A novel isoform of human Golgi complex-localized glycoprotein-1 (also known as E-selectin ligand-1, MG-160 and cysteine-rich fibroblast growth factor receptor) targets differential subcellular localization

Intrarenal Single-Cell Sequencing of Hepatitis B Virus Associated Membranous Nephropathy

To date, the pathogenesis of hepatitis B virus (HBV)-associated membranous nephropathy (MN) remains elusive. This study aimed to decipher the etiopathogenesis of HBV-associated MN by performing single-cell RNA sequencing (scRNA-seq) of kidney biopsy specimens from a patient with HBV-associated MN and two healthy individuals. We generated 4,114 intrarenal single-cell transcriptomes from the HBV-associated MN patient by scRNA-seq. Compared to healthy individuals, podocytes in the HBV-associated MN patient showed an increased expression of extracellular matrix formation-related genes, including HSPA5, CTGF, and EDIL3. Kidney endothelial cells (ECs) in the HBV-associated MN were enriched in inflammatory pathways, including NF-kappa B signaling, IL-17 signaling, TNF signaling and NOD-like receptor signaling. Gene ontology (GO) functional enrichment analysis and Gene Set Variation Analysis (GSVA) further revealed that differentially expressed genes (DEGs) of ECs from the HBV-associated MN patients were enriched in apoptotic signaling pathway, response to cytokine and leukocyte cell-cell adhesion. The up-regulated DEGs in glomerular ECs of HBV-associated MN patients were involved in biological processes such as viral gene expression, and protein targeting to endoplasmic reticulum. We further verified that the overexpressed genes in ECs from HBV-associated MN were mainly enriched in regulation of protein targeting to endoplasmic reticulum, exocytosis, viral gene expression, IL-6 and IL-1 secretion when compared with anti-phospholipase A2 receptor (PLA2R)-positive idiopathic membranous nephropathy (IMN). The receptor-ligand crosstalk analysis revealed potential interactions between endothelial cells and other cells in HBV-associated-MN. These results offer new insight into the pathogenesis of HBV-associated MN and may identify new therapeutic targets for HBV-associated MN.

Antitumor effect of memantine is related to the formation of the splicing isoform of GLG1, a decoy FGF‑binding protein

Drug repositioning is a strategy for repurposing the approved or investigational drugs that are outside the scope of the original medical indication. Memantine is used as a non‑competitive N‑methyl‑D‑aspartate receptor antagonist to prevent glutamate‑mediated excitotoxicity in Alzheimer's disease, and is one of the promising agents which is utilized for the purpose of cancer therapy. However, the association between memantine and Golgi glycoprotein 1 (GLG1), an intracellular fibroblast growth factor receptor, in cancers has not yet been clarified. The present study analyzed the expression and location of GLG1 in tumor cells treated with memantine. Memantine was found to suppress the growth of malignant glioma and breast cancer cells in a concentration‑dependent manner. The mRNA expression of GLG1 was upregulated in a concentration‑dependent manner, and the splicing variant profiles were altered in all cell lines examined. The results of western blot analysis revealed an increase in the full‑length and truncated forms of GLG1. Moreover, GLG1 spread in the cytosol of memantine‑treated cells, whereas it localized in the Golgi apparatus in control cells. Since GLG1 functions as a decoy FGF receptor, the modulation of GLG1 may prove to be one of the mechanisms underlying the cancer‑suppressive effects of memantine.

Loss of microRNA-7a2 induces hypogonadotropic hypogonadism and infertility

MicroRNAs (miRNAs) are negative modulators of gene expression that fine-tune numerous biological processes. miRNA loss-of-function rarely results in highly penetrant phenotypes, but rather, influences cellular responses to physiologic and pathophysiologic stresses. Here, we have reported that a single member of the evolutionarily conserved miR-7 family, miR-7a2, is essential for normal pituitary development and hypothalamic-pituitary-gonadal (HPG) function in adulthood. Genetic deletion of mir-7a2 causes infertility, with low levels of gonadotropic and sex steroid hormones, small testes or ovaries, impaired spermatogenesis, and lack of ovulation in male and female mice, respectively. We found that miR-7a2 is highly expressed in the pituitary, where it suppresses golgi glycoprotein 1 (GLG1) expression and downstream bone morphogenetic protein 4 (BMP4) signaling and also reduces expression of the prostaglandin F2a receptor negative regulator (PTGFRN), an inhibitor of prostaglandin signaling and follicle-stimulating hormone (FSH) and luteinizing hormone (LH) secretion. Our results reveal that miR-7a2 critically regulates sexual maturation and reproductive function by interconnecting miR-7 genomic circuits that regulate FSH and LH synthesis and secretion through their effects on pituitary prostaglandin and BMP4 signaling.

Profiling of concanavalin A-binding glycoproteins in human hepatic stellate cells activated with transforming growth factor-β1

Glycoproteins play important roles in maintaining normal cell functions depending on their glycosylations. Our previous study indicated that the abundance of glycoproteins recognized by concanavalin A (ConA) was increased in human hepatic stellate cells (HSCs) following activation by transforming growth factor-β1 (TGF-β1); however, little is known about the ConA-binding glycoproteins (CBGs) of HSCs. In this study, we employed a targeted glycoproteomics approach using lectin-magnetic particle conjugate-based liquid chromatography-tandem mass spectrometry to compare CBG profiles between LX-2 HSCs with and without activation by TGF-β1, with the aim of discovering novel CBGs and determining their possible roles in activated HSCs. A total of 54 and 77 proteins were identified in the quiescent and activated LX-2 cells, respectively. Of the proteins identified, 14.3% were glycoproteins and 73.3% were novel potential glycoproteins. Molecules involved in protein processing in the endoplasmic reticulum (e.g., calreticulin) and calcium signaling (e.g., 1-phosphatidylinositol-4,5-bisphosphate phosphodiesterase β-2 [PLCB2]) were specifically identified in activated LX-2 cells. Additionally, PLCB2 expression was upregulated in the cytoplasm of the activated LX-2 cells, as well as in the hepatocytes and sinusoidal cells of liver cirrhosis tissues. In conclusion, the results of this study may aid future investigations to find new molecular mechanisms involved in HSC activation and antifibrotic therapeutic targets.

Genome-wide RNAi screen reveals a role for multipass membrane proteins in endosome-to-golgi retrieval

Endosome-to-Golgi retrieval is an essential membrane trafficking pathway required for many important physiological processes and linked to neurodegenerative disease and infection by bacterial and viral pathogens. The prototypical cargo protein for this pathway is the cation-independent mannose 6-phosphate receptor (CIMPR), which delivers lysosomal hydrolases to endosomes. Efficient retrieval of CIMPR to the Golgi requires the retromer complex, but other aspects of the endosome-to-Golgi retrieval pathway are poorly understood. Employing an image-based antibody-uptake assay, we conducted a genome-wide RNAi loss-of-function screen for novel regulators of this trafficking pathway and report ∼90 genes that are required for endosome-to-Golgi retrieval of a CD8-CIMPR reporter protein. Among these regulators of endosome-to-Golgi retrieval are a number of multipass membrane-spanning proteins, a class of proteins often overlooked with respect to a role in membrane trafficking. We further demonstrate a role for three multipass membrane proteins, SFT2D2, ZDHHC5, and GRINA, in endosome-to-Golgi retrieval.

Function of alternative splicing

Almost all polymerase II transcripts undergo alternative pre-mRNA splicing. Here, we review the functions of alternative splicing events that have been experimentally determined. The overall function of alternative splicing is to increase the diversity of mRNAs expressed from the genome. Alternative splicing changes proteins encoded by mRNAs, which has profound functional effects. Experimental analysis of these protein isoforms showed that alternative splicing regulates binding between proteins, between proteins and nucleic acids as well as between proteins and membranes. Alternative splicing regulates the localization of proteins, their enzymatic properties and their interaction with ligands. In most cases, changes caused by individual splicing isoforms are small. However, cells typically coordinate numerous changes in 'splicing programs', which can have strong effects on cell proliferation, cell survival and properties of the nervous system. Due to its widespread usage and molecular versatility, alternative splicing emerges as a central element in gene regulation that interferes with almost every biological function analyzed.

Haploinsufficiency of E-selectin ligand-1 is associated with reduced atherosclerotic plaque macrophage content while complete deficiency leads to early embryonic lethality in mice

E-selectin-1 (ESL-1), also known as golgi complex-localized glycoprotein-1 (GLG1), homocysteine-rich fibroblast growth factor receptor (CGR-1), and latent transforming growth factor-β complex protein 1 (LTCP-1), is a multifunctional protein with widespread tissue distribution. To determine the functional consequences of ESL-1 deficiency, mice were generated carrying an ESL-1 gene trap. After backcrossing to C57BL6/J for 6 generations, mice heterozygous for the gene trap (ESL-1(+/-)) were intercrossed to produce ESL-1(-/-) mice, however ESL-1(-/-) mice were not viable, even at embryonic day E10.5. To determine the effect of heterozygous ESL-1 deficiency on atherosclerosis, apolipoprotein E deficient (ApoE(-/-)), ESL-1(+/-) mice were generated and fed western diet. Compared to ApoE(-/-), ESL-1(+)(/)(+) mice, atherosclerotic lesions from ApoE(-/-), ESL-1(+/-) contained more collagen and fewer macrophages, suggesting increased plaque stability. In conclusion, heterozygous deficiency of ESL-1 is associated with features of increased atherosclerotic plaque stability while complete deficiency of ESL-1 leads to embryonic lethality.

Cisterna-specific localization of glycosylation-related proteins to the Golgi apparatus

The Golgi apparatus is an intracellular organelle playing central roles in post-translational modification and in the secretion of membrane and secretory proteins. These proteins are synthesized in the endoplasmic reticulum (ER) and transported to the cis-, medial-and trans-cisternae of the Golgi. While trafficking through the Golgi, proteins are sequentially modified with glycan moieties by different glycosyltransferases. Therefore, it is important to analyze the glycosylation function of the Golgi at the level of cisternae. Markers widely used for cis-, medial- and trans-cisternae/trans Golgi network (TGN) in Drosophila are GM130, 120 kDa and Syntaxin16 (Syx16); however the anti-120 kDa antibody is no longer available. In the present study, Drosophila Golgi complex-localized glycoprotein-1 (dGLG1) was identified as an antigen recognized by the anti-120 kDa antibody. A monoclonal anti-dGLG1 antibody suitable for immunohistochemistry was raised in rat. Using these markers, the localization of glycosyltransferases and nucleotide-sugar transporters (NSTs) was studied at the cisternal level. Results showed that glycosyltransferases and NSTs involved in the same sugar modification are localized to the same cisternae. Furthermore, valuable functional information was obtained on the localization of novel NSTs with as yet incompletely characterized biochemical properties.

Retention in the Golgi apparatus and expression on the cell surface of Cfr/Esl-1/Glg-1/MG-160 are regulated by two distinct mechanisms

Cfr (cysteine-rich fibroblast growth factor receptor) is an Fgf (fibroblast growth factor)-binding protein without a tyrosine kinase. We have shown previously that Cfr is involved in Fgf18 signalling via Fgf receptor 3c. However, as Cfr is also known as Glg (Golgi apparatus protein)-1 or MG-160 and occurs in the Golgi apparatus, it remains unknown how the distribution of Cfr is regulated. In the present study, we performed a mutagenic analysis of Cfr to show that two distinct regions contribute to its distribution and stability. First, the C-terminal region retains Cfr in the Golgi apparatus. Secondly, the Cfr repeats in the extracellular juxtamembrane region destabilizes Cfr passed through the Golgi apparatus. This destabilization does not depend on the cleavage and secretion of the extracellular domain of Cfr. Furthermore, we found that Cfr with a GPI (glycosylphosphatidylinositol) anchor was predominantly expressed on the cell surface in Ba/F3 cells and affected Fgf18 signalling in a similar manner to the full-length Cfr, indicating that the interaction of Cfr with Fgfs on the cell surface is important for its function in Fgf signalling. These results suggest that the expression of Cfr in the Golgi apparatus and on the plasma membrane is finely tuned through two distinct mechanisms for exhibiting different functions.

E-selectin ligand-1 regulates growth plate homeostasis in mice by inhibiting the intracellular processing and secretion of mature TGF-beta

The majority of human skeletal dysplasias are caused by dysregulation of growth plate homeostasis. As TGF-beta signaling is a critical determinant of growth plate homeostasis, skeletal dysplasias are often associated with dysregulation of this pathway. The context-dependent action of TFG-beta signaling is tightly controlled by numerous mechanisms at the extracellular level and downstream of ligand-receptor interactions. However, TGF-beta is synthesized as an inactive precursor that is cleaved to become mature in the Golgi apparatus, and the regulation of this posttranslational intracellular processing and trafficking is much less defined. Here, we report that a cysteine-rich protein, E-selectin ligand-1 (ESL-1), acts as a negative regulator of TGF-beta production by binding TGF-beta precursors in the Golgi apparatus in a cell-autonomous fashion, inhibiting their maturation. Furthermore, ESL-1 inhibited the processing of proTGF-beta by a furin-like protease, leading to reduced secretion of mature TGF-beta by primary mouse chondrocytes and HEK293 cells. In vivo loss of Esl1 in mice led to increased TGF-beta/SMAD signaling in the growth plate that was associated with reduced chondrocyte proliferation and delayed terminal differentiation. Gain-of-function and rescue studies of the Xenopus ESL-1 ortholog in the context of early embryogenesis showed that this regulation of TGF-beta/Nodal signaling was evolutionarily conserved. This study identifies what we believe to be a novel intracellular mechanism for regulating TGF-beta during skeletal development and homeostasis.

Proteomic characterization of HIV-modulated membrane receptors, kinases and signaling proteins involved in novel angiogenic pathways

Background

Kaposi's sarcoma (KS), hemangioma, and other angioproliferative diseases are highly prevalent in HIV-infected individuals. While KS is etiologically linked to the human herpesvirus-8 (HHV8) infection, HIV-patients without HHV-8 and those infected with unrelated viruses also develop angiopathies. Further, HIV-Tat can activate protein-tyrosine-kinase (PTK-activity) of the vascular endothelial growth factor receptor involved in stimulating angiogenic processes. However, Tat by itself or HHV8-genes alone cannot induce angiogenesis in vivo unless specific proteins/enzymes are produced synchronously by different cell-types. We therefore tested a hypothesis that chronic HIV-replication in non-endothelial cells may produce novel factors that provoke angiogenic pathways.

Methods

Genome-wide proteins from HIV-infected and uninfected T-lymphocytes were tested by subtractive proteomics analyses at various stages of virus and cell growth in vitro over a period of two years. Several thousand differentially regulated proteins were identified by mass spectrometry (MS) and >200 proteins were confirmed in multiple gels. Each protein was scrutinized extensively by protein-interaction-pathways, bioinformatics, and statistical analyses.

Results

By functional categorization, 31 proteins were identified to be associated with various signaling events involved in angiogenesis. 88% proteins were located in the plasma membrane or extracellular matrix and >90% were found to be essential for regeneration, neovascularization and angiogenic processes during embryonic development.

Conclusion

Chronic HIV-infection of T-cells produces membrane receptor-PTKs, serine-threonine kinases, growth factors, adhesion molecules and many diffusible signaling proteins that have not been previously reported in HIV-infected cells. Each protein has been associated with endothelial cell-growth, morphogenesis, sprouting, microvessel-formation and other biological processes involved in angiogenesis (p = 10^-4 to 10^-12). Bioinformatics analyses suggest that overproduction of PTKs and other kinases in HIV-infected cells has suppressed VEGF/VEGFR-PTK expression and promoted VEGFR-independent pathways. This unique mechanism is similar to that observed in neovascularization and angiogenesis during embryogenesis. Validation of clinically relevant proteins by gene-silencing and translational studies in vivo would identify specific targets that can be used for early diagnosis of angiogenic disorders and future development of inhibitors of angiopathies. This is the first comprehensive study to demonstrate that HIV-infection alone, without any co-infection or treatment, can induce numerous "embryonic" proteins and kinases capable of generating novel VEGF-independent angiogenic pathways.

Lipopolysaccharide-induced early response genes in bovine peripheral blood mononuclear cells implicate GLG1/E-selectin as a key ligand-receptor interaction

This study uses integrated global gene expression information and knowledge of the regulatory events in cells to identify transcription networks controlling peripheral blood mononuclear cells' (PBMCs) immune response to lipopolysaccharide (LPS) and to identify the molecular and cellular pathways' responses to LPS. We identified that 464 genes, including at least 17 transcription factors, are significantly induced by 2-h LPS stimulation using a high-density bovine microarray platform at a very stringent false discovery rate = 0%. The networks show that, in the LPS-stimulated PBMCs, altered gene expression was transcriptionally regulated via those transcription factors through potential interaction within the pathway networks. Functional analyses revealed that LPS induces unique pathways, molecular functions, biological processes, and gene networks. In particular, gene expression data identified Golgi complex-localized glycoprotein 1/endothelial-selectin as a key ligand-receptor interaction in the early response of cells.

Early dysregulation of cripto-1 and immunomodulatory genes in the cerebral cortex in a macaque model of neuroAIDS

Human immunodeficiency virus type 1 (HIV-1) and related primate lentiviruses are known to enter the central nervous system (CNS) during the primary phase of infection. Neuroinvasion by simian immunodeficiency virus and simian human immunodeficiency virus (SHIV) is characterized by transient meningitis and astrocytosis. In this report, we used targeted cytokine cDNA arrays to analyze cortical brain tissue from four pig-tailed macaques inoculated for 2 weeks with pathogenic SHIV(50OLNV) and a normal age-matched pig-tailed macaque. Our results revealed that eight genes were significantly upregulated in all four macaques. These included: leukocyte interferon inducible peptide, corticotrophin releasing factor receptor 1, interleukin 6, CDW40 antigen, cysteine-rich fibroblast growth factor, neurotrophin 3, ciliary neurotrophin factor receptor and cripto-1. The upregulation of three of these genes was confirmed by reverse transcriptase PCR (RT-PCR). Since cripto-1 had not been previously identified within specific cell types within the primate central nervous system, we performed immunohistochemical studies, which revealed the presence of cripto-1 in neurons. RT-PCR studies demonstrated that cripto-1 mRNA was widely expressed in the CNS. These results indicate that immunomodulatory genes are upregulated during the primary phase of infection of the central nervous system. Cripto-1, which acts as a survival factor in tumor cells and may be neuroprotective, is expressed in neurons within the CNS and is upregulated during viral invasion.

The extracellular nucleotide UTP is a potent inducer of hematopoietic stem cell migration

Homing and engraftment of hematopoietic stem cells (HSCs) to the bone marrow (BM) involve a complex interplay between chemokines, cytokines, and nonpeptide molecules. Extracellular nucleotides and their cognate P2 receptors are emerging as key factors of inflammation and related chemotactic responses. In this study, we investigated the activity of extracellular adenosine triphosphate (ATP) and uridine triphosphate (UTP) on CXCL12-stimulated CD34+ HSC chemotaxis. In vitro, UTP significantly improved HSC migration, inhibited cell membrane CXCR4 down-regulation by migrating CD34+ cells, and increased cell adhesion to fibronectin. In vivo, preincubation with UTP significantly enhanced the BM homing efficiency of human CD34+ cells in immunodeficient mice. Pertussis toxin blocked CXCL12- and UTP-dependent chemotactic responses, suggesting that G-protein alpha-subunits (Galphai) may provide a converging signal for CXCR4- and P2Y-activated transduction pathways. In addition, gene expression profiling of UTP- and CXCL12-treated CD34+ cells and in vitro inhibition assays demonstrated that Rho guanosine 5'-triphosphatase (GTPase) Rac2 and downstream effectors Rho GTPase-activated kinases 1 and 2 (ROCK1/2) are involved in UTP-promoted/CXCL12-dependent HSC migration. Our data suggest that UTP may physiologically modulate the homing of HSCs to the BM, in concert with CXCL12, via the activation of converging signaling pathways between CXCR4 and P2Y receptors, involving Galphai proteins and RhoGTPases.

Characterization of a neural-specific splicing form of the human neuregulin 3 gene involved in oligodendrocyte survival

Neuregulins are a family of genes involved in key aspects of neural biology. Neuregulins 1, 2 and 3 (NRG1, NRG2 and NRG3) are expressed in the mammalian nervous system. It is well established that NRG1, with fifteen different splicing forms, is central for brain development and function. However, the biological relevance of NRG2 and NRG3 remains elusive. Here, we report the identification of a new isoform of NRG3 that is specifically expressed in the human embryonic central nervous system. Sequence alignment with the human genome suggests that this transcript is produced by alternative promoter usage. The encoded polypeptide is a type-I-glycosylated plasma membrane protein, which is shed into the extracellular space where it activates erbB4, a pivotal receptor for brain development. In addition, we show that the protein has a signal sequence that is cleaved after membrane insertion. Proteasome inhibition with Lactacystin enhances the expression of the protein, whereas impairment of ubiquitylation in the conditional mutant cell line ts20 protects the protein from degradation. These observations imply that the ubiquitin/proteasome pathway regulates biogenesis of the protein. We also show that recombinant neuregulin 3 acts as an oligodendrocyte survival factor by activating the phosphoinositide 3-kinase signalling pathway. Therefore, we report a new post-translationally regulated isoform of neuregulin 3 expressed in the developing human central nervous system with a role in oligodendrocyte survival.