The retinal specific CD147 Ig0 domain: from molecular structure to biological activity

SARS-CoV-2-associated lymphopenia: possible mechanisms and the role of CD147

T lymphocytes play a primary role in the adaptive antiviral immunity. Both lymphocytosis and lymphopenia were found to be associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While lymphocytosis indicates an active anti-viral response, lymphopenia is a sign of poor prognosis. T-cells, in essence, rarely express ACE2 receptors, making the cause of cell depletion enigmatic. Moreover, emerging strains posed an immunological challenge, potentially alarming for the next pandemic. Herein, we review how possible indirect and direct key mechanisms could contribute to SARS-CoV-2-associated-lymphopenia. The fundamental mechanism is the inflammatory cytokine storm elicited by viral infection, which alters the host cell metabolism into a more acidic state. This "hyperlactic acidemia" together with the cytokine storm suppresses T-cell proliferation and triggers intrinsic/extrinsic apoptosis. SARS-CoV-2 infection also results in a shift from steady-state hematopoiesis to stress hematopoiesis. Even with low ACE2 expression, the presence of cholesterol-rich lipid rafts on activated T-cells may enhance viral entry and syncytia formation. Finally, direct viral infection of lymphocytes may indicate the participation of other receptors or auxiliary proteins on T-cells, that can work alone or in concert with other mechanisms. Therefore, we address the role of CD147-a novel route-for SARS-CoV-2 and its new variants. CD147 is not only expressed on T-cells, but it also interacts with other co-partners to orchestrate various biological processes. Given these features, CD147 is an appealing candidate for viral pathogenicity. Understanding the molecular and cellular mechanisms behind SARS-CoV-2-associated-lymphopenia will aid in the discovery of potential therapeutic targets to improve the resilience of our immune system against this rapidly evolving virus.

The retina-specific basigin isoform does not induce IL-6 expression in mouse monocytes

Purpose

Basigin gene products are positioned on adjacent cell types in the neural retina and are thought to compose a lactate metabolon important for photoreceptor cell function. The Ig0 domain of basigin isoform 1 (basigin-1) is highly conserved throughout evolution, which suggests a conserved function. It has been suggested that the Ig0 domain has proinflammatory properties, and it is hypothesized to interact with basigin isoform 2 (basigin-2) for cell adhesion and lactate metabolon formation. Therefore, the purpose of the present study was to determine whether the Ig0 domain of basigin-1 binds to basigin-2 and whether the region of the domain used for binding is also used to stimulate interleukin-6 (IL-6) expression.

Methods

Binding was assessed using recombinant proteins corresponding to the Ig0 domain of basigin-1 and endogenously expressed basigin-2 from mouse neural retina and brain protein lysates. The proinflammatory properties of the Ig0 domain were analyzed with exposure of the recombinant proteins to the mouse monocyte RAW 264.7 cell line and subsequent measurement of the IL-6 concentration in the culture medium via enzyme-linked immunosorbent assay (ELISA).

Results

The data indicate that the Ig0 domain interacts with basigin-2 through a region within the amino half of the domain and that the Ig0 domain does not stimulate the expression of IL-6 in mouse cells in vitro.

Conclusions

The Ig0 domain of basigin-1 binds to basigin-2 in vitro. In addition, contrary to previous reports, there was no evidence that the Ig0 domain potentiates IL-6 expression in a mouse monocyte cell line in vitro. However, it is possible that the Ig0 domain stimulates the expression of proinflammatory cytokines other than IL-6, or that the potential involvement of the Ig0 domain of basigin-1 in the acute inflammatory response is dependent on species.

Reduced expression of Basigin gene products in response to chronic inflammation may contribute to vision loss

Chronic inflammation of the retina, like that of diabetic retinopathy, disrupts the blood-retina barrier (BRB). Disruption of the BRB increases vascular permeability and leads to vision loss. Basigin gene products, cell-adhesion molecules and members of the immunoglobulin superfamily, are expressed on endothelial cells, photoreceptor cells and Müller glial cells. Basigin variant-1 on photoreceptors interacts with Basigin variant-2 on Müller glial cells and to rod-derived cone viability factor (RdCVF) to form metabolic support mechanisms necessary for the survival of photoreceptor neurons. The goal of the current study was to determine the gene expression changes of Basigin gene products in ex vivo neonatal, adolescent, and adult retina when exposed to an inflammatory insult in acute and chronic phases. Retinas extracted from mice at postnatal day (P) 7, 30, and 180 were incubated with either phosphate-buffered saline (PBS), as a control, or lipopolysaccharide (LPS), an endotoxin, for 3, 6, 12, or 24 h. RNA was then extracted and Basigin gene products were quantified by qPCR. Analyses indicate both gene products are influenced by LPS exposure in a time and age dependent manner. Specifically, P180 retinas exposed to LPS showed significant decreases in both Basigin gene products, suggesting older retinas may be susceptible to chronic inflammation and subsequent vision loss.

Role of CD147 in the development and diagnosis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common primary liver cancer, and the third leading cause of cancer-related deaths worldwide. HCC is characterized by insidious onset, and most patients are diagnosed at an advanced stage with a poor prognosis. Identification of biomarkers for HCC onset and progression is imperative to development of effective diagnostic and therapeutic strategies. CD147 is a glycoprotein that is involved in tumor cell invasion, metastasis and angiogenesis through multiple mechanisms. In this review, we describe the molecular structure of CD147 and its role in regulating HCC invasion, metastasis and angiogenesis. We highlight its potential as a diagnostic and therapeutic target for HCC.

Local Attraction of Substrates and Co-Substrates Enhances Weak Acid and Base Transmembrane Transport

The transmembrane transport of weak acid and base metabolites depends on the local pH conditions that affect the protonation status of the substrates and the availability of co-substrates, typically protons. Different protein designs ensure the attraction of substrates and co-substrates to the transporter entry sites. These include electrostatic surface charges on the transport proteins and complexation with seemingly transport-unrelated proteins that provide substrate and/or proton antenna, or enzymatically generate substrates in place. Such protein assemblies affect transport rates and directionality. The lipid membrane surface also collects and transfers protons. The complexity in the various systems enables adjustability and regulation in a given physiological or pathophysiological situation. This review describes experimentally shown principles in the attraction and facilitation of weak acid and base transport substrates, including monocarboxylates, ammonium, bicarbonate, and arsenite, plus protons as a co-substrate.

Computational Modeling of T Cell Hypersensitivity during Coronavirus Infections Leading to Autoimmunity and Lethality

The human angiotensin-converting enzyme 2 (hACE2) receptor is the primary receptor for SARS-CoV-2 infection. However, the presence of alternative receptors such as the transmembrane glycoprotein CD147 has been proposed as a potential route for SARS-CoV-2 infection. The outcomes of SARS-CoV-2 spike protein binding to receptors have been shown to vary among individuals. Additionally, some patients infected with SARS-CoV-2 develop autoimmune responses. Given that CD147 is involved in the hyperactivation of memory T cells resulting in autoimmunity, we investigated the interaction of the SARS-CoV-2 viral spike protein with CD147 receptor and retinal specific CD147 Ig0 domain in silico using molecular docking and molecular dynamics (MD) simulations. The results indicated that binding involves two critical residues Lys63 and Asp65 in a ubiquitous CD147 isoform, potentially leading to the hyperactivation of T cells for only SARS-CoV-2, but not for SARS-CoV or MERS-CoV. Overall binding was confirmed by docking simulations. Next, MD analyses were completed to verify the docking poses. Polar interactions suggested that the interaction via Lys63 and Asp65 might be one of the determinants associated with severe COVID-19 outcomes. Neither did SARS-CoV nor MERS-CoV bind to these two critical residues when molecular docking analyses were performed. Interestingly, SARS-CoV was able to bind to CD147 with a lower affinity (-4.5 kcal/mol) than SARS-CoV-2 (-5.6 kcal/mol). Furthermore, Delta and Omicron variants of SARS-CoV-2 did not affect the polar interactions with Lys63 and Asp65 in CD147. This study further strengthens the link between SARS-CoV-2 infection and autoimmune responses and provides novel insights for prudent antiviral drug designs for COVID-19 treatment that have implications in the prevention of T cell hyperactivation.

Basigin drives intracellular accumulation of l-lactate by harvesting protons and substrate anions

Transmembrane transport of l-lactate by members of the monocarboxylate transporter family, MCT, is vital in human physiology and a malignancy factor in cancer. Interaction with an accessory protein, typically basigin, is required to deliver the MCT to the plasma membrane. It is unknown whether basigin additionally exerts direct effects on the transmembrane l-lactate transport of MCT1. Here, we show that the presence of basigin leads to an intracellular accumulation of l-lactate 4.5-fold above the substrate/proton concentrations provided by the external buffer. Using basigin truncations we localized the effect to arise from the extracellular Ig-I domain. Identification of surface patches of condensed opposite electrostatic potential, and experimental analysis of charge-affecting Ig-I mutants indicated a bivalent harvesting antenna functionality for both, protons and substrate anions. From these data, and determinations of the cytosolic pH with a fluorescent probe, we conclude that the basigin Ig-I domain drives lactate uptake by locally increasing the proton and substrate concentration at the extracellular MCT entry site. The biophysical properties are physiologically relevant as cell growth on lactate media was strongly promoted in the presence of the Ig-I domain. Lack of the domain due to shedding, or misfolding due to breakage of a stabilizing disulfide bridge reversed the effect. Tumor progression according to classical or reverse Warburg effects depends on the transmembrane l-lactate distribution, and this study shows that the basigin Ig-I domain is a pivotal determinant.

Heteromeric Solute Carriers: Function, Structure, Pathology and Pharmacology

Solute carriers form one of three major superfamilies of membrane transporters in humans, and include uniporters, exchangers and symporters. Following several decades of molecular characterisation, multiple solute carriers that form obligatory heteromers with unrelated subunits are emerging as a distinctive principle of membrane transporter assembly. Here we comprehensively review experimentally established heteromeric solute carriers: SLC3-SLC7 amino acid exchangers, SLC16 monocarboxylate/H⁺ symporters and basigin/embigin, SLC4A1 (AE1) and glycophorin A exchanger, SLC51 heteromer Ost α-Ost β uniporter, and SLC6 heteromeric symporters. The review covers the history of the heteromer discovery, transporter physiology, structure, disease associations and pharmacology - all with a focus on the heteromeric assembly. The cellular locations, requirements for complex formation, and the functional role of dimerization are extensively detailed, including analysis of the first complete heteromer structures, the SLC7-SLC3 family transporters LAT1-4F2hc, b^0,+AT-rBAT and the SLC6 family heteromer B⁰AT1-ACE2. We present a systematic analysis of the structural and functional aspects of heteromeric solute carriers and conclude with common principles of their functional roles and structural architecture.

Potential of Ocular Transmission of SARS-CoV-2: A Review

PURPOSE OF REVIEW

to provide a prospective on the current mechanisms by which SARS-CoV-2 enters cells and replicates, and its implications for ocular transmission. The literature was analyzed to understand ocular transmission as well as molecular mechanisms by which SARS-CoV-2 enters cells and replicates. Analysis of gene expression profiles from available datasets, published immunohistochemistry, as well as current literature was reviewed, to assess the likelihood that ocular inoculation of SARS-CoV-2 results in systemic infection.

RECENT FINDINGS

The ocular surface and retina have the necessary proteins, Transmembrane Serine Protease 2 (TMPRSS2), CD147, Angiotensin-Converting Enzyme 2 (ACE2) and Cathepsin L (CTSL) necessary to be infected with SARS-CoV-2. In addition to direct ocular infection, virus carried by tears through the nasolacrimal duct to nasal epithelium represent a means of ocular inoculation.

SUMMARY

There is evidence that SARS-CoV-2 may either directly infect cells on the ocular surface, or virus can be carried by tears through the nasolacrimal duct to infect the nasal or gastrointestinal epithelium.

Membrane-anchored carbonic anhydrase IV interacts with monocarboxylate transporters via their chaperones CD147 and GP70

Monocarboxylate transporters (MCTs) mediate the proton-coupled exchange of high-energy metabolites, including lactate and pyruvate, between cells and tissues. The transport activity of MCT1, MCT2, and MCT4 can be facilitated by the extracellular carbonic anhydrase IV (CAIV) via a noncatalytic mechanism. Combining physiological measurements in HEK-293 cells and Xenopus oocytes with pulldown experiments, we analyzed the direct interaction between CAIV and the two MCT chaperones basigin (CD147) and embigin (GP70). Our results show that facilitation of MCT transport activity requires direct binding of CAIV to the transporters chaperones. We found that this binding is mediated by the highly conserved His-88 residue in CAIV, which is also the central residue of the enzyme's intramolecular proton shuttle, and a charged amino acid residue in the Ig1 domain of the chaperone. Although the position of the CAIV-binding site in the chaperone was conserved, the amino acid residue itself varied among different species. In human CD147, binding of CAIV was mediated by the negatively charged Glu-73 and in rat CD147 by the positively charged Lys-73. In rat GP70, we identified the positively charged Arg-130 as the binding site. Further analysis of the CAIV-binding site revealed that the His-88 in CAIV can either act as H donor or H acceptor for the hydrogen bond, depending on the charge of the binding residue in the chaperone. Our results suggest that the CAIV-mediated increase in MCT transport activity requires direct binding between CAIV-His-88 and a charged amino acid in the extracellular domain of the transporter's chaperone.

Crosstalk in cancer resistance and metastasis

The main obstacles that lead to clinical failure in cancer treatment are the development of resistant to chemotherapy and a rise in invasive characteristics in cancer tumor cells due to prolonged chemotherapeutic processes. Recent studies have revealed some evidence about the existence of a direct relationship between development of drug resistance and triggering of invasive capability in tumor cells. Therefore, devising and application of chemotherapeutic procedures that are not prone to the development of chemotherapy resistance are necessary. Here, we focus on CD147, CD44, ANAX2, P-gp, MMPs, and UCH-L1 proteins involved in the crosstalk between metastasis and cancer treatment. We think that further structural and functional analysis of these proteins may direct scientists towards designing highly effective chemotherapy procedures.

CD147: a small molecule transporter ancillary protein at the crossroad of multiple hallmarks of cancer and metabolic reprogramming

Increased expression of CD147 in pancreatic cancer has been proposed to play a critical role in cancer progression via CD147 chaperone function for lactate monocarboxylate transporters (MCTs). Here, we show for the first time that CD147 interacts with membrane transporters beyond MCTs and exhibits a protective role for several of its interacting partners. CD147 prevents its interacting partner's proteasome-dependent degradation and incorrect plasma membrane localization through the CD147 transmembrane (TM) region. The interactions with transmembrane small molecule and ion transporters identified here indicate a central role of CD147 in pancreatic cancer metabolic reprogramming, particularly with respect to amino acid anabolism and calcium signaling. Importantly, CD147 genetic ablation prevents pancreatic cancer cell proliferation and tumor growth in vitro and in vivo in conjunction with metabolic rewiring towards amino acid anabolism, thus paving the way for future combined pharmacological treatments.

Extracellular matrix metalloproteinase inducer enhances host resistance against pseudomonas aeruginosa infection through MAPK signaling pathway

This study aims to explore the role of extra-cellular matrix metalloproteinase inducer (EMMPRIN) in the drug resistance of the pseudomonas aeruginosa (PA). The BALB/c mice were transfected with PA, then the mice were infected with the siRNA of EMMPRIN to silence the EMMPRIN gene. The EMMPRIN mRNA and protein were detected by using RT-PCR and western blot, respectively. In order to examine the function of EMMPRIN in drug resistance of PA, the BALB/c and C57BL/6 mice were treated with EMMPRIN siRNA. The cytokines, EMMPRIN and MMP9 were examined by the RP-PCR and ELISA, respectively, undergoing the silence of EMMPRIN siRNA. Moreover, the western blot assay was also used to test the phosphorylated MAPK in the murine macrophages after silenced by the EMMPRIN siRNA. The EMMPRIN was activated, with lipopolysaccharide stimulation and treated with the MAPK inhibitor, to evaluate whether the MAPK participates in the EMMPRIN-triggered drug resistance. The results indicated that the EMMPRIN expression was elevated in the infected BALB/c at 3 or 5 days post-infection. Silence of EMMPRIN Enhanced the Production of pro-inflammatory cytokines in PA keratitis. Silence of EMMPRIN significantly up-regulated Th1-type cytokines IFN-γ, IL-12, and IL-18, but down-regulated Th2-type cytokines IL-4, IL-5, and IL-10. MMP9 was increased in the cells with rEMMPRIN treatment. EMMPRIN inhibits pro-inflammatory cytokine production via a MAPK signaling pathway. In conclusion, EMMPRIN promotes host resistance against pseudomonas aeruginosa infection via MAPK signaling pathway.

Rod-derived cone viability factor promotes cone survival by stimulating aerobic glycolysis

Rod-derived cone viability factor (RdCVF) is an inactive thioredoxin secreted by rod photoreceptors that protects cones from degeneration. Because the secondary loss of cones in retinitis pigmentosa (RP) leads to blindness, the administration of RdCVF is a promising therapy for this untreatable neurodegenerative disease. Here, we investigated the mechanism underlying the protective role of RdCVF in RP. We show that RdCVF acts through binding to Basigin-1 (BSG1), a transmembrane protein expressed specifically by photoreceptors. BSG1 binds to the glucose transporter GLUT1, resulting in increased glucose entry into cones. Increased glucose promotes cone survival by stimulation of aerobic glycolysis. Moreover, a missense mutation of RdCVF results in its inability to bind to BSG1, stimulate glucose uptake, and prevent secondary cone death in a model of RP. Our data uncover an entirely novel mechanism of neuroprotection through the stimulation of glucose metabolism.

Basigin (CD147), a multifunctional transmembrane glycoprotein with various binding partners

Basigin, also called CD147 or EMMPRIN, is a transmembrane glycoprotein that belongs to the immunoglobulin superfamily. Basigin has isoforms; the common form (basigin or basigin-2) has two immunoglobulin domains, and the extended form (basigin-1) has three. Basigin is the receptor for cyclophilins, S100A9 and platelet glycoprotein VI, whereas basigin-1 serves as the receptor for the rod-derived cone viability factor. Basigin tightly associates with monocarboxylate transporters and is essential for their cell surface translocation and activities. In the same membrane plane, basigin also associates with other proteins including GLUT1, CD44 and CD98. The carbohydrate portion of basigin is recognized by lectins, such as galectin-3 and E-selectin. These molecular recognitions form the basis for the role of basigin in the transport of nutrients, migration of inflammatory leukocytes and induction of matrix metalloproteinases. Basigin is important in vision, spermatogenesis and other physiological phenomena, and plays significant roles in the pathogenesis of numerous diseases, including cancer. Basigin is also the receptor for an invasive protein RH5, which is present in malaria parasites.

The apicomplexan glideosome and adhesins - Structures and function

The apicomplexan family of pathogens, which includes Plasmodium spp. and Toxoplasma gondii, are primarily obligate intracellular parasites and invade multiple cell types. These parasites express extracellular membrane protein receptors, adhesins, to form specific pathogen-host cell interaction complexes. Various adhesins are used to invade a variety of cell types. The receptors are linked to an actomyosin motor, which is part of a complex comprised of many proteins known as the invasion machinery or glideosome. To date, reviews on invasion have focused primarily on the molecular pathways and signals of invasion, with little or no structural information presented. Over 75 structures of parasite receptors and glideosome proteins have been deposited with the Protein Data Bank. These structures include adhesins, motor proteins, bridging proteins, inner membrane complex and cytoskeletal proteins, as well as co-crystal structures with peptides and antibodies. These structures provide information regarding key interactions necessary for target receptor engagement, machinery complex formation, how force is transmitted, and the basis of inhibitory antibodies. Additionally, these structures can provide starting points for the development of antibodies and inhibitory molecules targeting protein-protein interactions, with the aim to inhibit invasion. This review provides an overview of the parasite adhesin protein families, the glideosome components, glideosome architecture, and discuss recent work regarding alternative models.

EMMPRIN, an upstream regulator of MMPs, in CNS biology

Matrix metalloproteinases (MMPs) are engaged in pathologies associated with infections, tumors, autoimmune disorders and neurological dysfunctions. With the identification of an upstream regulator of MMPs, EMMPRIN (Extracellular matrix metalloproteinase inducer, CD147), it is relevant to address if EMMPRIN plays a role in the pathology of central nervous system (CNS) diseases. This would enable the possibility of a more upstream and effective therapeutic target. Indeed, conditions including gliomas, Alzheimer's disease (AD), multiple sclerosis (MS), and other insults such as hypoxia/ischemia show elevated levels of EMMPRIN which correlate with MMP production. In contrast, given EMMPRIN's role in CNS homeostasis with respect to regulation of monocarboxylate transporters (MCTs) and interactions with adhesion molecules including integrins, we need to consider that EMMPRIN may also serve important regulatory or protective functions. This review summarizes the current understanding of EMMPRIN's involvement in CNS homeostasis, its possible roles in escalating or reducing neural injury, and the mechanisms of EMMPRIN including and apart from MMP induction.

Inherent dynamics within the Crimean-Congo Hemorrhagic fever virus protease are localized to the same region as substrate interactions

Crimean-Congo Hemorrhagic fever virus (CCHFV) is one of several lethal viruses that encodes for a viral ovarian tumor domain (vOTU), which serves to cleave and remove ubiquitin (Ub) and interferon stimulated gene product 15 (ISG15) from numerous proteins involved in cellular signaling. Such manipulation of the host cell machinery serves to downregulate the host response and, therefore, complete characterization of these proteases is important. While several structures of the CCHFV vOTU protease have been solved, both free and bound to Ub and ISG15, few structural differences have been found and little insight has been gained as to the structural plasticity of this protease. Therefore, we have used NMR relaxation experiments to probe the dynamics of CCHFV vOTU, both alone and in complex with Ub, discovering a highly dynamic protease that exhibits conformational exchange within the same regions found to engage its Ub substrate. These experiments reveal a structural plasticity around the N-terminal regions of CCHFV vOTU, which are unique to vOTUs, and provide a rationale for engaging multiple substrates with the same binding site.

The biological function and clinical utilization of CD147 in human diseases: a review of the current scientific literature

CD147 or EMMPRIN is a member of the immunoglobulin superfamily in humans. It is widely expressed in human tumors and plays a central role in the progression of many cancers by stimulating the secretion of matrix metalloproteinases (MMPs) and cytokines. CD147 regulates cell proliferation, apoptosis, and tumor cell migration, metastasis and differentiation, especially under hypoxic conditions. CD147 is also important to many organ systems. This review will provide a detailed overview of the discovery, characterization, molecular structure, diverse biological functions and regulatory mechanisms of CD147 in human physiological and pathological processes. In particular, recent studies have demonstrated the potential application of CD147 not only as a phenotypic marker of activated regulatory T cells but also as a potential diagnostic marker for early-stage disease. Moreover, CD147 is recognized as an effective therapeutic target for hepatocellular carcinoma (HCC) and other cancers, and exciting clinical progress has been made in HCC treatment using CD147-directed monoclonal antibodies.

Importance of N-glycosylation on CD147 for its biological functions

Glycosylation of glycoproteins is one of many molecular changes that accompany malignant transformation. Post-translational modifications of proteins are closely associated with the adhesion, invasion, and metastasis of tumor cells. CD147, a tumor-associated antigen that is highly expressed on the cell surface of various tumors, is a potential target for cancer diagnosis and therapy. A significant biochemical property of CD147 is its high level of glycosylation. Studies on the structure and function of CD147 glycosylation provide valuable clues to the development of targeted therapies for cancer. Here, we review current understanding of the glycosylation characteristics of CD147 and the glycosyltransferases involved in the biosynthesis of CD147 N-glycans. Finally, we discuss proteins regulating CD147 glycosylation and the biological functions of CD147 glycosylation.

Extracellular vesicles secreted from cancer cell lines stimulate secretion of MMP-9, IL-6, TGF-β1 and EMMPRIN

Extracellular vesicles (EVs) are key contributors to cancer where they play an integral role in cell-cell communication and transfer pro-oncogenic molecules to recipient cells thereby conferring a cancerous phenotype. Here, we purified EVs using straightforward biochemical approaches from multiple cancer cell lines and subsequently characterized these EVs via multiple biochemical and biophysical methods. In addition, we used fluorescence microscopy to directly show internalization of EVs into the recipient cells within a few minutes upon addition of EVs to recipient cells. We confirmed that the transmembrane protein EMMPRIN, postulated to be a marker of EVs, was indeed secreted from all cell lines studied here. We evaluated the response to EV stimulation in several different types of recipient cells lines and measured the ability of these purified EVs to induce secretion of several factors highly upregulated in human cancers. Our data indicate that purified EVs preferentially stimulate secretion of several proteins implicated in driving cancer in monocytic cells but only harbor limited activity in epithelial cells. Specifically, we show that EVs are potent stimulators of MMP-9, IL-6, TGF-β1 and induce the secretion of extracellular EMMPRIN, which all play a role in driving immune evasion, invasion and inflammation in the tumor microenvironment. Thus, by using a comprehensive approach that includes biochemical, biological, and spectroscopic methods, we have begun to elucidate the stimulatory roles.

Stimulation of GPR30 increases release of EMMPRIN-containing microvesicles in human uterine epithelial cells

CONTEXT

Uterine remodeling is highly dependent on the glycosylated transmembrane protein extracellular matrix metalloproteinase (MMP) inducer (EMMPRIN). Previous studies indicate estradiol can increase EMMPRIN expression in uterine cells and promote subsequent induction of MMP production.

OBJECTIVE

The aim of this study was to investigate the role of G protein-coupled receptor 30 (GPR30) stimulation on EMMPRIN microvesicle release in the human uterine epithelial cell line hTERT-EEC (EECs).

DESIGN

We examined EMMPRIN release by human EECs in response to GPR30 stimulation by microvesicle isolation, Western blot, and immunocytochemistry. We employed a pharmacological approach using the GPR30-selective agonist G1 and the antagonist G15 to determine the receptor specificity of this response.

RESULTS

We demonstrated GPR30 expression in EECs and release of EMMPRIN in microvesicles in response to stimulation of GPR30. G1, estradiol, and cholera toxin stimulated EMMPRIN release in microvesicles as detected by Western blot and immunocytochemistry, indicating that stimulation of GPR30 can induce EMMPRIN microvesicle release.

CONCLUSIONS

These data indicate that EMMPRIN release in microvesicles can be mediated by stimulation of GPR30 in human EECs, suggesting that inappropriate stimulation or expression of this receptor may be significant in uterine pathology.

Basigin: a multifunctional membrane protein with an emerging role in infections by malaria parasites

INTRODUCTION

Malaria is one of the most serious infectious diseases at the beginning of the twenty-first century. Various membrane proteins are present in Plasmodium falciparum, the principal malaria pathogen. Among them, P. falciparum reticulocyte-binding protein homolog 5 (PfRh5) is indispensable for erythrocyte invasion, and has become a promising vaccine target. Basigin (CD147, EMMPRIN) has been identified as the erythrocyte receptor of PfRh5, and shown to be essential for the invasion of multiple strains of the pathogen.

AREAS COVERED

Fundamental information on basigin is fully described, including structure as a member of the immunoglobulin superfamily and function based on its interactions with external molecules and with proteins within the same membrane. The involvement of basigin in many diseases such as cancer and inflammatory diseases is also described, the implication being that anti-basigin therapy might be helpful to treat certain illnesses. Finally, PfRh5 as a vaccine candidate is covered, and its interaction with basigin is evaluated.

EXPERT OPINION

The identification of basigin, a well-characterized membrane protein, as a receptor essential for malaria infection will contribute significantly to prevention and treatment of malaria. As an example, anti-basigin therapy can be considered an alternative approach to the treatment of drug-resistant malaria.

Extracellular cyclophilin-A stimulates ERK1/2 phosphorylation in a cell-dependent manner but broadly stimulates nuclear factor kappa B

Background

Although the peptidyl-prolyl isomerase, cyclophilin-A (peptidyl-prolyl isomerase, PPIA), has been studied for decades in the context of its intracellular functions, its extracellular roles as a major contributor to both inflammation and multiple cancers have more recently emerged. A wide range of activities have been ascribed to extracellular PPIA that include induction of cytokine and matrix metalloproteinase (MMP) secretion, which potentially underlie its roles in inflammation and tumorigenesis. However, there have been conflicting reports as to which particular signaling events are under extracellular PPIA regulation, which may be due to either cell-dependent responses and/or the use of commercial preparations recently shown to be highly impure.

Methods

We have produced and validated the purity of recombinant PPIA in order to subject it to a comparative analysis between different cell types. Specifically, we have used a combination of multiple methods such as luciferase reporter screens, translocation assays, phosphorylation assays, and nuclear magnetic resonance to compare extracellular PPIA activities in several different cell lines that included epithelial and monocytic cells.

Results

Our findings have revealed that extracellular PPIA activity is cell type-dependent and that PPIA signals via multiple cellular receptors beyond the single transmembrane receptor previously identified, Extracellular Matrix MetalloPRoteinase Inducer (EMMPRIN). Finally, while our studies provide important insight into the cell-specific responses, they also indicate that there are consistent responses such as nuclear factor kappa B (NFκB) signaling induced in all cell lines tested.

Conclusions

We conclude that although extracellular PPIA activates several common pathways, it also targets different receptors in different cell types, resulting in a complex, integrated signaling network that is cell type-specific.