Use of RNA interference-mediated gene silencing and adenoviral overexpression to elucidate the roles of AKT/protein kinase B isoforms in insulin actions

Component Characterization, In Vitro Activities and Molecular Mechanism of Cydonia oblonga Mill. against Diabetic

Cydonia Oblonga Mill. is widely distributed in Turkey, Uzbekistan and China and commonly used by the food industry to produce jam, jelly and candies. The aim of this study was to investigate the in vitro antidiabetic activity and anti-diabetic mechanism of Cydonia Oblonga Mill. fruit (COMF). The chemical compositions were further characterized in COMF by UPLC-Q-Orbitrap/MS and 65 components including 22 flavonoids, 16 organic acids, 11 polyphenols, 5 amino acids, 3 pentacyclic triterpenoids and 8 other compounds were identified. The antioxidant activity by DPPH scavenging method and α-glucosidase inhibitory activity were tested. Furthermore, we detected the effects of COMF extract on the proliferation activity of HUVECs, cell viability of HUVECs under H₂O₂-induced oxidative stress, and NO production. Then, molecular docking activity and α-glucosidase inhibitory activity of seven key flavonoid components selected by bioinformatics analysis and literature in the COMF were studied. Among them, quercetin showed potent inhibitory activity, kaempferol, isorhamnetin, luteolin and apigenin demonstrated moderate inhibitory activity, while rutin and epicatechin exhibited poor inhibitory activity. Subsequently, the effects of quercetin, kaempferol, isorhamnetin, leteolin and apigenin on the gene expression levels of AKT1, IL-6 and VEGFA were verified by real-time fluorescence quantification (RT-qPCR). Molecular biology result showed that different active ingredients can significantly recover the levels of AKT1, IL-6 and VEGFA in HUVECs injured by high glucose.

GSK3α phosphorylates dynamin-2 to promote GLUT4 endocytosis in muscle cells

Insulin-stimulated translocation of glucose transporter 4 (GLUT4) to plasma membrane of skeletal muscle is critical for postprandial glucose uptake; however, whether the internalization of GLUT4 is also regulated by insulin signaling remains unclear. Here, we discover that the activity of dynamin-2 (Dyn2) in catalyzing GLUT4 endocytosis is negatively regulated by insulin signaling in muscle cells. Mechanistically, the fission activity of Dyn2 is inhibited by binding with the SH3 domain of Bin1. In the absence of insulin, GSK3α phosphorylates Dyn2 to relieve the inhibition of Bin1 and promotes endocytosis. Conversely, insulin signaling inactivates GSK3α and leads to attenuated GLUT4 internalization. Furthermore, the isoform-specific pharmacological inhibition of GSK3α significantly improves insulin sensitivity and glucose tolerance in diet-induced insulin-resistant mice. Together, we identify a new role of GSK3α in insulin-stimulated glucose disposal by regulating Dyn2-mediated GLUT4 endocytosis in muscle cells. These results highlight the isoform-specific function of GSK3α on membrane trafficking and its potential as a therapeutic target for metabolic disorders.

Glucose and lipid metabolism abnormalities in Cushing's syndrome

Prolonged excess of glucocorticoids (GCs) has adverse systemic effects leading to significant morbidities and an increase in mortality. Metabolic alterations associated with the high level of the GCs are key risk factors for the poor outcome. These include GCs causing excess gluconeogenesis via upregulation of key enzymes in the liver, a reduction of insulin sensitivity in skeletal muscle, liver and adipose tissue by inhibiting the insulin receptor signalling pathway, and inhibition of insulin secretion in beta cells leading to dysregulated glucose metabolism. In addition, chronic GC exposure leads to an increase in visceral adipose tissue, as well as an increase in lipolysis resulting in higher circulating free fatty acid levels and in ectopic fat deposition. Remission of hypercortisolism improves these metabolic changes, but very often does not result in full resolution of the abnormalities. Therefore, long-term monitoring of metabolic variables is needed even after the resolution of the excess GC levels.

Conserved MicroRNAs in Human Nasopharynx Tissue Samples from Swabs Are Differentially Expressed in Response to SARS-CoV-2

The use of high-throughput small RNA sequencing is well established as a technique to unveil the miRNAs in various tissues. The miRNA profiles are different between infected and non-infected tissues. We compare the SARS-CoV-2 positive and SARS-CoV-2 negative RNA samples extracted from human nasopharynx tissue samples to show different miRNA profiles. We explored differentially expressed miRNAs in response to SARS-CoV-2 in the RNA extracted from nasopharynx tissues of 10 SARS-CoV-2-positive and 10 SARS-CoV-2-negative patients. miRNAs were identified by small RNA sequencing, and the expression levels of selected miRNAs were validated by real-time RT-PCR. We identified 943 conserved miRNAs, likely generated through posttranscriptional modifications. The identified miRNAs were expressed in both RNA groups, NegS and PosS: miR-148a, miR-21, miR-34c, miR-34b, and miR-342. The most differentially expressed miRNA was miR-21, which is likely closely linked to the presence of SARS-CoV-2 in nasopharynx tissues. Our results contribute to further understanding the role of miRNAs in SARS-CoV-2 pathogenesis, which may be crucial for understanding disease symptom development in humans.

AKT ISOFORMS-AS160-GLUT4: The defining axis of insulin resistance

The Akt isoforms-AS160-GLUT4 axis is the primary axis that governs glucose homeostasis in the body. The first step on the path to insulin resistance is deregulated Akt isoforms. This could be Akt isoform expression, its phosphorylation, or improper isoform-specific redistribution to the plasma membrane in a specific tissue system. The second step is deregulated AS160 expression, its phosphorylation, improper dissociation from glucose transporter storage vesicles (GSVs), or its inability to bind to 14-3-3 proteins, thus not allowing it to execute its function. The final step is improper GLUT4 translocation and aberrant glucose uptake. These processes lead to insulin resistance in a tissue-specific way affecting the whole-body glucose homeostasis, eventually progressing to an overt diabetic phenotype. Thus, the relationship between these three key proteins and their proper regulation comes out as the defining axis of insulin signaling and -resistance. This review summarizes the role of this central axis in insulin resistance and disease in a new light.

Cellular model system to dissect the isoform-selectivity of Akt inhibitors

The protein kinase Akt plays a pivotal role in cellular processes. However, its isoforms' distinct functions have not been resolved to date, mainly due to the lack of suitable biochemical and cellular tools. Against this background, we present the development of an isoform-dependent Ba/F3 model system to translate biochemical results on isoform specificity to the cellular level. Our cellular model system complemented by protein X-ray crystallography and structure-based ligand design results in covalent-allosteric Akt inhibitors with unique selectivity profiles. In a first proof-of-concept, the developed molecules allow studies on isoform-selective effects of Akt inhibition in cancer cells. Thus, this study will pave the way to resolve isoform-selective roles in health and disease and foster the development of next-generation therapeutics with superior on-target properties.

miR-18a increases insulin sensitivity by inhibiting PTEN

The miR-17-92 cluster (miR-17, miR-18a, miR-19a, miR-20a, miR-19b-1 and miR-92a) contributes to the occurrence and development of various diseases by inhibiting multiple target genes. Here, we explored the effects of miR-18a on insulin sensitivity. Quantitative real-time PCR indicated that serum miR-18a levels were lower in type 2 diabetes mellitus patients than in healthy controls, suggesting that miR-18a may influence blood glucose levels. Global overexpression of miR-18a in transgenic mice increased their glucose tolerance and insulin sensitivity, while it reduced expression of the phosphatase and tensin homolog deleted on chromosome ten (PTEN) in their skeletal muscle and adipose tissue. Western blotting indicated that overexpressing miR-18a in 3T3-L1 and C2C12 cells enhanced insulin-stimulated AKT phosphorylation and suppressed PTEN expression, while inhibiting miR-18a had the opposite effects. These results suggest that miR-18a improves insulin sensitivity by downregulating PTEN. This makes miR-18a a potentially useful target for the treatment of diabetes mellitus in the future.

Agriophyllum oligosaccharides ameliorate hepatic injury in type 2 diabetic db/db mice targeting INS-R/IRS-2/PI3K/AKT/PPAR-γ/Glut4 signal pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Agriophyllum squarrosum (L.) Moq. is a traditional Mongol medicine generally used to treat diabetes.

OBJECTIVE

To investigate the protective effects and potential mechanisms of Agriophyllum oligosaccharides (AOS) on liver injury in type 2 diabetic db/db mice.

MATERIALS AND METHODS

The db/db mice were divided into the model group (Model), metformin group (MET), high-dose AOS group (HAOS), and low-dose AOS group (LAOS). Nondiabetic littermate control db/m mice were used as the normal control group (Control). Mice in AOS groups were treated with AOS (380 or 750 mg/kg) daily, for 8 weeks. At 8 weeks, blood samples were collected to detect lipid and enzyme parameters concerning hepatic function, including alanine aminotransferase (ALT), aspartate aminotransferase (AST), total protein (TP), albumin (ALB), globulin (GLB), triglyceride (TG), total cholesterol (TC), and high-density lipoprotein cholesterol (HDL-C). Random blood glucose (RBG) test, oral glucose tolerance test (OGTT), and oral maltose tolerance test (OMTT) were also conducted. Microscopy was used to observe morphological changes in the liver of AOS-treated groups. Real-time PCR was used to detect the mRNA expression, including insulin receptor substrate 2 (IRS-2), phosphatidylinositol 3 kinase (PI3K), protein kinase B (AKT), peroxisome proliferator-activated receptor (PPAR)-γ, insulin receptor (INS-R), and Glut4. Furthermore, western blotting was performed to identify proteins, including phosphorylation of IRS-2 (p-IRS-2), PI3K, p-AKT, PPAR-γ, INS-R, and Glut4. Hepatic protein expression of p-IRS-2, PI3K, p-AKT, PPAR-γ, INS-R, and Glut4 was observed using immunohistochemical staining.

RESULTS

AOS treatment significantly decreased RBG, OGTT, and OMTT in mice, as well as serum ALT and AST activities. AOS groups demonstrated significantly higher expressions of p-IRS-2, PI3K, PPAR-γ, p-AKT, INS-R, and Glut4 protein and IRS-2, PI3K, AKT, PPAR-γ, INS-R, and Glut4 mRNA in the liver tissue of db/db mice; the degeneration and necrosis of hepatocytes and formation of collagen fibres markedly reduced, improving the structural disorder in the liver.

CONCLUSION

The results suggest that AOS could protect the liver in type 2 diabetes, in part by activating insulin in the INS-R/IRS2/PI3K/AKT/Glut4/PPAR-γ signal pathway, facilitating hepatocyte proliferation, and further reducing the blood glucose levels.

Expression and functional analysis of the Akt gene from Daphnia pulex

Daphnia pulex is a nutrient-rich freshwater crustacean with two different reproduction methods. Akt is a serine/threonine protein kinase that plays an important role in cell growth, survival, and lifespan regulation. To explore the function of Akt in the growth and aging process of Daphnia pulex, we cloned the cDNA sequence of the open reading frame (ORF) of the akt gene based on the bioinformatic analysis of the transcriptome data of D. pulex, and analyzed the structural features of the Akt protein. Gene silencing was performed using RNA interference (RNAi), and the expression of the Akt gene and protein before and after interference were analyzed using qPCR and western blotting. The results showed that the expression of akt in D. pulex at different ages showed a "W" pattern, being significantly higher at 20 days than at 10 days and 15 days (P < .05). The expression trend of Akt protein and mRNA were similar, with lower expression at a younger age (1-5 day), after which expression gradually increased from 10 days age, and showed no significant change after 25 days, which might be caused by a lag of protein translation. RNAi reduced the expression of the Akt gene and protein by at least 76%, and the survival rate and reproductive capacity of D. pulex were significantly lower in the RNAi group compared with those in the control group. This study provides a better understanding of the function of the akt gene in D. pulex.

Covalent-Allosteric Inhibitors to Achieve Akt Isoform-Selectivity

Isoforms of protein kinase Akt are involved in essential processes including cell proliferation, survival, and metabolism. However, their individual roles in health and disease have not been thoroughly evaluated. Thus, there is an urgent need for perturbation studies, preferably mediated by highly selective bioactive small molecules. Herein, we present a structure‐guided approach for the design of structurally diverse and pharmacologically beneficial covalent‐allosteric modifiers, which enabled an investigation of the isoform‐specific preferences and the important residues within the allosteric site of the different isoforms. The biochemical, cellular, and structural evaluations revealed interactions responsible for the selective binding profiles. The isoform‐selective covalent‐allosteric Akt inhibitors that emerged from this approach showed a conclusive structure–activity relationship and broke ground in the development of selective probes to delineate the isoform‐specific functions of Akt kinases.

Effects of Agriophyllum squarrosum extracts on glucose metabolism in KKAy mice and the associated underlying mechanisms

ETHNOPHARMACOLOGICAL RELEVANCE

Agriophyllum squarrosum (L.) Moq. is a traditional Mongol medicine commonly used in the treatment of diabetes.

AIM OF THE STUDY

To examine the effects of Agriophyllum squarrosum extract (ASE) on glucose metabolism in type 2 diabetic KKAy mice, and to investigate the mechanisms underlying these effects.

MATERIAL AND METHODS

KKAy mice were divided into a model control group (MCG), a low-dose Agriophyllum squarrosum extract group (LASEG), a medium-dose Agriophyllum squarrosum extract group (MASEG), a high-dose Agriophyllum squarrosum extract group (HASEG), and a metformin group (MEG). Syngeneic C57BL/6 mice were used as a normal control group (NCG). Drugs were administered to all mice by gavage for 8 weeks. Random blood glucose levels were measured in the mice at baseline and after 2, 4, and 8 weeks of treatment. Glucose tolerance was measured after 6 weeks of drug administration. After 8 weeks, glycated serum proteins (GSP) and advanced glycation end-products (AGEs) in the serum of all mice were measured. Sections of mouse liver tissues were used for periodic acid-Schiff staining (PAS) and the content of hepatic glycogen was determined. Immunohistochemistry was used to determine the effects of ASE on liver phospho-insulin receptor substrate 2 (P-IRS2) protein expression. Western blotting was used to quantify the protein expression levels of phosphatidylinositol 3-kinase (PI3K), AKT, phospho-AKT (S473) (P-AKT), glycogen synthase kinase 3β (GSK3β), and glucose transporters 4 (GLUT4), while PCR was used to quantify the mRNA expression levels of insulin receptor substrate 2 (IRS2), PI3K, AKT, GSK3β, and GLUT4.

RESULTS

ASE treatment decreased random blood glucose levels in type 2 diabetic KKAy mice; increased glucose tolerance; decreased serum GSP and AGEs content; increased glycogen synthesis in liver tissues; upregulated the protein expression levels of PI3K, AKT, GLUT4, and P-IRS2; downregulated the protein expression level of GSK3β in liver tissues; upregulated the mRNA expression levels of IRS2, PI3K, AKT, and GLUT4; and downregulated the mRNA expression level of GSK3β in liver tissues.

CONCLUSION

ASE treatment may increase glucose metabolism in KKAy mice and improve glucose tolerance. The underlying mechanisms of the beneficial effects of ASE may be associated with the increase of glycogen synthesis, the inhibition of AGEs production, the upregulation of IRS2, PI3K, AKT, and GLUT4 protein and mRNA expression, and the downregulation of GSK3β protein and mRNA expression.

Akt1-mediated CPR cooling protection targets regulators of metabolism, inflammation and contractile function in mouse cardiac arrest

Therapeutic hypothermia initiated during cardiopulmonary resuscitation (CPR) in pre-clinical studies appears to be highly protective against sudden cardiac arrest injury. Given the challenges to implementing CPR cooling clinically, insights into its critical mechanisms of protection could guide development of new CPR drugs that mimic hypothermia effects without the need for physical cooling. Here, we used Akt1-deficient mice that lose CPR hypothermia protection to identify hypothermia targets. Adult female C57BL/6 mice (Akt1^+/+ and Akt1^+/-) underwent 8 min of KCl-induced asystolic arrest and were randomized to receive hypothermia (30 ± 0.5°C) or normothermia. Hypothermia was initiated during CPR and extended for 1 h after resuscitation. Neurologically scored survival was measured at 72 h. Other outcomes included mean arterial pressure and target measures in heart and brain related to contractile function, glucose utilization and inflammation. Compared to northothermia, hypothermia improved both 2h mean arterial pressure and 72h neurologically intact survival in Akt1^+/+ mice but not in Akt1^+/- mice. In Akt1^+/+ mice, hypothermia increased Akt and GSK3β phosphorylation, pyruvate dehydrogenase activation, and NAD⁺ and ATP production while decreasing IκBα degradation and NF-κB activity in both heart and brain at 30 min after CPR. It also increased phospholamban phosphorylation in heart tissue. Further, hypothermia reduced metabolic and inflammatory blood markers lactate and Pre-B cell Colony Enhancing Factor. Despite hypothermia treatment, all these effects were reversed in Akt1^+/- mice. Taken together, drugs that target Akt1 and its effectors may have the potential to mimic hypothermia-like protection to improve sudden cardiac arrest survival when administered during CPR.

Effect of type 2 diabetes mellitus caveolin-3 K15N mutation on glycometabolism

Caveolin-3 (CAV3) is a muscle-specific protein present within the muscle cell membrane that affects signaling pathways, including the insulin signaling pathway. A previous assessment of patients with newly developed type 2 diabetes (T2DM) demonstrated that CAV3 gene mutations may lead to changes in protein secondary structure. A severe CAV3 P104L mutation has previously been indicated to influence the phosphorylation of skeletal muscle cells and result in impaired glucose metabolism. In the present study, the effect of CAV3 K15N gene transfection in C2C12 cells was assessed. Transfection with K15N reduced the expression of total CAV3 and AKT2 proteins in the cells, and the translocation of glucose transporter type 4 to the muscle cell membrane, which resulted in decreased glucose uptake and glycogen synthesis in myocytes. In conclusion, these results indicate that the CAV3 K15N mutation may cause insulin-stimulated impaired glucose metabolism in myocytes, which may contribute to the development of T2DM.

Predictive factors for the development of diabetes in cancer patients treated with phosphatidylinositol 3-kinase inhibitors

PURPOSE

Targeted therapy using phosphatidylinositol 3-kinase (PI3K) inhibitors is used to treat cancer such as lymphoma. In animal studies, its use raised concern about alteration of glucose metabolism. To date, clinical data are inconclusive; therefore, we investigated the incidence and clinical manifestations of diabetes in cancer patients treated with PI3K inhibitors.

METHODS

In a retrospective review of diabetes-free patients with advanced solid tumors treated with PI3K inhibitor, we performed Cox regression to identify independent predictors for the development of diabetes.

RESULTS

Of 38 patients (mean age: 54.5 years, 23.7% female) having a mean duration of follow-up of 238.5 days who initiated PI3K inhibitors, 55.3% developed diabetes during treatment (mean 29.1 days); among these, 28.6% experienced remission of diabetes after discontinuing PI3K inhibitors (mean 72.1 days). Patients with incident diabetes had higher anti-hypertensive medication use, higher HbA1c levels and fasting glucose at baseline, and longer duration of PI3K inhibitor use (P = 0.024, P = 0.005, P = 0.008, and P = 0.023, respectively). Previous steroid use and lower baseline HbA1c level were significantly associated with development of diabetes (HR = 8.41, 95% CI 1.89-37.33; HR = 2.16, 95% CI 1.09-4.25, respectively). Patients whose diabetes remitted after discontinuing PI3K inhibitors were younger (P = 0.035) and had lower fasting glucose levels during PI3K inhibitor treatment (P = 0.001) compared to those non-remitters.

CONCLUSIONS

Previous steroid use and lower baseline HbA1c level may be important predictors for developing diabetes in patients with advanced solid tumors treated with PI3K inhibitors, warranting close observation and careful intervention.

Iloprost supports early development of in vitro-produced porcine embryos through activation of the phosphatidylinositol 3-kinase/AKT signalling pathway

Despite evidence of the presence of prostaglandin (PG) I₂ in mammalian oviducts, its role in early development of in vitro-produced (IVP) embryos is largely unknown. Thus, in the present study we examined the effects of iloprost, a PGI₂ analogue, on the in vitro developmental competence of early porcine embryos and the underlying mechanism(s). To examine the effects of iloprost on the development rate of IVF embryos, iloprost was added to the in vitro culture (IVC) medium and cultured for 6 days. Supplementation of the IVC medium with iloprost significantly improved developmental parameters, such as blastocyst formation rate, the trophectoderm:inner cell mass ratio and cell survival in IVF and parthenogenetically activated (PA) embryos. In addition, post-blastulation development into the expanded blastocyst stage was improved in iloprost-treated groups compared with controls. Interestingly, the phosphatidylinositol 3-kinase (PI3K)/AKT signalling pathway was significantly activated by iloprost supplementation in a concentration-dependent manner (10-1000nM), and the beneficial effects of iloprost on the early development of porcine IVF and PA embryos was completely ablated by treatment with 2.5μM wortmannin, a PI3K/AKT signalling inhibitor. Importantly, expression of the PI3K/AKT signalling pathway was significantly reduced in somatic cell nuclear transfer (SCNT) compared with IVF embryos, and iloprost supported the early development of SCNT embryos, as was the case for IVF and PA embryos, suggesting a consistent effect of iloprost on the IVC of IVP porcine embryos. Together, these results indicate that iloprost can be a useful IVC supplement for production of IVP early porcine embryos with high developmental competence.

Phosphoinositide 3-Kinase Is Integral for the Acute Activity of Leptin and Insulin in Male Arcuate NPY/AgRP Neurons

Neuropeptide Y (NPY)/Agouti-related protein (AgRP) neurons in the arcuate nucleus of the hypothalamus are part of a neuroendocrine feedback loop that regulates feeding behavior and glucose homeostasis. NPY/AgRP neurons sense peripheral signals (including the hormones leptin, insulin, and ghrelin) and integrate those signals with inputs from other brain regions. These inputs modify both long-term changes in gene transcription and acute changes in the electrical activity of these neurons, leading to a coordinated response to maintain energy and glucose homeostasis. However, the mechanisms by which the hormones insulin and leptin acutely modify the electrical activity of these neurons remain unclear. In this study, we show that loss of the phosphoinositide 3-kinase catalytic subunits p110α and p110β in AgRP neurons abrogates the leptin- and insulin-induced inhibition of AgRP neurons. Moreover, continual disruption of p110α and p110β in AgRP neurons results in increased weight gain. The increased adiposity was concomitant with a hypometabolic phenotype: decreased energy expenditure independent of changes in food intake. Deficiency of p110α and p110β in AgRP neurons also impaired glucose homeostasis and insulin sensitivity. In summary, these data highlight the requirement of both p110α and p110β in AgRP neurons for the proper regulation of energy balance and glucose homeostasis.

Multi-factorial modulation of colorectal carcinoma cells motility - partial coordination by the tetraspanin Co-029/tspan8

Colorectal carcinoma cells Isreco1 display an ability to migrate controlled by a complex set of signals issued from the membrane. By comparing cells infected by mycoplasmas and mycoplasmas free cells, we have established that basal 2D migration is dependent on a double signal mediated by the collagen receptors integrins alpha1/2 and the Toll-Like receptor TLR2. The signal issued from mycoplasmas can be replaced by a TLR2 ligand and the functional effect is neutralized by silencing of MyD88. Following previous observation that downregulation of E-cadherin/p120 catenin increases cell motility, we now report that EGFR or CD44 inhibition have a similar effect on cell motility that is restricted to tetraspanin Co-029/tspan8 transduced IsrecoI cells (Is1-Co029). The modulation of cell migration linked to EGFR or CD44 can be neutralized by antagonizing Co-029 with the mAb Ts29.1 or by RNA interference. Altogether these data point to a crucial role of Co-029 in the modulation of colon cancer cell motility which could be related to the protumoral effect reported for this tetraspanin. Among surface molecules able to mediate Co-029 function, E-cadherin, EGFR and CD44 appear as likely candidates.

Action of Phytochemicals on Insulin Signaling Pathways Accelerating Glucose Transporter (GLUT4) Protein Translocation

Diabetes is associated with obesity, generally accompanied by a chronic state of oxidative stress and redox imbalances which are implicated in the progression of micro- and macro-complications like heart disease, stroke, dementia, cancer, kidney failure and blindness. All these complications rise primarily due to consistent high blood glucose levels. Insulin and glucagon help to maintain the homeostasis of glucose and lipids through signaling cascades. Pancreatic hormones stimulate translocation of the glucose transporter isoform 4 (GLUT4) from an intracellular location to the cell surface and facilitate the rapid insulin-dependent storage of glucose in muscle and fat cells. Malfunction in glucose uptake mechanisms, primarily contribute to insulin resistance in type 2 diabetes. Plant secondary metabolites, commonly known as phytochemicals, are reported to have great benefits in the management of type 2 diabetes. The role of phytochemicals and their action on insulin signaling pathways through stimulation of GLUT4 translocation is crucial to understand the pathogenesis of this disease in the management process. This review will summarize the effects of phytochemicals and their action on insulin signaling pathways accelerating GLUT4 translocation based on the current literature.

Metabolic Reprogramming by the PI3K-Akt-mTOR Pathway in Cancer

In the past decade, there has been a resurgence of interest in elucidating how metabolism is altered in cancer cells and how such dependencies can be targeted for therapeutic gain. At the core of this research is the concept that metabolic pathways are reprogrammed in cancer cells to divert nutrients toward anabolic processes to facilitate enhanced growth and proliferation. Importantly, physiological cellular signaling mechanisms normally tightly regulate the ability of cells to gain access to and utilize nutrients, posing a fundamental barrier to transformation. This barrier is often overcome by aberrations in cellular signaling that drive tumor pathogenesis by enabling cancer cells to make critical cellular decisions in a cell-autonomous manner. One of the most frequently altered pathways in human cancer is the PI3K-Akt-mTOR signaling pathway. Here, we describe mechanisms by which this signaling network is responsible for controlling cellular metabolism. Through both the post-translational regulation and the induction of transcriptional programs, the PI3K-Akt-mTOR pathway coordinates the uptake and utilization of multiple nutrients, including glucose, glutamine, nucleotides, and lipids, in a manner best suited for supporting the enhanced growth and proliferation of cancer cells. These regulatory mechanisms illustrate how metabolic changes in cancer are closely intertwined with oncogenic signaling pathways that drive tumor initiation and progression.

Zebrafish akt2 is essential for survival, growth, bone development, and glucose homeostasis

As one of three akt isoforms, akt2 plays a key role in the regulation of widely divergent cellular processes in mammals. However, its role and underlying mechanisms in zebrafish remain largely unknown. To elucidate the function of akt2 in zebrafish, we generated zebrafish lacking akt2 gene via CRISPR/Cas9 technology. Akt2-null zebrafish exhibit partial lethality and severe growth deficiency, which is different from those observed in akt2-null mice. Furthermore, akt2-null zebrafish display deficiency in fin ray development, but their cartilage is not affected. Similar to observations in akt2-null mice, akt2-null zebrafish display impaired glucose homeostasis. However, in contrast to that in akt2-null mice, insulin level is lower in akt2-null zebrafish, implicating the symptoms of type I diabetes exhibited in akt2-null zebrafish. In addition, transcriptome analysis reveals that the genes involved in metabolism and osteogenesis are disturbed in akt2-null zebrafish. Taken together, these data not only support an important role of akt2 in zebrafish survival, growth, bone development and glucose homeostasis, but also suggest that akt2 has divergent functions between mice and zebrafish, even though they are evolutionarily conserved.

Different functions of AKT1 and AKT2 in molecular pathways, cell migration and metabolism in colon cancer cells

AKT is a central protein in many cellular pathways such as cell survival, proliferation, glucose uptake, metabolism, angiogenesis, as well as radiation and drug response. The three isoforms of AKT (AKT1, AKT2 and AKT3) are proposed to have different physiological functions, properties and expression patterns in a cell type-dependent manner. As of yet, not much is known about the influence of the different AKT isoforms in the genome and their effects in the metabolism of colorectal cancer cells. In the present study, DLD-1 isogenic AKT1, AKT2 and AKT1/2 knockout colon cancer cell lines were used as a model system in conjunction with the parental cell line in order to further elucidate the differences between the AKT isoforms and how they are involved in various cellular pathways. This was done using genome wide expression analyses, metabolic profiling and cell migration assays. In conclusion, downregulation of genes in the cell adhesion, extracellular matrix and Notch-pathways and upregulation of apoptosis and metastasis inhibitory genes in the p53-pathway, confirm that the knockout of both AKT1 and AKT2 will attenuate metastasis and tumor cell growth. This was verified with a reduction in migration rate in the AKT1 KO and AKT2 KO and most explicitly in the AKT1/2 KO. Furthermore, the knockout of AKT1, AKT2 or both, resulted in a reduction in lactate and alanine, suggesting that the metabolism of carbohydrates and glutathione was impaired. This was further verified in gene expression analyses, showing downregulation of genes involved in glucose metabolism. Additionally, both AKT1 KO and AKT2 KO demonstrated an impaired fatty acid metabolism. However, genes were upregulated in the Wnt and cell proliferation pathways, which could oppose this effect. AKT inhibition should therefore be combined with other effectors to attain the best effect.

Optogenetic activation reveals distinct roles of PIP3 and Akt in adipocyte insulin action

Glucose transporter 4 (GLUT4; also known as SLC2A4) resides on intracellular vesicles in muscle and adipose cells, and translocates to the plasma membrane in response to insulin. The phosphoinositide 3-kinase (PI3K)-Akt signaling pathway plays a major role in GLUT4 translocation; however, a challenge has been to unravel the potentially distinct contributions of PI3K and Akt (of which there are three isoforms, Akt1-Akt3) to overall insulin action. Here, we describe new optogenetic tools based on CRY2 and the N-terminus of CIB1 (CIBN). We used these 'Opto' modules to activate PI3K and Akt selectively in time and space in 3T3-L1 adipocytes. We validated these tools using biochemical assays and performed live-cell kinetic analyses of IRAP-pHluorin translocation (IRAP is also known as LNPEP and acts as a surrogate marker for GLUT4 here). Strikingly, Opto-PIP3 largely mimicked the maximal effects of insulin stimulation, whereas Opto-Akt only partially triggered translocation. Conversely, drug-mediated inhibition of Akt only partially dampened the translocation response of Opto-PIP3 In spatial optogenetic studies, focal targeting of Akt to a region of the cell marked the sites where IRAP-pHluorin vesicles fused, supporting the idea that local Akt-mediated signaling regulates exocytosis. Taken together, these results indicate that PI3K and Akt play distinct roles, and that PI3K stimulates Akt-independent pathways that are important for GLUT4 translocation.

Modulation of the cellular content of metabolites in adipocytes by insulin

Although the insulin-mediated cell signaling pathway has been extensively examined, changes in the cellular content of metabolites currently remain unclear. We herein examined metabolite contents in 3T3-L1 adipocytes treated with insulin using a metabolomic analysis. Fifty-four compounds were detected, and the contents of metabolites from the citric acid cycle increased in response to the insulin treatment for 4 h, which was sensitive to U0126 and LY294002, inhibitors for mitogen-activated protein kinase kinase-1 and phosphoinositide 3-kinase, respectively. The cellular contents of fumaric acid and malic acid were increased more by insulin than those of citric acid and succinic acid. Time-course changes in metabolites from the citric acid cycle exhibited oscillations with a 2-h cycle. A metabolic pathway analysis also indicated that insulin affected the metabolism of alanine, aspartate and glutamate, as well as that of arginine and proline. The contents of free amino acids were slightly decreased by the insulin treatment, while the co-treatment with U0126 and LY294002 abrogated these insulin-mediated decreases. The present study revealed the unexpected accumulation of citric acid cycle metabolites in adipocytes by insulin. Our results indicate the usefulness of metabolomic analyses for obtaining a more comprehensive understanding of the regulation of metabolic pathways in cell-culture systems.

Glucose transporters: cellular links to hyperglycemia in insulin resistance and diabetes

Abnormal expression and/or function of mammalian hexose transporters contribute to the hallmark hyperglycemia of diabetes. Due to different roles in glucose handling, various organ systems possess specific transporters that may be affected during the diabetic state. Diabetes has been associated with higher rates of intestinal glucose transport, paralleled by increased expression of both active and facilitative transporters and a shift in the location of transporters within the enterocyte, events that occur independent of intestinal hyperplasia and hyperglycemia. Peripheral tissues also exhibit deregulated glucose transport in the diabetic state, most notably defective translocation of transporters to the plasma membrane and reduced capacity to clear glucose from the bloodstream. Expression of renal active and facilitative glucose transporters increases as a result of diabetes, leading to elevated rates of glucose reabsorption. However, this may be a natural response designed to combat elevated blood glucose concentrations and not necessarily a direct effect of insulin deficiency. Functional foods and nutraceuticals, by modulation of glucose transporter activity, represent a potential dietary tool to aid in the management of hyperglycemia and diabetes.

Calorie restriction leads to greater Akt2 activity and glucose uptake by insulin-stimulated skeletal muscle from old rats

Skeletal muscle insulin resistance is associated with many common age-related diseases, but moderate calorie restriction (CR) can substantially elevate glucose uptake by insulin-stimulated skeletal muscle from both young and old rats. The current study evaluated the isolated epitrochlearis muscle from ∼24.5-mo-old rats that were either fed ad libitum (AL) or subjected to CR (consuming ∼65% of ad libitum, AL, intake beginning at ∼22.5 mo old). Some muscles were also incubated with MK-2206, a potent and selective Akt inhibitor. The most important results were that in isolated muscles, CR vs. AL resulted in 1) greater insulin-stimulated glucose uptake 2) that was accompanied by significantly increased insulin-mediated activation of Akt2, as indicated by greater phosphorylation on both Thr(309) and Ser(474) along with greater Akt2 activity, 3) concomitant with enhanced phosphorylation of several Akt substrates, including an Akt substrate of 160 kDa on Thr(642) and Ser(588), filamin C on Ser(2213) and proline-rich Akt substrate of 40 kDa on Thr(246), but not TBC1D1 on Thr(596); and 4) each of the CR effects was eliminated by MK-2206. These data provide compelling new evidence linking greater Akt2 activation to the CR-induced elevation of insulin-stimulated glucose uptake by muscle from old animals.

Methods for Assessing the In Vivo Role of PTEN in Glucose Homeostasis

PTEN plays an important role in diabetes pathogenesis not only as a key negative regulator of the PI3K/Akt pathway required for insulin action, but also via its role in other cell processes required to maintain metabolic homeostasis. We describe the generation of tissue-specific PTEN knockout mice and models of both type 1 and type 2 diabetes, which we have found useful for the study of diabetes pathogenesis. We also outline common methods suitable for the characterization of glucose homeostasis in rodent models, including techniques to measure beta cell function and insulin sensitivity.

Phase I study of the anti-IGF1R antibody cixutumumab with everolimus and octreotide in advanced well-differentiated neuroendocrine tumors

Preclinical data suggest multiple roles for the IGF1 receptor (IGF1R) in neuroendocrine tumors (NETs), including mediating resistance to mammalian target of rapamycin (mTOR) inhibitors. Everolimus, an oral mTOR inhibitor, and octreotide long-acting repeatable (LAR) are approved for subgroups of well-differentiated NET. The primary objective of the present study was to establish the safety and recommended phase II dose (RP2D) of cixutumumab, a monoclonal antibody (MAB) against IGF1R, with everolimus and octreotide LAR. Patients with well-differentiated NET were treated with 10  mg everolimus p.o. daily, 20  mg octreotide LAR i.m. every 21 days, and escalating doses of cixutumumab. An expansion cohort was enrolled at RP2D. Correlative studies included the evaluation of mTOR pathway inhibition in paired tumor biopsies and the effects of this combination on metabolism via indirect calorimetry. Nineteen patients with progressive disease were enrolled, including nine to the expansion portion. Two patients had dose-limiting toxicities of grade 3 mucositis at 15  mg/kg cixutumumab. Long-term tolerance at RP2D was problematic, and the most common ≥grade 3 adverse event was fatigue. One patient with metastatic insulinoma had a confirmed partial response, whereas 17 had stable disease. The median progression-free survival was 43.6 weeks, and the median overall survival was 25.5 months. The RP2D of this combination per the predefined study protocol of 10  mg/kg cixutumumab i.v., 20  mg octreotide LAR i.m. every 21 days plus 10  mg everolimus p.o. daily is associated with non-dose-limiting toxicities that limit long-term tolerance. Although a signal of activity was noted in the present study, this will need to be reconciled with limited tolerance of the combination and data from larger studies of anti-IGF1R MABs in NET that have been disappointing.

MiR-191 Regulates Primary Human Fibroblast Proliferation and Directly Targets Multiple Oncogenes

miRNAs play a central role in numerous pathologies including multiple cancer types. miR-191 has predominantly been studied as an oncogene, but the role of miR-191 in the proliferation of primary cells is not well characterized, and the miR-191 targetome has not been experimentally profiled. Here we utilized RNA induced silencing complex immunoprecipitations as well as gene expression profiling to construct a genome wide miR-191 target profile. We show that miR-191 represses proliferation in primary human fibroblasts, identify multiple proto-oncogenes as novel miR-191 targets, including CDK9, NOTCH2, and RPS6KA3, and present evidence that miR-191 extensively mediates target expression through coding sequence (CDS) pairing. Our results provide a comprehensive genome wide miR-191 target profile, and demonstrate miR-191’s regulation of primary human fibroblast proliferation.

The Akt isoforms, their unique functions and potential as anticancer therapeutic targets

Akt (also known as protein kinase B or PKB) is the major downstream nodal point of the PI3K signaling pathway. This pathway is a promising anticancer therapeutic target, because constitutive activation of the PI3K-Akt pathway is correlated with tumor development, progression, poor prognosis, and resistance to cancer therapies. The Akt serine/threonine kinase regulates diverse cellular functions including cell growth, proliferation, glucose metabolism, and survival. Although all three known Akt isoforms (Akt1-3) are encoded by separate genes, their amino acid sequences show a high degree of similarity. For this and other reasons, it has long been assumed that all three Akt isoforms are activated in the same way, and their functions largely overlap. However, accumulating lines of evidence now suggest that the three Akt isoforms might have unique modes of activation and many distinct functions. In particular, it has recently been found that the Akt isoforms are localized at different subcellular compartments in both adipocytes and cancer cells. In this review, we highlight the unique roles of each Akt isoform by introducing published data obtained from both in vitro and in vivo studies. We also discuss the significant potential of the Akt isoforms as effective anticancer therapeutic targets.

PI3K signaling in the pathogenesis of obesity: The cause and the cure

With the steady rise in the incidence of obesity and its associated comorbidities, in the last decades research aimed at understanding molecular mechanisms that control body weight has gained new interest. Fat gain is frequently associated with chronic adipose tissue inflammation and with peripheral as well as central metabolic derangements, resulting in an impaired hypothalamic regulation of energy homeostasis. Recent attention has focused on the role of phosphatidylinositol 3-kinase (PI3K) in both immune and metabolic response pathways, being involved in the pathophysiology of obesity and its associated metabolic diseases. In this review, we focus on distinct PI3K isoforms, especially class I PI3Ks, mediating inflammatory cells recruitment to the enlarged fat as well as intracellular responses to key hormonal regulators of fat storage, both in adipocytes and in the central nervous system. This integrated view of PI3K functions may ultimately help to develop new therapeutic interventions for the treatment of obesity.

Targeting SREBP-1-driven lipid metabolism to treat cancer

Metabolic reprogramming is a hallmark of cancer. Oncogenic growth signaling regulates glucose, glutamine and lipid metabolism to meet the bioenergetics and biosynthetic demands of rapidly proliferating tumor cells. Emerging evidence indicates that sterol regulatory element-binding protein 1 (SREBP-1), a master transcription factor that controls lipid metabolism, is a critical link between oncogenic signaling and tumor metabolism. We recently demonstrated that SREBP-1 is required for the survival of mutant EGFR-containing glioblastoma, and that this pro-survival metabolic pathway is mediated, in part, by SREBP-1-dependent upregulation of the fatty acid synthesis and low density lipoprotein (LDL) receptor (LDLR). These results have identified EGFR/PI3K/Akt/SREBP-1 signaling pathway that promotes growth and survival in glioblastoma, and potentially other cancer types. Here, we summarize recent insights in the understanding of cancer lipid metabolism, and discuss the evidence linking SREBP-1 with PI3K/Akt signaling-controlled glycolysis and with Myc-regulated glutaminolysis to lipid metabolism. We also discuss the development of potential drugs targeting the SREBP-1- driven lipid metabolism as anti-cancer agents.

miR-503 represses human cell proliferation and directly targets the oncogene DDHD2 by non-canonical target pairing

Background

The pathways regulating the transition of mammalian cells from quiescence to proliferation are mediated by multiple miRNAs. Despite significant improvements in our understanding of miRNA targeting, the majority of miRNA regulatory networks are still largely unknown and require experimental validation.

Results

Here we identified miR-503, miR-103, and miR-494 as negative regulators of proliferation in primary human cells. We experimentally determined their genome wide target profiles using RNA-induced silencing complex (RISC) immunoprecipitations and gene expression profiling. Analysis of the genome wide target profiles revealed evidence of extensive regulation of gene expression through non-canonical target pairing by miR-503. We identified the proto-oncogene DDHD2 as a target of miR-503 that requires pairing outside of the canonical 5′ seed region of miR-503, representing a novel mode of miRNA-target pairing. Further bioinformatics analysis implicated miR-503 and DDHD2 in breast cancer tumorigenesis.

Conclusions

Our results provide an extensive genome wide set of targets for miR-503, miR-103, and miR-494, and suggest that miR-503 may act as a tumor suppressor in breast cancer by its direct non-canonical targeting of DDHD2.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1279-9) contains supplementary material, which is available to authorized users.

Differential effects of Akt isoforms on somatic cell reprogramming

Akt plays an important role in cell growth, proliferation and survival. The specific roles of the three Akt isoforms in somatic cell reprogramming have not been investigated. Here we report that, during iPSC generation, enhanced Akt1 activity promotes complete reprogramming mainly through increased activation of Stat3 in concert with leukemia inhibitory factor (LIF) and, to a lesser extent, through promotion of colony formation. Akt1 augments Stat3 activity through activation of mTOR and upregulation of LIF receptor expression. Similarly, enhanced Akt2 or Akt3 activation also promotes reprogramming and coordinates with LIF to activate Stat3. Blocking Akt1 or Akt3 but not Akt2 expression prohibits cell proliferation and reprogramming. Furthermore, the halt in cell proliferation and reprogramming caused by mTOR and Akt inhibitors can be reversed by inhibition of GSK3. Finally, we found that expressing the GSK3β target Esrrb overrides inhibition of Akt and restores reprogramming. Our data demonstrated that during reprogramming, Akt promotes establishment of pluripotency through co-stimulation of Stat3 activity with LIF. Akt1 and Akt3 are essential for the proliferation of reprogrammed cells, and Esrrb supports cell proliferation and complete reprogramming during Akt signaling.

Lysosomal interaction of Akt with Phafin2: a critical step in the induction of autophagy

Autophagy is an evolutionarily conserved mechanism for the gross disposal of intracellular proteins in mammalian cells and dysfunction in this pathway has been associated with human disease. Although the serine threonine kinase Akt is suggested to play a role in this process, little is known about the molecular mechanisms by which Akt induces autophagy. Using a yeast two-hybrid screen, Phafin2 (EAPF or PLEKHF2), a lysosomal protein with a unique structure of N-terminal PH (pleckstrin homology) domain and C-terminal FYVE (Fab 1, YOTB, Vac 1, and EEA1) domain was found to interact with Akt. A sucrose gradient fractionation experiment revealed that both Akt and Phafin2 co-existed in the same lysosome enriched fraction after autophagy induction. Confocal microscopic analysis and BiFC analysis demonstrated that both Akt and Phafin2 accumulate in the lysosome after induction of autophagy. BiFC analysis using PtdIns (3)P interaction defective mutant of Phafin2 demonstrated that lysosomal accumulation of the Akt-Phafin2 complex and subsequent induction of autophagy were lysosomal PtdIns (3)P dependent events. Furthermore, in murine macrophages, both Akt and Phafin2 were required for digestion of fluorescent bacteria and/or LPS-induced autophagy. Taken together, these findings establish that lysosomal accumulation of Akt and Phafin2 is a critical step in the induction of autophagy via an interaction with PtdIns (3)P.

Regulation of CYP3A genes by glucocorticoids in human lung cells

Inhaled glucocorticoids are the first-line treatment for patients with persistent asthma.  However, approximately thirty percent of patients exhibit glucocorticoid insensitivity, which may involve excess metabolic clearance of the glucocorticoids by CYP3A enzymes in the lung.  CYP3A4, 3A5, and 3A7 enzymes metabolize glucocorticoids, which in turn induce CYP3A genes.  However, the mechanism of CYP3A5 mRNA regulation by glucocorticoids in lung cells has not been determined.  In hepatocytes, glucocorticoids bind to the glucocorticoid receptor (GR), which induces the expression of the constitutive androstane receptor or pregnane X receptor; both of which bind to the retinoid X receptor alpha, leading to the induction of CYP3A4, 3A5, and 3A7.  There is also evidence to suggest a direct induction of CYP3A5 by GR activation in liver cells. In this study, these pathways were evaluated as the mechanism for CYP3A5 mRNA induction by glucocorticoids in freshly isolated primary tracheal epithelial, adenocarcinomic human alveolar basal epithelial (A549), immortalized bronchial epithelial (BEAS-2B), primary normal human bronchial/tracheal epithelial (NHBE), primary small airway epithelial (SAEC), and primary lobar epithelial lung cells. In A549 cells, beclomethasone 17-monopropionate ([M1]) induced CYP3A5 mRNA through the glucocorticoid receptor. CYP3A5 mRNA induction by five different glucocorticoids was attenuated by inhibiting the glucocorticoid receptor using ketoconazole, and for beclomethasone dipropionate, using siRNA-mediated knock-down of the glucocorticoid receptor. The constitutive androstane receptor was not expressed in lung cells. SAEC cells, a primary lung cell line, expressed CYP3A5, but CYP3A5 mRNA was not induced by glucocorticoid treatment despite evaluating a multitude of cell culture conditions. None of the other lung cells expressed CYP3A4, 3A5 or 3A7 mRNA. These studies demonstrate that CYP3A5 mRNA is induced by glucocorticoids in A549 cells via the glucocorticoid receptor, but that additional undefined regulatory processes exist in primary lung cells.

A Myc-microRNA network promotes exit from quiescence by suppressing the interferon response and cell-cycle arrest genes

The transition of mammalian cells from quiescence to proliferation is accompanied by the differential expression of several microRNAs (miRNAs) and transcription factors. However, the interplay between transcription factors and miRNAs in modulating gene regulatory networks involved in human cell proliferation is largely unknown. Here we show that the miRNA miR-22 promotes proliferation in primary human cells, and through a combination of Argonaute-2 immunoprecipitation and reporter assays, we identified multiple novel targets of miR-22, including several cell-cycle arrest genes that mediate the effects of the tumor-suppressor p53. In addition, we found that miR-22 suppresses interferon gene expression by directly targeting high mobility group box-1 and interferon regulatory factor (IRF)-5, preventing activation of IRF3 and NF-κB, which are activators of interferon genes. The expression of interferon genes is elevated in quiescent cells and their expression is inhibitory for cell proliferation. In addition, we find that miR-22 is activated by the transcription factor Myc when quiescent cells enter proliferation and that miR-22 inhibits the Myc transcriptional repressor MXD4, mediating a feed-forward loop to elevate Myc expression levels. Our results implicate miR-22 in downregulating the anti-proliferative p53 and interferon pathways and reveal a new transcription factor–miRNA network that regulates the transition of primary human cells from quiescence to proliferation.

Akt inactivation induces endoplasmic reticulum stress-independent autophagy in fibroblasts from patients with Pompe disease

Pompe disease (glycogen storage disease type II) is an autosomal recessive neuromuscular disorder arising from a deficiency of lysosomal acid α-glucosidase (GAA). Accumulation of autophagosomes is a key pathological change in skeletal muscle fibers and fibroblasts from patients with Pompe disease and is implicated in the poor response to enzyme replacement therapy (ERT). We previously found that mutant GAA-induced endoplasmic reticulum (ER) stress initiated autophagy in patient fibroblasts. However, the mechanism of induction of autophagy in fibroblasts from Pompe disease patients lacking ER stress remains unclear. In this study, we show that inactivated Akt induces ER stress-independent autophagy via mTOR suppression in patient fibroblasts. Activated autophagy as evidenced by increased levels of LC3-II and autophagic vesicles was observed in patient fibroblasts, whereas PERK phosphorylation reflecting the presence of ER stress was not observed in them. These patient fibroblasts showed decreased levels of not only phosphorylated Akt, but also phosphorylated p70 S6 kinase. Treatment with insulin, which acts as an activator of the Akt signaling pathway, resulted in increased phosphorylation of both Akt and p70 S6 kinase and suppression of autophagy in patient fibroblasts. In addition, following combination treatment with recombinant human GAA plus insulin, enhanced localization of the enzymes with lysosomes was observed in patient fibroblasts. These findings define a critical role of Akt suppression in the induction of autophagy in fibroblasts from patients with Pompe disease carrying an ER stress non-inducible mutation, and they provide evidence that insulin may potentiate the effect of ERT.

Identification of a role for CLASP2 in insulin action

Insulin stimulates the mobilization of glucose transporter 4 (GLUT4) storage vesicles to the plasma membrane, resulting in an influx of glucose into target tissues such as muscle and fat. We present evidence that CLIP-associating protein 2 (CLASP2), a protein previously unassociated with insulin action, is responsive to insulin stimulation. Using mass spectrometry-based protein identification combined with phosphoantibody immunoprecipitation in L6 myotubes, we detected a 4.8-fold increase of CLASP2 in the anti-phosphoserine immunoprecipitates upon insulin stimulation. Western blotting of CLASP2 immunoprecipitates with the phosphoantibody confirmed the finding that CLASP2 undergoes insulin-stimulated phosphorylation, and a number of novel phosphorylation sites were identified. Confocal imaging of L6 myotubes revealed that CLASP2 colocalizes with GLUT4 at the plasma membrane within areas of insulin-mediated cortical actin remodeling. CLASP2 is responsible for directing the distal end of microtubules to the cell cortex, and it has been shown that GLUT4 travels along microtubule tracks. In support of the concept that CLASP2 plays a role in the trafficking of GLUT4 at the cell periphery, CLASP2 knockdown by siRNA in L6 myotubes interfered with insulin-stimulated GLUT4 localization to the plasma membrane. Furthermore, siRNA mediated knockdown of CLASP2 in 3T3-L1 adipocytes inhibited insulin-stimulated glucose transport. We therefore propose a new model for CLASP2 in insulin action, where CLASP2 directs the delivery of GLUT4 to cell cortex landing zones important for insulin action.

Preventing the calorie restriction-induced increase in insulin-stimulated Akt2 phosphorylation eliminates calorie restriction's effect on glucose uptake in skeletal muscle

Calorie restriction (CR; ~60% of ad libitum, AL, consumption) improves insulin-stimulated glucose uptake in skeletal muscle. The precise cellular mechanism for this healthful outcome is unknown, but it is accompanied by enhanced insulin-stimulated activation of Akt. Previous research using Akt2-null mice demonstrated that Akt2 is essential for the full CR-effect on insulin-stimulated glucose uptake by muscle. However, because Akt2-null mice were completely deficient in Akt2 in every cell throughout life, it would be valuable to assess the efficacy of transient, muscle-specific Akt inhibition for attenuation of CR-effects on glucose uptake. Accordingly, we used a selective Akt inhibitor (MK-2206) to eliminate the CR-induced elevation in insulin-stimulated Akt2 phosphorylation and determined the effects on Akt substrates and glucose uptake. We incubated isolated epitrochlearis muscles from 9-month-old AL and CR (~60-65% of AL intake for 6months) rats with or without MK-2206 and measured insulin-stimulated (1.2nM) glucose uptake and phosphorylation of the insulin receptor (Tyr1162/1163), pan-Akt (Thr308 and Ser473), Akt2 (Thr308 and Ser473), AS160/TBC1D4 (Thr642), and Filamin C (Ser2213). Incubation of isolated skeletal muscles with a dose of a selective Akt inhibitor that eliminated the CR-induced increases in Akt2 phosphorylation prevented CR's effects on insulin-stimulated glucose uptake, pAS160(Thr642) and pFilamin C(Ser2213) without altering pIR(Tyr1162/1163). These data provide compelling new evidence linking the CR-induced increase in insulin-stimulated Akt2 phosphorylation to CR's effects on insulin-mediated phosphorylation of Akt substrates and glucose uptake in skeletal muscle.

Differential function of Akt1 and Akt2 in human adipocytes

Adipose tissue mass is determined by both cell size and cell number. Mouse models suggest that Akt isoforms are involved in the determination of fat mass by interfering with preadipocyte-to-adipocyte transition and regulating lipid storage. Here, we took advantage of a lentiviral mediated shRNA approach to study the role of Akt1 and Akt2 in differentiation and metabolism of human SGBS adipocytes. Adipogenic differentiation as measured by lipid accumulation was robustly inhibited in Akt2 deficient cells, whereas it was not affected by knockdown of Akt1. The knockdown of Akt2 caused an almost complete inhibition of preadipocyte proliferation. Furthermore, Akt2 deficient preadipocytes were significantly more sensitive to apoptosis induction by death receptor stimulation compared to Akt1 deficient cells. Both the knockdown of Akt1 or Akt2 equally affected insulin-stimulated lipogenesis as well as the anti-lipolytic effect of insulin. We conclude that Akt2 is indispensable for the regulation of preadipocyte and adipocyte number, whereas Akt1 and Akt2 are equally important for the regulation of insulin-stimulated metabolic pathways in human adipocytes. Recently proposed as an attractive target for the treatment of cancer, modulating Akt2 activity might also be a new molecular strategy to control adipose tissue mass.

Regulation of glucose transport by insulin: traffic control of GLUT4

Despite daily fasting and feeding, plasma glucose levels are normally maintained within a narrow range owing to the hormones insulin and glucagon. Insulin increases glucose uptake into fat and muscle cells through the regulated trafficking of vesicles that contain glucose transporter type 4 (GLUT4). New insights into insulin signalling reveal that phosphorylation events initiated by the insulin receptor regulate key GLUT4 trafficking proteins, including small GTPases, tethering complexes and the vesicle fusion machinery. These proteins, in turn, control GLUT4 movement through the endosomal system, formation and retention of specialized GLUT4 storage vesicles and targeted exocytosis of these vesicles. Understanding these processes may help to explain the development of insulin resistance in type 2 diabetes and provide new potential therapeutic targets.

Amplification and demultiplexing in insulin-regulated Akt protein kinase pathway in adipocytes

Akt plays a major role in insulin regulation of metabolism in muscle, fat, and liver. Here, we show that in 3T3-L1 adipocytes, Akt operates optimally over a limited dynamic range. This indicates that Akt is a highly sensitive amplification step in the pathway. With robust insulin stimulation, substantial changes in Akt phosphorylation using either pharmacologic or genetic manipulations had relatively little effect on Akt activity. By integrating these data we observed that half-maximal Akt activity was achieved at a threshold level of Akt phosphorylation corresponding to 5–22% of its full dynamic range. This behavior was also associated with lack of concordance or demultiplexing in the behavior of downstream components. Most notably, FoxO1 phosphorylation was more sensitive to insulin and did not exhibit a change in its rate of phosphorylation between 1 and 100 nm insulin compared with other substrates (AS160, TSC2, GSK3). Similar differences were observed between various insulin-regulated pathways such as GLUT4 translocation and protein synthesis. These data indicate that Akt itself is a major amplification switch in the insulin signaling pathway and that features of the pathway enable the insulin signal to be split or demultiplexed into discrete outputs. This has important implications for the role of this pathway in disease.

Inhibition of Aβ(25-35)-induced cell apoptosis by low-power-laser-irradiation (LPLI) through promoting Akt-dependent YAP cytoplasmic translocation

Deposition of amyloid-β-peptide (Aβ) in the brain is considered a pathological hallmark of Alzheimer's disease (AD). Our previous studies show that Yes-associated protein (YAP) is involved in the regulation of apoptosis induced by Aβ(25-35) through YAP nuclear translocation and its pro-apoptotic function is mediated by its interaction with p73. In the present study, we first found that Low-power laser irradiation (LPLI) promoted YAP cytoplasmic translocation and inhibited Aβ(25-35)-induced YAP nuclear translocation. Moreover, the cytoplasmic translocation was in an Akt-dependent manner. Activated Akt by LPLI phosphorylated YAP on ser127 (S127) and resulted in decreasing the interaction between YAP and p73, and in suppressing the proapoptotic gene bax expression following Aβ(25-35) treatment. Inhibition of Akt expression by siRNA significantly abolished the effect of LPLI. More importantly, LPLI could inhibit Aβ(25-35)-induced cell apoptosis through activation of Akt/YAP/p73 signaling pathway. Therefore, our findings first suggest that YAP may be a therapeutic target and these results directly point to a potential therapeutic strategy for the treatment of AD through Akt/YAP/p73 signaling pathway with LPLI.

Mechanisms for increased insulin-stimulated Akt phosphorylation and glucose uptake in fast- and slow-twitch skeletal muscles of calorie-restricted rats

Calorie restriction [CR; ~65% of ad libitum (AL) intake] improves insulin-stimulated glucose uptake (GU) and Akt phosphorylation in skeletal muscle. We aimed to elucidate the effects of CR on 1) processes that regulate Akt phosphorylation [insulin receptor (IR) tyrosine phosphorylation, IR substrate 1-phosphatidylinositol 3-kinase (IRS-PI3K) activity, and Akt binding to regulatory proteins (heat shock protein 90, Appl1, protein phosphatase 2A)]; 2) Akt substrate of 160-kDa (AS160) phosphorylation on key phosphorylation sites; and 3) atypical PKC (aPKC) activity. Isolated epitrochlearis (fast-twitch) and soleus (slow-twitch) muscles from AL or CR (6 mo duration) 9-mo-old male F344BN rats were incubated with 0, 1.2, or 30 nM insulin and 2-deoxy-[(3)H]glucose. Some CR effects were independent of insulin dose or muscle type: CR caused activation of Akt (Thr(308) and Ser(473)) and GU in both muscles at both insulin doses without CR effects on IRS1-PI3K, Akt-PP2A, or Akt-Appl1. Several muscle- and insulin dose-specific CR effects were revealed. Akt-HSP90 binding was increased in the epitrochlearis; AS160 phosphorylation (Ser(588) and Thr(642)) was greater for CR epitrochlearis at 1.2 nM insulin; and IR phosphorylation and aPKC activity were greater for CR in both muscles with 30 nM insulin. On the basis of these data, our working hypothesis for improved insulin-stimulated GU with CR is as follows: 1) elevated Akt phosphorylation is fundamental, regardless of muscle or insulin dose; 2) altered Akt binding to regulatory proteins (HSP90 and unidentified Akt partners) is involved in the effects of CR on Akt phosphorylation; 3) Akt effects on GU depend on muscle- and insulin dose-specific elevation in phosphorylation of Akt substrates, including, but not limited to, AS160; and 4) greater IR phosphorylation and aPKC activity may contribute at higher insulin doses.

Knockdown of Akt sensitizes osteosarcoma cells to apoptosis induced by cisplatin treatment

Akt plays an important role in the inhibition of apoptosis induced by chemotherapy and other stimuli. We therefore investigated if knockdown of Akt2 promoted drug-induced apoptosis in cultured osteosarcoma cells in vitro. SAOS-2 cells were transfected with Akt2 siRNA. The sensitivity of the transformed cell line to the chemotherapeutic drug cisplatin was assessed. Reduced expression of Akt2 did not directly inhibit the growth rate of the transfected cells; however, it significantly increased their sensitivity to cisplatin. Knockdown of Akt2, together with cisplatin treatment, promoted the expression of p53 up-regulated modulator of apoptosis (PUMA). It is possible that the augmentation of cisplatin cytotoxicity may be mediated by PUMA activation. The results of this study suggest that knockdown of Akt2 expression may have therapeutic applications in enhancing the efficacy of chemotherapy in patients with osteosarcoma.