A stepwise activation model for the insulin receptor

The binding of insulin to the insulin receptor (IR) triggers a cascade of receptor conformational changes and autophosphorylation, leading to the activation of metabolic and mitogenic pathways. Recent advances in the structural and functional analyses of IR have revealed the conformations of the extracellular domains of the IR in inactive and fully activated states. However, the early activation mechanisms of this receptor remain poorly understood. The structures of partially activated IR in complex with aptamers provide clues for understanding the initial activation mechanism. In this review, we discuss the structural and functional features of IR complexed with various ligands and propose a model to explain the sequential activation mechanism. Moreover, we discuss the structures of IR complexed with biased agonists that selectively activate metabolic pathways and provide insights into the design of selective agonists and their clinical implications.

Functional selectivity of insulin receptor revealed by aptamer-trapped receptor structures

Activation of insulin receptor (IR) initiates a cascade of conformational changes and autophosphorylation events. Herein, we determined three structures of IR trapped by aptamers using cryo-electron microscopy. The A62 agonist aptamer selectively activates metabolic signaling. In the absence of insulin, the two A62 aptamer agonists of IR adopt an insulin-accessible arrowhead conformation by mimicking site-1/site-2' insulin coordination. Insulin binding at one site triggers conformational changes in one protomer, but this movement is blocked in the other protomer by A62 at the opposite site. A62 binding captures two unique conformations of IR with a similar stalk arrangement, which underlie Tyr1150 mono-phosphorylation (m-pY1150) and selective activation for metabolic signaling. The A43 aptamer, a positive allosteric modulator, binds at the opposite side of the insulin-binding module, and stabilizes the single insulin-bound IR structure that brings two FnIII-3 regions into closer proximity for full activation. Our results suggest that spatial proximity of the two FnIII-3 ends is important for m-pY1150, but multi-phosphorylation of IR requires additional conformational rearrangement of intracellular domains mediated by coordination between extracellular and transmembrane domains.

Phospholipase D2 controls bone homeostasis by modulating M-CSF-dependent osteoclastic cell migration and microtubule stability

Phospholipase D2 (PLD2), a signaling protein, plays a central role in cellular communication and various biological processes. Here, we show that PLD2 contributes to bone homeostasis by regulating bone resorption through osteoclastic cell migration and microtubule-dependent cytoskeletal organization. Pld2-deficient mice exhibited a low bone mass attributed to increased osteoclast function without altered osteoblast activity. While Pld2 deficiency did not affect osteoclast differentiation, its absence promoted the migration of osteoclast lineage cells through a mechanism involving M-CSF-induced activation of the PI3K–Akt–GSK3β signaling pathway. The absence of Pld2 also boosted osteoclast spreading and actin ring formation, resulting in elevated bone resorption. Furthermore, Pld2 deletion increased microtubule acetylation and stability, which were later restored by treatment with a specific inhibitor of Akt, an essential molecule for microtubule stabilization and osteoclast bone resorption activity. Interestingly, PLD2 interacted with the M-CSF receptor (c-Fms) and PI3K, and the association between PLD2 and c-Fms was reduced in response to M-CSF. Altogether, our findings indicate that PLD2 regulates bone homeostasis by modulating osteoclastic cell migration and microtubule stability via the M-CSF-dependent PI3K–Akt–GSK3β axis.

A signaling protein that regulates bone resorption may prove a useful target in treating skeletal conditions such as osteoporosis and rheumatoid arthritis. Bone is synthesized by cells called osteoblasts, while osteoclasts trigger bone resorption, keeping the skeleton healthy. Imbalances in this recycling process are common in bone disorders. Je-Young Choi and Hyun-Ju Kim at Kyungpook National University in Daegu, South Korea, and co-workers demonstrated that phospholipase D2 (PLD2), a membrane protein, directly regulates bone resorption in mice. Mice without the Pld2 gene had increased osteoclast activity, resulting in low bone mass. The absence of PLD2 promotes the migration of osteoclasts via a particular signaling pathway. This increased the organization of microtubules, polymers that help form the cytoskeleton. The results suggest that regulating PLD2 activity could form the basis of a future treatment method.

An aptamer agonist of the insulin receptor acts as a positive or negative allosteric modulator, depending on its concentration

Aptamers are widely used as binders that interact with targets with high affinity or as inhibitors of the function of target molecules. However, they have also been used to modulate target protein function, which they achieve by activating the target or stabilizing its conformation. Here, we report a unique aptamer modulator of the insulin receptor (IR), IR-A62. Alone, IR-A62 acts as a biased agonist that preferentially induces Y1150 monophosphorylation of IR. However, when administered alongside insulin, IR-A62 shows variable binding cooperativity depending on the ligand concentration. At low concentrations, IR-A62 acts as a positive allosteric modulator (PAM) agonist that enhances insulin binding, but at high concentrations, it acts as a negative allosteric modulator (NAM) agonist that competes with insulin for IR. Moreover, the concentration of insulin affects the binding of IR-A62 to IR. Finally, the subcutaneous administration of IR-A62 to diabetic mice reduces blood glucose levels with a longer-lasting effect than insulin administration. These findings imply that aptamers can elicit various responses from receptors beyond those of a simple agonist or inhibitor. We expect further studies of IR-A62 to help reveal the mechanism of IR activation and greatly expand the range of therapeutic applications of aptamers.

Studying how an aptamer, a short section of RNA or DNA, affects the interaction of insulin with its membrane receptor protein offers further insights into aptamers in general. Aptamers can bind with high specificity and affinity to many target molecules, and affect the activity of many proteins. Researchers in South Korea led by Sun Sik Bae at Pusan National University and Sung Ho Ryu at Pohang University of Science and Technology explored the interaction of the aptamer IR-A62 with the membrane protein that binds to and responds to insulin. Whether IR-A62 activated or inhibited insulin’s interaction and effects depended on both the aptamer and insulin concentrations. While increasing understanding of the insulin receptor protein, investigating this subtly variable effect could more generally refine and expand the use of aptamers in medicine.

Formation of cellular close-ended tunneling nanotubes through mechanical deformation

Membrane nanotubes or tunneling nanotubes (TNTs) that connect cells have been recognized as a previously unidentified pathway for intercellular transport between distant cells. However, it is unknown how this delicate structure, which extends over tens of micrometers and remains robust for hours, is formed. Here, we found that a TNT develops from a double filopodial bridge (DFB) created by the physical contact of two filopodia through helical deformation of the DFB. The transition of a DFB to a close-ended TNT is most likely triggered by disruption of the adhesion of two filopodia by mechanical energy accumulated in a twisted DFB when one of the DFB ends is firmly attached through intercellular cadherin-cadherin interactions. These studies pinpoint the mechanistic questions about TNTs and elucidate a formation mechanism.

Targeting PLD2 in adipocytes augments adaptive thermogenesis by improving mitochondrial quality and quantity in mice

Phospholipase D (PLD)2 via its enzymatic activity regulates cell proliferation and migration and thus is implicated in cancer. However, the role of PLD2 in obesity and type 2 diabetes has not previously been investigated. Here, we show that during diet-induced thermogenesis and obesity, levels of PLD2 but not PLD1 in adipose tissue are inversely related with uncoupling protein 1, a key thermogenic protein. We demonstrate that the thermogenic program in adipose tissue is significantly augmented in mice with adipocyte-specific Pld2 deletion or treated with a PLD2-specific inhibitor and that these mice are resistant to high fat diet–induced obesity, glucose intolerance, and insulin resistance. Mechanistically, we show that Pld2 deletion in adipose tissue or PLD2 pharmacoinhibition acts via p62 to improve mitochondrial quality and quantity in adipocytes. Thus, PLD2 inhibition is an attractive therapeutic approach for obesity and type 2 diabetes by resolving defects in diet-induced thermogenesis.

Regulation of EGFR activation and signaling by lipids on the plasma membrane

Lipids on the plasma membrane are not only components of the membrane biophysical structures but also regulators of receptor functions. Recently, the critical roles of lipid-protein interactions have been intensively highlighted. Epidermal growth factor receptor (EGFR) is one of the most extensively studied receptors exhibiting various lipid interactions, including interactions with phosphatidylcholine, phosphatidylserine, phosphatidylinositol phosphate, cholesterol, gangliosides, and palmitate. Here, we review recent findings on how direct interaction with these lipids regulates EGFR activation and signaling, providing unprecedented insight into the comprehensive roles of various lipids in the control of EGFR functions. Finally, the current limitations in investigating lipid-protein interactions and novel technologies to potentially overcome these limitations are discussed.

Blue-conversion of organic dyes produces artifacts in multicolor fluorescence imaging

Multicolor fluorescence imaging is a powerful tool visualizing the spatiotemporal relationship among biomolecules. Here, we report that commonly employed organic dyes exhibit a blue-conversion phenomenon, which can produce severe multicolor image artifacts leading to false-positive colocalization by invading predefined spectral windows, as demonstrated in the case study using EGFR and Tensin2. These multicolor image artifacts become much critical in localization-based superresolution microscopy as the blue-converted dyes are photoactivatable. We provide a practical guideline for the use of organic dyes for multicolor imaging to prevent artifacts derived by blue-conversion.

Blue-conversion, a photooxidative conversion leading to the hypsochromic shift of absorption and emission spectra, occurs in popular organic dyes under conventional laser illumination and produces severe artifacts in multicolor fluorescence imaging.

A hotspot for enhancing insulin receptor activation revealed by a conformation-specific allosteric aptamer

Aptamers are single-stranded oligonucleotides that bind to a specific target with high affinity, and are widely applied in biomedical diagnostics and drug development. However, the use of aptamers has largely been limited to simple binders or inhibitors that interfere with the function of a target protein. Here, we show that an aptamer can also act as a positive allosteric modulator that enhances the activation of a receptor by stabilizing the binding of a ligand to that receptor. We developed an aptamer, named IR-A43, which binds to the insulin receptor, and confirmed that IR-A43 and insulin bind to the insulin receptor with mutual positive cooperativity. IR-A43 alone is inactive, but, in the presence of insulin, it potentiates autophosphorylation and downstream signaling of the insulin receptor. By using the species-specific activity of IR-A43 at the human insulin receptor, we demonstrate that residue Q272 in the cysteine-rich domain is directly involved in the insulin-enhancing activity of IR-A43. Therefore, we propose that the region containing residue Q272 is a hotspot that can be used to enhance insulin receptor activation. Moreover, our study implies that aptamers are promising reagents for the development of allosteric modulators that discriminate a specific conformation of a target receptor.

Efficacy of newly discovered DNA aptamers targeting AXL in a lung cancer cell with acquired resistance to Erlotinib

BACKGROUND

Accumulating evidences indicate that AXL overexpression or activation is associated with cancer progression and acquired resistance to targeted anti-cancer drugs such as epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs). Despite recent development of several drugs that target multiple receptor tyrosine kinases (RTKs), drugs that selectively target AXL signaling are extremely rare. Short nucleic acid aptamers are non-immunogenic molecules with high binding affinity and specificity to their target molecules that could potentially be used as a novel cancer treatment.

METHODS

Modified-DNA aptamers were selected on the basis of its ability to bind recombinant human AXL. AXL aptamers were selected for their inhibition of AXL and then selected aptamers were tested for their use to overcome acquired resistant to EGFR-TKI on a lung cancer cell with acquired resistance to erlotinib.

RESULTS

These new AXL aptamers inhibited cell viability to an extent of 30-40% in HCC827/ER cells with acquired resistance to erlotinib. The possible mechanism of overcoming the acquired resistance may be by inhibiting the activation of Akt and Erk. Although, aptamers effectively decreased cell viability of erlotinib-resistant cell line, the combination of aptamers and erlotinib did not synergistically decrease the survival of the resistant cell line.

CONCLUSIONS

We developed newly modified DNA aptamers that selectively bind to AXL receptors, and assessed their efficacy in a human lung cancer cell with acquired resistance to EGFR-TKI.

Structural Basis for the Antibiotic Resistance of Eukaryotic Isoleucyl-tRNA Synthetase

Pathogenic aminoacyl-tRNA synthetases (ARSs) are attractive targets for anti-infective agents because their catalytic active sites are different from those of human ARSs. Mupirocin is a topical antibiotic that specifically inhibits bacterial isoleucy-ltRNA synthetase (IleRS), resulting in a block to protein synthesis. Previous studies on Thermus thermophilus IleRS indicated that mupirocin-resistance of eukaryotic IleRS is primarily due to differences in two amino acids, His581 and Leu583, in the active site. However, without a eukaryotic IleRS structure, the structural basis for mupirocin-resistance of eukaryotic IleRS remains elusive. Herein, we determined the crystal structure of Candida albicans IleRS complexed with Ile-AMP at 2.9 Å resolution. The largest difference between eukaryotic and prokaryotic IleRS enzymes is closure of the active site pocket by Phe55 in the HIGH loop; Arg410 in the CP core loop; and the second Lys in the KMSKR loop. The Ile-AMP product is lodged in a closed active site, which may restrict its release and thereby enhance catalytic efficiency. The compact active site also prevents the optimal positioning of the 9-hydroxynonanoic acid of mupirocin and plays a critical role in resistance of eukaryotic IleRS to anti-infective agents.

Specific Inhibition of Soluble γc Receptor Attenuates Collagen-Induced Arthritis by Modulating the Inflammatory T Cell Responses

IL-17 produced by Th17 cells has been implicated in the pathogenesis of rheumatoid arthritis (RA). It is important to prevent the differentiation of Th17 cells in RA. Homodimeric soluble γc (sγc) impairs IL-2 signaling and enhances Th17 differentiation. Thus, we aimed to block the functions of sγc by inhibiting the formation of homodimeric sγc. The homodimeric form of sγc was strikingly disturbed by sγc-binding DNA aptamer. Moreover, the aptamer effectively inhibited Th17 cell differentiation and restored IL-2 and IL-15 signaling impaired by sγc with evidences of increased survival of T cells. sγc was highly expressed in SF of RA patients and increased in established CIA mice. The therapeutic effect of PEG-aptamer was tested in CIA model and its treatment alleviated arthritis pathogenesis with impaired differentiation of pathogenic Th17, NKT1, and NKT17 cells in inflamed joint. Homodimeric sγc has pathogenic roles to exacerbate RA progression with differentiation of local Th17, NKT1, and NKT17 cells. Therefore, sγc is suggested as target of a therapeutic strategy for RA.

Water Extract of Pleurotus eryngii var. ferulae Prevents High-Fat Diet-Induced Obesity by Inhibiting Pancreatic Lipase

Pleurotus eryngii var. ferulae (PEF) is traditionally used in the prevention and treatment of lifestyle-related diseases. In this study, we investigated the ability of PEF extract to prevent obesity and metabolic diseases and explored the underlying mechanism. Mice were fed a high-fat diet (HFD) containing PEF extract for 12 weeks, and their body weight, adipose tissue and liver weights, and lipid profiles and blood glucose levels, were monitored. Fecal triglyceride (TG) levels were also measured and olive oil-loading tests were performed. Furthermore, the effect of PEF extract on pancreatic lipase (PL) activity was examined in vitro. Treatment with PEF extract for 12 weeks resulted in a significant decrease in the HFD-induced increases in body weight, white adipose tissue weight, liver weights, and lipid profiles, and improved glucose tolerance and insulin sensitivity. To assess the mechanism underlying the effect of PEF extract on obesity and diabetes, we investigated its role in inhibiting lipid absorption. Consumption of an HFD containing PEF extract significantly increased the TG level in feces compared with the controls, suggesting inhibition of TG absorption in the digestive tract. Furthermore, PEF extract suppressed the increase in serum TG levels resulting from oral administration of a lipid emulsion to mice, confirming inhibition of TG absorption. Moreover, PEF extract inhibited PL activity in vitro. Our combined results indicate that the anti-obesity and antidiabetic effect of PEF extract in mice fed an HFD may be caused by inhibition of lipid absorption as a result of reduced PL activity.

NOTUM Is Involved in the Progression of Colorectal Cancer

BACKGROUND

There are limitations to current colorectal cancer (CRC)-specific diagnostic methods and therapies. Tumorigenesis proceeds because of interaction between cancer cells and various surrounding cells; discovering new molecular mediators through studies of the CRC secretome is a promising approach for the development of CRC diagnostics and therapies.

MATERIALS AND METHODS

A comparative secretomic analysis was performed using primary and metastatic human isogenic CRC cells. Proliferation was determined by MTT and thymidine incorporation assay, migration was determined by wound-healing assay (ELISA). The level of palmitoleoyl-protein carboxylesterase (NOTUM) in plasma from patients with CRC was determined by enzyme-linked immunosorbent assay.

RESULTS

NOTUM expression was increased in metastatic cells. Proliferation was suppressed by inhibiting expression of NOTUM. Knockdown of NOTUM genes inhibited proliferation as well as migration, with possible involvement of p38 and c-JUN N-terminal kinase in this process. The result was verified in patients with CRC.

CONCLUSION

NOTUM may be a new candidate for diagnostics and therapy of CRC.

Direct visualization of single-molecule membrane protein interactions in living cells

Interactions between membrane proteins are poorly understood despite their importance in cell signaling and drug development. Here, we present a co-immunoimmobilization assay (Co-II) enabling the direct observation of membrane protein interactions in single living cells that overcomes the limitations of currently prevalent proximity-based indirect methods. Using Co-II, we investigated the transient homodimerizations of epidermal growth factor receptor (EGFR) and beta-2 adrenergic receptor (β2-AR) in living cells, revealing the differential regulation of these receptors’ dimerizations by molecular conformations and microenvironment in a plasma membrane. Co-II should provide a simple, rapid, and robust platform for visualizing both weak and strong protein interactions in the plasma membrane of living cells.

Protein–protein interactions govern cellular processes. The majority of these physical interactions previously identified are strong/permanent interactions, which typically remain unbroken even after purification. The weak/transient interactions between proteins have been implicated in the control of dynamic cellular process that maintain cellular homeostasis and trigger signaling cascades upon environmental changes. However, these interactions are poorly investigated, mainly due to the methodological limitations. Here, we have developed a co-immunoimmobilization assay called Co-II that enables the direct visualization of protein–protein interactions in the membrane of living cells at the single-molecule level. Co-II is based on the intuitive concept that if the protein of interest is immobilized, the interacting protein must be co-immobilized. The use of intrinsic protein diffusivity fundamentally overcomes the limitations of proximity-based methods. Using Co-II, we study the transient homodimerizations of EGFR and β2-AR in living cells, which have been implicated in several types of cancers and heart diseases. We show that the dimerization of these receptors is differently regulated by molecular conformations and the microenvironment in the plasma membrane.

Cellular phosphatase activity of C1-Ten/Tensin2 is controlled by Phosphatidylinositol-3,4,5-triphosphate binding through the C1-Ten/Tensin2 SH2 domain

Regulation of tyrosine phosphorylation on insulin receptor substrate-1 (IRS-1) is essential for insulin signaling. The protein tyrosine phosphatase (PTP) C1-Ten/Tensin2 has been implicated in the regulation of IRS-1, but the molecular basis of this dephosphorylation is not fully understood. Here, we demonstrate that the cellular phosphatase activity of C1-Ten/Tensin2 on IRS-1 is mediated by the binding of the C1-Ten/Tensin2 Src-homology 2 (SH2) domain to phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P₃). We show that the role of C1-Ten/Tensin2 is dependent on insulin-induced phosphoinositide 3-kinase activity. The C1-Ten/Tensin2 SH2 domain showed strong preference and high affinity for PtdIns(3,4,5)P₃. Using site-directed mutagenesis, we identified three basic residues in the C1-Ten/Tensin2 SH2 domain that were critical for PtdIns(3,4,5)P₃ binding but were not involved in phosphotyrosine binding and PTP activity. Using a PtdIns(3,4,5)P₃ binding-deficient mutant, we showed that the specific binding of the C1-Ten/Tensin2 SH2 domain to PtdIns(3,4,5)P₃ allowed C1-Ten/Tensin2 to function as a PTP in cells. Collectively, our findings suggest that the interaction between the C1-Ten/Tensin2 SH2 domain and PtdIns(3,4,5)P₃ produces a negative feedback loop of insulin signaling through IRS-1.

A secretome profile indicative of oleate-induced proliferation of HepG2 hepatocellular carcinoma cells

Increased fatty acid (FA) is often observed in highly proliferative tumors. FAs have been shown to modulate the secretion of proteins from tumor cells, contributing to tumor survival. However, the secreted factors affected by FA have not been systematically explored. Here, we found that treatment of oleate, a monounsaturated omega-9 FA, promoted the proliferation of HepG2 cells. To examine the secreted factors associated with oleate-induced cell proliferation, we performed a comprehensive secretome profiling of oleate-treated and untreated HepG2 cells. A comparison of the secretomes identified 349 differentially secreted proteins (DSPs; 145 upregulated and 192 downregulated) in oleate-treated samples, compared to untreated samples. The functional enrichment and network analyses of the DSPs revealed that the 145 upregulated secreted proteins by oleate treatment were mainly associated with cell proliferation-related processes, such as lipid metabolism, inflammatory response, and ER stress. Based on the network models of the DSPs, we selected six DSPs (MIF, THBS1, PDIA3, APOA1, FASN, and EEF2) that can represent such processes related to cell proliferation. Thus, our results provided a secretome profile indicative of an oleate-induced proliferation of HepG2 cells.

By exposing liver cancer cells to oleate, an unsaturated fatty acid, researchers have discovered a group of secreted proteins that may help explain why fatty acids increase proliferative capacity in tumors. Soyeon Park from Pohang University of Science and Technology in South Korea and coworkers treated liver cancer cells with oleate and then measured all the proteins released from the cells. Comparison with untreated cells revealed 145 proteins secreted at elevated levels—most of which were involved in metabolism, stress responses and other proliferation-related processes—and another 192 proteins secreted at reduced levels. The researchers ran additional biochemical analyses on six secreted proteins to validate the changes following exposure to oleate. The authors suggest that these validated proteins could now serve as biomarkers of tumor aggressiveness or as future drug targets.

Direct Profiling the Post-Translational Modification Codes of a Single Protein Immobilized on a Surface Using Cu-free Click Chemistry

Combinatorial post-translational modifications (PTMs), which can serve as dynamic "molecular barcodes", have been proposed to regulate distinct protein functions. However, studies of combinatorial PTMs on single protein molecules have been hindered by a lack of suitable analytical methods. Here, we describe erasable single-molecule blotting (eSiMBlot) for combinatorial PTM profiling. This assay is performed in a highly multiplexed manner and leverages the benefits of covalent protein immobilization, cyclic probing with different antibodies, and single molecule fluorescence imaging. Especially, facile and efficient covalent immobilization on a surface using Cu-free click chemistry permits multiple rounds (>10) of antibody erasing/reprobing without loss of antigenicity. Moreover, cumulative detection of coregistered multiple data sets for immobilized single-epitope molecules, such as HA peptide, can be used to increase the antibody detection rate. Finally, eSiMBlot enables direct visualization and quantitative profiling of combinatorial PTM codes at the single-molecule level, as we demonstrate by revealing the novel phospho-codes of ligand-induced epidermal growth factor receptor. Thus, eSiMBlot provides an unprecedentedly simple, rapid, and versatile platform for analyzing the vast number of combinatorial PTMs in biological pathways.

Osteoclast-secreted SLIT3 coordinates bone resorption and formation

Coupling is the process that links bone resorption to bone formation in a temporally and spatially coordinated manner within the remodeling cycle. Several lines of evidence point to the critical roles of osteoclast-derived coupling factors in the regulation of osteoblast performance. Here, we used a fractionated secretomic approach and identified the axon-guidance molecule SLIT3 as a clastokine that stimulated osteoblast migration and proliferation by activating β-catenin. SLIT3 also inhibited bone resorption by suppressing osteoclast differentiation in an autocrine manner. Mice deficient in Slit3 or its receptor, Robo1, exhibited osteopenic phenotypes due to a decrease in bone formation and increase in bone resorption. Mice lacking Slit3 specifically in osteoclasts had low bone mass, whereas mice with either neuron-specific Slit3 deletion or osteoblast-specific Slit3 deletion had normal bone mass, thereby indicating the importance of SLIT3 as a local determinant of bone metabolism. In postmenopausal women, higher circulating SLIT3 levels were associated with increased bone mass. Notably, injection of a truncated recombinant SLIT3 markedly rescued bone loss after an ovariectomy. Thus, these results indicate that SLIT3 plays an osteoprotective role by synchronously stimulating bone formation and inhibiting bone resorption, making it a potential therapeutic target for metabolic bone diseases.

Inositol hexakisphosphate kinase 1 is a metabolic sensor in pancreatic β-cells

Diphosphoinositol pentakisphosphate (IP₇) is critical for the exocytotic capacity of the pancreatic β-cell, but its regulation by the primary instigator of β-cell exocytosis, glucose, is unknown. The high K_m for ATP of the IP₇-generating enzymes, the inositol hexakisphosphate kinases (IP6K1 and 2) suggests that these enzymes might serve as metabolic sensors in insulin secreting β-cells and act as translators of disrupted metabolism in diabetes. We investigated this hypothesis and now show that glucose stimulation, which increases the ATP/ADP ratio, leads to an early rise in IP₇ concentration in β-cells. RNAi mediated knock down of the IP6K1 isoform inhibits both glucose-mediated increase in IP₇ and first phase insulin secretion, demonstrating that IP6K1 integrates glucose metabolism and insulin exocytosis. In diabetic mouse islets the deranged ATP/ADP levels under both basal and glucose-stimulated conditions are mirrored in both disrupted IP₇ generation and insulin release. Thus the unique metabolic sensing properties of IP6K1 guarantees appropriate concentrations of IP₇ and thereby both correct basal insulin secretion and intact first phase insulin release. In addition, our data suggest that a specific cell signaling defect, namely, inappropriate IP₇ generation may be an essential convergence point integrating multiple metabolic defects into the commonly observed phenotype in diabetes.

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Glucose increases IP7 levels transiently through IP6K1 in pancreatic β-cells.

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IP6K1 decodes glucose-driven increases in ATP/ADP ratio into 1st phase insulin release.

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IP7 production and insulin release mirror perturbed metabolism in diabetic islets.

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IP6K1 acts as a β-cell metabolic sensor under normal and pathological conditions.

G-protein-coupled receptor 81 promotes a malignant phenotype in breast cancer through angiogenic factor secretion

G-protein-coupled receptor 81 (GPR81) functions as a receptor for lactate and plays an important role in the regulation of anti-lipolytic effects in adipocytes. However, to data, a role for GPR81 in the tumor microenvironment has not been clearly defined. Here, GPR81 expression in breast cancer patients and several breast cancer cell lines was significantly increased compared with normal mammary tissues and cells. GPR81 knockdown resulted in impaired breast cancer growth and led to apoptosis both in vitro and in vivo. Furthermore, the inhibition of GPR81 signaling suppressed angiogenesis through a phosphoinositide 3-OH kinase (PI3K)/Akt-cAMP response element binding protein (CREB) pathway, which led to decreased production of the pro-angiogenic mediator amphiregulin (AREG). Overall, these findings identify GPR81 as a tumor-promoting receptor in breast cancer progression and suggest a novel mechanism that regulates GPR81-dependent activation of the PI3K/Akt signaling axis in tumor microenvironment.

Inhibition of C1-Ten PTPase activity reduces insulin resistance through IRS-1 and AMPK pathways

Insulin resistance causes type 2 diabetes; therefore, increasing insulin sensitivity is a therapeutic approach against type 2 diabetes. Activating AMP-activated protein kinase (AMPK) is an effective approach for treating diabetes, and reduced insulin receptor substrate-1 (IRS-1) protein levels have been suggested as a molecular mechanism causing insulin resistance. Thus, dual targeting of AMPK and IRS-1 might provide an ideal way to treat diabetes. We found that 15,16-dihydrotanshinone I (DHTS), as a C1-Ten protein tyrosine phosphatase inhibitor, increased IRS-1 stability, improved glucose tolerance and reduced muscle atrophy. Identification of DHTS as a C1-Ten inhibitor revealed a new function of C1-Ten in AMPK inhibition, possibly through regulation of IRS-1. These findings suggest that C1-Ten inhibition by DHTS could provide a novel therapeutic strategy for insulin resistance-associated metabolic syndrome through dual targeting of IRS-1 and AMPK.

Acute toxicity of organic antifouling biocides to phytoplankton Nitzschia pungens and zooplankton Artemia larvae

The toxicity of the antifouling biocides Irgarol 1051, Diuron, Chlorothalonil, Dichlofluanid, Sea-nine 211, Copper pyrithione, Zinc pyrithione, Ziram and Zineb were evaluated on Nitzschia pungens and Artemia larvae. Results showed that EC₅₀ for Irgarol 1051 was 0.586μgl^-1 was the strongest effect on N. pungens following by Copper pyrithione (4.908μgl^-1), Ziram (5.421μgl^-1), Zinc pyrithione (5.513μgl^-1), Diuron (6.640μgl^-1), Zineb (232.249μgl^-1), Sea-nine 211(267.368μgl^-1), Chlorothalonil (360.963μgl^-1) and Dichlofluanid (377.010μgl^-1) in 96h. In Artemia larvae, the biocides were evaluated the LC₅₀ for larval survivals at 48h. Sea-nine 211 and Copper pyrithione were 0.318 and 0.319mgl^-1. Chlorothalonil, Zinc pyrithione and Ziram were 2.683, 3.147 and 4.778mgl^-1. Irgarol 1051, Diuron, Zineb and Dichlofluanid were 9.734, 30.573, 41.170 and 154.944mgl^-1. These results provide baseline data concerning the toxicity of antifouling biocides against marine environment.

Molecular Mechanisms Underlying Psychological Stress and Cancer

Psychological stress is an emotion experienced when people are under mental pressure or encounter unexpected problems. Extreme or repetitive stress increases the risk of developing human disease, including cardiovascular disease (CVD), immune diseases, mental disorders, and cancer. Several studies have shown an association between psychological stress and cancer growth and metastasis in animal models and case studies of cancer patients. Stress induces the secretion of stress-related mediators, such as catecholamine, cortisol, and oxytocin, via the activation of the hypothalamic-pituitary-adrenocortical (HPA) axis or the sympathetic nervous system (SNS). These stress-related hormones and neurotransmitters adversely affect stress-induced tumor progression and cancer therapy. Catecholamine is the primary factor that influences tumor progression. It can regulate diverse cellular signaling pathways through adrenergic receptors (ADRs), which are expressed by several types of cancer cells. Activated ADRs enhance the proliferation and invasion abilities of cancer cells, alter cell activity in the tumor microenvironment, and regulate the interaction between cancer and its microenvironment to promote tumor progression. Additionally, other stress mediators, such as glucocorticoids and oxytocin, and their cognate receptors are involved in stress-induced cancer growth and metastasis. Here, we will review how each receptor-mediated signal cascade contributes to tumor initiation and progression and discuss how we can use these molecular mechanisms for cancer therapy.

C1-Ten is a PTPase of nephrin, regulating podocyte hypertrophy through mTORC1 activation

Hypertrophy is a prominent feature of damaged podocytes in diabetic kidney disease (DKD). mTORC1 hyperactivation leads to podocyte hypertrophy, but the detailed mechanism of how mTORC1 activation occurs under pathological conditions is not completely known. Moreover, reduced nephrin tyrosine phosphorylation has been observed in podocytes under pathological conditions, but the molecular mechanism linking nephrin phosphorylation and pathology is unclear so far. In this study, we observed a significant increase in C1-Ten level in diabetic kidney and in high glucose-induced damaged podocytes. C1-Ten acts as a protein tyrosine phosphatase (PTPase) at the nephrin-PI3K binding site and renders PI3K for IRS-1, thereby activating mTORC1. Furthermore, C1-Ten causes podocyte hypertrophy and proteinuria by increasing mTORC1 activity in vitro and in vivo. These findings demonstrate the relationship between nephrin dephosphorylation and the mTORC1 pathway, mediated by C1-Ten PTPase activity. We suggest that C1-Ten contributes to the pathogenesis of DKD by inducing podocyte hypertrophy under high glucose conditions.

Insulin modulates the frequency of Ca2+ oscillations in mouse pancreatic islets

Pancreatic islets can adapt to oscillatory glucose to produce synchronous insulin pulses. Can islets adapt to other oscillatory stimuli, specifically insulin? To answer this question, we stimulated islets with pulses of exogenous insulin and measured their Ca²⁺ oscillations. We observed that sufficiently high insulin (> 500 nM) with an optimal pulse period (~ 4 min) could make islets to produce synchronous Ca²⁺ oscillations. Glucose and insulin, which are key stimulatory factors of islets, modulate islet Ca²⁺ oscillations differently. Glucose increases the active-to-silent ratio of phases, whereas insulin increases the period of the oscillation. To examine the dual modulation, we adopted a phase oscillator model that incorporated the phase and frequency modulations. This mathematical model showed that out-of-phase oscillations of glucose and insulin were more effective at synchronizing islet Ca²⁺ oscillations than in-phase stimuli. This finding suggests that a phase shift in glucose and insulin oscillations can enhance inter-islet synchronization.

Dynamic relocalization of NHERF1 mediates chemotactic migration of ovarian cancer cells toward lysophosphatidic acid stimulation

NHERF1/EBP50 (Na⁺/H⁺ exchanger regulating factor 1; Ezrin-binding phosphoprotein of 50 kDa) organizes stable protein complexes beneath the apical membrane of polar epithelial cells. By contrast, in cancer cells without any fixed polarity, NHERF1 often localizes in the cytoplasm. The regulation of cytoplasmic NHERF1 and its role in cancer progression remain unclear. In this study, we found that, upon lysophosphatidic acid (LPA) stimulation, cytoplasmic NHERF1 rapidly translocated to the plasma membrane, and subsequently to cortical protrusion structures, of ovarian cancer cells. This movement depended on direct binding of NHERF1 to C-terminally phosphorylated ERM proteins (cpERMs). Moreover, NHERF1 depletion downregulated cpERMs and further impaired cpERM-dependent remodeling of the cell cortex, suggesting reciprocal regulation between these proteins. The LPA-induced protein complex was highly enriched in migratory pseudopodia, whose formation was impaired by overexpression of NHERF1 truncation mutants. Consistent with this, NHERF1 depletion in various types of cancer cells abolished chemotactic cell migration toward a LPA gradient. Taken together, our findings suggest that the high dynamics of cytosolic NHERF1 provide cancer cells with a means of controlling chemotactic migration. This capacity is likely to be essential for ovarian cancer progression in tumor microenvironments containing LPA.

Single particle tracking-based reaction progress kinetic analysis reveals a series of molecular mechanisms of cetuximab-induced EGFR processes in a single living cell

Cellular processes occur through the orchestration of multi-step molecular reactions. Reaction progress kinetic analysis (RPKA) can provide the mechanistic details to elucidate the multi-step molecular reactions. However, current tools have limited ability to simultaneously monitor dynamic variations in multiple complex states at the single molecule level to apply RPKA in living cells. In this research, a single particle tracking-based reaction progress kinetic analysis (sptRPKA) was developed to simultaneously determine the kinetics of multiple states of protein complexes in the membrane of a single living cell. The subpopulation ratios of different states were quantitatively (and statistically) reliably extracted from the diffusion coefficient distribution rapidly acquired by single particle tracking at constant and high density over a long period of time using super-resolution microscopy. Using sptRPKA, a series of molecular mechanisms of epidermal growth factor receptor (EGFR) cellular processing induced by cetuximab were investigated. By comprehensively measuring the rate constants and cooperativity of the molecular reactions involving four EGFR complex states, a previously unknown intermediate state was identified that represents the rate limiting step responsible for the selectivity of cetuximab-induced EGFR endocytosis to cancer cells.

Phase modulation of insulin pulses enhances glucose regulation and enables inter-islet synchronization

Insulin is secreted in a pulsatile manner from multiple micro-organs called the islets of Langerhans. The amplitude and phase (shape) of insulin secretion are modulated by numerous factors including glucose. The role of phase modulation in glucose homeostasis is not well understood compared to the obvious contribution of amplitude modulation. In the present study, we measured Ca²⁺ oscillations in islets as a proxy for insulin pulses, and we observed their frequency and shape changes under constant/alternating glucose stimuli. Here we asked how the phase modulation of insulin pulses contributes to glucose regulation. To directly answer this question, we developed a phenomenological oscillator model that drastically simplifies insulin secretion, but precisely incorporates the observed phase modulation of insulin pulses in response to glucose stimuli. Then, we mathematically modeled how insulin pulses regulate the glucose concentration in the body. The model of insulin oscillation and glucose regulation describes the glucose-insulin feedback loop. The data-based model demonstrates that the existence of phase modulation narrows the range within which the glucose concentration is maintained through the suppression/enhancement of insulin secretion in conjunction with the amplitude modulation of this secretion. The phase modulation is the response of islets to glucose perturbations. When multiple islets are exposed to the same glucose stimuli, they can be entrained to generate synchronous insulin pulses. Thus, we conclude that the phase modulation of insulin pulses is essential for glucose regulation and inter-islet synchronization.

Loss of phospholipase D2 impairs VEGF-induced angiogenesis

Vascular endothelial growth factor (VEGF) is a key mediator of angiogenesis and critical for normal embryonic development and repair of pathophysiological conditions in adults. Although phospholipase D (PLD) activity has been implicated in angiogenic processes, its role in VEGF signaling during angiogenesis in mammals is unclear. Here, we found that silencing of PLD2 by siRNA blocked VEGF-mediated signaling in immortalized human umbilical vein endothelial cells (iHUVECs). Also, VEGF-induced endothelial cell survival, proliferation, migration, and tube formation were inhibited by PLD2 silencing. Furthermore, while Pld2-knockout mice exhibited normal development, loss of PLD2 inhibited VEGF-mediated ex vivo angiogenesis. These findings suggest that PLD2 functions as a key mediator in the VEGF-mediated angiogenic functions of endothelial cells. [BMB Reports 2016; 49(3): 191-196]

Nudix-type motif 2 contributes to cancer proliferation through the regulation of Rag GTPase-mediated mammalian target of rapamycin complex 1 localization

Lysosomal localization of mammalian target of rapamycin complex 1 (mTORC1) is a critical step for activation of the molecule. Rag GTPases are essential for this translocation. Here, we demonstrate that Nudix-type motif 2 (NUDT2) is a novel positive regulator of mTORC1 activation. Activation of mTORC1 is impaired in NUDT2-silenced cells. Mechanistically, NUDT2 binds to Rag GTPase and controls mTORC1 translocation to the lysosomal membrane. Furthermore, NUDT2-dependent mTORC1 regulation is critical for proliferation of breast cancer cells, as NUDT2-silenced cells arrest in G0/G1 phases. Taken together, these results show that NUDT2 is a novel complex formation enhancing factor regulating mTORC1-Rag GTPase signaling that is crucial for cell growth control.

A simple modular aptasensor platform utilizing cucurbit[7]uril and a ferrocene derivative as an ultrastable supramolecular linker

A simple modular aptamer-based sensor (aptasensor) platform was prepared by combining the merits of the rapid and efficient preparation of a self-assembled monolayer of cucurbit[7]uril (CB[7] SAM) and the strong and specific binding affinity of CB[7] to ferrocenemethylammonium (FA), as an ultrastable supramolecular linker, to immobilize aptamers on CB[7] SAM.

Accumulating insights into the role of phospholipase D2 in human diseases

Phospholipase D2 (PLD2) is a lipid-signaling enzyme that produces the signaling molecule phosphatidic acid (PA) by catalyzing the hydrolysis of phosphatidylcholine (PC). The molecular characteristics of PLD2, the mechanisms of regulation of its activity, its functions in the signaling pathway involving PA and binding partners, and its role in cellular physiology have been extensively studied over the past decades. Although several potential roles of PLD2 have been proposed based on the results of molecular and cell-based studies, the pathophysiological functions of PLD2 in vivo have not yet been fully investigated at the organismal level. Here, we address accumulated evidences that provide insight into the role of PLD2 in human disease. We summarize recent studies using animal models that provide direct evidence of the function of PLD2 in several pathological conditions such as vascular disease, immunological disease, and neurological disease. In light of the use of recently developed PLD2-specific inhibitors showing potential in alleviating pathological conditions, improving our understanding of the role of PLD2 in human disease would be necessary to target the regulation of PLD2 activity as a therapeutic strategy.

Potential pancreatic lipase inhibitory activity of phenolic constituents from the root bark of Morus alba L

Detailed phytochemical investigation from the root bark of Morus alba resulted in the isolation of eleven new compounds, including seven 2-arylbenzofuran derivatives (morusalfurans A-G), three flavonoids (morusalnols A-C), and one geranylated stilbene (morusibene A), as well as 22 known compounds. The structures of the identified compounds were elucidated based on a comprehensive analysis of spectroscopic data and Mosher's method. Compounds 2, 3, 6-8, 11, 23, 24, and 29 showed potent inhibition of PL in comparison with the positive control treatment (orlistat, IC50=0.012μM), with IC50 values ranging from 0.09 to 0.92μM.

Elevated O-GlcNAcylation promotes colonic inflammation and tumorigenesis by modulating NF-κB signaling

O-GlcNAcylation is a reversible post-translational modification. O-GlcNAc addition and removal is catalyzed by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. More recent evidence indicates that regulation of O-GlcNAcylation is important for inflammatory diseases and tumorigenesis. In this study, we revealed that O-GlcNAcylation was increased in the colonic tissues of dextran sodium sulfate (DSS)-induced colitis and azoxymethane (AOM)/DSS-induced colitis-associated cancer (CAC) animal models. Moreover, the O-GlcNAcylation level was elevated in human CAC tissues compared with matched normal counterparts. To investigate the functional role of O-GlcNAcylation in colitis, we used OGA heterozygote mice, which have an increased level of O-GlcNAcylation. OGA(+/-) mice have higher susceptibility to DSS-induced colitis than OGA(+/+) mice. OGA(+/-) mice exhibited a higher incidence of colon tumors than OGA(+/+) mice. In molecular studies, elevated O-GlcNAc levels were shown to enhance the activation of NF-κB signaling through increasing the binding of RelA/p65 to its target promoters. We also found that Thr-322 and Thr352 in the p65-O-GlcNAcylation sites are critical for p65 promoter binding. These results suggest that the elevated O-GlcNAcylation level in colonic tissues contributes to the development of colitis and CAC by disrupting regulation of NF-κB-dependent transcriptional activity.

Resveratrol induces autophagy by directly inhibiting mTOR through ATP competition

Resveratrol (RSV) is a natural polyphenol that has a beneficial effect on health, and resveratrol-induced autophagy has been suggested to be a key process in mediating many beneficial effects of resveratrol, such as reduction of inflammation and induction of cancer cell death. Although various resveratrol targets have been suggested, the molecule that mediates resveratrol-induced autophagy remains unknown. Here, we demonstrate that resveratrol induces autophagy by directly inhibiting the mTOR-ULK1 pathway. We found that inhibition of mTOR activity and presence of ULK1 are required for autophagy induction by resveratrol. In line with this mTOR dependency, we found that resveratrol suppresses the viability of MCF7 cells but not of SW620 cells, which are mTOR inhibitor sensitive and insensitive cancer cells, respectively. We also found that resveratrol-induced cancer cell suppression occurred ULK1 dependently. For the mechanism of action of resveratrol on mTOR inhibition, we demonstrate that resveratrol directly inhibits mTOR. We found that resveratrol inhibits mTOR by docking onto the ATP-binding pocket of mTOR (i.e., it competes with ATP). We propose mTOR as a novel direct target of resveratrol, and inhibition of mTOR is necessary for autophagy induction.

Roles of phosphoinositide-specific phospholipase Cγ1 in brain development

Over the past decade, converging evidence suggests that PLCγ1 signaling has key roles in controlling neural development steps. PLCγ1 functions as a signal transducer that converts an extracellular stimulus into intracellular signals by generating second messengers such as DAG and IP3. DAG functions as an activator of either PKC or transient receptor potential cation channels (TRPCs), while IP3 induces the calcium release from intracellular calcium stores. These second messengers regulate the morphological change of neuron, such as neurite outgrowth, migration, axon pathfinding, and synapse formation. These morphological changes depend on finely tuned calcium signaling following receptor tyrosine kinase-mediated PLCγ1 signaling. Thus, deregulation of PLCγ1 signaling causes various abnormalities of neuronal development and it may be associated with diverse neurological disorders. Herein, we discuss the current understanding of the PLCγ1 signaling pathway in neural development and provide recent advances of how PLCγ1 signaling is involved in the formation of neuronal processes for functionally faithful brain development.

Obesity resistance and increased energy expenditure by white adipose tissue browning in Oga(+/-) mice

AIMS/HYPOTHESIS

O-GlcNAcylation plays a role as a metabolic sensor regulating cellular signalling, transcription and metabolism. Transcription factors and signalling pathways related to metabolism are modulated by N-acetyl-glucosamine (O-GlcNAc) modification. Aberrant regulation of O-GlcNAcylation is closely linked to insulin resistance, type 2 diabetes and obesity. Current evidence shows that increased O-GlcNAcylation negatively regulates insulin signalling, which is associated with insulin resistance and type 2 diabetes. Here, we aimed to evaluate the effects of Oga (also known as Mgea5) haploinsufficiency, which causes hyper-O-GlcNAcylation, on metabolism.

METHODS

We examined whether Oga(+/-) mice developed insulin resistance. Metabolic variables were determined including body weight, glucose and insulin tolerance, metabolic rate and thermogenesis.

RESULTS

Oga deficiency does not affect insulin signalling even at hyper-O-GlcNAc levels. Oga(+/-) mice are lean with reduced fat mass and improved glucose tolerance. Furthermore, Oga(+/-) mice resist high-fat diet-induced obesity with ameliorated hepatic steatosis and improved glucose metabolism. Oga haploinsufficiency potentiates energy expenditure through the enhancement of brown adipocyte differentiation from the stromal vascular fraction of subcutaneous white adipose tissue (WAT).

CONCLUSIONS/INTERPRETATION

Our observations suggest that O-GlcNAcase (OGA) is essential for energy metabolism via regulation of the thermogenic WAT program.

PI3K-C2α Knockdown Results in Rerouting of Insulin Signaling and Pancreatic Beta Cell Proliferation

Insulin resistance is a syndrome that affects multiple insulin target tissues, each having different biological functions regulated by insulin. A remaining question is to mechanistically explain how an insulin target cell/tissue can be insulin resistant in one biological function and insulin sensitive in another at the same time. Here, we provide evidence that in pancreatic β cells, knockdown of PI3K-C2α expression results in rerouting of the insulin signal from insulin receptor (IR)-B/PI3K-C2α/PKB-mediated metabolic signaling to IR-B/Shc/ERK-mediated mitogenic signaling, which allows the β cell to switch from a highly glucose-responsive, differentiated state to a proliferative state. Our data suggest the existence of IR-cascade-selective insulin resistance, which allows rerouting of the insulin signal within the same target cell. Hence, factors involved in the rerouting of the insulin signal represent tentative therapeutic targets in the treatment of insulin resistance.

GTP-dependent interaction between phospholipase D and dynamin modulates fibronectin-induced cell spreading

Phospholipase D (PLD) is one of the key enzymes to mediate a variety of cellular phenomena including endocytosis, actin rearrangement, proliferation, differentiation, and migration. Dynamin as a PLD-interacting partner is a large GTP binding protein that has been considered a mechanochemical enzyme involved in endocytosis by hydrolyzing GTP. Although both PLD and dynamin have been implicated in the regulation of actin cytoskeleton, it is not known how they have a link to regulate fibronectin (FN)-induced cell spreading. Furthermore, it is unknown whether dynamin can work as a GTP-dependent regulator through its interaction with other proteins. Here, we demonstrate that PLD can be regulated by dynamin in a GTP-dependent manner and that this is critical for FN-mediated cell spreading. First, we verified that GTP-loaded dynamin can mediate the cell spreading by FN by using dynamin's GTP binding deficient mutant (K44A). Also, we confirmed that blocking the PLD activity inhibited FN-induced cell spreading, not cell adhesion. Moreover, PLD interacted with dynamin in a GTP-dependent manner in FN signaling, and this interaction was crucial for FN-induced PLD activation and cell spreading. Also, we found that PLD mutant (R128K) that didn't have GAP activity increased the GTP-dependent interaction between PLD and dynamin; it also increased PLD activity and cell spreading. These findings suggest that the observed increase in PLD activity was through boosting the binding of PLD with dynamin and it facilitated FN-induced cell spreading. These results imply that GTP-loaded dynamin, like a small GTPase could mediate a "switch on" signaling via interaction with PLD that has a role as an effector.

Phospholipase D2 drives mortality in sepsis by inhibiting neutrophil extracellular trap formation and down-regulating CXCR2

Lee et al. find that phospholipase D2 deficiency increases survival and decreases organ damage during experimental sepsis in mice which could be reversed with a CXCR2 antagonist. Thus, targeting PLD2 may offer therapeutics for septic patients.

We determined the function of phospholipase D2 (PLD2) in host defense in highly lethal mouse models of sepsis using PLD2^−/− mice and a PLD2-specific inhibitor. PLD2 deficiency not only increases survival but also decreases vital organ damage during experimental sepsis. Production of several inflammatory cytokines (TNF, IL-1β, IL-17, and IL-23) and the chemokine CXCL1, as well as cellular apoptosis in immune tissues, kidney, and liver, are markedly decreased in PLD2^−/− mice. Bactericidal activity is significantly increased in PLD2^−/− mice, which is mediated by increased neutrophil extracellular trap formation and citrullination of histone 3 through peptidylarginine deiminase activation. Recruitment of neutrophils to the lung is markedly increased in PLD2^−/− mice. Furthermore, LPS-induced induction of G protein–coupled receptor kinase 2 (GRK2) and down-regulation of CXCR2 are markedly attenuated in PLD2^−/− mice. A CXCR2-selective antagonist abolishes the protection conferred by PLD2 deficiency during experimental sepsis, suggesting that enhanced CXCR2 expression, likely driven by GRK2 down-regulation in neutrophils, promotes survival in PLD2^−/− mice. Furthermore, adoptively transferred PLD2^−/− neutrophils significantly protect WT recipients against sepsis-induced death compared with transferred WT neutrophils. We suggest that PLD2 in neutrophils is essential for the pathogenesis of experimental sepsis and that pharmaceutical agents that target PLD2 may prove beneficial for septic patients.

O-GlcNAc cycling enzymes control vascular development of the placenta by modulating the levels of HIF-1α

INTRODUCTION

Placental vasculogenesis is essential for fetal growth and development, and is affected profoundly by oxygen tension (hypoxia). Hypoxia-inducible factor-1α (HIF-1α), which is stabilized at the protein level in response to hypoxia, is essential for vascular morphogenesis in the placenta. Many studies suggested that responses to hypoxia is influenced by O-GlcNAcylation. O-GlcNAcylation is regulated by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) that catalyze the addition and removal of O-GlcNAc respectively.

METHODS

We generated OGA deficient mice and evaluated OGA(-/-) placentas. The analysis of OGA(-/-) placentas was focused on morphological change and placental vasculogenesis. HIF-1α protein stability or transcriptional activity under dysregulation of O-GlcNAcylation were evaluated by Western blot, RT-qPCR and luciferase reporter gene assays in MEFs or MS1 cell line.

RESULTS

Deletion of OGA results in defective placental vasculogenesis. OGA(-/-) placentas showed an abnormal placental shape and reduced vasculature in the labyrinth, which caused a developmental delay in the embryos. OGA deletion, which elevates O-GlcNAcylation and downregulates O-GlcNAc transferase (OGT), suppressed HIF-1α stabilization and the transcription of its target genes. In contrast, the overexpression of O-GlcNAc cycling enzymes enhanced the expression and transcriptional activity of HIF-1α.

DISCUSSION

These results suggest that OGA plays a critical role in placental vasculogenesis by modulating HIF-1α stabilization. Control of O-GlcNAcylation is essential for placental development.

Agonistic aptamer to the insulin receptor leads to biased signaling and functional selectivity through allosteric modulation

Due to their high affinity and specificity, aptamers have been widely used as effective inhibitors in clinical applications. However, the ability to activate protein function through aptamer-protein interaction has not been well-elucidated. To investigate their potential as target-specific agonists, we used SELEX to generate aptamers to the insulin receptor (IR) and identified an agonistic aptamer named IR-A48 that specifically binds to IR, but not to IGF-1 receptor. Despite its capacity to stimulate IR autophosphorylation, similar to insulin, we found that IR-A48 not only binds to an allosteric site distinct from the insulin binding site, but also preferentially induces Y1150 phosphorylation in the IR kinase domain. Moreover, Y1150-biased phosphorylation induced by IR-A48 selectively activates specific signaling pathways downstream of IR. In contrast to insulin-mediated activation of IR, IR-A48 binding has little effect on the MAPK pathway and proliferation of cancer cells. Instead, AKT S473 phosphorylation is highly stimulated by IR-A48, resulting in increased glucose uptake both in vitro and in vivo. Here, we present IR-A48 as a biased agonist able to selectively induce the metabolic activity of IR through allosteric binding. Furthermore, our study also suggests that aptamers can be a promising tool for developing artificial biased agonists to targeted receptors.