Viral defense, carcinogenesis and ISG15: novel roles for an old ISG

IFI44L as a novel epigenetic silencing tumor suppressor promotes apoptosis through JAK/STAT1 pathway during lung carcinogenesis

Numerous evidence showed that the occurrence and development of lung cancer is closely related to environmental pollution. Therefore, new environmental response predictive markers are urgently needed for early diagnosis and screening of lung cancer. Interferon-induced protein 44-like (IFI44L) has been shown to be related in a variety of tumors, but its function and mechanism during lung carcinogenesis still have remained largely unknown. In this study, gene expression and methylation status were analyzed through online tools and malignant transformation models. Differentially expressed cell models and xenograft tumor models were established and used to clarify the gene function. RT-qPCR, western blotting, immunohistochemistry, and co-immunoprecipitation (Co-IP) were used to explore the mechanism. Results showed that IFI44L was dramatically downexpressed during lung carcinogenesis, and its low expression may be attributed to DNA methylation. Overexpression of IFI44L obviously inhibited cell growth and promoted apoptosis. After knockdown of IFI44L expression, the proliferation ability was remarkably increased and the apoptosis was significantly reduced. Functional enrichment showed that IFI44L was involved in apoptosis and JAK/STAT1 signaling pathway, and was highly correlated with downstream molecules. After overexpression of IFI44L, the expression of P-STAT1 and downstream molecules XAF1, OAS1, OAS2 and OAS3 were significantly increased. After knockdown of STAT1 expression, the pro-apoptotic effect of IFI44L was reduced. Co-IP results showed that IFI44L had protein interaction with STAT1. Results proved that IFI44L promoted STAT1 phosphorylation and activated the JAK/STAT1 signaling pathway by directly binding to STAT1 protein, thereby leading to cell apoptosis. Our study revealed that IFI44L promotes cell apoptosis and exerts tumor suppressors by activating the JAK/STAT1 signaling pathway. It further suggests that IFI44L has clinical therapeutic potential and may be a promising biomarker during lung carcinogenesis.

DNA damage contributes to transcriptional and immunological dysregulation of testicular cells during Chlamydia infection

Chlamydia is the most commonly reported sexually transmitted bacterial infection, with 127 million notifications worldwide each year. Both males and females are susceptible to the pathological impacts on fertility that Chlamydia infections can induce. However, male chlamydial infections, particularly within the upper reproductive tract, including the testis, are not well characterized. In this study, using mouse testicular cell lines, we examined the impact of infection on testicular cell lineage transcriptomes and potential mechanisms for this impact. The somatic cell lineages exhibited significantly fragmented genomes during infection. Likely resulting from this, each of the Leydig, Sertoli and germ cell lineages experienced extensive transcriptional dysregulation, leading to significant changes in cellular biological pathways, including interferon and germ-Sertoli cell signalling. The cell lineages, as well as isolated spermatozoa from infected mice, also contained globally hypomethylated DNA. Cumulatively, the DNA damage and epigenetic-mediated transcriptional dysregulation observed within testicular cells during chlamydial infection could result in the production of spermatozoa with abnormal epigenomes, resulting in previously observed subfertility in infected animals and congenital defects in their offspring.

A Comparative Analysis of Edwardsiella tarda-Induced Transcriptome Profiles in RAW264.7 Cells Reveals New Insights into the Strategy of Bacterial Immune Evasion

Edwardsiella tarda is a Gram-negative bacterial pathogen with a broad host range, including fish, reptiles, and mammals. One prominent virulence feature of E. tarda is its ability to survive and replicate in host phagocytes, but the relevant molecular mechanism is largely unknown. In this study, we examined the transcriptome profiles of RAW264.7 cells, a murine macrophage cell line, infected with live E. tarda or stimulated with dead E. tarda for 4 h and 8 h. Eighteen libraries were constructed, and an average of 69 million clean reads per library were obtained, with ~81.63% of the reads being successfully mapped to the reference genome. In total, 208 and 232 differentially expressed genes (DEGs) were identified between live and dead E. tarda-treated cells at 4 h and 8 h post-infection, respectively. The DEGs were markedly enriched in the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways associated with immunity. Live E. tarda differed strikingly from dead E. tarda in the regulation of immune related genes. Compared with dead E. tarda-treated cells, live E. tarda-treated cells exhibited marked and significant suppression in the induction of a large amount of immune genes, including RIG-I-like receptors, cytokines, and interferon-related genes. Furthermore, some of the immune genes highly regulated by live E. tarda formed complicated interaction networks with each other. Together, the results of this study revealed a transcriptome profile specifically induced by the active virulence elements of live E. tarda during the infection process, thus adding new insights into the intracellular infection mechanism of E. tarda. This study also provided a valuable set of target genes for further study of the immune evasion strategy of E. tarda.

Early transcriptome profile of goat peripheral blood mononuclear cells (PBMCs) infected with peste des petits ruminant's vaccine virus (Sungri/96) revealed induction of antiviral response in an interferon independent manner

Sungri/96 vaccine strain is considered the most potent vaccine providing long-term immunity against peste des petits ruminants (PPR) in India. Previous studies in our laboratory highlighted induction of robust antiviral response in an interferon independent manner at 48 h and 120 h post infection (p.i.). However, immune response at the earliest time point 6 h p.i. (time taken to complete one PPRV life cycle), in PBMCs infected with Sungri/96 vaccine virus has not been investigated. This study was taken up to understand the global gene expression profiling of goat PBMCs after Sungri/96 PPRV vaccine strain infection at 6 h post infection (p.i.). A total of 1926 differentially expressed genes (DEGs) were identified with 616 - upregulated and 1310 - downregulated. TLR7/TLR3, IRF7/IRF1, ISG20, IFIT1/IFIT2, IFITM3, IL27 and TREX1 were identified as key immune sensors and antiviral candidate genes. Interestingly, type I interferons (IFNα/β) were not differentially expressed at this time point as well. TREX1, an exonuclease which inhibits type I interferons at the early stage of virus infection was found to be highly upregulated. IL27, an important antiviral host immune factor was significantly upregulated. ISG20, an antiviral interferon induced gene with exonuclease activity specific to ssRNA viruses was highly expressed. Functional profiling of DEGs showed significant enrichment of immune system processes with 233 genes indicating initiation of immune defense response in host cells. Protein interaction network showed important innate immune molecules in the immune network with high connectivity. The study highlights important immune and antiviral genes at the earliest time point.

Host and Viral Proteins Modulating Ebola and Marburg Virus Egress

The filoviruses Ebolavirus and Marburgvirus are among the deadliest viral pathogens known to infect humans, causing emerging diseases with fatality rates of up to 90% during some outbreaks. The replication cycles of these viruses are comprised of numerous complex molecular processes and interactions with their human host, with one key feature being the means by which nascent virions exit host cells to spread to new cells and ultimately to a new host. This review focuses on our current knowledge of filovirus egress and the viral and host factors and processes that are involved. Within the virus, these factors consist of the major matrix protein, viral protein 40 (VP40), which is necessary and sufficient for viral particle release, and nucleocapsid and glycoprotein that interact with VP40 to promote egress. In the host cell, some proteins are hijacked by filoviruses in order to enhance virion budding capacity that include members of the family of E3 ubiquitin ligase and the endosomal sorting complexes required for transport (ESCRT) pathway, while others such as tetherin inhibit viral egress. An understanding of these molecular interactions that modulate viral particle egress provides an important opportunity to identify new targets for the development of antivirals to prevent and treat filovirus infections.

ISG15 in the tumorigenesis and treatment of cancer: An emerging role in malignancies of the digestive system

The interferon-stimulated gene 15 ubiquitin-like modifier (ISG15) encodes an IFN-inducible, ubiquitin-like protein. The ISG15 protein forms conjugates with numerous cellular proteins that are involved in a multitude of cellular functions, including interferon-induced immune responses and the regulation of cellular protein turnover. The expression of ISG15 and ISG15-mediated conjugation has been implicated in a wide range of human tumors and cancer cell lines, but the roles of ISG15 in tumorigenesis and responses to anticancer treatments remain largely unknown. In this review, we discuss the findings of recent studies with regard to the role of ISG15 pathways in cancers of the digestive system.

UBE2L6/UBCH8 and ISG15 attenuate autophagy in esophageal cancer cells

Esophageal cancer remains a poor prognosis cancer due to advanced stage of presentation and drug resistant disease. To understand the molecular mechanisms influencing response to chemotherapy, we examined genes that are differentially expressed between drug sensitive, apoptosis competent esophageal cancer cells (OE21, OE33, FLO-1) and those which are more resistant and do not exhibit apoptosis (KYSE450 and OE19). Members of the ISG15 (ubiquitin-like) protein modification pathway, including UBE2L6 and ISG15, were found to be more highly expressed in the drug sensitive cell lines. In this study, we evaluated the contribution of these proteins to the response of drug sensitive cells. Depletion of UBE2L6 or ISG15 with siRNA did not influence caspase-3 activation or nuclear fragmentation following treatment with 5-fluorouracil (5-FU). We assessed autophagy by analysis of LC3II expression and Cyto-ID staining. Depletion of either ISG15 or UBE2L6 resulted in enhanced endogenous autophagic flux. An increase in autophagic flux was also observed following treatment with cytotoxic drugs (5-FU, rapamycin). In ISG15 depleted cells, this increase in autophagy was associated with improved recovery of drug treated cells. In contrast, UBE2L6 depleted cells, did not show enhanced recovery. UBE2L6 may therefore influence additional targets that limit the pro-survival effect of ISG15 depletion. These data identify UBE2L6 and ISG15 as novel inhibitors of autophagy, with the potential to influence chemosensitivity in esophageal cancer cells.

Free ISG15 triggers an antitumor immune response against breast cancer: a new perspective

Interferon-Stimulated Gene 15 (ISG15), an antagonist of the canonical ubiquitin pathway, is frequently overexpressed in various cancers. In cancer cells, ISG15 is detected as free (intracellular) and conjugated to cellular proteins (ISGylation). Free ISG15 is also secreted into the extracellular milieu. ISGylation has protumor functions and extracellular free ISG15 has immunomodulatory properties in vitro. Therefore, whether ISG15 is a tumor suppressor or tumor promoter in vivo remains controversial. The current study aimed to clarify the role of free ISG15 in tumorigenesis. Breast cancer cells stably expressing control, ISG15, and UbcH8 (ISG15-specific E2 ligase) shRNAs were used to assess the immunoregulatory and antitumor function of free ISG15 in cell culture (in vitro) and in nude mice (in vivo). We show that extracellular free ISG15 suppresses breast tumor growth and increases NK cell infiltration into xenografted breast tumors in nude mice, and intracellular free ISG15 enhances major histocompatibility complex (MHC) class I surface expression in breast cancer cells. We conclude that free ISG15 may have antitumor and immunoregulatory function in vivo. These findings provides the basis for developing strategies to increase systemic levels of free ISG15 to treat cancer patients overexpressing the ISG15 pathway.

ISG15 as a novel prognostic biomarker for hepatitis B virus-related hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related mortality worldwide. Interferon-alpha (IFN-α) has recently been recognized to harbor therapeutic potential in prevention and treatment of HCC. IFN-stimulated gene 15 (ISG15) is an ubiquitin-like molecule that is strongly upregulated by type I interferons as a primary response to diverse microbial and cellular stress stimuli. Several studies have shown that the overexpression of ISG15 is correlated with multiply tumor types. However, the role of ISG15 in hepatitis B virus (HBV)-related HCC remains undetermined. ISG15 expression was found to be obviously higher in HBV-related HCC tissues than that in non-tumor tissues. ISG15 is a novel prognostic marker for predicting 5-year overall survival of HBV-related HCC patients. Overexpression of ISG15 was associated with clinicopathological characteristics and poor patient outcomes. ISG15 may serve as a novel prognostic marker for HBV-related HCC. Therefore, ISG15 may represent a novel HCC marker with prognostic significance and may be helpful in selecting patients for and predicting response to the treatment of HBV-related HCC.

Molecular cloning and expression analysis of interferon stimulated gene 15 (ISG15) in turbot, Scophthalmus maximus

The interferon stimulated gene 15 (ISG15) is strongly induced in many cell types by double-stranded RNA (polyinosinic: polycytidylic acid, poly I:C) and viral infection. In this study, we described the nucleotide, mRNA tissue distribution and regulation of an ISG15 gene from turbot, Scophthalmus maximus (SmISG15). SmISG15 gene is 862 bp in length, composed of two exons and one intron, and encodes 158 amino acids. The deduced protein exhibits the highest homology (44.7-71.2% identity) with ISG15s from other fishes and possesses two conserved tandem ubiquitin-like (UBL) domains and a C-terminal RLRGG conjugating motif known to be important for the functions of ISG15s in vertebrates. Phylogenetic analysis grouped SmISG15 into fish ISG15. SmISG15 mRNA was constitutively expressed in all tissues examined, with higher levels observed in immune organs. Gene expression analysis was performed for SmISG15 in the spleen, head kidney, gills and muscle of turbots challenged with poly I:C or turbot reddish body iridovirus (TRBIV) over a 7-day time course. The result showed that SmISG15 was upregulated by both stimuli in all four tissues, with induction by poly I:C apparently stronger and initiated more quickly. A two-wave induced expression of SmISG15 was seen in the spleen, head kidney and gills, suggesting an induction of SmISG15 either by IFN-dependent or -independent pathway. These results provide insights into the roles of fish ISG15 in antiviral immunity.

Proteomic analysis of mitochondria in respiratory epithelial cells infected with human respiratory syncytial virus and functional implications for virus and cell biology

OBJECTIVES

The aim of this study was to quantitatively characterise the mitochondrial proteome of airway epithelial cells infected with human respiratory syncytial virus (HRSV), a major cause of paediatric illness.

METHODS

Quantitative proteomics, underpinned by stable isotope labelling with amino acids in cell culture, coupled to LC-MS/MS, was applied to mitochondrial fractions prepared from HRSV-infected and mock-infected cells 12 and 24 h post-infection. Datasets were analysed using ingenuity pathway analysis, and the results were validated and characterised using bioimaging, targeted inhibition and gene depletion.

KEY FINDINGS

The data quantitatively indicated that antiviral signalling proteins converged on mitochondria during HRSV infection. The mitochondrial receptor protein Tom70 was found to act in an antiviral manner, while its chaperone, Hsp90, was confirmed to be a positive viral factor. Proteins associated with different organelles were also co-enriched in the mitochondrial fractions from HRSV-infected cells, suggesting that alterations in organelle dynamics and membrane associations occur during virus infection.

CONCLUSIONS

Protein and pathway-specific alterations occur to the mitochondrial proteome in a spatial and temporal manner during HRSV infection, suggesting that this organelle may have altered functions. These could be targeted as part of potential therapeutic strategies to disrupt virus biology.

Nef, the shuttling molecular adaptor of HIV, influences the cytokine network

Several viruses manipulate host innate immune responses to avoid immune recognition and improve viral replication and spreading. The viral protein Nef of Human Immunodeficiency Virus is mainly involved in this "hijacking" activity and is a well established virulence factor. In the last few years there have been remarkable advances in outlining a defined framework of its functions. In particular Nef appears to be a shuttling molecular adaptor able to exert its effects both on infected and non infected bystander cell. In addition it is emerging fact that it has an important impact on the chemo-cytokine network. Nef protein represents an interesting new target to develop therapeutic drugs for treatment of seropositive patients. In this review we have tried to provide a unifying view of the multiple functions of this viral protein on the basis of recently available experimental data.

Cloning and Sequence Analysis of Wild Argali ISG15 cDNA

The complete coding sequence of Wild Argali ISG15 cDNA was generated by rapid amplification of cDNA ends. The ISG15 cDNA was 642 bp with an open reading frame of 474 bp, which encoded a 17.47 kDa protein composed of 157 amino acids. Its amino acid sequence shared 97.9%, 80.8%, 91.4%, 94.3%, 78.3% identity with those of ISG15cDNA from Ovis aries (accession no. NM001009735.1), Capra hircus (accession no. HQ329186.1), Bos taurus (accession no. BC102318.1), Bubalus bubalis (accession no. HM543269.1), and Sus scrofa (accession no. EU647216.1), respectively. The entire coding sequence was inserted into the pET-28a vector and expressed in E. coli. The recombinant protein corresponded to the expected molecular mass of 25 kDa as judged by SDS-PAGE, and it was detected in the bacterial inclusion bodies. The expressed protein could be purified by Ni²⁺ chelate affinity chromatography and the results from the lymphocyte proliferation test showed that the product could stimulate lymphocyte proliferation very well (p<0.05), which further confirmed its biological activity.

Wanderings in biochemistry

My Ph.D. thesis in the laboratory of Severo Ochoa at New York University School of Medicine in 1962 included the determination of the nucleotide compositions of codons specifying amino acids. The experiments were based on the use of random copolyribonucleotides (synthesized by polynucleotide phosphorylase) as messenger RNA in a cell-free protein-synthesizing system. At Yale University, where I joined the faculty, my co-workers and I first studied the mechanisms of protein synthesis. Thereafter, we explored the interferons (IFNs), which were discovered as antiviral defense agents but were revealed to be components of a highly complex multifunctional system. We isolated pure IFNs and characterized IFN-activated genes, the proteins they encode, and their functions. We concentrated on a cluster of IFN-activated genes, the p200 cluster, which arose by repeated gene duplications and which encodes a large family of highly multifunctional proteins. For example, the murine protein p204 can be activated in numerous tissues by distinct transcription factors. It modulates cell proliferation and the differentiation of a variety of tissues by binding to many proteins. p204 also inhibits the activities of wild-type Ras proteins and Ras oncoproteins.

Interferon lambda 1 expression in cervical cells differs between low-risk and high-risk human papillomavirus-positive women

Persistent infection by high-risk (HR) human papillomavirus (HPV) types is a prerequisite for progression to cancer. HR-HPVs may lead to a deregulation of innate immunity by interfering with the epithelial type I interferon (IFN) response, whereas very little is known about type III IFNs, a key component of the mucosal antiviral response. This study reports a first attempt to evaluate the activation of type III IFN genes (IFN lambda 1-3), IFN lambda receptor genes (IFN-lambdaR1 and IL10R2), and IFN-induced genes (MxA, ISG15, ISG56) in HPV-positive and HPV-negative cervical cells from 154 women attending the gynecological unit of a university hospital in Rome. Despite an increased individual variability, a coordinated expression of several IFN lambda-related genes was observed. Furthermore, IFN lambda 1 and IFN-lambdaR1 genes were expressed at higher levels in cervical cells positive to low-risk (LR) HPV compared to HR-HPV and HPV-negative cells. Consistently, ISG15 expression was significantly higher in LR-HPV-infected women than in the other groups. Moreover, IFN lambda 1 expression decreased significantly with abnormal cytological results. This study is the first to show the activation of a type III IFN response in LR-HPV-positive cervical cells and suggests that the lack of this response in HR-HPV infection may be related to lesion progression.

Global Identification of EVI1 Target Genes in Acute Myeloid Leukemia

The ecotropic virus integration site 1 (EVI1) transcription factor is associated with human myeloid malignancy of poor prognosis and is overexpressed in 8-10% of adult AML and strikingly up to 27% of pediatric MLL-rearranged leukemias. For the first time, we report comprehensive genomewide EVI1 binding and whole transcriptome gene deregulation in leukemic cells using a combination of ChIP-Seq and RNA-Seq expression profiling. We found disruption of terminal myeloid differentiation and cell cycle regulation to be prominent in EVI-induced leukemogenesis. Specifically, we identified EVI1 directly binds to and downregulates the master myeloid differentiation gene Cebpe and several of its downstream gene targets critical for terminal myeloid differentiation. We also found EVI1 binds to and downregulates Serpinb2 as well as numerous genes involved in the Jak-Stat signaling pathway. Finally, we identified decreased expression of several ATP-dependent P2X purinoreceptors genes involved in apoptosis mechanisms. These findings provide a foundation for future study of potential therapeutic gene targets for EVI1-induced leukemia.

Primary immunodeficiencies: a rapidly evolving story

The characterization of primary immunodeficiencies (PIDs) in human subjects is crucial for a better understanding of the biology of the immune response. New achievements in this field have been possible in light of collaborative studies; attention paid to new phenotypes, infectious and otherwise; improved immunologic techniques; and use of exome sequencing technology. The International Union of Immunological Societies Expert Committee on PIDs recently reported on the updated classification of PIDs. However, new PIDs are being discovered at an ever-increasing rate. A series of 19 novel primary defects of immunity that have been discovered after release of the International Union of Immunological Societies report are discussed here. These new findings highlight the molecular pathways that are associated with clinical phenotypes and suggest potential therapies for affected patients.

Molecular cloning, expression and functional analysis of ISG15 in orange-spotted grouper, Epinephelus coioides

Interferon-stimulated gene 15 (ISG15) is an ubiquitin homolog that is significantly induced by type I interferons or viral infections. Groupers, Epinephelus spp. being maricultured in China and Southeast Asian countries, always suffer from virus infection, including iridovirus and nodavirus. To date, the roles of grouper genes, especially interferon related genes in virus infection remained largely unknown. Here, the ISG15 homolog (EcISG15) was cloned from grouper Epinephelus coioides and its immune response to Singapore grouper iridovirus (SGIV) and grouper nervous necrosis virus (GNNV) was investigated. The full-length EcISG15 cDNA was composed of 948 bp and encoded a polypeptide of 155 amino acids with 37-68% identity with the known ISG15 homologs from other fish species. Amino acid alignment analysis indicated that EcISG15 contained two ubiquitin-like (UBL) domains and an Ub-conjugation domain (LRGG). Expressional analysis showed that EcISG15 was dramatically induced by GNNV infection, poly I:C or poly dA-dT treatment, but no obvious changes were observed during SGIV infection. Immunofluorescence assay showed that EcISG15 localized mainly in the cytoplasm of grouper cells in response to poly I:C stimulation or GNNV infection, but not in mock or SGIV infected cells. Western blot analysis indicated that the ISGylation was absent in SGIV-infected cells, but significantly enhanced in GNNV-infected or poly I:C transfected cells, suggesting that EcISG15 might play different roles in SGIV and GNNV infection. Furthermore, overexpression of EcISG15 in vitro inhibited the transcription of GNNV genes significantly. Taken together, the results indicated that fish ISG15 might exert important roles against RNA virus infection.

Mycobacterial disease and impaired IFN-γ immunity in humans with inherited ISG15 deficiency

ISG15 is an interferon (IFN)-α/β-inducible, ubiquitin-like intracellular protein. Its conjugation to various proteins (ISGylation) contributes to antiviral immunity in mice. Here, we describe human patients with inherited ISG15 deficiency and mycobacterial, but not viral, diseases. The lack of intracellular ISG15 production and protein ISGylation was not associated with cellular susceptibility to any viruses that we tested, consistent with the lack of viral diseases in these patients. By contrast, the lack of mycobacterium-induced ISG15 secretion by leukocytes-granulocyte, in particular-reduced the production of IFN-γ by lymphocytes, including natural killer cells, probably accounting for the enhanced susceptibility to mycobacterial disease. This experiment of nature shows that human ISGylation is largely redundant for antiviral immunity, but that ISG15 plays an essential role as an IFN-γ-inducing secreted molecule for optimal antimycobacterial immunity.

Cynoglossus semilaevis ISG15: a secreted cytokine-like protein that stimulates antiviral immune response in a LRGG motif-dependent manner

ISG15 is an ubiquitin-like protein that is induced rapidly by interferon stimulation. Like ubiquitin, ISG15 forms covalent conjugates with its target proteins in a process called ISGylation, which in mammals is known to play a role in antiviral immunity. In contrast to mammalian ISG15, the function of teleost ISG15 is unclear. In this study, we identified and analyzed the function of an ISG15 homologue, CsISG15, from tongue sole (Cynoglossus semilaevis). CsISG15 is composed of 162 residues and possesses two tandem ubiquitin-like domains and the highly conserved LRGG motif found in all known ISG15. Expression of CsISG15 occurred in a wide range of tissues and was upregulated in kidney and spleen by viral and bacterial infection. In vitro study with primary head kidney (HK) lymphocytes showed that megalocytivirus infection caused induction of CsISG15 expression and extracellular release of CsISG15 protein. Purified recombinant CsISG15 (rCsISG15) activated HK macrophages and enhanced the expression of immune genes in HK lymphocytes, both these effects, however, were significantly reduced when the conserved LRGG sequence was mutated to LAAG. Further study showed that the presence of rCsISG15 during megalocytivirus infection of HK lymphocytes reduced intracellular viral load, whereas antibody blocking of CsISG15 enhanced viral infection. Likewise, interference with CsISG15 expression by RNAi promoted viral infection. Taken together, these results indicate that CsISG15, a teleost ISG15, promotes antiviral immune response and that, unlike mammalian ISG15, CsISG15 exerts its immunoregulatory effect in the form of an unconjugated extracellular cytokine. In addition, these results also suggest a role for the LRGG motif other than that in protein conjugation.

Modulation of activation-associated host cell gene expression by the apicomplexan parasite Theileria annulata

Infection of bovine leucocytes by Theileria annulata results in establishment of transformed, infected cells. Infection of the host cell is known to promote constitutive activation of pro-inflammatory transcription factors that have the potential to be beneficial or detrimental. In this study we have compared the effect of LPS activation on uninfected bovine leucocytes (BL20 cells) and their Theileria-infected counterpart (TBL20). Gene expression profiles representing activated uninfected BL20 relative to TBL20 cells were also compared. The results show that while prolonged stimulation with LPS induces cell death and activation of NF-κB in BL20 cells, the viability of Theileria-infected cells was unaffected. Analysis of gene expression networks provided evidence that the parasite establishes tight control over pathways associated with cellular activation by modulating reception of extrinsic stimuli and by significantly altering the expression outcome of genes targeted by infection-activated transcription factors. Pathway analysis of the data set identified novel candidate genes involved in manipulation of cellular functions associated with the infected transformed cell. The data indicate that the T. annulata parasite can irreversibly reconfigure host cell gene expression networks associated with development of inflammatory disease and cancer to generate an outcome that is beneficial to survival and propagation of the infected leucocyte.

Budding of Enveloped Viruses: Interferon-Induced ISG15-Antivirus Mechanisms Targeting the Release Process

Pathogenic strains of viruses that infect humans are encapsulated in membranes derived from the host cell in which they infect. After replication, these viruses are released by a budding process that requires cell/viral membrane scission. As such, this represents a natural target for innate immunity mechanisms to interdict enveloped virus spread and recent advances in this field will be the subject of this paper.

Sphingosine analogue AAL-R increases TLR7-mediated dendritic cell responses via p38 and type I IFN signaling pathways

Sphingosine analogues display immunosuppressive activities and thus have therapeutic potential in the treatment of autoimmune diseases. In this study, we investigated the effects of the sphingosine analogue AAL-R (FTY720 derivative) on dendritic cell (DC) response upon TLR stimulation. Unlike its known immunosuppressive activity, AAL-R increased TLR7-mediated DC responses by elevating the levels of MHC class I and costimulatory molecules and type I IFN expression and by enhancing the capacity of DCs to induce CD8(+) T cell proliferation. Importantly, the stimulatory activity of AAL-R was dependent on type I IFN signaling, as type I IFN receptor-deficient DCs failed to respond to AAL-R. Also, AAL-R activated p38 MAPK to increase type I IFN synthesis and TLR7-mediated DC maturation. These findings enhance our understanding of sphingosine regulation of the host immune system, in particular upon pathogenic infections.

ISG15 disrupts cytoskeletal architecture and promotes motility in human breast cancer cells

The interferon-stimulated gene 15 (ISG15) pathway is highly elevated in breast cancer; however, very little is known about how the ISG15 pathway contributes to breast tumorigenesis. In the current study, using the gene disruption approach, we demonstrate that both ISG15 and UbcH8 (ISG15-specific conjugating enzyme) disrupt F-actin architecture and formation of focal adhesions in ZR-75-1 breast cancer cells. In addition, ISG15 and UbcH8 promote breast cancer cell migration. We also demonstrate that ISG15 inhibits ubiquitin/26S proteasome-mediated turnover of proteins implicated in tumor cell motility, invasion and metastasis. Together, our results suggest that the aberrant activation of the ISG15 pathway confers a motile phenotype to breast cancer cells by disrupting cell architecture and stabilizing proteins involved in cell motility, invasion and metastasis. Because the cellular architecture is conserved and the ISG15 pathway is constitutively activated in tumor cells of different lineages, it is reasonable to assume that our observations in breast cancer must hold true for many other tumors.

Lack of reelin modifies the gene expression in the small intestine of mice

We recently demonstrated that the mucosa of the small intestine of the rat expresses reelin and some components of its signaling system. The current study evaluates whether reelin affects the intestinal gene expression profile using microarray analysis and reeler mice, a natural mutant in which reelin is not expressed. The effect of the mutation on body weight and intestinal morphology is also evaluated. The mutation reduces body and intestinal weight during the first 2 months of age and modifies the morphology of the crypts and villi. For the microarray assays, total RNA was obtained from either isolated epithelial cells or intact small intestine. Of the 45,101 genes present in the microarray the mutation significantly alters the expression of 62 genes in the isolated epithelial cell samples and of 84 in the intact small intestine. The expression of 83% of the genes tested for validation was substantiated by reverse transcriptase polymerase chain reaction. The mutation notably up-regulates genes involved in intestinal metabolism, while it down-regulates genes related with immune response, inflammation, and tumor development. Genes involved in cell proliferation, differentiation, apoptosis, membrane transport and cytoskeleton are also differently expressed in the reeler mice as compared with the control. This is the first report showing that the lack of reelin modifies intestinal morphology and gene expression profile and suggests a role for reelin in intestinal epithelium homeostasis.

Molecular predictors of gemcitabine response in pancreatic cancer

Gemcitabine is one of the most used anti-neoplastic drugs with documented activity in almost all major localizations of cancer. In pancreatic cancer treatment, gemcitabine occupies a prominent place as a first line chemotherapy, partly because of the paucity of other efficacious chemotherapy options. In fact, only a minority of pancreatic cancer patients display a response or even stability of disease with the drug. There are currently no clinically applicable means of predicting which patient will derive a clinical benefit from gemcitabine although several proposed markers have been studied. These markers are proteins involved in drug up-take, activation and catabolism or proteins that define the ability of the cell to undergo apoptosis in response to the drug. Several of these markers are reviewed in this paper. We also briefly discuss the possible role of stem cells in drug resistance to gemcitabine.

ISG15 facilitates cellular antiviral response to dengue and west nile virus infection in vitro

BACKGROUND

Dengue virus (DENV) and West Nile virus (WNV), close siblings of the Flaviviridae family, are the causative agents of Dengue hemorraghic shock or West Nile meningoencephalitis respectively. Vaccines against these two flaviviruses are currently unavailable. Interferon- Stimulated Gene 15 (ISG15), encoding an ubiquitin-like protein, is significantly induced by type I interferons or viral infections. Its roles in viral infections, however, vary with viruses, being either anti- or pro-viral. The exact roles of ISG15 in DENV and WNV infections remain unknown. In the current study, we evaluated the relevancies of ISG15 to DENV and WNV infection of a mouse macrophage cell line RAW264.7.

FINDINGS

Quantitative PCR showed that mouse Isg15 was dramatically induced in DENV or WNV- infected RAW264.7 cells compared with non-infected cells. Isg15 and two other Jak-Stat related genes, Socs1 and Socs3, were silenced using siRNA mediated RNA interference. The intracellular DENV and WNV loads, as determined by quantitative PCR, were significantly higher in Isg15 silenced cells than control cells. The expression levels of interferon beta 1 (Ifnb1) were increased significantly in Isg15, Socs1 or Socs3 siRNA treated cells. Further investigation indicated that protein modification by ISG15, so called ISGylation, was significantly enhanced in DENV-infected cells compared to that in non-infected cells.

CONCLUSIONS

These findings suggest that ISG15 plays an anti-DENV/WNV function via protein ISGylation.

Inverse association of IL28B genotype and liver mRNA expression of genes promoting or suppressing antiviral state

High intrahepatic expression levels of interferon stimulated genes (ISGs) in chronic hepatitis C patients are associated with poor response to interferon plus ribavirin combination therapy. Expression levels of 16 genes (OAS1, PKR, MxA, ISG15, RIG-I, TLR8, IRF7, IRF9, NFKBIA, IL28A/IL28B, IL29, IL28RA, IL10RB, IFNAR2, and STAT1) that promote antiviral state and 4 genes (SOCS1, SOCS3, Zc3h12a, and A20) that suppress antiviral state were analyzed using real-time PCR assays in 133 liver biopsy samples from patients infected with genotypes 1 or 2. Expression levels of genes promoting antiviral state were positively correlated with each other but were not correlated with those that suppress antiviral state. Expression levels of some ISGs were inversely associated with common polymorphisms within the IL28B locus. Genes promoting antiviral state were expressed lower (e.g., ISG15, P = 1.42E-12 and MxA, P = 6.40E-11) in individuals with the protective rs12979860 CC genotype, and genes suppressing antiviral state were expressed higher (A20, P = 0.00107 and Zc3h12a, P = 0.00129, respectively), although some ISGs were not significant after the Bonferroni correction. The expression levels of both an antiviral (MxA) and a suppressor (SOCS1) ISG were independent predictors for non-response. These results suggest that rs12979860 genotype may be associated with response to combination therapy through an inverse relationship between antiviral and suppressor ISGs in the liver.

Absent in Melanoma 2 (AIM2) is an important mediator of interferon-dependent and -independent HLA-DRA and HLA-DRB gene expression in colorectal cancers

Absent in Melanoma 2 (AIM2) is a member of the HIN-200 family of hematopoietic, IFN-inducible, nuclear proteins, associated with both, infection defense and tumor pathology. Recently, AIM2 was found to act as a DNA sensor in innate immunity. In addition, we and others have previously demonstrated a high frequency of AIM2-alterations in microsatellite unstable (MSI-H) tumors. To further elucidate AIM2 function in colorectal tumors, we here addressed AIM2-responsive target genes by microarray based gene expression profiling of 22 244 human genes. A total of 111 transcripts were significantly upregulated, whereas 80 transcripts turned out to be significantly downregulated in HCT116 cells, constitutively expressing AIM2, compared with AIM2-negative cells. Among the upregulated genes that were validated by quantitative PCR and western blotting we recognized several interferon-stimulated genes (ISGs: IFIT1, IFIT2, IFIT3, IFI6, IRF7, ISG15, HLA-DRA, HLA-DRB, TLR3 and CIITA), as well as genes involved in intercellular adhesion and matrix remodeling. Expression of ISGs correlated with expression of AIM2 in 10 different IFN-γ treated colorectal cancer cell lines. Moreover, small interfering RNA-mediated knock-down of AIM2 resulted in reduced expression of HLA-DRA, HLA-DRB and CIITA in IFN-γ-treated cells. IFN-γ independent induction of HLA-DR genes and their encoded proteins was also demonstrated upon doxycyclin-regulated transient induction of AIM2. Luciferase reporter assays revealed induction of the HLA-DR promoter upon AIM2 transfection in different cell lines. STAT-signaling was not involved in IFN-γ independent induction of ISGs, arguing against participation of cytokines released in an autostimulating manner. Our data indicate that AIM2 mediates both IFN-γ dependent and independent induction of several ISGs, including genes encoding the major histocompatibility complex (MHC) class II antigens HLA-DR-α and -β. This suggests a novel role of the IFN/AIM2/ISG cascade likewise in cancer cells.

Interferon-Induced Gene Expression in Cervical Mucosa during Human Papillomavirus Infection

The aim of this study is to monitor type I interferon (IFN) activation in the cervical mucosa of Human Papillomavirus (HPV)-infected and uninfected women attending a routine gynaecologic clinic. The expression of three IFN-induced genes (MxA coding for human Mixovirus resistance protein A, ISG15 Interferon Stimulated Gene coding for a 15 kDa ubiquitin-like protein and UBP43 coding for the ISG15 isopeptidase) was determined as the mRNA copy number in cervical cells, normalized to the mRNA ones of the beta-glucuronidase gene. Type-specific HPV-DNA load was concurrently determined in the HPV-positive samples. Out of 127 samples tested, 54 were sufficient for both DNA and RNA extraction. The type-specific HPV-DNA copy numbers in the 34 HPV-positive samples varied widely. No significant association was found between copy numbers of MxA, ISG15, UBP43 and HPV status or viral load. However, despite a marked inter-individual variability, ISG15 expression was significantly higher when low-risk HPV infections were compared with HPV-negative samples, while high-risk HPV infections had very low ISG15 levels. The lack of ISG15 activation in high-risk HPV-infected cervical cells could be due to the lack of p53-mediated induction or to HPV-directed specific inhibition of type I IFN pathways. This study approach might be of value in clarifying the role of type I IFN activation in determining the clearance or persistence of HPV infections.

The functions of signal transducers and activators of transcriptions 1 and 3 as cytokine-inducible proteins

The signal transducers and activators of transcription (STAT)1 and STAT3 genes are specifically activated by phosphorylated STATs 1 and 3, respectively, resulting in large and prolonged increases in the levels of unphosphorylated STATs (U-STATs) in response to interferons (for STAT1) or ligands that activate gp130, such as IL-6 (for STAT3). U-STATs 1 and 3 are transcription factors that drive gene expression by mechanisms distinct from those used by phosphorylated STATs. U-STAT3 drives expression of many proteins not induced by phospho-STAT3, including several that are important in tumorigenesis. U-STAT1 prolongs and increases expression of a subset of proteins induced initially in response to phospho-STAT1, leading to antiviral and immune responses that are long-lived. U-STAT1 levels are also high in some cancers, and the protein products of genes induced by U-STAT1 enhance resistance to DNA damage. Therefore, interferons not only drive short-term expression of proteins that inhibit growth and promote apoptosis and immune surveillance, but also promote long-term expression of proteins that facilitate tumor survival.

Antiviral activity of innate immune protein ISG15

The host innate immune response, including the production of type-I IFN, represents the primary line of defense against invading viral pathogens. Of the hundreds of IFN-stimulated genes (ISGs) discovered to date, ISG15 was one of the first identified and shown to encode a ubiquitin-like protein that functions, in part, as a modifier of protein function. Evidence implicating ISG15 as an innate immune protein with broad-spectrum antiviral activity continues to accumulate rapidly. This review will summarize recent findings on the innate antiviral activity of ISG15, with a focus on the interplay between ubiquitination and ISGylation pathways resulting in modulation of RNA virus assembly/budding. Indeed, ubiquitination is known to be proviral for some RNA viruses, whereas the parallel ISGylation pathway is known to be antiviral. A better understanding of the antiviral activities of ISG15 will enhance our fundamental knowledge of host innate responses to viral pathogens and may provide insight useful for the development of novel therapeutic approaches designed to enhance the immune response against such pathogens.

Identification and analysis of a Sciaenops ocellatus ISG15 homologue that is involved in host immune defense against bacterial infection

ISG15 is an interferon-stimulated gene that encodes a ubiquitin-like protein. ISG15 homologues have been identified in a number of fish species, some of which are known to be regulated at expression level by virus infection and lipopolysaccharide (LPS) treatment. However, the relationship between ISG15 and live bacterial infection has not been investigated in piscine models. In this study, an ISG15 homologue, SoISG15, was identified from red drum Sciaenops ocellatus and analyzed at expression and functional levels. The open reading frame of SoISG15 is 477 base pairs (bp) and intronless, with a 5'-untranslated region (UTR) of 91 bp and a 3'-UTR of 415 bp. The deduced amino acid sequence of SoISG15 shares 60-67% overall identities with the ISG15 of several fish species. SoISG15 possesses two conserved ubiquitin-like domains and the canonical ubiquitin conjugation motif, LRGG, at the C-terminus. Expressional analysis showed that constitutive expression of SoISG15 was highest in blood and lowest in kidney. Experimental challenges with LPS and bacterial pathogens induced significant SoISG15 expression in the kidney but not in the liver. Similar differential induction was also observed at cellular level with primary hepatocytes and head kidney (HK) lymphocytes. Poly(I:C), however, effected drastic induction of SoISG15 expression in kidney and liver at both tissue and cellular levels. Immunoblot analysis showed that SoISG15 was secreted by cultured HK lymphocytes into the extracellular milieu. Recombinant SoISG15 expressed in and purified from Escherichia coli was able to enhance the respiratory burst activity, acid phosphatase activity, and bactericidal activity of HK macrophages. Taken together, the results of this study indicated that SoISG15 possesses apparent immunological property and is likely to be involved in host immune defense against bacterial infection.

Candidate serological biomarkers for cancer identified from the secretomes of 23 cancer cell lines and the human protein atlas

Although cancer cell secretome profiling is a promising strategy used to identify potential body fluid-accessible cancer biomarkers, questions remain regarding the depth to which the cancer cell secretome can be mined and the efficiency with which researchers can select useful candidates from the growing list of identified proteins. Therefore, we analyzed the secretomes of 23 human cancer cell lines derived from 11 cancer types using one-dimensional SDS-PAGE and nano-LC-MS/MS performed on an LTQ-Orbitrap mass spectrometer to generate a more comprehensive cancer cell secretome. A total of 31,180 proteins was detected, accounting for 4,584 non-redundant proteins, with an average of 1,300 proteins identified per cell line. Using protein secretion-predictive algorithms, 55.8% of the proteins appeared to be released or shed from cells. The identified proteins were selected as potential marker candidates according to three strategies: (i) proteins apparently secreted by one cancer type but not by others (cancer type-specific marker candidates), (ii) proteins released by most cancer cell lines (pan-cancer marker candidates), and (iii) proteins putatively linked to cancer-relevant pathways. We then examined protein expression profiles in the Human Protein Atlas to identify biomarker candidates that were simultaneously detected in the secretomes and highly expressed in cancer tissues. This analysis yielded 6-137 marker candidates selective for each tumor type and 94 potential pan-cancer markers. Among these, we selectively validated monocyte differentiation antigen CD14 (for liver cancer), stromal cell-derived factor 1 (for lung cancer), and cathepsin L1 and interferon-induced 17-kDa protein (for nasopharyngeal carcinoma) as potential serological cancer markers. In summary, the proteins identified from the secretomes of 23 cancer cell lines and the Human Protein Atlas represent a focused reservoir of potential cancer biomarkers.

Herc5 attenuates influenza A virus by catalyzing ISGylation of viral NS1 protein

Ubiquitin-like protein ISG15, which is robustly induced by IFN or virus, is implicated to inhibit influenza A virus (IAV) in vivo. But the underlying mechanism still remains largely unknown. In this study, we report that Herc5 could catalyze conjugation of ISG15 onto IAV-NS1 protein, the critical virulence factor of IAV. This modification produces two more species, respectively mapped to IAV-NS1 at lysine 20, 41, 217, 219, and 108, 110, and 126. The ISGylated IAV-NS1 fails to form homodimers and inhibits relevant antiviral processes. Knockdown of Herc5 or ISG15 could partially alleviate IFN-beta-induced antiviral activities against IAV, whereas ectopic expression of the Herc5-mediated ISGylation system could distinctly potentiate IFN-beta-induced antiviral effects against IAV. Notably, IAV-NS1s of H5N1 avian IAVs display less ISGylation species than that of IAV-PR8/34 (human H1N1). Consistently, IAV-PR8/34 mutants deprived of IAV-NS1's ISGylation exhibit augmented viral propagation and virulence in both cultured cells and mice. Our study reports the first microbial target of ISGylation and uncovers the direct antiviral function and mechanism of this novel modification.

The interferon-induced gene ISG15 blocks retrovirus release from cells late in the budding process

The release of retroviruses from cells requires ubiquitination of Gag and recruitment of cellular proteins involved in endosome sorting, including the ESCRT-III proteins and the Vps4 ATPase. In response to infection, cells have evolved an interferon-induced mechanism to block virus replication through expression of the interferon-stimulated gene 15 (ISG15), a dimer homologue of ubiquitin, which interferes with ubiquitin pathways in cells. Previously, it has been reported that ISG15 expression inhibited the E3 ubiquitin ligase, Nedd4, and prevented association of the ESCRT-I protein Tsg101 with human immunodeficiency virus type 1 (HIV-1) Gag. The budding of avian sarcoma leukosis virus and HIV-1 Gag virus-like particles containing L-domain mutations can be rescued by fusion to ESCRT proteins, which cause entry into the budding pathway beyond these early steps. The release of these fusions from cells was susceptible to inhibition by ISG15, indicating that there was a block late in the budding process. We now demonstrate that the Vps4 protein does not associate with the avian sarcoma leukosis virus or the HIV-1 budding complexes when ISG15 is expressed. This is caused by a loss in interaction between Vps4 with its coactivator protein LIP5 needed to promote the formation of the ESCRT-III-Vps4 double-hexamer complex required for membrane scission and virus release. The inability of LIP5 to interact with Vps4 is the probable result of ISG15 conjugation to the ESCRT-III protein, CHMP5, which regulates the availability of LIP5. Thus, there appear to be multiple levels of ISG15-induced inhibition acting at different stages of the virus release process.

Dual Role of p53 in Innate Antiviral Immunity

Tumor suppressor p53 is widely known as 'the guardian of the genome' due to its ability to prevent the emergence of transformed cells by the induction of cell cycle arrest and apoptosis. However, recent studies indicate that p53 is also a direct transcriptional target of type I interferons (IFNs) and thus, it is activated by these cytokines upon viral infection. p53 has been shown to contribute to virus-induced apoptosis, therefore dampening the ability of a wide range of viruses to replicate and spread. Interestingly, recent studies also indicate that several IFN-inducible genes such as interferon regulatory factor 9 (IRF9), IRF5, IFN-stimulated gene 15 (ISG15) and toll-like receptor 3 (TLR3) are in fact, p53 direct transcriptional targets. These findings indicate that p53 may play a key role in antiviral innate immunity by both inducing apoptosis in response to viral infection, and enforcing the type I IFN response, and provide a new insight into the evolutionary reasons why many viruses encode p53 antagonistic proteins.

Atlantic cod (Gadus morhua L.) possesses three homologues of ISG15 with different expression kinetics and conjugation properties

Two new interferon stimulated gene 15 (ISG15) family members were identified in a subtractive cDNA library constructed from a mixture of head kidney and spleen of Atlantic cod (Gadus morhua) stimulated with polyinosinic:polycytidylic acid (poly I:C). Two full-length Atlantic cod (Ac) ISG15-2 and AcISG15-3 cDNAs were cloned with rapid amplification of cDNA ends (RACE). The cDNA sequence of AcISG15-2 encodes a 16.9kDa protein and AcISG15-3 encodes a 18.4kDa protein, both of which possess the characteristic structural features of two tandem ubiquitin-like domains and the LRGG motif necessary for conjugation. Furthermore, the AcISG15-3 protein is expressed with a C-terminal extension in common with the human ISG15 protein. Gene expression analysis using quantitative reverse transcriptase PCR (RT-qPCR) showed that AcISG15-1, AcISG15-2, and AcISG15-3 transcripts were up-regulated in head kidney after poly I:C stimulation, suggesting that these proteins may be involved in the cod immune response. However, transient expression of myc-tagged AcISG15 proteins revealed differences in their abilities to form conjugates in vitro. We show that AcISG15-2 forms covalent conjugates to a range of cellular protein as a response to poly I:C, recombinant Atlantic salmon IFNa1 (rSasaIFNa1) and infectious pancreatic necrosis virus (IPNV), whereas conjugation was absent for AcISG15-1 and AcISG15-3. Thus, these results suggest there are three ISG15 homologues in Atlantic cod and that the three proteins may play different roles in innate immunity.

Enhanced interferon signaling pathway in oral cancer revealed by quantitative proteome analysis of microdissected specimens using 16O/18O labeling and integrated two-dimensional LC-ESI-MALDI tandem MS

Oral squamous cell carcinoma (OSCC) remains one of the most common cancers worldwide, and the mortality rate of this disease has increased in recent years. No molecular markers are available to assist with the early detection and therapeutic evaluation of OSCC; thus, identification of differentially expressed proteins may assist with the detection of potential disease markers and shed light on the molecular mechanisms of OSCC pathogenesis. We performed a multidimensional (16)O/(18)O proteomics analysis using an integrated ESI-ion trap and MALDI-TOF/TOF MS system and a computational data analysis pipeline to identify proteins that are differentially expressed in microdissected OSCC tumor cells relative to adjacent non-tumor epithelia. We identified 1233 unique proteins in microdissected oral squamous epithelia obtained from three pairs of OSCC specimens with a false discovery rate of <3%. Among these, 977 proteins were quantified between tumor and non-tumor cells. Our data revealed 80 dysregulated proteins (53 up-regulated and 27 down-regulated) when a 2.5-fold change was used as the threshold. Immunohistochemical staining and Western blot analyses were performed to confirm the overexpression of 12 up-regulated proteins in OSCC tissues. When the biological roles of 80 differentially expressed proteins were assessed via MetaCore analysis, the interferon (IFN) signaling pathway emerged as one of the most significantly altered pathways in OSCC. As many as 20% (10 of 53) of the up-regulated proteins belonged to the IFN-stimulated gene (ISG) family, including ubiquitin cross-reactive protein (UCRP)/ISG15. Using head-and-neck cancer tissue microarrays, we determined that UCRP is overexpressed in the majority of cheek and tongue cancers and in several cases of larynx cancer. In addition, we found that IFN-beta stimulates UCRP expression in oral cancer cells and enhances their motility in vitro. Our findings shed new light on OSCC pathogenesis and provide a basis for the future development of novel biomarkers.

Interferon-dependent engagement of eukaryotic initiation factor 4B via S6 kinase (S6K)- and ribosomal protein S6K-mediated signals

Although the roles of Jak-Stat pathways in type I and II interferon (IFN)-dependent transcriptional regulation are well established, the precise mechanisms of mRNA translation for IFN-sensitive genes remain to be defined. We examined the effects of IFNs on the phosphorylation/activation of eukaryotic translation initiation factor 4B (eIF4B). Our data show that eIF4B is phosphorylated on Ser422 during treatment of sensitive cells with alpha IFN (IFN-alpha) or IFN-gamma. Such phosphorylation is regulated, in a cell type-specific manner, by either the p70 S6 kinase (S6K) or the p90 ribosomal protein S6K (RSK) and results in enhanced interaction of the protein with eIF3A (p170/eIF3A) and increased associated ATPase activity. Our data also demonstrate that IFN-inducible eIF4B activity and IFN-stimulated gene 15 protein (ISG15) or IFN-gamma-inducible chemokine CXCL-10 protein expression are diminished in S6k1/S6k2 double-knockout mouse embryonic fibroblasts. In addition, IFN-alpha-inducible ISG15 protein expression is blocked by eIF4B or eIF3A knockdown, establishing a requirement for these proteins in mRNA translation/protein expression by IFNs. Importantly, the generation of IFN-dependent growth inhibitory effects on primitive leukemic progenitors is dependent on activation of the S6K/eIF4B or RSK/eIF4B pathway. Taken together, our findings establish critical roles for S6K and RSK in the induction of IFN-dependent biological effects and define a key regulatory role for eIF4B as a common mediator and integrator of IFN-generated signals from these kinases.

Respiratory syncytial virus (RSV) attachment and nonstructural proteins modify the type I interferon response associated with suppressor of cytokine signaling (SOCS) proteins and IFN-stimulated gene-15 (ISG15)

Respiratory syncytial virus (RSV) is a major cause of severe lower airway disease in infants and young children, but no safe and effective RSV vaccine is yet available. Factors attributing to this problem are associated with an incomplete understanding of the mechanisms by which RSV modulates the host cell response to infection. In the present study, we investigate suppressor of cytokine signaling (SOCS)-1 and SOCS3 expression associated with the type I IFN and IFN-stimulated gene (ISG)-15 response following infection of mouse lung epithelial (MLE-15) cells with RSV or RSV mutant viruses lacking the G gene, or NS1 and NS2 gene deletions. Studies in MLE-15 cells are important as this cell line represents the distal bronchiolar and alveolar epithelium of mice, the most common animal model used to evaluate the host cell response to RSV infection, and exhibit morphologic characteristics of alveolar type II cells, a primary cell type targeted during RSV infection. These results show an important role for SOCS1 regulation of the antiviral host response to RSV infection, and demonstrate a novel role for RSV G protein manipulation of SOCS3 and modulation of ISG15 and IFNβ mRNA expression.

Gene profiling analysis of ALVAC infected human monocyte derived dendritic cells

The recombinant canarypox virus ALVAC is being extensively studied as vaccine vector for the development of new vaccine strategies against chronic infectious diseases and cancer. However, the mechanisms by which ALVAC initiates the immune response have not been completely elucidated. In order to determine the type of innate immunity triggered by ALVAC, we characterized the gene expression profile of human monocyte derived dendritic cells (MDDCs) upon ALVAC infection. These cells are permissive to poxvirus infection and play a key role in the initiation of immune responses. The majority of the genes that were up-regulated by ALVAC belong to the type I interferon signaling pathway including IRF7, STAT1, RIG-1, and MDA-5. Genes involved in the NF-κB pathway were not up-regulated. The gene encoding for the chemokine CXCL10, a direct target of the transcription factor IRF3 was among those up-regulated and DC secretion of CXCL10 following exposure to ALVAC was confirmed by ELISA. Many downstream type I interferon activated genes with anti-viral activity (PKR, Mx, ISG15 and OAS among others) were also up-regulated in response to ALVAC. Among these, ISG15 expression in its unconjugated form by Western blot analysis was demonstrated. In view of these results we propose that ALVAC induces type I interferon anti-viral innate immunity via a cytosolic pattern-recognition-receptor (PRR) sensing double-stranded DNA, through activation of IRF3 and IRF7. These findings may aid in the design of more effective ALVAC-vectored vaccines.

The ubiquitin-like molecule interferon-stimulated gene 15 (ISG15) is a potential prognostic marker in human breast cancer

INTRODUCTION

ISG15 is an ubiquitin-like molecule that is strongly upregulated by type I interferons as a primary response to diverse microbial and cellular stress stimuli. However, alterations in the ISG15 signalling pathway have also been found in several human tumour entities. To the best of our knowledge, in the current study we present for the first time a systematic characterisation of ISG15 expression in human breast cancer and normal breast tissue both at the mRNA and protein level.

METHOD

Using semiquantitative real-time PCR, cDNA dot-blot hybridisation and immunohistochemistry, we systematically analysed ISG15 expression in invasive breast carcinomas (n = 910) and normal breast tissues (n = 135). ISG15 protein expression was analysed in two independent cohorts on tissue microarrays; in an initial evaluation set of 179 breast carcinomas and 51 normal breast tissues; and in a second large validation set of 646 breast carcinomas and 10 normal breast tissues. In addition, a collection of benign and malignant mammary cell lines (n = 9) were investigated for ISG15 expression.

RESULTS

ISG15 was overexpressed in breast carcinoma cells compared with normal breast tissue, both at the RNA and protein level. Recurrence-free (p = 0.030), event-free (p = 0.001) and overall (p = 0.001) survival analyses showed a significant correlation between ISG15 overexpression and unfavourable prognosis.

CONCLUSION

Therefore, ISG15 may represent a novel breast tumour marker with prognostic significance and may be helpful in selecting patients for and predicting response to the treatment of human breast cancer.