Biomedical subjects

P M Pitha

Publications and source records attributed to P M Pitha.

At least 19 recordsLinked to original sources

PubMed2000

Reconstitution of virus-mediated expression of interferon alpha genes in human fibroblast cells by ectopic interferon regulatory factor-7.

Type I interferons constitute an important part of the innate immune response against viral infection. Unlike the expression of interferon (IFN) B gene, the expression of IFNA genes is restricted to the lymphoid cells. Both IFN regulatory factor 3 and 7 (IRF-3 and IRF-7) were suggested to play positive roles in these genes expression. However, their role in the differential expression of individual subtypes of human IFNA genes is unknown. Using various IFNA reporter constructs in transient transfection assay we found that overexpression of IRF-3 in virus infected 2FTGH cells selectively activated IFNA1 VRE, whereas IRF-7 was able to activate IFNA1, A2, and A4. The binding of recombinant IRF-7 and IRF-3 to these VREs correlated with their transcriptional activation. Nuclear proteins from infected and uninfected IRF-7 expressing 2FTGH cells formed multiple DNA-protein complexes with IFNA1 VRE, in which two unique DNA-protein complexes containing IRF-7 were detected. In 2FTGH cells, virus stimulated expression of IFNB gene but none of the IFNA genes. Reconstitution of IRF-7 synthesis in these cells resulted, upon virus infection, in the activation of seven endogenous IFNA genes in which IFNA1 predominated. These studies suggest that IRF-7 is a critical determinant for the induction of IFNA genes in infected cells.

Animals↗

PubMed2000

Inhibition of CD3/CD28-mediated activation of the MEK/ERK signaling pathway represses replication of X4 but not R5 human immunodeficiency virus type 1 in peripheral blood CD4(+) T lymphocytes.

Binding of human immunodeficiency virus type 1 (HIV-1) to CD4 receptors induces multiple cellular signaling pathways, including the MEK/ERK cascade. While the interaction of X4 HIV-1 with CXCR4 does not seem to activate this pathway, viruses using CCR5 for entry efficiently activate MEK/ERK kinases (W. Popik, J. E. Hesselgesser, and P. M. Pitha, J. Virol. 72:6406-6413, 1998; W. Popik and P. M. Pitha, Virology 252:210-217, 1998). Since the importance of MEK/ERK in the initial steps of viral replication is poorly understood, we have examined the role of MEK/ERK signaling in the CD3- and CD28 (CD3/CD28)-mediated activation of HIV-1 replication in resting peripheral blood CD4(+) T lymphocytes infected with X4 or R5 HIV-1. We have found that the MEK/ERK inhibitor U0126 selectively inhibited CD3/CD28-stimulated replication of X4 HIV-1, while it did not affect the replication of R5 HIV-1. Inhibition of the CD3/CD28-stimulated MEK/ERK pathway did not affect the formation of the early proviral transcripts in cells infected with either X4 or R5 HIV-1, indicating that virus reverse transcription is not affected in the absence of MEK/ERK signaling. In contrast, the levels of nuclear provirus in cells infected with X4 HIV-1, detected by the formation of circular proviral DNA, was significantly lower in cells stimulated in the presence of MEK/ERK inhibitor than in the absence of the inhibitor. However, in cells infected with R5 HIV-1, the inhibition of the MEK/ERK pathway did not affect nuclear localization of the proviral DNA. These data suggest that the nuclear import of X4, but not R5, HIV-1 is dependent on a CD3/CD28-stimulated MEK/ERK pathway.

Biological Transport↗

PubMed1999

Type I interferon is a powerful inhibitor of in vivo HIV-1 infection and preserves human CD4(+) T cells from virus-induced depletion in SCID mice transplanted with human cells.

Although several studies are available on the in vitro inhibitory activities of type I interferon (IFN) on HIV-1 replication, the role of these cytokines in the pathogenesis of AIDS is still matter of conjecture. Both beneficial and adverse effects have been envisaged and considered as a possible rationale for the development of either IFN or anti-IFN therapies in HIV-1-infected patients. In the present study, we have evaluated the efficacy of human type I IFN on HIV-1 infection and virus-induced depletion of human CD4 T cells in two models established in SCID mice. In SCID mice transplanted with human U937 cells (U937-SCID mouse model), continuous treatment with type I consensus IFN (CIFN) resulted in a total suppression of HIV-1 infection. This inhibitory effect was superior to that obtained after AZT treatments. Results from an ensemble of experiments in SCID mice transplanted with either control or genetically modified human U937 cells transduced with a Tat-inducible IFN-alpha gene (LTR-IFN-A2 U937) indicated that low levels of IFN-alpha, produced locally as a result of virus infection, were extremely effective in inhibiting acute HIV infection and virus replication. Of interest, LTR-IFN-A2 U937 cells conferred a strong anti-HIV-1 protection to coinjected bystander U937 cells. Notably, experiments with SCID mice reconstituted with human PBL (hu-PBL-SCID mouse model) showed that treatment with CIFN inhibited HIV-1 replication more effectively than AZT treatment. Remarkably, treatment with CIFN resulted in a clear-cut protection from the virus-induced depletion of human CD4 T cells, which was also associated with the generation of an antibody response toward HIV-1 antigens in 50% of the virus-injected xenografts. These results suggest that type I IFN efficiently preserves human CD4(+) cells from virus-induced damage in hu-PBL-SCID mice, not only by inducing an antiviral state in target cells but also by stimulating anti-HIV-1 human immune responses in vivo.

Animals↗

PubMed1999

Retinoic acid resistance in NB4 APL cells is associated with lack of interferon alpha synthesis Stat1 and p48 induction.

In the t(15;17) acute promyelocytic leukaemia (APL), all trans-retinoic (RA) treatment induces maturation leading to clinically complete but not durable remission, as RA resistance develops in the treated patients as well as in vitro. RA and interferons (IFNs) are known inhibitors of proliferation in various cells including those from APL. In this report, we show that they can act cooperatively to inhibit growth and to induce differentiation of NB4 cells but not of two RA-resistant NB4 derived cell lines, NB4-R1 and NB4-R2. However, the resistant cell lines respond to IFN. In NB4 cells, RA increases the expression of Stat1, p48 and IRF-1, three transcription factors playing a central role in the IFN response and induces the synthesis and the secretion of IFN alpha. RA-induced IFN alpha seems to play a role in inhibition of NB4 cell growth but not in their differentiation. In the resistant cells, NB4-R1 and NB4-R2, both the induction of IFN and the increase of Statl and p48 expression by RA are completely blocked. In contrast, IRF-1 mRNA and protein expressions are induced in the three cell lines. This suggests that increase of IRF-1 expression is not sufficient for IFN induction. Our results identify some defects linked to RA-resistance in APL and support the hypothesis that RA-induced Stat1 expression and IFN secretion may be one of the mechanisms mediating growth inhibition by RA.

Cell Differentiation↗

PubMed1999

Lipopolysaccharide inhibits virus-mediated induction of interferon genes by disruption of nuclear transport of interferon regulatory factors 3 and 7.

We have studied the effects of lipopolysaccharide (LPS) on the Newcastle disease virus (NDV)-mediated induction of cytokine genes expression. Raw cells treated with LPS before or after virus infection showed down-regulation in the expression of interferon A and, to a lesser extent, interferon B genes. In contrast, induction of the interleukin (IL)-6 gene was enhanced. The effects of LPS were not a result of the suppression of virus replication, because the transcription of viral nucleocapsid gene was not affected. Consistent with these findings, LPS also suppressed the NDV-mediated induction of chloramphenicol acetyltransferase reporter gene driven by murine interferon A4 promoter in a transient transfection assay. Furthermore, LPS inhibited virus-mediated phosphorylation of interferon regulatory factor (IRF)-3 and the consequent translocation of IRF-3 from cytoplasm to nucleus. The LPS-mediated inhibition of IFNA gene expression was much weaker in infected Raw cells that constitutively overexpressed IRF-3. The nuclear translocation of IRF-7 in infected cells was also inhibited by LPS. These data suggest that LPS down-regulates the virus-mediated induction of IFNA genes by post-translationally targeting the IRF-3 and IRF-7 proteins.

Animals↗

PubMed1999

Identification and genetic mapping of differentially expressed genes in mice differing at the If1 interferon regulatory locus.

A subtractive cDNA library was used to identify differentially expressed genes in mouse strains that differ at If1, a locus that regulates response to interferon induction by Newcastle Disease Virus infection. Among the isolated clones, sequence analysis identified the ribosomal proteins L37a and S8 as well as cDNAs for thymosine beta4, the QM transcriptional factor, and a novel genetic sequence. Analysis of two multilocus mouse crosses showed that the thymosine beta4 gene, Ptmb4, is present as a single-copy gene that maps to distal Chr X. The L37a, S8, and QM clones are all members of large multilocus families. These five clones were used to determine the map locations for 37 loci, of which 31 had not previously been described. The novel genetic sequence, D3Ppr1, mapped to distal Chr 3 near the position of the If1 locus, suggesting it may be a candidate for this regulatory gene.

Animals↗

PubMed1999

Cloning and functional analysis of the human IRF-3 promoter.

We have isolated a genomic clone of the human IRF-3 gene containing 779 nucleotides of the 5' flanking region and the complete intron exon sequence. The gene has eight exons which span about 6 kb on chromosome 19q13.3. The IRF-3 promoter has neither a conserved TATA box nor a CCAAT box motif but is GC rich. Several putative DNA-binding elements were identified, including three SP-1 sites, a USF element, a HOX box, a CarG box, and an NF-1 site. Deletion analysis of the promoter region showed that the core basal promoter, consisting of 113 bp 5' of the first transcription start site, was sufficient for constitutive expression. This region contains only one of the SP-1 sites as well as the HOX element and NF-1 site, and although it is GC rich, it does not contain any of the other putative DNA-binding sites. In contrast, the mouse IRF-3 promoter, while displaying a high degree of homology with the human promoter, contains both TATA and CCAAT box motifs, suggesting that, at least at the level of transcription initiation, these genes may be differentially regulated.

Animals↗

PubMed1999

Functional analysis of human herpesvirus 8-encoded viral interferon regulatory factor 1 and its association with cellular interferon regulatory factors and p300.

Human herpesvirus 8/Kaposi sarcoma-associated virus (HHV-8/KSHV) contains, in addition to genes required for viral replication, a unique set of nonstructural genes which may be part of viral mimicry and contribute to viral replication and pathogenesis in vivo. Among these, HHV-8 encodes four open reading frames (ORFs) that showed homology to the transcription factors of the interferon regulatory factor (IRF) family. The ORF K9, viral IRF 1 (vIRF-1), has been cloned, and it was shown that, when overexpressed, it down modulates the interferon-mediated transcriptional activation of the interferon-stimulated gene 15 (ISG 15) promoter, and the role of vIRF-1 in viral mimicry was implied. However, the molecular mechanism of this effect has not been clarified. Here, we extend this observation and show that vIRF-1 also downregulates the transcriptional activity of IFNA gene promoter in infected cells by interfering with the transactivating activity of cellular IRFs, including IRF-1 and IRF-3. We further show that ectopic expression of vIRF-1 in NIH 3T3 cells confers resistance to tumor necrosis factor alpha-induced apoptosis. While vIRF-1 is unable to bind DNA with the same specificity as cellular IRFs, we demonstrate by in vitro binding assay that it can associate with the family of cellular IRFs, such as IRF-1 and the interferon consensus sequence binding protein. vIRF-1 interaction domain was localized between amino acids (aa) 152 and 243. While no binding between the full-size IRF-3 and vIRF-1 could be detected by the same assay, we show that vIRF-1 also targets the carboxy-terminal region (aa 1623 to 2414) of the transcriptional coactivator p300 which could also bind IRF-3 and IRF-1. These results demonstrate that vIRF-1 can modulate the transcription of the IFNA genes by direct heterodimerization with members of the IRF family, as well as by competitive binding with cellular transcription factors to the carboxy-terminal region of p300.

3T3 Cells↗

PubMed1999

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.

Base Sequence↗

PubMed1998

Early activation of mitogen-activated protein kinase kinase, extracellular signal-regulated kinase, p38 mitogen-activated protein kinase, and c-Jun N-terminal kinase in response to binding of simian immunodeficiency virus to Jurkat T cells expressing CCR5 receptor.

We have shown that the binding of simian immunodeficiency virus (SIV) to Jurkat T cells expressing CD4 receptor strongly induces mitogen-activated protein (MAP) kinase kinase (MEK) and extracellular signal-regulated kinases 1 and 2 (ERK1/2) and only weakly induces p38 MAP kinase and c-Jun N-terminal kinase (JNK). Similarly, T-tropic NL4-3 virus, which uses both CD4 and CXCR4 receptors for entry, stimulated in these cells the MEK/ERK MAP kinase (MAPK) pathway in a CD4 receptor-dependent manner (Popik and Pitha, 1998). In contrast, both macrophage-tropic SIVmac316 and T cell-tropic SIVmac239, which in addition to CD4 require CCR5 coreceptor for entry, significantly enhanced early MEK/ERK, p38 MAPK, and JNK signaling in Jurkat cells expressing constitutively or transiently the CCR5 receptor. Together, this study provides the evidence that viruses using CXCR4 or CCR5 receptors for entry may differentially use signaling properties of their specific coreceptors to stimulate MAP kinase cascades. In addition, although SIVmac239 and SIVmac316 use different structural domains of the CCR5 receptor for entry, both viruses stimulate early phosphorylation of MEK, ERK, p38, and JNK independently of their tropism and replication.

CD4-Positive T-Lymphocytes↗

PubMed1998

Characterization of the interferon regulatory factor-7 and its potential role in the transcription activation of interferon A genes.

The family of interferon regulatory factors (IRFs) plays an important role in modulating cellular responses to viral infection and cytokines, including IFNs. The transcription factors that are involved in the transcriptional activation of the IFNB gene have been extensively studied. However, the molecular mechanism by which virus activates the expression of the IFNA gene remains to be defined. Recently, we have identified a new IRF-7 isoform, denoted as IRF-7H, which encodes a protein of 514 amino acids and is most closely related to the IRF-3. The expression of IRF-7 is restricted to the lymphoid cell types and is inducible by virus, lipopolysaccharide, and IFNA. The functional characterization of IRF-7H reveals a presence of transactivation domain located carboxyl-terminal to its DNA binding domain. Overexpression of IRF-7H results in an activation of IFNA promoter in transient transfection assay and a strong enhancement of virus-mediated activation of this promoter. Whereas in uninfected cells, overexpressed IRF-7H is present mainly in the cytoplasm, viral infection facilitates the transfer of IRF-7H to the nucleus; overexpression of IRF-3 interferes with the virus-induced translocation of IRF-7H. Thus, IRF-7 exhibits functional similarity to IRF-3; however, the preferential expression of IRF-7 in lymphoid cells (the cell type that expresses IFNA) suggests that IRF-7 may play a critical role in regulating the IFNA gene expression.

Alternative Splicing↗

PubMed1998

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.

Adenoviridae↗

PubMed1998

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.

Amino Acid Sequence↗

PubMed1998

Binding of human immunodeficiency virus type 1 to CD4 and CXCR4 receptors differentially regulates expression of inflammatory genes and activates the MEK/ERK signaling pathway.

We have previously shown that binding of human immunodeficiency virus type 1 (HIV-1) virions to CD4 receptors stimulates association of Lck with Raf-1 and results in the activation of Raf-1 kinase in a Ras-independent manner. In the present study, we demonstrate that HIV-1 envelope glycoproteins of both T-cell-tropic and macrophagetropic strains rapidly activate the ERK/mitogen-activated protein (MAP) kinase pathway and the binding of nuclear transcription factors (AP-1, NF-kappaB, and C/EBP) and stimulate expression of cytokine and chemokine genes. The activation of this signaling pathway requires functional CD4 receptors and is independent of binding to CXCR4. Binding of the natural ligand stromal cell-derived factor 1 (SDF-1) to CXCR4, which inhibits entry of T-cell-tropic HIV-1, activates also the ERK/MAP kinase pathway. However, SDF-1 did not affect the CD4-mediated expression of cytokine and chemokine genes. These results provide firm molecular evidence that binding of HIV-1 envelope glycoproteins to CD4 receptor initiates a signaling pathway(s) independent of the binding to the chemokine receptor that leads to the aberrant expression of inflammatory genes and may contribute significantly to HIV-1 replication as well as to deregulation of the immune system.

Antibodies, Monoclonal↗

PubMed1998

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.

Amino Acid Sequence↗

PubMed1998

Infection with human immunodeficiency virus type 1 upregulates DNA methyltransferase, resulting in de novo methylation of the gamma interferon (IFN-gamma) promoter and subsequent downregulation of IFN-gamma production.

The immune response to pathogens is regulated by a delicate balance of cytokines. The dysregulation of cytokine gene expression, including interleukin-12, tumor necrosis factor alpha, and gamma interferon (IFN-gamma), following human retrovirus infection is well documented. One process by which such gene expression may be modulated is altered DNA methylation. In subsets of T-helper cells, the expression of IFN-gamma, a cytokine important to the immune response to viral infection, is regulated in part by DNA methylation such that mRNA expression inversely correlates with the methylation status of the promoter. Of the many possible genes whose methylation status could be affected by viral infection, we examined the IFN-gamma gene as a candidate. We show here that acute infection of cells with human immunodeficiency virus type 1 (HIV-1) results in (i) increased DNA methyltransferase expression and activity, (ii) an overall increase in methylation of DNA in infected cells, and (iii) the de novo methylation of a CpG dinucleotide in the IFN-gamma gene promoter, resulting in the subsequent downregulation of expression of this cytokine. The introduction of an antisense methyltransferase construct into lymphoid cells resulted in markedly decreased methyltransferase expression, hypomethylation throughout the IFN-gamma gene, and increased IFN-gamma production, demonstrating a direct link between methyltransferase and IFN-gamma gene expression. The ability of increased DNA methyltransferase activity to downregulate the expression of genes like the IFN-gamma gene may be one of the mechanisms for dysfunction of T cells in HIV-1-infected individuals.

CD4-Positive T-Lymphocytes↗

PubMed1997

The IRS-pathway operates distinctively from the Stat-pathway in hematopoietic cells and transduces common and distinct signals during engagement of the insulin or interferon-alpha receptors.

Binding of interferon-alpha (IFN-alpha) to its receptor on hematopoietic cells activates the signal transducers and activators of transcription (Stat)- and insulin receptor substrate (IRS)-pathways, and regulates expression of antiproliferative and antiviral activities. However, it remains unknown whether these two pathways cooperate in the generation of IFN-alpha responses or function independently, and whether IRS-proteins transduce distinct downstream signals in response to IFNs or insulin/insulin-like growth factor (IGF)-1-mediated activation. Our data show that in response to IFN-alpha treatment, IRS-1 functions selectively as a docking protein for the SH2 domains of the p85 subunit of the PI 3'-kinase, but not the SH2 domain of Grb-2 which is engaged during insulin/IGF-1 signaling. In studies with THP-1 human myelomonocytic cells and 32D mouse myeloid cells, which are IRS-defective, we found that the IFN-alpha-regulated activation of Stat-1, Stat-2, and Stat-3 does not require the function of the IRS-system. Furthermore, THP-1 cells are responsive to the protective effect of IFN-alpha against vesicular stomatitis virus. Both 32D and THP-1 cells were resistant to the growth inhibitory effect of IFN-alpha, but this effect was not reversible by expression of IRS-1 or IRS-2 alone in 32D cells. Taken altogether these data show that: (1) The IRS-system transduces common and distinct signals in response to IFN-alpha or insulin/lGF-1 stimulation of hematopoietic cells. (2) The IRS-pathway operates separately from the Stat-pathway, and its function is not essential for the generation of the antiviral effect of IFN-alpha. (3) Neither the IRS- nor the Stat-pathways alone are sufficient to mediate the antiproliferative effects of IFN-alpha in hematopoietic cells, and additional signaling elements are required.

Animals↗

PubMed1997

Interferons and cytokines on a grand scale.

The first joint meeting of the International Cytokine Society and the International Society for Interferon and Cytokine Research was held in Geneva on 6-10 October 1996. In this report, Fran Balkwill and Paula Pitha relate how signal transduction, molecular genetics and structural biology have helped to provide a unifying focus to presentations dealing with 100+ cytokines and an even larger assortment of receptors and associated signal transducers.

Animals↗