Binding of IFITM1 enhances the inhibiting effect of caveolin-1 on ERK activation

Palmitoylation of hIFITM1 inhibits JEV infection and contributes to BBB stabilization

Human brain microvascular endothelial cells (hBMECs) are the main component cells of the blood-brain barrier (BBB) and play a crucial role in responding to viral infections to prevent the central nervous system (CNS) from viral invasion. Interferon-inducible transmembrane protein 1 (IFITM1) is a multifunctional membrane protein downstream of type-I interferon. In this study, we discovered that hIFITM1 expression was highly upregulated in hBMECs during Japanese encephalitis virus (JEV) infection. Depletion of hIFITM1 with CRISPR/Cas9 in hBMECs enhanced JEV replication, while overexpression of hIFITM1 restricted the viruses. Additionally, overexpression of hIFITM1 promoted the monolayer formation of hBMECs with a better integrity and a higher transendothelial electrical resistance (TEER), and reduced the penetration of JEV across the BBB. However, the function of hIFITM1 is governed by palmitoylation. Mutations of palmitoylation residues in conserved CD225 domain of hIFITM1 impaired its antiviral capacity. Moreover, mutants retained hIFITM1 in the cytoplasm and lessened its interaction with tight junction protein Occludin. Taken together, palmitoylation of hIFITM1 is essential for its antiviral activity in hBMECs, and more notably, for the maintenance of BBB homeostasis.

The novel role of IFITM1-3 in myogenic differentiation of C2C12 cells

Interferon-induced transmembrane proteins (IFITMs 1, 2, and 3) play a critical role in preventing pathogen infection in vertebrates. They are also involved in the occurrence and prognosis of cancer. Myogenesis is a complex process regulated by several factors. This study disclosed that Ifitm1-3 were upregulated in the process of myogenic differentiation of C2C12 myoblasts on days 3, 5, and 7. This positively correlated with the expression of differentiation factors MyoD, myogenin, Mrf5, and desmin. Furthermore, knockdown of Ifitm1-3 by their individual siRNAs inhibited myogenesis of C2C12 myoblasts, with relative downregulation of MyoD, myogenin, Mrf5, and desmin. Subsequently, myotube formation and fusion percentage decreased. Co-immunoprecipitation combined with LC-MS/MS analysis uncovered the interaction proteins of IFITM1 and IFITM3 in C2C12 myoblasts. A total of 84 overlapped interaction proteins of IFITM1 and IFITM3 were identified, and one of the clusters was engaged in cytoskeletal and sarcomere proteins, including desmin, myosin, actin, vimentin, nestin, ankycorbin, and nucleolin. Hence, we hypothesize that these interacting proteins may function as scaffolds for IFITM1-3, possibly through the interaction protein desmin to initiate further interaction with other proteins to participate in myogenesis; however, the molecular mechanisms remain unclear. Our study may contribute to the development of novel therapeutics for myopathic diseases.

Emergent Role of IFITM1/3 towards Splicing Factor (SRSF1) and Antigen-Presenting Molecule (HLA-B) in Cervical Cancer

The IFITM restriction factors play a role in cancer cell progression through undefined mechanisms. We investigate new protein-protein interactions for IFITM1/3 in the context of cancer that would shed some light on how IFITM1/3 attenuate the expression of targeted proteins such as HLA-B. SBP-tagged IFITM1 protein was used to identify an association of IFITM1 protein with the SRSF1 splicing factor and transporter of mRNA to the ribosome. Using in situ proximity ligation assays, we confirmed a predominant cytosolic protein-protein association for SRSF1 and IFITM1/3. Accordingly, IFITM1/3 interacted with HLA-B mRNA in response to IFNγ stimulation using RNA-protein proximity ligation assays. In addition, RT-qPCR assays in IFITM1/IFITM3 null cells and wt-SiHa cells indicated that HLA-B gene expression at the mRNA level does not account for lowered HLA-B protein synthesis in response to IFNγ. Complementary, shotgun RNA sequencing did not show major transcript differences between IFITM1/IFITM3 null cells and wt-SiHa cells. Furthermore, ribosome profiling using sucrose gradient sedimentation identified a reduction in 80S ribosomal fraction an IFITM1/IFITM3 null cells compared to wild type. It was partially reverted by IFITM1/3 complementation. Our data link IFITM1/3 proteins to HLA-B mRNA and SRSF1 and, all together, our results begin to elucidate how IFITM1/3 catalyze the synthesis of target proteins. IFITMs are widely studied for their role in inhibiting viruses, and multiple studies have associated IFITMs with cancer progression. Our study has identified new proteins associated with IFITMs which support their role in mediating protein expression; a pivotal function that is highly relevant for viral infection and cancer progression. Our results suggest that IFITM1/3 affect the expression of targeted proteins; among them, we identified HLA-B. Changes in HLA-B expression could impact the presentation and recognition of oncogenic antigens on the cell surface by cytotoxic T cells and, ultimately, limit tumor cell eradication. In addition, the role of IFITMs in mediating protein abundance is relevant, as it has the potential for regulating the expression of viral and oncogenic proteins.

Association between ARID2 and RAS-MAPK pathway in intellectual disability and short stature

BACKGROUND

ARID2 belongs to the Switch/sucrose non-fermenting complex, in which the genetic defects have been found in patients with dysmorphism, short stature and intellectual disability (ID). As the phenotypes of patients with ARID2 mutations partially overlap with those of RASopathy, this study evaluated the biochemical association between ARID2 and RAS-MAPK pathway.

METHODS

The phenotypes of 22 patients with either an ARID2 heterozygous mutation or haploinsufficiency were reviewed. Comprehensive molecular analyses were performed using somatic and induced pluripotent stem cells (iPSCs) of a patient with ARID2 haploinsufficiency as well as using the mouse model of Arid2 haploinsufficiency by CRISPR/Cas9 gene editing.

RESULTS

The phenotypic characteristics of ARID2 deficiency include RASopathy, Coffin-Lowy syndrome or Coffin-Siris syndrome or undefined syndromic ID. Transient ARID2 knockout HeLa cells using an shRNA increased ERK1 and ERK2 phosphorylation. Impaired neuronal differentiation with enhanced RAS-MAPK activity was observed in patient-iPSCs. In addition, Arid2 haploinsufficient mice exhibited reduced body size and learning/memory deficit. ARID2 haploinsufficiency was associated with reduced IFITM1 expression, which interacts with caveolin-1 (CAV-1) and inhibits ERK activation.

DISCUSSION

ARID2 haploinsufficiency is associated with enhanced RAS-MAPK activity, leading to reduced IFITM1 and CAV-1 expression, thereby increasing ERK activity. This altered interaction might lead to abnormal neuronal development and a short stature.

Identification of IFN-Induced Transmembrane Protein 1 With Prognostic Value in Pancreatic Cancer Using Network Module-Based Analysis

Despite improvements reported in diagnosis and treatments in recent decades, pancreatic cancer is still characterized by poor prognosis and low survival rate among solid tumors. Intensive interests have grown in exploring novel predictive biomarkers, aiming to enhance the efficiency in early detection and treatment prognosis. In this study, we identified the differentially expressed genes (DEGs) in pancreatic cancer by analyzing five gene expression profiles and established the functional modules according to the functional interaction (FI) network between the DEGs. A significant upregulation of the selected DEG, interferon (IFN)-induced transmembrane protein 1 (IFITM1), was evaluated in several bioinformatics online tools and verified with immunohistochemistry staining from samples of 90 patients with pancreatic cancer. Prognostic data showed that high expression of IFITM1 associated with poor survival, and multivariate Cox regression analysis showed IFITM1 was one of the independent prognostic factors for overall survival. Meanwhile, significant correlations of the expression of IFITM1 and the infiltration of immune cells were found by TIMER. Furthermore, a higher level of IFITM1 was assessed in pancreatic cancer cell lines compared to normal human pancreatic duct epithelial cells, and silencing IFITM1 in tumor cells remarkedly inhibited cancer tumorigenicity. Collectively, our findings suggested that IFITM1 might have promising utility for pancreatic cancer.

Knockdown of interferon-induced transmembrane protein 1 inhibited proliferation, induced cell cycle arrest and apoptosis, and suppressed MAPK signaling pathway in pancreatic cancer cells

Pancreatic cancer (PC), highly malignant, is one of the most lethal cancers. Interferon-induced transmembrane protein 1 (IFITM1) has recently been regarded as a new molecular marker in human cancers. However, the role of IFITM1 in PC remains unclear. In this study, a short hairpin RNA (shRNA) was constructed to assess the effect of IFITM1 on PANC-1 and ASPC-1 cells. The level of IFITM1 was downregulated in cells transfected with shRNA targeting IFITM1 (sh-IFITM1). Silencing of IFITM1 significantly decreased cell viability, downregulated the level of Ki-67, arrested cell at G1/S phase, reduced the number of cells in S phase, and decreased cyclinD1, cyclinE, CDK2, and CDK4 levels. Moreover, Hoechst staining and Western blotting analysis showed that cell apoptosis was induced by IFITM1. IFITM1 knockdown suppressed the MAPK signaling pathway by downregulation of p-ERK, p-P38, and p-JNK levels. These findings suggested that IFITM1 could be considered a potential therapeutic target for PC.

The IFITM protein family in adaptive immunity

Interferon‐inducible transmembrane (IFITM) proteins are a family of small homologous proteins, localized in the plasma and endolysosomal membranes, which confer cellular resistance to many viruses. In addition, several distinct functions have been associated with different IFITM family members, including germ cell specification (IFITM1–IFITM3), osteoblast function and bone mineralization (IFITM5) and immune functions (IFITM1–3, IFITM6). IFITM1–3 are expressed by T cells and recent experiments have shown that the IFITM proteins are directly involved in adaptive immunity and that they regulate CD4⁺ T helper cell differentiation in a T‐cell‐intrinsic manner. Here we review the role of the IFITM proteins in T‐cell differentiation and function.

Porcine IFITM1 is a host restriction factor that inhibits pseudorabies virus infection

Interferon-inducible transmembrane proteins (IFITMs) restrict infection by several viruses, such as influenza A virus, West Nile virus and dengue virus. It has not been determined whether porcine IFITMs (pIFITMs) inhibit infection by pseudorabies virus (PRV), an enveloped, double-stranded DNA virus, which is the etiological agent of Aujeszky's disease in pigs. Here, we report that PRV infection elicited pIFITM1 expression in PK15 porcine kidney epithelial cells and 3D4/21 alveolar macrophages. pIFITM2 and pIFITM3 expression was only elevated in PK15 cells during PRV infection. Depletion of pIFITM1 using RNA interference, either in PK15 or in 3D4/21 cells, enhanced PRV infection while overexpression of pIFITM1 had the opposite effect. Knockdown of pIFITM2 and pIFITM3 did not influence PRV infection, suggesting that pIFITM2 and pIFITM3 are independent of PRV infection. PRV-induced pIFITM1 expression was dependent on the cGAS/STING/TBK1/IRF3 innate immune pathway and interferon-alpha receptor-1, suggesting that pIFITM1 is up-regulated by the type I interferon signaling pathway. The anti-PRV role of pIFITM1 was inhibited upon PRV entry. Our data demonstrate that pIFITM1 is a host restriction factor that inhibits PRV entry that may shed light on a strategy for prevention of PRV infection.

More than meets the I: the diverse antiviral and cellular functions of interferon-induced transmembrane proteins

The first responders of human antiviral immunity are components of the intrinsic immune response that reside within each and every one of our cells. This cell-autonomous arsenal consists of nucleic acid sensors and antiviral effectors strategically placed by evolution to detect and restrict invading viruses. While some factors are present at baseline to allow for constant surveillance of the cell interior, others are upregulated by cytokines (such as interferons) that signal a viral infection underway in neighboring cells. In this review, we highlight the multiple roles played by the interferon-induced transmembrane (IFITM) proteins during viral infection, with focuses on IFITM3 and HIV-1. Moreover, we discuss the cellular pathways in which IFITM proteins are intertwined and the various functions they have been ascribed outside the context of infection. While appreciated as broadly-acting, potent restriction factors that prevent virus infection and pathogenesis in cell culture and in vivo, questions remain regarding their precise mode of action and importance in certain viral contexts. Continued efforts to study IFITM protein function will further cement their status as critical host determinants of virus susceptibility and prioritize them in the development of new antiviral therapies.

Intragenic CNVs for epigenetic regulatory genes in intellectual disability: Survey identifies pathogenic and benign single exon changes

The disruption of genes involved in epigenetic regulation is well known to cause Intellectual Disability (ID). We reported a custom microarray study that interrogated among others, the epigenetic regulatory gene-class, at single exon resolution. Here we elaborate on identified intragenic CNVs involving epigenetic regulatory genes; specifically discussing those in three genes previously unreported in ID etiology-ARID2, KDM3A, and ARID4B. The changes in ARID2 and KDM3A are likely pathogenic while the ARID4B variant is uncertain. Previously, we found a CNV involving only exon 6 of the JARID2 gene occurred apparently de novo in seven patients. JARID2 is known to cause ID and other neurodevelopmental conditions. However, exon 6 of this gene encodes one of a series of repeated motifs. We therefore, investigated the impact of this variant in two cohorts and present a genotype-phenotype assessment. We find the JARID2 exon 6 CNV is benign, with a high population frequency (>14%), but nevertheless could have a contributory effect. We also present results from an interrogation of the exomes of 2,044 patients with neurocognitive phenotypes for the incidence of potentially damaging mutation in the epigenetic regulatory gene-class. This paper provides a survey of the fine-scale CNV landscape for epigenetic regulatory genes in the context of ID, describing likely pathogenic as well as benign single exon imbalances. © 2016 Wiley Periodicals, Inc.

IFITM-Family Proteins: The Cell's First Line of Antiviral Defense

Animal cells use a wide variety of mechanisms to slow or prevent replication of viruses. These mechanisms are usually mediated by antiviral proteins whose expression and activities can be constitutive but are frequently amplified by interferon induction. Among these interferon-stimulated proteins, members of the IFITM (interferon-induced transmembrane) family are unique because they prevent infection before a virus can traverse the lipid bilayer of the cell. At least three human IFITM proteins-IFITM1, IFITM2, and IFITM3-have antiviral activities. These activities limit infection in cultured cells by many viruses, including dengue virus, Ebola virus, influenza A virus, severe acute respiratory syndrome coronavirus, and West Nile virus. Murine Ifitm3 controls influenza A virus infection in vivo, and polymorphisms in human IFITM3 correlate with the severity of both seasonal and highly pathogenic avian influenza virus. Here we review the discovery and characterization of the IFITM proteins, describe the spectrum of their antiviral activities, and discuss potential mechanisms underlying these effects.

Evidence for Paralichthys olivaceus IFITM1 antiviral effect by impeding viral entry into target cells

Interferon-inducible transmembrane (IFITM) protein family is novel viral restriction factors with representative transmembrane structure. These proteins also exist in fish, however, their roles in the innate immune response remain unknown. Here, we report a characterization of teleost IFITM1 from flounder Paralichthys olivaceus (PoIFITM1), which exhibits conserved structure characteristic of the IFITM family but comprises a relatively longer N-terminal region. The expression and promoter activity of PoIFITM1 are markedly induced by aquatic animal viruses: Rana grylio virus (RGV) and Scophthalmus maximus rhabdovirus (SMRV). Overexpression and siRNA-mediated knockdown demonstrate that PoIFITM1 exhibits strong antiviral effects against both DNA virus (RGV) and RNA virus (SMRV), expanding the spectrum of viruses inhibited by IFITM proteins. Further analysis shows that PoIFITM1 suppresses viral entry into host cells, confirming that the IFITM-mediated restriction is conserved from lower vertebrates to mammals. Deletion mutagenesis reveals that PoIFITM1 exerts antiviral activity by targeting to Golgi complex and the N-terminal region is required for its subcellular localization, which is not observed in other known IFITM family members. Our current data provide the first evidence that IFITM1 functions as a key effector of the innate immune to restrict virus replication in lower vertebrates, through the action of impeding viral entry.

IFITM proteins restrict viral membrane hemifusion

The interferon-inducible transmembrane (IFITM) protein family represents a new class of cellular restriction factors that block early stages of viral replication; the underlying mechanism is currently not known. Here we provide evidence that IFITM proteins restrict membrane fusion induced by representatives of all three classes of viral membrane fusion proteins. IFITM1 profoundly suppressed syncytia formation and cell-cell fusion induced by almost all viral fusion proteins examined; IFITM2 and IFITM3 also strongly inhibited their fusion, with efficiency somewhat dependent on cell types. Furthermore, treatment of cells with IFN also markedly inhibited viral membrane fusion and entry. By using the Jaagsiekte sheep retrovirus envelope and influenza A virus hemagglutinin as models for study, we showed that IFITM-mediated restriction on membrane fusion is not at the steps of receptor- and/or low pH-mediated triggering; instead, the creation of hemifusion was essentially blocked by IFITMs. Chlorpromazine (CPZ), a chemical known to promote the transition from hemifusion to full fusion, was unable to rescue the IFITM-mediated restriction on fusion. In contrast, oleic acid (OA), a lipid analog that generates negative spontaneous curvature and thereby promotes hemifusion, virtually overcame the restriction. To explore the possible effect of IFITM proteins on membrane molecular order and fluidity, we performed fluorescence labeling with Laurdan, in conjunction with two-photon laser scanning and fluorescence-lifetime imaging microscopy (FLIM). We observed that the generalized polarizations (GPs) and fluorescence lifetimes of cell membranes expressing IFITM proteins were greatly enhanced, indicating higher molecularly ordered and less fluidized membranes. Collectively, our data demonstrated that IFITM proteins suppress viral membrane fusion before the creation of hemifusion, and suggested that they may do so by reducing membrane fluidity and conferring a positive spontaneous curvature in the outer leaflets of cell membranes. Our study provides novel insight into the understanding of how IFITM protein family restricts viral membrane fusion and infection.

Many pathogenic viruses contain an envelope that must fuse with the cell membrane in order to gain entry and initiate infection. This process is mediated by one or more glycoproteins present on the surface of the virions, known as viral fusion proteins. Recently, a family of interferon-inducible transmembrane (IFITM) protein has been shown to block viral infection, including those of highly pathogenic viruses. Here we provide evidence that these IFITM proteins potently suppress membrane fusion induced by representatives of all three classes of viral fusion proteins. Interestingly, we found that the block is not at the steps of receptor binding or low pH that triggers conformational changes of viral fusion proteins required for membrane fusion. Rather, we discovered that the creation of hemifusion, an intermediate in which the outer membranes of the two lipid bilayers have merged but the inner membranes still remain intact is blocked by IFITM proteins. We further demonstrated that overexpression of IFITM proteins rigidify the cell membrane, thereby reducing membrane fluidity and fusion potential. Our study provides novel insight into the understanding of how IFITM proteins restrict viral entry and infection.

7-Ketocholesteryl-9-carboxynonanoate enhances the expression of ATP-binding cassette transporter A1 via CD36

BACKGROUND

CD36 signal transductions have been reported by a variety of lipid moiety of oxidized low-density lipoprotein (oxLDL), however, CD36 signal induced by 7-ketocholesteryl-9-carboxynonanoate (oxLig-1), a lipid moiety of oxLDL has not been elucidated.

METHODS AND RESULTS

OxLig-1 leads to activation and recruitment of Src kinase Fyn, Lyn and caveolin-1 to CD36 in J774A.1 cells, but not in CD36 knockdown cells. The mitogen-activated protein (MAP) kinases c-Jun N-terminal kinase 2 (JNK2) and extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) are specifically phosphorylated in J774A.1 cells after treatment with oxLig-1 and inhibited by pretreatment of Src inhibitor, AG1879. The expression of ABCA1 is up-regulated by treatment with oxLig-1in J774A.1 cells, and the increased expression of ABCA1 is dramatically down-regulated by pretreatment with pharmacological inhibitors of ERK (PD98059) and JNK (SP600125).

CONCLUSIONS

The specific CD36 signal induced by oxLig-1 initiated the activation of Fyn, Lyn, caveolin-1, JNK2 and ERK1/2, and resulted in the up-regulation of ABCA1.

In vivo functional requirement of the mouse Ifitm1 gene for germ cell development, interferon mediated immune response and somitogenesis

The mammalian Interferon induced transmembrane protein 1 (Ifitm1) gene was originally identified as a member of a gene family highly inducible by type I and type II interferons. Based on expression analyses, it was suggested to be required for normal primordial germ cell migration. The knockdown of Ifitm1 in mouse embryos provided evidence for a role in somitogenesis. We generated the first targeted knockin allele of the Ifitm1 gene to systematically reassess all inferred functions. Sperm motility and the fertility of male and female mutant mice are as in wild type littermates. Embryonic somites and the adult vertebral column appear normal in homozygous Ifitm1 knockout mice, demonstrating that Ifitm1 is not essential for normal segmentation of the paraxial mesoderm. Proportions of leucocyte subsets, including granulocytes, monocytes, B-cells, T-cells, NK-cells, and NKT-cells, are unchanged in mutant mice. Based on a normal immune response to Listeria monocytogenes infection, there is no evidence for a dysfunction in downstream IFNγ signaling in Ifitm1 mutant mice. Expression from the Ifitm1 locus from E8.5 to E14.5 is highly dynamic. In contrast, in adult mice, Ifitm1 expression is highly restricted and strong in the bronchial epithelium. Intriguingly, IFITM1 is highly overexpressed in tumor epithelia cells of human squamous cell carcinomas and in adenocarcinomas of NSCLC patients. These analyses underline the general importance of targeted in vivo studies for the functional annotation of the mammalian genome. The first comprehensive description of the Ifitm1 expression pattern provides a rational basis for the further examination of Ifitm1 gene functions. Based on our data, the fact that IFITM1 can function as a negative regulator of cell proliferation, and because the gene maps to chromosome band 11p15.5, previously associated with NSCLC, it is likely that IFITM1 in man has a key role in tumor formation.

Voluntary running in mice beneficially modulates myocardial ischemic tolerance, signaling kinases, and gene expression patterns

Exercise triggers hormesis, conditioning hearts against damaging consequences of subsequent ischemia-reperfusion (I/R). We test whether “low-stress” voluntary activity modifies I/R tolerance and molecular determinants of cardiac survival. Male C57BL/6 mice were provided 7-day access to locked (7SED) or rotating (7EX) running-wheels before analysis of cardiac prosurvival (Akt, ERK 1/2) and prodeath (GSK3β) kinases, transcriptomic adaptations, and functional tolerance of isolated hearts to 25-min ischemia/45-min reperfusion. Over 7 days, 7EX mice increased running from 2.1 ± 0.2 to 5.3 ± 0.3 km/day (mean speed 38 ± 2 m/min), with activity improving myocardial I/R tolerance: 7SED hearts recovered 43 ± 3% of ventricular force with diastolic contracture of 33 ± 3 mmHg, whereas 7EX hearts recovered 63 ± 5% of force with diastolic dysfunction reduced to 23 ± 2 mmHg ( P < 0.05). Cytosolic expression (total protein) of Akt and GSK3β was unaltered, while ERK 1/2 increased 30% in 7EX vs. 7SED hearts. Phosphorylation of Akt and ERK 1/2 was unaltered, whereas GSK3β phosphorylation increased ∼90%. Microarray interrogation identified significant changes (≥1.3-fold expression change, ≤5% FDR) in 142 known genes, the majority (92%) repressed. Significantly modified paths/networks related to inflammatory/immune function (particularly interferon-dependent), together with cell movement, growth, and death. Of only 14 induced transcripts, 3 encoded interrelated sarcomeric proteins titin, α-actinin, and myomesin-2, while transcripts for protective actin-stabilizing ND1-L and activator of mitochondrial biogenesis ALAS1 were also induced. There was no transcriptional evidence of oxidative heat-shock or other canonical “stress” responses. These data demonstrate that relatively brief voluntary activity substantially improves cardiac ischemic tolerance, an effect independent of shifts in Akt, but associated with increased total ERK 1/2 and phospho-inhibition of GSK3β. Transcriptomic data implicate inflammatory/immune and sarcomeric modulation in activity-dependent protection.

Interferon-inducible transmembrane proteins of the innate immune response act as membrane organizers by influencing clathrin and v-ATPase localization and function

The innate response interferon-inducible transmembrane (Ifitm) proteins have been characterized as influencing proliferation, signaling complexes and restricting virus infections. Treatment of cells lacking these proteins (IfitmDel) with IFN-β resulted in the loss of clathrin from membrane compartments and the inhibition of clathrin-mediated phagocytosis, suggesting a molecular interaction between clathrin and Ifitm proteins. The pH of endosomes of IfitmDel cells, with or without IFN activation, was neutralized, suggesting the function of the vacular ATPase proton pumps in such cells was compromised. Co-immunoprecipitation of Ifitm3 with Atp6v0b demonstrated a direct interaction between the Ifitm proteins and the v-ATPase. These data suggest that the Ifitm proteins help stabilize v-ATPase complexes in cellular membranes which, in turn, facilitates the appropriate subcellular localization of clathrin.

B cell signature during inactive systemic lupus is heterogeneous: toward a biological dissection of lupus

Systemic lupus erythematosous (SLE) is an autoimmune disease with an important clinical and biological heterogeneity. B lymphocytes appear central to the development of SLE which is characterized by the production of a large variety of autoantibodies and hypergammaglobulinemia. In mice, immature B cells from spontaneous lupus prone animals are able to produce autoantibodies when transferred into immunodeficient mice, strongly suggesting the existence of intrinsic B cell defects during lupus. In order to approach these defects in humans, we compared the peripheral B cell transcriptomas of quiescent lupus patients to normal B cell transcriptomas. When the statistical analysis is performed on the entire group of patients, the differences between patients and controls appear quite weak with only 14 mRNA genes having a false discovery rate ranging between 11 and 17%, with 6 underexpressed genes (PMEPA1, TLR10, TRAF3IP2, LDOC1L, CD1C and EGR1). However, unforced hierarchical clustering of the microarrays reveals a subgroup of lupus patients distinct from both the controls and the other lupus patients. This subgroup has no detectable clinical or immunological phenotypic peculiarity compared to the other patients, but is characterized by 1/an IL-4 signature and 2/the abnormal expression of a large set of genes with an extremely low false discovery rate, mainly pointing to the biological function of the endoplasmic reticulum, and more precisely to genes implicated in the Unfolded Protein Response, suggesting that B cells entered an incomplete BLIMP1 dependent plasmacytic differentiation which was undetectable by immunophenotyping. Thus, this microarray analysis of B cells during quiescent lupus suggests that, despite a similar lupus phenotype, different biological roads can lead to human lupus.

The small interferon-induced transmembrane genes and proteins

Interferon-induced transmembrane (IFITM) genes are transcribed in most tissues and are with the exception of IFITM5 interferon inducible. They are involved in early development, cell adhesion, and control of cell growth. Most IFITM genes are activated in response to bacterial and viral infections, and the exact host immune defense mechanisms are still unknown. Elevated gene expression triggered by past or chronic inflammation could prevent spreading of pathogens by limiting host cell proliferation. Accordingly, induction in cells with low basal protein levels is sufficient to drive growth arrest and a senescence-like morphology. On the other hand, loss of IFITM levels in cancer is correlated with pronounced malignancy; thus, these genes are considered as tumor suppressors. However, several cancer cells have deregulated high levels of IFITM transcripts, indicating a tumor progression stage where at least one of the interferon-controlled antiproliferative pathways has been silenced. Phylogenetic analyses of the protein coding genomic sequences suggest a single interferon-inducible gene in the common ancestor of rodents and primates. Biological functions studied so far may have evolved in parallel, and functional characterization of IFITM proteins will provide insight into innate immune defense, cancer development, and other pathways.

Interferon-induced cell membrane proteins, IFITM3 and tetherin, inhibit vesicular stomatitis virus infection via distinct mechanisms

Tetherin and IFITM3 are recently identified interferon-induced cellular proteins that restrict infections by retroviruses and filoviruses and of influenza virus and flaviviruses, respectively. In our efforts to further explore their antiviral activities against other viruses and determine their antiviral mechanisms, we found that the two antiviral proteins potently inhibit the infection of vesicular stomatitis virus (VSV), a prototype member of the Rhabdoviridae family. Taking advantage of this well-studied virus infection system, we show that although both tetherin and IFITM3 are plasma membrane proteins, tetherin inhibits virion particle release from infected cells, while IFITM3 disrupts an early event after endocytosis of virion particles but before primary transcription of incoming viral genomes. Furthermore, we demonstrate that both the N-terminal 21 amino acid residues and C-terminal transmembrane region of IFITM3 are required for its antiviral activity. Collectively, our work sheds light on the mechanisms by which tetherin and IFITM3 restrict infection with rhabdoviruses and possibly other pathogenic viruses.

Activation of CD147 with cyclophilin a induces the expression of IFITM1 through ERK and PI3K in THP-1 cells

CD147, as a receptor for Cyclophilins, is a multifunctional transmembrane glycoprotein. In order to identify genes that are induced by activation of CD147, THP-1 cells were stimulated with Cyclophilin A and differentially expressed genes were detected using PCR-based analysis. Interferon-induced transmembrane 1 (IFITM1) was detected to be induced and it was confirmed by RT-PCR and Western blot analysis. CD147-induced expression of IFITM1 was blocked by inhibitors of ERK, PI3K, or NF-κB, but not by inhibitors of p38, JNK, or PKC. IFITM1 appears to mediate inflammatory activation of THP-1 cells since cross-linking of IFITM1 with specific monoclonal antibody against it induced the expression of proinflammatory mediators such as IL-8 and MMP-9. These data indicate that IFITM1 is one of the pro-inflammatory mediators that are induced by signaling initiated by the activation of CD147 in macrophages and activation of ERK, PI3K, and NF-κB is required for the expression of IFITM1.