoride, and immunoblotted with indicated antibodies.…”

Nck2, an unexpected regulator of adipogenesis

“…[26][27][28] Within this context, we identified a major role for Nck in regulating signaling from the ER through direct interaction with IRE1-a (Inositol-required enzyme 1-a) and PERK (double-stranded RNA-like ER kinase), [28][29][30][31][32] 2 fundamental components of the unfolded protein response (UPR), whose dysregulation has been implicated in the development of obesity. 33 It is noteworthy that obesity creates ER stress inducing sustained activation of the UPR in liver and adipose tissue, 34,35 potentially through increased production of reactive oxygen species 35 and impaired Ca 2C homeostasis.…”

Une protéine uNick en son genre

“…Nck module aussi la signalisation d'IRE1α (inositol requiring enzyme 1), autre protéine de la membrane du RE qui possède une activité kinase et une activité endonucléase activées dans les mêmes conditions de stress [10,32]. L'importance de Nck dans ce contexte s'est récemment accrue avec la découverte que les souris dont le gène Nck1 est inactivé sont protégées de la résistance à l'insuline résultant de l'activation anormale de la signalisation par IRE1α induite par l'obésité [26]. D'autre part, Nck joue aussi un rôle dans la réponse des cellules aux rayons UV, stress génomique qui provoque le transfert de Nck au noyau après son interaction avec SOCS7 (suppressor of cytokine signaling) [11].…”