ABSTRACT
Heterogeneous nuclear ribonucleoprotein (hnRNP) A1 is involved in pre-mRNA splicing in the nucleus and translational regulation in the cytoplasm. The cytoplasmic redistribution of hnRNP A1 is a regulated process during viral infection and cellular stress. Here we demonstrate that hnRNP A1 not only is an internal ribosome entry site (IRES) trans-acting factor that binds specifically to the 5' untranslated region (UTR) of enterovirus 71 (EV71) and regulates IRES-dependent translation but also binds to the 5' UTR of Sindbis virus (SV) and facilitates its translation. The cytoplasmic relocalization of hnRNP A1 in EV71-infected cells leads to the enhancement of EV71 IRES-mediated translation, and its function can be substituted by hnRNP A2, whereas the cytoplasmic relocalization of hnRNP A1 following SV infection enhances the SV translation, but this function cannot be replaced by hnRNP A2. Our study provides the first direct evidence that the cytoplasmic relocalization of hnRNP A1 controls not only the IRES-dependent but also non-IRES-dependent translation initiations of RNA viruses.
Subject(s)
5' Untranslated Regions , Enterovirus A, Human/genetics , Heterogeneous-Nuclear Ribonucleoprotein Group A-B/metabolism , Sindbis Virus/genetics , Animals , Binding Sites , Chick Embryo , Chlorocebus aethiops , Cytoplasm/metabolism , Enterovirus A, Human/physiology , Gene Expression Regulation, Viral , Gene Knockdown Techniques , HeLa Cells , Heterogeneous Nuclear Ribonucleoprotein A1 , Humans , Peptide Chain Initiation, Translational , Protein Binding , RNA, Viral/genetics , Sindbis Virus/physiology , Vero Cells , Virus ReplicationABSTRACT
Regulatory T cells (Tregs) play an important role in protection against autoimmune disease and are also known to be potent inhibitors of anti-tumor immune responses. The New Zealand Black (NZB) mouse is a murine model for both autoimmune diseases, since high levels of autoantibodies are present, and human CLL, due to the expansion of malignant B-1 cells. In this study, we examined the functional role of CD4(+)CD25(+) Foxp3(+) Tregs in these different manifestations. Flow cytometric analysis showed increased levels of Tregs in NZB mice compared to healthy C57Bl/6 controls. Aged NZB mice that have developed a B-1 cell malignancy identified as IgM(+)CD5(+), have the most pronounced increase in Tregs. Ex vivo treatment of splenocytes from NZB mice with IFN-alpha resulted in a decrease in the frequency of Tregs and malignant B-1 cells. In vivo treatment of both NZB and C57Bl/6 mice with poly (I:C), a potent inducer of IFN-alpha, also led to a decrease in the levels of Tregs and malignant B-1 cells (NZB only) while amplifying autoimmune manifestations. These results indicate that while high levels of Tregs found in NZB mice might suppress a more severe autoimmune disease, they may also contribute to the development of the B cell malignancy.
Subject(s)
Autoimmune Diseases/immunology , Autoimmunity/immunology , Leukemia, B-Cell/immunology , Leukemia, B-Cell/pathology , T-Lymphocytes, Regulatory/immunology , Age Factors , Animals , Antibodies/blood , Antibodies/immunology , Antibodies/pharmacology , Antibodies, Antinuclear/blood , Ascitic Fluid/cytology , Ascitic Fluid/immunology , Autoimmune Diseases/pathology , B-Lymphocytes/cytology , B-Lymphocytes/drug effects , B-Lymphocytes/immunology , Erythrocytes/immunology , Forkhead Transcription Factors/genetics , Immune Tolerance/immunology , Interferon-alpha/blood , Interferon-alpha/pharmacology , Interferons/genetics , Interferons/pharmacology , Interleukin-10/blood , Interleukin-10/genetics , Interleukin-2 Receptor alpha Subunit/immunology , Lymph Nodes/cytology , Lymph Nodes/immunology , Mice , Mice, Inbred C57BL , Mice, Inbred NZB , Poly I-C/pharmacology , Spleen/cytology , Spleen/drug effects , Spleen/immunology , T-Lymphocyte Subsets/cytology , T-Lymphocyte Subsets/drug effects , T-Lymphocyte Subsets/immunology , T-Lymphocyte Subsets/metabolism , T-Lymphocytes, Regulatory/cytology , T-Lymphocytes, Regulatory/drug effects , T-Lymphocytes, Regulatory/metabolism , ZAP-70 Protein-Tyrosine Kinase/geneticsABSTRACT
Type I interferons (IFNs) are multifunctional cytokines that activate cellular responses by binding a common receptor consisting of two subunits, IFNAR-1 and IFNAR-2. Although the binding of IFNs to IFNAR-2 is well characterized, the binding to the lower affinity IFNAR-1 remains less well understood. Previous reports identified a region of human IFN-alpha2 on the B and C helices ("site 1A": N65, L80, Y85, Y89) that plays a key role in binding IFNAR-1 and contributes strongly to differential activation by various type I IFNs. The current studies demonstrate that residues on the D helix are also involved in IFNAR-1 binding. In particular, residue 120 (Arg in IFN-alpha2; Lys in IFN-alpha2/alpha1) appears to be a "hot-spot" residue: substitution by alanine significantly decreased biological activity, and the charge-reversal mutation of residue 120 to Glu caused drastic loss of antiviral and antiproliferative activity for both IFN-alpha2 and IFN-alpha2/alpha1. Mutations in residues of helix D maintained their affinity for IFNAR-2 but had decreased affinity for IFNAR-1. Single-site or multiple-site mutants in the IFNAR-1 binding site that had little or no detectable in vitro biological activity were capable of blocking in vitro antiviral and antiproliferative activity of native IFN-alpha2; i.e., they are type I IFN antagonists. These prototype IFN antagonists can be developed further for possible therapeutic use in systemic lupus erythematosus, and analogous molecules can be designed for use in animal models.
