Virus-dependent phosphorylation of the IRF-3 transcription factor regulates nuclear translocation, transactivation potential, and proteasome-mediated degradation

The interferon regulatory factors (IRF) consist of a growing family of related transcription proteins first identified as regulators of the alpha beta interferon (IFN-alpha/beta) gene promoters, as well as the interferon-stimulated response element (ISRE) of some IFN-stimulated genes. IRF-3 was originally identified as a member of the IRF family based on homology with other IRF family members and on binding to the ISRE of the ISG15 promoter. IRF-3 is expressed constitutively in a variety of tissues, and the relative levels of IRF-3 mRNA do not change in virus-infected or IFN-treated cells. In the present study, we demonstrate that following Sendai virus infection, IRF-3 is posttranslationally modified by protein phosphorylation at multiple serine and threonine residues, which are located in the carboxy terminus of IRF-3. A combination of IRF-3 deletion and point mutations localized the inducible phosphorylation sites to the region -ISNSHPLSLTSDQ- between amino acids 395 and 407; point mutation of residues Ser-396 and Ser-398 eliminated virus-induced phosphorylation of IRF-3 protein, although residues Ser-402, Thr-404, and Ser-405 were also targets. Phosphorylation results in the cytoplasm-to-nucleus translocation of IRF-3, DNA binding, and increased transcriptional activation. Substitution of the Ser-Thr sites with the phosphomimetic Asp generated a constitutively active form of IRF-3 that functioned as a very strong activator of promoters containing PRDI-PRDIII or ISRE regulatory elements. Phosphorylation also appears to represent a signal for virus-mediated degradation, since the virus-induced turnover of IRF-3 was prevented by mutation of the IRF-3 Ser-Thr cluster or by proteasome inhibitors. Interestingly, virus infection resulted in the association of IRF-3 with the CREB binding protein (CBP) coactivator, as detected by coimmunoprecipitation with anti-CBP antibody, an interaction mediated by the C-terminal domains of both proteins. Mutation of residues Ser-396 and Ser-398 in IRF-3 abrogated its binding to CBP. These results are discussed in terms of a model in which virus-inducible, C-terminal phosphorylation of IRF-3 alters protein conformation to permit nuclear translocation, association with transcriptional partners, and primary activation of IFN- and IFN-responsive genes.

Mitotic phosphorylation of histone H3 is governed by Ipl1/aurora kinase and Glc7/PP1 phosphatase in budding yeast and nematodes

Phosphorylation of histone H3 at serine 10 occurs during mitosis and meiosis in a wide range of eukaryotes and has been shown to be required for proper chromosome transmission in Tetrahymena. Here we report that Ipl1/aurora kinase and its genetically interacting phosphatase, Glc7/PP1, are responsible for the balance of H3 phosphorylation during mitosis in Saccharomyces cerevisiae and Caenorhabditis elegans. In these models, both enzymes are required for H3 phosphorylation and chromosome segregation, although a causal link between the two processes has not been demonstrated. Deregulation of human aurora kinases has been implicated in oncogenesis as a consequence of chromosome missegregation. Our findings reveal an enzyme system that regulates chromosome dynamics and controls histone phosphorylation that is conserved among diverse eukaryotes.

Wnt signaling and an APC-related gene specify endoderm in early C. elegans embryos

In a 4-cell stage C. elegans embryo, signaling by the P2 blastomere induces anterior-posterior polarity in the adjacent EMS blastomere, leading to endoderm formation. We have taken genetic and reverse genetic approaches toward understanding the molecular basis for this induction. These studies have identified a set of genes with sequence similarity to genes that have been shown to be, or are implicated in, Wnt/Wingless signaling pathways in other systems. The C. elegans genes described here are related to wnt/wingless, porcupine, frizzled, beta-catenin/armadillo, and the human adenomatous polyposis coli gene, APC. We present evidence that there may be partially redundant inputs into endoderm specification and that a subset of these genes appear also to function in determining cytoskeletal polarity in certain early blastomeres.

An exceptionally bright flare from SGR 1806–20 and the origins of short-duration γ-ray bursts

Soft-gamma-ray repeaters (SGRs) are galactic X-ray stars that emit numerous short-duration (about 0.1 s) bursts of hard X-rays during sporadic active periods. They are thought to be magnetars: strongly magnetized neutron stars with emissions powered by the dissipation of magnetic energy. Here we report the detection of a long (380 s) giant flare from SGR 1806-20, which was much more luminous than any previous transient event observed in our Galaxy. (In the first 0.2 s, the flare released as much energy as the Sun radiates in a quarter of a million years.) Its power can be explained by a catastrophic instability involving global crust failure and magnetic reconnection on a magnetar, with possible large-scale untwisting of magnetic field lines outside the star. From a great distance this event would appear to be a short-duration, hard-spectrum cosmic gamma-ray burst. At least a significant fraction of the mysterious short-duration gamma-ray bursts may therefore come from extragalactic magnetars.

A large noncoding RNA is a marker for murine hepatocellular carcinomas and a spectrum of human carcinomas

Tumor markers can facilitate understanding molecular cell biology of neoplasia and provide potential targets for the diagnosis and insight for intervention. We here identify a novel murine gene, hepcarcin (hcn), encoding a 7-kb mRNA-like transcript. The gene appears to be the murine ortholog of the human alpha gene, that is, MALAT-1. The gene and homologs lack credible open reading frames, consistent with a highly conserved large noncoding RNA (ncRNA). In all nodules of procarcinogen-induced murine hepatocellular carcinomas (HCCs) and human HCCs, expression was markedly elevated compared to the uninvolved liver. Quantitative analyses indicated a 6-7-fold increased RNA level in HCCs versus uninvolved liver, advancing this as a molecule of interest. This ncRNA was overexpressed in all five non-hepatic human carcinomas analysed, consistent with a potential marker for neoplastic cells and potential participant in the molecular cell biology of neoplasia.

Interferon regulatory factors: the next generation

Interferons are a large family of multifunctional secreted proteins involved in antiviral defense, cell growth regulation and immune activation. Viral infection induces transcription of multiple IFN genes, a response that is in part mediated by the interferon regulatory factors (IRFs). The initially characterized members IRF-1 and IRF-2 are now part of a growing family of transcriptional regulators that has expanded to nine members. The functions of the IRFs have also expanded to include distinct roles in biological processes such as pathogen response, cytokine signaling, cell growth regulation and hematopoietic development. The aim of this review is to provide an update on the novel discoveries in the area of IRF transcription factors and the important roles of the new generation of IRFs--particularly IRF-3, IRF-4 and IRF-7.

Structural and functional analysis of interferon regulatory factor 3: localization of the transactivation and autoinhibitory domains

The interferon regulatory factor 3 (IRF-3) gene encodes a 55-kDa protein which is expressed constitutively in all tissues. In unstimulated cells, IRF-3 is present in an inactive cytoplasmic form; following Sendai virus infection, IRF-3 is posttranslationally modified by protein phosphorylation at multiple serine and threonine residues located in the carboxy terminus. Virus-induced phosphorylation of IRF-3 leads to cytoplasmic to nuclear translocation of phosphorylated IRF-3, association with the transcriptional coactivator CBP/p300, and stimulation of DNA binding and transcriptional activities of virus-inducible genes. Using yeast and mammalian one-hybrid analysis, we now demonstrate that an extended, atypical transactivation domain is located in the C terminus of IRF-3 between amino acids (aa) 134 and 394. We also show that the C-terminal domain of IRF-3 located between aa 380 and 427 participates in the autoinhibition of IRF-3 activity via an intramolecular association with the N-terminal region between aa 98 and 240. After Sendai virus infection, an intermolecular association between IRF-3 proteins is detected, demonstrating a virus-dependent formation of IRF-3 homodimers; this interaction is also observed in the absence of virus infection with a constitutively activated form of IRF-3. Substitution of the C-terminal Ser-Thr phosphorylation sites with the phosphomimetic Asp in the region ISNSHPLSLTSDQ between amino acids 395 and 407 [IRF-3(5D)], but not the adjacent S385 and S386 residues, generates a constitutively activated DNA binding form of IRF-3. In contrast, substitution of S385 and S386 with either Ala or Asp inhibits both DNA binding and transactivation activities of the IRF-3(5D) protein. These studies thus define the transactivation domain of IRF-3, two domains that participate in the autoinhibition of IRF-3 activity, and the regulatory phosphorylation sites controlling IRF-3 dimer formation, DNA binding activity, and association with the CBP/p300 coactivator.

pop-1 encodes an HMG box protein required for the specification of a mesoderm precursor in early C. elegans embryos

In C. elegans embryogenesis, the MS blastomere produces predominantly mesodermal cell types, while its sister E generates only endodermal tissue. We show that a maternal gene, pop-1, is essential for the specification of MS fate and that a mutation in pop-1 results in MS adopting an E fate. Previous studies have shown that the maternal gene skn-1 is required for both MS and E development and that skn-1 encodes a transcription factor. We show here that the pop-1 gene encodes a protein with an HMG box similar to the HMG boxes in the vertebrate lymphoid-specific transcriptional regulators TCF-1 and LEF-1. We propose that POP-1 and SKN-1 function together in the early embryo to allow MS-specific differentiation.

Regulation of type I interferon gene expression by interferon regulatory factor-3

The genes of the family of interferon (IFN) regulatory factors (IRF) encode DNA binding transcriptional factors that are involved in modulation of transcription of IFN and interferon-induced genes (ISG). The presence of IRF binding sites in the promoter region of IFNA and IFNB genes indicates that IRF factors recognizing these sites play an important role in the virus-mediated induction of these genes. We have described a novel human gene of this family, IRF-3, that is constitutively expressed in a variety of cell types. IRF-3 binds to the interferon-sensitive response element (ISRE) present in the ISG15 gene promoter and activates its transcriptional activity. In the present study, we examined whether IRF-3 can modulate transcriptional activity of IFNA and IFNB promoter regions. Our results demonstrate that IRF-3 can bind to the IRF-like binding sites present in the virus-inducible region of the IFNA4 promoter and to the PRDIII region of the IFNB promoter but cannot alone stimulate their transcriptional activity in the human cell line, 293. However, the fusion protein generated from the IRF-3 binding domain and the RelA(p65) activation domain effectively activates both IFNA4 and IFNB promoters. Cotransfection of IRF-3 and RelA(p65) expression plasmids activates the IFNB gene promoter but not the promoter of IFNA4 gene that does not contain the NF-kB binding site. Surprisingly, activation of the IFNA4 gene promoter by virus and IRF-1 in these cells was inhibited by IRF-3. These data indicate that in 293 cells IRF-3 does not stimulate expression of IFN genes but can cooperate with RelA(p65) to stimulate the IFNB promoter.

Essential role of interferon regulatory factor 3 in direct activation of RANTES chemokine transcription

Localized and systemic cytokine production in virus-infected cells play an important role in the outcome of viral infection and pathogenicity. Activation of the interferon regulatory factors (IRF) in turn is a critical mediator of cytokine gene transcription. Recent studies have focused on the 55-kDa IRF-3 gene product as a direct transcriptional regulator of type 1 interferon (IFN-alpha and IFN-beta) activation in response to virus infection. Virus infection induces phosphorylation of IRF-3 on specific C-terminal serine residues and permits cytoplasmic-to-nuclear translocation of IRF-3, activation of DNA binding and transactivation potential, and association with the CBP/p300 coactivator. We previously generated constitutively active [IRF-3(5D)] and dominant-negative forms of IRF-3 that control IFN-beta and IFN-alpha gene expression. In an effort to characterize the range of immunoregulatory genes controlled by IRF-3, we now demonstrate that endogenous human RANTES gene transcription is directly induced in tetracycline-inducible IRF-3(5D)-expressing cells or paramyxovirus-infected cells. We also show that a dominant-negative IRF-3 mutant inhibits virus-induced expression of the RANTES promoter. Specific mutagenesis of overlapping ISRE-like sites located between nucleotides -123 and -96 in the RANTES promoter reduces virus-induced and IRF-3-dependent activation. These studies broaden the range of IRF-3 immunoregulatory target genes to include at least one member of the chemokine superfamily.

WRM-1 activates the LIT-1 protein kinase to transduce anterior/posterior polarity signals in C. elegans

During C. elegans development, Wnt/WG signaling is required for differences in cell fate between sister cells born from anterior/posterior divisions. A beta-catenin-related gene, wrm-1, and the lit-1 gene are effectors of this signaling pathway and appear to downregulate the activity of POP-1, a TCF/LEF-related protein, in posterior daughter cells. We show here that lit-1 encodes a serine/threonine protein kinase homolog related to the Drosophila tissue polarity protein Nemo. We demonstrate that the WRM-1 protein binds to LIT-1 in vivo and that WRM-1 can activate the LIT-1 protein kinase when coexpressed in vertebrate tissue culture cells. This activation leads to phosphorylation of POP-1 and to apparent changes in its subcellular localization. Our findings provide evidence for novel regulatory avenues for an evolutionarily conserved Wnt/WG signaling pathway.

POP-1 and anterior-posterior fate decisions in C. elegans embryos

Blastomeres in C. elegans embryos execute lineage programs wherein the fate of a cell is correlated reproducibly with the division sequence by which that cell is born. We provide evidence that the pop-1 gene functions to link anterior-posterior cell divisions with cell fate decisions. Each anterior cell resulting from an anterior-posterior division appears to have a higher level of nuclear POP-1 protein than does its posterior sister. Genes in the C. elegans Wnt pathway are required for this inequality in POP-1 levels. We show that loss of pop-1(+) activity leads to several types of anterior cells adopting the fates of their posterior sisters. These results suggest a mechanism for the invariance of blastomere lineages.

Selective DNA binding and association with the CREB binding protein coactivator contribute to differential activation of alpha/beta interferon genes by interferon regulatory factors 3 and 7

Recent studies implicate the interferon (IFN) regulatory factors (IRF) IRF-3 and IRF-7 as key activators of the alpha/beta IFN (IFN-alpha/beta) genes as well as the RANTES chemokine gene. Using coexpression analysis, the human IFNB, IFNA1, and RANTES promoters were stimulated by IRF-3 coexpression, whereas the IFNA4, IFNA7, and IFNA14 promoters were preferentially induced by IRF-7 only. Chimeric proteins containing combinations of different IRF-7 and IRF-3 domains were also tested, and the results provided evidence of distinct DNA binding properties of IRF-3 and IRF-7, as well as a preferential association of IRF-3 with the CREB binding protein (CBP) coactivator. Interestingly, some of these fusion proteins led to supraphysiological levels of IFN promoter activation. DNA binding site selection studies demonstrated that IRF-3 and IRF-7 bound to the 5'-GAAANNGAAANN-3' consensus motif found in many virus-inducible genes; however, a single nucleotide substitution in either of the GAAA half-site motifs eliminated IRF-3 binding and transactivation activity but did not affect IRF-7 interaction or transactivation activity. These studies demonstrate that IRF-3 possesses a restricted DNA binding site specificity and interacts with CBP, whereas IRF-7 has a broader DNA binding specificity that contributes to its capacity to stimulate delayed-type IFN gene expression. These results provide an explanation for the differential regulation of IFN-alpha/beta gene expression by IRF-3 and IRF-7 and suggest that these factors have complementary rather than redundant roles in the activation of the IFN-alpha/beta genes.

Primary activation of interferon A and interferon B gene transcription by interferon regulatory factor 3

The family of interferon (IFN) regulatory factors (IRFs) encodes DNA-binding transcription factors, some of which function as modulators of virus-induced signaling. The IRF-3 gene is constitutively expressed in many tissues and cell types, and neither virus infection nor IFN treatment enhances its transcription. In infected cells, however, IRF-3 protein is phosphorylated at the carboxyl terminus, which facilitates its binding to the CBP/p300 coactivator. In the present study, we demonstrate that overexpression of IRF-3 significantly enhances virus-mediated transcription of the IFNA and IFNB genes in infected cells as well as IFN synthesis. IRF-3-mediated activation of IFN genes depends in part on carboxyl-terminal phosphorylation of a cluster of Ser/Thr residues, because a mutant with Ser/Thr to Ala substitutions activates the IFN promoter less efficiently. However, overexpression of IRF-3 in human 2FTGH cells alone results in the induction of an antiviral state, which depends on functional IFN signaling, because IRF-3 does not induce an antiviral state in mutant 2FTGH cells defective in either JAK-1 or p48 functions; also no antiviral effect of IRF-3 could be demonstrated in Vero cells that lack the IFNA and IFNB genes. This finding indicates that the observed antiviral activity of IRF-3 in 2FTGH cells results mainly from the induction of IFNs. Furthermore, E1A protein inhibited IRF-3-mediated stimulation of the IFNA4 promoter in transient expression assays; this inhibition could be reversed partially by overexpression of CBP/p300 and was not demonstrated with the mutant of E1A that does not bind p300. These results identify IRF-3 and CBP/p300 as integral components of the virus-induced complex that stimulates type 1 IFN gene transcription. The observation that adenovirus E1A antagonizes IRF-3 mediated activation suggests that E1A and IRF-3 may compete for binding to CBP/p300 and implicates a novel mechanism by which adenovirus may overcome the antiviral effects of the IFN pathway.

Multiple regulatory domains control IRF-7 activity in response to virus infection

Recent studies implicate the interferon regulatory factors (IRF), IRF-3 and IRF-7, as key activators of Type 1 interferon genes, as well as the RANTES (regulated on activation normal T cell expressed) chemokine gene. Both IRF-3 and IRF-7 are regulated in part by virus-induced C-terminal phosphorylation, leading to nuclear translocation, stimulation of DNA binding, and transcriptional activities. Structure-function studies with IRF-7 suggested a complex organization of the C-terminal region, with a constitutive activation domain located between amino acids 150-246, an accessory inducibility region at the very end of IRF-7 between amino acids 467 and 503, and an inhibitory region (amino acids 341-467) adjacent to the C-terminal end that interferes with transactivation. Furthermore, an element that increases basal and virus-inducible activity is located between amino acids 278 and 305. A transcriptionally active form of IRF-7 was also generated by substitution of Ser-477 and Ser-479 residues with the phosphomimetic Asp. IRF-7, particularly IRF-7(S477D/S479D), was a strong transactivator of type I interferon and RANTES chemokine gene expression. Unlike wild type IRF-3, IRF-7 overexpression was able to stimulate inteferon gene expression in the absence of virus infection. Using tagged versions of IRF-7 and IRF-3, the formation of homo- and heterodimers was detected by co-immunoprecipitation. These results demonstrate that IRF-3 and IRF-7 transcription factors possess distinct structural characteristics that impart complementary rather than redundant functional roles in cytokine gene activation.

Triggering the interferon response: the role of IRF-3 transcription factor

The interferon (IFN) regulatory factors (IRF) consist of a growing family of related transcription proteins first identified as regulators of the IFN-alpha/beta gene promoters, as well as the IFN-stimulated response element (ISRE) of some IFN-stimulated genes. IRF-3 was originally identified as a member of the IRF family based on homology with other IRF family members and on binding to the ISRE of the IFN-stimulated gene 15 (ISG15) promoter. Several recent studies have focused attention on the unique molecular properties of IRF-3 and its role in the regulation of IFN gene expression. IRF-3 is expressed constitutively in a variety of tissues, and the relative levels of IRF-3 mRNA do not change in virus-infected or IFN-treated cells. Following virus infection, IRF-3 is posttranslationally modified by protein phosphorylation at multiple serine and threonine residues, located in the carboxy-terminus of IRF-3. Phosphorylation causes the cytoplasmic to nuclear translocation of IRF-3, stimulation of DNA binding, and increased transcriptional activation, mediated through the association of IRF-3 with the CBP/p300 coactivator. The purpose of this review is to summarize recent investigations demonstrating the important role of IRF-3 in cytokine gene transcription. These studies provide the framework for a model in which virus-dependent phosphorylation of IRF-3 alters protein conformation to permit nuclear translocation, association with transcriptional partners, and primary activation of IFN and IFN-responsive genes.

Regulation of RANTES chemokine gene expression requires cooperativity between NF-kappa B and IFN-regulatory factor transcription factors

Virus infection of host cells activates a set of cellular genes, including cytokines, IFNs, and chemokines, involved in antiviral defense and immune activation. Previous studies demonstrated that virus-induced transcriptional activation of a member of the human CC-chemokine RANTES required activation of the latent transcription factors IFN-regulatory factor (IRF)-3 and NF-kappa B via posttranslational phosphorylation. In the present study, we further characterized the regulatory control of RANTES transcription during virus infection using in vivo genomic footprinting analyses. IRF-3, the related IRF-7, and NF-kappa B are identified as important in vivo binding factors required for the cooperative induction of RANTES transcription after virus infection. Using fibroblastic or myeloid cells, we demonstrate that the kinetics and strength of RANTES virus-induced transcription are highly dependent on the preexistence of IRFs and NF-kappa B. Use of dominant negative mutants of either I kappa B-alpha or IRF-3 demonstrate that disruption of either pathway dramatically abolishes the ability of the other to bind and activate RANTES expression. Furthermore, coexpression of IRF-3, IRF-7, and p65/p50 leads to synergistic activation of RANTES promoter transcription. These studies reveal a model of virus-mediated RANTES promoter activation that involves cooperative synergism between IRF-3/IRF-7 and NF-kappa B factors.

Phosphorylation of IkappaBalpha in the C-terminal PEST domain by casein kinase II affects intrinsic protein stability

The NF-kappaB/Rel transcription factors participate in the activation of immune system regulatory genes and viral early genes including the human immunodeficiency virus type 1 long terminal repeat. NF-kappaB/Rel proteins are coupled to inhibitory molecules, collectively termed IkappaB, which are responsible for cytoplasmic retention of NF-kappaB. Cell activation leads to the phosphorylation and degradation of IkappaBalpha, permitting NG-kappaB/Rel translocation to the nucleus and target gene activation. To further characterize the signaling events that contribute to IkappaBalpha phosphorylation, a kinase activity was isolated from Jurkat T cells that specifically interacted with IkappaBalpha in an affinity chromatography step and phosphorylated IkappaBalpha with high specificity in vitro. By using an in-gel kinase assay with recombinant IkappaBalpha as substrate, two forms of the kinase (43 and 38 kDa) were identified. Biochemical criteria and immunological cross-reactivity identified the kinase activity as the alpha catalytic subunit of casein kinase II (CKII). Deletion mutants of IkappaBalpha delta1 to delta4) localized phosphorylation to the C-terminal PEST domain of IkappaBalpha. Point mutation of residues T-291, S-283, and T-299 dramatically reduced phosphorylation of IkappaBalpha by the kinase in vitro. NIH-3T3 cells that stably expressed wild-type IkappaBalpha (wtIkappaB), double-point-mutated IkappaBalpha (T291A, S283A), or triple-point-mutated IkappaBalpha (T291A, S283A, T299A) under the control of the tetracycline-responsive promoter were generated. Constitutive phosphorylation of the triple point mutant was eliminated in vivo, although tumor necrosis factor-inducible IkappaBalpha degradation was unaffected. In cell lines and in transiently transfected cells, mutation of the CKII sites in IkappaBalpha resulted in a protein with increased intrinsic stability. Together with results demonstrating a role for N-terminal sites in inducer-mediated phosphorylation and degradation of IkappaBalpha, these studies indicate that CKII sites in the C-terminal PEST domain are important for constitutive phosphorylation and intrinsic stability of IkappaBalpha.

The gamma-subunit of the coatomer complex binds Cdc42 to mediate transformation

The Ras-related GTP-binding protein Cdc42 is implicated in a variety of biological activities including the establishment of cell polarity in yeast, the regulation of cell morphology, motility and cell-cycle progression in mammalian cells and the induction of malignant transformation. We identified a Cdc42 mutant (Cdc42F28L) which binds GTP in the absence of a guanine nucleotide exchange factor, but still hydrolyses GTP with a turnover number identical to that for wild-type Cdc42. Expression of this mutant in NIH 3T3 fibroblasts causes cellular transformation, mimicking many of the characteristics of cells transformed by the Dbl oncoprotein, a known guanine nucleotide exchange factor for Cdc42. Here we searched for new Cdc42 targets in an effort to understand how Cdc42 mediates cellular transformation. We identified the gamma-subunit of the coatomer complex (gammaCOP) as a specific binding partner for activated Cdc42. The binding of Cdc42 to gammaCOP is essential for a transforming signal distinct from those elicited by Ras.

MEX-5 and MEX-6 function to establish soma/germline asymmetry in early C. elegans embryos

An asymmetrical network of cortically localized PAR proteins forms shortly after fertilization of the C. elegans egg. This network is required for subsequent asymmetries in the expression patterns of several proteins that are encoded by nonlocalized, maternally expressed mRNAs. We provide evidence that two nearly identical genes, mex-5 and mex-6, link PAR asymmetry to those subsequent protein asymmetries. MEX-5 is a novel, cytoplasmic protein that is localized through PAR activities to the anterior pole of the 1-cell stage embryo. MEX-5 localization is reciprocal to that of a group of posterior-localized proteins called germline proteins. Ectopic expression of MEX-5 is sufficient to inhibit the expression of germline proteins, suggesting that MEX-5 functions to inhibit anterior expression of the germline proteins.

A novel Cdc42Hs mutant induces cellular transformation

Cdc42Hs is a small GTPase of the Rho-subfamily, which regulates signaling pathways that influence cell morphology and polarity, cell-cycle progression and transcription. An essential role for Cdc42Hs in cell growth regulation has been suggested by the finding that the Dbl oncoprotein is an upstream activator-a guanine nucleotide exchange factor (GEF)-for Cdc42Hs, and that activated mutants of the closely related GTPases Rac and Rho are transforming. As we were unable to obtain significant over-expression of GTPase-defective Cdc42Hs mutants, we have generated a mutant, Cdc42Hs(F28L), which can undergo spontaneous GTP-GDP exchange while maintaining full GTPase activity, and thus should exhibit functional activities normally imparted by Dbl. In cultured fibroblasts, Cdc42Hs(F28L) activated the c-Jun kinase (JNK1) and stimulated filopodia formation. Cells stably expressing Cdc42Hs(F28L) also exhibited several hallmarks of transformation-reduced contact inhibition, lower dependence on serum for growth, and anchorage-independent growth. Our findings indicate that Cdc42Hs plays a role in cell proliferation, and is a likely physiological mediator of Dbl-induced transformation.

Identification of distinct signaling pathways leading to the phosphorylation of interferon regulatory factor 3

Infection of host cells by viruses leads to the activation of multiple signaling pathways, resulting in the expression of host genes involved in the establishment of the antiviral state. Among the transcription factors mediating the immediate response to virus is interferon regulatory factor-3 (IRF-3) which is post-translationally modified as a result of virus infection. Phosphorylation of latent cytoplasmic IRF-3 on serine and threonine residues in the C-terminal region leads to dimerization, cytoplasmic to nuclear translocation, association with the p300/CBP coactivator, and stimulation of DNA binding and transcriptional activities. We now demonstrate that IRF-3 is a phosphoprotein that is uniquely activated via virus-dependent C-terminal phosphorylation. Paramyxoviridae including measles virus and rhabdoviridae, vesicular stomatitis virus, are potent inducers of a unique virus-activated kinase activity. In contrast, stress inducers, growth factors, DNA-damaging agents, and cytokines do not induce C-terminal IRF-3 phosphorylation, translocation or transactivation, but rather activate a MAPKKK-related signaling pathway that results in N-terminal IRF-3 phosphorylation. The failure of numerous well characterized pharmacological inhibitors to abrogate virus-induced IRF-3 phosphorylation suggests the involvement of a novel kinase activity in IRF-3 regulation by viruses.

HHV-8 encoded vIRF-1 represses the interferon antiviral response by blocking IRF-3 recruitment of the CBP/p300 coactivators

Human herpes virus 8 (HHV-8) has developed unique mechanisms for altering cellular proliferative and apoptotic control pathways by incorporating viral homologs to several cellular regulatory genes into its genome. One of the important pirated genes encoded by the ORF K9 reading frame is a viral homolog of the interferon regulatory factors (IRF), a family of cellular transcription proteins that regulates expression of genes involved in pathogen response, immune modulation and cell proliferation. vIRF-1 has been shown to downregulate the interferon- and IRF-mediated transcriptional activation of ISG and murine IFNA4 gene promoters. In this study we demonstrate that vIRF-1 efficiently inhibited virus-induced expression of endogenous interferon B, CC chemokine RANTES and CXC chemokine IP-10 genes. Co-expression analysis revealed that vIRF-1 selectively blocked IRF-3 but not IRF-7-mediated transactivation. vIRF-1 was able to bind to both IRF-3 and IRF-7 in vivo as detected by coimmunoprecipitation analysis, but did not affect IRF-3 dimerization, nuclear translocation and DNA binding activity. Rather, vIRF-1 interacted with the CBP/p300 coactivators and efficiently inhibited the formation of transcriptionally competent IRF-3-CBP/p300 complexes. These results illustrate that vIRF-1 is able to block the early stages of the IFN response to virus infection by interfering with the activation of IRF-3 responsive, immediate early IFN genes.

The value of detecting anti-VZV IgG antibody in CSF to diagnose VZV vasculopathy

BACKGROUND

Factors that may obscure the diagnosis of varicella zoster virus (VZV) vasculopathy include the absence of rash before TIAs or stroke as well as similar clinical features and imaging, angiographic, and CSF abnormalities to those of other vasculopathies. Diagnosis relies on virologic confirmation that detects VZV DNA, anti-VZV IgG antibody, or both in the CSF.

METHODS

We reviewed our current 14 cases of patients diagnosed with VZV vasculopathy based on combined clinical, imaging, angiographic, or CSF abnormalities. All CSFs must have been tested for VZV DNA by PCR and for anti-VZV IgG antibody by enzyme immunoassay and found to be positive for either or both. Of the 14 subjects, 8 had a history of recent zoster, whereas 6 had no history of zoster rash before developing vasculopathy.

RESULTS

All 14 subjects (100%) had anti-VZV IgG antibody in their CSF, whereas only 4 (28%) had VZV DNA. The detection of anti-VZV IgG antibody in CSF was a more sensitive indicator of VZV vasculopathy than detection of VZV DNA (p < 0.001).

CONCLUSIONS

In varicella zoster virus (VZV) vasculopathy, the diagnostic value of detecting anti-VZV IgG antibody in CSF is greater than that of detecting VZV DNA. Although a positive PCR for VZV DNA in CSF is helpful, a negative PCR does not exclude the diagnosis of VZV vasculopathy. Only when the CSF is negative for both VZV DNA and anti-VZV IgG antibody can the diagnosis of VZV vasculopathy be excluded.