Structural basis for inhibition of the insulin receptor by the adaptor protein Grb14

Lipedema: Progress, Challenges, and the Road Ahead

INTRODUCTION

Lipedema is a chronic and progressive disease that predominantly affects women, characterized by a disproportionate increase in subcutaneous adipose tissue (AT), particularly in the lower limbs. It is associated with significant physical disability, chronic pain, thromboembolism, and psychosocial distress. Despite its profound impact on women's health and quality of life, lipedema remains underrecognized and insufficiently studied, with an estimated prevalence of approximately 10% among women worldwide. Although the exact etiology of lipedema remains unclear, emerging evidence suggests a multifactorial origin involving genetic predisposition, hormonal influences, and vascular dysfunction-all contributing to its development and progression. Current therapeutic options provide only partial symptom relief and remain noncurative, highlighting the urgent need for expanded research and improved management strategies.

METHODS

A systematic review was conducted to assess the current understanding of lipedema pathophysiology and current treatment options. Research articles were sourced from PubMed, Web of Science, ScienceDirect, and Scopus databases. Over 100 studies were incorporated.

RESULTS

This review provides a comprehensive overview of lipedema, encompassing its clinical features, pathophysiological mechanisms, diagnostic challenges, and current treatment modalities. Additionally, the review discusses whether the molecular and metabolic differences between abdominal and femoral AT depots mirror those observed in classical obesity.

CONCLUSIONS

Multidisciplinary, research-informed care is essential for managing lipedema, combining conservative therapies, tailored exercise, and liposuction for advanced cases. More research to better understand the underlying pathophysiology is critical to developing targeted treatments, improving diagnostic accuracy, and informing standardized, evidence-based care.

Grb7, Grb10 and Grb14, encoding the growth factor receptor-bound 7 family of signalling adaptor proteins have overlapping functions in the regulation of fetal growth and post-natal glucose metabolism

BACKGROUND

The growth factor receptor bound protein 7 (Grb7) family of signalling adaptor proteins comprises Grb7, Grb10 and Grb14. Each can interact with the insulin receptor and other receptor tyrosine kinases, where Grb10 and Grb14 inhibit insulin receptor activity. In cell culture studies they mediate functions including cell survival, proliferation, and migration. Mouse knockout (KO) studies have revealed physiological roles for Grb10 and Grb14 in glucose-regulated energy homeostasis. Both Grb10 KO and Grb14 KO mice exhibit increased insulin signalling in peripheral tissues, with increased glucose and insulin sensitivity and a modestly increased ability to clear a glucose load. In addition, Grb10 strongly inhibits fetal growth such that at birth Grb10 KO mice are 30% larger by weight than wild type littermates.

RESULTS

Here, we generate a Grb7 KO mouse model. We show that during fetal development the expression patterns of Grb7 and Grb14 each overlap with that of Grb10. Despite this, Grb7 and Grb14 did not have a major role in influencing fetal growth, either alone or in combination with Grb10. At birth, in most respects both Grb7 KO and Grb14 KO single mutants were indistinguishable from wild type, while Grb7:Grb10 double knockout (DKO) were near identical to Grb10 KO single mutants and Grb10:Grb14 DKO mutants were slightly smaller than Grb10 KO single mutants. In the developing kidney Grb7 had a subtle positive influence on growth. An initial characterisation of Grb7 KO adult mice revealed sexually dimorphic effects on energy homeostasis, with females having a significantly smaller renal white adipose tissue depot and an enhanced ability to clear glucose from the circulation, compared to wild type littermates. Males had elevated fasted glucose levels with a trend towards smaller white adipose depots, without improved glucose clearance.

CONCLUSIONS

Grb7 and Grb14 do not have significant roles as inhibitors of fetal growth, unlike Grb10, and instead Grb7 may promote growth of the developing kidney. In adulthood, Grb7 contributes subtly to glucose mediated energy homeostasis, raising the possibility of redundancy between all three adaptors in physiological regulation of insulin signalling and glucose handling.

Common and ethnic-specific derangements in skeletal muscle transcriptome associated with obesity

BACKGROUND

Obesity is a common disease with a higher prevalence among African Americans. Obesity alters cellular function in many tissues, including skeletal muscle, and is a risk factor for many life-threatening diseases, including cardiovascular disease and diabetes. The similarities and differences in molecular mechanisms that may explain ethnic disparities in obesity between African and European ancestry individuals have not been studied.

METHODS

In this study, data from transcriptome-wide analyses on skeletal muscle tissues from well-powered human cohorts were used to compare genes and biological pathways affected by obesity in European and African ancestry populations. Data on obesity-induced differentially expressed transcripts and GWAS-identified SNPs were integrated to prioritize target genes for obesity-associated genetic variants.

RESULTS

Linear regression analysis in the FUSION (European, N = 301) and AAGMEx (African American, N = 256) cohorts identified a total of 2569 body mass index (BMI)-associated transcripts (q < 0.05), of which 970 genes (at p < 0.05) are associated in both cohorts, and the majority showed the same direction of effect on BMI. Biological pathway analyses, including over-representation and gene-set enrichment analyses, identified enrichment of protein synthesis pathways (e.g., ribosomal function) and the ceramide signaling pathway in both cohorts among BMI-associated down- and up-regulated transcripts, respectively. A comparison using the IPA-tool suggested the activation of inflammation pathways only in Europeans with obesity. Interestingly, these analyses suggested repression of the mitochondrial oxidative phosphorylation pathway in Europeans but showed its activation in African Americans. Integration of SNP-to-Gene analyses-predicted target genes for obesity-associated genetic variants (GWAS-identified SNPs) and BMI-associated transcripts suggested that these SNPs might cause obesity by altering the expression of 316 critical target genes (e.g., GRB14) in the muscle.

CONCLUSIONS

This study provides a replication of obesity-associated transcripts and biological pathways in skeletal muscle across ethnicities, but also identifies obesity-associated processes unique in either African or European ancestry populations.

Computational Screening and Experimental Validation of Inhibitor Targeting the Complex Formation of Grb14 and Insulin Receptor

The development of drugs targeting gene products associated with insulin resistance holds the potential to enhance our understanding of type 2 diabetes mellitus (T2DM). The virtual screening, based on a three-dimensional (3D) protein structure, is a potential technique to accelerate the development of molecular target drugs. Among the targets implicated in insulin resistance, the genetic characterization and protein function of Grb14 have been clarified without contradiction. The Grb14 gene displays significant variations in T2DM, and its gene product is known to inhibit the function of the insulin receptor (IR) by directly binding to the tyrosine kinase domain. In the present study, a virtual screening, based on a 3D structure of the IR tyrosine kinase domain (IRβ) in complex with part of Grb14, was conducted to find compounds that can disrupt the complex formation between Grb14 and IRβ. First, ten compounds were selected from 154,118 compounds via hierarchical in silico structure-based drug screening, composed of grid docking-based and genetic algorithm-based programs. The experimental validations suggested that the one compound can affect the blood glucose level. The molecular dynamics simulations and co-immunoprecipitation analysis showed that the compound did not completely suppress the protein-protein interaction between Grb14 and IR, though competitively bound to IR with the tyrosine kinase pseudosubstrate region in Grb14.

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.

A non-coding variant linked to metabolic obesity with normal weight affects actin remodelling in subcutaneous adipocytes

Recent large-scale genomic association studies found evidence for a genetic link between increased risk of type 2 diabetes and decreased risk for adiposity-related traits, reminiscent of metabolically obese normal weight (MONW) association signatures. However, the target genes and cellular mechanisms driving such MONW associations remain to be identified. Here, we systematically identify the cellular programmes of one of the top-scoring MONW risk loci, the 2q24.3 risk locus, in subcutaneous adipocytes. We identify a causal genetic variant, rs6712203, an intronic single-nucleotide polymorphism in the COBLL1 gene, which changes the conserved transcription factor motif of POU domain, class 2, transcription factor 2, and leads to differential COBLL1 gene expression by altering the enhancer activity at the locus in subcutaneous adipocytes. We then establish the cellular programme under the genetic control of the 2q24.3 MONW risk locus and the effector gene COBLL1, which is characterized by impaired actin cytoskeleton remodelling in differentiating subcutaneous adipocytes and subsequent failure of these cells to accumulate lipids and develop into metabolically active and insulin-sensitive adipocytes. Finally, we show that perturbations of the effector gene Cobll1 in a mouse model result in organismal phenotypes matching the MONW association signature, including decreased subcutaneous body fat mass and body weight along with impaired glucose tolerance. Taken together, our results provide a mechanistic link between the genetic risk for insulin resistance and low adiposity, providing a potential therapeutic hypothesis and a framework for future identification of causal relationships between genome associations and cellular programmes in other disorders.

Metabolic Effects of the Waist-To-Hip Ratio Associated Locus GRB14/COBLL1 Are Related to GRB14 Expression in Adipose Tissue

GRB14/COBLL1 locus has been shown to be associated with body fat distribution (FD), but neither the causal gene nor its role in metabolic diseases has been elucidated. We hypothesize that GRB14/COBLL1 may act as the causal genes for FD-related SNPs (rs10195252 and rs6738627), and that they may be regulated by SNP to effect obesity-related metabolic traits. We genotyped rs10195252 and rs6738627 in 2860 subjects with metabolic phenotypes. In a subgroup of 560 subjects, we analyzed GRB14/COBLL1 gene expression in paired visceral and subcutaneous adipose tissue (AT) samples. Mediation analyses were used to determine the causal relationship between SNPs, AT GRB14/COBLL1 mRNA expression, and obesity-related traits. In vitro gene knockdown of Grb14/Cobll1 was used to test their role in adipogenesis. Both gene expressions in AT are correlated with waist circumference. Visceral GRB14 mRNA expression is associated with FPG and HbA1c. Both SNPs are associated with triglycerides, FPG, and leptin levels. Rs10195252 is associated with HbA1c and seems to be mediated by visceral AT GRB14 mRNA expression. Our data support the role of the GRB14/COBLL1 gene expression in body FD and its locus in metabolic sequelae: in particular, lipid metabolism and glucose homeostasis, which is likely mediated by AT GRB14 transcript levels.

Receptor tyrosine kinases regulate signal transduction through a liquid-liquid phase separated state

The recruitment of signaling proteins into activated receptor tyrosine kinases (RTKs) to produce rapid, high-fidelity downstream response is exposed to the ambiguity of random diffusion to the target site. Liquid-liquid phase separation (LLPS) overcomes this by providing elevated, localized concentrations of the required proteins while impeding competitor ligands. Here, we show a subset of phosphorylation-dependent RTK-mediated LLPS states. We then investigate the formation of phase-separated droplets comprising a ternary complex including the RTK, (FGFR2); the phosphatase, SHP2; and the phospholipase, PLCγ1, which assembles in response to receptor phosphorylation. SHP2 and activated PLCγ1 interact through their tandem SH2 domains via a previously undescribed interface. The complex of FGFR2 and SHP2 combines kinase and phosphatase activities to control the phosphorylation state of the assembly while providing a scaffold for active PLCγ1 to facilitate access to its plasma membrane substrate. Thus, LLPS modulates RTK signaling, with potential consequences for therapeutic intervention.

Structure-based survey of ligand binding in the human insulin receptor

The insulin receptor is a membrane protein responsible for regulation of nutrient balance and therefore an attractive target in the treatment of diabetes and metabolic syndrome. Pharmacology of the insulin receptor involves two distinct mechanisms, (1) activation of the receptor by insulin mimetics that bind in the extracellular domain and (2) inhibition of the receptor tyrosine kinase enzymatic activity in the cytoplasmic domain. While a complete structural picture of the full-length receptor comprising the entire sequence covering extracellular, transmembrane, juxtamembrane and cytoplasmic domains is still elusive, recent progress through cryoelectron microscopy has made it possible to describe the initial insulin ligand binding events at atomistic detail. We utilize this opportunity to obtain structural insights into the pharmacology of the insulin receptor. To this end, we conducted a comprehensive docking study of known ligands to the new structures of the receptor. Through this approach, we provide an in-depth, structure-based review of human insulin receptor pharmacology in light of the new structures.

Regulation of Phosphoinositide Levels in the Retina by Protein Tyrosine Phosphatase 1B and Growth Factor Receptor-Bound Protein 14

Protein tyrosine kinases and protein phosphatases play a critical role in cellular regulation. The length of a cellular response depends on the interplay between activating protein kinases and deactivating protein phosphatases. Protein tyrosine phosphatase 1B (PTP1B) and growth factor receptor-bound protein 14 (Grb14) are negative regulators of receptor tyrosine kinases. However, in the retina, we have previously shown that PTP1B inactivates insulin receptor signaling, whereas phosphorylated Grb14 inhibits PTP1B activity. In silico docking of phosphorylated Grb14 and PTP1B indicate critical residues in PTP1B that may mediate the interaction. Phosphoinositides (PIPs) are acidic lipids and minor constituents in the cell that play an important role in cellular processes. Their levels are regulated by growth factor signaling. Using phosphoinositide binding protein probes, we observed increased levels of PI(3)P, PI(4)P, PI(3,4)P₂, PI(4,5)P2, and PI(3,4,5)P₃ in PTP1B knockout mouse retina and decreased levels of these PIPs in Grb14 knockout mouse retina. These observations suggest that the interplay between PTP1B and Grb14 can regulate PIP metabolism.

S-Allylmercaptocysteine improves alcoholic liver disease partly through a direct modulation of insulin receptor signaling

Alcoholic liver disease (ALD) causes insulin resistance, lipid metabolism dysfunction, and inflammation. We investigated the protective effects and direct regulating target of S-allylmercaptocysteine (SAMC) from aged garlic on liver cell injury. A chronic ethanol-fed ALD in vivo model (the NIAAA model) was used to test the protective functions of SAMC. It was observed that SAMC (300 mg/kg, by gavage method) effectively ameliorated ALD-induced body weight reduction, steatosis, insulin resistance, and inflammation without affecting the health status of the control mice, as demonstrated by histological, biochemical, and molecular biology assays. By using biophysical assays and molecular docking, we demonstrated that SAMC directly targeted insulin receptor (INSR) protein on the cell membrane and then restored downstream IRS-1/AKT/GSK3β signaling. Liver-specific knock-down in mice and siRNA-mediated knock-down in AML-12 cells of Insr significantly impaired SAMC (250 μmol/L in cells)-mediated protection. Restoration of the IRS-1/AKT signaling partly recovered hepatic injury and further contributed to SAMC's beneficial effects. Continuous administration of AKT agonist and recombinant IGF-1 in combination with SAMC showed hepato-protection in the mice model. Long-term (90-day) administration of SAMC had no obvious adverse effect on healthy mice. We conclude that SAMC is an effective and safe hepato-protective complimentary agent against ALD partly through the direct binding of INSR and partial regulation of the IRS-1/AKT/GSK3β pathway.

Sustained Stimulation of β2AR Inhibits Insulin Signaling in H9C2 Cardiomyoblast Cells Through the PKA-Dependent Signaling Pathway

INTRODUCTION

This study aimed to investigate the role of β2 adrenergic receptor (β2AR) in insulin signaling transduction in H9C2 cardiomyoblast cells to understand the formation of the β2AR-insulin receptor (IR) protein complex and its role in insulin-induced Glut4 expression.

METHODS

H9C2 cells were treated with various protein inhibitors (CGP, β1AR inhibitor CGP20712; ICI, β2AR inhibitor ICI 118,551; PKI, PKA inhibitor myristoylated PKI; PD 0325901, MEK inhibitor; SP600125, JNK inhibitor) with or without insulin or isoproterenol (ISO) before RNA-sequencing (RNA-Seq) and quantitative-PCR (Q-PCR). Yeast two-hybrid, co-immunoprecipitation and His-tag pull-down assay were carried out to investigate the formation of the β2AR-IR protein complex. The intracellular concentrations of cAMP in H9C2 cells were tested by high performance liquid chromatography (HPLC) and the phosphorylation of JNK was tested by Western blot.

RESULTS

Gene Ontology (GO) analysis revealed that the most significantly enriched processes in the domain of molecular function (MF) were catalytic activity and binding, whereas in the domain of biological processes (BP) were metabolic process and cellular process. Furthermore, the enriched processes in the domain of cellular components (CC) were cell and cell parts. The Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis showed that the most significant pathways that have been altered included the PI3K-Akt and MAPK signaling pathways. Q-PCR, which was performed to verify the gene expression levels exhibited consistent results. In evaluating the signaling pathways, the sustained stimulation of β2AR by ISO inhibited insulin signalling, and the effect was primarily through the cAMP-PKA-JNK pathway and MEK/JNK signaling pathway. Yeast two-hybrid, co-immunoprecipitation and His-tag pull-down assay revealed that β2AR, IR, insulin receptor substrate 1 (IRS1), Grb2-associated binding protein 1 (GAB1) and Grb2 existed in the same protein complex.

CONCLUSION

The sustained stimulation of β2AR might inhibit insulin signaling transduction through the cAMP-PKA-JNK and MEK/JNK pathways in H9C2 cells.

Inhibition of Grb14, a negative modulator of insulin signaling, improves glucose homeostasis without causing cardiac dysfunction

Insulin resistance increases patients' risk of developing type 2 diabetes (T2D), non-alcoholic steatohepatitis (NASH) and a host of other comorbidities including cardiovascular disease and cancer. At the molecular level, insulin exerts its function through the insulin receptor (IR), a transmembrane receptor tyrosine kinase. Data from human genetic studies have shown that Grb14 functions as a negative modulator of IR activity, and the germline Grb14-knockout (KO) mice have improved insulin signaling in liver and skeletal muscle. Here, we show that Grb14 knockdown in liver, white adipose tissues, and heart with an AAV-shRNA (Grb14-shRNA) improves glucose homeostasis in diet-induced obese (DIO) mice. A previous report has shown that germline deletion of Grb14 in mice results in cardiac hypertrophy and impaired systolic function, which could severely limit the therapeutic potential of targeting Grb14. In this report, we demonstrate that there are no significant changes in cardiac function as measured by echocardiography in the Grb14-knockdown mice fed a high-fat diet for a period of four months. While additional studies are needed to further confirm the efficacy and to de-risk potential negative cardiac effects in preclinical models, our data support the therapeutic strategy of inhibiting Grb14 to treat diabetes and related conditions.

Dephosphorylation of clustered phosphoserine residues in human Grb14 by protein phosphatase 1 and its effect on insulin receptor complex formation

The physical interaction of the human growth factor receptor-bound protein 14 (hGrb14) and the insulin receptor (IR) represses insulin signaling. With respect to the recruiting mechanism of hGrb14 to IR respond to insulin stimulus, our previous reports have suggested that phosphorylation of Ser³⁵⁸ , Ser³⁶² , and Ser³⁶⁶ in hGrb14 by glycogen synthase kinase-3 repressed hGrb14-IR complex formation. In this study, we investigated phosphatase-mediated dephosphorylation of the hGrb14 phosphoserine residues. An in vitro phosphatase assay with hGrb14-derived synthetic phosphopeptides suggested that protein phosphatase 1 (PP1) is involved in the dephosphorylation of Ser³⁵⁸ and Ser³⁶² . Furthermore, coimmunoprecipitation experiments suggested that insulin-induced hGrb14-IR complex formation was repressed by the substitution of Ser³⁵⁸ or Ser³⁶² with glutamic acid. These findings suggested that phosphate groups on Ser³⁵⁸ and Ser³⁶² in hGrb14 are dephosphorylated by PP1, and the dephosphorylation facilitates hGrb14-IR complex formation.

Grb7, a Critical Mediator of EGFR/ErbB Signaling, in Cancer Development and as a Potential Therapeutic Target

The partner of activated epidermal growth factor receptor (EGFR), growth factor receptor bound protein-7 (Grb7), a functionally multidomain adaptor protein, has been demonstrated to be a pivotal regulator for varied physiological and pathological processes by interacting with phospho-tyrosine-related signaling molecules to affect the transmission through a number of signaling pathways. In particular, critical roles of Grb7 in erythroblastic leukemia viral oncogene homolog (ERBB) family-mediated cancer development and malignancy have been intensively evaluated. The overexpression of Grb7 or the coamplification/cooverexpression of Grb7 and members of the ERBB family play essential roles in advanced human cancers and are associated with decreased survival and recurrence of cancers, emphasizing Grb7's value as a prognostic marker and a therapeutic target. Peptide inhibitors of Grb7 are being tested in preclinical trials for their possible therapeutic effects. Here, we review the molecular, functional, and clinical aspects of Grb7 in ERBB family-mediated cancer development and malignancy with the aim to reveal alternative and effective therapeutic strategies.

A Perspective to the Correlation Between Brain Insulin Resistance and Alzheimer: Medicinal Chemistry Approach

Substantial terms have been recognized on the associated risk elements, comorbidities as well as, putative pathophysiological processes of Alzheimer disease and related dementias (ADRDs) as well as, type 2 diabetes mellitus (T2DM), a few from greatest important disease from the moments. Very much is considered regarding the biology and chemistry of each predicament, nevertheless T2DM and ADRDs are an actually similar pattern developing from the similar origins of maturing or synergistic conditions connected by aggressive patho-corporeal terms and continues to be ambiguous. In this depth-critique article, we aimed to investigate all possibilities and represented a novel and applicable approach from the Medicinal Chemistry concepts.

The molecular basis of JAK/STAT inhibition by SOCS1

The SOCS family of proteins are negative-feedback inhibitors of signalling induced by cytokines that act via the JAK/STAT pathway. SOCS proteins can act as ubiquitin ligases by recruiting Cullin5 to ubiquitinate signalling components; however, SOCS1, the most potent member of the family, can also inhibit JAK directly. Here we determine the structural basis of both these modes of inhibition. Due to alterations within the SOCS box domain, SOCS1 has a compromised ability to recruit Cullin5; however, it is a direct, potent and selective inhibitor of JAK catalytic activity. The kinase inhibitory region of SOCS1 targets the substrate binding groove of JAK with high specificity and thereby blocks any subsequent phosphorylation. SOCS1 is a potent inhibitor of the interferon gamma (IFNγ) pathway, however, it does not bind the IFNγ receptor, making its mode-of-action distinct from SOCS3. These findings reveal the mechanism used by SOCS1 to inhibit signalling by inflammatory cytokines.

The molecular basis of JAK/STAT inhibition by SOCS1

The SOCS family of proteins are negative-feedback inhibitors of signalling induced by cytokines that act via the JAK/STAT pathway. SOCS proteins can act as ubiquitin ligases by recruiting Cullin5 to ubiquitinate signalling components; however, SOCS1, the most potent member of the family, can also inhibit JAK directly. Here we determine the structural basis of both these modes of inhibition. Due to alterations within the SOCS box domain, SOCS1 has a compromised ability to recruit Cullin5; however, it is a direct, potent and selective inhibitor of JAK catalytic activity. The kinase inhibitory region of SOCS1 targets the substrate binding groove of JAK with high specificity and thereby blocks any subsequent phosphorylation. SOCS1 is a potent inhibitor of the interferon gamma (IFNγ) pathway, however, it does not bind the IFNγ receptor, making its mode-of-action distinct from SOCS3. These findings reveal the mechanism used by SOCS1 to inhibit signalling by inflammatory cytokines.

Cytokines are key molecules in controlling haematopoiesis that signal via the JAK/STAT pathway. Here the authors present the structures of SOCS1 bound to its JAK1 target as well as in complex with elonginB and elonginC, providing a molecular explanation for the potent JAK- inhibitory activity of SOCS1.

Ablation of Grb10 Specifically in Muscle Impacts Muscle Size and Glucose Metabolism in Mice

Grb10 is an adaptor-type signaling protein most highly expressed in tissues involved in insulin action and glucose metabolism, such as muscle, pancreas, and adipose. Germline deletion of Grb10 in mice creates a phenotype with larger muscles and improved glucose homeostasis. However, it has not been determined whether Grb10 ablation specifically in muscle is sufficient to induce hypermuscularity or affect whole body glucose metabolism. In this study we generated muscle-specific Grb10-deficient mice (Grb10-mKO) by crossing Grb10flox/flox mice with mice expressing Cre recombinase under control of the human α-skeletal actin promoter. One-year-old Grb10-mKO mice had enlarged muscles, with greater cross-sectional area of fibers compared with wild-type (WT) mice. This degree of hypermuscularity did not affect whole body glucose homeostasis under basal conditions. However, hyperinsulinemic/euglycemic clamp studies revealed that Grb10-mKO mice had greater glucose uptake into muscles compared with WT mice. Insulin signaling was increased at the level of phospho-Akt in muscle of Grb10-mKO mice compared with WT mice, consistent with a role of Grb10 as a modulator of proximal insulin receptor signaling. We conclude that ablation of Grb10 in muscle is sufficient to affect muscle size and metabolism, supporting an important role for this protein in growth and metabolic pathways.

A systematic analysis highlights multiple long non-coding RNAs associated with cardiometabolic disorders

Genome-wide association studies (GWAS) have identified many susceptibility loci for cardiometabolic disorders. Most of the associated variants reside in non-coding regions of the genome including long non-coding RNAs (lncRNAs), which are thought to play critical roles in diverse biological processes. Here, we leveraged data from the available GWAS meta-analyses on lipid and obesity-related traits, blood pressure, type 2 diabetes, and coronary artery disease and identified 179 associated single-nucleotide polymorphisms (SNPs) in 102 lncRNAs (p-value < 2.3 × 10^-7). Of these, 55 SNPs, either the lead SNP or in strong linkage disequilibrium with the lead SNP in the related loci, were selected for further investigations. Our in silico predictions and functional annotations of the SNPs as well as expression and DNA methylation analysis of their lncRNAs demonstrated several lncRNAs that fulfilled predefined criteria for being potential functional targets. In particular, we found evidence suggesting that LOC157273 (at 8p23.1) is involved in regulating serum lipid-cholesterol. Our results showed that rs4841132 in the second exon and cg17371580 in the promoter region of LOC157273 are associated with lipids; the lncRNA is expressed in liver and associates with the expression of its nearby coding gene, PPP1R3B. Collectively, we highlight a number of loci associated with cardiometabolic disorders for which the association may act through lncRNAs.

Activation of oncogenic tyrosine kinase signaling promotes insulin receptor-mediated cone photoreceptor survival

In humans, daylight vision is primarily mediated by cone photoreceptors. These cells die in age-related retinal degenerations. Prolonging the life of cones for even one decade would have an enormous beneficial effect on usable vision in an aging population. Photoreceptors are postmitotic, but shed 10% of their outer segments daily, and must synthesize the membrane and protein equivalent of a proliferating cell each day. Although activation of oncogenic tyrosine kinase and inhibition of tyrosine phosphatase signaling is known to be essential for tumor progression, the cellular regulation of this signaling in postmitotic photoreceptor cells has not been studied. In the present study, we report that a novel G-protein coupled receptor–mediated insulin receptor (IR) signaling pathway is regulated by non-receptor tyrosine kinase Src through the inhibition of protein tyrosine phosphatase IB (PTP1B). We demonstrated the functional significance of this pathway through conditional deletion of IR and PTP1B in cones, in addition to delaying the death of cones in a mouse model of cone degeneration by activating the Src. This is the first study demonstrating the molecular mechanism of a novel signaling pathway in photoreceptor cells, which provides a window of opportunity to save the dying cones in retinal degenerative diseases.

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.

Calmodulin as a protein linker and a regulator of adaptor/scaffold proteins

Calmodulin (CaM) is a universal regulator for a huge number of proteins in all eukaryotic cells. Best known is its function as a calcium-dependent modulator of the activity of enzymes, such as protein kinases and phosphatases, as well as other signaling proteins including membrane receptors, channels and structural proteins. However, less well known is the fact that CaM can also function as a Ca²⁺-dependent adaptor protein, either by bridging between different domains of the same protein or by linking two identical or different target proteins together. These activities are possible due to the fact that CaM contains two independently-folded Ca²⁺ binding lobes that are able to interact differentially and to some degree separately with targets proteins. In addition, CaM can interact with and regulates several proteins that function exclusively as adaptors. This review provides an overview over our present knowledge concerning the structural and functional aspects of the role of CaM as an adaptor protein and as a regulator of known adaptor/scaffold proteins.

The role of small adaptor proteins in the control of oncogenic signalingr driven by tyrosine kinases in human cancer

Protein phosphorylation on tyrosine (Tyr) residues has evolved as an important mechanism to coordinate cell communication in multicellular organisms. The importance of this process has been revealed by the discovery of the prominent oncogenic properties of tyrosine kinases (TK) upon deregulation of their physiological activities, often due to protein overexpression and/or somatic mutation. Recent reports suggest that TK oncogenic signaling is also under the control of small adaptor proteins. These cytosolic proteins lack intrinsic catalytic activity and signal by linking two functional members of a catalytic pathway. While most adaptors display positive regulatory functions, a small group of this family exerts negative regulatory functions by targeting several components of the TK signaling cascade. Here, we review how these less studied adaptor proteins negatively control TK activities and how their loss of function induces abnormal TK signaling, promoting tumor formation. We also discuss the therapeutic consequences of this novel regulatory mechanism in human oncology.

Identification of insulin-sensitizing molecules acting by disrupting the interaction between the Insulin Receptor and Grb14

Metabolic diseases are characterized by a decreased action of insulin. During the course of the disease, usual treatments frequently fail and patients are finally submitted to insulinotherapy. There is thus a need for innovative therapeutic strategies to improve insulin action. Growth factor receptor-bound protein 14 (Grb14) is a molecular adapter that specifically binds to the activated insulin receptor (IR) and inhibits its tyrosine kinase activity. Molecules disrupting Grb14-IR binding are therefore potential insulin-sensitizing agents. We used Structure-Based Virtual Ligand Screening to generate a list of 1000 molecules predicted to hinder Grb14-IR binding. Using an acellular bioluminescence resonance energy transfer (BRET) assay, we identified, out of these 1000 molecules, 3 compounds that inhibited Grb14-IR interaction. Their inhibitory effect on insulin-induced Grb14-IR interaction was confirmed in co-immunoprecipitation experiments. The more efficient molecule (C8) was further characterized. C8 increased downstream Ras-Raf and PI3-kinase insulin signaling, as shown by BRET experiments in living cells. Moreover, C8 regulated the expression of insulin target genes in mouse primary hepatocytes. These results indicate that C8, by reducing Grb14-IR interaction, increases insulin signalling. The use of C8 as a lead compound should allow for the development of new molecules of potential therapeutic interest for the treatment of diabetes.

Genetics of Insulin Resistance and the Metabolic Syndrome

Insulin resistance and the metabolic syndrome are complex metabolic traits and key risk factors for the development of cardiovascular disease. They result from the interplay of environmental and genetic factors but the full extent of the genetic background to these conditions remains incomplete. Large-scale genome-wide association studies have helped advance the identification of common genetic variation associated with insulin resistance and the metabolic syndrome, and more recently, exome sequencing has allowed the identification of rare variants associated with the pathogenesis of these conditions. Many variants associated with insulin resistance are directly involved in glucose metabolism; however, functional studies are required to assess the contribution of other variants to the development of insulin resistance. Many genetic variants involved in the pathogenesis of the metabolic syndrome are associated with lipid metabolism.

Structure and dynamics of the insulin receptor: implications for receptor activation and drug discovery

Recently, major progress has been made in uncovering the mechanisms of how insulin engages its receptor and modulates downstream signal transduction. Here, we present in detail the current structural knowledge surrounding the individual components of the complex, binding sites, and dynamics during the activation process. A novel kinase triggering mechanism, the 'bow-arrow model', is proposed based on current knowledge and computational simulations of this system, in which insulin, after its initial interaction with binding site 1, engages with site 2 between the fibronectin type III (FnIII)-1 and -2 domains, which changes the conformation of FnIII-3 and eventually translates into structural changes across the membrane. This model provides a new perspective on the process of insulin binding to its receptor and, thus, could lead to future novel drug discovery efforts.

The adaptors Grb10 and Grb14 are calmodulin-binding proteins

We identified the Grb7 family members, Grb10 and Grb14, as Ca²⁺ -dependent CaM-binding proteins using Ca²⁺ -dependent CaM-affinity chromatography as we previously did with Grb7. The potential CaM-binding sites were identified and experimentally tested using fluorescent-labeled peptides corresponding to these sites. The apparent affinity constant of these peptides for CaM, and the minimum number of calcium ions bound to CaM that are required for effective binding to these peptides were also determined. We prepared deletion mutants of the three adaptor proteins lacking the identified sites and determined that they lost or strongly diminished their CaM-binding capacity following the sequence Grb7 > > Grb14 > Grb10. More than one CaM-binding site and/or accessory CaM-binding sites appear to exist in Grb10 and Grb14, as compared to a single one present in Grb7.

De Novo Transcriptome Characterization and Growth-Related Gene Expression Profiling of Diploid and Triploid Bighead Catfish (Clarias macrocephalus Günther, 1864)

To enhance understanding of triploid gene expression, the transcriptome information from bighead catfish (Clarias macrocephalus Günther, 1864) was studied using the paired-end Illumina HiSeq™ 2000 sequencing platform. In total, 68,227,832 raw reads were generated from liver tissues and 53,149 unigenes were assembled, with an average length of 765 bp and N50 length of 1283 bp. Of these unigenes, 33,428 (62.89%) could be annotated according to their homology with matches in the NCBI non-redundant (Nr), NCBI nucleotide (Nt), Swiss-Prot, Clusters of Orthologous Groups (COG), gene ontology (GO), or Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. Relative expression of liver genes between diploid and triploid bighead catfish revealed more than 90% of the annotated unigenes similarly expressed, regardless of ploidy, whereas 362 upregulated and 83 downregulated with at least a twofold change in triploid relative to diploid. Quantitative real-time PCR of 15 differentially expressed growth-related genes showed consistency between the expression profiles of those genes with the results from RNA-seq analysis. Our results showed that genes in C. macrocephalus liver responded independently to triploidy with the majority showing similar expression levels between diploid and triploid (a dosage compensation phenomenon). The underlying mechanism of the varying gene expression patterns was discussed. Notably, 5 of the top 20 upregulated genes associated with stress response and thus may reflect stress caused by triploidy. The present study adds a substantial contribution to the sequence data available for C. macrocephalus and hence provides valuable resources for further studies. Furthermore, it gives information that may enhance understanding of triploid physiology.

An electrostatic selection mechanism controls sequential kinase signaling downstream of the T cell receptor

The sequence of events that initiates T cell signaling is dictated by the specificities and order of activation of the tyrosine kinases that signal downstream of the T cell receptor. Using a platform that combines exhaustive point-mutagenesis of peptide substrates, bacterial surface-display, cell sorting, and deep sequencing, we have defined the specificities of the first two kinases in this pathway, Lck and ZAP-70, for the T cell receptor ζ chain and the scaffold proteins LAT and SLP-76. We find that ZAP-70 selects its substrates by utilizing an electrostatic mechanism that excludes substrates with positively-charged residues and favors LAT and SLP-76 phosphosites that are surrounded by negatively-charged residues. This mechanism prevents ZAP-70 from phosphorylating its own activation loop, thereby enforcing its strict dependence on Lck for activation. The sequence features in ZAP-70, LAT, and SLP-76 that underlie electrostatic selectivity likely contribute to the specific response of T cells to foreign antigens.

Novel Grb14-Mediated Cross Talk between Insulin and p62/Nrf2 Pathways Regulates Liver Lipogenesis and Selective Insulin Resistance

A long-standing paradox in the pathophysiology of metabolic diseases is the selective insulin resistance of the liver. It is characterized by a blunted action of insulin to reduce glucose production, contributing to hyperglycemia, while de novo lipogenesis remains insulin sensitive, participating in turn to hepatic steatosis onset. The underlying molecular bases of this conundrum are not yet fully understood. Here, we established a model of selective insulin resistance in mice by silencing an inhibitor of insulin receptor catalytic activity, the growth factor receptor binding protein 14 (Grb14) in liver. Indeed, Grb14 knockdown enhanced hepatic insulin signaling but also dramatically inhibited de novo fatty acid synthesis. In the liver of obese and insulin-resistant mice, downregulation of Grb14 markedly decreased blood glucose and improved liver steatosis. Mechanistic analyses showed that upon Grb14 knockdown, the release of p62/sqstm1, a partner of Grb14, activated the transcription factor nuclear factor erythroid-2-related factor 2 (Nrf2), which in turn repressed the lipogenic nuclear liver X receptor (LXR). Our study reveals that Grb14 acts as a new signaling node that regulates lipogenesis and modulates insulin sensitivity in the liver by acting at a crossroad between the insulin receptor and the p62-Nrf2-LXR signaling pathways.

A Molecular Signature of Myalgia in Myotonic Dystrophy 2

Background

Chronic muscle pain affects close to 20% of the population and is a major health burden. The underlying mechanisms of muscle pain are difficult to investigate as pain presents in patients with very diverse histories. Treatment options are therefore limited and not tailored to underlying mechanisms. To gain insight into the pathophysiology of myalgia we investigated a homogeneous group of patients suffering from myotonic dystrophy type 2 (DM2), a monogenic disorder presenting with myalgia in at least 50% of affected patients.

Methods

After IRB approval we performed an observational cross-sectional cohort study and recruited 42 patients with genetically confirmed DM2 plus 20 healthy age and gender matched control subjects. All participants were subjected to an extensive sensory-testing protocol. In addition, RNA sequencing was performed from 12 muscle biopsy specimens obtained from DM2 patients.

Findings

Clinical sensory testing as well as RNA sequencing clearly separated DM2 myalgic from non-myalgia patients and also from healthy controls. In particular pressure pain thresholds were significantly lowered for all muscles tested in myalgic DM2 patients but were not significantly different between non-myalgic patients and healthy controls. The expression of fourteen muscle expressed genes in myalgic patients was significantly up or down-regulated in myalgic compared to non-myalgic DM2 patients.

Interpretation

Our data support the idea that molecular changes in the muscles of DM2 patients are associated with muscle pain. Further studies should address whether muscle-specific molecular pathways play a significant role in myalgia in order to facilitate the development of mechanism-based therapeutic strategies to treat musculoskeletal pain.

Funding

This study was funded by the German Research Society (DFG, GK1631), KAP programme of Charité Universitätsmedizin Berlin and Max Delbrück Center for Molecular Medicine.

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Pressure pain thresholds were reduced in myotonic dystrophy 2 (DM2) and myalgias, but not in DM2 without myalgias

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RNASeq from skeletal muscle differed significantly in 14 genes between DM2 with myalgias and DM2 without myalgias

Patients with a rare type of muscle dystrophy (myotonic dystrophy type 2) that is caused by a single genetic mutation usually suffer from muscle weakness and wasting but a majority also suffer from chronic muscle pain in their extremities. In our study, we found that these patients are sensitive to pressure stimuli over muscles that are not usually perceived as painful. We also identified several muscle genes that might highlight a molecular link to muscle pain. These findings call for further research to learn how and whether the genetic impairments in muscle contribute to muscle pain.

High expression of growth factor receptor-bound protein 14 predicts poor prognosis for colorectal cancer patients

OBJECTS

To explore the roles of growth factor receptor-bound protein 14 (GRB14) in colorectal cancer (CRC) and its correlation with clinicopathological characteristics and prognosis of CRC patients.

RESULTS

GRB14 was localized in the cytoplasm of CRC and benign glandular epithelium cells, showing higher levels in CRC tissues compared with normal colon samples (P < 0.001). High GRB14 was associated with a high pathological grade (P = 0.045), advanced clinical stage (P = 0.018), enhanced tumor invasion (P < 0.001) and lymph node metastasis (P = 0.028). The cancer genome atlas (TCGA) mRNA sequence data showed that GRB14 was upregulated in CRC at an advanced clinical stage (P = 0.011) with enhanced tumor invasion (P < 0.001) and lymph node metastasis (P = 0.014). Kaplan-Meier survival curves revealed that CRC patients with high GRB14 levels had a shorter survival compared with those showing low GRB14 expression (P = 0.007). High GRB14 expression was an independent prognostic factor for CRC patients (HR 2.847, 95 %CI 1.058-7.659; P = 0.038).

CONCLUSIONS

GRB14 may be an important cancer promoter that enhances CRC progression. Upregulated GRB14 levels may predict a poor clinical outcome in CRC patients.

Genome-wide meta-analysis uncovers novel loci influencing circulating leptin levels

Leptin is an adipocyte-secreted hormone, the circulating levels of which correlate closely with overall adiposity. Although rare mutations in the leptin (LEP) gene are well known to cause leptin deficiency and severe obesity, no common loci regulating circulating leptin levels have been uncovered. Therefore, we performed a genome-wide association study (GWAS) of circulating leptin levels from 32,161 individuals and followed up loci reaching P<10(-6) in 19,979 additional individuals. We identify five loci robustly associated (P<5 × 10(-8)) with leptin levels in/near LEP, SLC32A1, GCKR, CCNL1 and FTO. Although the association of the FTO obesity locus with leptin levels is abolished by adjustment for BMI, associations of the four other loci are independent of adiposity. The GCKR locus was found associated with multiple metabolic traits in previous GWAS and the CCNL1 locus with birth weight. Knockdown experiments in mouse adipose tissue explants show convincing evidence for adipogenin, a regulator of adipocyte differentiation, as the novel causal gene in the SLC32A1 locus influencing leptin levels. Our findings provide novel insights into the regulation of leptin production by adipose tissue and open new avenues for examining the influence of variation in leptin levels on adiposity and metabolic health.

Ras Conformational Ensembles, Allostery, and Signaling

Ras proteins are classical members of small GTPases that function as molecular switches by alternating between inactive GDP-bound and active GTP-bound states. Ras activation is regulated by guanine nucleotide exchange factors that catalyze the exchange of GDP by GTP, and inactivation is terminated by GTPase-activating proteins that accelerate the intrinsic GTP hydrolysis rate by orders of magnitude. In this review, we focus on data that have accumulated over the past few years pertaining to the conformational ensembles and the allosteric regulation of Ras proteins and their interpretation from our conformational landscape standpoint. The Ras ensemble embodies all states, including the ligand-bound conformations, the activated (or inactivated) allosteric modulated states, post-translationally modified states, mutational states, transition states, and nonfunctional states serving as a reservoir for emerging functions. The ensemble is shifted by distinct mutational events, cofactors, post-translational modifications, and different membrane compositions. A better understanding of Ras biology can contribute to therapeutic strategies.

Towards breed formation by island model divergence in Korean cattle

Background

The main cattle breed in Korea is the brown Hanwoo, which has been under artificial selection within a national breeding program for several decades. Varieties of the Hanwoo known as Jeju Black and Chikso were not included in the breeding program and remained isolated from the effects of recent artificial selection advancements. We analysed the Jeju Black and Chikso populations in regards to their genetic variability, state of inbreeding, as well as level of differentiation from the mainland Hanwoo population.

Results

Jeju Black and Chikso were found to have small estimated effective population sizes (N_e) of only 11 and 7, respectively. Despite a small N_e, higher than expected heterozygosity levels were observed (0.303 and 0.306), however, lower allelic richness was found for the two island populations (1.76 and 1.77) compared to the mainland population (1.81). The increase in heterozygosity could be due to environmental disease challenges that promoted maintenance of higher genetic variability; however, no direct proof exists. Increased heterozygosity due to a first generation crossing of genetically different populations is not recorded. The differentiation between the Korean populations had F_ST values between 0.014 and 0.036 which is not as high as the differentiation within European beef or dairy cattle breeds (0.047–0.111). This suggests that the three populations have not separated into independent breeds.

Conclusion

Results agree with an island model of speciation where the brown Hanwoo represents the ancestral breed, whilst the Jeju Black and Chikso diverge from this common ancestor, following different evolutionary trajectories. Nevertheless, differences are minor and whether Jeju Black and Chikso cattle will develop into discrete breeds or reintegrate with the main population has to be seen in the future and will largely depend on human management decisions. This offers a rare opportunity to accompany the development of new breeds but also poses challenges on how to preserve these incipient breeds and ensure their long term viability.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0563-2) contains supplementary material, which is available to authorized users.

Genetics of non-conventional lipoprotein fractions

Lipoprotein subclass measures associate with cardiometabolic disease risk. Currently the information that lipoproteins convey on disease risk over that of traditional demographic and lipid measures is minimal, and so their use is clinics is limited. However, lipoprotein subclass perturbations represent some of the earliest manifestations of metabolic dysfunction, and their etiology is partially distinct from lipids, so information on the genetic etiology of lipoproteins offers promise for improved risk prediction, and unique mechanistic insights into IR and atherosclerosis. Here, I review the genetic variants validated as associating with lipoprotein measures to date, and show that the majority of identified variants have functionality that is best understood as related to lipid measures. Until we focus on the genes as they relate to lipoprotein subclass production, we are limiting our understanding of biological mechanisms underlying cardiometabolic disease.

The transcriptome of the bowhead whale Balaena mysticetus reveals adaptations of the longest-lived mammal

Mammals vary dramatically in lifespan, by at least two-orders of magnitude, but the molecular basis for this difference remains largely unknown. The bowhead whale Balaena mysticetus is the longest-lived mammal known, with an estimated maximal lifespan in excess of two hundred years. It is also one of the two largest animals and the most cold-adapted baleen whale species. Here, we report the first genome-wide gene expression analyses of the bowhead whale, based on the de novo assembly of its transcriptome. Bowhead whale or cetacean-specific changes in gene expression were identified in the liver, kidney and heart, and complemented with analyses of positively selected genes. Changes associated with altered insulin signaling and other gene expression patterns could help explain the remarkable longevity of bowhead whales as well as their adaptation to a lipid-rich diet. The data also reveal parallels in candidate longevity adaptations of the bowhead whale, naked mole rat and Brandt's bat. The bowhead whale transcriptome is a valuable resource for the study of this remarkable animal, including the evolution of longevity and its important correlates such as resistance to cancer and other diseases.

Insulin-induced cell division is controlled by the adaptor Grb14 in a Chfr-dependent manner

Beyond its key role in the control of energy metabolism, insulin is also an important regulator of cell division and neoplasia. However, the molecular events involved in insulin-driven cell proliferation are not fully elucidated. Here, we show that the ubiquitin ligase Chfr, a checkpoint protein involved in G2/M transition, is a new effector involved in the control of insulin-induced cell proliferation. Chfr is identified as a partner of the molecular adapter Grb14, an inhibitor of insulin signalling. Using mammalian cell lines and the Xenopus oocyte as a model of G2/M transition, we demonstrate that Chfr potentiates the inhibitory effect of Grb14 on insulin-induced cell division. Insulin stimulates Chfr binding to the T220 residue of Grb14. Both Chfr binding site and Grb14 C-ter BPS-SH2 domain, mediating IR binding and inhibition, are required to prevent insulin-induced cell division. Targeted mutagenesis revealed that Chfr ligase activity and phosphorylation of its T39 residue, a target of Akt, are required to potentiate Grb14 inhibitory activity. In the presence of insulin, the binding of Chfr to Grb14 activates its ligase activity, leading to Aurora A and Polo-like kinase degradation and blocking cell division. Collectively, our results show that Chfr and Grb14 collaborate in a negative feedback loop controlling insulin-stimulated cell division.

An epigenetic map of age-associated autosomal loci in northern European families at high risk for the metabolic syndrome

BACKGROUND

The prevalence of chronic diseases such as cancer, type 2 diabetes, metabolic syndrome (MetS), and cardiovascular disease increases with age in all populations. Epigenetic features are hypothesized to play important roles in the pathophysiology of age-associated diseases, but a map of these markers is lacking. We searched for genome-wide age-associated methylation signatures in peripheral blood of individuals at high risks for MetS by profiling 485,000 CpG sites in 192 individuals of Northern European ancestry using the Illumina HM450 array. Subjects (ages 6-85 years) were part of seven extended families, and 73% of adults and 32% of children were overweight or obese.

RESULTS

We found 22,122 genome-wide significant age-associated CpG sites (P α=0.05 = 3.65 × 10(-7) after correction for multiple testing) of which 14,155 are positively associated with age while 7,967 are negatively associated. By applying a positional density-based clustering algorithm, we generated a map of epigenetic 'hot-spots' of age-associated genomic segments, which include 290 age-associated differentially methylated CpG clusters (aDMCs), of which 207 are positively associated with age. Gene/pathway enrichment analyses were performed on these clusters using FatiGO. Genes localized to both the positively (n = 241) and negatively (n = 16) age-associated clusters are significantly enriched in specific KEGG pathways and GO terms. The most significantly enriched pathways are the hedgehog signaling pathway (adjusted P = 3.96 × 10(-3)) and maturity-onset diabetes of the young (MODY) (adjusted P = 6.26 × 10(-3)) in the positive aDMCs and type I diabetes mellitus (adjusted P = 3.69 × 10(-7)) in the negative aDMCs. We also identified several epigenetic loci whose age-associated change rates differ between subjects diagnosed with MetS and those without.

CONCLUSION

We conclude that in a family cohort at high risk for MetS, age-associated epigenetic features enrich in biological pathways important for determining the fate of fat cells and for insulin production. We also observe that several genes known to be related to MetS show differential epigenetic response to age in individuals with and without MetS.

Effect of knocking down the insulin receptor on mouse rod responses

Previous experiments have shown that the insulin receptor (IR) is expressed in mammalian rods and contributes to the protection of photoreceptors during bright-light exposure. The role of the insulin receptor in the production of the light response is however unknown. We have used suction-electrode recording to examine the responses of rods after conditionally knocking down the insulin receptor. Our results show that these IR knock-down rods have an accelerated decay of the light response and a small decrease in sensitivity by comparison to littermate WT rods. Our results indicate that the insulin receptor may have some role in controlling the rate of rod response decay, but they exclude a major role of the insulin receptor pathway in phototransduction.

A Gaussian network model study suggests that structural fluctuations are higher for inactive states than active states of protein kinases

Protein kinases participate extensively in cellular signalling. Using Gaussian normal mode analysis of kinases in active and diverse inactive forms, authors show that structural fluctuations are significantly higher in inactive forms and are localized in functionally sensitive sites.

How IGF-1 activates its receptor

The type I insulin-like growth factor receptor (IGF1R) is involved in growth and survival of normal and neoplastic cells. A ligand-dependent conformational change is thought to regulate IGF1R activity, but the nature of this change is unclear. We point out an underappreciated dimer in the crystal structure of the related Insulin Receptor (IR) with Insulin bound that allows direct comparison with unliganded IR and suggests a mechanism by which ligand regulates IR/IGF1R activity. We test this mechanism in a series of biochemical and biophysical assays and find the IGF1R ectodomain maintains an autoinhibited state in which the TMs are held apart. Ligand binding releases this constraint, allowing TM association and unleashing an intrinsic propensity of the intracellular regions to autophosphorylate. Enzymatic studies of full-length and kinase-containing fragments show phosphorylated IGF1R is fully active independent of ligand and the extracellular-TM regions. The key step triggered by ligand binding is thus autophosphorylation.

[Control of insulin signalisation and action by the Grb14 protein]

The action of insulin on metabolism and cell growth is mediated by a specific receptor tyrosine kinase, which, through phosphorylation of several substrates, triggers the activation of two major signaling pathways, the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway and the Ras/extracellular signal-regulated kinase (ERK) pathway. Insulin-induced activation of the receptor and downstream signaling is also subjected to a negative feedback control involving several mechanisms, among which the interaction of the insulin receptor and its substrates with inhibitory proteins. After summarizing the major mechanisms underlying the activation and attenuation of insulin signaling, this review focuses on its control by the Grb14 adaptor protein. Grb14 has been identif-ied as an inhibitor of insulin signaling and action, and is involved in insulin resistance associated with type 2 diabetes and obesity. Studies on the molecular mechanism of action of Grb14 have shown that, through interaction with the activated insulin receptor, Grb14 inhibits its catalytic activity and the activation of downstream signaling. However, the consequences of Grb14 gene invalidation are complex and tissue-specific, and some effects of Grb14 on insulin signaling appear to be linked to its interaction with effector proteins downstream the insulin receptor. Pharmacological inhibition of Grb14 should allow to enhance insulin sensitivity and improve energy homeostasis in insulin-resistant states.

Pleiotropic genes for metabolic syndrome and inflammation

Metabolic syndrome (MetS) has become a health and financial burden worldwide. The MetS definition captures clustering of risk factors that predict higher risk for diabetes mellitus and cardiovascular disease. Our study hypothesis is that additional to genes influencing individual MetS risk factors, genetic variants exist that influence MetS and inflammatory markers forming a predisposing MetS genetic network. To test this hypothesis a staged approach was undertaken. (a) We analyzed 17 metabolic and inflammatory traits in more than 85,500 participants from 14 large epidemiological studies within the Cross Consortia Pleiotropy Group. Individuals classified with MetS (NCEP definition), versus those without, showed on average significantly different levels for most inflammatory markers studied. (b) Paired average correlations between 8 metabolic traits and 9 inflammatory markers from the same studies as above, estimated with two methods, and factor analyses on large simulated data, helped in identifying 8 combinations of traits for follow-up in meta-analyses, out of 130,305 possible combinations between metabolic traits and inflammatory markers studied. (c) We performed correlated meta-analyses for 8 metabolic traits and 6 inflammatory markers by using existing GWAS published genetic summary results, with about 2.5 million SNPs from twelve predominantly largest GWAS consortia. These analyses yielded 130 unique SNPs/genes with pleiotropic associations (a SNP/gene associating at least one metabolic trait and one inflammatory marker). Of them twenty-five variants (seven loci newly reported) are proposed as MetS candidates. They map to genes MACF1, KIAA0754, GCKR, GRB14, COBLL1, LOC646736-IRS1, SLC39A8, NELFE, SKIV2L, STK19, TFAP2B, BAZ1B, BCL7B, TBL2, MLXIPL, LPL, TRIB1, ATXN2, HECTD4, PTPN11, ZNF664, PDXDC1, FTO, MC4R and TOMM40. Based on large data evidence, we conclude that inflammation is a feature of MetS and several gene variants show pleiotropic genetic associations across phenotypes and might explain a part of MetS correlated genetic architecture. These findings warrant further functional investigation.

Dimeric switch of Hakai-truncated monomers during substrate recognition: insights from solution studies and NMR structure

Hakai, an E3 ubiquitin ligase, disrupts cell-cell contacts in epithelial cells and is up-regulated in human colon and gastric adenocarcinomas. Hakai acts through its phosphotyrosine-binding (HYB) domain, which bears a dimeric fold that recognizes the phosphotyrosine motifs of E-cadherin, cortactin, DOK1, and other Src substrates. Unlike the monomeric nature of the SH2 and phosphotyrosine-binding domains, the architecture of the HYB domain consists of an atypical, zinc-coordinated tight homodimer. Here, we report a C-terminal truncation mutant of the HYB domain (HYB(ΔC)), comprising amino acids 106-194, which exists as a monomer in solution. The NMR structure revealed that this deletion mutant undergoes a dramatic structural change caused by a rearrangement of the atypical zinc-coordinated unit in the C terminus of the HYB domain to a C2H2-like zinc finger in HYB(ΔC). Moreover, using isothermal titration calorimetry, we show that dimerization of HYB(ΔC) can be induced using a phosphotyrosine substrate peptide. This ligand-induced dimerization of HYB(ΔC) is further validated using analytical ultracentrifugation, size-exclusion chromatography, NMR relaxation studies, dynamic light scattering, and circular dichroism experiments. Overall, these observations suggest that the dimeric architecture of the HYB domain is essential for the phosphotyrosine-binding property of Hakai.

Phosphorylation of Grb14 BPS domain by GSK-3 correlates with complex forming of Grb14 and insulin receptor

Growth factor receptor-bound protein 14 (Grb14) interacts with insulin receptor (IR) through the between PH and SH2 (BPS) domain. Grb14-IR complex formation is initiated by insulin stimulation, and the binding event results in the inhibition of insulin signalling. Thus, Grb14 is regarded as an endogenous suppressor of insulin signal transduction; however, there are no studies describing the mechanism whereby Grb14-IR complex formation is suppressed in the absence of insulin stimulation. In the present study, multiple phosphorylation motifs for glycogen synthase kinase 3 (GSK-3) were identified within the Grb14 BPS domain (Ser(358), Ser(362) and Ser(366) of human Grb14). Pharmacological inhibition as well as knockdown of GSK-3 facilitated complex formation between Grb14 and IR, implicating GSK-3 activity in regulating Grb14-IR binding. In situ proximity ligation assay and in vitro kinase assays of phosphopeptides suggested that serine residues in the BPS domain would be substrates for GSK-3. The kinase assays also indicated phosphoserine 370 (in human Grb14) was required for the phosphorylation of Ser(358), Ser(362) and Ser(366) by GSK-3. Grb14-IR binding was also facilitated by replacement of the serines with Ala. We also observed that Ser(366) of endogenous Grb14 in Hep G2 cell was phosphorylated and the phosphorylation was influenced by treatments with insulin, as well as the GSK-3 inhibitor.

Inhibition of IL-6 family cytokines by SOCS3

IL-6 a multi-functional cytokine with important effects in both inflammation and haematopoiesis. SOCS3 is the primary inhibitor of IL-6 signalling, interacting with gp130, the common shared chain of the IL-6 family of cytokines, and JAK1, JAK2 and TYK2 to control both the duration of signalling and the biological response. Recent biochemical and structural studies have shown SOCS3 binds to only these three JAKs, all of which are associated with IL-6 signalling, and not JAK3. This specificity is determined by a three residue "GQM" motif in the kinase domain of JAK1, JAK2 and TYK2. SOCS3 binds to JAK and gp130 simultaneously, and inhibits JAK activity in an ATP-independent manner by partially occluding the kinase's substrate binding groove with its kinase inhibitory region. We therefore propose a model in which each of gp130, JAK and SOCS3 are directly bound to the other two, allowing SOCS3 to inhibit IL6 signalling with high potency and specificity.

Spatial and temporal aspects and the interplay of Grb14 and protein tyrosine phosphatase-1B on the insulin receptor phosphorylation

Background

Growth factor receptor-bound protein 14 (Grb14) is an adapter protein implicated in receptor tyrosine kinase signaling. Grb14 knockout studies highlight both the positive and negative roles of Grb14 in receptor tyrosine kinase signaling, in a tissue specific manner. Retinal cells are post-mitotic tissue, and insulin receptor (IR) activation is essential for retinal neuron survival. Retinal cells express protein tyrosine phosphatase-1B (PTP1B), which dephosphorylates IR and Grb14, a pseudosubstrate inhibitor of IR. This project asks the following major question: in retinal neurons, how does the IR overcome inactivation by PTP1B and Grb14?

Results

Our previous studies suggest that ablation of Grb14 results in decreased IR activation, due to increased PTP1B activity. Our research propounds that phosphorylation in the BPS region of Grb14 inhibits PTP1B activity, thereby promoting IR activation. We propose a model in which phosphorylation of the BPS region of Grb14 is the key element in promoting IR activation, and failure to undergo phosphorylation on Grb14 leads to both PTP1B and Grb14 exerting their negative roles in IR. Consistent with this hypothesis, we found decreased phosphorylation of Grb14 in diabetic type 1 Ins2^Akita mouse retinas. Decreased retinal IR activation has previously been reported in this mouse line.

Conclusions

Our results suggest that phosphorylation status of the BPS region of Grb14 determines the positive or negative role it will play in IR signaling.