Cloning and characterization of a novel GRP78-binding protein in the rat brain

GRP75 as a functional element of cholix transcytosis

Cholix (Chx) is secreted by non-pandemic strains of Vibrio cholerae in the intestinal lumen. For this exotoxin to induce cell death in non-polarized cells in the intestinal lamina propria, it must traverse the epithelium in the fully intact form. We identified host cell elements in polarized enterocytes associated with Chx endocytosis and apical to basal (A→B) vesicular transcytosis. This pathway overcomes endogenous mechanisms of apical vesicle recycling and lysosomal targeting by interacting with several host cell proteins that include the 75 kDa glucose-regulated protein (GRP75). Apical endocytosis of Chx appears to involve the single membrane spanning protein TMEM132A, and interaction with furin before it engages GRP75 in apical vesicular structures. Sorting within these apical vesicles results in Chx being trafficked to the basal region of cells in association with the Lectin, Mannose Binding 1 protein LMAN1. In this location, Chx interacts with the basement membrane-specific heparan sulfate proteoglycan perlecan in recycling endosomes prior to its release from this basal vesicular compartment to enter the underlying lamina propria. While the furin and LMAN1 elements of this Chx transcytosis pathway undergo cellular redistribution that are reflective of the polarity shifts noted for coatamer complexes COPI and COPII, GRP75 and perlecan fail to show these dramatic rearrangements. Together, these data define essential steps in the A→B transcytosis pathway accessed by Chx to reach the intestinal lamina propria where it can engage and intoxicate certain non-polarized cells.

TMEM132A ensures mouse caudal neural tube closure and regulates integrin-based mesodermal migration

Coordinated migration of the mesoderm is essential for accurate organization of the body plan during embryogenesis. However, little is known about how mesoderm migration influences posterior neural tube closure in mammals. Here, we show that spinal neural tube closure and lateral migration of the caudal paraxial mesoderm depend on transmembrane protein 132A (TMEM132A), a single-pass type I transmembrane protein, the function of which is not fully understood. Our study in Tmem132a-null mice and cell models demonstrates that TMEM132A regulates several integrins and downstream integrin pathway activation as well as cell migration behaviors. Our data also implicates mesoderm migration in elevation of the caudal neural folds and successful closure of the caudal neural tube. These results suggest a requirement for paraxial mesodermal cell migration during spinal neural tube closure, disruption of which may lead to spina bifida.

Differential expression of the Tmem132 family genes in the developing mouse nervous system

The family of novel transmembrane proteins (TMEM) 132 have been associated with multiple neurological disorders and cancers in humans, but have hardly been studied in vivo. Here we report the expression patterns of the five Tmem132 genes (a, b, c, d and e) in developing mouse nervous system with RNA in situ hybridization in wholemount embryos and tissue sections. Our results reveal differential and partially overlapping expression of multiple Tmem132 family members in both the central and peripheral nervous system, suggesting potential partial redundancy among them.

Identification of novel potential biomarkers in infantile hemangioma via weighted gene co-expression network analysis

Background

Infantile hemangioma (IH) is the most common benign tumor in children and is characterized by endothelial cells proliferation and angiogenesis. Some hub genes may play a critical role in angiogenesis. This study aimed to identify the hub genes and analyze their biological functions in IH.

Methods

Differentially expressed genes (DEGs) in hemangioma tissues, regardless of different stages, were identified by microarray analysis. The hub genes were selected through integrated weighted gene co-expression network analysis (WGCNA) and protein–protein interaction (PPI) network. Subsequently, detailed bioinformatics analysis of the hub genes was performed by gene set enrichment analysis (GSEA). Finally, quantitative real-time polymerase chain reaction (qRT-PCR) analysis was conducted to validate the hub genes expression in hemangioma-derived endothelial cells (HemECs) and human umbilical vein endothelial cells (HUVECs).

Results

In total, 1115 DEGs were identified between the hemangiomas and normal samples, including 754 upregulated genes and 361 downregulated genes. Two co-expression modules were identified by WGCNA and green module eigengenes were highly correlated with hemangioma (correlation coefficient = 0.87). Using module membership (MM) > 0.8 and gene significance (GS) > 0.8 as the cut-off criteria, 108 candidate genes were selected and put into the PPI network, and three most correlated genes (APLN, APLNR, TMEM132A) were identified as the hub genes. GSEA predicted that the hub genes would regulate endothelial cell proliferation and angiogenesis. The differential expression of these genes was validated by qRT-PCR.

Conclusions

This research suggested that the identified hub genes may be associated with the angiogenesis of IH. These genes may improve our understanding of the mechanism of IH and represent potential anti-angiogenesis therapeutic targets for IH.

Finding New Ways How to Control BACE1

Recently, all applications of BACE1 inhibitors failed as therapeutical targets for Alzheimer´s disease (AD) due to severe side effects. Therefore, alternative ways for treatment development are a hot research topic. The present analysis investigates BACE1 protein-protein interaction networks and attempts to solve the absence of complete knowledge about pathways involving BACE1. A bioinformatics analysis matched the functions of the non-substrate interaction network with Voltage-gated potassium channels, which also appear as top priority protein nodes. Targeting BACE1 interactions with PS1 and GGA-s, blocking of BACE1 access to APP by BRI3 and RTN-s, activation of Wnt signaling and upregulation of β-catenin, and brain delivery of the extracellular domain of p75^NTR, are the main alternatives to the use of BACE 1 inhibitors highlighted by the analysis. The pathway enrichment analysis also emphasized substrates and substrate candidates with essential biological functions, which cleavage must remain controlled. They include ephrin receptors, ROBO1, ROBO2, CNTN-s, CASPR-s, CD147, CypB, TTR, APLP1/APLP2, NRXN-s, and PTPR-s. The analysis of the interaction subnetwork of BACE1 functionally related to inflammation identified a connection to three cardiomyopathies, which supports the hypothesis of the common molecular mechanisms with AD. A lot of potential shows the regulation of BACE1 activity through post-translational modifications. The interaction network of BACE1 and its phosphorylation enzyme CSNK1D functionally match the Circadian clock, p53, and Hedgehog signaling pathways. The regulation of BACE1 glycosylation could be achieved through N-acetylglucosamine transferases, α-(1→6)-fucosyltransferase, β-galactoside α-(2→6)-sialyltransferases, galactosyltransferases, and mannosidases suggested by the interaction network analysis of BACE1-MGAT3. The present analysis proposes possibilities for the alternative control of AD pathology.

TMEM132A, a Novel Wnt Signaling Pathway Regulator Through Wntless (WLS) Interaction

Wnt signaling pathway plays indispensable roles in embryonic development and adult tissue homeostasis. However, the regulatory mechanisms involved in Wnt ligand trafficking within and secretion from the signal sending cells is still relatively uncharacterized. Here, we discover a novel regulator of Wnt signaling pathway called transmembrane protein 132A (TMEM132A). Our evidence shows a physical and functional interaction of TMEM132A with the Wnt ligand transporting protein Wntless (WLS). We show that TMEM132A stabilizes Wnt ligand, enhances WLS–Wnt ligand interaction, and activates the Wnt signaling pathway. Our results shed new light on the cellular mechanism underlying the fundamental aspect of WNT secretion from Wnt signal sending cells.

Genetic loci for alcohol-related life events and substance-induced affective symptoms: indexing the "dark side" of addiction

A limited number of genetic variants have been identified in traditional GWAS as risk or protective factors for alcohol use disorders (AUD) and related phenotypes. We herein report whole-genome association and rare-variant analyses on AUD traits in American Indians (AI) and European Americans (EA). We evaluated 742 AIs and 1711 EAs using low-coverage whole-genome sequencing. Phenotypes included: (1) a metric based on the occurrence of 36 alcohol-related life events that reflect AUD severity; (2) two alcohol-induced affective symptoms that accompany severe AUDs. We identified two new loci for alcohol-related life events with converging evidence from both cohorts: rare variants of K_2P channel gene KCNK2, and rare missense and splice-site variants in pro-inflammatory mediator gene PDE4C. A NAF1-FSTL5 intergenic variant and an FSTL5 variant were respectively associated with alcohol-related life events in AI and EA. PRKG2 of serine/threonine protein kinase family, and rare variants in interleukin subunit gene EBI3 (IL-27B) were uniquely associated with alcohol-induced affective symptoms in AI. LncRNA LINC02347 on 12q24.32 was uniquely associated with alcohol-induced depression in EA. The top GWAS findings were primarily rare/low-frequency variants in AI, and common variants in EA. Adrenal gland was the most enriched in tissue-specific gene expression analysis for alcohol-related life events, and nucleus accumbens was the most enriched for alcohol-induced affective states in AI. Prefrontal cortex was the most enriched in EA for both traits. These studies suggest that whole-genome sequencing can identify novel, especially uncommon, variants associated with severe AUD phenotypes although the findings may be population specific.

TMEM132: an ancient architecture of cohesin and immunoglobulin domains define a new family of neural adhesion molecules

Summary

The molecular functions of TMEM132 genes remain poorly understood and under-investigated despite their mutations associated with non-syndromic hearing loss, panic disorder and cancer. Here we show the full domain architecture of human TMEM132 family proteins solved using in-depth sequence and structural analysis. We reveal them to be five previously unappreciated cell adhesion molecules whose domain architecture has an early holozoan origin prior to the emergence of choanoflagellates and metazoa. The extra-cellular portions of TMEM132 proteins contain five conserved domains including three tandem immunoglobulin domains, and a cohesin domain homologue, the first such domain found in animals. These findings strongly predict a cellular adhesion function for TMEM132 family, connecting the extracellular medium with the intracellular actin cytoskeleton.

Contact

luis.sanchez-pulido@igmm.ed.ac.uk.

Supplementary information

Supplementary data are available at Bioinformatics online.

Genome-wide association analyses of sleep disturbance traits identify new loci and highlight shared genetics with neuropsychiatric and metabolic traits

Chronic sleep disturbances, associated with cardiometabolic diseases, psychiatric disorders and all-cause mortality, affect 25-30% of adults worldwide. Although environmental factors contribute substantially to self-reported habitual sleep duration and disruption, these traits are heritable and identification of the genes involved should improve understanding of sleep, mechanisms linking sleep to disease and development of new therapies. We report single- and multiple-trait genome-wide association analyses of self-reported sleep duration, insomnia symptoms and excessive daytime sleepiness in the UK Biobank (n = 112,586). We discover loci associated with insomnia symptoms (near MEIS1, TMEM132E, CYCL1 and TGFBI in females and WDR27 in males), excessive daytime sleepiness (near AR-OPHN1) and a composite sleep trait (near PATJ (INADL) and HCRTR2) and replicate a locus associated with sleep duration (at PAX8). We also observe genetic correlation between longer sleep duration and schizophrenia risk (rg = 0.29, P = 1.90 × 10-13) and between increased levels of excessive daytime sleepiness and increased measures for adiposity traits (body mass index (BMI): rg = 0.20, P = 3.12 × 10-9; waist circumference: rg = 0.20, P = 2.12 × 10-7).

Endoplasmic Reticulum Stress-Related Genes in Yellow Catfish Pelteobagrus fulvidraco: Molecular Characterization, Tissue Expression, and Expression Responses to Dietary Copper Deficiency and Excess

Two endoplasmic reticulum (ER) molecular chaperones [glucose-regulated protein 78 (grp78) and calreticulin (crt)] and three ER stress sensors [PKR-like ER kinase (perk), inositol requiring enzyme (ire)-1α, and activating transcription factor (atf)-6α] cDNAs were first characterized from yellow catfish, Pelteobagrus fulvidraco. The predicted amino acid sequences for the yellow catfish grp78, crt, perk, ire-1α, and atf-6α revealed that the proteins contained all of the structural features that were characteristic of the five genes in other species, including the KDEL motif, signal peptide, sensor domain, and effector domain. mRNAs of the five genes mentioned above were expressed in various tissues, but their mRNA levels varied among tissues. Dietary Cu excess, but not Cu deficiency, activated the chaperones (grp78 and crt) and folding sensors in ER, and the UPR signaling pathways (i.e., perk–eif2α and the ire1–xbp1) in a tissue-specific manner. For the first time, our study cloned grp78, crt, perk, ire-1α, and atf-6α genes in yellow catfish and demonstrated their differential expression among tissues. Moreover, the present study also indicated differential regulation of these ER stress–related genes by dietary Cu deficiency and excess, which will be beneficial for us to evaluate effects of dietary Cu levels in fish at the molecular level, based on the upstream pathway of lipid metabolism (the ER) and thus provide novel insights regarding the nutrition of Cu in fish.

Reference genome of wild goat (capra aegagrus) and sequencing of goat breeds provide insight into genic basis of goat domestication

BACKGROUND

Domestic goats (Capra hircus) have been selected to play an essential role in agricultural production systems, since being domesticated from their wild progenitor, bezoar (Capra aegagrus). A detailed understanding of the genetic consequences imparted by the domestication process remains a key goal of evolutionary genomics.

RESULTS

We constructed the reference genome of bezoar and sequenced representative breeds of domestic goats to search for genomic changes that likely have accompanied goat domestication and breed formation. Thirteen copy number variation genes associated with coat color were identified in domestic goats, among which ASIP gene duplication contributes to the generation of light coat-color phenotype in domestic goats. Analysis of rapidly evolving genes identified genic changes underlying behavior-related traits, immune response and production-related traits.

CONCLUSION

Based on the comparison studies of copy number variation genes and rapidly evolving genes between wild and domestic goat, our findings and methodology shed light on the genetic mechanism of animal domestication and will facilitate future goat breeding.

Transcriptional and post-transcriptional regulation of transmembrane protein 132A

Transmembrane protein 132A (TMEM132A) was first isolated from rat brain using PCR-selected cDNA subtraction, and it was found to be predominantly expressed in the brain. However, the transcriptional regulation of the TMEM132A gene has not been fully characterized. In this study, we characterized the promoter activity of the 880-bp region upstream of the mouse TMEM132A, identifying several putative sites recognized by transcription factors, which are highly conserved between the mouse and human TMEM132A genes. Using four different mouse cell lines (Neuro2a, NSC-34, NIH3T3, and Raw264.7), we first evaluated the intrinsic levels of TMEM132A mRNA and protein expression. Interestingly, TMEM132A mRNA was expressed in all four cell lines, whereas the protein was negligible in Raw264.7 cells even by transfection of TMEM132A gene. Then, we analyzed the TMEM132A promoter activity using serial deleted constructs, finding it was nearly same pattern in all four cell lines. A mutational analysis of the TMEM132A promoter identified a critical region for its activation just upstream of the transcriptional start site. Finally, we investigated the levels of TMEM132A mRNA and protein after exposure to five different neurotoxic stimuli, including thapsigargin, tunicamycin, serum starvation, homocysteine, and hydrogen peroxide. Treatment with thapsigargin, a calcium modulating agent, markedly attenuated the levels of TMEM132A mRNA and protein in NSC-34 cells. These results give new insight into the mechanisms involved in regulating TMEM132A expression, and suggest that several transcriptional and post-transcriptional pathways regulate TMEM132A expression under developmental and pathophysiological conditions.

Co-chaperones of the mammalian endoplasmic reticulum

In mammalian cells, the rough endoplasmic reticulum or ER plays a central role in the biogenesis of most extracellular plus many organellar proteins and in cellular calcium homeostasis. Therefore, this organelle comprises molecular chaperones that are involved in import, folding/assembly, export, and degradation of polypeptides in millimolar concentrations. In addition, there are calcium channels/pumps and signal transduction components present in the ER membrane that affect and are affected by these processes. The ER lumenal Hsp70, termed immunoglobulin-heavy chain binding protein or BiP, is the central player in all these activities and involves up to seven different co-chaperones, i.e. ER-membrane integrated as well as ER-lumenal Hsp40s, which are termed ERj or ERdj, and two nucleotide exchange factors.

The WAVE regulatory complex links diverse receptors to the actin cytoskeleton

The WAVE regulatory complex (WRC) controls actin cytoskeletal dynamics throughout the cell by stimulating the actin-nucleating activity of the Arp2/3 complex at distinct membrane sites. However, the factors that recruit the WRC to specific locations remain poorly understood. Here, we have identified a large family of potential WRC ligands, consisting of ∼120 diverse membrane proteins, including protocadherins, ROBOs, netrin receptors, neuroligins, GPCRs, and channels. Structural, biochemical, and cellular studies reveal that a sequence motif that defines these ligands binds to a highly conserved interaction surface of the WRC formed by the Sra and Abi subunits. Mutating this binding surface in flies resulted in defects in actin cytoskeletal organization and egg morphology during oogenesis, leading to female sterility. Our findings directly link diverse membrane proteins to the WRC and actin cytoskeleton and have broad physiological and pathological ramifications in metazoans.

Characterization of the expression and cell-surface localization of transmembrane protein 132A

Transmembrane protein 132A (TMEM132A, KIAA1583) was first isolated as a novel gene that is enriched during the embryonic and postnatal stages of rat brain development and interacts with GRP78. However, the biological functions of TMEM132A are scarcely characterized because the protein does not contain any known structural domains. Using a cell-surface biotinylation assay and immunocytochemical staining, we found that TMEM132A is a transmembrane glycoprotein consisting of a large extracellular domain in the N-terminal region and a small cytosolic domain in the C-terminal region. Partial deletions of the intracellular domain of TMEM132A had little effect on its expression level and cell-surface localization in transfected HEK293 cells, whereas deletions of the extracellular domain hampered transport to the cell surface. The expression pattern of each N-terminal mutant was immunocytochemically confirmed in HeLa cells transfected with the same constructs. Treatment with tunicamycin, an inhibitor of protein glycosylation, led to the accumulation of the unglycosylated form of TMEM132A in inverse proportion to the glycosylated form; however, both forms were localized at the cell surface at almost equal rates. In contrast, GRP78 overexpression led to the accumulation of unglycosylated TMEM132A, which was not detected on the cell surface. Inhibition of ER-Golgi transport by treatment with brefeldin A or the overexpression of mutant Sar1 attenuated the amount of cell-surface localized TMEM132A in HEK293 cells. Treatment with reagents disrupting intracellular calcium rapidly down-regulated the amount of TMEM132A protein in Neuro2a cells without affecting the expression level of its mRNA. Taken together, our data show that the novel cell-surface localized glycoprotein, TMEM132A, is regulated by several factors, including GRP78, Sar1, and intracellular calcium, in a post-transcriptional manner.

Biosynthesis and secretion of mouse cysteine-rich with EGF-like domains 2

In this study, we found that Cysteine-rich with EGF-like domains 2 (CRELD2), a novel endoplasmic reticulum stress-inducible protein, is not only localized in the ER-Golgi apparatus but also spontaneously secreted. Deletion of four C-terminal amino acids from mouse CRELD2 or addition of tag-peptides to its C-terminus dramatically enhanced CRELD2 secretion. Intra- and extra-cellular CRELD2 is differentially glycosylated and its spontaneous secretion was significantly prevented by overexpression of a dominant negative mutant Sar1 and treatment with brefeldin A. Overexpression of wild-type GRP78 remarkably enhanced the secretion of wild-type but not mutant CRELD2. Our results demonstrate both that CRELD2 is a novel secretory glycoprotein regulated by Sar1 and GRP78 and that the C-terminal of CRELD2 plays a crucial role in its secretion.

Human stanniocalcin-1 interacts with nuclear and cytoplasmic proteins and acts as a SUMO E3 ligase

Human stanniocalcin-1 (STC1) is a glycoprotein that has been implicated in different physiological process, including angiogenesis, apoptosis and carcinogenesis. Here we identified STC1 as a putative molecular marker for the leukemic bone marrow microenvironment and identified new interacting protein partners for STC1. Seven selected interactions retrieved from yeast two-hybrid screens were confirmed by GST-pull down assays in vitro. The N-terminal region was mapped to be the region that mediates the interaction with cytoplasmic, mitochondrial and nuclear proteins. STC1 interacts with SUMO-1 and several proteins that have been shown to be SUMOylated and localized to SUMOylation related nuclear bodies. Although STC1 interacts with SUMO-1 and has a high theoretical prediction score for a SUMOylation site, endogenous co-immunoprecipitation and in vitro SUMOylation assays with the purified recombinant protein could not detect STC1 SUMOylation. However, when we tested STC1 for SUMO E3 ligase activity, we found in an in vitro assay, that it significantly increases the SUMOylation of two other proteins. Confocal microscopic subcellular localization studies using both transfected cells and specific antibodies for endogenous STC1 revealed a cytoplasmic and nuclear deposition, the latter in the form of some specific dot-like substructure resembling SUMOylation related nuclear bodies. Together, these findings suggest a new role for STC1 in SUMOylation pathways, in nuclear bodies.

Knockdown of transmembrane protein 132A by RNA interference facilitates serum starvation-induced cell death in Neuro2a cells

Transmembrane protein 132A (TMEM132A) is a novel GRP78 binding protein that we recently discovered. However, the biological functions of TMEM132A are merely characterized because it does not encode any known structural domains. In this study, we down regulated intrinsic TMEM132A by RNA interference and identified a variety of genes that fluctuated during TMEM132A gene silencing using microarray analysis. TMEM132A-knockdown in Neuro2a cells caused neurite-like projection without any stimuli and enhanced the expression of ATF6 mRNA, an ER stress transducer, and GADD153 mRNA, a stress inducible gene. Under serum-deprived condition, TMEM132A-knockdown cells gradually retarded neurite-like projection and decreased cell viability. Moreover, TMEM132A knockdown markedly induced GADD153 expression due to serum starvation without affecting the level of cleaved caspase-3. Our data suggest that TMEM132A is an important factor of cell survival in regulating certain ER stress-related gene expression in neuronal cells.

CRELD2 is a novel endoplasmic reticulum stress-inducible gene

Recently, endoplasmic reticulum (ER) stress responses have been suggested to play important roles in maintaining various cellular functions and to underlie many tissue dysfunctions. In this study, we first identified cysteine-rich with EGF-like domains 2 (CRELD2) as an ER stress-inducible gene by analyzing a microarray analysis of thapsigargin (Tg)-inducible genes in Neuro2a cells. CRELD2 mRNA is also shown to be immediately induced by treatment with the ER stress-inducing reagents tunicamycin and brefeldin A. In the genomic sequence of the mouse CRELD2 promoter, we found a typical ER stress responsible element (ERSE), which is well conserved among various species. Using a luciferase reporter analyses, we demonstrated that the ERSE in mouse CRELD2 is functional and responds to Tg and ATF6-overexpression. Each mutation of ATF6- or NF-Y-binding sites in the ERSE of the mouse CRELD2 promoter dramatically decreased both the basal activity and responsiveness toward the ER stress stimuli. Our study suggests that CRELD2 could be a novel mediator in regulating the onset and progression of various ER stress-associated diseases.

Low dose rotenone treatment causes selective transcriptional activation of cell death related pathways in dopaminergic neurons in vivo

Mitochondrial complex I inhibition has been implicated in the degeneration of midbrain dopaminergic (DA) neurons in Parkinson's disease. However, the mechanisms and pathways that determine the cellular fate of DA neurons downstream of the mitochondrial dysfunction have not been fully identified. We conducted cell-type specific gene array experiments with nigral DA neurons from rats treated with the complex I inhibitor, rotenone, at a dose that does not induce cell death. The genome wide screen identified transcriptional changes in multiple cell death related pathways that are indicative of a simultaneous activation of both degenerative and protective mechanisms. Quantitative PCR analyses of a subset of these genes in different neuronal populations of the basal ganglia revealed that some of the changes are specific for DA neurons, suggesting that these neurons are highly sensitive to rotenone. Our data provide insight into potentially defensive strategies of DA neurons against disease relevant insults.

The mutation of the LEW.1AR1-iddm rat maps to the telomeric end of rat chromosome 1

The LEW.1AR1-iddm rat is an animal model of human type 1 diabetes mellitus (T1DM) with an autosomal recessive mode of inheritance. T1DM susceptibility loci could be localized on chromosome (RNO) 20 in the major histocompatibility complex region (Iddm1) and on RNO1 (Iddm8, Iddm9) in a BN backcross cohort. In this study the impact of the different susceptibility regions on diabetes development was investigated in a backcross population of the diabetes-resistant PAR strain. A cohort of 130 [(PAR x LEW.1AR1-iddm) x LEW.1AR1-iddm] N2 rats was monitored for blood glucose and analyzed by linkage analysis. Sixteen percent of the PAR backcross animals developed T1DM. Genetic analysis revealed significant linkage to T1DM in the MHC region on RNO20p12. In contrast to the linkage analysis of the BN backcross cohort, only one susceptibility locus for T1DM could be identified on RNO1. This susceptibility region on RNO1 mapped to the telomeric end corresponding to Iddm8. Eighty-nine percent of diabetic PAR backcross animals were homozygous for Iddm8. The Iddm9 diabetes susceptibility region showed no linkage to diabetes in the PAR backcross cohort. The data of this study provide evidence that the mutation leading to T1DM in the LEW.1AR1-iddm rat is located at the telomeric end of RNO1 corresponding to Iddm8.

Salusins protect neonatal rat cardiomyocytes from serum deprivation-induced cell death through upregulation of GRP78

Salusin-alpha and salusin-beta are newly identified bioactive peptides with hemodynamic and mitogenic activities. Recent studies have shown that salusins improve calcium uptake and protein synthesis in neonatal rat cardiomyocytes, suggesting that salusins may be regulatory factors for myocardial growth and hypertrophy. In this study, we investigated whether salusins improve the survival of cardiomyocytes after serum deprivation. Cultured neonatal cardiomyocytes were treated with or without salusins (salusin-alpha or salusin-beta) at a concentration range of 10 to 10 mol/L for 24 h under serum deprivation conditions. Cardiomyocytes viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazonium bromide assay. Cell death or apoptosis rate was identified by flow cytometry analysis. Compared to serum deprivation-only groups, cardiomyocyte viability was significantly increased in salusin-alpha or salusin-beta groups. Cell death rate was decreased after administration of 10 mol/L salusin-alpha or salusin-beta. Salusin-beta was able to decrease the apoptotic rate. Salusins also increased the expression of cardiomyocyte glucose-regulated protein 78 (GRP78) as estimated by Western blot. Furthermore, antisense oligodeoxynucleotide specifically against GRP78 attenuated or abrogated antiapoptosis or survival effects of salusin-beta. These findings suggest that salusin-alpha and salusin-beta may be a potential survival factor against serum deprivation-induced myocardial cell death and that this cardioprotective effect may involve an upregulation of GRP78 expression in cardiomyocytes.

Functional implications of calcium permeability of the channel formed by pannexin 1

Although human pannexins (PanX) are homologous to gap junction molecules, their physiological function in vertebrates remains poorly understood. Our results demonstrate that overexpression of PanX1 results in the formation of Ca²⁺-permeable gap junction channels between adjacent cells, thus, allowing direct intercellular Ca²⁺ diffusion and facilitating intercellular Ca²⁺ wave propagation. More intriguingly, our results strongly suggest that PanX1 may also form Ca²⁺-permeable channels in the endoplasmic reticulum (ER). These channels contribute to the ER Ca²⁺ leak and thereby affect the ER Ca²⁺ load. Because leakage remains the most enigmatic of those processes involved in intracellular calcium homeostasis, and the molecular nature of the leak channels is as yet unknown, the results of this work provide new insight into calcium signaling mechanisms. These results imply that for vertebrates, a new protein family, referred to as pannexins, may not simply duplicate the connexin function but may also provide additional pathways for intra- and intercellular calcium signaling and homeostasis.

GRP78-binding protein regulates cAMP-induced glial fibrillary acidic protein expression in rat C6 glioblastoma cells

We previously reported that a novel GRP78-binding protein (GBP) is predominantly expressed in rat brain and its expression declines through the aging process. To characterize its biological function, we established C6 glioblastoma cells that stably overexpressed GBP. Stable overexpression of GBP attenuated cAMP-induced expression of the glial fibrillary acidic protein (GFAP) gene, which was accompanied by a decrease in cAMP-induced signal transducer and activators of transcription 3 (STAT3) phosphorylation. Other distinct cAMP-induced events, including a transient reduction in extracellular signal-regulated protein kinase phosphorylation and a slowdown in cell proliferation, were hardly affected by GBP overexpression. Most importantly, treatment with siRNA against endogenous GBP markedly downregulated GBP expression in C6 glioblastoma cells, and dramatically augmented cAMP-induced GFAP mRNA expression in parallel with hyper-phosphorylation of STAT3. These results suggest a novel function of GBP in regulating GFAP gene expression via STAT3 phosphorylation.

A novel receptor function for the heat shock protein Grp78: silencing of Grp78 gene expression attenuates alpha2M*-induced signalling

The activated proteinase inhibitor alpha2-macroglobulin (alpha2M*) binds to two receptors, the low density lipoprotein receptor-related protein (LRP-1) and the alpha2M* signalling receptor (alpha2MSR). Silencing LRP-1 gene expression in macrophages by RNA interference does not block alpha2M* activation of signalling cascades. We now demonstrate that transfection of macrophages with a double-stranded RNA homologous in sequence to the Grp78 gene markedly decreased induction of inositol 1,4,5-trisphosphate (IP3) and subsequent IP3-dependent elevation of [Ca2+]i induced by alpha2M*. Concomitantly, alpha2M*-induced increase in [3H]thymidine uptake was abolished in these transfected cells. Insulin treatment significantly upregulates alpha2MSR and it also caused a marked increase in Grp78 expression which could be blocked by RNA interference. alpha2M* treatment of cells activates the Ras- and PI 3-kinase-dependent signalling pathways. Suppressing Grp78 expression leads to the loss of these activation events in transfected macrophages. We thus conclude that Grp78 is the alpha2M* signalling receptor.

In vivo imaging of the dynamics of glucose uptake in the cytosol of COS-7 cells by fluorescent nanosensors

Glucose homeostasis is a function of glucose supply, transport across the plasma membrane, and metabolism. To monitor glucose dynamics in individual cells, a glucose nanosensor was developed by flanking the Escherichia coli periplasmic glucose/galactose-binding protein with two different green fluorescent protein variants. Upon binding of substrate the FLIPglu-170n sensor showed a concentration-dependent decrease in fluorescence resonance energy transfer between the attached chromophores with a binding affinity for glucose of 170 nm. Fluorescence resonance energy transfer measurements with different sugars indicated a broad selectivity for monosaccharides. An affinity mutant with a Kd of approximately 600 microM was generated, which showed higher substrate specificity, and thus allowed specific monitoring of reversible glucose dynamics in COS-7 cells in the physiological range. At external glucose concentrations between 0.5 and 10 mM, reflecting typical blood levels, free cytosolic glucose concentrations remained at approximately 50% of external levels. The removal of glucose lead to reduced glucose levels in the cell, demonstrating reversibility and visualizing homeostasis. Glucose levels dropped even in the presence of the transport inhibitor cytochalasin B, indicating rapid metabolism. Consistently, the addition of 2-deoxyglucose, which is not recognized by the sensor, affects glucose uptake and metabolism rates. Within the physiological range, glucose utilization, i.e. hexokinase activity, was not limiting. Furthermore, the results show that in COS-7 cells, cytosolic glucose concentrations can vary over at least two orders of magnitude. The glucose nanosensor provides a novel tool with numerous scientific, medical, and environmental applications.