The lipid phosphatase SHIP2 controls insulin sensitivity

Molecular Aspects in the Development of Type 2 Diabetes and Possible Preventive and Complementary Therapies

The incidence of diabetes, including type 2 diabetes (T2DM), is increasing sharply worldwide. To reverse this, more effective approaches in prevention and treatment are needed. In our review, we sought to summarize normal insulin action and the pathways that primarily influence the development of T2DM. Normal insulin action involves mitogenic and metabolic pathways, as both are important in normal metabolic processes, regeneration, etc. However, through excess energy, both can be hyperactive or attenuated/inactive leading to disturbances in the cellular and systemic regulation with the consequence of cellular stress and systemic inflammation. In this review, we detailed the beneficial molecular changes caused by some important components of nutrition and by exercise, which act in the same molecular targets as the developed drugs, and can revert the damaged pathways. Moreover, these induce entire networks of regulatory mechanisms and proteins to restore unbalanced homeostasis, proving their effectiveness as preventive and complementary therapies. These are the main steps for success in prevention and treatment of developed diseases to rid the body of excess energy, both from stored fats and from overnutrition, while facilitating fat burning with adequate, regular exercise in healthy people, and together with necessary drug treatment as required in patients with insulin resistance and T2DM.

Alteration of gene expression and protein solubility of the PI 5-phosphatase SHIP2 are correlated with Alzheimer's disease pathology progression

A recent large genome-wide association study has identified EGFR (encoding the epidermal growth factor EGFR) as a new genetic risk factor for late-onset AD. SHIP2, encoded by INPPL1, is taking part in the signalling and interactome of several growth factor receptors, such as the EGFR. While INPPL1 has been identified as one of the most significant genes whose RNA expression correlates with cognitive decline, the potential alteration of SHIP2 expression and localization during the progression of AD remains largely unknown. Here we report that gene expression of both EGFR and INPPL1 was upregulated in AD brains. SHIP2 immunoreactivity was predominantly detected in plaque-associated astrocytes and dystrophic neurites and its increase was correlated with amyloid load in the brain of human AD and of 5xFAD transgenic mouse model of AD. While mRNA of INPPL1 was increased in AD, SHIP2 protein undergoes a significant solubility change being depleted from the soluble fraction of AD brain homogenates and co-enriched with EGFR in the insoluble fraction. Using FRET-based flow cytometry biosensor assay for tau-tau interaction, overexpression of SHIP2 significantly increased the FRET signal while siRNA-mediated downexpression of SHIP2 significantly decreased FRET signal. Genetic association analyses suggest that some variants in INPPL1 locus are associated with the level of CSF pTau. Our data support the hypothesis that SHIP2 is an intermediate key player of EGFR and AD pathology linking amyloid and tau pathologies in human AD.

INPP5D/SHIP1: Expression, Regulation and Roles in Alzheimer's Disease Pathophysiology

Alzheimer's disease (AD) is the most common form of dementia, accounting for approximately 38.5 million cases of all-cause dementia. Over 60% of these individuals live in low- and middle-income countries and are the worst affected, especially by its deleterious effects on the productivity of both patients and caregivers. Numerous risk factors for the disease have been identified and our understanding of gene-environment interactions have shed light on several gene variants that contribute to the most common, sporadic form of AD. Microglial cells, the innate immune cells of the central nervous system (CNS), have long been established as guardians of the brain by providing neuroprotection and maintaining cellular homeostasis. A protein with a myriad of effects on various important signaling pathways that is expressed in microglia is the Src Homology 2 (SH2) domain-containing Inositol 5' Phosphatase 1 (SHIP1) protein. Encoded by the INPP5D (Inositol Polyphosphate-5-Phosphatase D) gene, SHIP1 has diminutive effects on most microglia signaling processes. Polymorphisms of the INPP5D gene have been found to be associated with a significantly increased risk of AD. Several studies have elucidated mechanistic processes by which SHIP1 exerts its perturbations on signaling processes in peripheral immune cells. However, current knowledge of the controllers of INPP5D/SHIP1 expression and the idiosyncrasies of its influences on signaling processes in microglia and their relevance to AD pathophysiology is limited. In this review, we summarize these discoveries and discuss the potential of leveraging INPP5D/SHIP1 as a therapeutic target for Alzheimer's disease.

Phosphoinositides and intracellular calcium signaling: novel insights into phosphoinositides and calcium coupling as negative regulators of cellular signaling

Intracellular calcium (Ca2+) and phosphoinositides (PIPs) are crucial for regulating cellular activities such as metabolism and cell survival. Cells maintain precise intracellular Ca2+ and PIP levels via the actions of a complex system of Ca2+ channels, transporters, Ca2+ ATPases, and signaling effectors, including specific lipid kinases, phosphatases, and phospholipases. Recent research has shed light on the complex interplay between Ca2+ and PIP signaling, suggesting that elevated intracellular Ca2+ levels negatively regulate PIP signaling by inhibiting the membrane localization of PIP-binding proteins carrying specific domains, such as the pleckstrin homology (PH) and Ca2+-independent C2 domains. This dysregulation is often associated with cancer and metabolic diseases. PIPs recruit various proteins with PH domains to the plasma membrane in response to growth hormones, which activate signaling pathways regulating metabolism, cell survival, and growth. However, abnormal PIP signaling in cancer cells triggers consistent membrane localization and activation of PIP-binding proteins. In the context of obesity, an excessive intracellular Ca2+ level prevents the membrane localization of the PIP-binding proteins AKT, IRS1, and PLCδ via Ca2+-PIPs, contributing to insulin resistance and other metabolic diseases. Furthermore, an excessive intracellular Ca2+ level can cause functional defects in subcellular organelles such as the endoplasmic reticulum (ER), lysosomes, and mitochondria, causing metabolic diseases. This review explores how intracellular Ca2+ overload negatively regulates the membrane localization of PIP-binding proteins.

Nuclear Phosphoinositides as Key Determinants of Nuclear Functions

Polyphosphoinositides (PPIns) are signalling messengers representing less than five per cent of the total phospholipid concentration within the cell. Despite their low concentration, these lipids are critical regulators of various cellular processes, including cell cycle, differentiation, gene transcription, apoptosis and motility. PPIns are generated by the phosphorylation of the inositol head group of phosphatidylinositol (PtdIns). Different pools of PPIns are found at distinct subcellular compartments, which are regulated by an array of kinases, phosphatases and phospholipases. Six of the seven PPIns species have been found in the nucleus, including the nuclear envelope, the nucleoplasm and the nucleolus. The identification and characterisation of PPIns interactor and effector proteins in the nucleus have led to increasing interest in the role of PPIns in nuclear signalling. However, the regulation and functions of PPIns in the nucleus are complex and are still being elucidated. This review summarises our current understanding of the localisation, biogenesis and physiological functions of the different PPIns species in the nucleus.

The Activation Mechanism of the Insulin Receptor: A Structural Perspective

The insulin receptor (IR) is a type II receptor tyrosine kinase that plays essential roles in metabolism, growth, and proliferation. Dysregulation of IR signaling is linked to many human diseases, such as diabetes and cancers. The resolution revolution in cryo-electron microscopy has led to the determination of several structures of IR with different numbers of bound insulin molecules in recent years, which have tremendously improved our understanding of how IR is activated by insulin. Here, we review the insulin-induced activation mechanism of IR, including (a) the detailed binding modes and functions of insulin at site 1 and site 2 and (b) the insulin-induced structural transitions that are required for IR activation. We highlight several other key aspects of the activation and regulation of IR signaling and discuss the remaining gaps in our understanding of the IR activation mechanism and potential avenues of future research.

Genome-wide CRISPR/Cas9 screens reveal shared and cell-specific mechanisms of resistance to SHP2 inhibition

SHP2 (PTPN11) acts upstream of SOS1/2 to enable RAS activation. Allosteric SHP2 inhibitors (SHP2i) in the clinic prevent SHP2 activation, block proliferation of RTK- or cycling RAS mutant-driven cancers, and overcome "adaptive resistance." To identify SHP2i resistance mechanisms, we performed genome-wide CRISPR/Cas9 knockout screens on two SHP2i-sensitive cell lines, recovering genes expected to cause resistance (NF1, PTEN, CDKN1B, LZTR1, and RASA2) and novel targets (INPPL1, MAP4K5, epigenetic modifiers). We screened 14 additional lines with a focused CRISPR library targeting common "hits" from the genome-wide screens. LZTR1 deletion conferred resistance in 12/14 lines, followed by MAP4K5 (8/14), SPRED2/STK40 (6/14), and INPPL1 (5/14). INPPL1, MAP4K5, or LZTR1 deletion reactivated ERK signaling. INPPL1-mediated sensitization to SHP2i required its NPXY motif but not lipid phosphatase activity. MAP4K5 acted upstream of MEK through a kinase-dependent target(s); LZTR1 had cell-dependent effects on RIT and RAS stability. INPPL1, MAP4K5, or LZTR1 deletion also conferred SHP2i resistance in vivo. Defining the SHP2i resistance landscape could suggest effective combination approaches.

The Role of C2 Domains in Two Different Phosphatases: PTEN and SHIP2

Phosphatase and tensin homologue (PTEN) and SH2-containing inositol 5'-phosphatase 2 (SHIP2) are structurally and functionally similar. They both consist of a phosphatase (Ptase) domain and an adjacent C2 domain, and both proteins dephosphorylate phosphoinositol-tri(3,4,5)phosphate, PI(3,4,5)P₃; PTEN at the 3-phophate and SHIP2 at the 5-phosphate. Therefore, they play pivotal roles in the PI3K/Akt pathway. Here, we investigate the role of the C2 domain in membrane interactions of PTEN and SHIP2, using molecular dynamics simulations and free energy calculations. It is generally accepted that for PTEN, the C2 domain interacts strongly with anionic lipids and therefore significantly contributes to membrane recruitment. In contrast, for the C2 domain in SHIP2, we previously found much weaker binding affinity for anionic membranes. Our simulations confirm the membrane anchor role of the C2 domain in PTEN, as well as its necessity for the Ptase domain in gaining its productive membrane-binding conformation. In contrast, we identified that the C2 domain in SHIP2 undertakes neither of these roles, which are generally proposed for C2 domains. Our data support a model in which the main role of the C2 domain in SHIP2 is to introduce allosteric interdomain changes that enhance catalytic activity of the Ptase domain.

Massive Loss of Transcription Factors Promotes the Initial Diversification of Placental Mammals

As one of the most successful group of organisms, mammals occupy a variety of niches on Earth as a result of macroevolution. Transcription factors (TFs), the fundamental regulators of gene expression, may also have evolved. To examine the relationship between TFs and mammalian macroevolution, we analyzed 140,821 de novo-identified TFs and their birth and death histories from 96 mammalian species. Gene tree vs. species tree reconciliation revealed that placental mammals experienced an upsurge in TF losses around 100 million years ago (Mya) and also near the Cretaceous–Paleogene boundary (K–Pg boundary, 66 Mya). Early Euarchontoglires, Laurasiatheria and marsupials appeared between 100 and 95 Mya and underwent initial diversification. The K-Pg boundary was associated with the massive extinction of dinosaurs, which lead to adaptive radiation of mammals. Surprisingly, TF loss decelerated, rather than accelerated, molecular evolutionary rates of their target genes. As the rate of molecular evolution is affected by the mutation rate, the proportion of neutral mutations and the population size, the decrease in molecular evolution may reflect increased functional constraints to survive target genes.

Cell-Dependent Pathogenic Roles of Filamin B in Different Skeletal Malformations

Mutations of filamin B (FLNB) gene can lead to a spectrum of autosomal skeletal malformations including spondylocarpotarsal syndrome (SCT), Larsen syndrome (LRS), type I atelosteogenesis (AO1), type III atelosteogenesis (AO3), and boomerang dysplasia (BD). Among them, LRS is milder while BD causes a more severe phenotype. However, the molecular mechanism underlying the differences in clinical phenotypes of different FLNB variants has not been fully determined. Here, we presented two patients suffering from autosomal dominant LRS and autosomal recessive vitamin D-dependent rickets type IA (VDDR-IA). Whole-exome sequencing revealed two novel missense variants in FLNB, c.4846A>G (p.T1616A) and c.7022T>G (p.I2341R), which are located in repeat 15 and 22 of filamin B, respectively. The expression of FLNB^I2341R in the muscle tissue from our LRS patient was remarkably increased. And in vitro studies showed that both variants led to a lack of filopodia and accumulation of the mutants in the perinuclear region in HEK293 cells. We also found that c.4846A>G (p.T1616A) and c.7022T>G (p.I2341R) regulated endochondral osteogenesis in different ways. c.4846A>G (p.T1616A) activated AKT pathways through inhibiting SHIP2, suppressed the Smad3 pathway, and impaired the expression of Runx2 in both Saos-2 and ATDC5 cells. c.7022T>G (p.I2341R) activated both AKT and Smad3 pathways and increased the expression of Runx2 in Saos-2 cells, while in ATDC5 cells it activated AKT pathways through inhibiting SHIP2, suppressed the Smad3 pathway, and reduced the expression of Runx2. Our study demonstrated the pathogenic mechanisms of two novel FLNB variants in two different clinical settings and proved that FLNB variants could not only directly cause skeletal malformations but also worsen skeletal symptoms in the setting of other skeletal diseases. Besides, FLNB variants differentially affect skeletal development which contributes to clinical heterogeneity of FLNB-related disorders.

Discovery of a novel SHIP1 agonist that promotes degradation of lipid-laden phagocytic cargo by microglia

Here, we describe the use of artificial intelligence to identify novel agonists of the SH2-containing 5′ inositol phosphatase 1 (SHIP1). One of the compounds, K306, represents the most potent agonist identified to date. We find that K306 exhibits selectivity for SHIP1 vs. the paralog enzyme SHIP2, and this activation does not require the C2 domain of SHIP1 which other known SHIP1 agonists require. Thus, K306 represents a new class of SHIP1 agonists with a novel mode of agonism. Importantly, we find that K306 can suppress induction of inflammatory cytokines and iNOS in macrophages or microglia, but not by their SHIP1-deficient counterparts. K306 also reduces TNF-α production in vivo in an LPS-induced endotoxemia assay. Finally, we show that K306 enhances phagolysosomal degradation of synaptosomes and dead neurons by microglia revealing a novel function for SHIP1 that might be exploited therapeutically in dementia.

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Discovery of a potent SHIP1 selective agonist (K306) via artificial intelligence

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SHIP1 agonism via K306 is independent of the C2 domain and increases PI(3,4)P₂ levels

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K306 reduces IL-6, TNF-α, and iNOS induction in microglia and macrophages

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K306 promotes phagocytic degradation of lipid-laden but not protein cargo in microglia

The manifold roles of protein S-nitrosylation in the life of insulin

Insulin, which is released by pancreatic islet β-cells in response to elevated levels of glucose in the blood, is a critical regulator of metabolism. Insulin triggers the uptake of glucose and fatty acids into the liver, adipose tissue and muscle, and promotes the storage of these nutrients in the form of glycogen and lipids. Dysregulation of insulin synthesis, secretion, transport, degradation or signal transduction all cause failure to take up and store nutrients, resulting in type 1 diabetes mellitus, type 2 diabetes mellitus and metabolic dysfunction. In this Review, we make the case that insulin signalling is intimately coupled to protein S-nitrosylation, in which nitric oxide groups are conjugated to cysteine thiols to form S-nitrosothiols, within effectors of insulin action. We discuss the role of S-nitrosylation in the life cycle of insulin, from its synthesis and secretion in pancreatic β-cells, to its signalling and degradation in target tissues. Finally, we consider how aberrant S-nitrosylation contributes to metabolic diseases, including the roles of human genetic mutations and cellular events that alter S-nitrosylation of insulin-regulating proteins. Given the growing influence of S-nitrosylation in cellular metabolism, the field of metabolic signalling could benefit from renewed focus on S-nitrosylation in type 2 diabetes mellitus and insulin-related disorders.

Insulin signaling in health and disease

The molecular mechanisms of cellular insulin action have been the focus of much investigation since the discovery of the hormone 100 years ago. Insulin action is impaired in metabolic syndrome, a condition known as insulin resistance. The actions of the hormone are initiated by binding to its receptor on the surface of target cells. The receptor is an α2β2 heterodimer that binds to insulin with high affinity, resulting in the activation of its tyrosine kinase activity. Once activated, the receptor can phosphorylate a number of intracellular substrates that initiate discrete signaling pathways. The tyrosine phosphorylation of some substrates activates phosphatidylinositol-3-kinase (PI3K), which produces polyphosphoinositides that interact with protein kinases, leading to activation of the kinase Akt. Phosphorylation of Shc leads to activation of the Ras/MAP kinase pathway. Phosphorylation of SH2B2 and of Cbl initiates activation of G proteins such as TC10. Activation of Akt and other protein kinases produces phosphorylation of a variety of substrates, including transcription factors, GTPase-activating proteins, and other kinases that control key metabolic events. Among the cellular processes controlled by insulin are vesicle trafficking, activities of metabolic enzymes, transcriptional factors, and degradation of insulin itself. Together these complex processes are coordinated to ensure glucose homeostasis.

An auxiliary binding interface of SHIP2-SH2 for Y292-phosphorylated FcγRIIB reveals diverse recognition mechanisms for tyrosine-phosphorylated receptors involved in different cell signaling pathways

SH2 domain-containing inositol 5-phosphatase 2 (SHIP2) plays an essential role in regulating phosphatidylinositol level in human cell, and is recruited to many phosphotyrosine (pY)-dependent signal transduction pathways by the SH2 domain. In immunity signaling, immunoreceptor FcγRIIB binds to SHIP2-SH2 via its Y292-phosphorylated immunoreceptor tyrosine-based inhibitory motif (ITIM) and transmits inhibitory signal, which regulates B cell and neuronal cell activity and is associated with immune diseases and Alzheimer's disease. To date, the interaction between SHIP2 and FcγRIIB has not been analyzed from a structural point of view. Here, the binding of SHIP2-SH2 with Y292-phosphorylated FcγRIIB-ITIM was analyzed using NMR spectroscopy. The results demonstrated that SHIP2-SH2 mainly utilizes two regions including a pY-binding pocket and a specificity pocket formed by βD, βE, and EF-loop, to bind with FcγRIIB-ITIM in high affinity. In addition to the two regions, the BG-loop of SHIP2-SH2 functions as an auxiliary interface enhancing affinity. By comparing the binding of SHIP2-SH2 with ligands from FcγRIIB and c-MET, a hepatocyte growth factor receptor associated with tumorigenesis, significant differences in interface and affinity were found, suggesting that SHIP2-SH2 applies diverse patterns for binding to different ligand proteins. Moreover, S49, S51, and R70 of SHIP2 were identified to mediate the binding of both FcγRIIB and c-MET, while R28 and Q107 were found to only participate in the binding of c-MET and FcγRIIB respectively. Taken together, this study reveals the diverse mechanisms of SHIP2-SH2 for recognizing different ligands, and provides important clues for selectively manipulating various signaling pathways and specific drug design.

Targeting SHIP1 and SHIP2 in Cancer

Simple Summary

Phosphoinositol signaling pathways and their dysregulation have been shown to have a fundamental role in health and disease, respectively. The SH2-containing 5′ inositol phosphatases, SHIP1 and SHIP2, are regulators of the PI3K/AKT pathway that have crucial roles in cancer progression. This review aims to summarize the role of SHIP1 and SHIP2 in cancer signaling and the immune response to cancer, the discovery and use of SHIP inhibitors and agonists as possible cancer therapeutics.

Abstract

Membrane-anchored and soluble inositol phospholipid species are critical mediators of intracellular cell signaling cascades. Alterations in their normal production or degradation are implicated in the pathology of a number of disorders including cancer and pro-inflammatory conditions. The SH2-containing 5′ inositol phosphatases, SHIP1 and SHIP2, play a fundamental role in these processes by depleting PI(3,4,5)P₃, but also by producing PI(3,4)P₂ at the inner leaflet of the plasma membrane. With the intent of targeting SHIP1 or SHIP2 selectively, or both paralogs simultaneously, small molecule inhibitors and agonists have been developed and tested in vitro and in vivo over the last decade in various disease models. These studies have shown promising results in various pre-clinical models of disease including cancer and tumor immunotherapy. In this review the potential use of SHIP inhibitors in cancer is discussed with particular attention to the molecular structure, binding site and efficacy of these SHIP inhibitors.

Tribbles Pseudokinase 2 (TRIB2) Regulates Expression of Binding Partners in Bovine Granulosa Cells

Members of the Tribbles (TRIB) family of pseudokinases are critical components of intracellular signal transduction pathways in physiological and pathological processes. TRIBs, including TRIB2, have been previously shown as signaling mediators and scaffolding proteins regulating numerous cellular events such as proliferation, differentiation and cell death through protein stability and activity. However, the signaling network associated with TRIB2 and its binding partners in granulosa cells during ovarian follicular development is not fully defined. We previously reported that TRIB2 is differentially expressed in growing dominant follicles while downregulated in ovulatory follicles following the luteinizing hormone (LH) surge or human chorionic gonadotropin (hCG) injection. In the present study, we used the yeast two-hybrid screening system and in vitro coimmunoprecipitation assays to identify and confirm TRIB2 interactions in granulosa cells (GCs) of dominant ovarian follicles (DFs), which yielded individual candidate binding partners including calmodulin 1 (CALM1), inhibin subunit beta A (INHBA), inositol polyphosphate phosphatase-like 1 (INPPL1), 5'-nucleotidase ecto (NT5E), stearoyl-CoA desaturase (SCD), succinate dehydrogenase complex iron sulfur subunit B (SDHB) and Ras-associated protein 14 (RAB14). Further analyses showed that all TRIB2 binding partners are expressed in GCs of dominant follicles but are differentially regulated throughout the different stages of follicular development. CRISPR/Cas9-driven inhibition along with pQE-driven overexpression of TRIB2 showed that TRIB2 differently regulates expression of binding partners, which reveals the importance of TRIB2 in the control of gene expression linked to various biological processes such as proliferation, differentiation, cell migration, apoptosis, calcium signaling and metabolism. These data provide a larger view of potential TRIB2-regulated signal transduction pathways in GCs and provide strong evidence that TRIB2 may act as a regulator of target genes during ovarian follicular development.

PTEN and Other PtdIns(3,4,5)P3 Lipid Phosphatases in Breast Cancer

The phosphoinositide 3-kinase (PI3K)/AKT signalling pathway is hyperactivated in ~70% of breast cancers. Class I PI3K generates PtdIns(3,4,5)P₃ at the plasma membrane in response to growth factor stimulation, leading to AKT activation to drive cell proliferation, survival and migration. PTEN negatively regulates PI3K/AKT signalling by dephosphorylating PtdIns(3,4,5)P₃ to form PtdIns(4,5)P₂. PtdIns(3,4,5)P₃ can also be hydrolysed by the inositol polyphosphate 5-phosphatases (5-phosphatases) to produce PtdIns(3,4)P₂. Interestingly, while PTEN is a bona fide tumour suppressor and is frequently mutated/lost in breast cancer, 5-phosphatases such as PIPP, SHIP2 and SYNJ2, have demonstrated more diverse roles in regulating mammary tumourigenesis. Reduced PIPP expression is associated with triple negative breast cancers and reduced relapse-free and overall survival. Although PIPP depletion enhances AKT phosphorylation and supports tumour growth, this also inhibits cell migration and metastasis in vivo, in a breast cancer oncogene-driven murine model. Paradoxically, SHIP2 and SYNJ2 are increased in primary breast tumours, which correlates with invasive disease and reduced survival. SHIP2 or SYNJ2 overexpression promotes breast tumourigenesis via AKT-dependent and independent mechanisms. This review will discuss how PTEN, PIPP, SHIP2 and SYNJ2 distinctly regulate multiple functional targets, and the mechanisms by which dysregulation of these distinct phosphoinositide phosphatases differentially affect breast cancer progression.

Scaffold dependent role of the inositol 5'-phosphatase SHIP2, in regulation of oxidative stress induced apoptosis

Cell apoptosis is an important process that occurs during development or in response to stress stimuli such as oxidative stress. The serine-threonine kinase Akt enhances survival and suppress apoptosis. SHIP2 is known as a negative regulator of Akt. In addition to its lipid 5'-phosphatase activity, SHIP2 interacts and signals as a scaffolding complex with several proteins. Several findings have pointed out a possible role of SHIP2 in apoptosis regulation. However, the molecular mechanisms behind remain unknown. Using embryonic fibroblast lacking the lipid 5'-phosphatase domain as a genetic model system and human liver cancer cells treated with SHIP2 inhibitor (AS1949490), as a pharmacological model system. We provide the first evidence that SHIP2 regulates apoptosis independently of its 5'-phosphates activity. Indeed, absence of the 5'-phosphatase domain of SHIP2 did not prevent H2O2-induced apoptosis in fibroblasts. Whereas chemical inactivation or RNAi knockdown of SHIP2 blocked H2O2-induced apoptosis in HepG2 cells. We found that suppression of apoptosis upon SHIP2 inhibition is PI3K/Akt independent but rather MAP kinase dependent. In addition, we found that AS1949490 altered both 5'-phosphatase and scaffolding function of SHIP2. Indeed, AS1949490 mediated SHIP2 inhibition promotes protein complex formation of SHIP2 together with non-receptor tyrosine kinase SRC and ABL which in turn enhances PI3K/Akt and MAP kinase pathways activation. Dual inhibition of SRC/ABL blocked activation of both pathways upon SHIP2 inhibition and H2O2 treatment. Altogether, these findings indicate that SHIP2 protein play a determinant role in H2O2-induced apoptosis.

SHIP2 inhibition alters redox-induced PI3K/AKT and MAP kinase pathways via PTEN over-activation in cervical cancer cells

Phosphatidylinositol (3,4,5)‐trisphosphate (PI(3,4,5)P3) is required for protein kinase B (AKT) activation. The level of PI(3,4,5)P3 is constantly regulated through balanced synthesis by phosphoinositide 3‐kinase (PI3K) and degradation by phosphoinositide phosphatases phosphatase and tensin homologue (PTEN) and SH2‐domain containing phosphatidylinositol‐3,4,5‐trisphosphate 5‐phosphatase 2 (SHIP2), known as negative regulators of AKT. Here, I show that SHIP2 inhibition in cervical cancer cell lines alters H₂O₂‐mediated AKT and mitogen‐activated protein kinase/extracellular signal‐regulated kinase pathway activation. In addition, SHIP2 inhibition enhances reactive oxygen species generation. Interestingly, I found that SHIP2 inhibition and H₂O₂ treatment enhance lipid and protein phosphatase activity of PTEN. Pharmacological targeting or RNA interference(RNAi) mediated knockdown of PTEN rescues extracellular signal‐regulated kinase and AKT activation. Using a series of pharmacological and biochemical approaches, I provide evidence that crosstalk between SHIP2 and PTEN occurs upon an increase in oxidative stress to modulate the activity of mitogen‐activated protein kinase and phosphoinositide 3/ATK pathways.

Phosphatidylinositol 5 Phosphate 4-Kinase Regulates Plasma-Membrane PIP3 Turnover and Insulin Signaling

Phosphatidylinositol 3,4,5-trisphosphate (PIP₃) generation at the plasma membrane is a key event during activation of receptor tyrosine kinases such as the insulin receptor required for normal growth and metabolism. We report that in Drosophila, phosphatidylinositol 5 phosphate 4-kinase (PIP4K) is required to limit PIP₃ levels during insulin receptor activation. Depletion of PIP4K increases the levels of PIP₃ produced in response to insulin stimulation. We find that PIP4K function at the plasma membrane enhances class I phosphoinositide 3-kinase (PI3K) activity, although the catalytic ability of PIP4K to produce phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂] at the plasma membrane is dispensable for this regulation. Animals lacking PIP4K show enhanced insulin signaling-dependent phenotypes and are resistant to the metabolic consequences of a high-sugar diet, highlighting the importance of PIP4K in normal metabolism and development. Thus, PIP4Ks are key regulators of receptor tyrosine kinase signaling with implications for growth factor-dependent processes including tumor growth, T cell activation, and metabolism.

Genome-wide copy number variation analysis identified ANO1 as a novel oncogene and prognostic biomarker in esophageal squamous cell cancer

Copy number variations (CNVs) represent one of the most common genomic alterations. This study aimed to evaluate the roles of genes within highly aberrant genome regions in the prognosis of esophageal squamous cell cancer (ESCC). Exome sequencing data from 81 paired ESCC tissues were used to screen aberrant genomic regions. The associations between CNVs and gene expression were evaluated using gene expression data from the same individuals. Then, an RNA expression array profile from 119 ESCC samples was adopted for differential gene expression and prognostic analyses. Two independent ESCC cohorts with 315 subjects were further recruited to validate the prognostic value using immunohistochemistry tests. Finally, we explored the potential mechanism of our identified novel oncogene in ESCC. In total, 2003 genes with CNVs were observed, of which 76 genes showed recurrent CNVs in more than three samples. Among them, 32 genes were aberrantly expressed in ESCC tumor tissues and statistically correlated with CNVs. Strikingly, 4 (CTTN, SHANK2, INPPL1 and ANO1) of the 32 genes were significantly associated with the prognosis of ESCC patients. Patients with a positive expression of ANO1 had a poorer prognosis than ANO1 negative patients (overall survival rate: 42.91% versus 26.22% for ANO1-/+ samples, P < 0.001). Functionally, ANO1 promoted ESCC cell proliferation, migration and invasion by activating transforming growth factor-β pathway. Knockdown of ANO1 significantly inhibited tumor progression in vitro and in vivo. In conclusion, ANO1 is a novel oncogene in ESCC and may serve as a prognostic biomarker for ESCC.

Excess Accumulation of Lipid Impairs Insulin Sensitivity in Skeletal Muscle

Both glucose and free fatty acids (FFAs) are used as fuel sources for energy production in a living organism. Compelling evidence supports a role for excess fatty acids synthesized in intramuscular space or dietary intermediates in the regulation of skeletal muscle function. Excess FFA and lipid droplets leads to intramuscular accumulation of lipid intermediates. The resulting downregulation of the insulin signaling cascade prevents the translocation of glucose transporter to the plasma membrane and glucose uptake into skeletal muscle, leading to metabolic disorders such as type 2 diabetes. The mechanisms underlining metabolic dysfunction in skeletal muscle include accumulation of intracellular lipid derivatives from elevated plasma FFAs. This paper provides a review of the molecular mechanisms underlying insulin-related signaling pathways after excess accumulation of lipids.

Small molecule targeting of SHIP1 and SHIP2

Modulating the activity of the Src Homology 2 (SH2) — containing Inositol 5′-Phosphatase (SHIP) enzyme family with small molecule inhibitors provides a useful and unconventional method of influencing cell signaling in the PI3K pathway. The development of small molecules that selectively target one of the SHIP paralogs (SHIP1 or SHIP2) as well as inhibitors that simultaneously target both enzymes have provided promising data linking the phosphatase activity of the SHIP enzymes to disorders and disease states that are in dire need of new therapeutic targets. These include cancer, immunotherapy, diabetes, obesity, and Alzheimer's disease. In this mini-review, we will provide a brief overview of research in these areas that support targeting SHIP1, SHIP2 or both enzymes for therapeutic purposes.

SHIPping out diabetes-Metformin, an old friend among new SHIP2 inhibitors

SHIP2 (Src homology 2 domain‐containing inositol 5′‐phosphatase 2) belongs to the family of 5′‐phosphatases. It regulates the phosphoinositide 3‐kinase (PI3K)‐mediated insulin signalling cascade by dephosphorylating the 5′‐position of PtdIns(3,4,5)P3 to generate PtdIns(3,4)P2, suppressing the activity of the pathway. SHIP2 mouse models and genetic studies in human propose that increased expression or activity of SHIP2 contributes to the pathogenesis of the metabolic syndrome, hypertension and type 2 diabetes. This has raised great interest to identify SHIP2 inhibitors that could be used to design new treatments for metabolic diseases. This review summarizes the central mechanisms associated with the development of diabetic kidney disease, including the role of insulin resistance, and then moves on to describe the function of SHIP2 as a regulator of metabolism in mouse models. Finally, the identification of SHIP2 inhibitors and their effects on metabolic processes in vitro and in vivo are outlined. One of the newly identified SHIP2 inhibitors is metformin, the first‐line medication prescribed to patients with type 2 diabetes, further boosting the attraction of SHIP2 as a treatment target to ameliorate metabolic disorders.

Downregulation of SHIP2 by Hepatitis B Virus X Promotes the Metastasis and Chemoresistance of Hepatocellular Carcinoma through SKP2

Hepatitis B virus (HBV)-encoded X protein (HBx) plays an important role in the development of hepatocellular carcinoma (HCC). The protein SH2 domain containing inositol 5-phosphatase 2 (SHIP2) belongs to the family of enzymes that dephosphorylate the 5 position of PI(3,4,5)P3 to produce PI(3,4)P2. Expression of SHIP2 has been associated with several cancers including HCC. However, its role in the development of HBV-related HCC remains elusive. In this study, we performed tissue microarray analysis using 49 cases of HCC to explore SHIP2 expression changes and found that SHIP2 was downregulated in HBV-positive HCC. In addition, S-phase kinase-associated protein 2 (SKP2), a component of the E3 ubiquitin–ligase complex, was increased in HCC cell lines that overexpressed HBx, which also showed a notable accumulation of polyubiquitinated SHIP2. Moreover, HCC cells with silenced SHIP2 had increased expression of mesenchymal markers, which promotes cell migration, enhances glucose uptake, and leads to resistance to the chemotherapy drug (5-Fluorouracil, 5-FU). Taken together, our results demonstrate that HBx downregulates SHIP2 through SKP2 and suggest a potential role for SHIP2 in HBx-mediated HCC migration.

Maternal and Post-weaning High-Fat Diets Produce Distinct DNA Methylation Patterns in Hepatic Metabolic Pathways within Specific Genomic Contexts

Calorie-dense high-fat diets (HF) are associated with detrimental health outcomes, including obesity, cardiovascular disease, and diabetes. Both pre- and post-natal HF diets have been hypothesized to negatively impact long-term metabolic health via epigenetic mechanisms. To understand how the timing of HF diet intake impacts DNA methylation and metabolism, male Sprague–Dawley rats were exposed to either maternal HF (MHF) or post-weaning HF diet (PHF). At post-natal week 12, PHF rats had similar body weights but greater hepatic lipid accumulation compared to the MHF rats. Genome-wide DNA methylation was evaluated, and analysis revealed 1744 differentially methylation regions (DMRs) between the groups with the majority of the DMR located outside of gene-coding regions. Within differentially methylated genes (DMGs), intragenic DNA methylation closer to the transcription start site was associated with lower gene expression, whereas DNA methylation further downstream was positively correlated with gene expression. The insulin and phosphatidylinositol (PI) signaling pathways were enriched with 25 DMRs that were associated with 20 DMGs, including PI3 kinase (Pi3k), pyruvate kinase (Pklr), and phosphodiesterase 3 (Pde3). Together, these results suggest that the timing of HF diet intake determines DNA methylation and gene expression patterns in hepatic metabolic pathways that target specific genomic contexts.

Expansion and Functional Divergence of Inositol Polyphosphate 5-Phosphatases in Angiosperms

Inositol polyphosphate 5-phosphatase (5PTase), a key enzyme that hydrolyzes the 5` position of the inositol ring, has essential functions in growth, development, and stress responses in plants, yeasts, and animals. However, the evolutionary history and patterns of 5PTases have not been examined systematically. Here, we report a comprehensive molecular evolutionary analysis of the 5PTase gene family and define four groups. These four groups are different from former classifications, which were based on in vitro substrate specificity. Most orthologous groups appear to be conserved as single or low-copy genes in all lineages in Groups II-IV, whereas 5PTase genes in Group I underwent several duplication events in angiosperm, resulting in multiple gene copies. Whole-genome duplication (WGD) was the main mechanism for 5PTase duplications in angiosperm. Plant 5PTases have more members than that of animals, and most plant 5PTase genes appear to have evolved under strong purifying selection. The paralogs have diverged in substrate specificity and expression pattern, showing evidence of selection pressure. Meanwhile, the increase in 5PTases and divergences in sequence, expression, and substrate might have contributed to the divergent functions of 5PTase genes, allowing the angiosperms to successfully adapt to a great number of ecological niches.

Genome-wide association study for backfat thickness at 100 kg and loin muscle thickness in domestic pigs based on genotyping by sequencing

Both backfat thickness at 100 kg (B100) and loin muscle thickness (LMT) are economically important traits in pigs. In this study, a total of 1,200 pigs (600 Landrace and 600 Yorkshire pigs) were examined with genotyping by sequencing. A total of 345,570 single nucleotide polymorphisms (SNPs) were obtained from 1,200 pigs. Then, a single marker regression test was used to conduct a genome-wide association study for B100 and LMT. A total of 8 and 90 significant SNPs were detected for LMT and B100, respectively. Interestingly, two shared significant loci [located at Sus scrofa chromosome (SSC) 6: 149876694 and SSC12: 46226580] were detected in two breeds for B100. Furthermore, three potential candidate genes were found for LMT and B100. The positional candidate gene FAM3C (SSC18: 25573656, P = 2.48 × 10^-9), which controls the survival, growth, and differentiation of tissues and cells, was found for LMT in Landrace pigs. At SSC9: 6.78-6.82 Mb in Landrace pigs, the positional candidate gene, INPPL1, which has a negative regulatory effect on diet-induced obesity and is involved in the regulation of insulin function, was found for B100. The candidate gene, RAB35, which regulates the adipocyte glucose transporter SLC2A4/GLUT4, was identified at approximately SSC14: 40.09-40.13 Mb in Yorkshire pigs. The results of this GWAS will greatly advance our understanding of the genetic architecture of the LMT and B100 traits. However, these identified loci and genes need to be further verified in more pig populations, and their functions also need to be validated by more biological experiments in pigs.

miRNAs, target genes expression and morphological analysis on the heart in gestational protein-restricted offspring

Gestational protein restriction was associated with low birth weight, hypertension and higher prevalence of cardiac disorders in adults. Several mechanisms, including epigenetics, could be related with the cardiovascular phenotype on protein-restricted offspring. Thus, we investigated the morphological cardiac effects of gestational protein restriction and left ventricle miRNAs and target genes expression pattern in both 12-day and 16-week old gestational protein-restricted male offspring. Pregnant Wistar rats were allocated into two groups, according to protein supply during pregnancy: NP (normal protein diet- 17%) or LP (low protein diet-6%). Dams on the gestational protein-restricted diet had lower body weight gain and higher food intake. Gestational protein-restricted offspring had low birth weight, followed by rapidly body weight recovery, hypertension, and increased myocytes cross-sectional area and collagen fraction at 16-week old age. At 12-days old, miR-184, miR-192, miR-376c, miR-380-3p, miR-380-5p, miR-451, and miR-582-3p had increased expression, and miR-547 and miR-743a had decreased expression in the gestational protein-restricted left ventricle. At 16-week old, let-7b, miR-125a-3p, miR-142-3p, miR-182 and miR-188-5p had increased expression and let-7g, miR-107, miR-127, miR-181a, miR-181c, miR-184, miR-324-5p, miR-383, miR-423-5p and miR-484 had decreased expression in gestational protein-restricted left ventricle. Target predicted gene expression analysis showed higher expression of Dnmt3a, Oxct1, Rictor and Trps1 and lower expression of Bbs1 and Calml3 in 12-day old protein-restricted offspring. 16-week old protein-restricted offspring had higher expression of Adrbk1, Bbs1, Dnmt3a, Gpr22, Inppl1, and Oxct1 genes. In conclusion, gestational protein restriction was related to offspring low birth weight, increased systolic blood pressure and morphological heart alterations that could be related to early heart miRNA expression changes that perpetuate into adulthood and which are associated with the regulation of essential genes involved in cardiovascular development, heart morphology, function, and metabolism.

Involvement of Hepatic SHIP2 and PI3K/Akt Signalling in the Regulation of Plasma Insulin by Xiaoyaosan in Chronic Immobilization-Stressed Rats

Background: Long-term exposure to chronic stress is thought to be a factor closely correlated with the development of metabolic disorders, such as diabetes mellitus and metabolic syndrome. Xiaoyaosan, a Chinese herbal formula, has been described in many previous studies to exert anxiolytic-like or antidepressant effects in chronically stressed rats. However, few studies have observed the effects of Xiaoyaosan on the metabolic disorders induced by chronic stress. Objective: We sought to investigate the effective regulation of Xiaoyaosan on 21-day chronic immobility stress (CIS, which is 3 h of restraint immobilization every day)-induced behavioural performance and metabolic responses and to further explore whether the effects of Xiaoyaosan were related to SHIP2 expression in the liver. Methods: Sixty male Sprague Dawley rats were randomly divided into a control group, a CIS group, a Xiaoyaosan group and a rosiglitazone group. The latter three groups were subjected to 21 days of CIS to generate the stress model. After 21 days of CIS, the effects of Xiaoyaosan on body weight, food intake, and behaviour in the open field test, the sucrose preference test and the forced swimming test were observed following chronic stress. Plasma insulin, cholesterol (CHOL), triglyceride (TG), low-density lipoprotein (LDL-C) and high-density lipoprotein (HDL-C) concentrations and blood glucose were examined, and the protein and mRNA expression levels of SHIP2, p85 and Akt in the liver were measured using RT-qPCR and immunohistochemical staining. Results: Rats exposed to CIS exhibited depression-like behaviours, decreased levels of plasma insulin, CHOL, LDL-C, TG and HDL-C, and increased blood glucose. Increased SHIP2 expression and reduced Akt, p-Akt and p85 expression were also observed in the liver. Xiaoyaosan exerted antidepressant effects and effectively reversed the changes caused by CIS. Conclusions: These results suggest that Xiaoyaosan attenuates depression-like behaviours and ameliorates stress-induced abnormal levels of insulin, blood glucose, CHOL, LDL-C and HDL-C in the plasma of stressed rats, which may be associated with the regulation of SHIP2 expression to enhance PI3K/Akt signalling activity in the liver.

The inositol phosphatase SHIP2 enables sustained ERK activation downstream of FGF receptors by recruiting Src kinases

Sustained activation of extracellular signal-regulated kinase (ERK) drives pathologies caused by mutations in fibroblast growth factor receptors (FGFRs). We previously identified the inositol phosphatase SHIP2 (also known as INPPL1) as an FGFR-interacting protein and a target of the tyrosine kinase activities of FGFR1, FGFR3, and FGFR4. We report that loss of SHIP2 converted FGF-mediated sustained ERK activation into a transient signal and rescued cell phenotypes triggered by pathologic FGFR-ERK signaling. Mutant forms of SHIP2 lacking phosphoinositide phosphatase activity still associated with FGFRs and did not prevent FGF-induced sustained ERK activation, demonstrating that the adaptor rather than the catalytic activity of SHIP2 was required. SHIP2 recruited Src family kinases to the FGFRs, which promoted FGFR-mediated phosphorylation and assembly of protein complexes that relayed signaling to ERK. SHIP2 interacted with FGFRs, was phosphorylated by active FGFRs, and promoted FGFR-ERK signaling at the level of phosphorylation of the adaptor FRS2 and recruitment of the tyrosine phosphatase PTPN11. Thus, SHIP2 is an essential component of canonical FGF-FGFR signal transduction and a potential therapeutic target in FGFR-related disorders.

Solution structure of SHIP2 SH2 domain and its interaction with a phosphotyrosine peptide from c-MET

SH2 domain-containing inositol 5-phosphatase 2 (SHIP2) binds with the Y1356-phosphorylated hepatocyte growth factor (HGF) receptor, c-MET, through its SH2 domain, which is essential for the role of SHIP2 in HGF-induced cell scattering and cell spreading. Previously, the experimental structure of the SH2 domain from SHIP2 (SHIP2-SH2) had not been reported, and its interaction with the Y1356-phosphorylated c-MET had not been investigated from a structural point of view. In this study, the solution structure of SHIP2-SH2 was determined by NMR spectroscopy, where it was found to adopt a typical SH2-domain fold that contains a positively-charged pocket for binding to phosphotyrosine (pY). The interaction between SHIP2-SH2 and a pY-containing peptide from c-MET (Y1356 phosphorylated) was investigated through NMR titrations. The results showed that the binding affinity of SHIP2-SH2 with the phosphopeptide is at low micromolar level, and the binding interface consists of the positively-charged pocket and its surrounding regions. Furthermore, R28, S49 and R70 were identified as key residues for the binding and may directly interact with the pY. Taken together, these findings provide structural insights into the binding of SHIP2-SH2 with the Y1356-phosphorylated c-MET, and lay a foundation for further studies of the interactions between SHIP2-SH2 and its various binding partners.

Molecular Pathways: Targeting the PI3K Pathway in Cancer-BET Inhibitors to the Rescue

The PI3K signaling pathway is a complex and tightly regulated network that is critical for many physiologic processes, such as cell growth, proliferation, metabolism, and survival. Aberrant activation of this pathway can occur through mutation of almost any of its major nodes and has been implicated in a number of human diseases, including cancer. The high frequency of mutations in this pathway in multiple types of cancer has led to the development of small-molecule inhibitors of PI3K, several of which are currently in clinical trials. However, several feedback mechanisms either within the PI3K pathway or in compensatory pathways can render tumor cells resistant to therapy. Recently, targeting proteins of the bromodomain and extraterminal (BET) family of epigenetic readers of histone acetylation has been shown to effectively block adaptive signaling response of cancer cells to inhibitors of the PI3K pathway, which at least in some cases can restore sensitivity. BET inhibitors also enforce blockade of the MAPK, JAK/STAT, and ER pathways, suggesting they may be a rational combinatorial partner for divergent oncogenic signals that are subject to homeostatic regulation. Here, we review the PI3K pathway as a target for cancer therapy and discuss the potential use of BET inhibition to enhance the clinical efficacy of PI3K inhibitors. Clin Cancer Res; 22(11); 2605-10. ©2016 AACR.

Biochemical and cellular properties of insulin receptor signalling

The mechanism of insulin action is a central theme in biology and medicine. In addition to the rather rare condition of insulin deficiency caused by autoimmune destruction of pancreatic β-cells, genetic and acquired abnormalities of insulin action underlie the far more common conditions of type 2 diabetes, obesity and insulin resistance. The latter predisposes to diseases ranging from hypertension to Alzheimer disease and cancer. Hence, understanding the biochemical and cellular properties of insulin receptor signalling is arguably a priority in biomedical research. In the past decade, major progress has led to the delineation of mechanisms of glucose transport, lipid synthesis, storage and mobilization. In addition to direct effects of insulin on signalling kinases and metabolic enzymes, the discovery of mechanisms of insulin-regulated gene transcription has led to a reassessment of the general principles of insulin action. These advances will accelerate the discovery of new treatment modalities for diabetes.

Endothelial SHIP2 Suppresses Nox2 NADPH Oxidase-Dependent Vascular Oxidative Stress, Endothelial Dysfunction, and Systemic Insulin Resistance

Shc homology 2-containing inositol 5' phosphatase-2 (SHIP2) is a lipid phosphatase that inhibits insulin signaling downstream of phosphatidylinositol 3-kinase (PI3K); its role in vascular function is poorly understood. To examine its role in endothelial cell (EC) biology, we generated mice with catalytic inactivation of one SHIP2 allele selectively in ECs (ECSHIP2^Δ/+). Hyperinsulinemic-euglycemic clamping studies revealed that ECSHIP2^Δ/+ was resistant to insulin-stimulated glucose uptake in adipose tissue and skeletal muscle compared with littermate controls. ECs from ECSHIP2^Δ/+ mice had increased basal expression and activation of PI3K downstream targets, including Akt and endothelial nitric oxide synthase, although incremental activation by insulin and shear stress was impaired. Insulin-mediated vasodilation was blunted in ECSHIP2^Δ/+ mice, as was aortic nitric oxide bioavailability. Acetylcholine-induced vasodilation was also impaired in ECSHIP2^Δ/+ mice, which was exaggerated in the presence of a superoxide dismutase/catalase mimetic. Superoxide abundance was elevated in ECSHIP2^Δ/+ ECs and was suppressed by PI3K and NADPH oxidase 2 inhibitors. These findings were phenocopied in healthy human ECs after SHIP2 silencing. Our data suggest that endothelial SHIP2 is required to maintain normal systemic glucose homeostasis and prevent oxidative stress-induced endothelial dysfunction.

Biofluid lipidome: a source for potential diagnostic biomarkers

Lipidomics is the identification and quantitation of changes in the lipidome of a cell, tissue, organ or biofluid in health and disease using high resolution mass spectrometry. Lipidome of a particular organism has relevance to the disease manifestation as it reflects the metabolic changes which can be a consequence of the disease. Hence these changes in the molecules can be considered as potential markers for screening and early detection of the disease. Biological fluids as blood/serum/plasma, urine, saliva, tear and cerebrospinal fluid, due to their accessibility, offer ease of collection with minimal or no discomfort to the patient and provide a ready footprint of the metabolic changes occurring during disease. This review provides a brief introduction to lipidomics and its role in understanding the metabolic changes in health and disease followed by discussion on the chemical diversity of the lipid species and their biological role, mammalian lipids and their metabolism and role of lipids in pathogens and the immune response before dwelling further into importance of studying lipidome in various biological fluids. The challenges in performing a lipidomic analysis at the experimental and data analysis stages are discussed.

PI(3,4)P2 plays critical roles in the regulation of focal adhesion dynamics of MDA-MB-231 breast cancer cells

Phosphoinositides play pivotal roles in the regulation of cancer cell phenotypes. Among them, phosphatidylinositol 3,4‐bisphosphate (PI(3,4)P₂) localizes to the invadopodia, and positively regulates tumor cell invasion. In this study, we examined the effect of PI(3,4)P₂ on focal adhesion dynamics in MDA‐MB‐231 basal breast cancer cells. Knockdown of SHIP2, a phosphatidylinositol 3,4,5‐trisphosphatase (PIP₃) 5‐phosphatase that generates PI(3,4)P₂, in MDA‐MB‐231 breast cancer cells, induced the development of focal adhesions and cell spreading, leading to the suppression of invasion. In contrast, knockdown of PTEN, a 3‐phosphatase that de‐phosphorylates PIP₃ and PI(3,4)P₂, induced cell shrinkage and increased cell invasion. Interestingly, additional knockdown of SHIP2 rescued these phenotypes. Overexpression of the TAPP1 PH domain, which binds to PI(3,4)P₂, and knockdown of Lpd, a downstream effector of PI(3,4)P₂, resulted in similar phenotypes to those induced by SHIP2 knockdown. Taken together, our results suggest that inhibition of PI(3,4)P₂ generation and/or downstream signaling could be useful for inhibiting breast cancer metastasis.

PI3K/SHIP2/PTEN pathway in cell polarity and hepatitis C virus pathogenesis

Hepatitis C virus (HCV) infects hepatocytes, polarized cells in the liver. Chronic HCV infection often leads to steatosis, fibrosis, cirrhosis and hepatocellular carcinoma, and it has been identified as the leading cause of liver transplantation worldwide. The HCV replication cycle is dependent on lipid metabolism and particularly an accumulation of lipid droplets in host cells. Phosphoinositides (PIs) are minor phospholipids enriched in different membranes and their levels are tightly regulated by specific PI kinases and phosphatases. PIs are implicated in a vast array of cellular responses that are central to morphogenesis, such as cytoskeletal changes, cytokinesis and the recruitment of downstream effectors to govern mechanisms involved in polarization and lumen formation. Important reviews of the literature identified phosphatidylinositol (PtdIns) 4-kinases, and their lipid products PtdIns(4)P, as critical regulators of the HCV life cycle. SH2-containing inositol polyphosphate 5-phosphatase (SHIP2), phosphoinositide 3-kinase (PI3K) and their lipid products PtdIns(3,4)P2 and PtdIns(3,4,5)P3, respectively, play an important role in the cell membrane and are key to the establishment of apicobasal polarity and lumen formation. In this review, we will focus on these new functions of PI3K and SHIP2, and their deregulation by HCV, causing a disruption of apicobasal polarity, actin organization and extracellular matrix assembly. Finally we will highlight the involvement of this pathway in the event of insulin resistance and nonalcoholic fatty liver disease related to HCV infection.

Emerging evidence of signalling roles for PI(3,4)P2 in Class I and II PI3K-regulated pathways

There are eight members of the phosphoinositide family of phospholipids in eukaryotes; PI, PI3P, PI4P, PI5P, PI(4,5)P2, PI(3,4)P2, PI(3,5)P2 and PI(3,4,5)P3. Receptor activation of Class I PI3Ks stimulates the phosphorylation of PI(4,5)P2 to form PI(3,4,5)P3. PI(3,4,5)P3 is an important messenger molecule that is part of a complex signalling network controlling cell growth and division. PI(3,4,5)P3 can be dephosphorylated by both 3- and 5-phosphatases, producing PI(4,5)P2 and PI(3,4)P2, respectively. There is now strong evidence that PI(3,4)P2 generated by this route does not merely represent another pathway for removal of PI(3,4,5)P3, but can act as a signalling molecule in its own right, regulating macropinocytosis, fast endophilin-mediated endocytosis (FEME), membrane ruffling, lamellipodia and invadopodia. PI(3,4)P2 can also be synthesized directly from PI4P by Class II PI3Ks and this is important for the maturation of clathrin-coated pits [clathrin-mediated endocytosis (CME)] and signalling in early endosomes. Thus PI(3,4)P2 is emerging as an important signalling molecule involved in the coordination of several specific membrane and cytoskeletal responses. Further, its inappropriate accumulation contributes to pathology caused by mutations in genes encoding enzymes responsible for its degradation, e.g. Inpp4B.

Molecular and cellular mechanisms linking inflammation to insulin resistance and β-cell dysfunction

Obesity is a major public health problem worldwide, and it is associated with an increased risk of developing type 2 diabetes. It is now commonly accepted that chronic inflammation associated with obesity induces insulin resistance and β-cell dysfunction in diabetic patients. Obesity-associated inflammation is characterized by increased abundance of macrophages and enhanced production of inflammatory cytokines in adipose tissue. Adipose tissue macrophages are suggested to be the major source of local and systemic inflammatory mediators such as tumor necrosis factor α, interleukin (IL)-1β, and IL-6. These cytokines induce insulin resistance in insulin target tissues by activating the suppressors of cytokine signaling proteins, several kinases such as c-Jun N-terminal kinase, IκB kinase β, and protein kinase C, inducible nitric oxide synthase, extracellular signal-regulated kinase, and protein tyrosine phosphatases such as protein tyrosine phosphatase 1B. These activated factors impair the insulin signaling at the insulin receptor and the insulin receptor substrates levels. The same process most likely occurs in the pancreas as it contains a pool of tissue-resident macrophages. High concentrations of glucose or palmitate via the chemokine production promote further immune cell migration and infiltration into the islets. These events ultimately induce inflammatory responses leading to the apoptosis of the pancreatic β cells. In this review, the cellular and molecular players that participate in the regulation of obesity-induced inflammation are discussed, with particular attention being placed on the roles of the molecular players linking inflammation to insulin resistance and β-cell dysfunction.

Insulin Signaling in the Control of Glucose and Lipid Homeostasis

A continuous supply of glucose is necessary to ensure proper function and survival of all organs. Plasma glucose levels are thus maintained in a narrow range around 5 mM, which is considered the physiological set point. Glucose homeostasis is controlled primarily by the liver, fat, and skeletal muscle. Following a meal, most glucose disposals occur in the skeletal muscle, whereas fasting plasma glucose levels are determined primarily by glucose output from the liver. The balance between the utilization and production of glucose is primarily maintained at equilibrium by two opposing hormones, insulin and glucagon. In response to an elevation in plasma glucose and amino acids (after consumption of a meal), insulin is released from the beta cells of the islets of Langerhans in the pancreas. When plasma glucose falls (during fasting or exercise), glucagon is secreted by α cells, which surround the beta cells in the pancreas. Both cell types are extremely sensitive to glucose concentrations, can regulate hormone synthesis, and are released in response to small changes in plasma glucose levels. At the same time, insulin serves as the major physiological anabolic agent, promoting the synthesis and storage of glucose, lipids, and proteins and inhibiting their degradation and release back into the circulation. This chapter will focus mainly on signal transduction mechanisms by which insulin exerts its plethora of effects in liver, muscle, and fat cells, focusing on those pathways that are crucial in the control of glucose and lipid homeostasis.

Antidiabetic properties of dietary flavonoids: a cellular mechanism review

Background

Natural food products have been used for combating human diseases for thousands of years. Naturally occurring flavonoids including flavones, flavonols, flavanones, flavonols, isoflavones and anthocyanidins have been proposed as effective supplements for management and prevention of diabetes and its long-term complications based on in vitro and animal models.

Aim

To summarize the roles of dietary flavonoids in diabetes management and their molecular mechanisms.

Findings

Tremendous studies have found that flavonoids originated from foods could improve glucose metabolism, lipid profile, regulating the hormones and enzymes in human body, further protecting human being from diseases like obesity, diabetes and their complications.

Conclusion

In the current review, we summarize recent progress in understanding the biological action, mechanism and therapeutic potential of the dietary flavonoids and its subsequent clinical outcomes in the field of drug discovery in management of diabetes mellitus.

Perturbation of the Vacuolar ATPase: A NOVEL CONSEQUENCE OF INOSITOL DEPLETION

Depletion of inositol has profound effects on cell function and has been implicated in the therapeutic effects of drugs used to treat epilepsy and bipolar disorder. We have previously shown that the anticonvulsant drug valproate (VPA) depletes inositol by inhibiting myo-inositol-3-phosphate synthase, the enzyme that catalyzes the first and rate-limiting step of inositol biosynthesis. To elucidate the cellular consequences of inositol depletion, we screened the yeast deletion collection for VPA-sensitive mutants and identified mutants in vacuolar sorting and the vacuolar ATPase (V-ATPase). Inositol depletion caused by starvation of ino1Δ cells perturbed the vacuolar structure and decreased V-ATPase activity and proton pumping in isolated vacuolar vesicles. VPA compromised the dynamics of phosphatidylinositol 3,5-bisphosphate (PI3,5P2) and greatly reduced V-ATPase proton transport in inositol-deprived wild-type cells. Osmotic stress, known to increase PI3,5P2 levels, did not restore PI3,5P2 homeostasis nor did it induce vacuolar fragmentation in VPA-treated cells, suggesting that perturbation of the V-ATPase is a consequence of altered PI3,5P2 homeostasis under inositol-limiting conditions. This study is the first to demonstrate that inositol depletion caused by starvation of an inositol synthesis mutant or by the inositol-depleting drug VPA leads to perturbation of the V-ATPase.

Novel therapeutics for type 2 diabetes: insulin resistance

Insulin resistance (IR) plays an important role in the pathogenesis of type 2 diabetes (T2D) and cardiovascular disease. Hence improving IR is a major target of treatment in patients with T2D. Obesity and lack of exercise are major causes of IR. However, recent evidence implicates sleep disorders and disorders of the circadian rhythm in the pathogenesis of IR. Weight loss and lifestyle changes are the cornerstone and most effective treatments of IR, but adherence and patient's acceptability are poor. Bariatric surgery results in significant and sustainable long-term weight loss associated with beneficial impact on IR and glucose metabolism, making this an attractive treatment option for patients with T2D. Currently available pharmacological options targeting IR (such as metformin and thiazolidinediones) do not maintain glycaemic measures within targets long term and can be associated with significant side effects. Over the last two decades, many pharmacological agents targeting different aspects of the insulin signalling pathway were developed to improve IR, but only a minority reached clinical trials. Such treatments need to be specific and reversible as many of the components of the insulin signalling pathway are involved in other cellular functions such as apoptosis. Recent evidence highlighted the role of circadian rhythm and sleep-related disorders in the pathogenesis of IR. In this article, we review the latest developments in the pharmacological and non-pharmacological interventions targeting IR including bariatric surgery. We will also review the role of circadian rhythm and sleep-related disorders in the development and treatment of IR.

Mendelian disorders of PI metabolizing enzymes

More than twenty different genetic diseases have been described that are caused by mutations in phosphoinositide metabolizing enzymes, mostly in phosphoinositide phosphatases. Although generally ubiquitously expressed, mutations in these enzymes, which are mainly loss-of-function, result in tissue-restricted clinical manifestations through mechanisms that are not completely understood. Here we analyze selected disorders of phosphoinositide metabolism grouped according to the principle tissue affected: the nervous system, muscle, kidney, the osteoskeletal system, the eye, and the immune system. We will highlight what has been learnt so far from the study of these disorders about not only the cellular and molecular pathways that are involved or are governed by phosphoinositides, but also the many gaps that remain to be filled to gain a full understanding of the pathophysiological mechanisms underlying the clinical manifestations of this steadily growing class of diseases, most of which still remain orphan in terms of treatment. This article is part of a Special Issue entitled Phosphoinositides.