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Sun J, Zhang H, Wei W, Xiao X, Huang C, Wang L, Zhong H, Jiang Y, Zheng F, Yang H, Jiang G, Zhang X. Regulation of CD8 + T cells infiltration and immunotherapy by circMGA/HNRNPL complex in bladder cancer. Oncogene 2023; 42:1247-1262. [PMID: 36869127 DOI: 10.1038/s41388-023-02637-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2022] [Revised: 02/08/2023] [Accepted: 02/15/2023] [Indexed: 03/05/2023]
Abstract
The limited success of immunotherapies targeting immune checkpoint inhibitors is largely ascribed to the lack of infiltrating CD8+ T lymphocytes. Circular RNAs (circRNAs) are a novel type of prevalent noncoding RNA that have been implicated in tumorigenesis and progression, while their roles in modulating CD8+ T cells infiltration and immunotherapy in bladder cancer have not yet been investigated. Herein, we uncover circMGA as a tumor-suppressing circRNA triggering CD8+ T cells chemoattraction and boosting the immunotherapy efficacy. Mechanistically, circMGA functions to stabilize CCL5 mRNA by interacting with HNRNPL. In turn, HNRNPL increases the stability of circMGA, forming a feedback loop that enhances the function of circMGA/HNRNPL complex. Intriguingly, therapeutic synergy between circMGA and anti-PD-1 could significantly suppress xenograft bladder cancer growth. Taken together, the results demonstrate that circMGA/HNRNPL complex may be targetable for cancer immunotherapy and the study advances our understanding of the physiological roles of circRNAs in antitumor immunity.
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Affiliation(s)
- Jiayin Sun
- Department of Urology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Hui Zhang
- Department of Urology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Wenjie Wei
- Department of Urology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Xingyuan Xiao
- Department of Urology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Chao Huang
- Department of Urology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Liang Wang
- Department of Urology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - He Zhong
- Department of Urology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Yangkai Jiang
- Department of Urology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Fuxin Zheng
- Department of Urology, Wuhan No.1 Hospital, Wuhan, 430022, China
| | - Hongmei Yang
- Department of Pathogenic Biology, School of Basic Medicine, Huazhong University of Science and Technology, Wuhan, China.
| | - Guosong Jiang
- Department of Urology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China.
| | - Xiaoping Zhang
- Department of Urology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China.
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2
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Koike Y, Pickles S, Estades Ayuso V, Jansen-West K, Qi YA, Li Z, Daughrity LM, Yue M, Zhang YJ, Cook CN, Dickson DW, Ward M, Petrucelli L, Prudencio M. TDP-43 and other hnRNPs regulate cryptic exon inclusion of a key ALS/FTD risk gene, UNC13A. PLoS Biol 2023; 21:e3002028. [PMID: 36930682 PMCID: PMC10057836 DOI: 10.1371/journal.pbio.3002028] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 03/29/2023] [Accepted: 02/08/2023] [Indexed: 03/18/2023] Open
Abstract
A major function of TAR DNA-binding protein-43 (TDP-43) is to repress the inclusion of cryptic exons during RNA splicing. One of these cryptic exons is in UNC13A, a genetic risk factor for amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The accumulation of cryptic UNC13A in disease is heightened by the presence of a risk haplotype located within the cryptic exon itself. Here, we revealed that TDP-43 extreme N-terminus is important to repress UNC13A cryptic exon inclusion. Further, we found hnRNP L, hnRNP A1, and hnRNP A2B1 bind UNC13A RNA and repress cryptic exon inclusion, independently of TDP-43. Finally, higher levels of hnRNP L protein associate with lower burden of UNC13A cryptic RNA in ALS/FTD brains. Our findings suggest that while TDP-43 is the main repressor of UNC13A cryptic exon inclusion, other hnRNPs contribute to its regulation and may potentially function as disease modifiers.
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Affiliation(s)
- Yuka Koike
- Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America
- Mayo Clinic Graduate School of Biomedical Sciences, Jacksonville, Florida, United States of America
| | - Sarah Pickles
- Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America
- Mayo Clinic Graduate School of Biomedical Sciences, Jacksonville, Florida, United States of America
| | - Virginia Estades Ayuso
- Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America
| | - Karen Jansen-West
- Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America
| | - Yue A. Qi
- Center for Alzheimer’s and Related Dementias, National Institute on Aging, NIH, Bethesda, Maryland, United States of America
| | - Ziyi Li
- Center for Alzheimer’s and Related Dementias, National Institute on Aging, NIH, Bethesda, Maryland, United States of America
| | - Lillian M. Daughrity
- Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America
| | - Mei Yue
- Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America
| | - Yong-Jie Zhang
- Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America
- Mayo Clinic Graduate School of Biomedical Sciences, Jacksonville, Florida, United States of America
| | - Casey N. Cook
- Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America
- Mayo Clinic Graduate School of Biomedical Sciences, Jacksonville, Florida, United States of America
| | - Dennis W. Dickson
- Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America
- Mayo Clinic Graduate School of Biomedical Sciences, Jacksonville, Florida, United States of America
| | - Michael Ward
- Center for Alzheimer’s and Related Dementias, National Institute on Aging, NIH, Bethesda, Maryland, United States of America
- National Institute of Neurological Disorders and Stroke, NIH, Bethesda, Maryland, United States of America
| | - Leonard Petrucelli
- Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America
- Mayo Clinic Graduate School of Biomedical Sciences, Jacksonville, Florida, United States of America
| | - Mercedes Prudencio
- Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America
- Mayo Clinic Graduate School of Biomedical Sciences, Jacksonville, Florida, United States of America
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3
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Noh JH, Gorospe M. AKTions by Cytoplasmic lncRNA CASC9 Promote Hepatocellular Carcinoma Survival. Hepatology 2018; 68:1675-1677. [PMID: 30014487 PMCID: PMC6277902 DOI: 10.1002/hep.30165] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Revised: 04/22/2018] [Accepted: 06/23/2018] [Indexed: 12/19/2022]
Affiliation(s)
- Ji Heon Noh
- Laboratory of Genetics and Genomics, National Institute on Aging Intramural Research Program, National Institutes of Health, Baltimore, Maryland
| | - Myriam Gorospe
- Laboratory of Genetics and Genomics, National Institute on Aging Intramural Research Program, National Institutes of Health, Baltimore, Maryland
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4
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Söderberg M, Raffalli-Mathieu F, Lang MA. Inflammation modulates the interaction of heterogeneous nuclear ribonucleoprotein (hnRNP) I/polypyrimidine tract binding protein and hnRNP L with the 3'untranslated region of the murine inducible nitric-oxide synthase mRNA. Mol Pharmacol 2002; 62:423-31. [PMID: 12130696 DOI: 10.1124/mol.62.2.423] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Interaction of two members of the heterogeneous nuclear ribonucleoprotein (hnRNP) family with the 3'untranslated region (UTR) of the murine inducible nitric-oxide synthase (iNOS) mRNA is demonstrated in this study. An iNOS RNA-protein complex is formed using protein extracts from untreated and septic shock treated mouse liver. UV cross-linking reveals that the complex consists of at least two proteins, with apparent molecular masses of 60 and 70 kDa, respectively. The 60-kDa protein binding site lies within a 112-nt pyrimidine-rich sequence, approximately 160 nt from the coding sequence, and the RNA-protein complex can be precipitated by a monoclonal antibody directed against hnRNP I [also named polypyrimidine tract binding protein (PTB)]. The 70-kDa protein binds a 43-nt sequence near the 3'end of the 3'UTR and is immunoprecipitated by a monoclonal antibody against hnRNP L. A computer-simulated conformation of the 3'UTR suggests that both binding sites reside in regions easily accessible for a protein. Supershifts of the native RNA-protein complex could only be achieved with anti-hnRNP L, suggesting that within this multiprotein RNA complex, only hnRNP L is exposed to the antibodies, whereas the hnRNP I/PTB is mainly responsible for its interaction with the mRNA. Up-regulation of iNOS by septic shock reduces the RNA-protein complex formation, thus showing that hnRNP I/PTB and hnRNP L binding to the iNOS mRNA is modulated by inflammation. This suggests a novel function for the two previously described proteins as regulators of the iNOS gene.
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Affiliation(s)
- Malin Söderberg
- Division of Biochemistry, Department of Pharmaceutical Biosciences, Uppsala University, Uppsala, Sweden.
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5
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Kuninger DT, Izumi T, Papaconstantinou J, Mitra S. Human AP-endonuclease 1 and hnRNP-L interact with a nCaRE-like repressor element in the AP-endonuclease 1 promoter. Nucleic Acids Res 2002; 30:823-9. [PMID: 11809897 PMCID: PMC100287 DOI: 10.1093/nar/30.3.823] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The major human AP-endonuclease 1 (APE1) is a multifunctional protein that plays a central role in the repair of damaged DNA by acting as a dual-function nuclease in the base excision repair pathway. This enzyme was also independently identified as a redox activator of AP-1 DNA-binding activity and has subsequently been shown to activate a variety of transcription factors via a redox mechanism. In a third distinct role, APE1 was identified as a component of a trans-acting complex that acts as a repressor by binding to the negative calcium responsive elements (nCaRE)-A and nCaRE-B, which were first discovered in the promoter of the human parathyroid gene and later in the APE1 promoter itself. Here we show that the nuclear protein complex which binds to the nCaRE-B2 of the hAPE1 gene contains APE1 itself and the heterogeneous nuclear ribonucleoprotein L (hnRNP-L). The interaction between the APE1 and hnRNP-L proteins does not require the presence of nCaRE-B2. Our results support the possibility that the APE1 gene is down-regulated by its own product, which would be the first such example of the regulation of a DNA repair enzyme, and identify a novel function of hnRNP-L in transcriptional regulation.
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Affiliation(s)
- David T Kuninger
- Department of Human Biological Chemistry and Genetics and Sealy Center for Molecular Science, University of Texas Medical Branch, 6.136 Medical Research Building, Route 1079, Galveston, TX 77555, USA
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6
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Abstract
The product of the von Hippel-Lindau (VHL) tumor suppressor gene, pVHL, functions as a ubiquitin-protein isopeptide ligase in regulating HIF-1 protein turnover, thus accounting for the increased transcription of hypoxia-inducible genes that accompanies VHL mutations. The increased vascular endothelial growth factor mRNA stability in cells lacking pVHL has been hypothesized to be due to a similar regulation of an RNA-binding protein. We report the expression of the GLUT-1 3'-untranslated region RNA-binding protein, heteronuclear ribonucleoprotein (hnRNP) A2, is specifically increased in pVHL-deficient cell lines. Enhanced hnRNP A2 expression was apparent in all cell fractions, including polysomes, where a similar modest effect on hnRNP L (a GLUT-1 and VEGF 3'-untranslated region-binding protein), was seen. Steady state levels of hnRNP A2 mRNA were unaffected. Regulation of hnRNP A2 levels correlated with the ability of pVHL to bind elongin C. Proteasome inhibition of cells expressing wild type pVHL selectively increased cytoplasmic hnRNP A2 levels to that seen in pVHL-deficient cells. Finally, an in vivo interaction between pVHL and hnRNP A2 was demonstrated in both the nucleus and the cytoplasm. Collectively, these data indicate that hnRNP A2 expression is regulated by pVHL in a manner that is dependent on elongin C interactions as well as functioning proteasomes.
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Affiliation(s)
- P A Pioli
- Department of Medicine, Dartmouth Medical School, Lebanon, New Hampshire 03756, USA
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7
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Gutiérrez-Escolano AL, Brito ZU, del Angel RM, Jiang X. Interaction of cellular proteins with the 5' end of Norwalk virus genomic RNA. J Virol 2000; 74:8558-62. [PMID: 10954557 PMCID: PMC116368 DOI: 10.1128/jvi.74.18.8558-8562.2000] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2000] [Accepted: 06/20/2000] [Indexed: 11/20/2022] Open
Abstract
The lack of a susceptible cell line and an animal model for Norwalk virus (NV) infection has prompted the development of alternative strategies to generate in vitro RNAs that approximate the authentic viral genome. This approach has allowed the study of viral RNA replication and gene expression. In this study, using mobility shift and cross-linking assays, we detected several cellular proteins from HeLa and CaCo-2 cell extracts that bind to, and form stable complexes with, the first 110 nucleotides of the 5' end of NV genomic RNA, a region previously predicted to form a double stem-loop structure. These proteins had molecular weights similar to those of the HeLa cellular proteins that bind to the internal ribosomal entry site of poliovirus RNA. HeLa proteins La, PCBP-2, and PTB, which are important for poliovirus translation, and hnRNP L, which is possibly implicated in hepatitis C virus translation, interact with NV RNA. These protein-RNA interactions are likely to play a role in NV translation and/or replication.
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Affiliation(s)
- A L Gutiérrez-Escolano
- Departamento de Patología Experimental, Centro de Investigación y de Estudios Avanzados del IPN, Mexico City, Mexico.
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8
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Shnyreva M, Schullery DS, Suzuki H, Higaki Y, Bomsztyk K. Interaction of two multifunctional proteins. Heterogeneous nuclear ribonucleoprotein K and Y-box-binding protein. J Biol Chem 2000; 275:15498-503. [PMID: 10809782 DOI: 10.1074/jbc.275.20.15498] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The heterogeneous nuclear ribonucleoprotein (hnRNP) K, a component of the hnRNP particles, appears to be involved in several steps of regulation of gene expression. To gain insight into mechanisms of K protein action, we performed two-hybrid screens using full-length hnRNP K as a bait. Several novel protein partners were identified, including Y-box-binding protein (YB-1), splicing factors 9G8 and SRp20, DNA-methyltransferase, hnRNP L, and hnRNP U. In vitro binding studies and co-immunoprecipitation from cellular extracts provided evidence for direct interaction between hnRNP K and YB-1. Two distinct domains in YB-1 were responsible for binding to K protein. Each protein was able to transactivate transcription from a polypyrimidine-rich promoter; however, this effect was reduced when K and YB-1 proteins were coexpressed suggesting a functional interaction between these two proteins.
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Affiliation(s)
- M Shnyreva
- Department of Medicine, University of Washington, Seattle, Washington 98195, USA
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9
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Abstract
Heterogeneous nuclear ribonucleoproteins (hnRNPs) are involved in several RNA-related biological processes such as transcription, pre-mRNA processing, mature mRNA transport to the cytoplasm, and translation. About 20 major hnRNPs from A1 to U are known. Among them, hnRNP A, D, E, I, and K are known to shuttle between the nucleus and the cytoplasm. hnRNP E2 has been seen to stabilize alpha-globin mRNA and to enhance polioviral mRNA translation. hnRNP K modulates transcription and translation of some mRNAs. hnRNP I and its homologue hnRNP L have been suggested to enhance translation of some IRES-dependent mRNAs. In order to better understand the molecular mechanisms of the biological functions of hnRNPs, we investigated protein-protein interactions of six hnRNPs (hnRNP A1, C1, E2, I, K, and L) using the yeast two-hybrid system and in vitro co-precipitation assays. All of the hnRNPs tested exerted homomeric interactions, and hnRNP E2, I, K, and L interacted with each other. In the case of hnRNP E2 and hnRNP K, the N-terminal half of the proteins containing two KH (K homologous) domains were required for protein-protein interaction, and the second quarter of hnRNP I and hnRNP L containing RRM2 (RNA recognition motif 2) was essential for protein-protein interaction. hnRNP A1 and C1 did not form complexes with other hnRNPs in our assay systems. This suggests that the hnRNPs could fall into two groups: one group, including hnRNP A1 and C1, involved in hnRNP core complex formation and another group, including hnRNP E2, I, K, and L, involved in a variety of RNA-related biological processes. Different combinations of the proteins of the second group may facilitate different biological processes in conjunction with other factors.
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Affiliation(s)
- J H Kim
- Department of Life Science, Pohang University of Science and Technology, Hyoja-Dong San31, Pohang, Kyungbuk, 790-784, Korea
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10
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Hamilton BJ, Nichols RC, Tsukamoto H, Boado RJ, Pardridge WM, Rigby WF. hnRNP A2 and hnRNP L bind the 3'UTR of glucose transporter 1 mRNA and exist as a complex in vivo. Biochem Biophys Res Commun 1999; 261:646-51. [PMID: 10441480 DOI: 10.1006/bbrc.1999.1040] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Recent work identified an RNA binding protein whose presence in brain tumors correlated with translational repression of Glut1 expression. RNase T1 mapping demonstrated that this protein bound an AU-rich response element (AURE) in the Glut1 3'UTR. Facilitated by its differential expression in brain tumor cytosols, we identified this Glut1 RNA binding protein as hnRNP A2. Studies further demonstrated that hnRNP A2 was the major Glut1 RNA binding activity in other cell lines. Recombinant hnRNP A2 exhibited equivalent Glut1 RNA binding specificity, quite distinct from the related AURE binding protein hnRNP A1. These data indicate that hnRNP A2 is the Glut1 AURE binding protein whose cytoplasmic expression in gliomas is associated with translational repression and mRNA instability. Using this approach, we also identified the other major Glut1 3'UTR RNA binding activity as hnRNP L. Stimuli (hypoxia and hypoglycemia) which increase Glut1 mRNA stability selectively decreased polysomal levels of hnRNP A2 and L. Immunoprecipitation demonstrated that hnRNP A2 and L exist as a complex in vivo. As a result of these and other studies, we conclude that hnRNP A2 and L associate in vivo and independently bind the 3'UTR of Glut1 mRNA.
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Affiliation(s)
- B J Hamilton
- Department of Medicine, Dartmouth Medical School, Lebanon, New Hampshire, 03756, USA.
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11
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Shih SC, Claffey KP. Regulation of human vascular endothelial growth factor mRNA stability in hypoxia by heterogeneous nuclear ribonucleoprotein L. J Biol Chem 1999; 274:1359-65. [PMID: 9880507 DOI: 10.1074/jbc.274.3.1359] [Citation(s) in RCA: 162] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A 126-base region of human vascular endothelial growth factor (VEGF) 3'-untranslated region, which we identified as the hypoxia stability region, forms seven hypoxia-inducible RNA-protein complexes with apparent molecular masses ranging from 40 to 90 kDa in RNA-UV-cross-linking assays. In this study, we show that proteins that form the 60-kDa RNA-protein complex with the hypoxia stability region were present in both cytoplasmic and nuclear compartments. We purified the protein associated in the 60-kDa complex and identified it as heterogeneous nuclear ribonucleoprotein L (hnRNP L) by protein sequencing. Removal of hnRNP L by immunoprecipitation specifically abolished formation of the 60-kDa complex. Synthetic deoxyribonucleotide competition studies defined the RNA-binding site of hnRNP L as a 21-base-long sequence, 5'-CACCCACCCACAUACAUACAU-3'. Immunoprecipitation of hnRNP L followed by reverse transcription-polymerase chain reaction showed that hnRNP L specifically interacts with VEGF mRNA in hypoxic cells in vivo. Furthermore, when M21 cells transfected with antisense oligodeoxyribonucleotide to the hnRNP L RNA-binding site, the VEGF mRNA half-life was significantly reduced under hypoxic conditions. Thus, we propose that specific association of hnRNP L with VEGF mRNA under hypoxia may play an important role in hypoxia-induced post-transcriptional regulation of VEGF mRNA expression.
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Affiliation(s)
- S C Shih
- Departments of Pathology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA
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12
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Hahm B, Kim YK, Kim JH, Kim TY, Jang SK. Heterogeneous nuclear ribonucleoprotein L interacts with the 3' border of the internal ribosomal entry site of hepatitis C virus. J Virol 1998; 72:8782-8. [PMID: 9765422 PMCID: PMC110294 DOI: 10.1128/jvi.72.11.8782-8788.1998] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Translation initiation of hepatitis C virus (HCV) RNA occurs by internal entry of a ribosome into the 5' nontranslated region in a cap-independent manner. The HCV RNA sequence from about nucleotide 40 up to the N terminus of the coding sequence of the core protein is required for efficient internal initiation of translation, though the precise border of the HCV internal ribosomal entry site (IRES) has yet to be determined. Several cellular proteins have been proposed to direct HCV IRES-dependent translation by binding to the HCV IRES. Here we report on a novel cellular protein that specifically interacts with the 3' border of the HCV IRES in the core-coding sequence. This protein with an apparent molecular mass of 68 kDa turned out to be heterogeneous nuclear ribonucleoprotein L (hnRNP L). The binding of hnRNP L to the HCV IRES correlates with the translational efficiencies of corresponding mRNAs. This finding suggests that hnRNP L may play an important role in the translation of HCV mRNA through the IRES element.
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Affiliation(s)
- B Hahm
- Department of Life Science, Pohang University of Science and Technology, Hyoja-Dong, Pohang, Kyungbuk 790-784, Korea
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13
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Abstract
Polypyrimidine tract-binding protein (PTB) is involved in pre-mRNA splicing and internal ribosomal entry site (IRES)-dependent translation. In order to identify cellular protein(s) interacting with PTB, we performed a yeast two-hybrid screening. Heterogeneous nuclear ribonucleoprotein L (hnRNP L) was identified as a PTB-binding protein. The interaction between PTB and hnRNP L was confirmed in an in vitro binding assay. Both PTB and hnRNP L were found to localize in the nucleoplasm, excepting the nucleoli, in HeLa cells by the green fluorescent protein (GFP)-fused protein detection method. The N-terminal half of PTB (aa 1-329) and most of hnRNP L (aa 141-558) is required for the interaction between PTB and hnRNP L.
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Affiliation(s)
- B Hahm
- Department of Life Science, Pohang University of Science and Technology, Kyungbuk, South Korea
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14
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Abstract
Most pre-mRNAs require an intron for efficient processing in higher eukaryotes. To test the hypothesis that intron-independent gene expression involves positive, cis-acting RNA sequence elements, we constructed chimeric genes in which various regions of the naturally intronless HSV-TK gene were inserted into an intronless variant of the highly intron-dependent human beta-globin gene. Using a transient transfection assay, we identified a 119-nucleotide sequence element contained within the transcribed region of the HSV-TK gene that enables efficient cytoplasmic accumulation of globin RNA in the absence of splicing. RNA UV-cross-linking assays indicated that a 68-kD protein present in nuclear extracts of HeLa and COS cells specifically binds to this HSV-TK sequence element. This 68-kD protein was found to cross-react with an antiserum specific to hnRNP L. Recombinant hnRNP L was shown to bind with high sequence specificity to this RNA sequence element. Analysis of substitution mutants in this element indicated that binding of hnRNP L correlates with accumulation of the RNA in the cytoplasm. Thus, we conclude that (1) hnRNP L binds in a sequence-specific manner to this RNA sequence element that enables intron-independent gene expression, and (2) intron-independent pre-mRNA processing and transport involves sequence-specific RNA-protein interactions between cis-acting RNA sequence elements and proteins such as hnRNP L. This sequence element may be of general use for the efficient expression of cDNA versions of intron-dependent genes.
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Affiliation(s)
- X Liu
- McArdle Laboratory for Cancer Research, University of Wisconsin, Madison 53706-1559, USA
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15
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Ghetti A, Piñol-Roma S, Michael WM, Morandi C, Dreyfuss G. hnRNP I, the polypyrimidine tract-binding protein: distinct nuclear localization and association with hnRNAs. Nucleic Acids Res 1992; 20:3671-8. [PMID: 1641332 PMCID: PMC334017 DOI: 10.1093/nar/20.14.3671] [Citation(s) in RCA: 255] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Many hnRNP proteins and snRNPs interact with hnRNA in the nucleus of eukaryotic cells and affect the fate of hnRNA and its processing into mRNA. There are at least 20 abundant proteins in vertebrate cell hnRNP complexes and their structure and arrangement on specific hnRNAs is likely to be important for the processing of pre-mRNAs. hnRNP I, a basic protein of ca. 58,000 daltons by SDS-PAGE, is one of the abundant hnRNA-binding proteins. Monoclonal antibodies to hnRNP I were produced and full length cDNA clones for hnRNP I were isolated and sequenced. The sequence of hnRNP I (59,632 daltons and pI 9.86) demonstrates that it is identical to the previously described polypyrimidine tract-binding protein (PTB) and shows that it is highly related to hnRNP L. The sequences of these two proteins, I and L, define a new family of hnRNP proteins within the large superfamily of the RNP consensus RNA-binding proteins. Here we describe experiments which reveal new and unique properties on the association of hnRNP I/PTB with hnRNP complexes and on its cellular localization. Micrococcal nuclease digestions show that hnRNP I, along with hnRNP S and P, is released from hnRNP complexes by nuclease digestion more readily than most other hnRNP proteins. This nuclease hypersensitivity suggests that hnRNP I is bound to hnRNA regions that are particularly exposed in the complexes. Immunofluorescence microscopy shows that hnRNP I is found in the nucleoplasm but in addition high concentrations are detected in a discrete perinucleolar structure. Thus, the PTB is one of the major proteins that bind pre-mRNAs; it is bound to nuclease-hypersensitive regions of the hnRNA-protein complexes and shows a novel pattern of nuclear localization.
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Affiliation(s)
- A Ghetti
- Universita di Verona, Facolta di Medicina e Chirurgia, Istituto di Scienze Biologiche, Italy
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