A novel pleckstrin homology domain-containing protein enhances insulin-stimulated Akt phosphorylation and GLUT4 translocation in adipocytes

Osteogenesis imperfecta: shifting paradigms in pathophysiology and care in children

The formation of functional bone requires a delicate interplay between osteogenesis and osteolysis. Disturbances in this subtle balance result in an increased risk for fractures. Besides its mechanical function, bone tissue represents a key player in the regulation of calcium homeostasis. Impaired bone formation results in bone fragility, which is especially pronounced in osteogenesis imperfecta (OI). This rare genetic disorder is characterized by frequent fractures as well as extraskeletal manifestations. The current classification of OI includes 23 distinct types. In recent years, several new mutations in different genes have been identified, although the exact pathomechanisms leading to the clinical presentation of OI often remain unclear. While bisphosphonates are still the standard of care, novel therapeutic approaches are emerging. Especially, targeted antibody therapies, originally developed for osteoporosis, are increasingly being investigated in children with OI and represent a promising approach to alleviate the consequences of impaired osteogenesis and improve quality of life in OI patients. This review aims to provide insight into the pathophysiology of OI and the consequences of distinct disease-causing mutations affecting the regulation of bone homeostasis. In this context, we describe the four most recently identified OI-causing genes and provide an update on current approaches for diagnosis and treatment.

Interfering with the ERC1-LL5β interaction disrupts plasma membrane-Associated platforms and affects tumor cell motility

Cell migration requires a complex array of molecular events to promote protrusion at the front of motile cells. The scaffold protein LL5β interacts with the scaffold ERC1, and recruits it at plasma membrane-associated platforms that form at the front of migrating tumor cells. LL5 and ERC1 proteins support protrusion during migration as shown by the finding that depletion of either endogenous protein impairs tumor cell motility and invasion. In this study we have tested the hypothesis that interfering with the interaction between LL5β and ERC1 may be used to interfere with the function of the endogenous proteins to inhibit tumor cell migration. For this, we identified ERC1(270-370) and LL5β(381-510) as minimal fragments required for the direct interaction between the two proteins. The biochemical characterization demonstrated that the specific regions of the two proteins, including predicted intrinsically disordered regions, are implicated in a reversible, high affinity direct heterotypic interaction. NMR spectroscopy further confirmed the disordered nature of the two fragments and also support the occurrence of interaction between them. We tested if the LL5β protein fragment interferes with the formation of the complex between the two full-length proteins. Coimmunoprecipitation experiments showed that LL5β(381-510) hampers the formation of the complex in cells. Moreover, expression of either fragment is able to specifically delocalize endogenous ERC1 from the edge of migrating MDA-MB-231 tumor cells. Coimmunoprecipitation experiments show that the ERC1-binding fragment of LL5β interacts with endogenous ERC1 and interferes with the binding of endogenous ERC1 to full length LL5β. Expression of LL5β(381-510) affects tumor cell motility with a reduction in the density of invadopodia and inhibits transwell invasion. These results provide a proof of principle that interfering with heterotypic intermolecular interactions between components of plasma membrane-associated platforms forming at the front of tumor cells may represent a new approach to inhibit cell invasion.

Phosphoproteomics Profiling Defines a Target Landscape of the Basophilic Protein Kinases AKT, S6K, and RSK in Skeletal Myotubes

Phosphorylation-dependent signal transduction plays an important role in regulating the functions and fate of skeletal muscle cells. Central players in the phospho-signaling network are the protein kinases AKT, S6K, and RSK as part of the PI3K-AKT-mTOR-S6K and RAF-MEK-ERK-RSK pathways. However, despite their functional importance, knowledge about their specific targets is incomplete because these kinases share the same basophilic substrate motif RxRxxp[ST]. To address this, we performed a multifaceted quantitative phosphoproteomics study of skeletal myotubes following kinase inhibition. Our data corroborate a cross talk between AKT and RAF, a negative feedback loop of RSK on ERK, and a putative connection between RSK and PI3K signaling. Altogether, we report a kinase target landscape containing 49 so far unknown target sites. AKT, S6K, and RSK phosphorylate numerous proteins involved in muscle development, integrity, and functions, and signaling converges on factors that are central for the skeletal muscle cytoskeleton. Whereas AKT controls insulin signaling and impinges on GTPase signaling, nuclear signaling is characteristic for RSK. Our data further support a role of RSK in glucose metabolism. Shared targets have functions in RNA maturation, stability, and translation, which suggests that these basophilic kinases establish an intricate signaling network to orchestrate and regulate processes involved in translation.

Phosphoproteomics reveals rewiring of the insulin signaling network and multi-nodal defects in insulin resistance

The failure of metabolic tissues to appropriately respond to insulin ("insulin resistance") is an early marker in the pathogenesis of type 2 diabetes. Protein phosphorylation is central to the adipocyte insulin response, but how adipocyte signaling networks are dysregulated upon insulin resistance is unknown. Here we employ phosphoproteomics to delineate insulin signal transduction in adipocyte cells and adipose tissue. Across a range of insults causing insulin resistance, we observe a marked rewiring of the insulin signaling network. This includes both attenuated insulin-responsive phosphorylation, and the emergence of phosphorylation uniquely insulin-regulated in insulin resistance. Identifying dysregulated phosphosites common to multiple insults reveals subnetworks containing non-canonical regulators of insulin action, such as MARK2/3, and causal drivers of insulin resistance. The presence of several bona fide GSK3 substrates among these phosphosites led us to establish a pipeline for identifying context-specific kinase substrates, revealing widespread dysregulation of GSK3 signaling. Pharmacological inhibition of GSK3 partially reverses insulin resistance in cells and tissue explants. These data highlight that insulin resistance is a multi-nodal signaling defect that includes dysregulated MARK2/3 and GSK3 activity.

Biallelic frameshift variants inPHLDB1cause mild-type osteogenesis imperfecta with regressive spondylometaphyseal changes

Background

Osteogenesis imperfecta (OI) is a heterogeneous group of inherited disorders characterised by susceptibility to fractures, primarily due to defects in type 1 collagen. The aim of this study is to present a novel OI phenotype and its causative candidate gene.

Methods

Whole-exome sequencing and clinical evaluation were performed in five patients from two unrelated families.PHLDB1mRNA expression in blood and fibroblasts was investigated by real-time PCR, and western blot analysis was further performed on skin fibroblasts.

Results

The common findings among the five affected children were recurrent fractures and/or osteopaenia, platyspondyly, short and bowed long bones, and widened metaphyses. Metaphyseal and vertebral changes regressed after early childhood, and no fractures occurred under bisphosphonate treatment. We identified biallelic NM_001144758.3:c.2392dup and NM_001144758.3:c.2690_2693del pathogenic variants inPHLDB1in the affected patients, respectively, in the families; parents were heterozygous for these variants.PHLDB1encodes pleckstrin homology-like domain family B member-1 (PHLDB1) protein, which has a role in insulin-dependent Akt phosphorylation. Compared with controls, a decrease in the expression levels ofPHLDB1in the blood and skin fibroblast samples was detected. Western blot analysis of cultured fibroblasts further confirmed the loss of PHLDB1.

Conclusion

Two biallelic frameshift variants in the candidate genePHLDB1were identified in independent families with a novel, mild-type, autosomal recessive OI. The demonstration of decreasedPHLDB1mRNA expression levels in blood and fibroblast samples supports the hypothesis thatPHLDB1pathogenic variants are causative for the observed phenotype.

Analysis of WDFY4 rs7097397 and PHLDB1 rs7389 polymorphisms in Chinese patients with systemic lupus erythematosus

OBJECTIVES

To explore the relationship among patient-specific SNPs from one SLE family, lupus susceptibility, and laboratory indicators in a western Chinese population.

METHODS

We previously performed whole exome sequencing in one SLE family and screened 5 SLE candidate SNPs. In this study, we verified them in 634 SLE patients and 400 healthy controls and analyzed the relationship between SNPs and laboratory indicators.

RESULTS

Among the 5 candidate SNPs, PHLDB1 rs7389T/G (dominant model, OR = 0.627, 95%CI = 0.480-0.820, P = 0.001) and WDFY4 rs7097397G/A (dominant model, OR = 0.653, 95%CI = 0.438-0.973, P = 0.035) were associated with SLE susceptibility. In addition, the G allele of rs7389 was related to an increased level of TNF-α (q = 0.013). The A allele of rs7097397 was related to reduced levels of IL-1β (q = 0.033) and IL-6 (q = 0.039) and high positive rate of antinuclear antibodies (q = 0.021).

CONCLUSIONS

Our study indicated that both the rs7389T/G and rs7097397G/A polymorphisms were related to SLE susceptibility in western China. rs7389T/G was related to increased TNF-α content, while rs7097397G/A was associated with reduced IL-1β and IL-6 content and increased antinuclear antibody positive rate. Key Points • The G allele of rs7389 was related to reduced susceptibility to SLE. • The A allele of rs7097397 was associated with reduced susceptibility to SLE. • The G allele of rs7389 was related to increased levels of TNF-α. • The A allele of rs7097397 was related to decreased concentrations of IL-1β and IL-6, as well as an increased positive rate of antinuclear antibody.

Microtubules in insulin action: what's on the tube?

Microtubules (MT) have a role in the intracellular response to insulin stimulation and subsequent glucose transport by glucose transporter 4 (GLUT4), which resides in specialized storage vesicles that travel through the cell. Before GLUT4 is inserted into the plasma membrane for glucose transport, it undergoes complex trafficking through the cell via the integration of cytoskeletal networks. In this review, we highlight the importance of MT elements in insulin action in adipocytes through a summary of MT depolymerization studies, MT-based GLUT4 movement, molecular motor proteins involved in GLUT4 trafficking, as well as MT-related phenomena in response to insulin and links between insulin action and MT-associated proteins.

Meta-Analyses of Splicing and Expression Quantitative Trait Loci Identified Susceptibility Genes of Glioma

BACKGROUND

The functions of most glioma risk alleles are unknown. Very few studies had evaluated expression quantitative trait loci (eQTL), and insights of susceptibility genes were limited due to scarcity of available brain tissues. Moreover, no prior study had examined the effect of glioma risk alleles on alternative RNA splicing.

OBJECTIVE

This study explored splicing quantitative trait loci (sQTL) as molecular QTL and improved the power of QTL mapping through meta-analyses of both cis eQTL and sQTL.

METHODS

We first evaluated eQTLs and sQTLs of the CommonMind Consortium (CMC) and Genotype-Tissue Expression Project (GTEx) using genotyping, or whole-genome sequencing and RNA-seq data. Alternative splicing events were characterized using an annotation-free method that detected intron excision events. Then, we conducted meta-analyses by pooling the eQTL and sQTL results of CMC and GTEx using the inverse variance-weighted model. Afterward, we integrated QTL meta-analysis results (Q < 0.05) with the Glioma International Case Control Study (GICC) GWAS meta-analysis (case:12,496, control:18,190), using a summary statistics-based mendelian randomization (SMR) method.

RESULTS

Between CMC and GTEx, we combined the QTL data of 354 unique individuals of European ancestry. SMR analyses revealed 15 eQTLs in 11 loci and 32 sQTLs in 9 loci relevant to glioma risk. Two loci only harbored sQTLs (1q44 and 16p13.3). In seven loci, both eQTL and sQTL coexisted (2q33.3, 7p11.2, 11q23.3 15q24.2, 16p12.1, 20q13.33, and 22q13.1), but the target genes were different for five of these seven loci. Three eQTL loci (9p21.3, 20q13.33, and 22q13.1) and 4 sQTL loci (11q23.3, 16p13.3, 16q12.1, and 20q13.33) harbored multiple target genes. Eight target genes of sQTLs (C2orf80, SEC61G, TMEM25, PHLDB1, RP11-161M6.2, HEATR3, RTEL1-TNFRSF6B, and LIME1) had multiple alternatively spliced transcripts.

CONCLUSION

Our study revealed that the regulation of transcriptome by glioma risk alleles is complex, with the potential for eQTL and sQTL jointly affecting gliomagenesis in risk loci. QTLs of many loci involved multiple target genes, some of which were specific to alternative splicing. Therefore, quantitative trait loci that evaluate only total gene expression will miss many important target genes.

Common Signal Transduction Molecules Activated by Bacterial Entry into a Host Cell and by Reactive Oxygen Species

Significance: An increasing number of pathogens are acquiring resistance to antibiotics. Efficient antimicrobial drug regimens are important even for the most advanced therapies, which range from cutting-edge invasive clinical protocols, such as robotic surgeries, to the treatment of harmless bacterial diseases and to minor scratches to the skin. Therefore, there is an urgent need to survey alternative antimicrobial drugs that can reinforce or replace existing antibiotics. Recent Advances: Bacterial proteins that are critical for energy metabolism, promising novel anticancer thiourea derivatives, and the use of synthetic molecules that increase the sensitivity of currently used antibiotics are among the recently discovered antimicrobial drugs. Critical Issues: In the development of new drugs, serious consideration should be given to the previous bacterial evolutionary selection caused by antibiotics, by the high proliferation rate of bacteria, and by the simple prokaryotic structure of bacteria. Future Directions: The survey of drug targets has mainly focused on bacterial proteins, although host signaling molecules involved in the treatment of various pathologies may have unknown antimicrobial characteristics. Recent data have suggested that small molecule inhibitors might enhance the effect of antibiotics, for example, by limiting bacterial entry into host cells. Phagocytosis, the mechanism by which host cells internalize pathogens through β-actin cytoskeletal rearrangement, induces calcium signaling, small GTPase activation, and phosphorylation of the phosphatidylinositol 3-kinase-serine/threonine-specific protein kinase B pathway. Antioxid. Redox Signal. 34, 486-503.

NOTCH3, a crucial target of miR-491-5p/miR-875-5p, promotes gastric carcinogenesis by upregulating PHLDB2 expression and activating Akt pathway

Aberrant Notch activation has been implicated in multiple malignancies and the identification of NOTCH receptors and related pathways is critical for targeted therapy. In this study, we aim to delineate the most prominent dysregulated NOTCH receptor and comprehensively reveal its deregulation in gastric cancer (GC). In the four Notch members, NOTCH3 was found uniformly upregulated and associated with poor clinical outcomes in multiple GC datasets. siRNA-mediated NOTCH3 knockdown demonstrated antitumor effects by suppressing cell proliferation, inhibiting monolayer formation, and impairing cell invasion abilities. Its depletion also induced early and late apoptosis. NOTCH3 was confirmed to be a direct target of two tumor suppressor microRNAs (miRNAs), namely miR-491-5p and miR-875-5p. The activation of NOTCH3 is partly due to the silence of these two miRNAs. Through RNA-seq profiling and functional validation, PHLDB2 was identified as a potent functional downstream modulator for NOTCH3 in gastric carcinogenesis. PHLDB2 expression demonstrated a positive correlation with NOTCH3, but was negatively correlated with miR-491-5p. Akt-mTOR was revealed as the downstream signaling of PHLDB2. The NOTCH3-PHLDB2-Akt co-activation was found in 33.7% GC patients and the activation of this axis predicted poor clinical outcome. GC cells treated with siNOTCH3, siPHLDB2, miR-491-5p, miR-875-5p, were more sensitive to Cisplatin and 5-FU. Taken together, the NOTCH3-PHLDB2-Akt cascade plays oncogenic role in gastric carcinogenesis and serves as a therapeutic target. Our study provided insights into Notch-mediated underlying molecular mechanisms and implied translational potential.

PHLD Class Proteins: A Family of New Players in the p53 Network

The Pleckstrin Homology-like Domain (PHLD) class of proteins are multifunctional proteins. The class is comprised of two families of proteins, PHLDA and PHLDB, each with 3 members. All members of the families possess a pleckstrin homology (PH) domain. Though identified nearly 30 years ago, this class of proteins remains understudied with PHLDA family members receiving most of the research attention. Recent studies have also begun to reveal the functions of the PHLDB family proteins in regulation of p53 and AKT signaling pathways important for cancer and metabolism. This review will discuss current research and offer some prospects on the possible roles of both families in cancer and metabolism.

Role of Polymorphisms of FAM13A, PHLDB1, and CYP24A1 in Breast Cancer Risk

Background:

Single-nucleotide polymorphisms (SNPs) are important indicators of susceptibility to breast cancer.

Objective:

To assess the associations between SNPs in the FAM13A, PHLDB1, and CYP24A1 gene and breast cancer risk in the Chinese Han population.

Methods:

We performed a case-control study including 379 female breast cancer patients and 407 female healthy controls. The three SNPs were genotyped using Agena MassARRAY platform. The χ2 test was used to compare alleles and genotypes frequencies of polymorphisms between case and control groups. Genetic models analyses to assess the associations between SNPs and breast cancer risk by computing odds ratios (ORs) and 95% confidence intervals (CIs) using logistic regression. RegulomeDB and HaploReg databases were used to calculate possible functional effects of polymorphisms.

Results:

Overall analysis results showed that rs4809957 was associated with an increased risk of breast cancer (allele A: OR = 1.27, 95% CI: 1.03-1.55, p = 0.024; AA vs. GG: OR = 1.80, 95% CI: 1.15–2.82, p = 0.010; recessive model: OR = 1.70, 95% CI: 1.12–2.58, p = 0.012); and rs1059122 was found to be associated with a reduced breast cancer risk in the recessive model (OR = 0.71, 95% CI: 0.51–0.98, p = 0.039). Stratification analysis found significant associations between the three SNPs (rs1059122, rs17748, and rs4809957) and breast cancer risk.

Conclusion:

Our results suggested that rs1059122 (FAM13A), rs17748 (PHLDB1), and rs4809957 (CYP24A1) might contribute to breast cancer susceptibility in the Chinese Han population. Future studies with large samples are required to confirm our findings, as well as functional studies are needed to explore their function in the breast cancer development.

Diffuse gliomas classified by 1p/19q co-deletion, TERT promoter and IDH mutation status are associated with specific genetic risk loci

Recent genome-wide association studies of glioma have led to the discovery of single nucleotide polymorphisms (SNPs) at 25 loci influencing risk. Gliomas are heterogeneous, hence to investigate the relationship between risk SNPs and glioma subtype we analysed 1659 tumours profiled for IDH mutation, TERT promoter mutation and 1p/19q co-deletion. These data allowed definition of five molecular subgroups of glioma: triple-positive (IDH mutated, 1p/19q co-deletion, TERT promoter mutated); TERT-IDH (IDH mutated, TERT promoter mutated, 1p/19q-wild-type); IDH-only (IDH mutated, 1p/19q wild-type, TERT promoter wild-type); triple-negative (IDH wild-type, 1p/19q wild-type, TERT promoter wild-type) and TERT-only (TERT promoter mutated, IDH wild-type, 1p/19q wild-type). Most glioma risk loci showed subtype specificity: (1) the 8q24.21 SNP for triple-positive glioma; (2) 5p15.33, 9p21.3, 17p13.1 and 20q13.33 SNPs for TERT-only glioma; (3) 1q44, 2q33.3, 3p14.1, 11q21, 11q23.3, 14q12, and 15q24.2 SNPs for IDH mutated glioma. To link risk SNPs to target candidate genes we analysed Hi-C and gene expression data, highlighting the potential role of IDH1 at 2q33.3, MYC at 8q24.21 and STMN3 at 20q13.33. Our observations provide further insight into the nature of susceptibility to glioma.

Genome-Wide Association Studies in Glioma

Since the first reports in 2009, genome-wide association studies (GWAS) have been successful in identifying germline variants associated with glioma susceptibility. In this review, we describe a chronological history of glioma GWAS, culminating in the most recent study comprising 12,496 cases and 18,190 controls. We additionally summarize associations at the 27 glioma-risk SNPs that have been reported so far. Future efforts are likely to be principally focused on assessing association of germline-risk SNPs with particular molecular subgroups of glioma, as well as investigating the functional basis of the risk loci in tumor formation. These ongoing studies will be important to maximize the impact of research into glioma susceptibility, both in terms of insight into tumor etiology as well as opportunities for clinical translation. Cancer Epidemiol Biomarkers Prev; 27(4); 418-28. ©2018 AACRSee all articles in this CEBP Focus section, "Genome-Wide Association Studies in Cancer."

Characterization of the CLASP2 Protein Interaction Network Identifies SOGA1 as a Microtubule-Associated Protein

CLASP2 is a microtubule-associated protein that undergoes insulin-stimulated phosphorylation and co-localization with reorganized actin and GLUT4 at the plasma membrane. To gain insight to the role of CLASP2 in this system, we developed and successfully executed a streamlined interactome approach and built a CLASP2 protein network in 3T3-L1 adipocytes. Using two different commercially available antibodies for CLASP2 and an antibody for epitope-tagged, overexpressed CLASP2, we performed multiple affinity purification coupled with mass spectrometry (AP-MS) experiments in combination with label-free quantitative proteomics and analyzed the data with the bioinformatics tool Significance Analysis of Interactome (SAINT). We discovered that CLASP2 coimmunoprecipitates (co-IPs) the novel protein SOGA1, the microtubule-associated protein kinase MARK2, and the microtubule/actin-regulating protein G2L1. The GTPase-activating proteins AGAP1 and AGAP3 were also enriched in the CLASP2 interactome, although subsequent AGAP3 and CLIP2 interactome analysis suggests a preference of AGAP3 for CLIP2. Follow-up MARK2 interactome analysis confirmed reciprocal co-IP of CLASP2 and revealed MARK2 can co-IP SOGA1, glycogen synthase, and glycogenin. Investigating the SOGA1 interactome confirmed SOGA1 can reciprocal co-IP both CLASP2 and MARK2 as well as glycogen synthase and glycogenin. SOGA1 was confirmed to colocalize with CLASP2 and with tubulin, which identifies SOGA1 as a new microtubule-associated protein. These results introduce the metabolic function of these proposed novel protein networks and their relationship with microtubules as new fields of cytoskeleton-associated protein biology.

p53 target miR-29c-3p suppresses colon cancer cell invasion and migration through inhibition of PHLDB2

miR-29c-3p is a potential tumor suppressor microRNA that is reportedly downregulated in several types of human cancers, but its role in colon cancer remains to be elucidated. Meanwhile, TP53, one of the most important tumor suppressors, is highly mutated in colon cancer. In the attempt to connect p53 and miR-29c-3p, we found that the upstream of miR-29c-3p gene contains a functional p53 consensus responsive element that is driven by p53 transcriptional factor activity, suggesting miR-29c-3p as a direct p53 target gene. Through online software prediction and in vivo validation, we demonstrated that Pleckstrin Homology Like Domain Family Member 2 (PHLDB2) is a valid miR-29c-3p target gene. Analysis of human cancer databases available from PROGgeneV2 showed that higher expression of PHLDB2 is associated with shorter overall survival and metastasis-free survival of colon cancer patients. Further, suppression of colon cancer cell invasion and migration by miR-29c-3p was significantly attenuated in the presence of ectopic PHLDB2, indicating PHLDB2 is a critical downstream target of miR-29c-3p. Collectively, our findings present the first to elucidate that miR-29c is a direct p53 target gene, and also identify PHLDB2 as an important miR-29c target gene involved in colon cancer metastasis.

Pleckstrin homology domain-containing protein PHLDB3 supports cancer growth via a negative feedback loop involving p53

The tumour suppressor p53 transactivates the expression of its target genes to exert its functions. Here, we identify a pleckstrin homology domain-containing protein (PHLDB3)-encoding gene as a p53 target. PHLDB3 overexpression increases proliferation and restrains apoptosis of wild-type p53-harboring cancer cells by reducing p53 protein levels. PHLDB3 binds to MDM2 (mouse double minute 2 homolog) and facilitates MDM2-mediated ubiquitination and degradation of p53. Knockdown of PHLDB3 more efficiently inhibits the growth of mouse xenograft tumours derived from human colon cancer HCT116 cells that contain wild type p53 compared with p53-deficient HCT116 cells, and also sensitizes tumour cells to doxorubicin and 5-Fluorouracil. Analysis of cancer genomic databases reveals that PHLDB3 is amplified and/or highly expressed in numerous human cancers. Altogether, these results demonstrate that PHLDB3 promotes tumour growth by inactivating p53 in a negative feedback fashion and suggest PHLDB3 as a potential therapeutic target in various human cancers.

p53 is an oncosuppressor regulating several genes at the transcriptional level. Here, the authors identify a negative feedback loop between PHLDB3 and p53; PHLDB3 is a transcriptional target of p53 which facilitates MDM2-mediated p53 ubiquitination and degradation, impacting on tumorigenesis.

EGFR oligomerization organizes kinase-active dimers into competent signalling platforms

Epidermal growth factor receptor (EGFR) signalling is activated by ligand-induced receptor dimerization. Notably, ligand binding also induces EGFR oligomerization, but the structures and functions of the oligomers are poorly understood. Here, we use fluorophore localization imaging with photobleaching to probe the structure of EGFR oligomers. We find that at physiological epidermal growth factor (EGF) concentrations, EGFR assembles into oligomers, as indicated by pairwise distances of receptor-bound fluorophore-conjugated EGF ligands. The pairwise ligand distances correspond well with the predictions of our structural model of the oligomers constructed from molecular dynamics simulations. The model suggests that oligomerization is mediated extracellularly by unoccupied ligand-binding sites and that oligomerization organizes kinase-active dimers in ways optimal for auto-phosphorylation in trans between neighbouring dimers. We argue that ligand-induced oligomerization is essential to the regulation of EGFR signalling.

Epidermal growth factor receptors have been shown to oligomerise upon binding to their cognate ligands. Here, the authors use biochemical, biophysical and cell biology techniques to analyse the structures of these oligomers, and argue that these formations are required for signalling.

Role of Host Type IA Phosphoinositide 3-Kinase Pathway Components in Invasin-Mediated Internalization of Yersinia enterocolitica

Many bacterial pathogens subvert mammalian type IA phosphoinositide 3-kinase (PI3K) in order to induce their internalization into host cells. How PI3K promotes internalization is not well understood. Also unclear is whether type IA PI3K affects different pathogens through similar or distinct mechanisms. Here, we performed an RNA interference (RNAi)-based screen to identify components of the type IA PI3K pathway involved in invasin-mediated entry of Yersinia enterocolitica, an enteropathogen that causes enteritis and lymphadenitis. The 69 genes targeted encode known upstream regulators or downstream effectors of PI3K. A similar RNAi screen was previously performed with the food-borne bacterium Listeria monocytogenes The results of the screen with Y. enterocolitica indicate that at least nine members of the PI3K pathway are needed for invasin-mediated entry. Several of these proteins, including centaurin-α1, Dock180, focal adhesion kinase (FAK), Grp1, LL5α, LL5β, and PLD2 (phospholipase D2), were recruited to sites of entry. In addition, centaurin-α1, FAK, PLD2, and mTOR were required for remodeling of the actin cytoskeleton during entry. Six of the human proteins affecting invasin-dependent internalization also promote InlB-mediated entry of L. monocytogenes Our results identify several host proteins that mediate invasin-induced effects on the actin cytoskeleton and indicate that a subset of PI3K pathway components promote internalization of both Y. enterocolitica and L. monocytogenes.

Functional analysis of the 11q23.3 glioma susceptibility locus implicates PHLDB1 and DDX6 in glioma susceptibility

Glioma is the most common malignant primary brain tumor and is associated with poor prognosis. Genetic factors contributing to glioma risk have recently been investigated through genome-wide association studies (GWAS), implicating seven independent glioma risk loci in six chromosomal regions. Here, we performed an in-depth functional analysis of the risk locus proximal to the PHLDB1 gene on 11q23.3. We retrieved all SNPs in linkage disequilibrium (r² ≥ 0.2) with the glioma-associated SNP (rs498872) and performed a comprehensive bioinformatics and experimental functional analysis for the region. After testing candidate SNPs for allele-specific activity in a luciferase-based enhancer scanning assay, we established a subset of 10 functional SNPs in the promoters of PHLDB1 and DDX6, and in a putative enhancer element. Chromatin conformation capture (3C) identified a physical interaction between the enhancer element containing a functional SNP (rs73001406) and the promoter of the DDX6 gene. Knockdown experiments in cell culture and 3D assays to evaluate the role of PHLDB1 and DDX6 suggest that both genes may contribute to the phenotype. These studies reveal the functional landscape of the 11q23.3 glioma susceptibility locus and identify a network of functional SNPs in regulatory elements and two target genes as a possible mechanism driving glioma risk association.

Association between RTEL1, PHLDB1, and TREH Polymorphisms and Glioblastoma Risk: A Case-Control Study

Background

Glioblastoma (GBM) is a highly invasive, aggressive, and incurable brain tumor. Genetic factors play important roles in GBM risk. The aim of this study was to elucidate the influence of gene polymorphism on GBM susceptibility.

Material/Methods

In this case-control study, we included 72 GBM patients and 320 healthy controls to analyze the association between 29 single-nucleotide polymorphisms and GBM cancer risk in the Chinese Han population. The single-nucleotide polymorphisms were determined by Sequenom MassARRAY RS1000 and statistical analysis was performed using SPSS software and SNPStats software.

Results

Using the χ² test, we found that rs2297440 and rs6010620 in RTEL1 increased risk of GBM. In the recessive model, we also found that the genotypes “CC” of rs2297440 and “GG” of rs6010620 in RTEL1 significantly increased GBM risk. The variant TT genotype of TREH rs17748 and the variant TT genotype of PHLDB1 rs498872 decreased GBM risk in the recessive model. We also found that the TREH rs17748 variant C allele showed an increased risk in males in the dominant model.

Conclusions

Our results suggest a significant association between the RETL1, TREH, and PHLDB1 genes and GBM development in the Han Chinese population.

Suppression of phosphatase and tensin homolog protects insulin-resistant cells from apoptosis

In the present study, a glucosamine-induced model of insulin-resistant skeletal muscle cells was established in order to investigate the effect of inhibition of phosphatase and tensin homolog (PTEN)/5'-adenosine monophosphate-activated protein kinase (AMPK) on these cells. The glucosamine-induced insulin-resistant skeletal muscle cells were produced and the rate of glucose uptake was measured using the glucose oxidase-peroxidase method. The expression levels of PTEN and phosphorylated PTEN (p-PTEN) were assessed using western blotting. Glucose transporter 4 (GLUT4) translocation was detected by immunofluorescence. Cell apoptosis was evaluated using flow cytometry. Following insulin stimulation, the rate of glucose uptake was significantly reduced in the cells with glucosamine-induced insulin-resistance in comparison with those in the control group. The expression and translocation of GLUT4 were reduced in the insulin-resistant muscle cells. By contrast, the expression of PTEN and p-PTEN as well as apoptosis were significantly increased. Following treatment with bisperoxopicolinatooxovanadate (BPV) or metformin in the insulin-resistant skeletal muscle cells, there was an increase in the rate of glucose uptake, an increase in GLUT4 expression and its translocation, a reduction in the expression of PTEN and p-PTEN, and a decrease in cell apoptosis compared with untreated insulin-resistant cells. Glucosamine may be used to produce an effective model of insulin-resistant skeletal muscle cells. Cells with glucosamine-induced insulin-resistance exhibited a reduced expression of GLUT4 and dysfunction in GLUT4 translocation, as well as increased activation of PTEN and increased cell apoptosis. Inhibition of PTEN or its upstream regulator, AMPK, protects glucosamine-induced insulin-resistant skeletal muscle cells from apoptosis.

Transmembrane tumor necrosis factor-alpha sensitizes adipocytes to insulin

Transmembrane TNF-α (tmTNF-α) acts both as a ligand, delivering 'forward signaling' via TNFR, and as a receptor, transducing 'reverse signaling'. The contradiction of available data regarding the effect of tmTNF-α on insulin resistance may be due to imbalance in both signals. Here, we demonstrated that high glucose-induced impairment of insulin-stimulated glucose uptake by 3T3-L1 adipocytes was concomitant with decreased tmTNF-α expression and increased soluble TNF-α (sTNF-α) secretion. However, when TACE was inhibited, preventing the conversion of tmTNF-α to sTNF-α, this insulin resistance was partially reversed, indicating a salutary role of tmTNF-α. Treatment of 3T3-L1 adipocytes with exogenous tmTNF-α promoted insulin-induced phosphorylation of IRS-1 and Akt, facilitated GLUT4 expression and membrane translocation, and increased glucose uptake while addition of sTNF-α resulted in the opposite effect. Furthermore, tmTNF-α downregulated the production of IL-6 and MCP-1 via NF-κB inactivation, as silencing of A20, an inhibitor for NF-κB, by siRNA, abolished this effect of tmTNF-α. However, tmTNF-α upregulated adiponectin expression through the PPAR-γ pathway, as inhibition of PPAR-γ by GW9662 abrogated both tmTNF-α-induced adiponectin transcription and glucose uptake. Our data suggest that tmTNF-α functions as an insulin sensitizer via forward signaling.

Insulin regulates monocyte trans-endothelial migration through surface expression of macrophage-1 antigen

During the pathogenesis of atherosclerosis, adhesion of monocytes to vascular endothelium and subsequent migration across the endothelium has been recognized as a key process in the chronic inflammatory response in atherosclerosis. As type 2 diabetes is closely associated with the pathogenesis of atherosclerosis, we investigated whether monocyte adhesion and migration were affected by insulin. We found that insulin activated Akt and induced subsequent migration in THP-1. However, glucose and insulin-like growth factor-1, which is a growth factor that is structurally similar to insulin, were not effective. Insulin-dependent migration of THP-1 was blocked by inhibition of PI3K or Akt and by silencing of Akt1. Insulin-dependent migration of bone marrow-derived monocytic cells (BDMCs) was attenuated by inhibition of PI3K and Akt. In addition, BDMCs from Akt1(-/-) mice showed defects in insulin-dependent migration. Stimulation of THP-1 with insulin caused adhesion with human vein endothelial cells (HUVECs) that was blocked by silencing of Akt1. However, stimulation of HUVECs did not cause adhesion with THP-1. Moreover, BDMCs from Akt1(-/-) mice showed defects in insulin-dependent adhesion with HUVECs. Insulin induced surface expression of Mac-1, and neutralization of Mac-1 blocked insulin-induced adhesion of THP-1 as well as BDMCs. Surface expression of Mac-1 was blocked in THP-1 with silenced Akt1, and in BDMCs isolated from mice lacking Akt1. Finally, trans-endothelial migration of THP-1 and BDMCs was blocked by Mac-1-neutralizing antibody, in THP-1 with silenced Akt1 and in BDMCs from Akt1(-/-) mice. These results suggest that insulin stimulates monocyte trans-endothelial migration through Akt-dependent surface expression of Mac-1, which may be part of the atherogenesis in type 2 diabetes.

Small chemicals with inhibitory effects on PtdIns(3,4,5)P3 binding of Btk PH domain

Phosphatidylinositol-3,4-5-triphosphates (PtdIns(3,4,5)P3) formed by phosphoinositide-3-kinase (PI3K) had been known as a signaling molecule that plays important roles in diverse cellular processes such as cell signaling, metabolism, cell differentiation, and apoptosis. PtdIns(3,4,5)P3 regulates diverse cellular processes by recruiting effector proteins to the specific cellular locations for correct functions. In this study, we reported the inhibitory effect of small chemicals on the interaction between PtdIns(3,4,5)P3-Btk PH domain. Small chemicals were synthesized based on structural similarity of PtdInsP head-groups, and tested the inhibitory effects in vitro via surface plasmon resonance (SPR). As a result, the chemical 8 showed highest inhibitory effect with 17μM of IC50 value. To elucidate diverse inhibitory effects of different small chemicals we employed in silico docking experiment using molecular modeling and simulation. The result of docking experiments showed chemical 8 has more hydrogen bonding with the residues in PtdIns(3,4,5)P3 binding site of Btk PH domain than others. Overall, our studies demonstrate the efficient approach to develop lipid binding inhibitors, and further we can use these chemicals to regulate effector proteins. In addition, our study would provide new insight that lipid binding domain may be the attractive therapeutic targets to treat severe human diseases.

Three SNPs in chromosome 11q23.3 are independently associated with systemic lupus erythematosus in Asians

Systemic lupus erythematosus (SLE) has a complex etiology and is affected by both genetic and environmental factors. Although more than 40 loci have shown robust association with SLE, the details of these loci, such as the independent contributors and the genes involved, are still unclear. In this study, we performed meta-analysis of two existing genome-wide association studies (GWASs) on Chinese Han populations from Hong Kong and Anhui, China, and followed the findings by further replication on three additional Chinese and Thailand cohorts with a total of 4254 cases and 6262 controls matched geographically and ethnically. We discovered multiple susceptibility variants for SLE in the 11q23.3 region, including variants in/near PHLDB1 (rs11603023, P(_combined) = 1.25E-08, OR = 1.20), DDX6 (rs638893, P(_combined) = 5.19E-07, OR = 1.22) and CXCR5 (rs10892301, P(_combined) = 2.51E-08, OR = 0.85). Genetic contributions from the newly identified variants were all independent of SNP rs4639966, whose association was reported from the previous GWAS. In addition, the three newly identified variants all showed independent association with the disease through modeling by both stepwise and conditional logistic regression. The presence of multiple independent variants in this region emphasizes its role in SLE susceptibility, and also hints the possibility that distinct biological mechanisms might be involved in the disease involving this genomic region.

Genome-wide association analyses suggest NELL1 influences adverse metabolic response to HCTZ in African Americans

Hydrochlorothiazide (HCTZ) is one of the most widely prescribed antihypertensive medications. Although it is well known that HCTZ is associated with hyperglycemia and hypertriglyceridemia, the mechanisms underlying these adverse effects are not well understood. We performed a genome-wide association study and meta-analysis of the change in fasting plasma glucose and triglycerides in response to HCTZ from two different clinical trials: the Pharmacogenomic Evaluation of Antihypertensive Responses and the Genetic Epidemiology of Responses to Antihypertensive studies. Two single-nucleotide polymorphisms (rs12279250 and rs4319515 (r²=0.73)), located at 11p15.1 in the NELL1 gene, achieved genome-wide significance for association with change in fasting plasma triglycerides in African Americans, whereby each variant allele was associated with a 28 mg dl⁻¹ increase in the change in triglycerides. NELL1 encodes a cytoplasmic protein that contains epidermal growth factor-like repeats and has been shown to represses adipogenic differentiation. These findings may represent a novel mechanism underlying HCTZ-induced adverse metabolic effects.

Loss of TDAG51 results in mature-onset obesity, hepatic steatosis, and insulin resistance by regulating lipogenesis

Regulation of energy metabolism is critical for the prevention of obesity, diabetes, and hepatic steatosis. Here, we report an important role for the pleckstrin homology-related domain family member, T-cell death-associated gene 51 (TDAG51), in the regulation of energy metabolism. TDAG51 expression was examined during adipocyte differentiation. Adipogenic potential of preadipocytes with knockdown or absence of TDAG51 was assessed. Weight gain, insulin sensitivity, metabolic rate, and liver lipid content were also compared between TDAG51-deficient (TDAG51(-/-)) and wild-type mice. In addition to its relatively high expression in liver, TDAG51 was also present in white adipose tissue (WAT). TDAG51 was downregulated during adipogenesis, and TDAG51(-/-) preadipocytes exhibited greater lipogenic potential. TDAG51(-/-) mice fed a chow diet exhibited greater body and WAT mass, had reduced energy expenditure, displayed mature-onset insulin resistance (IR), and were predisposed to hepatic steatosis. TDAG51(-/-) mice had increased hepatic triglycerides and SREBP-1 target gene expression. Furthermore, TDAG51 expression was inversely correlated with fatty liver in multiple mouse models of hepatic steatosis. Taken together, our findings suggest that TDAG51 is involved in energy homeostasis at least in part by regulating lipogenesis in liver and WAT, and hence, may constitute a novel therapeutic target for the treatment of obesity and IR.

Fine mapping of a region of chromosome 11q23.3 reveals independent locus associated with risk of glioma

Background

A single nucleotide polymorphism (SNP) at locus 11q23.3 (rs498872) in the near 5′-UTR of the PHLDB1 gene was recently implicated as a risk factor for gliomas in a genome-wide association study, and this involvement was confirmed in three additional studies.

Methodology/Principal Findings

To identify possible causal variants in the region, the authors genotyped 15 tagging SNPs in the 200 kb genomic region at 11q23.3 locus in a Chinese Han population-based case-control study with 983 cases and 1024 controls. We found evidence for an association between two independent loci (both the PHLDB1 and the ACRN1 genes) and a predisposition for gliomas. Among the multiple significant SNPs in the PHLDB1 gene region, the rs17749 SNP was the most significant [P = 1.31×10⁻⁶ in a recessive genetic model]. Additionally, two novel SNPs (rs2236661 and rs494560) that were independent of rs17749 were significantly associated with glioma risk in a recessive genetic model [P = 1.31×10⁻⁵ and P = 3.32×10⁻⁵, respectively]. The second novel locus was within the ARCN1 gene, and it was associated with a significantly reduced risk for glioma.

Conclusions/Significance

Our data strongly support PHLDB1 as a susceptibility gene for glioma, also shedding light on a new potentially candidate gene, ARCN1.

Greater insulin-mediated Akt phosphorylation concomitant with heterogeneous effects on phosphorylation of Akt substrates in soleus of calorie-restricted rats

Akt is a serine/threonine kinase that plays a key role in numerous cellular functions including metabolism, growth, protein synthesis, apoptosis, and cell proliferation. The most consistent and robust effect of moderate calorie restriction (CR; ~60% of ad libitum, AL, food consumption) on insulin signaling in rodent muscle has been enhanced insulin-induced phosphorylation of Akt (pAkt). However, there is limited knowledge regarding the mechanism for this enhancement and its consequences in predominantly slow-twitch muscle. Accordingly, in soleus muscle of 9-mo-old rats, we analyzed the effect of CR and insulin on important signaling events that are proximal to Akt activation including: pIR(Tyr1162/1163), pIRS1(Tyr), pIRS1(Ser312), IRS1-associated phosphatidylinositol 3-kinase activity, or pPTEN(Ser380). In addition, we analyzed the effect of CR and insulin on Akt substrates that have established or putative roles in glucose metabolism, cellular growth, maintenance of muscle structure, or protein synthesis including pGSK3α(Ser21), pGSK3β(Ser9), pTSC2(Ser939), pP70S6K(Thr412), pAS160(Thr642), and pFLNc(Ser2213). The current study demonstrated that the CR-induced increase in pAkt in isolated soleus muscles from 9-mo-old rats can occur without concomitant enhancement of several important insulin signaling events that are proximal to Akt activation. These results suggest that the greater pAkt in the soleus muscles from CR rats was attributable to an alternative mechanism. We also observed that the effects of CR were not uniform for phosphorylation of six insulin-regulated Akt substrates in the soleus. The differential response in phosphorylation by Akt substrates likely has important implications for explaining the complex effect of CR diverse cellular functions.

Identification of a role for CLASP2 in insulin action

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

Genetic causes of glioma: new leads in the labyrinth

PURPOSE OF REVIEW

A small percentage of gliomas are caused by inheritance in cancer syndromes but there is also a general familial aggregation of glioma. Recently, low penetrant genes associated with glioma risk have been identified.

RECENT FINDINGS

Seven independent chromosomal loci have robustly been associated with glioma risk: 5p15.33 (rs2736100, TERT), 8q24.21 (rs4295627, CCDC26), 9p21.3 (rs4977756, CDKN2A-CDKN2B), 20q13.33 (rs6010620, RTEL1), and 11q23.3 (rs498872, PHLDB1), and two loci at 7p11.2 (rs11979158 and rs2252586, EGFR). Several of these genes are obvious candidates in their role for chromosomal integrity and glioma progression. Moreover, all loci but the EGFR and CDKN2A genes display a pattern of association to certain glioma subtypes.

SUMMARY

The causes of glioma have until recently been unknown for most cases, partly due to lack of statistically powered studies enabling subclassification of glioma subtypes. The novel chromosomal loci associated with different glioma subtypes have provided us with an additional understanding of causes of glioma. All low penetrant genes contribute with a modest increased risk and cannot by themselves be used for risk prediction. Nevertheless, they could provide a tool to understand the underlying biology of glioma progression and to be used in future studies of gene-environment studies of specific glioma subtypes.

C2 domain-containing phosphoprotein CDP138 regulates GLUT4 insertion into the plasma membrane

The protein kinase B(β) (Akt2) pathway is known to mediate insulin-stimulated glucose transport through increasing glucose transporter GLUT4 translocation from intracellular stores to the plasma membrane (PM). Combining quantitative phosphoproteomics with RNAi-based functional analyses, we show that a previously uncharacterized 138 kDa C2 domain-containing phosphoprotein (CDP138) is a substrate for Akt2, and is required for optimal insulin-stimulated glucose transport, GLUT4 translocation, and fusion of GLUT4 vesicles with the PM in live adipocytes. The purified C2 domain is capable of binding Ca(2+) and lipid membranes. CDP138 mutants lacking the Ca(2+)-binding sites in the C2 domain or Akt2 phosphorylation site S197 inhibit insulin-stimulated GLUT4 insertion into the PM, a rate-limiting step of GLUT4 translocation. Interestingly, CDP138 is dynamically associated with the PM and GLUT4-containing vesicles in response to insulin stimulation. Together, these results suggest that CDP138 is a key molecule linking the Akt2 pathway to the regulation of GLUT4 vesicle-PM fusion.

Mapping insulin/GLUT4 circuitry

One of the most important metabolic actions of insulin is catalysing glucose uptake into skeletal muscle and adipose tissue. This is accomplished via activation of the phosphatidylinositol-3-kinase/Akt signalling pathway and subsequent translocation of GLUT4 from intracellular storage vesicles to the plasma membrane. As such, this represents an ideal system for studying the convergence of signal transduction and protein trafficking. The GLUT4 translocation process is complex, but can be dissected into at least four discrete trafficking steps. This raises the question as to which of these is the major regulated step in insulin-stimulated GLUT4 translocation. Numerous molecules have been reported to regulate GLUT4 trafficking. However, with the exception of TBC1D4, the molecular details of these distal signalling arms of the insulin signalling network and how they modify distinct steps of GLUT4 trafficking have not been established. We discuss the need to adopt a more global approach to expand and deepen our understanding of the molecular processes underpinning this system. Strategies that facilitate the generation of detailed models of the entire insulin signalling network will enable us to identify the critical nodes that control GLUT4 traffic and decipher emergent properties of the system that are not currently apparent.