siRNA-based gene silencing reveals specialized roles of IRS-1/Akt2 and IRS-2/Akt1 in glucose and lipid metabolism in human skeletal muscle

Sequential phosphorylation of insulin receptor substrate-2 by glycogen synthase kinase-3 and c-Jun NH2-terminal kinase plays a role in hepatic insulin signaling

Serine phosphorylation of insulin receptor substrate (IRS) proteins is a potential inhibitory mechanism in insulin signaling. Here we show that IRS-2 is phosphorylated by glycogen synthase kinase (GSK)-3. Phosphorylation by GSK-3 requires prior phosphorylation of its substrates, prompting us to identify the "priming kinase." It was found that the stress activator anisomycin enhanced the ability of GSK-3 to phosphorylate IRS-2. Use of a selective c-Jun NH(2)-terminal kinase (JNK) inhibitor and cells overexpressing JNK implicated JNK as the priming kinase. This allowed us to narrow down the number of potential GSK-3 phosphorylation sites within IRS-2 to four regions that follow the motif SXXXSP. IRS-2 deletion mutants enabled us to localize the GSK-3 and JNK phosphorylation sites to serines 484 and 488, respectively. Mutation at serine 488 reduced JNK phosphorylation of IRS-2, and mutation of each site separately abolished GSK-3 phosphorylation of IRS-2. Treatment of H4IIE liver cells with anisomycin inhibited insulin-induced tyrosine phosphorylation of IRS-2; inhibition was reversed by pretreatment with the JNK and GSK-3 inhibitors. Moreover, overexpression of JNK and GSK-3 in H4IIE cells reduced insulin-induced tyrosine phosphorylation of IRS-2 and its association with the p85 regulatory subunit of phosphatidylinositol 3-kinase. Finally, both GSK-3 and JNK are abnormally upregulated in the diabetic livers of ob/ob mice. Together, our data indicate that IRS-2 is sequentially phosphorylated by JNK and GSK-3 at serines 484/488 and provide evidence for their inhibitory role in hepatic insulin signaling.

Exercise training-induced improvements in insulin action

Individuals with insulin resistance are characterized by impaired insulin action on whole-body glucose uptake, in part due to impaired insulin-stimulated glucose uptake into skeletal muscle. A single bout of exercise increases skeletal muscle glucose uptake via an insulin-independent mechanism that bypasses the typical insulin signalling defects associated with these conditions. However, this 'insulin sensitizing' effect is short-lived and disappears after approximately 48 h. In contrast, repeated physical activity (i.e. exercise training) results in a persistent increase in insulin action in skeletal muscle from obese and insulin-resistant individuals. The molecular mechanism(s) for the enhanced glucose uptake with exercise training have been attributed to the increased expression and/or activity of key signalling proteins involved in the regulation of glucose uptake and metabolism in skeletal muscle. Evidence now suggests that the improvements in insulin sensitivity associated with exercise training are also related to changes in the expression and/or activity of proteins involved in insulin signal transduction in skeletal muscle such as the AMP-activated protein kinase (AMPK) and the protein kinase B (Akt) substrate AS160. In addition, increased lipid oxidation and/or turnover is likely to be another mechanism by which exercise improves insulin sensitivity: exercise training results in an increase in the oxidative capacity of skeletal muscle by up-regulating lipid oxidation and the expression of proteins involved in mitochondrial biogenesis. Determination of the underlying biological mechanisms that result from exercise training is essential in order to define the precise variations in physical activity that result in the most desired effects on targeted risk factors, and to aid in the development of such interventions.

Akt2 is implicated in skeletal muscle differentiation and specifically binds Prohibitin2/REA

Akt1 and Akt2 are the major isoforms of Akt expressed in muscle cells and muscle tissue. We have performed siRNA silencing of Akt1 and Akt2 in C2 myoblasts to characterize their specific implication in muscle differentiation. Whereas silencing Akt2, and not Akt1, inhibited cell cycle exit and myoblast differentiation, Akt2 overexpression led to an increased proportion of differentiated myoblasts. In addition, we demonstrate that Akt2 is required for myogenic conversion induced by MyoD overexpression in fibroblasts. We show Akt2, but not Akt1, binds Prohibitin2/Repressor of Estrogen Activator, PHB2/REA, a protein recently implicated in transcriptionnal repression of myogenesis. Co-immunoprecipitation experiments on endogenous proteins showed the Akt2-REA complex does not contain Prohibitin1. We have analyzed expression and localization of PHB2/REA during proliferation and differentiation of mouse and human myoblasts. PHB2/REA shows punctated nuclear staining which partially co-localizes with Akt2 in differentiated myotubes and PHB2 levels decrease at the onset of myogenic differentiation concomitant with an increase in Akt2. There appears to be an inverse correlation between Akt2 and PHB2 protein levels where cells silenced for Akt2 expression show increased level of PHB2/REA and overexpression of Akt2 resulted in decreased Prohibitin2/REA. Taken together, these results, along with our previous observations, clearly show that Akt2 and not Akt1 plays a major and early role in cell cycle exit and myogenic differentiation and this function involves its specific interaction with PHB2/REA.

The direct involvement of SirT1 in insulin-induced insulin receptor substrate-2 tyrosine phosphorylation

NAD+ -dependent Sir2 family deacetylases and insulin signaling pathway are both conserved across species to regulate aging process. The interplay between these two genetic programs is investigated in this study. Protein deacetylase activity of SirT1, the mammalian homologue of Sir2, was suppressed through either nicotinamide treatment or RNA interference in several cell lines, and these cells displayed impaired insulin responses. Suppression of SirT1 activity also selectively inhibited insulin-induced tyrosine phosphorylation of insulin receptor substrate 2 (IRS-2), whereas it had minimal effect on that of IRS-1. Further analyses showed that both IRS-1 and IRS-2 interacted with SirT1, and the acetylation level of IRS-2 was down-regulated by insulin treatment. Inhibition of SirT1 activity prevented deacetylation and insulin-induced tyrosine phosphorylation of IRS-2. Mutations of four lysine residues to alanine in IRS-2 protein, on the other hand, led to its reduced basal level acetylation and insulin-induced tyrosine phosphorylation. These results suggest a possible regulatory effect of SirT1 on insulin-induced tyrosine phosphorylation of IRS-2, a vital step in insulin signaling pathway, through deacetylation of IRS-2 protein. More importantly, this study may imply a pathway through which Sir2 family protein deacetylases and insulin signaling pathway jointly regulate various metabolic processes, including aging and diabetes.

Role of glycogen synthase kinase-3 alpha in insulin action in cultured human skeletal muscle cells

An association between glycogen synthase kinase-3 (GSK3) in skeletal muscle and insulin resistance has been demonstrated in type 2 diabetic patients. In addition, inhibition of GSK3 improves insulin action. The aim of the present study was to elucidate the role of the alpha-isoform of GSK3 in insulin resistance in human skeletal muscle cells from nondiabetic subjects maintained in culture. Transfection of muscle cells with specific antisense oligonucleotides resulted in a 30-50% decrease of GSK3alpha protein expression (P < 0.05). Whereas neither the basal fractional velocity of glycogen synthase (GS FV) (an indicator of the activation state of the enzyme) nor glucose uptake (GU) were altered, reducing GSK3alpha expression resulted in increases in insulin stimulation of both GS FV and GU. GSK3alpha overexpression (60-100% increase over control) did not alter basal GS FV or GU but impaired insulin stimulation of both responses. Knockdown of GSK alpha also led to an increase in insulin receptor substrate-1 protein expression but did not alter insulin stimulation of pS473-Akt phosphorylation. However, GSK3alpha overexpression impaired insulin action on pS473-Akt. In summary, we concluded the following: 1) modulation of GSK3alpha expression has no effect on basal GU and glycogen synthase activities; 2) reduction of GSK3alpha expression results in improvements in insulin action; and 3) elevation of GSK3alpha in human skeletal muscle cells can induce insulin resistance for several responses. We conclude that GSK3alpha is an important regulator of muscle insulin action.

Role of Akt substrate of 160 kDa in insulin-stimulated and contraction-stimulated glucose transport

Insulin and exercise, the most important physiological stimuli to increase glucose transport in skeletal muscle, trigger a redistribution of GLUT4 glucose transporter proteins from the cell interior to the cell surface, thereby increasing glucose transport capacity. The most distal insulin signaling protein that has been linked to GLUT4 translocation, Akt substrate of 160 kDa (AS160), becomes phosphorylated in insulin-stimulated 3T3-L1 adipocytes; this is important for insulin-stimulated GLUT4 translocation and glucose transport. Insulin also induces a rapid and dose-dependent increase in AS160 phosphorylation in skeletal muscle. Available data from skeletal muscle support the concepts developed in adipocytes with regard to the role AS160 plays in the regulation of insulin-stimulated glucose transport. In vivo exercise, in vitro contractions, or in situ contractions can also stimulate AS160 phosphorylation. AMP-activated protein kinase (AMPK) is likely important for phosphorylating AS160 in response to exercise/contractile activity, whereas Akt2 appears to be important for insulin-stimulated AS160 phosphorylation in muscle. Evidence of a role for AS160 in exercise/contraction-stimulated glucose uptake is currently inconclusive. The distinct signaling pathways that are stimulated by insulin and exercise/contraction converge at AS160. Although AS160 phosphorylation is apparently important for insulin-stimulated GLUT4 translocation and glucose transport, it is uncertain whether elevated AS160 phosphorylation plays a similar role with exercise/contraction.

The GLUT4 code

Despite being one of the first recognized targets of insulin action, the acceleration of glucose transport into muscle and fat tissue remains one of the most enigmatic processes in the insulin action cascade. Glucose transport is accomplished by a shift in the distribution of the insulin-responsive glucose transporter GLUT4 from intracellular compartments to the plasma membrane in the presence of insulin. The complexity in deciphering the molecular blueprint of insulin regulation of glucose transport arises because it represents a convergence of two convoluted biological systems-vesicular transport and signal transduction. Whereas more than 60 molecular players have been implicated in this orchestral performance, it has been difficult to distinguish between mainly passive participants vs. those that are clearly driving the process. The maze-like nature of the endosomal system makes it almost impossible to dissect the anatomical nature of what appears to be a medley of many overlapping and rapidly changing transitions. A major limitation is technology. It is clear that further progress in teasing apart the GLUT4 code will require the development and application of novel and advanced technologies that can discriminate one molecule from another in the living cell and to superimpose this upon a system in which the molecular environment can be carefully manipulated. Many are now taking on this challenge.

Effects of endurance exercise training on insulin signaling in human skeletal muscle: interactions at the level of phosphatidylinositol 3-kinase, Akt, and AS160

The purpose of this study was to investigate the mechanisms explaining improved insulin-stimulated glucose uptake after exercise training in human skeletal muscle. Eight healthy men performed 3 weeks of one-legged knee extensor endurance exercise training. Fifteen hours after the last exercise bout, insulin-stimulated glucose uptake was approximately 60% higher (P < 0.01) in the trained compared with the untrained leg during a hyperinsulinemic-euglycemic clamp. Muscle biopsies were obtained before and after training as well as after 10 and 120 min of insulin stimulation in both legs. Protein content of Akt1/2 (55 +/- 17%, P < 0.05), AS160 (25 +/- 8%, P = 0.08), GLUT4 (52 +/- 19%, P < 0.001), hexokinase 2 (HK2) (197 +/- 40%, P < 0.001), and insulin-responsive aminopeptidase (65 +/- 15%, P < 0.001) increased in muscle in response to training. During hyperinsulinemia, activities of insulin receptor substrate-1 (IRS-1)-associated phosphatidylinositol 3-kinase (PI3-K) (P < 0.005), Akt1 (P < 0.05), Akt2 (P < 0.005), and glycogen synthase (GS) (percent I-form, P < 0.05) increased similarly in both trained and untrained muscle, consistent with increased phosphorylation of Akt Thr(308), Akt Ser(473), AS160, glycogen synthase kinase (GSK)-3alpha Ser(21), and GSK-3beta Ser(9) and decreased phosphorylation of GS site 3a+b (all P < 0.005). Interestingly, training improved insulin action on thigh blood flow, and, furthermore, in both basal and insulin-stimulated muscle tissue, activities of Akt1 and GS and phosphorylation of AS160 increased with training (all P < 0.05). In contrast, training reduced IRS-1-associated PI3-K activity (P < 0.05) in both basal and insulin-stimulated muscle tissue. Our findings do not support generally improved insulin signaling after endurance training; rather it seems that improved insulin-stimulated glucose uptake may result from hemodynamic adaptations as well as increased cellular protein content of individual insulin signaling components and molecules involved in glucose transport and metabolism.

Fluorogenic surrogate substrates for toluene-degrading bacteria—Are they useful for activity analysis?

Cultivated bacterial toluene degraders use one or several of four described pathways for the aerobic degradation of this priority groundwater contaminant. To be able to identify un-cultivated toluene-degrading bacteria within enriched or natural consortia, we attempted to develop a set of staining techniques that invariably label toluene-degrading bacteria while differentiating between the different degradation pathways. In the literature, we found suggestions for pathway-specific labels of individual cells that rely on the conversion of toluene surrogates into specific colored and fluorescent products. These surrogate substrates were phenylacetylene (PA), cinnamonitrile, 3-hydroxyphenylacetylene (3-HPA), and indole. We were able to confirm that the chromogenic reactions reliably verified the pathway-specific reactions of well-characterized toluene-degrading bacterial species. However, it was most surprising to find out that three (PA, 3-HPA and cinnamonitrile) of the four supplied surrogate substrates did not lead to any product fluorescence above the cultures' autofluorescence, neither inside of cells nor in supernatants. More disturbingly, the original surrogate compound 3-HPA was inherently fluorescent and found to stain cells at intensities that depended on their states in the cell cycle. Indoxyl originating from the surrogate substrate indole was the only fluorescent product that was formed. It was detected intracellularly when the cells were sealed with para-formaldehyde, but its appearance was unrelated to the presence of expressed toluene degradation pathways. These findings were scrutinized by fluorescence spectroscopy, fluorescence microscopy, and flow cytometry. Activity and growth of the test bacteria were determined by analyzing chromosome numbers and membrane integrity. Our results contradict literature reports that propose the surrogate fluorogenic substrates for the identification of toluene degraders and the identification of specific pathways used by them.

Tissue-specific effects of rosiglitazone and exercise in the treatment of lipid-induced insulin resistance

Both pharmacological intervention (i.e., thiazolidinediones [TZDs]) and lifestyle modification (i.e., exercise training) are clinically effective treatments for improving whole-body insulin sensitivity. However, the mechanism(s) by which these therapies reverse lipid-induced insulin resistance in skeletal muscle is unclear. We determined the effects of 4 weeks of rosiglitazone treatment and exercise training and their combined actions (rosiglitazone treatment and exercise training) on lipid and glucose metabolism in high-fat-fed rats. High-fat feeding resulted in decreased muscle insulin sensitivity, which was associated with increased rates of palmitate uptake and the accumulation of the fatty acid metabolites ceramide and diacylglycerol. Impairments in lipid metabolism were accompanied by defects in the Akt/AS160 signaling pathway. Exercise training, but not rosiglitazone treatment, reversed these impairments, resulting in improved insulin-stimulated glucose transport and increased rates of fatty acid oxidation in skeletal muscle. The improvements to glucose and lipid metabolism observed with exercise training were associated with increased AMP-activated protein kinase alpha1 activity; increased expression of Akt1, peroxisome proliferator-activated receptor gamma coactivator 1, and GLUT4; and a decrease in AS160 expression. In contrast, rosiglitazone treatment exacerbated lipid accumulation and decreased insulin-stimulated glucose transport in skeletal muscle. However, rosiglitazone, but not exercise training, increased adipose tissue GLUT4 and acetyl CoA carboxylase expression. Both exercise training and rosiglitazone decreased liver triacylglycerol content. Although both interventions can improve whole-body insulin sensitivity, our results show that they produce divergent effects on protein expression and triglyceride storage in different tissues. Accordingly, exercise training and rosiglitazone may act as complementary therapies for the treatment of insulin resistance.

Role of AMP Kinase and PPARδ in the Regulation of Lipid and Glucose Metabolism in Human Skeletal Muscle

The peroxisome proliferator-activated receptor (PPAR)delta has been implicated in the regulation of lipid metabolism in skeletal muscle. Furthermore, activation of PPARdelta has been proposed to improve insulin sensitivity and reduce glucose levels in animal models of type 2 diabetes. We recently demonstrated that the PPARdelta agonist GW501516 activates AMP-activated protein kinase (AMPK) and stimulates glucose uptake in skeletal muscle. However, the underlying mechanism remains to be clearly identified. In this study, we first confirmed that incubation of primary cultured human muscle cells with GW501516 induced AMPK phosphorylation and increased fatty acid transport and oxidation and glucose uptake. Using small interfering RNA, we have demonstrated that PPARdelta expression is required for the effect of GW501516 on the intracellular accumulation of fatty acids. Furthermore, we have shown that the subsequent increase in fatty acid oxidation induced by GW501516 is dependent on both PPARdelta and AMPK. Concomitant with these metabolic changes, we provide evidence that GW501516 increases the expression of key genes involved in lipid metabolism (FABP3, CPT1, and PDK4) by a PPARdelta-dependent mechanism. Finally, we have also demonstrated that the GW501516-mediated increase in glucose uptake requires AMPK but not PPARdelta. In conclusion, the PPARdelta agonist GW501516 promotes changes in lipid/glucose metabolism and gene expression in human skeletal muscle cells by PPARdelta- and AMPK-dependent and -independent mechanisms.

Postpartum glycemic homeostasis in early lactating rats is accompanied by transient and specific increase of soleus insulin response through IRS2/AKT pathway

It is known that at the moment of delivery immediate lost of conceptus (main site of glucose disposal in late pregnancy) is not able to disturb glucose homeostasis in early lactating mothers. However, the mechanism by which this adaptation takes place in early lactation is still unknown. Most studies concerning insulin sensitivity in lactating rats were carried out at 11–13 days postpartum and did not describe functional changes in insulin response in early lactation. Here we show that lactation hypersensitivity to insulin is observed as early as 3 days after delivery (L3). We show that the oxidative soleus muscle displays a transient increased maximal insulin-induced glucose uptake and CO2production, which is temporally limited to L3. Response of soleus muscle was accompanied by an increase in glucose transporter 4 (GLUT4) content at L3. This adaptive response was not detected in the glycolytic plantaris muscle, which displayed lower content of GLUT4. We also found that soleus muscle from early lactating rats have higher insulin receptor expression and tyrosine phosphorylation. Downstream steps of insulin signaling pathway; e.g., insulin receptor substrate 2 tyrosine phosphorylation and its association with phosphatidylinositol 3-kinase were also upregulated in soleus muscle. In parallel, protein tyrosine phosphatase 1B expression, a negative regulator of insulin signal, was reduced. Importantly, all of these molecular alterations were time limited to L3 and were not observed in plantaris muscle. These results suggest that improved insulin action in oxidative, but not in glycolytic muscle might contribute to achievement of glucose homeostasis postpartum.

Exercise improves phosphatidylinositol-3,4,5-trisphosphate responsiveness of atypical protein kinase C and interacts with insulin signalling to peptide elongation in human skeletal muscle

We investigated if acute endurance-type exercise interacts with insulin-stimulated activation of atypical protein kinase C (aPKC) and insulin signalling to peptide chain elongation in human skeletal muscle. Four hours after acute one-legged exercise, insulin-induced glucose uptake was approximately 80% higher (N = 12, P < 0.05) in previously exercised muscle, measured during a euglycaemic-hyperinsulinaemic clamp (100 microU ml(-1)). Insulin increased (P < 0.05) both insulin receptor substrate (IRS)-1 and IRS-2 associated phosphatidylinositol (PI)-3 kinase activity and led to increased (P < 0.001) phosphorylation of Akt on Ser(473) and Thr(308) in skeletal muscle. Interestingly, in response to prior exercise IRS-2-associated PI-3 kinase activity was higher (P < 0.05) both at basal and during insulin stimulation. This coincided with correspondingly altered phosphorylation of the extracellular-regulated protein kinase 1/2 (ERK 1/2), p70S6 kinase (P70S6K), eukaryotic elongation factor 2 (eEF2) kinase and eEF2. aPKC was similarly activated by insulin in rested and exercised muscle, without detectable changes in aPKC Thr(410) phosphorylation. However, when adding phosphatidylinositol-3,4,5-triphosphate (PIP3), the signalling product of PI-3 kinase, to basal muscle homogenates, aPKC was more potently activated (P = 0.01) in previously exercised muscle. Collectively, this study shows that endurance-type exercise interacts with insulin signalling to peptide chain elongation. Although protein turnover was not evaluated, this suggests that capacity for protein synthesis after acute endurance-type exercise may be improved. Furthermore, endurance exercise increased the responsiveness of aPKC to PIP3 providing a possible link to improved insulin-stimulated glucose uptake after exercise.

MAP4K4 gene silencing in human skeletal muscle prevents tumor necrosis factor-alpha-induced insulin resistance

Tumor necrosis factor-alpha (TNF-alpha) induces skeletal muscle insulin resistance by impairing insulin signaling events involved in GLUT4 translocation. We tested whether mitogenic-activated protein kinase kinase kinase kinase isoform 4 (MAP4K4) causes the TNF-alpha-induced negative regulation of extracellular signal-regulated kinase-1/2 (ERK-1/2), c-Jun NH2-terminal kinase (JNK), and the insulin receptor substrate-1 (IRS-1) on the insulin signaling pathway governing glucose metabolism. Using small interfering RNA (siRNA) to suppress the expression of MAP4K4 protein 85% in primary human skeletal muscle cells, we provide evidence that TNF-alpha-induced insulin resistance on glucose uptake was completely prevented. MAP4K4 silencing inhibited TNF-alpha-induced negative signaling inputs by preventing excessive JNK and ERK-1/2 phosphorylation, as well as IRS-1 serine phosphorylation. These results highlight the MAPK4K4/JNK/ERK/IRS module in the negative regulation of insulin signaling to glucose transport in response to TNF-alpha. Depletion of MAP4K4 also prevented TNF-alpha-induced insulin resistance on Akt and the Akt substrate 160 (AS160), providing evidence that appropriate insulin signaling inputs for glucose metabolism were rescued. Silencing of MAP2K1 and MAP2K4, signaling proteins downstream of MAP4K4, recapitulated the effect of MAP4K4 siRNA in TNF-alpha-treated cells. Thus, strategies to inhibit MAP4K4 may be efficacious in the prevention of TNF-alpha-induced inhibitory signals that cause skeletal muscle insulin resistance on glucose metabolism in humans. Moreover, in myotubes from insulin-resistant type II diabetic patients, siRNA against MAP4K4, MAP2K4, or MAP2K1 restored insulin action on glucose uptake to levels observed in healthy subjects. Collectively, our results demonstrate that MAP4K4 silencing prevents insulin resistance in human skeletal muscle and restores appropriate signaling inputs to enhance glucose uptake.

Selective control of skeletal muscle differentiation by Akt1

The phosphatidylinositol 3-kinase-Akt pathway plays a central role in growth, development, and metabolism in both normal and neoplastic cells. In skeletal muscle, Akt has been implicated in regulating regeneration and hypertrophy and in counteracting atrophy. Here we provide evidence that Akt1 and not Akt2 is essential for muscle differentiation. Using a robust model of MyoD-mediated muscle development, in which dominant-negative Akt blocked differentiation, we show that targeted loss of Akt1 was equally inhibitory. Selective elimination of Akt1 had no effect on myoblast viability or proliferation but prevented differentiation by impairing the transcriptional actions of MyoD. In contrast, knockdown of Akt2 had no effect on myoblast survival or differentiation and minimally inhibited MyoD-regulated transcription. Our results define isoform-specific Akt-regulated signaling pathways in muscle cells that act through Akt1 to sustain muscle gene activation and promote differentiation.

Increased insulin-stimulated Akt pSer473 and cytosolic SHP2 protein abundance in human skeletal muscle following acute exercise and short-term training

The purpose of the present study was to determine in human skeletal muscle whether a single exercise bout and 7 days of consecutive endurance (cycling) training 1) increased insulin-stimulated Akt pSer(473) and 2) altered the abundance of the protein tyrosine phosphatases (PTPases), PTP1B and SHP2. In healthy, untrained men (n = 8; 24 +/- 1 yr), glucose infusion rate during a hyperinsulinemic euglycemic clamp, when compared with untrained values, was not improved 24 h following a single 60-min bout of endurance cycling but was significantly increased ( approximately 30%; P < 0.05) 24 h following completion of 7 days of exercise training. Insulin-stimulated Akt pSer(473) was approximately 50% higher (P < 0.05) 24 h following the acute bout of exercise, with this effect remaining after 7 days of training (P < 0.05). Insulin-stimulated insulin receptor and insulin receptor substrate-1 tyrosine phosphorylation were not altered 24 h after acute exercise and short-term training. Insulin did not acutely regulate the localization of the PTPases, PTP1B or SHP2, although cytosolic protein abundance of SHP2 was increased (P < 0.05; main effect) 24 h following acute exercise and short-term training. In conclusion, insulin-sensitive Akt pSer(473) and cytosolic SHP2 protein abundance are higher after acute exercise and short-term training, and this effect appears largely due to the residual effects of the last bout of prior exercise. The significance of exercise-induced alterations in cytosolic SHP2 and insulin-stimulated Akt pSer(473) on the improvement in insulin sensitivity requires further elucidation.