1
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Huang SC, Liang JY, Vu LV, Yu FH, Ou AC, Ou JP, Zhang HS, Burnett KM, Benz EJ. Epithelial-specific isoforms of protein 4.1R promote adherens junction assembly in maturing epithelia. J Biol Chem 2020; 295:191-211. [PMID: 31776189 PMCID: PMC6952607 DOI: 10.1074/jbc.ra119.009650] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Revised: 11/20/2019] [Indexed: 01/13/2023] Open
Abstract
Epithelial adherens junctions (AJs) and tight junctions (TJs) undergo disassembly and reassembly during morphogenesis and pathological states. The membrane-cytoskeleton interface plays a crucial role in junctional reorganization. Protein 4.1R (4.1R), expressed as a diverse array of spliceoforms, has been implicated in linking the AJ and TJ complex to the cytoskeleton. However, which specific 4.1 isoform(s) participate and the mechanisms involved in junctional stability or remodeling remain unclear. We now describe a role for epithelial-specific isoforms containing exon 17b and excluding exon 16 4.1R (4.1R+17b) in AJs. 4.1R+17b is exclusively co-localized with the AJs. 4.1R+17b binds to the armadillo repeats 1-2 of β-catenin via its membrane-binding domain. This complex is linked to the actin cytoskeleton via a bispecific interaction with an exon 17b-encoded peptide. Exon 17b peptides also promote fodrin-actin complex formation. Expression of 4.1R+17b forms does not disrupt the junctional cytoskeleton and AJs during the steady-state or calcium-dependent AJ reassembly. Overexpression of 4.1R-17b forms, which displace the endogenous 4.1R+17b forms at the AJs, as well as depletion of the 4.1R+17b forms both decrease junctional actin and attenuate the recruitment of spectrin to the AJs and also reduce E-cadherin during the initial junctional formation of the AJ reassembly process. Expressing 4.1R+17b forms in depleted cells rescues junctional localization of actin, spectrin, and E-cadherin assembly at the AJs. Together, our results identify a critical role for 4.1R+17b forms in AJ assembly and offer additional insights into the spectrin-actin-4.1R-based membrane skeleton as an emerging regulator of epithelial integrity and remodeling.
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Affiliation(s)
- Shu-Ching Huang
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115; Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115; Department of Medicine, Harvard Medical School, Boston, Massachusetts 02115.
| | - Jia Y Liang
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115
| | - Long V Vu
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115
| | - Faye H Yu
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115
| | - Alexander C Ou
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115
| | - Jennie Park Ou
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115
| | - Henry S Zhang
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115
| | - Kimberly M Burnett
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115
| | - Edward J Benz
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115; Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115; Department of Medicine, Harvard Medical School, Boston, Massachusetts 02115; Department of Pediatrics and Genetics, Harvard Medical School, Boston, Massachusetts 02115; Dana-Farber/Harvard Cancer Center, Boston, Massachusetts 02115
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2
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Rangel L, Lospitao E, Ruiz-Sáenz A, Alonso MA, Correas I. Alternative polyadenylation in a family of paralogous EPB41 genes generates protein 4.1 diversity. RNA Biol 2016; 14:236-244. [PMID: 27981895 DOI: 10.1080/15476286.2016.1270003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Alternative polyadenylation (APA) is a step in mRNA 3'-end processing that contributes to the complexity of the transcriptome by generating isoforms that differ in either their coding sequence or their 3'-untranslated regions (UTRs). The EPB41 genes, EPB41, EPB41L2, EPB41L3 and EPB41L1, encode an impressively complex array of structural adaptor proteins (designated 4.1R, 4.1G, 4.1B and 4.1N, respectively) by using alternative transcriptional promoters and tissue-specific alternative pre-mRNA splicing. The great variety of 4.1 proteins mainly results from 5'-end and internal processing of the EPB41 pre-mRNAs. Thus, 4.1 proteins can vary in their N-terminal extensions but all contain a highly homologous C-terminal domain (CTD). Here we study a new group of EPB41-related mRNAs that originate by APA and lack the exons encoding the CTD characteristic of prototypical 4.1 proteins, thereby encoding a new type of 4.1 protein. For the EPB41 gene, this type of processing was observed in all 11 human tissues analyzed. Comparative genomic analysis of EPB41 indicates that APA is conserved in various mammals. In addition, we show that APA also functions for the EPB41L2, EPB41L3 and EPB41L1 genes, but in a more restricted manner in the case of the latter 2 than it does for the EPB41 and EPB41L2 genes. Our study shows alternative polyadenylation to be an additional mechanism for the generation of 4.1 protein diversity in the already complex EPB41-related genes. Understanding the diversity of EPB41 RNA processing is essential for a full appreciation of the many 4.1 proteins expressed in normal and pathological tissues.
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Affiliation(s)
- Laura Rangel
- a Departamento de Biología Molecular , Universidad Autónoma de Madrid (UAM), Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas (CSIC), Nicolás Cabrera , Cantoblanco, Madrid , Spain
| | - Eva Lospitao
- a Departamento de Biología Molecular , Universidad Autónoma de Madrid (UAM), Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas (CSIC), Nicolás Cabrera , Cantoblanco, Madrid , Spain
| | - Ana Ruiz-Sáenz
- a Departamento de Biología Molecular , Universidad Autónoma de Madrid (UAM), Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas (CSIC), Nicolás Cabrera , Cantoblanco, Madrid , Spain
| | - Miguel A Alonso
- a Departamento de Biología Molecular , Universidad Autónoma de Madrid (UAM), Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas (CSIC), Nicolás Cabrera , Cantoblanco, Madrid , Spain
| | - Isabel Correas
- a Departamento de Biología Molecular , Universidad Autónoma de Madrid (UAM), Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas (CSIC), Nicolás Cabrera , Cantoblanco, Madrid , Spain
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3
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Liu C, Weng H, Chen L, Yang S, Wang H, Debnath G, Guo X, Wu L, Mohandas N, An X. Impaired intestinal calcium absorption in protein 4.1R-deficient mice due to altered expression of plasma membrane calcium ATPase 1b (PMCA1b). J Biol Chem 2013; 288:11407-15. [PMID: 23460639 DOI: 10.1074/jbc.m112.436659] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Protein 4.1R was first identified in the erythrocyte membrane skeleton. It is now known that the protein is expressed in a variety of epithelial cell lines and in the epithelia of many tissues, including the small intestine. However, the physiological function of 4.1R in the epithelial cells of the small intestine has not so far been explored. Here, we show that 4.1R knock-out mice exhibited a significantly impaired small intestinal calcium absorption that resulted in secondary hyperparathyroidism as evidenced by increased serum 1,25-(OH)2-vitamin D3 and parathyroid hormone levels, decreased serum calcium levels, hyperplasia of the parathyroid, and demineralization of the bones. 4.1R is located on the basolateral membrane of enterocytes, where it co-localizes with PMCA1b (plasma membrane calcium ATPase 1b). Expression of PMCA1b in enterocytes was decreased in 4.1(-/-) mice. 4.1R directly associated with PMCA1b, and the association involved the membrane-binding domain of 4.1R and the second intracellular loop and C terminus of PMCA1b. Our findings have enabled us to define a functional role for 4.1R in small intestinal calcium absorption through regulation of membrane expression of PMCA1b.
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Affiliation(s)
- Congrong Liu
- Red Cell Physiology Laboratory, New York Blood Center, New York, New York 10065, USA
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4
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Baklouti F, Morinière M, Haj-Khélil A, Fénéant-Thibault M, Gruffat H, Couté Y, Ninot A, Guitton C, Delaunay J. Homozygous deletion of EPB41 genuine AUG-containing exons results in mRNA splicing defects, NMD activation and protein 4.1R complete deficiency in hereditary elliptocytosis. Blood Cells Mol Dis 2011; 47:158-65. [DOI: 10.1016/j.bcmd.2011.07.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2011] [Revised: 07/05/2011] [Indexed: 12/23/2022]
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5
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Parra MK, Gee S, Mohandas N, Conboy JG. Efficient in vivo manipulation of alternative pre-mRNA splicing events using antisense morpholinos in mice. J Biol Chem 2010; 286:6033-9. [PMID: 21156798 DOI: 10.1074/jbc.m110.158154] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Mammalian pre-mRNA alternative splicing mechanisms are typically studied using artificial minigenes in cultured cells, conditions that may not accurately reflect the physiological context of either the pre-mRNA or the splicing machinery. Here, we describe a strategy to investigate splicing of normal endogenous full-length pre-mRNAs under physiological conditions in live mice. This approach employs antisense vivo-morpholinos (vMOs) to mask cis-regulatory sequences or to disrupt splicing factor expression, allowing functional evaluation of splicing regulation in vivo. We applied this strategy to gain mechanistic insight into alternative splicing events involving exons 2 and 16 (E2 and E16) that control the structure and function of cytoskeletal protein 4.1R. In several mouse tissues, inclusion of E16 was substantially inhibited by interfering with a splicing enhancer mechanism using a target protector morpholino that blocked Fox2-dependent splicing enhancers in intron 16 or a splice-blocking morpholino that disrupted Fox2 expression directly. For E2, alternative 3'-splice site choice is coordinated with upstream promoter use across a long 5'-intron such that E1A splices almost exclusively to the distal acceptor (E2dis). vMOs were used to test the in vivo relevance of a deep intron element previously proposed to determine use of E2dis via a two-step intrasplicing model. Two independent vMOs designed against this intronic regulatory element inhibited intrasplicing, robustly switching E1A splicing to the proximal acceptor (E2prox). This finding strongly supports the in vivo physiological relevance of intrasplicing. vMOs represent a powerful tool for alternative splicing studies in vivo and may facilitate exploration of alternative splicing networks in vivo.
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Affiliation(s)
- Marilyn K Parra
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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6
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Morinière M, Delhommeau F, Calender A, Ribeiro L, Delaunay J, Baklouti F. Nonsense-mediated mRNA decay (NMD) blockage promotes nonsense mRNA stabilization in protein 4.1R deficient cells carrying the 4.1R Coimbra variant of hereditary elliptocytosis. Blood Cells Mol Dis 2010; 45:284-8. [PMID: 20863723 DOI: 10.1016/j.bcmd.2010.08.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2010] [Accepted: 08/19/2010] [Indexed: 12/31/2022]
Abstract
We describe a new approach to stabilize nonsense mRNA, based on the inhibition of the NMD mechanism, by combining cycloheximide-mediated inhibition of translation, and caffeine-mediated inhibition of UPF1 phosphorylation. This approach aimed to identify the impact of a 4.1R splicing mutation. This mutation is involved in a partial deficiency of 4.1R in the homozygous state in a patient with hereditary elliptocytosis and a moderated hemolytic anemia. We show that, in addition to two known minor shortened and stable spliceoforms, the mutation activates an intronic cryptic splice site, which results in a nonsense mRNA major isoform, targeted to degradation in intact cells by NMD. This accounts for the main cause of 4.1R partial deficiency. In a general perspective, blocking the NMD mechanism would help to identify a missing isoform, and pave the path for a molecular targeting strategy to circumvent a deleterious splicing pathway in favor of a therapeutic splicing pathway.
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Affiliation(s)
- Madeleine Morinière
- mRNA Metabolism in Normal and Pathological Cells, CGMC, CNRS, Université Lyon 1, Villeurbanne, France
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7
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Mattagajasingh SN, Huang SC, Benz EJ. Inhibition of protein 4.1 R and NuMA interaction by mutagenization of their binding-sites abrogates nuclear localization of 4.1 R. Clin Transl Sci 2010; 2:102-11. [PMID: 20443879 DOI: 10.1111/j.1752-8062.2008.00087.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Protein 4.1R(4.1R) is a multifunctional structural protein recently implicated in nuclear assembly and cell division. We earlier demonstrated that 4.1R forms a multiprotein complex with mitotic spindle and spindle pole organizing proteins, such as NuMA, dynein, and dynactin, by binding to residues 1788-1810 of NuMA through amino acids encoded by exons 20 and 21 in 24 kD domain. Employing random-and site-directed mutagenesis combined with glycine- and alanine-scanning, we have identified amino acids of 4.1 R and NuMA that sustain their interaction, and have analyzed the effect of mutating the binding sites on their intracellular colocalization. We found that V762, V765, and V767 of 4.1 R, and 11800, 11801,11803, Tl 804, and M1805 of NuMA are necessary for their interaction. GST-fusion peptides of the 4.1R24 kD domain bound to residues 1785-2115 of NuMA in in vitro binding assays, but the binding was inhibited by alanine substitutions of V762, V765, and V767 of 4.1 R, or residues 1800-1805 of NuMA. Additionally, expression of variants of 4.1 R or NuMA that inhibit their in vitro binding also abrogated nuclear localization of 4.1 Rand colocalization with NuMA. Our findings suggest a crucial role of 4.1 R/NuMA interaction in localization and function of 4.1 R in the nucleus.
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8
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Yao W, Sung LA. Erythrocyte tropomodulin isoforms with and without the N-terminal actin-binding domain. J Biol Chem 2010; 285:31408-17. [PMID: 20675374 DOI: 10.1074/jbc.m110.130278] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Erythrocyte tropomodulin (E-Tmod or Tmod1) of 41 kDa is a tropomyosin (TM)-binding protein that caps the slow-growing end of the actin filaments. Its N-terminal half is flexible, whereas the C-terminal half has a single domain structure. E-Tmod/TM5 complex may function as a "molecular ruler" generating actin protofilaments of ∼37 nm. Here we report the discovery of a short isoform of 29 kDa that lacks the N-terminal actin-binding domain (N-ABD) but retains the C-terminal actin-binding domain (C-ABD). E-Tmod29 can be generated by alternative splicing from an upstream promoter or by multiple transcriptional start sites from a downstream promoter. Promoter switching leads to a surge of E-Tmod41 in reticulocytes, which degrades quickly in the cytosol. We expressed recombinant isoforms in Escherichia coli and tested their binding toward TM5, G-actin, and F-actin. Solid-phase binding assays show that, without the N-terminal 102 residues, E-Tmod29 binds to TM5 or G-actin more strongly than E-Tmod41 does, but barely binds to F-actin after TM5 binding. Differential bindings explain the distinct localizations of E-Tmod29 in the cytosol and E-Tmod41 on the membrane. Sequential bindings and immunofluorescent staining further suggest that 1) TM5 binding to E-Tmod41 may open up the flexible N-terminal half, exposing N-ABD and unblocking C-ABD; 2) N-ABD binds to F-actin and C-ABD binds to G-actin; and 3) F-actin binding to N-ABD may prevent G-actin from binding to C-ABD. E-Tmod29 may thus modulate the availability of TM5 and G-actin for E-Tmod41 to construct the protofilament-based membrane skeletal network for circulating erythrocytes.
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Affiliation(s)
- Weijuan Yao
- Department of Bioengineering, University of California, San Diego, California 92093-0412, USA
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9
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Coupled transcription-splicing regulation of mutually exclusive splicing events at the 5' exons of protein 4.1R gene. Blood 2009; 114:4233-42. [PMID: 19729518 DOI: 10.1182/blood-2009-02-206219] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The tightly regulated production of distinct erythrocyte protein 4.1R isoforms involves differential splicing of 3 mutually exclusive first exons (1A, 1B, 1C) to the alternative 3' splice sites (ss) of exon 2'/2. Here, we demonstrate that exon 1 and 2'/2 splicing diversity is regulated by a transcription-coupled splicing mechanism. We also implicate distinctive regulatory elements that promote the splicing of exon 1A to the distal 3' ss and exon 1B to the proximal 3' ss in murine erythroleukemia cells. A hybrid minigene driven by cytomegalovirus promoter mimicked 1B-promoter-driven splicing patterns but differed from 1A-promoter-driven splicing patterns, suggesting that promoter identity affects exon 2'/2 splicing. Furthermore, splicing factor SF2/ASF ultraviolet (UV) cross-linked to the exon 2'/2 junction CAGAGAA, a sequence that overlaps the distal U2AF(35)-binding 3' ss. Consequently, depletion of SF2/ASF allowed exon 1B to splice to the distal 3' ss but had no effect on exon 1A splicing. These findings identify for the first time that an SF2/ASF binding site also can serve as a 3' ss in a transcript-dependent manner. Taken together, our results suggest that 4.1R gene expression involves transcriptional regulation coupled with a complex splicing regulatory network.
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10
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Fu RH, Liu SP, Ou CW, Yu HH, Li KW, Tsai CH, Shyu WC, Lin SZ. Alternative Splicing Modulates Stem Cell Differentiation. Cell Transplant 2009; 18:1029-38. [PMID: 19523332 DOI: 10.3727/096368909x471260] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Stem cells have the surprising potential to develop into many different cell types. Therefore, major research efforts have focused on transplantation of stem cells and/or derived progenitors for restoring depleted diseased cells in degenerative disorders. Understanding the molecular controls, including alternative splicing, that arise during lineage differentiation of stem cells is crucial for developing stem cell therapeutic approaches in regeneration medicine. Alternative splicing to allow a single gene to encode multiple transcripts with different protein coding sequences and RNA regulatory elements increases genomic complexities. Utilizing differences in alternative splicing as a molecular marker may be more sensitive than simply gene expression in various degrees of stem cell differentiation. Moreover, alternative splicing maybe provide a new concept to acquire induced pluripotent stem cells or promote cell–cell transdifferentiation for restorative therapies and basic medicine researches. In this review, we highlight the recent advances of alternative splicing regulation in stem cells and their progenitors. It will hopefully provide much needed knowledge into realizing stem cell biology and related applications.
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Affiliation(s)
- Ru-Huei Fu
- Center for Neuropsychiatry, China Medical University Hospital, Taichung, Taiwan
- Graduate Institute of Immunology, China Medical University, Taichung, Taiwan
| | - Shih-Ping Liu
- Center for Neuropsychiatry, China Medical University Hospital, Taichung, Taiwan
- Graduate Institute of Basic Medical Science, China Medical University, Taichung, Taiwan
| | - Chen-Wei Ou
- Graduate Institute of Immunology, China Medical University, Taichung, Taiwan
| | - Hsiu-Hui Yu
- Center for Neuropsychiatry, China Medical University Hospital, Taichung, Taiwan
| | - Kuo-Wei Li
- Center for Neuropsychiatry, China Medical University Hospital, Taichung, Taiwan
| | - Chang-Hai Tsai
- Department of Pediatrics, China Medical University Hospital, Taichung, Taiwan
- Department of Healthcare Administration, Asia University, Taichung, Taiwan
| | - Woei-Cherng Shyu
- Center for Neuropsychiatry, China Medical University Hospital, Taichung, Taiwan
- Graduate Institute of Immunology, China Medical University, Taichung, Taiwan
| | - Shinn-Zong Lin
- Center for Neuropsychiatry, China Medical University Hospital, Taichung, Taiwan
- Graduate Institute of Immunology, China Medical University, Taichung, Taiwan
- China Medical University Beigang Hospital, Yunlin, Taiwan
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11
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Chromatin architecture and transcription factor binding regulate expression of erythrocyte membrane protein genes. Mol Cell Biol 2009; 29:5399-412. [PMID: 19687298 DOI: 10.1128/mcb.00777-09] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Erythrocyte membrane protein genes serve as excellent models of complex gene locus structure and function, but their study has been complicated by both their large size and their complexity. To begin to understand the intricate interplay of transcription, dynamic chromatin architecture, transcription factor binding, and genomic organization in regulation of erythrocyte membrane protein genes, we performed chromatin immunoprecipitation (ChIP) coupled with microarray analysis and ChIP coupled with massively parallel DNA sequencing in both erythroid and nonerythroid cells. Unexpectedly, most regions of GATA-1 and NF-E2 binding were remote from gene promoters and transcriptional start sites, located primarily in introns. Cooccupancy with FOG-1, SCL, and MTA-2 was found at all regions of GATA-1 binding, with cooccupancy of SCL and MTA-2 also found at regions of NF-E2 binding. Cooccupancy of GATA-1 and NF-E2 was found frequently. A common signature of histone H3 trimethylation at lysine 4, GATA-1, NF-E2, FOG-1, SCL, and MTA-2 binding and consensus GATA-1-E-box binding motifs located 34 to 90 bp away from NF-E2 binding motifs was found frequently in erythroid cell-expressed genes. These results provide insights into our understanding of membrane protein gene regulation in erythropoiesis and the regulation of complex genetic loci in erythroid and nonerythroid cells and identify numerous candidate regions for mutations associated with membrane-linked hemolytic anemia.
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12
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Yamamoto ML, Clark TA, Gee SL, Kang JA, Schweitzer AC, Wickrema A, Conboy JG. Alternative pre-mRNA splicing switches modulate gene expression in late erythropoiesis. Blood 2009; 113:3363-70. [PMID: 19196664 PMCID: PMC2665901 DOI: 10.1182/blood-2008-05-160325] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2008] [Accepted: 12/02/2008] [Indexed: 12/19/2022] Open
Abstract
Differentiating erythroid cells execute a unique gene expression program that insures synthesis of the appropriate proteome at each stage of maturation. Standard expression microarrays provide important insight into erythroid gene expression but cannot detect qualitative changes in transcript structure, mediated by RNA processing, that alter structure and function of encoded proteins. We analyzed stage-specific changes in the late erythroid transcriptome via use of high-resolution microarrays that detect altered expression of individual exons. Ten differentiation-associated changes in erythroblast splicing patterns were identified, including the previously known activation of protein 4.1R exon 16 splicing. Six new alternative splicing switches involving enhanced inclusion of internal cassette exons were discovered, as well as 3 changes in use of alternative first exons. All of these erythroid stage-specific splicing events represent activated inclusion of authentic annotated exons, suggesting they represent an active regulatory process rather than a general loss of splicing fidelity. The observation that 3 of the regulated transcripts encode RNA binding proteins (SNRP70, HNRPLL, MBNL2) may indicate significant changes in the RNA processing machinery of late erythroblasts. Together, these results support the existence of a regulated alternative pre-mRNA splicing program that is critical for late erythroid differentiation.
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Affiliation(s)
- Miki L Yamamoto
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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13
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Mattagajasingh SN, Huang SC, Benz EJ. Inhibition of Protein 4.1 R and NuMA Interaction by Mutagenization of Their Binding-Sites Abrogates Nuclear Localization of 4.1 R. Clin Transl Sci 2009. [DOI: 10.1111/j.1752-8062.2009.00087.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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14
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Lospitao E, Pérez-Ferreiro CM, Gosálbez A, Alonso MA, Correas I. An internal ribosome entry site element directs the synthesis of the 80 kDa isoforms of protein 4.1R. BMC Biol 2008; 6:51. [PMID: 19055807 PMCID: PMC2614411 DOI: 10.1186/1741-7007-6-51] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2008] [Accepted: 12/04/2008] [Indexed: 11/12/2022] Open
Abstract
Background In red blood cells, protein 4.1 (4.1R) is an 80 kDa protein that stabilizes the spectrin-actin network and anchors it to the plasma membrane through its FERM domain. While the expression pattern of 4.1R in mature red cells is relatively simple, a rather complex array of 4.1R protein isoforms varying in N-terminal extensions, internal sequences and subcellular locations has been identified in nucleated cells. Among these, 135 kDa and 80 kDa isoforms have different N-terminal extensions and are expressed either from AUG1- or AUG2-containing mRNAs, respectively. These two types of mRNAs, varying solely by presence/absence of 17 nucleotides (nt) which contain the AUG1 codon, are produced by alternative splicing of the 4.1R pre-mRNA. It is unknown whether the 699 nt region comprised between AUG1 and AUG2, kept as a 5' untranslated region in AUG2-containing mRNAs, plays a role on 4.1R mRNA translation. Results By analyzing the in vitro expression of a panel of naturally occurring 4.1R cDNAs, we observed that all AUG1/AUG2-containing cDNAs gave rise to both long, 135 kDa, and short, 80 kDa, 4.1R isoforms. More importantly, similar results were also observed in cells transfected with this set of 4.1R cDNAs. Mutational studies indicated that the short isoforms were not proteolytic products of the long isoforms but products synthesized from AUG2. The presence of a cryptic promoter in the 4.1R cDNA sequence was also discounted. When a 583 nt sequence comprised between AUG1 and AUG2 was introduced into bicistronic vectors it directed protein expression from the second cistron. This was also the case when ribosome scanning was abolished by introduction of a stable hairpin at the 5' region of the first cistron. Deletion analysis of the 583 nt sequence indicated that nucleotides 170 to 368 are essential for expression of the second cistron. The polypyrimidine tract-binding protein bound to the 583 nt active sequence but not to an inactive 3'-fragment of 149 nucleotides. Conclusion Our study is the first demonstration of an internal ribosome entry site as a mechanism ensuring the production of 80 kDa isoforms of protein 4.1R. This mechanism might also account for the generation of 60 kDa isoforms of 4.1R from a downstream AUG3. Our results reveal an additional level of control to 4.1R gene expression pathways and will contribute to the understanding of the biology of proteins 4.1R and their homologues, comprising an ample family of proteins involved in cytoskeletal organization.
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Affiliation(s)
- Eva Lospitao
- Departamento de Biología Molecular, Universidad Autónoma de Madrid y Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas, Nicolás Cabrera, Madrid, Spain.
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15
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Intrasplicing coordinates alternative first exons with alternative splicing in the protein 4.1R gene. EMBO J 2007; 27:122-31. [PMID: 18079699 DOI: 10.1038/sj.emboj.7601957] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2007] [Accepted: 11/19/2007] [Indexed: 11/08/2022] Open
Abstract
In the protein 4.1R gene, alternative first exons splice differentially to alternative 3' splice sites far downstream in exon 2'/2 (E2'/2). We describe a novel intrasplicing mechanism by which exon 1A (E1A) splices exclusively to the distal E2'/2 acceptor via two nested splicing reactions regulated by novel properties of exon 1B (E1B). E1B behaves as an exon in the first step, using its consensus 5' donor to splice to the proximal E2'/2 acceptor. A long region of downstream intron is excised, juxtaposing E1B with E2'/2 to generate a new composite acceptor containing the E1B branchpoint/pyrimidine tract and E2 distal 3' AG-dinucleotide. Next, the upstream E1A splices over E1B to this distal acceptor, excising the remaining intron plus E1B and E2' to form mature E1A/E2 product. We mapped branchpoints for both intrasplicing reactions and demonstrated that mutation of the E1B 5' splice site or branchpoint abrogates intrasplicing. In the 4.1R gene, intrasplicing ultimately determines N-terminal protein structure and function. More generally, intrasplicing represents a new mechanism by which alternative promoters can be coordinated with downstream alternative splicing.
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16
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Yang G, Huang SC, Wu JY, Benz EJ. Regulated Fox-2 isoform expression mediates protein 4.1R splicing during erythroid differentiation. Blood 2007; 111:392-401. [PMID: 17715393 PMCID: PMC2200819 DOI: 10.1182/blood-2007-01-068940] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A regulated splicing event in protein 4.1R pre-mRNA-the inclusion of exon 16-encoding peptides for spectrin-actin binding-occurs in late erythroid differentiation. We defined the functional significance of an intronic splicing enhancer, UGCAUG, and its cognate splicing factor, mFox2A, on exon 16 splicing during differentiation. UGCAUG displays cell-type-specific splicing regulation in a test neutral reporter and has a dose-dependent enhancing effect. Erythroid cells express 2 UGCAUG-binding mFox-2 isoforms, an erythroid differentiation-inducible mFox-2A and a commonly expressed mFox-2F. When overexpressed, both enhanced internal exon splicing in an UGCAUG-dependent manner, with mFox-2A exerting a much stronger effect than mFox-2F. A significant reciprocal increase in mFox-2A and decrease in mFox-2F occurred during erythroid differentiation and correlated with exon 16 inclusion. Furthermore, isoform-specific expression reduction reversed mFox-2A-enhancing activity, but not that of mFox-2F on exon 16 inclusion. Our results suggest that an erythroid differentiation-inducible mFox-2A isoform is a critical regulator of the differentiation-specific exon 16 splicing switch, and that its up-regulation in late erythroid differentiation is vital for exon 16 splicing.
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Affiliation(s)
- Guang Yang
- Department of Medical Oncology, Dana-Farber Cancer Institute, 44 Binney St, Boston, MA 02115, USA
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17
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Ohno N, Terada N, Yamakawa H, Komada M, Ohara O, Trapp BD, Ohno S. Expression of protein 4.1G in Schwann cells of the peripheral nervous system. J Neurosci Res 2006; 84:568-77. [PMID: 16752423 DOI: 10.1002/jnr.20949] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The membrane-associated cytoskeletal proteins, including protein 4.1 family, play important roles in membrane integrity, protein targeting, and signal transduction. Although protein 4.1G (4.1G) is expressed ubiquitously in mammalian tissues, it can have very discrete distributions within cells. The present study investigated the expression and distributions of 4.1G in rodent sciatic nerve. Northern and Western blot analysis detected abundant 4.1G mRNA and protein in rat sciatic nerve extracts. Immunohistochemical staining with a 4.1G-specific antibody and double immunolabeling with E-cadherin, betaIV spectrin, and connexin 32 detected 4.1G in paranodal loops, Schmidt-Lanterman incisures, and periaxonal, mesaxonal, and abaxonal membranes of rodent sciatic nerve. Immunoelectron microscopy confirmed the immunodistribution of 4.1G in Schwann cells. In developing mouse sciatic nerves, 4.1G was diffusely distributed in immature Schwann cells and gradually localized at paranodes, incisures, and periaxonal and mesaxonal membranes during their maturation. These data support the concept that 4.1G plays an important role in the membrane expansion and specialization that occurs during formation and maintenance of myelin internodes in the peripheral nervous system.
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Affiliation(s)
- Nobuhiko Ohno
- Department of Anatomy, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo-City, Yamanashi, Japan
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18
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Costessi L, Devescovi G, Baralle FE, Muro AF. Brain-specific promoter and polyadenylation sites of the beta-adducin pre-mRNA generate an unusually long 3'-UTR. Nucleic Acids Res 2006; 34:243-53. [PMID: 16414955 PMCID: PMC1326019 DOI: 10.1093/nar/gkj425] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Adducins are a family of membrane skeleton proteins composed of α-, β- and γ-subunits that promote actin and spectrin association in erythrocytes. The α- and γ-subunits are expressed ubiquitously, while the β-subunit is found in brain and erythropoietic tissues. The brain β-adducin protein is similar in size to that of spleen, but the mRNA transcript is a brain-specific one that has not been yet characterized, having an estimated length of 8–9 kb instead of the 3–4 kb of spleen mRNA. Here, we show the molecular basis for these differences by determining the structure of the brain-specific β-adducin transcript in rats, mice and humans. We identified a brain-specific promoter in rodents that, apparently, was not conserved in humans. In addition, we present evidence that the brain-mRNAs are formed by a common mechanism consisting in the tissue-specific use of alternative polyadenylation sites generating unusually long 3′-untranslated region of up to 6.6 kb. This hypothesis is supported by the presence of highly-conserved regions flanking the brain-specific polyadenylation site that suggest the involvement of these sequences in the translational regulation, stability and/or subcellular localization of the β-adducin transcript in the brain.
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Affiliation(s)
| | | | | | - Andrés F. Muro
- To whom correspondence should be addressed. Tel: +39 040 3757312; Fax: +39 040 226555;
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19
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Tan JS, Mohandas N, Conboy JG. High frequency of alternative first exons in erythroid genes suggests a critical role in regulating gene function. Blood 2005; 107:2557-61. [PMID: 16293607 PMCID: PMC1895744 DOI: 10.1182/blood-2005-07-2957] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The human genome uses alternative pre-mRNA splicing as an important mechanism to encode a complex proteome from a relatively small number of genes. An unknown number of these genes also possess multiple transcriptional promoters and alternative first exons that contribute another layer of complexity to gene expression mechanisms. Using a collection of more than 100 erythroid-expressed genes as a test group, we used genome browser tools and genetic databases to assess the frequency of alternative first exons in the genome. Remarkably, 35% of these erythroid genes show evidence of alternative first exons. The majority of the candidate first exons are situated upstream of the coding exons, whereas a few are located internally within the gene. Computational analyses predict transcriptional promoters closely associated with many of the candidate first exons, supporting their authenticity. Importantly, the frequent presence of consensus translation initiation sites among the alternative first exons suggests that many proteins have alternative N-terminal structures whose expression can be coupled to promoter choice. These findings indicate that alternative promoters and first exons are more widespread in the human genome than previously appreciated and that they may play a major role in regulating expression of selected protein isoforms in a tissue-specific manner.
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Affiliation(s)
- Jeff S Tan
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
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20
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Tan JS, Mohandas N, Conboy JG. Evolutionarily conserved coupling of transcription and alternative splicing in the EPB41 (protein 4.1R) and EPB41L3 (protein 4.1B) genes. Genomics 2005; 86:701-7. [PMID: 16242908 DOI: 10.1016/j.ygeno.2005.08.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2005] [Revised: 07/27/2005] [Accepted: 08/11/2005] [Indexed: 01/14/2023]
Abstract
Recent studies have shown that transcription and alternative splicing can be mechanistically coupled. In the EPB41 (protein 4.1R) and EPB41L3 (protein 4.1B) genes, we showed previously that promoter/alternative first exon choice is coupled to downstream splicing events in exon 2. Here we demonstrate that this coupling is conserved among several vertebrate classes from fish to mammals. The EPB41 and EPB41L3 genes from fish, bird, amphibian, and mammal genomes exhibit shared features including alternative first exons and differential splice acceptors in exon 2. In all cases, the 5'-most exon (exon 1A) splices exclusively to a weaker internal acceptor site in exon 2, skipping a fragment designated as exon 2'. Conversely, alternative first exons 1B and 1C always splice to the stronger first acceptor site, retaining exon 2'. These correlations are independent of cell type or species of origin. Since exon 2' contains a translation initiation site, splice variants generate protein isoforms with distinct N-termini. We propose that these genes represent a physiologically relevant model system for mechanistic analysis of transcription-coupled alternative splicing.
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Affiliation(s)
- Jeff S Tan
- Life Sciences Division and Genomics Department, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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21
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Renaudineau Y, Hillion S, Saraux A, Mageed RA, Youinou P. An alternative exon 1 of the CD5 gene regulates CD5 expression in human B lymphocytes. Blood 2005; 106:2781-9. [PMID: 15998834 DOI: 10.1182/blood-2005-02-0597] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
T lymphocytes and a subpopulation of B lymphocytes express the CD5 coreceptor. Its functional importance is evident from the multiple levels and developmental stages of the regulation of its expression. We here report the discovery of a novel regulatory exon upstream of the noncoding region of the CD5 gene in humans. This alternate exon 1 is designated E1B (with the conventional exon 1 renamed E1A) and was shown to regulate the expression of CD5. E1B-containing transcripts existed exclusively in B lymphocytes and encoded a protein that was truncated and retained intracellularly. As a consequence, the amount of E1A-containing transcripts was down-regulated and the membrane CD5 expression was diminished in the presence of E1B-containing transcripts. High levels of E1A transcripts were found in chronic lymphocytic leukemia, and there were no E1A transcripts in 697 pre-B cells, which have no membrane CD5. Introduction of E1B into Jurkat cells reduced their membrane expression of CD5, and sequence analysis revealed that the E1B motif is a defective human endogenous retrovirus. A balance between the 2 alternative exons 1 might be central to the regulation of membrane CD5 in human B cells, and, through CD5-associated SH2-containing phosphatase 1, to the modulation of B-cell antigen receptor-transduced signals.
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Affiliation(s)
- Yves Renaudineau
- Laboratory of Immunology, Brest University Medical School, BP824, F29609 Brest Cedex, France
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22
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García-Sacristán A, Fernández-Nestosa MJ, Hernández P, Schvartzman JB, Krimer DB. Protein kinase clk/STY is differentially regulated during erythroleukemia cell differentiation: a bias toward the skipped splice variant characterizes postcommitment stages. Cell Res 2005; 15:495-503. [PMID: 16045812 DOI: 10.1038/sj.cr.7290319] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Clk/STY is a LAMMER protein kinase capable to phosphorylate serine/arginine-rich (SR) proteins that modulate pre-mRNA splicing. Clk/STY alternative splicing generates transcripts encoding a full-length kinase and a truncated catalytically inactive protein. Here we showed that clk/STY, as well as other members of the family (e.g. clk2, clk3 and clk4), are up-regulated during HMBA-induced erythroleukemia cell differentiation. mRNAs coding for the full-length and the truncated forms were responsible for the overall increased expression. In clk/STY, however, a switch was observed for the ratio of the two alternative spliced products. In undifferentiated cells the full-length transcript was more abundant whereas the transcript encoding for the truncated form predominated at latter stages of differentiation. Surprisingly, overexpression of clk/STY did not alter the splicing switch upon differentiation in MEL cells. These results suggest that clk/STY might contribute to control erythroid differentiation by a mechanism that implicates a balance between these two isoforms.
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Affiliation(s)
- Ana García-Sacristán
- Department of Cell and Developmental Biology, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu 9, Madrid 28040, Spain
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23
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Delhommeau F, Dalla Venezia N, Morinière M, Collin H, Maillet P, Guerfali I, Leclerc P, Fardeau M, Delaunay J, Baklouti F. Protein 4.1R expression in normal and dystrophic skeletal muscle. C R Biol 2005; 328:43-56. [PMID: 15714879 DOI: 10.1016/j.crvi.2004.11.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
4.1R pre-mRNA alternative splicing results in multiple mRNA and protein isoforms that are expressed in virtually all tissues. More specifically, isoforms containing the alternative exon 17a, are exclusively expressed in muscle tissues. In this report, we show that these isoforms are preferentially present in the myoplasm of fast myofibres. 4.1R epitopes are also found at the sarcolemma of both slow and fast myofibres in normal muscle. Interestingly, they are absent from dystrophin-deficient sarcolemma of DMD muscle, and colocalize with partially expressed dystrophin in BMD muscle. We also show that alternative splicing of exons 16 and 17a is regulated during muscle differentiation in an asynchronous fashion, with an early inclusion of exon 16 in forming myotubes, and a late inclusion of exon 17a. Consistently, Western blot analysis led to characterize mainly an approximately 96/98-kDa doublet bearing exons 16-17a-encoding peptide, exclusively occurring in the differentiated muscle.
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Affiliation(s)
- François Delhommeau
- Inserm U473 & Service d'hématologie, hôpital de Bicêtre and faculté de médecine Paris-Sud, 63, rue Gabriel-Péri, 94270 Le Kremlin-Bicêtre cedex, France
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24
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Gascard P, Parra MK, Zhao Z, Calinisan VR, Nunomura W, Rivkees SA, Mohandas N, Conboy JG. Putative tumor suppressor protein 4.1B is differentially expressed in kidney and brain via alternative promoters and 5' alternative splicing. ACTA ACUST UNITED AC 2004; 1680:71-82. [PMID: 15488987 DOI: 10.1016/j.bbaexp.2004.08.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2004] [Revised: 08/03/2004] [Accepted: 08/10/2004] [Indexed: 10/26/2022]
Abstract
Protein 4.1B has been reported as a tumor suppressor in brain, but not in kidney, despite high expression in both tissues. Here we demonstrate that N-terminal variability in kidney and brain 4.1B isoforms arises through an unusual coupling of RNA processing events in the 5' region of the gene. We describe two transcriptional promoters at far upstream alternative exons 1A and 1B, and show that their respective transcripts splice differentially to exon 2'/2 in a manner that determines mRNA coding capacity. The consequence of this unique processing is that exon 1B transcripts initiate translation at AUG1 (in exon 2') and encode larger 4.1B isoforms with an N-terminal extension; exon 1A transcripts initiate translation at AUG2 (in exon 4) and encode smaller 4.1B isoforms. Tissue-specific differences in promoter utilization may thus explain the abundance of larger 4.1B isoforms in brain but not in kidney. In cell studies, differentiation of PC12 cells was accompanied by translocation of large protein 4.1B isoforms into the nucleus. We propose that first exon specification is coupled to downstream splicing events, generating 4.1B isoforms with diverse roles in kidney and brain physiology, and potentially unique functions in cell proliferation and tumor suppression.
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Affiliation(s)
- Philippe Gascard
- Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Mail stop 74-157, Berkeley CA 94720, USA
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25
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Huang SC, Liu ES, Chan SH, Munagala ID, Cho HT, Jagadeeswaran R, Benz EJ. Mitotic regulation of protein 4.1R involves phosphorylation by cdc2 kinase. Mol Biol Cell 2004; 16:117-27. [PMID: 15525677 PMCID: PMC539157 DOI: 10.1091/mbc.e04-05-0426] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The nonerythrocyte isoform of the cytoskeletal protein 4.1R (4.1R) is associated with morphologically dynamic structures during cell division and has been implicated in mitotic spindle function. In this study, we define important 4.1R isoforms expressed in interphase and mitotic cells by RT-PCR and mini-cDNA library construction. Moreover, we show that 4.1R is phosphorylated by p34cdc2 kinase on residues Thr60 and Ser679 in a mitosis-specific manner. Phosphorylated 4.1R135 isoform(s) associate with tubulin and Nuclear Mitotic Apparatus protein (NuMA) in intact HeLa cells in vivo as well as with the microtubule-associated proteins in mitotic asters assembled in vitro. Recombinant 4.1R135 is readily phosphorylated in mitotic extracts and reconstitutes mitotic aster assemblies in 4.1R-immunodepleted extracts in vitro. Furthermore, phosphorylation of these residues appears to be essential for the targeting of 4.1R to the spindle poles and for mitotic microtubule aster assembly in vitro. Phosphorylation of 4.1R also enhances its association with NuMA and tubulin. Finally, we used siRNA inhibition to deplete 4.1R from HeLa cells and provide the first direct genetic evidence that 4.1R is required to efficiently focus mitotic spindle poles. Thus, we suggest that 4.1R is a member of the suite of direct cdc2 substrates that are required for the establishment of a bipolar spindle.
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Affiliation(s)
- Shu-Ching Huang
- Department of Medical Oncology, Dana Farber Cancer Institute, Boston, MA 02115, USA.
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26
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Yang G, Huang SC, Wu JY, Benz EJ. An erythroid differentiation-specific splicing switch in protein 4.1R mediated by the interaction of SF2/ASF with an exonic splicing enhancer. Blood 2004; 105:2146-53. [PMID: 15522963 DOI: 10.1182/blood-2004-05-1757] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Protein 4.1R is a vital component of the red blood cell membrane cytoskeleton. Promotion of cytoskeletal junctional complex stability requires an erythroid differentiation stage-specific splicing switch promoting inclusion of exon 16 within the spectrin/actin binding domain. We showed earlier that an intricate combination of positive and negative RNA elements controls exon 16 splicing. In this report, we further identified 3 putative exonic splicing enhancers within exon 16 and investigated the function of the sequence CAGACAT in the regulation of exon 16 splicing. Mutation of these sequences leads to increased exclusion of exon 16 in both in vivo and in vitro splicing assays, indicating that CAGACAT is a functional exonic splicing enhancer. UV cross-linking further detects an approximately 33-kDa protein that specifically binds to the CAGACAT-containing transcript. An anti-SF2/ASF antibody specifically immunoprecipitates the approximately 33-kDa protein. Furthermore, SF2/ASF stimulates exon 16 inclusion in both in vitro complementation assays and minigene-transfected mouse erythroleukemia cells (MELCs). Finally, SF2/ASF expression is up-regulated and correlates with exon 16 inclusion in differentiated MELCs. These results suggest that increased splicing factor 2/alternative splicing factor (SF2/ASF) expression in differentiated mouse erythroleukemia mediates a differentiation stage-specific exon 16 splicing switch through its interaction with the exonic splicing enhancer.
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Affiliation(s)
- Guang Yang
- D610, 44 Binney Street, Department of Medical Oncology, Dana Farber Cancer Institute, Boston, MA 02115, USA
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27
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Birkenmeier CS, Barker JE. Hereditary haemolytic anaemias: unexpected sequelae of mutations in the genes for erythroid membrane skeletal proteins. J Pathol 2004; 204:450-9. [PMID: 15495268 DOI: 10.1002/path.1636] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Although the haemolytic anaemia may be the primary concern for hereditary spherocytosis and elliptocytosis patients, it is clear that their situation can be compromised by primary and secondary defects in erythroid and non-erythroid systems of the body. All seven of the red cell membrane skeletal proteins discussed in this review are also expressed in non-erythroid tissues, and mutations in their genes have the potential to cause non-erythroid defects. In some instances, such as the protein 4.1R and ANK1 neurological deficits, the diagnosis is clear. In other instances, because of the complex expression patterns involved, the non-erythroid effects may be difficult to assess. An example is the large multidomain, multifunctional band 3 protein. In this case, the location of the mutation can cause defects in one functional domain or isoform and not the other. In other cases, such as the beta-adducin null mutation, other isoforms may partially compensate for the primary deficiency. In such cases, it may be that the effects of the deficit are subtle but could increase under stress or with age. To be completely successful, treatment strategies must address both primary and secondary effects of the anaemia. If gene replacement therapy is to be used, the more that is known about the underlying genetic mechanisms producing the multiple isoforms the better we will be able to design the best replacement gene. The various animal models that are now available should be invaluable in this regard. They continue to contribute to our understanding of both the primary and the secondary effects and their treatment.
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28
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Parra M, Gee S, Chan N, Ryaboy D, Dubchak I, Mohandas N, Gascard PD, Conboy JG. Differential domain evolution and complex RNA processing in a family of paralogous EPB41 (protein 4.1) genes facilitate expression of diverse tissue-specific isoforms. Genomics 2004; 84:637-46. [PMID: 15475241 DOI: 10.1016/j.ygeno.2004.06.004] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2004] [Accepted: 06/08/2004] [Indexed: 11/30/2022]
Abstract
The EPB41 (protein 4.1) genes epitomize the resourcefulness of the mammalian genome to encode a complex proteome from a small number of genes. By utilizing alternative transcriptional promoters and tissue-specific alternative pre-mRNA splicing, EPB41, EPB41L2, EPB41L3, and EPB41L1 encode a diverse array of structural adapter proteins. Comparative genomic and transcript analysis of these 140- to 240-kb genes indicates several unusual features: differential evolution of highly conserved exons encoding known functional domains interspersed with unique exons whose size and sequence variations contribute substantially to intergenic diversity; alternative first exons, most of which map far upstream of the coding regions; and complex tissue-specific alternative pre-mRNA splicing that facilitates synthesis of functionally different complements of 4.1 proteins in various cells. Understanding the splicing regulatory networks that control protein 4.1 expression will be critical to a full appreciation of the many roles of 4.1 proteins in normal cell biology and their proposed roles in human cancer.
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Affiliation(s)
- Marilyn Parra
- Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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29
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Huang SC, Jagadeeswaran R, Liu ES, Benz EJ. Protein 4.1R, a Microtubule-associated Protein Involved in Microtubule Aster Assembly in Mammalian Mitotic Extract. J Biol Chem 2004; 279:34595-602. [PMID: 15184364 DOI: 10.1074/jbc.m404051200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Non-erythroid protein 4.1R (4.1R) consists of a complex family of isoforms. We have shown that 4.1R isoforms localize at the mitotic spindle/spindle poles and associate in a complex with the mitotic-spindle organization proteins Nuclear Mitotic Apparatus protein (NuMA), dynein, and dynactin. We addressed the mitotic function of 4.1R by investigating its association with microtubules, the main component of the mitotic spindles, and its role in mitotic aster assembly in vitro. 4.1R appears to partially co-localize with microtubules throughout the mitotic stages of the cell cycle. In vitro sedimentation assays showed that 4.1R isoforms directly interact with microtubules. Glutathione S-transferase (GST) pull-down assays using GST-4.1R fusions and mitotic cell extracts further showed that the association of 4.1R with tubulin results from both the membrane-binding domain and C-terminal domain of 4.1R. Moreover, 4.1R, but not actin, is a mitotic microtubule-associated protein; 4.1R associates with microtubules in the microtubule pellet of the mitotic asters assembled in mammalian cell-free mitotic extract. The organization of microtubules into asters depends on 4.1R in that immunodepletion of 4.1R from the extract resulted in randomly dispersed microtubules. Furthermore, adding a 135-kDa recombinant 4.1R reconstituted the mitotic asters. Finally, we demonstrated that a mitotic 4.1R isoform appears to form a complex in vivo with tubulin and NuMA in highly synchronized mitotic HeLa extracts. Our results suggest that a 135-kDa non-erythroid 4.1R is important to cell division, because it participates in the formation of mitotic spindles and spindle poles through its interaction with mitotic microtubules.
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Affiliation(s)
- Shu-Ching Huang
- Department of Medical Oncology, Dana Farber Cancer Institute, 44 Binney Street, Boston, MA 02115, USA.
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