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Ponthier JL, Schluepen C, Chen W, Lersch RA, Gee SL, Hou VC, Lo AJ, Short SA, Chasis JA, Winkelmann JC, Conboy JG. Fox-2 splicing factor binds to a conserved intron motif to promote inclusion of protein 4.1R alternative exon 16. J Biol Chem 2006; 281:12468-74. [PMID: 16537540 DOI: 10.1074/jbc.m511556200] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.0] [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: 11/06/2022] Open
Abstract
Activation of protein 4.1R exon 16 (E16) inclusion during erythropoiesis represents a physiologically important splicing switch that increases 4.1R affinity for spectrin and actin. Previous studies showed that negative regulation of E16 splicing is mediated by the binding of heterogeneous nuclear ribonucleoprotein (hnRNP) A/B proteins to silencer elements in the exon and that down-regulation of hnRNP A/B proteins in erythroblasts leads to activation of E16 inclusion. This article demonstrates that positive regulation of E16 splicing can be mediated by Fox-2 or Fox-1, two closely related splicing factors that possess identical RNA recognition motifs. SELEX experiments with human Fox-1 revealed highly selective binding to the hexamer UGCAUG. Both Fox-1 and Fox-2 were able to bind the conserved UGCAUG elements in the proximal intron downstream of E16, and both could activate E16 splicing in HeLa cell co-transfection assays in a UGCAUG-dependent manner. Conversely, knockdown of Fox-2 expression, achieved with two different siRNA sequences resulted in decreased E16 splicing. Moreover, immunoblot experiments demonstrate mouse erythroblasts express Fox-2. These findings suggest that Fox-2 is a physiological activator of E16 splicing in differentiating erythroid cells in vivo. Recent experiments show that UGCAUG is present in the proximal intron sequence of many tissue-specific alternative exons, and we propose that the Fox family of splicing enhancers plays an important role in alternative splicing switches during differentiation in metazoan organisms.
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Affiliation(s)
- Julie L Ponthier
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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Abstract
NspA is a conserved membrane protein that elicits protective antibody responses in mice against Neisseria meningitidis. A recent crystallographic study showed that NspA adopts an eight-stranded beta-barrel structure when reconstituted in detergent. In order to define the segments of NspA-containing epitopes recognized by protective murine anti-NspA antibodies, we studied the binding of two bactericidal and protective anti-NspA monoclonal antibodies (MAbs), AL12 and 14C7. Neither MAb binds to overlapping synthetic peptides (10-mers, 12-mers, and cyclic 12-mers) corresponding to the entire mature sequence of NspA, or to denatured recombinant NspA (rNspA), although binding to the protein can be restored by refolding in liposomes. Based on the ability of the two MAbs to bind to Escherichia coli microvesicles prepared from a set of rNspA variants created by site-specific mutagenesis, the most important contacts between the MAbs and NspA appear to be located within the LGG segment of loop 3. The conformation of loop 2 also appears to be an important determinant, as particular combinations of residues in this segment resulted in loss of antibody binding. Thus, the two anti-NspA MAbs recognize discontinuous conformational epitopes that result from the close proximity of loops 2 and 3 in the three-dimensional structure of NspA. The data suggest that optimally immunogenic vaccines using rNspA will require formulations that permit proper folding of the protein.
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Affiliation(s)
- Victor C Hou
- Children's Hospital Oakland Research Institute, Oakland, California, USA
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Hou VC, Lersch R, Gee SL, Ponthier JL, Lo AJ, Wu M, Turck CW, Koury M, Krainer AR, Mayeda A, Conboy JG. Decrease in hnRNP A/B expression during erythropoiesis mediates a pre-mRNA splicing switch. EMBO J 2002; 21:6195-204. [PMID: 12426391 PMCID: PMC137214 DOI: 10.1093/emboj/cdf625] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
A physiologically important alternative pre-mRNA splicing switch, involving activation of protein 4.1R exon 16 (E16) splicing, is required for the establishment of proper mechanical integrity of the erythrocyte membrane during erythropoiesis. Here we identify a conserved exonic splicing silencer element (CE(16)) in E16 that interacts with hnRNP A/B proteins and plays a role in repression of E16 splicing during early erythropoiesis. Experiments with model pre-mRNAs showed that CE(16) can repress splicing of upstream introns, and that mutagenesis or replacement of CE(16) can relieve this inhibition. An affinity selection assay with biotinylated CE(16) RNA demonstrated specific binding of hnRNP A/B proteins. Depletion of hnRNP A/B proteins from nuclear extract significantly increased E16 inclusion, while repletion with recombinant hnRNP A/B restored E16 silencing. Most importantly, differentiating mouse erythroblasts exhibited a stage-specific activation of the E16 splicing switch in concert with a dramatic and specific down-regulation of hnRNP A/B protein expression. These findings demonstrate that natural developmental changes in hnRNP A/B proteins can effect physiologically important switches in pre-mRNA splicing.
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Affiliation(s)
| | | | | | | | | | - Michael Wu
- Lawrence Berkeley National Laboratory, Life Sciences Division and
Department of Molecular and Cellular Biology, University of California at Berkeley, Berkeley, CA 94720, University of California, San Francisco, HHMI, Department of Medicine and Cardiovascular Research Institute, San Francisco, CA 94143, Department of Medicine, Vanderbilt University, Veterans Affairs Medical Centers, Nashville, TN 37232, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724 and University of Miami School of Medicine, Department of Biochemistry and Molecular Biology, Miami, FL 33136, USA Corresponding author e-mail:
| | - Chris W. Turck
- Lawrence Berkeley National Laboratory, Life Sciences Division and
Department of Molecular and Cellular Biology, University of California at Berkeley, Berkeley, CA 94720, University of California, San Francisco, HHMI, Department of Medicine and Cardiovascular Research Institute, San Francisco, CA 94143, Department of Medicine, Vanderbilt University, Veterans Affairs Medical Centers, Nashville, TN 37232, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724 and University of Miami School of Medicine, Department of Biochemistry and Molecular Biology, Miami, FL 33136, USA Corresponding author e-mail:
| | - Mark Koury
- Lawrence Berkeley National Laboratory, Life Sciences Division and
Department of Molecular and Cellular Biology, University of California at Berkeley, Berkeley, CA 94720, University of California, San Francisco, HHMI, Department of Medicine and Cardiovascular Research Institute, San Francisco, CA 94143, Department of Medicine, Vanderbilt University, Veterans Affairs Medical Centers, Nashville, TN 37232, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724 and University of Miami School of Medicine, Department of Biochemistry and Molecular Biology, Miami, FL 33136, USA Corresponding author e-mail:
| | - Adrian R. Krainer
- Lawrence Berkeley National Laboratory, Life Sciences Division and
Department of Molecular and Cellular Biology, University of California at Berkeley, Berkeley, CA 94720, University of California, San Francisco, HHMI, Department of Medicine and Cardiovascular Research Institute, San Francisco, CA 94143, Department of Medicine, Vanderbilt University, Veterans Affairs Medical Centers, Nashville, TN 37232, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724 and University of Miami School of Medicine, Department of Biochemistry and Molecular Biology, Miami, FL 33136, USA Corresponding author e-mail:
| | - Akila Mayeda
- Lawrence Berkeley National Laboratory, Life Sciences Division and
Department of Molecular and Cellular Biology, University of California at Berkeley, Berkeley, CA 94720, University of California, San Francisco, HHMI, Department of Medicine and Cardiovascular Research Institute, San Francisco, CA 94143, Department of Medicine, Vanderbilt University, Veterans Affairs Medical Centers, Nashville, TN 37232, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724 and University of Miami School of Medicine, Department of Biochemistry and Molecular Biology, Miami, FL 33136, USA Corresponding author e-mail:
| | - John G. Conboy
- Lawrence Berkeley National Laboratory, Life Sciences Division and
Department of Molecular and Cellular Biology, University of California at Berkeley, Berkeley, CA 94720, University of California, San Francisco, HHMI, Department of Medicine and Cardiovascular Research Institute, San Francisco, CA 94143, Department of Medicine, Vanderbilt University, Veterans Affairs Medical Centers, Nashville, TN 37232, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724 and University of Miami School of Medicine, Department of Biochemistry and Molecular Biology, Miami, FL 33136, USA Corresponding author e-mail:
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Abstract
Although the mature enucleated erythrocyte is no longer active in nuclear processes such as pre-mRNA splicing, the function of many of its major structural proteins is dependent on alternative splicing choices made during the earlier stages of erythropoiesis. These splicing decisions fundamentally regulate many aspects of protein structure and function by governing the inclusion or exclusion of exons that encode protein interaction domains, regulatory signals, or translation initiation or termination sites. Alternative splicing events may be partially or entirely erythroid-specific, ie, distinct from the splicing patterns imposed on the same transcripts in nonerythroid cells. Moreover, differentiation stage-specific splicing "switches" may alter the structure and function of erythroid proteins in physiologically important ways as the cell is morphologically and functionally remodeled during normal differentiation. Derangements in the splicing of individual mutated pre-mRNAs can produce synthesis of truncated or unstable proteins that are responsible for numerous erythrocyte disorders. This review will summarize the salient features of regulated alternative splicing in general, review existing information concerning the widespread extent of alternative splicing among erythroid genes, and describe recent studies that are beginning to uncover the mechanisms that regulate an erythroid splicing switch in the protein 4.1R gene.
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Affiliation(s)
- V C Hou
- Lawrence Berkeley National Laboratory, Life Sciences Division, Berkeley, California, USA.
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