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1.
Clin Exp Immunol ; 174(2): 326-34, 2013 Nov.
Article in English | MEDLINE | ID: mdl-23919682

ABSTRACT

Dengue disease is a mosquito-borne infection caused by Dengue virus. Infection may be asymptomatic or variably manifest as mild Dengue fever (DF) to the most severe form, Dengue haemorrhagic fever (DHF). Mechanisms that influence disease severity are not understood. Complement, an integral component of the immune system, is activated during Dengue infection and the degree of activation increases with disease severity. Activation of the complement alternative pathway is influenced by polymorphisms within activation (factor B rs12614/rs641153, C3 rs2230199) and regulatory [complement factor H (CFH) rs800292] proteins, collectively termed a complotype. Here, we tested the hypothesis that the complotype influences disease severity during secondary Dengue infection. In addition to the complotype, we also assessed two other disease-associated CFH polymorphisms (rs1061170, rs3753394) and a structural polymorphism within the CFH protein family. We did not detect any significant association between the examined polymorphisms and Dengue infection severity in the Thai population. However, the minor allele frequencies of the factor B and C3 polymorphisms were less than 10%, so our study was not sufficiently powered to detect an association at these loci. We were also unable to detect a direct interaction between CFH and Dengue NS1 using both recombinant NS1 and DV2-infected culture supernatants. We conclude that the complotype does not influence secondary Dengue infection severity in the Thai population.


Subject(s)
Complement Factor H/genetics , Complement Pathway, Alternative/genetics , Dengue Virus , Dengue/genetics , Dengue/immunology , Adolescent , Adult , Cells, Cultured , Child , Child, Preschool , Complement C3/genetics , Complement Factor B/genetics , Female , Genetic Association Studies , Genetic Predisposition to Disease , Humans , Male , Middle Aged , Polymorphism, Genetic , Thailand , Young Adult
2.
J Biol Chem ; 276(52): 48908-14, 2001 Dec 28.
Article in English | MEDLINE | ID: mdl-11684676

ABSTRACT

We have characterized two RNA-binding proteins, of apparent molecular masses of approximately 40 and 35 kDa, which possess a single N-terminal RNA-recognition motif (RRM) followed by a C-terminal domain rich in serine-arginine dipeptides. Their primary structures resemble the single-RRM serine-arginine (SR) protein, SC35; however their functional effects are quite distinctive. The 40-kDa protein cannot complement SR protein-deficient HeLa cell S100 extract and showed a dominant negative effect in vitro against the authentic SR proteins, SF2/ASF and SC35. Interestingly, the 40- and 35-kDa proteins antagonize SR proteins and activate the most distal alternative 5' splice site of adenovirus E1A pre-mRNA in vivo, an activity that is similar to that characterized previously for the heterogeneous nuclear ribonucleoprotein particles A/B group of proteins. A series of recombinant chimeric proteins consisting of domains from these proteins and SC35 in various combinations showed that the RRM, but not the C-terminal domain rich in serine-arginine dipeptides, has a dominant role in this activity. Because of the similarity to SR proteins we have named these proteins SRrp40 and SRrp35, respectively, for SR-repressor proteins of approximately 40 and approximately 35 kDa. Both factors show tissue- and cell type-specific patterns of expression. We propose that these two proteins are SR protein-like alternative splicing regulators that antagonize authentic SR proteins in the modulation of alternative 5' splice site choice.


Subject(s)
Alternative Splicing/genetics , Neoplasm Proteins , RNA-Binding Proteins/metabolism , Repressor Proteins/metabolism , 3T3 Cells , Active Transport, Cell Nucleus , Amino Acid Sequence , Animals , Cell Cycle Proteins , Cell Nucleus/metabolism , Cloning, Molecular , Genes, Reporter , HeLa Cells , Humans , Immunohistochemistry , Mice , Molecular Sequence Data , Molecular Weight , RNA-Binding Proteins/chemistry , RNA-Binding Proteins/genetics , Recombinant Fusion Proteins/metabolism , Repressor Proteins/chemistry , Repressor Proteins/genetics , Sequence Alignment , Serine-Arginine Splicing Factors , Tissue Distribution
3.
Immunity ; 14(5): 591-602, 2001 May.
Article in English | MEDLINE | ID: mdl-11371361

ABSTRACT

In this study, we have compared the effector functions and fate of a number of human CTL clones in vitro or ex vivo following contact with variant peptides presented either on the cell surface or in a soluble multimeric format. In the presence of CD8 coreceptor binding, there is a good correlation between TCR signaling, killing of the targets, and FasL-mediated CTL apoptosis. Blocking CD8 binding using alpha3 domain mutants of MHC class I results in much reduced signaling and reduced killing of the targets. Surprisingly, however, FasL expression is induced to a similar degree on these CTLs, and apoptosis of CTL is unaffected. The ability to divorce these events may allow the deletion of antigen-specific and pathological CTL populations without the deleterious effects induced by full CTL activation.


Subject(s)
Apoptosis/immunology , HLA-A2 Antigen/immunology , HLA-B Antigens/immunology , Lymphocyte Activation/immunology , Peptides/immunology , T-Lymphocytes, Cytotoxic/immunology , Viral Proteins , CD8-Positive T-Lymphocytes/immunology , Fas Ligand Protein , Gene Products, gag/genetics , Gene Products, gag/immunology , HIV Antigens/genetics , HIV Antigens/immunology , HLA-A2 Antigen/genetics , HLA-B Antigens/genetics , HLA-B44 Antigen , Humans , Influenza A virus/genetics , Influenza A virus/immunology , Membrane Glycoproteins/immunology , Membrane Proteins/immunology , Mutagenesis , Peptide Fragments/genetics , Peptide Fragments/immunology , Phosphorylation , Receptors, Antigen, T-Cell/immunology , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/immunology , Viral Matrix Proteins/genetics , Viral Matrix Proteins/immunology , beta 2-Microglobulin/genetics , beta 2-Microglobulin/immunology , fas Receptor/immunology , gag Gene Products, Human Immunodeficiency Virus
4.
Proc Natl Acad Sci U S A ; 98(9): 5158-63, 2001 Apr 24.
Article in English | MEDLINE | ID: mdl-11309507

ABSTRACT

TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) is a recently identified member of the tumor necrosis factor cytokine superfamily. TRAIL has been shown to induce apoptosis in various tumor cell lines, whereas most primary cells seem to be resistant. These observations have raised considerable interest in the use of TRAIL in tumor therapy. Yet little is known about the physiological function of TRAIL. This is particularly the case in the immune system, where TRAIL has been suggested by some to be involved in target cell killing and lymphocyte death. We have developed a panel of mAbs and soluble proteins to address the role of TRAIL in lymphocyte development. These studies demonstrate activation-induced sensitization of thymocytes to TRAIL-mediated apoptosis and expression of the apoptosis-inducing TRAIL receptors. However, with the use of several model systems, our subsequent experiments rule out the possibility that TRAIL plays a major role in antigen-induced deletion of thymocytes. In contrast to thymocytes, there is no up-regulation of TRAIL receptors in peripheral T cells on activation, which remain resistant to TRAIL. Thus, susceptibility to TRAIL-induced apoptosis is controlled differently by central and peripheral T cells.


Subject(s)
Apoptosis/drug effects , Membrane Glycoproteins/pharmacology , T-Lymphocytes/cytology , T-Lymphocytes/drug effects , Thymus Gland/cytology , Thymus Gland/drug effects , Tumor Necrosis Factor-alpha/pharmacology , ATP Binding Cassette Transporter, Subfamily B, Member 2 , ATP-Binding Cassette Transporters/genetics , Animals , Antibodies, Monoclonal , Apoptosis Regulatory Proteins , CD4 Antigens/analysis , CD8 Antigens/analysis , Cells, Cultured , Child, Preschool , Clonal Deletion/drug effects , Cytotoxicity, Immunologic , Flow Cytometry , Genes, RAG-1/genetics , Humans , Infant , Jurkat Cells , Lymphocyte Activation , Membrane Glycoproteins/metabolism , Mice , Mice, Knockout , Organ Culture Techniques , Receptors, TNF-Related Apoptosis-Inducing Ligand , Receptors, Tumor Necrosis Factor/metabolism , T-Lymphocytes/immunology , T-Lymphocytes/metabolism , TNF-Related Apoptosis-Inducing Ligand , Thymus Gland/immunology , Thymus Gland/metabolism , Tumor Necrosis Factor-alpha/metabolism
5.
Immunity ; 15(6): 867-70, 2001 Dec.
Article in English | MEDLINE | ID: mdl-11754809

ABSTRACT

Many viruses establish life-long infections in their natural host with few if any clinical manifestations. The relationship between virus and host is a dynamic process in which the virus has evolved the means to coexist by reducing its visibility, while the host immune system attempts to suppress and eliminate infection without damage to itself. This short review describes a variety of strategies that are employed by viruses to evade host immune responses. These include virus-associated escape from T cell recognition, and resistance to apoptosis and counterattack, with special reference to two papers published in this issue of Immunity (Mueller et al., 2001; Raftery et al., 2001).


Subject(s)
Virus Diseases/virology , Virus Physiological Phenomena , Animals , Apoptosis , HIV/immunology , HIV/physiology , Herpesviridae/immunology , Herpesviridae/physiology , Humans , Models, Biological , T-Lymphocytes, Cytotoxic/immunology , Viral Proteins/physiology , Virus Diseases/immunology , Virus Latency
6.
J Immunol ; 164(10): 5287-95, 2000 May 15.
Article in English | MEDLINE | ID: mdl-10799890

ABSTRACT

CD45 is a transmembrane glycoprotein possessing tyrosine phosphatase activity, which is involved in cell signaling. CD45 is expressed on the surface of most leukocytes and can be alternatively spliced by the inclusion or skipping of three variable exons (4, 5, and 6 or A, B, and C) to produce up to eight isoforms. In T cells, the splicing pattern of CD45 isoforms changes after activation; naive cells express high m.w. isoforms of CD45 which predominantly express exon A (CD45RA), whereas activated cells lose expression of exon A to form low m.w. isoforms of CD45 including CD45RO. Little is known about the specific factors controlling the switch in CD45 splicing which occurs on activation. In this study, we examined the influence of the SR family of splicing factors, which, like CD45, are expressed in tissue-specific patterns and have been shown to modulate the alternative splicing of a variety of transcripts. We show that specific SR proteins have antagonistic effects on CD45 splicing, leading either to exon inclusion or skipping. Furthermore, we were able to demonstrate specific changes in the SR protein expression pattern during T cell activation.


Subject(s)
Alternative Splicing/immunology , Leukocyte Common Antigens/genetics , Nuclear Proteins/physiology , Phosphoproteins/physiology , RNA-Binding Proteins/physiology , Animals , Arginine/physiology , COS Cells , Exons/immunology , Humans , Leukocyte Common Antigens/metabolism , Nuclear Proteins/biosynthesis , Phosphoproteins/biosynthesis , Protein Isoforms/antagonists & inhibitors , Protein Isoforms/genetics , Protein Structure, Tertiary/physiology , RNA Precursors/physiology , RNA-Binding Proteins/biosynthesis , Serine/physiology , Serine-Arginine Splicing Factors , T-Lymphocytes/immunology , T-Lymphocytes/metabolism , Transfection
7.
Nucleic Acids Res ; 28(24): 4822-31, 2000 Dec 15.
Article in English | MEDLINE | ID: mdl-11121472

ABSTRACT

The SR proteins constitute a family of nuclear phosphoproteins which are required for constitutive splicing and also influence alternative splicing regulation. They have a modular structure consisting of one or two RNA recognition motifs (RRMs) and a C-terminal domain, rich in arginine and serine residues. The functional role of the different domains of SR proteins in constitutive splicing activity has been extensively studied in vitro; however, their contribution to alternative splicing specificity in vivo has not been clearly established. We sought to address how the modular domains of SR proteins contribute to alternative splicing specificity. The activity of a series of chimeric proteins consisting of domain swaps between different SR proteins showed that splice site selection is determined by the nature of the RRMs and that RRM2 of SF2/ASF has a dominant role and can confer specificity to a heterologous protein. In contrast, the identity of the RS domain is not important, as the RS domains are functionally interchangeable. The contribution of the RRMs to alternative splicing specificity in vivo suggests that sequence-specific RNA binding by SR proteins is required for this activity.


Subject(s)
Alternative Splicing , Nuclear Proteins/chemistry , Nuclear Proteins/metabolism , Phosphoproteins/chemistry , Phosphoproteins/metabolism , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/metabolism , Adenovirus E1A Proteins/genetics , Amino Acid Motifs , Fibronectins/genetics , Genes, Reporter/genetics , HeLa Cells , Humans , Nuclear Proteins/genetics , Phosphoproteins/genetics , Protein Structure, Tertiary , RNA Precursors/genetics , RNA Precursors/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolism , RNA-Binding Proteins/chemistry , RNA-Binding Proteins/genetics , RNA-Binding Proteins/metabolism , Serine-Arginine Splicing Factors , Substrate Specificity , Transfection
8.
Nat Struct Biol ; 6(11): 1048-53, 1999 Nov.
Article in English | MEDLINE | ID: mdl-10542098

ABSTRACT

TRAIL, an apoptosis inducing ligand, has at least four cell surface receptors including the death receptor DR5. Here we report the crystal structure at 2.2 A resolution of a complex between TRAIL and the extracellular region of DR5. TRAIL forms a central homotrimer around which three DR5 molecules bind. Radical differences in the surface charge of the ligand, together with variation in the alignment of the two receptor domains confer specificity between members of these ligand and receptor families. The existence of a switch mechanism allowing variation in receptor domain alignment may mean that it is possible to engineer receptors with multiple specificities by exploiting contact positions unique to individual receptor-ligand pairs.


Subject(s)
Apoptosis , Membrane Glycoproteins/chemistry , Membrane Glycoproteins/metabolism , Receptors, Tumor Necrosis Factor/chemistry , Receptors, Tumor Necrosis Factor/metabolism , Tumor Necrosis Factor-alpha/chemistry , Tumor Necrosis Factor-alpha/metabolism , Amino Acid Sequence , Apoptosis Regulatory Proteins , Crystallography, X-Ray , Humans , Ligands , Membrane Glycoproteins/genetics , Models, Molecular , Molecular Sequence Data , Protein Binding , Protein Conformation , Receptors, TNF-Related Apoptosis-Inducing Ligand , Sequence Alignment , Structure-Activity Relationship , Substrate Specificity , TNF-Related Apoptosis-Inducing Ligand , Tumor Necrosis Factor-alpha/genetics
9.
J Exp Med ; 189(9): 1489-96, 1999 May 03.
Article in English | MEDLINE | ID: mdl-10224289

ABSTRACT

During HIV/SIV infection, there is widespread programmed cell death in infected and, perhaps more importantly, uninfected cells. Much of this apoptosis is mediated by Fas-Fas ligand (FasL) interactions. Previously we demonstrated in macaques that induction of FasL expression and apoptotic cell death of both CD4(+) and CD8(+) T cells by SIV is dependent on a functional nef gene. However, the molecular mechanism whereby HIV-1 induces the expression of FasL remained poorly understood. Here we report a direct association of HIV-1 Nef with the zeta chain of the T cell receptor (TCR) complex and the requirement of both proteins for HIV-mediated upregulation of FasL. Expression of FasL through Nef depended upon the integrity of the immunoreceptor tyrosine-based activation motifs (ITAMs) of the TCR zeta chain. Conformation for the importance of zeta for Nef-mediated signaling in T cells came from an independent finding. A single ITAM motif of zeta but not CD3epsilon was both required and sufficient to promote activation and binding of the Nef-associated kinase (NAK/p62). Our data imply that Nef can form a signaling complex with the TCR, which bypasses the requirement of antigen to initiate T cell activation and subsequently upregulation of FasL expression. Thus, our study may provide critical insights into the molecular mechanism whereby the HIV-1 accessory protein Nef contributes to the pathogenesis of HIV.


Subject(s)
Gene Products, nef/metabolism , HIV-1/metabolism , Membrane Glycoproteins/biosynthesis , Membrane Proteins/metabolism , Receptors, Antigen, T-Cell/metabolism , Fas Ligand Protein , HIV-1/physiology , Humans , Jurkat Cells , Protein Kinases/metabolism , Protein Serine-Threonine Kinases/metabolism , Up-Regulation , nef Gene Products, Human Immunodeficiency Virus , p21-Activated Kinases
10.
Mol Cell Biol ; 19(3): 1853-63, 1999 Mar.
Article in English | MEDLINE | ID: mdl-10022872

ABSTRACT

We report striking differences in the substrate specificities of two human SR proteins, SF2/ASF and SC35, in constitutive splicing. beta-Globin pre-mRNA (exons 1 and 2) is spliced indiscriminately with either SR protein. Human immunodeficiency virus tat pre-mRNA (exons 2 and 3) and immunoglobulin mu-chain (IgM) pre-mRNA (exons C3 and C4) are preferentially spliced with SF2/ASF and SC35, respectively. Using in vitro splicing with mutated or chimeric derivatives of the tat and IgM pre-mRNAs, we defined specific combinations of segments in the downstream exons, which mediate either positive or negative effects to confer SR protein specificity. A series of recombinant chimeric proteins consisting of domains of SF2/ASF and SC35 in various combinations was used to localize trans-acting domains responsible for substrate specificity. The RS domains of SF2/ASF and SC35 can be exchanged without effect on substrate specificity. The RNA recognition motifs (RRMs) of SF2/ASF are active only in the context of a two-RRM structure, and RRM2 has a dominant role in substrate specificity. In contrast, the single RRM of SC35 can function alone, but its substrate specificity can be influenced by the presence of an additional RRM. The RRMs behave as modules that, when present in different combinations, can have positive, neutral, or negative effects on splicing, depending upon the specific substrate. We conclude that SR protein-specific recognition of specific positive and negative pre-mRNA exonic elements via one or more RRMs is a crucial determinant of the substrate specificity of SR proteins in constitutive splicing.


Subject(s)
Exons , Gene Products, tat/genetics , Globins/genetics , Immunoglobulin mu-Chains/genetics , Nuclear Proteins/metabolism , RNA Precursors , RNA Splicing , Ribonucleoproteins , Binding Sites , Chromosome Mapping , Humans , RNA-Binding Proteins , Serine-Arginine Splicing Factors , Substrate Specificity
11.
Blood ; 93(5): 1506-10, 1999 Mar 01.
Article in English | MEDLINE | ID: mdl-10029578

ABSTRACT

Human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL) probably play the major role in controlling HIV replication. However, the value of adoptive transfer of HIV-specific CTL expanded in vitro to HIV+ patients has been limited: this contrasts with the success of CTL therapy in treating or preventing Epstein-Barr virus and cytomegalovirus disease after bone marrow transplantation (BMT). We investigated the fate of expanded HIV-specific CTL clones in vivo following adoptive transfer to a patient with acquired immunodeficiency syndrome (AIDS). Two autologous CTL clones specific for HIV Gag and Pol were expanded to large numbers (>10(9)) in vitro and infused into an HIV-infected patient whose viral load was rising despite antiretroviral therapy. The fate of one clone was monitored by staining peripheral blood mononuclear cells (PBMCs) with T-cell receptor-specific tetrameric major histocompatibility complex (MHC)-peptide complexes. Although the CTL transfer was well tolerated, there were no significant changes in CD4 and CD8 lymphocyte counts and virus load. By tracking an infused clone using soluble MHC-peptide complexes, we show that cells bearing the Gag-specific T-cell receptors were rapidly eliminated within hours of infusion through apoptosis. Thus, the failure of adoptively transferred HIV-specific CTL to reduce virus load in AIDS may be due to rapid apoptosis of the infused cells, triggered by a number of potential mechanisms. Further trials of adoptive transfer of CTL should take into account the susceptibility of infused cells to in vivo apoptosis.


Subject(s)
Cytotoxicity, Immunologic , HIV Infections/immunology , HIV-1/isolation & purification , T-Lymphocytes, Cytotoxic/pathology , Adoptive Transfer , Amino Acid Sequence , Cell Death/immunology , HIV Infections/pathology , HIV Infections/therapy , Homosexuality, Male , Humans , Male , Molecular Sequence Data , Receptors, Antigen, T-Cell, alpha-beta/immunology , T-Lymphocytes, Cytotoxic/immunology , Viral Load
12.
Mol Cell Biol ; 18(10): 5930-41, 1998 Oct.
Article in English | MEDLINE | ID: mdl-9742110

ABSTRACT

Although the splicing of transcripts from most eukaryotic genes occurs in a constitutive fashion, some genes can undergo a process of alternative splicing. This is a genetically economical process which allows a single gene to give rise to several protein isoforms by the inclusion or exclusion of sequences into or from the mature mRNA. CD44 provides a unique example; more than 1,000 possible isoforms can be produced by the inclusion or exclusion of a central tandem array of 10 alternatively spliced exons. Certain alternatively spliced exons have been ascribed specific functions; however, independent regulation of the inclusion or skipping of each of these exons would clearly demand an extremely complex regulatory network. Such a network would involve the interaction of many exon-specific trans-acting factors with the pre-mRNA. Therefore, to assess whether the exons are indeed independently regulated, we have examined the alternative exon content of a large number of individual CD44 cDNA isoforms. This analysis shows that the downstream alternatively spliced exons are favored over those lying upstream and that alternative exons are often included in blocks rather than singly. Using a novel in vivo alternative splicing assay, we show that intron length has a major influence upon the alternative splicing of CD44. We propose a kinetic model in which short introns may overcome the poor recognition of alternatively spliced exons. These observations suggest that for CD44, intron length has been exploited in the evolution of the genomic structure to enable tissue-specific patterns of splicing to be maintained.


Subject(s)
Alternative Splicing , Hyaluronan Receptors/genetics , Introns , Animals , COS Cells , Exons , Humans , Mice , Purines
13.
J Immunol ; 160(1): 3-6, 1998 Jan 01.
Article in English | MEDLINE | ID: mdl-9551946

ABSTRACT

Apoptosis can be triggered by the engagement of cell surface receptors by their ligands. A growing number of receptors belonging to the TNF receptor family have been identified that contain a conserved cytoplasmic death domain. These include Fas, TNF-R1, lymphocyte-associated receptor of death (LARD), DR4, and TNF-related apoptosis-inducing ligand receptor inducer of cell killing-2 (TRICK2). The latter two are receptors for the cytotoxic ligand TNF-related apoptosis-inducing ligand (TRAIL), and one of the paradoxes raised by the cloning of these molecules was why do most cells not die upon contact with the widely expressed TRAIL molecule? This is a particular problem for lymphocytes that express DR4 and TRICK2 and are in constant circulation through TRAIL-expressing tissues. We have cloned LIT (lymphocyte inhibitor of TRAIL), which lacks a death domain. LIT is expressed predominantly on PBL, where it can competitively inhibit TRAIL-induced apoptosis through DR4/TRICK2, and may function to modulate lymphocyte sensitivity to TRAIL.


Subject(s)
Apoptosis , Membrane Glycoproteins/antagonists & inhibitors , Receptors, Immunologic/genetics , Tumor Necrosis Factor-alpha/antagonists & inhibitors , Amino Acid Sequence , Apoptosis Regulatory Proteins , Humans , Membrane Proteins/genetics , Molecular Sequence Data , Receptors, Immunologic/physiology , Repetitive Sequences, Nucleic Acid , Sequence Alignment , Sequence Homology, Amino Acid , TNF-Related Apoptosis-Inducing Ligand , Tissue Distribution
14.
Genes Dev ; 12(1): 55-66, 1998 Jan 01.
Article in English | MEDLINE | ID: mdl-9420331

ABSTRACT

The SR proteins constitute a large family of nuclear phosphoproteins required for constitutive pre-mRNA splicing. These factors also have global, concentration-dependent effects on alternative splicing regulation and this activity is antagonized by members of the hnRNP A/B family of proteins. We show here that whereas some human SR proteins are confined to the nucleus, three of them-SF2/ASF, SRp20, and 9G8-shuttle rapidly and continuously between the nucleus and the cytoplasm. By swapping the corresponding domains between shuttling and nonshuttling SR proteins, we show that the carboxy-terminal arginine/serine-rich (RS) domain is required for shuttling. This domain, however, is not sufficient to promote shuttling of an unrelated protein reporter, suggesting that stable RNA binding mediated by the RNA-recognition motifs may be required for shuttling. Consistent with such a requirement, a double point-mutation in RRM1 of SF2/ASF that impairs RNA binding prevents the protein from shuttling. In addition, we show that phosphorylation of the RS domain affects the shuttling properties of SR proteins. These findings show that different SR proteins have unique intracellular transport properties and suggest that the family members that shuttle may have roles not only in nuclear pre-mRNA splicing but also in mRNA transport, cytoplasmic events, and/or processes that involve communication between the nucleus and the cytoplasm.


Subject(s)
Nuclear Proteins/metabolism , Nucleocytoplasmic Transport Proteins , RNA-Binding Proteins/metabolism , 3T3 Cells , Animals , Binding Sites , Biological Transport , Cell Nucleus/metabolism , Cytoplasm/metabolism , HeLa Cells , Heterogeneous-Nuclear Ribonucleoproteins , Humans , Mice , Nuclear Proteins/genetics , Phosphoproteins/genetics , Phosphoproteins/metabolism , Phosphorylation , RNA-Binding Proteins/genetics , Ribonucleoproteins/genetics , Ribonucleoproteins/metabolism , Serine-Arginine Splicing Factors
15.
Curr Biol ; 7(9): 693-6, 1997 Sep 01.
Article in English | MEDLINE | ID: mdl-9285725

ABSTRACT

A subset of the tumour necrosis factor (TNF) receptor family contain a conserved intracellular motif, the death domain. Engagement of these receptors by their respective ligands initiates a signalling cascade that rapidly leads to cell death by apoptosis. We have cloned a new member of this family, TRICK2, the TRAIL (TNF-related apoptosis-inducing ligand) receptor inducer of cell killing 2. TRICK2 is expressed in a number of cell types, and to particularly high levels in lymphocytes and spleen. Two isoforms of the TRICK2 mRNA are generated by alternative pre-mRNA splicing and differ by a 29 amino-acid extension to the extracellular domain. Overexpression of TRICK2 rapidly induced apoptosis in 293T cells; this induction was dependent upon the presence of the death domain of TRICK2. Using a soluble molecule containing the TRICK2 extracellular domain, we demonstrated that TRICK2, like DR4 [1], is a receptor for TRAIL/APO-2L [2,3] and could inhibit TRAIL-induced killing of lymphocyte lines, such as the Jurkat T-cell line. TRAIL is upregulated upon lymphocyte activation, as is the intensively studied ligand for Fas, FasL [4]. TRAIL and its receptors might therefore provide another system for the regulation of lymphocyte selection and proliferation, as well as providing an additional weapon in the armoury of cytotoxic lymphocytes.


Subject(s)
Alternative Splicing , Membrane Glycoproteins/metabolism , Receptors, Tumor Necrosis Factor/metabolism , Signal Transduction , Tumor Necrosis Factor-alpha/metabolism , Amino Acid Sequence , Animals , Apoptosis , Apoptosis Regulatory Proteins , Binding Sites , COS Cells , Cloning, Molecular , Molecular Sequence Data , Receptors, TNF-Related Apoptosis-Inducing Ligand , Receptors, Tumor Necrosis Factor/genetics , TNF-Related Apoptosis-Inducing Ligand
16.
J Cell Biol ; 138(2): 225-38, 1997 Jul 28.
Article in English | MEDLINE | ID: mdl-9230067

ABSTRACT

SR proteins are required for constitutive pre-mRNA splicing and also regulate alternative splice site selection in a concentration-dependent manner. They have a modular structure that consists of one or two RNA-recognition motifs (RRMs) and a COOH-terminal arginine/serine-rich domain (RS domain). We have analyzed the role of the individual domains of these closely related proteins in cellular distribution, subnuclear localization, and regulation of alternative splicing in vivo. We observed striking differences in the localization signals present in several human SR proteins. In contrast to earlier studies of RS domains in the Drosophila suppressor-of-white-apricot (SWAP) and Transformer (Tra) alternative splicing factors, we found that the RS domain of SF2/ASF is neither necessary nor sufficient for targeting to the nuclear speckles. Although this RS domain is a nuclear localization signal, subnuclear targeting to the speckles requires at least two of the three constituent domains of SF2/ASF, which contain additive and redundant signals. In contrast, in two SR proteins that have a single RRM (SC35 and SRp20), the RS domain is both necessary and sufficient as a targeting signal to the speckles. We also show that RRM2 of SF2/ASF plays an important role in alternative splicing specificity: deletion of this domain results in a protein that, although active in alternative splicing, has altered specificity in 5' splice site selection. These results demonstrate the modularity of SR proteins and the importance of individual domains for their cellular localization and alternative splicing function in vivo.


Subject(s)
Cell Nucleus/chemistry , Nuclear Proteins/analysis , Nuclear Proteins/genetics , RNA Splicing/genetics , Alternative Splicing/genetics , Cytoplasm/chemistry , HeLa Cells , Humans , Mutation , RNA, Messenger/metabolism , RNA-Binding Proteins/genetics , Recombinant Fusion Proteins , Serine-Arginine Splicing Factors
17.
J Exp Med ; 186(1): 7-16, 1997 Jul 07.
Article in English | MEDLINE | ID: mdl-9206992

ABSTRACT

Inoculation of macaques with live attenuated SIV strains has been shown to protect against subsequent challenge with wild-type SIV. The protective mechanism(s) remain obscure. To study the effect in more detail, we have investigated the role of virus-specific CTL responses in macaques infected with an attenuated SIV strain (pC8), which has a four-amino acid deletion in the nef gene, as compared with the wild-type SIVmac32H clone (pJ5). Cynomolgus macaques infected with pC8 were protected against subsequent challenge with pJ5 and did not develop any AIDS-like symptoms in the 12 months after infection. The pC8-induced protection was associated with high levels of virus-specific CTL responses to a variety of viral antigens. In contrast, pJ5-infected macaques had little, if any, detectable CTL response to the viral proteins after three months. The latter group of macaques also showed increased Fas expression and apoptotic cell death in both the CD4(+) and CD8(+) populations. In vitro, pJ5 but not pC8 leads to an increase in FasL expression on infected cells. Thus the expression of FasL may protect infected cells from CTL attack, killing viral-specific CTLs in the process, and providing a route for escaping the immune response, leading to the increased pathogenicity of pJ5. pC8, on the other hand does not induce FasL expression, allowing the development of a protective CTL response. Furthermore, interruption of the Fas-FasL interaction allows the regeneration of viral-specific CTL responses in pJ5-infected animals. This observation suggests an additional therapeutic approach to the treatment of AIDS.


Subject(s)
CD4-Positive T-Lymphocytes/immunology , CD8-Positive T-Lymphocytes/immunology , Immunity, Cellular , Membrane Glycoproteins/immunology , Simian Acquired Immunodeficiency Syndrome/immunology , Simian Immunodeficiency Virus , Acquired Immunodeficiency Syndrome/immunology , Animals , Fas Ligand Protein , Flow Cytometry , Humans , Jurkat Cells
18.
Proc Natl Acad Sci U S A ; 94(9): 4615-9, 1997 Apr 29.
Article in English | MEDLINE | ID: mdl-9114039

ABSTRACT

Fas and TNF-R1 are cysteine-rich cell surface receptors related to the low-affinity nerve growth factor receptor family. Engagement of these receptors by their respective ligands, FasL and tumor necrosis factor, leads to apoptosis that is signaled through a conserved intracellular portion of the receptor termed the "death domain." We have cloned a new member of this family, lymphocyte-associated receptor of death (LARD), which leads to spontaneous apoptosis when expressed in 293T cells. The expression of LARD is more tightly regulated than that of either Fas or TNF-R1 as it is found predominantly on lymphocytes (T and B cells) but not on macrophages or a number of transformed lymphocyte cell lines. Alternative pre-mRNA splicing generates at least 11 distinct isoforms of LARD. The full-length isoform, LARD-1, extends to include the transmembrane and death domains, whereas the other isoforms encode potentially secreted molecules. Naive B and T cells express very little LARD-1 but express combinations of the other isoforms. Upon T cell activation, a programmed change in alternative splicing occurs so that the full-length, membrane-bound LARD-1 predominates. This may have implications for the control of lymphocyte proliferation following activation.


Subject(s)
Alternative Splicing , Apoptosis , Lymphocytes/immunology , Lymphoid Tissue/immunology , Receptors, Tumor Necrosis Factor/genetics , Amino Acid Sequence , Cloning, Molecular , Gene Expression , HeLa Cells , Humans , Molecular Sequence Data , RNA Precursors/metabolism , RNA, Messenger/metabolism , Receptors, Nerve Growth Factor/genetics , Receptors, Tumor Necrosis Factor/biosynthesis , Receptors, Tumor Necrosis Factor, Member 25 , Recombinant Proteins/biosynthesis , Sequence Analysis, DNA , Sequence Homology, Amino Acid
19.
EMBO J ; 14(17): 4336-49, 1995 Sep 01.
Article in English | MEDLINE | ID: mdl-7556075

ABSTRACT

SR proteins have a characteristic C-terminal Ser/Arg-rich repeat (RS domain) of variable length and constitute a family of highly conserved nuclear phosphoproteins that can function as both essential and alternative pre-mRNA splicing factors. We have cloned a cDNA encoding a novel human SR protein designated SRp30c, which has an unusually short RS domain. We also cloned cDNAs encoding the human homologues of Drosophila SRp55/B52 and rat SRp40/HRS. Recombinant proteins expressed from these cDNAs are active in constitutive splicing, as shown by their ability to complement a HeLa cell S100 extract deficient in SR proteins. Additional cDNA clones reflect extensive alternative splicing of SRp40 and SRp55 pre-mRNAs. The predicted protein isoforms lack the C-terminal RS domain and might be involved in feedback regulatory loops. The ability of human SRp30c, SRp40 and SRp55 to modulate alternative splicing in vivo was compared with that of other SR proteins using a transient contransfection assay. The overexpression of individual SR proteins in HeLa cells affected the choice of alternative 5' splice sites of adenovirus E1A and/or human beta-thalassemia reporters. The resulting splicing patterns were characteristic for each SR protein. Consistent with the postulated importance of SR proteins in alternative splicing in vivo, we demonstrate complex changes in the levels of mRNAs encoding the above SR proteins upon T cell activation, concomitant with changes in the expression of alternatively spliced isoforms of CD44 and CD45.


Subject(s)
Alternative Splicing , Nuclear Proteins/biosynthesis , Nuclear Proteins/chemistry , Phosphoproteins/biosynthesis , Phosphoproteins/chemistry , Amino Acid Sequence , Animals , Arginine , Base Sequence , Conserved Sequence , DNA Primers , DNA, Complementary , Drosophila , HeLa Cells , Humans , Kinetics , Mice , Molecular Sequence Data , Organ Specificity , Polymerase Chain Reaction , RNA Precursors/biosynthesis , RNA, Messenger/biosynthesis , RNA-Binding Proteins , Recombinant Proteins/biosynthesis , Repetitive Sequences, Nucleic Acid , Sequence Homology, Amino Acid , Serine , Serine-Arginine Splicing Factors
20.
Hum Mol Genet ; 4(4): 501-6, 1995 Apr.
Article in English | MEDLINE | ID: mdl-7633396

ABSTRACT

A 4.1 kb genomic region, spanning the insulin (INS) gene, confers genetic susceptibility to Type 1 or insulin-dependent diabetes mellitus (IDDM). Ten polymorphisms within this region form two predominant, complementary haplotypes. We have been studying the effects of these polymorphisms on the levels of insulin mRNA. Cloned genomic DNA fragments representing these two separate haplotypes were transiently transfected into a rodent pancreatic beta cell line, HIT-T15. These studies revealed that insulin mRNA levels were consistently higher in the transfectants expressing the diabetic haplotype. Over-expression of insulin mRNA may provide the basic mechanism for the diabetic susceptibility encoded at the INS locus.


Subject(s)
Diabetes Mellitus, Type 1/genetics , Gene Expression Regulation/genetics , Haplotypes , Insulin/genetics , Animals , Base Sequence , Chromosome Mapping , Cloning, Molecular , DNA Primers , Guinea Pigs , Humans , Molecular Sequence Data , RNA, Messenger/genetics , RNA, Messenger/metabolism , Transfection , Tumor Cells, Cultured
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