Insulin-Mediated Phosphorylation of the Proline-Rich Akt Substrate PRAS40 Is Impaired in Insulin Target Tissues of High-Fat Diet-Fed Rats
ABSTRACT Clinical insulin resistance is associated with decreased activation of phosphatidylinositol 3'-kinase (PI3K) and its downstream substrate protein kinase B (PKB)/Akt. However, its physiological protein substrates remain poorly characterized. In the present study, the effect of in vivo insulin action on phosphorylation of the PKB/Akt substrate 40 (PRAS40) was examined. In rat and mice, insulin stimulated PRAS40-Thr246 phosphorylation in skeletal and cardiac muscle, the liver, and adipose tissue in vivo. Physiological hyperinsulinemia increased PRAS40-Thr246 phosphorylation in human skeletal muscle biopsies. In cultured cell lines, insulin-mediated PRAS40 phosphorylation was prevented by the PI3K inhibitors wortmannin and LY294002. Immunohistochemical and immunofluorescence studies showed that phosphorylated PRAS40 is predominantly localized to the nucleus. Finally, in rats fed a high-fat diet (HFD), phosphorylation of PRAS40 was markedly reduced compared with low-fat diet-fed animals in all tissues examined. In conclusion, the current study identifies PRAS40 as a physiological target of in vivo insulin action. Phosphorylation of PRAS40 is increased by insulin in human, rat, and mouse insulin target tissues. In rats, this response is reduced under conditions of HFD-induced insulin resistance.
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- "The importance of the AKT for amphetamine responsivity is demonstrated by the ability of the AKT1 inhibitor LY294002 to block amphetamineinduced dopamine release and reuptake (Williams et al. 2007). There is also evidence that phosphorylation of the AKT substrate PRAS40 is markedly reduced in rats fed a high-fat diet (Nascimento et al. 2007), suggesting a mechanism through which diet may influence DAT expression and dopamine release. Given this combination of clinical and preclinical data, AKT1 may be an important candidate for understanding genetic relations between dopamine functioning and overeating. "
ABSTRACT: Data suggest that low levels of dopamine D2 receptors and attenuated responsivity of dopamine-target regions to food intake is associated with increased eating and elevated weight. There is also growing (although mixed) evidence that genotypes that appear to lead to reduced dopamine signaling (e.g., DRD2, DRD4, and DAT) and certain appetite-related hormones and peptides (e.g., ghrelin, orexin A, leptin) moderate the relation between dopamine signaling, overeating, and obesity. This chapter reviews findings from studies that have investigated the relation between dopamine functioning and food intake and how certain genotypes and appetite-related hormones and peptides affect this relation.01/2011; 6:81-93. DOI:10.1007/7854_2010_89
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- "The induction of PRAS40-Thr246 phosphorylation by insulin in vivo is reduced in skeletal muscle, heart, liver, and adipose tissue from insulin-resistant highfat diet fed rats, and skeletal muscle from ob/ob mice (Nascimento et al., 2006; Ouwens et al., 2007; Miller et al., 2008). Also incubation of rat soleus muscle with palmitate lowers the induction of PRAS40-Thr246 phosphorylation by insulin (Alkhateeb et al., 2007). "
ABSTRACT: Alterations in signalling via protein kinase B (PKB/Akt) and the mammalian target of rapamycin (mTOR) frequently occur in type 2 diabetes and various human malignancies. Proline-rich Akt substrate of 40-kDa (PRAS40) has a regulatory function at the intersection of these pathways. The interaction of PRAS40 with the mTOR complex 1 (mTORC1) inhibits the activity of mTORC1. Phosphorylation of PRAS40 by PKB/Akt and mTORC1 disrupts the binding between mTORC1 and PRAS40, and relieves the inhibitory constraint of PRAS40 on mTORC1 activity. This review summarizes the signalling pathways regulating PRAS40 phosphorylation, as well as the dual function of PRAS40 as substrate and inhibitor of mTORC1 in the physiological situation, and under pathological conditions, such as insulin resistance and cancer.Archives of Physiology and Biochemistry 06/2009; 115(4):163-75. DOI:10.1080/13813450902988580
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- "A recent study showed that pPRAS40 was increased in premalignant and malignant breast and lung cancer cell lines, which indicates that pPRAS40 may contribute to cell survival downstream of the PI3K/ Akt pathway (Huang and Porter, 2005). An in vivo study showed that insulin mediated phosphorylation of PRAS40 in various tissues, such as skeletal, muscle, and liver, through the PI3K/Akt pathway (Nascimento et al, 2006). We demonstrated similar results showing that an increase in pPRAS40 decreased motor neuron death and that downregulation of pPRAS40, using an inhibitor of the PI3K pathway, increased apoptotic cell death after SCI. "
ABSTRACT: The serine-threonine kinase, Akt, plays an important role in the cell survival signaling pathway. A proline-rich Akt substrate, PRAS40, has been characterized, and an increase in phospho-PRAS40 (pPRAS40) is neuroprotective after transient focal cerebral ischemia. However, the involvement of PRAS40 in the cell death/survival pathway after spinal cord injury (SCI) is unclear. Liposome-mediated PRAS40 transfection was performed to study whether overexpression of pPRAS40 is neuroprotective. We further examined the expression of pPRAS40 after SCI by immunohistochemistry and Western blot using copper/zinc-superoxide dismutase (SOD1) transgenic (Tg) rats and wild-type (Wt) littermates. We then examined the relationship between PRAS40 and Akt by injection of LY294002, a phosphatidylinositol 3-kinase (PI3K) pathway inhibitor, or Akt inhibitor IV, a compound that inhibits Akt activation after SCI. Our data demonstrated that increased pPRAS40 resulted in survival of more motor neurons compared with control complementary DNA transfection. Phosphorylated PRAS40 increased in the Wt rats after SCI, whereas there was a greater and prolonged increase in the SOD1 Tg rats. Coimmunoprecipitation showed that binding of pPRAS40 with 14-3-3 increased 1 day after SCI in the Wt rats, whereas there was a significant increase in the Tg rats. The inhibitor studies showed that phospho-Akt and pPRAS40 were decreased after injection of LY294002 or Akt inhibitor IV. We conclude that an increase in pPRAS40 by transfection after SCI results in survival of motor neurons, and overexpression of SOD1 in the Tg rats results in an increase in endogenous pPRAS40 and a decrease in motor neuron death through the PI3K/Akt pathway.Journal of Cerebral Blood Flow & Metabolism 02/2008; 28(1):44-52. DOI:10.1038/sj.jcbfm.9600501 · 5.34 Impact Factor