Biology subjects

Chen, M.

Publications and source records attributed to Chen, M..

At least 541 records · Page 30Linked to original sources

bioRxiv2018

Boosting subdominant neutralizing antibody responses with a computationally designed epitope-focused immunogen

Throughout the last decades, vaccination has been key to prevent and eradicate infectious diseases. However, many pathogens (e.g. respiratory syncytial virus (RSV), influenza, dengue and others) have resisted vaccine development efforts, largely due to the failure to induce potent antibody responses targeting conserved epitopes. Deep profiling of human B-cells often reveals potent neutralizing antibodies that emerge from natural infection, but these specificities are generally subdominant (i.e., are present in low titers). A major challenge for next-generation vaccines is to overcome established immunodominance hierarchies and focus antibody responses on crucial neutralization epitopes. Here, we show that a computationally designed epitope-focused immunogen presenting a single RSV neutralization epitope elicits superior epitope-specific responses compared to the viral fusion protein. In addition, the epitope-focused immunogen efficiently boosts antibodies targeting the Palivizumab epitope, resulting in enhanced neutralization. Overall, we show that epitope-focused immunogens can boost subdominant neutralizing antibody responses in vivo and reshape established antibody hierarchies.

immunology↗

bioRxiv2018

Genome-wide selection footprints and deleterious variations in young Asian allotetraploid rapeseed

Brassica napus (AACC, 2n=38), is an important oilseed crop grown worldwide. However, little is known about the population evolution of this species, the genomic difference between its major genetic clusters, such as European and Asian rapeseed, and impacts of historical large-sale introgression events in this young tetraploid. In this study, we reported the de novo assembly of the genome sequences of an Asian rapeseed (B. napus), Ningyou 7 and its four progenitors and carried out de novo assembly-based comparison, pedigree and population analysis with other available genomic data from diverse European and Asian cultivars. Our results showed that Asian rapeseed originally derived from European rapeseed, but it had subsequently significantly diverged, with rapid genome differentiation after intensive local breeding selection. The first historical introgression of B. rapa dramatically broadened the allelic pool of Asian B. napus, but decreased their deleterious variations. The secondary historical introgression of European rapeseed (canola-quality) has reshaped Asian rapeseed into two groups, accompanied by an increase in genetic load. This study demonstrates distinctive genomic footprints by recent intra- and inter-species introgression events for local adaptation, and provide novel insights for understanding the rapid genome evolution of a young allopolyploid crop.

genomics↗

bioRxiv2018

Local Homogeneity of Tonotopic Organization in the Primary Auditory Cortex of Marmosets

Marmoset has emerged as a useful non-human primate species for studying the brain structure and function. Previous studies on the mouse primary auditory cortex (A1) showed that neurons with preferential frequency tuning responses are mixed within local cortical regions, despite a large-scale tonotopic organization. Here we found that frequency tuning properties of marmoset A1 neurons are highly uniform within local cortical regions. We first defined tonotopic map of A1 using intrinsic optical imaging, and then used in vivo two-photon calcium imaging of large neuronal populations to examine the tonotopic preference at the single-cell level. We found that tuning preferences of layer 2/3 neurons were highly homogeneous over hundreds of micrometers in both horizontal and vertical directions. Thus, marmoset A1 neurons are distributed in a tonotopic manner at both macro- and microscopic levels. Such organization is likely to be important for the organization of auditory circuits in the primate brain.

neuroscience↗

bioRxiv2018

Toxoplasma gondii ROP18 Inhibits Human Glioblastoma Cell Apoptosis through Mitochondrial Pathway by Targeting Host Cell P2X1

It is known that Toxoplasma gondii infection both initiates and inhibits host cell apoptosis through different proapoptotic signaling cascades, but the parasitic factors involved in these processes remain unclear. T. gondii virulence factor ROP18 has been reported to regulate host cell apoptosis, but the results of this regulation are few reported and contradictory. In this study, we found that immune or neuro cells infected by any one of the T. gondii strains (RH-type I, ME49-type II, and VEG-type III) showed a significantly lower apoptosis index than their uninfected controls when apoptosis was induced by staurosporine (STS). We further found that ROP18 of RH strain inhibited ATP induced apoptosis in human glioblastoma cells (SF268) with endogenous expression of human proapoptotic protein purinergic receptor 1 (P2X1), but had no effects on the immune cells of RAW264.7 and THP-1 without detectable P2X1 expression, which may indicate that ROP18s inhibition of host cell apoptosis is related to P2X1. Interestingly, we further identified that ROP18 (RH strain) interacted with P2X1, and over-expression of ROP18 in COS-7 cells inhibited the cell apoptosis mediated by P2X1. We also found that ROP18 of RH strain inhibited P2X1-mediated Ca2+ influx, translocation of cytochrome C from mitochondria to cytoplasm, and 1 ATP-triggered caspases activation. Collectively, these findings supported that ROP18 inhibited the host cell apoptosis through the intrinsic mitochondria pathway by targeting host cell P2X1, thereby suggesting a sensor role of the host proapoptotic protein P2X1 in this process\n\nAuthor summaryThe obligate intracellular protozoan Toxoplasma gondii has been shown to modulate cell apoptosis through different apoptotic pathways. However, the consequences are various and even contradictory, and the parasite effectors and the precise biological mechanisms remain unclear. Herein we showed that T. gondii of type I, II, and III strains could inhibit the apoptosis of neuro cells and immune cells. Toxoplasma gondii ROP18 (RH strain) inhibited apoptosis of human glioblastoma cell SF268 by targeting C terminal of host cell P2X1 protein, but not through proteasome-dependent degradation of P2X1.

molecular biology↗

bioRxiv2018

Balance of Mechanical Forces Drives Endothelial Gap Formation and May Facilitate Cancer and Immune-Cell Extravasation

The formation of gaps in the endothelium is a crucial process underlying both cancer and immune cell extravasation, contributing to the functioning of the immune system during infection, the unfavorable development of chronic inflammation and tumor metastasis. Here, we present a stochastic-mechanical multiscale model of an endothelial cell monolayer and show that the dynamic nature of the endothelium leads to spontaneous gap formation, even without intervention from the transmigrating cells. These gaps preferentially appear at the vertices between three endothelial cells, as opposed to the border between two cells. We quantify the frequency and lifetime of these gaps, and validate our predictions experimentally. Interestingly, we find experimentally that cancer cells also preferentially extravasate at vertices, even when they first arrest on borders. This suggests that extravasating cells, rather than initially signaling to the endothelium, might exploit the autonomously forming gaps in the endothelium to initiate transmigration.

bioengineering↗

bioRxiv2018

Heritability Estimation and Differential Analysis with Generalized Linear Mixed Models in Genomic Sequencing Studies

MotivationGenomic sequencing studies, including RNA sequencing and bisulfite sequencing studies, are becoming increasingly common and increasingly large. Large genomic sequencing studies open doors for accurate molecular trait heritability estimation and powerful differential analysis. Heritability estimation and differential analysis in sequencing studies requires the development of statistical methods that can properly account for the count nature of the sequencing data and that are computationally efficient for large data sets.\n\nResultsHere, we develop such a method, PQLseq (Penalized Quasi-Likelihood for sequencing count data), to enable effective and efficient heritability estimation and differential analysis using the generalized linear mixed model framework. With extensive simulations and comparisons to previous methods, we show that PQLseq is the only method currently available that can produce unbiased heritability estimates for sequencing count data. In addition, we show that PQLseq is well suited for differential analysis in large sequencing studies, providing calibrated type I error control and more power compared to the standard linear mixed model methods. Finally, we apply PQLseq to perform gene expression heritability estimation and differential expression analysis in a large RNA sequencing study in the Hutterites.\n\nAvailability and implementationPQLseq is implemented as an R package with source code freely available at www.xzlab.org/software.html and https://cran.r-project.org/web/packages/PQLseq/index.html.\n\nContactXZ (xzhousph@umich.edu)\n\nSupplementary informationSupplementary data are available online.

genomics↗

bioRxiv2018

Seed Genome Hypomethylated Regions Are Enriched In Transcription Factor Genes

The precise mechanisms that control gene activity during seed development remain largely unknown. Previously, we showed that several genes essential for seed development, including those encoding storage proteins, fatty acid biosynthesis enzymes, and transcriptional regulators, such as ABI3 and FUS3, are located within hypomethylated regions of the soybean genome. These hypomethylated regions are similar to the DNA methylation valleys (DMVs), or canyons, found in mammalian cells. Here, we address the question of the extent to which DMVs are present within seed genomes, and what role they might play in seed development. We scanned soybean and Arabidopsis seed genomes from post-fertilization through dormancy and germination for regions that contain < 5% or < 0.4% bulk methylation in CG-, CHG-, and CHH-contexts over all developmental stages. We found that DMVs represent extensive portions of seed genomes, range in size from 5 to 76 kb, are scattered throughout all chromosomes, and are hypomethylated throughout the plant life cycle. Significantly, DMVs are enriched greatly in transcription factor genes, and other developmental genes, that play critical roles in seed formation. Many DMV genes are regulated with respect to seed stage, region, and tissue - and contain H3K4me3, H3K27me3, or bivalent marks that fluctuate during development. Our results indicate that DMVs are a unique regulatory feature of both plant and animal genomes, and that a large number of seed genes are regulated in the absence of methylation changes during development - probably by the action of specific transcription factors and epigenetic events at the chromatin level.\n\nSignificanceWe scanned soybean and Arabidopsis seed genomes for hypomethylated regions, or DNA Methylation Valleys (DMVs), present in mammalian cells. A significant fraction of seed genomes contain DMV regions that have < 5% bulk DNA methylation, or, in many cases, no detectable DNA methylation. Methylation levels of seed DMVs do not vary detectably during seed development with respect to time, region, and tissue, and are present prior to fertilization. Seed DMVs are enriched in transcription factor genes and other genes critical for seed development, and are also decorated with histone marks that fluctuate with developmental stage, resembling in significant ways their animal counterparts. We conclude that many genes playing important roles in seed formation are regulated in the absence of detectable DNA methylation events, and suggest that selective action of transcriptional activators and repressors, as well as chromatin epigenetic events play important roles in making a seed - particularly embryo formation.

plant biology↗

bioRxiv2018

Identification and characterization of cherry (Cerasus pseudocerasus G. Don) genes in response to parthenocarpy induced by GA3 through transcriptome analysis

Fruit set after successful pollination is a key process in the production of sweet cherries, but low fruit rate is the main problem for crop production in sweet cherries. Gibberellin treatment can directly induce parthenogenesis without pollination; therefore, gibberellin treatment is a very important method to improve the fruit setting rate of sweet cherries. Exogenous gibberellin can satisfy the hormone requirement during fruit growth and development. Some related studies have mainly focused on physiological aspects, such as breeding, branching, fertilization, etc., and the molecular mechanism is not clear. In this study, we analyzed the transcriptome of Meizao sweet cherry fruit treated with gibberellin during the anthesis and hard-core period to determine the genes associated with parthenocarpic fruit set. A total of 765 and 186 differentially expressed genes (DEGs) were found at anthesis and the hard-core stage after gibberellin 3 (GA3) treatment, respectively. The differentially expressed genes between the control and GA3 treatment showed that the GA3 response mainly included parthenocarpic fruit set and cell division. Exogenous gibberellin stimulated sweet cherry parthenocarpy and enlargement, which were verified by qRT-PCR results of related genes and the parthenocarpic fruit set and fruit size. Based on our research and previous studies on Arabidopsis thaliana, we identified the key genes associated with parthenocarpic fruit set and cell division. Briefly, we found patterns in the sweet cherry fruit setting-related DEGs, especially those associated with hormone balance, cytoskeleton formation and cell wall modification. Overall, the result provides a possible molecular mechanism regulating parthenocarpic fruit set, which is important for basic research and industrial development of sweet cherries.\n\nHighlightcherry genes in response to parthenocarpy and promote to fruit setting induced by GA3.

molecular biology↗

bioRxiv2018

Tripal Developer Toolkit

Tripal is an open-source biological community database construction toolkit utilizing the content management system Drupal. Tripal is used to make biological, genetic and genomic data more discoverable, shareable, searchable, and standardized. As funding for community level genomics databases declines, Tripals open source codebase provides a means for sites to be built and maintained with a minimal investment in staff and new development. Tripal is ultimately as strong as the community of sites and developers that use it. We present a set of developer tools that will make building and maintaining Tripal 3 sites easier for new and returning users. These tools break down barriers to entry such as setting up developer and testing environments, acquiring and loading test datasets, working with controlled vocabulary terms, and writing new Drupal classes.

bioinformatics↗

bioRxiv2018

Long noncoding RNA ANRIL supports proliferation of adult T-cell leukemia cells through cooperation with EZH2

Adult T-cell leukemia (ATL) is a highly aggressive T-cell malignancy induced by human T-cell leukemia virus type 1 (HTLV-1) infection. Long noncoding RNA (lncRNA) plays a critical role in the development and progression of multiple human cancers. However, the function of lncRNA on HTLV-1-induced oncogenesis has not been elucidated. In the present study, we show that the expression of the lncRNA ANRIL was elevated in HTLV-1 infected cell lines and clinical ATL samples. E2F1 induced ANRIL transcription by enhancing its promoter activity. Knocking down of ANRIL in ATL cells repressed cellular proliferation and increased apoptosis in vitro and in vivo. As a mechanism for these actions, we found that ANRIL targeted EZH2, and activated the NF-{kappa}B pathway in ATL cells. This activation was independent of the histone methyltransferase (HMT) activity of EZH2, but required the formation of an ANRIL/EZH2/p65 ternary complex. Chromatin immunoprecipitation assay revealed that ANRIL/EZH2 enhanced p65 DNA binding capability. In addition, we observed that ANRIL/EZH2 complex repressed p21/CDKN1A transcription through H3K27 trimethylation of the p21/CDKN1A promoter. Taken together, our results implicate that lncRNA ANRIL, by cooperating with EZH2, supports the proliferation of HTLV-1 infected cells, which is thought to be critical for oncogenesis.\n\nIMPORTANCEHuman T-cell leukemia virus type 1 (HTLV-1) is the pathogen that causes adult T-cell leukemia (ATL), which is a unique malignancy of CD4+ T cells. A role for long noncoding RNA (lncRNA) in HTLV-1-mediated cellular transformation has not been described. In this study, we demonstrated that lncRNA ANRIL was important for maintaining proliferation of ATL cells in vitro and in vivo. ANRIL was shown to activate NF-{kappa}B signaling through forming a ternary complex with EZH2 and p65. Further, epigenetic inactivation of p21/CDKN1A was involved in the oncogenic function of ANRIL. To the best of our knowledge, this is the first study to address the regulatory role of the lncRNA ANRIL in ATL and provides an important clue to prevent or treat HTLV-1 associated human diseases.

cancer biology↗

bioRxiv2018

New interfaces on MiD51 for Drp1 recruitment and regulation

Mitochondrial fission is facilitated by dynamin-related protein Drp1 and a variety of its receptors. However, the molecular mechanism of how Drp1 is recruited to the mitochondrial surface by receptors MiD49 and MiD51 remains elusive. Here, we showed that the interaction between Drp1 and MiD51 is regulated by GTP binding and depends on the polymerization of Drp1. We identified two regions on MiD51 that directly bind to Drp1, and found that dimerization of MiD51 via an intermolecular disulfide bond between C452 residues is required for MiD51 to directly interact with Drp1. Our Results have suggested a multi-faceted regulatory mechanism for the interaction between Drp1 and MiD51 that illustrates the potentially complicated and tight regulation of mitochondrial fission.

biophysics↗

bioRxiv2018

Discordant expression profile between RNA and protein for the genes involved in immune response network in adenovirus type 2 infected cells

Alternation of cellular genes expressions during Adenovirus type 2 (Ad2) infection in IMR-90 cells was studied using paired-end sequencing and stable isotope labeling of amino acids in cell culture mass spectrometric analysis (SILAC-MS). At transcriptional level, cellular genes involved in different pathways revealed distinct expression profiles. At early phase, the genes involved in regulation of cellular immune response, cellular signaling and cell growth control were among the most deregulated. Later follows, in an orderly fashion, genes involved in cell cycle control, DNA replication and further on genes engaged in RNA processing and protein translation. Comparison of cellular gene expression at transcriptional and posttranscriptional levels revealed low correlation. Here we highlight the genes which expose opposite expression profiles with an emphasis on key factors that play important roles in cellular immune pathways including NF{kappa}B, JAK/STAT, caspases and MAVS. Transcription of many of these genes was transiently induced early, but became down-regulated in the late phase. In contrast, their expressions at protein level were up-regulated early and so sustained until late phase of infection. Suppression at the transcriptional level and enhancement at the protein level of immune response genes most likely illustrate counteractions between Ad2 and its host cell.\n\nImportanceOur paper comprises a state of the art quality transcriptomics data set unravelling the alterations in gene expression that take place during different phases of an adenovirus infection. The information allows us to draw conclusion about the cellular pathways that are perturbed by the virus. The data set also provides an important resource for scientists in general for future studies on mechanisms behind host/virus interactions in efforts to design tools for combatting virus infections.\n\nMoreover, our paper includes novel proteomics information unravelling an unexpected role of post transcriptional events in cellular gene expression, demonstrating that the current picture of the adenovirus replication cycle is simplified.

microbiology↗

bioRxiv2018

Insufficient fumarase contributes to generating reactive oxygen species in Dahl salt sensitive rats

Dahl SS rats exhibit greater levels of renal medullary oxidative stress and lower levels of fumarase activities. Fumarase insufficiencies can increase reactive oxygen species (ROS), the mechanism of which, however, is not clear. A proteomic analysis indicated fumarase knockdown in HK-2 cells resulted in changes in the expression or activity of NADPH oxidase, mitochondrial respiratory chain complex I and III, ATP synthase subunits, and -oxoglutarate dehydrogenase, all of which are sites of ROS formation. Meantime, the activities of key antioxidant enzymes such as G6PD, 6PGD, GR, GPx and GST increased significantly too. The apparent activation of antioxidant defense appeared insufficient as glutathione precursors, glutathione and GSH/GSSG ratio were decreased. SS rats exhibited changes in redox metabolism similar to HK-2 cells with fumarase knockdown. Supplementation with fumarate and malate, the substrate and product of fumarase, increased and decreased, respectively, blood pressure and the levels of H2O2 and MDA in kidney tissues of SS rats. These results indicate fumarase insufficiencies cause a wide range of changes at several sites of ROS production and antioxidant mechanisms.

molecular biology↗

bioRxiv2018

Functional repair after ischemic injury through high efficiency in situ astrocyte-to-neuron conversion

Mammalian brains have largely lost internal neural regeneration capability except for a few discrete neurogenic niches. After brain injury, the cerebral cortex is especially difficult to repair due to its extremely low rate of adult neurogenesis. Previous studies have converted glial cells into neurons, but the total number of neurons generated is rather limited, casting doubt about its therapeutic potential. Here, we demonstrate that high-efficiency neuroregeneration can be achieved in adult mammalian brains by making use of an engineered AAV Cre-FLEX system to convert a large number of reactive astrocytes into functional neurons. Specifically, using a combination of GFAP::Cre and FLEX-NeuroD1 AAV system, we were able to regenerate enough new neurons from astrocytes to cover about 40% of the neurons lost from an ischemic injury (400 NeuN+ new neurons/mm2), compared to previously reported an average of <1% of cortical neurons (2-8 NeuN+ neurons/mm2) in an ischemic-injured adult mammalian cortex. Importantly, this in situ astrocyte-to-neuron conversion process also improved survival of injured pre-existing neurons, (additional 400 neurons/mm2), leading to a repaired motor cortex with layered cortical structures. Moreover, NeuroD1-converted neurons not only form functional neural circuits but also rescue motor and memory deficits after ischemic injury. Our results establish the proof-of-principle that a highly efficient in situ astrocyte-to-neuron conversion approach provides a novel treatment for neurological disorders that are in need of new neurons.

neuroscience↗

bioRxiv2018

Characterisation of carried and invasive Neisseria meningitidis isolates in Shanghai, China from 1950 to 2016: implications for serogroup B vaccine implementation

BackgroundSerogroup B invasive meningococcal disease (IMD) is increasing in China, little is known however, about these meningococci. This study characterises a collection of isolates associated with IMD and carriage in Shanghai and assesses current vaccine strategies.\n\nMethodsIMD epidemiological data in Shanghai from 1950-2016 were obtained from the National Notifiable Diseases Registry System, with 460 isolates collected for analysis including, 169 from IMD and 291 from carriage. Serogroup B meningococcal (MenB) vaccine coverage was evaluated using Bexsero(R) Antigen Sequence Type (BAST).\n\nResultsSeven IMD epidemic periods have been observed in Shanghai since 1950, with incidence peaking from February to April. Analyses were divided according to the period of meningococcal polysaccharide vaccine (MPV) introduction: (i) pre-MPV-A, 1965-1980; (ii) post-MPV-A, 1981-2008; and (iii) post-MPV-A+C, 2009-2016. IMD incidence decreased from 55.4/100,000 to 0.71 then to 0.02, and corresponded with shifts from serogroup A ST-5 complex (MenA:cc5) to MenC:cc4821 then MenB:cc4821. MenB IMD became predominant (63.2%) in the post-MPV-A+C period, of which 50% were caused by cc4821, with the highest incidence in infants (0.45/100,000) and a case-fatality rate of 9.5%. IMD was positively correlated with carriage rates. Data indicate that fewer than 25% of MenB isolates in the post-MPV-A+C period may be covered by the vaccines Bexsero(R), Trumenba(R), or a PorA-based vaccine, NonaMen.\n\nConclusionsA unique IMD epidemiology is found in China, changing periodically from hyperepidemic to low-level endemic disease. MenB IMD now dominates in Shanghai, with isolates harbouring diverse antigenic variants potentially beyond coverage with licenced OMV- and protein-based MenB vaccines.\n\nSummaryMeningococcal disease in Shanghai, China is described and current vaccine approaches evaluated. Since 1950, MenA:cc5 shifted to MenC:cc4821 then MenB:cc4821, with MenB dominating since 2009. Distinct antigens potentially beyond coverage with licensed OMV- and protein-based MenB vaccines were found.

epidemiology↗

bioRxiv2018

Single-step Enzymatic Glycoengineering for the Construction of Antibody-cell Conjugates

Employing live cells as therapeutics is a direction of future drug discovery. An easy and robust method to modify the surfaces of cells directly to incorporate novel functionalities is highly desirable. However, many current methods for cell-surface engineering interfere with cells endogenous properties. Here we report an enzymatic approach that enables the transfer of biomacromolecules, such as a full length IgG antibody, to the glycocalyx on the surfaces of live cells when the antibody is conjugated to the enzymes natural donor substrate GDP-fucose. This method is fast and biocompatible with little interference to cells endogenous functions. We applied this method to construct two antibody-cell conjugates (ACCs) using different immune cells, and the modified cells exhibited specific tumor targeting and resistance to inhibitory signals produced by tumor cells, respectively. Remarkably, Herceptin-NK-92MI conjugates exhibits enhanced activities to induce the lysis of HER2+ cancer cells both ex vivo and in a murine tumor model, indicating its potential for further development as a clinical candidate.

bioengineering↗

bioRxiv2018

Stimulus-responsive self-assembly of enzymatic fractal structures by computational design

Fractal topologies, which are statistically self-similar over multiple length scales, are pervasive in nature. The recurrence of patterns at increasing length scales in fractal-shaped branched objects, e.g., trees, lungs, and sponges, results in high effective surface areas, and provides key functional advantages, e.g., for molecular trapping and exchange. Mimicking these topologies in designed protein-based assemblies will provide access to novel classes of functional biomaterials for wide ranging applications. Here, we describe a modular, multi-scale computational design method for the reversible self-assembly of proteins into tunable supramolecular fractal-like topologies in response to phosphorylation. Computationally-guided atomic-resolution modeling of fusions of symmetric, oligomeric proteins with Src homology 2 (SH2) binding domain and its phosphorylatable ligand peptide was used to design iterative branching leading to fractal-like assembly formation by enzymes of the atrazine degradation pathway. Structural characterization using various microscopy techniques and Cryo-electron tomography revealed a variety of dendritic, hyperbranched, and sponge-like topologies which are self-similar over three decades ([~]10nm-10m) of length scale, in agreement with models from multi-scale computational simulations. We demonstrate control over mesoscale topology (by linker design), formation dynamics, and functional enhancements due to dynamic multi-component assemblies constructed with three atrazine degradation pathway enzymes. The described design method should enable the construction of a variety of novel, spatiotemporally responsive catalytic biomaterials featuring fractal topologies.

biophysics↗

bioRxiv2018

The Specificity of IQGAP1 Toward the PI3K-Akt Pathway is Dependent on the IQ3 motif

Epidermal growth factor receptor (EGFR) and its downstream phosphatidylinositol 3-kinase (PI3K) pathway are commonly deregulated in many cancers including head and neck cancer (HNC). Recently, we have shown that the IQ motif-containing GTPase-activating protein 1 (IQGAP1) provides a molecular platform to scaffold all the components from the PI3K-Akt pathway and results in the sequential generation of phosphatidylinositol-3,4,5-triphosphate (PI3,4,5P3). This makes the IQGAP1-PI3K scaffold a promising therapeutic target. In addition to the PI3K-Akt pathway, IQGAP1 also scaffolds the Ras-ERK pathway. To identify an IQGAP1 mutant that specifically loses IQGAP1-PI3K signaling but not other functions, we have focused on the IQ3 motif since this region binds with both the PIPK1 and PI3K enzymes and a short peptide derived from this sequence blocks binding and PI3K signaling. An IQ3 deletion mutant ({Delta}IQ3) in IQGAP1 was functionally compared with wild-type (WT) IQGAP1. We found that the IQ3 domain specifically mediates the PI3K-Akt pathway but does not regulate the Ras-ERK pathway. The IQ3 deletion mutant lost interactions with PI3K-Akt components but retained its binding of ERK pathway components and cell surface receptors, EGFR and integrins. In addition, the IQ3 deletion mutant lost regulation of cell migration. Consistently, the IQ3 motif derived peptide blocked Akt activation and led to the blockage of invasion mediated by EGFR organized into an integrin complex by syndecan-4. Taken together, this work has defined the IQGAP1 IQ3 motif as a specific target sequence for the scaffolding of the PI3K-AKT pathway.

cell biology↗