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Campbell MD, Martín-Pérez M, Egertson JD, Gaffrey MJ, Wang L, Bammler T, Rabinovitch PS, MacCoss M, Qian WJ, Villen J, Marcinek D. Elamipretide effects on the skeletal muscle phosphoproteome in aged female mice. GeroScience 2022; 44:2913-2924. [PMID: 36322234 PMCID: PMC9768078 DOI: 10.1007/s11357-022-00679-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2022] [Accepted: 10/20/2022] [Indexed: 12/24/2022] Open
Abstract
The age-related decline in skeletal muscle mass and function is known as sarcopenia. Sarcopenia progresses based on complex processes involving protein dynamics, cell signaling, oxidative stress, and repair. We have previously found that 8-week treatment with elamipretide improves skeletal muscle function, reverses redox stress, and restores protein S-glutathionylation changes in aged female mice. This study tested whether 8-week treatment with elamipretide also affects global phosphorylation in skeletal muscle consistent with functional improvements and S-glutathionylation. Using female 6-7-month-old mice and 28-29-month-old mice, we found that phosphorylation changes did not relate to S-glutathionylation modifications, but that treatment with elamipretide did partially reverse age-related changes in protein phosphorylation in mouse skeletal muscle.
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Affiliation(s)
- Matthew D Campbell
- Department of Radiology, University of Washington, South Lake Union Campus, 850 Republican St., Brotman D142, Box 358050, Seattle, WA, 98109, USA
| | | | - Jarrett D Egertson
- Department of Genome Sciences, University of Washington, Seattle, WA, USA
| | - Matthew J Gaffrey
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Lu Wang
- Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, WA, USA
| | - Theo Bammler
- Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, WA, USA
| | - Peter S Rabinovitch
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, USA
| | - Michael MacCoss
- Department of Genome Sciences, University of Washington, Seattle, WA, USA
| | - Wei-Jun Qian
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Judit Villen
- Department of Genome Sciences, University of Washington, Seattle, WA, USA
| | - David Marcinek
- Department of Radiology, University of Washington, South Lake Union Campus, 850 Republican St., Brotman D142, Box 358050, Seattle, WA, 98109, USA.
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, USA.
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2
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Scherer AN, Anand NS, Koleske AJ. Cortactin stabilization of actin requires actin-binding repeats and linker, is disrupted by specific substitutions, and is independent of nucleotide state. J Biol Chem 2018; 293:13022-13032. [PMID: 29929984 DOI: 10.1074/jbc.ra118.004068] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2018] [Revised: 06/13/2018] [Indexed: 11/06/2022] Open
Abstract
The actin-binding protein cortactin promotes the formation and maintenance of actin-rich structures, including lamellipodial protrusions in fibroblasts and neuronal dendritic spines. Cortactin cellular functions have been attributed to its activation of the Arp2/3 complex, which stimulates actin branch nucleation, and to its recruitment of Rho family GTPase regulators. Cortactin also binds actin filaments and significantly slows filament depolymerization, but the mechanism by which it does so and the relationship between actin binding and stabilization are unclear. Here we elucidated the cortactin regions that are necessary and sufficient for actin filament binding and stabilization. Using actin cosedimentation assays, we found that the cortactin repeat region binds actin but that the adjacent linker region is required for binding with the same affinity as full-length cortactin. Using total internal reflection fluorescence microscopy to measure the rates of single filament actin depolymerization, we observed that cortactin-actin interactions are sufficient to stabilize actin filaments. Moreover, conserved charged residues in repeat 4 were necessary for high-affinity actin binding, and substitution of these residues significantly impaired cortactin-mediated actin stabilization. Cortactin bound actin with higher affinity than did its paralog, hematopoietic cell-specific Lyn substrate 1 (HS1), and the effects on actin stability were specific to cortactin. Finally, cortactin stabilized ADP-actin filaments, indicating that the stabilization mechanism does not depend on the actin nucleotide state. Together, these results indicate that cortactin binding to actin is necessary and sufficient to stabilize filaments in a concentration-dependent manner, specific to conserved residues in the cortactin repeats, and independent of the actin nucleotide state.
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Affiliation(s)
| | | | - Anthony J Koleske
- Molecular Biophysics and Biochemistry, and .,Neuroscience, Yale University, New Haven, Connecticut 06520
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3
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Hernandez DA, Bennett CM, Dunina-Barkovskaya L, Wedig T, Capetanaki Y, Herrmann H, Conover GM. Nebulette is a powerful cytolinker organizing desmin and actin in mouse hearts. Mol Biol Cell 2016; 27:3869-3882. [PMID: 27733623 PMCID: PMC5170609 DOI: 10.1091/mbc.e16-04-0237] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Revised: 08/31/2016] [Accepted: 10/05/2016] [Indexed: 12/11/2022] Open
Abstract
Nebulette physically links desmin to sarcomeric actin in hearts. An intact desmin network is required for nebulette to function as major actin-binding protein in sarcomeres. This study provides biochemical evidence that the desmin–nebulette complex is involved in filament-forming desminopathy. In the hearts of patients bearing nebulette mutations, a severe general disorganization in cardiomyocytes of the extrasarcomeric desmin intermediate filament system is frequently observed. However, the molecular and functional relationship between the desmin cytoskeleton and nebulette-containing sarcomeres is still unclear. Here we report a high-affinity in vitro interaction between nebulette and desmin filaments. A major interaction site has been mapped to the desmin α-helical rod domain, indicating that the filament core is directly involved in the binding of nebulette. The disease-mutant desmin variants E245D and T453I exhibited increased binding affinity for nebulette, delayed filament assembly kinetics, and caused significant weakening of networks. In isolated chick cardiomyocytes and sections from canine heart, we revealed by ground-state depletion and confocal microscopies that module 5 of nebulette extends outward from Z-disk–associated desmin filaments toward the center of the sarcomere. Accordingly, in the myocardium of Des−/− mice, elevated levels of cardiac actin correlated with alterations in the distribution of nebulette. Our data suggest that a well-organized desmin network is required to accommodate an optimal conformation of nebulette on sarcomeres to bind and recruit cardiac α-actin. Hence we propose that nebulette acts in synergy with nebulin to reinforce and temporally fine-tune striated muscle relaxation–contraction cycles.
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Affiliation(s)
- Daniel A Hernandez
- Department of Biochemistry & Biophysics, Texas A&M University, College Station, TX 77843-3474
| | - Christina M Bennett
- Department of Biochemistry & Biophysics, Texas A&M University, College Station, TX 77843-3474
| | | | - Tatjana Wedig
- Division of Molecular Genetics, German Cancer Research Center (DKFZ), D-69120 Heidelberg, Germany
| | - Yassemi Capetanaki
- Center of Basic Research, Biomedical Research Foundation Academy of Athens, Athens 11527, Greece
| | - Harald Herrmann
- Division of Molecular Genetics, German Cancer Research Center (DKFZ), D-69120 Heidelberg, Germany.,Institute of Neuropathology, University Hospital Erlangen, D-91054 Erlangen, Germany
| | - Gloria M Conover
- Department of Biochemistry & Biophysics, Texas A&M University, College Station, TX 77843-3474
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4
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Kebir S, Orfanos Z, Schuld J, Linhart M, Lamberz C, van der Ven PFM, Schrickel J, Kirfel G, Fürst DO, Meyer R. Sarcomeric lesions and remodeling proximal to intercalated disks in overload-induced cardiac hypertrophy. Exp Cell Res 2016; 348:95-105. [PMID: 27639425 DOI: 10.1016/j.yexcr.2016.09.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2016] [Revised: 09/09/2016] [Accepted: 09/13/2016] [Indexed: 10/21/2022]
Abstract
Pressure overload induces cardiac remodeling involving both the contractile machinery and intercalated disks (IDs). Filamin C (FlnC) and Xin actin-binding repeat-containing proteins (XIRPs) are multi-adapters localizing in IDs of higher vertebrates. Knockout of the gene encoding Xin (Xirp1) in mice leads to a mild cardiac phenotype with ID mislocalization. In order to amplify this phenotype, we performed transverse aortic constriction (TAC) on control and Xirp1-deficient mice. TAC induced similar left ventricular hypertrophy in both genotypes, suggesting that the lack of Xin does not lead to higher susceptibility to cardiac overload. However, in both genotypes, FlnC appeared in "streaming" localizations across multiple sarcomeres proximal to the IDs, suggesting a remodeling response. Furthermore, FlnC-positive areas of remodeling, reminiscent of sarcomeric lesions previously described for skeletal muscles (but so far unreported in the heart), were also observed. These adaptations reflect a similarly strong effect of the pressure induced by TAC in both genotypes. However, 2 weeks post-operation TAC-treated knockout hearts had reduced levels of connexin43 and slightly increased incidents of ventricular tachycardia compared to their wild-type (WT) counterparts. Our findings highlight the FlnC-positive sarcomeric lesions and ID-proximal streaming as general remodeling responses in cardiac overload-induced hypertrophy.
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Affiliation(s)
- Sied Kebir
- Institute of Physiology II, University Hospital Bonn, Nussallee 11, 53115 Bonn, Germany.
| | - Zacharias Orfanos
- Institute for Cell Biology, Department of Molecular Cell Biology, University of Bonn, Ulrich-Haberland-Str. 61a, 53121 Bonn, Germany.
| | - Julia Schuld
- Institute for Cell Biology, Department of Molecular Cell Biology, University of Bonn, Ulrich-Haberland-Str. 61a, 53121 Bonn, Germany.
| | - Markus Linhart
- Department of Medicine-Cardiology, University of Bonn Medical Center, Sigmund-Freud-Straße 25, 53127 Bonn, Germany.
| | - Christian Lamberz
- Institute for Cell Biology, Department of Molecular Cell Biology, University of Bonn, Ulrich-Haberland-Str. 61a, 53121 Bonn, Germany.
| | - Peter F M van der Ven
- Institute for Cell Biology, Department of Molecular Cell Biology, University of Bonn, Ulrich-Haberland-Str. 61a, 53121 Bonn, Germany.
| | - Jan Schrickel
- Department of Medicine-Cardiology, University of Bonn Medical Center, Sigmund-Freud-Straße 25, 53127 Bonn, Germany.
| | - Gregor Kirfel
- Institute for Cell Biology, Department of Molecular Cell Biology, University of Bonn, Ulrich-Haberland-Str. 61a, 53121 Bonn, Germany.
| | - Dieter O Fürst
- Institute for Cell Biology, Department of Molecular Cell Biology, University of Bonn, Ulrich-Haberland-Str. 61a, 53121 Bonn, Germany.
| | - Rainer Meyer
- Institute of Physiology II, University Hospital Bonn, Nussallee 11, 53115 Bonn, Germany.
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Abstract
Efficient muscle contraction in skeletal muscle is predicated on the regulation of actin filament lengths. In one long-standing model that was prominent for decades, the giant protein nebulin was proposed to function as a 'molecular ruler' to specify the lengths of the thin filaments. This theory was questioned by many observations, including experiments in which the length of nebulin was manipulated in skeletal myocytes; this approach revealed that nebulin functions to stabilize filamentous actin, allowing thin filaments to reach mature lengths. In addition, more recent data, mostly from in vivo models and identification of new interacting partners, have provided evidence that nebulin is not merely a structural protein. Nebulin plays a role in numerous cellular processes including regulation of muscle contraction, Z-disc formation, and myofibril organization and assembly.
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Affiliation(s)
- Miensheng Chu
- Department of Cellular and Molecular Medicine and the Sarver Molecular Cardiovascular Research Program, The University of Arizona, 1656 East Mabel, MRB315, Tucson, AZ 85724, USA
| | - Carol C Gregorio
- Department of Cellular and Molecular Medicine and the Sarver Molecular Cardiovascular Research Program, The University of Arizona, 1656 East Mabel, MRB315, Tucson, AZ 85724, USA
| | - Christopher T Pappas
- Department of Cellular and Molecular Medicine and the Sarver Molecular Cardiovascular Research Program, The University of Arizona, 1656 East Mabel, MRB315, Tucson, AZ 85724, USA
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6
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Al-Sajee D, Nissar AA, Coleman SK, Rebalka IA, Chiang A, Wathra R, van der Ven PFM, Orfanos Z, Hawke TJ. Xin-deficient mice display myopathy, impaired contractility, attenuated muscle repair and altered satellite cell functionality. Acta Physiol (Oxf) 2015; 214:248-60. [PMID: 25582411 DOI: 10.1111/apha.12455] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Revised: 09/20/2014] [Accepted: 01/07/2015] [Indexed: 12/26/2022]
Abstract
AIM Xin is an F-actin-binding protein expressed during development of cardiac and skeletal muscle. We used Xin-/- mice to determine the impact of Xin deficiency on different aspects of skeletal muscle health, including functionality and regeneration. METHODS Xin-/- skeletal muscles and their satellite cell (SC) population were investigated for the presence of myopathic changes by a series of histological and immunofluorescent stains on resting uninjured muscles. To further understand the effect of Xin loss on muscle health and its SCs, we studied SCs responses following cardiotoxin-induced muscle injury. Functional data were determined using in situ muscle stimulation protocol. RESULTS Compared to age-matched wild-type (WT), Xin-/- muscles exhibited generalized myopathy and increased fatigability with a significantly decreased force recovery post-fatiguing contractions. Muscle regeneration was attenuated in Xin-/- mice. This impaired regeneration prompted an investigation into SC content and functionality. Although SC content was not different, significantly more activated SCs were present in Xin-/- vs. WT muscles. Primary Xin-/- myoblasts displayed significant reductions (approx. 50%) in proliferative capacity vs. WT; a finding corroborated by significantly decreased MyoD-positive nuclei in 3 days post-injury Xin-/- muscle vs. WT. As more activated SCs did not translate to more proliferating myoblasts, we investigated whether Xin-/- SCs displayed an exaggerated loss by apoptosis. More apoptotic SCs (TUNEL+/Pax7+) were present in Xin-/- muscle vs. WT. Furthermore, more Xin-/- myoblasts were expressing nuclear caspase-3 compared to WT at 3 days post-injury. CONCLUSION Xin deficiency leads to a myopathic condition characterized by increased muscle fatigability, impaired regeneration and SC dysfunction.
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Affiliation(s)
- D. Al-Sajee
- Pathology and Molecular Medicine; McMaster University; Hamilton ON Canada
| | - A. A. Nissar
- Pathology and Molecular Medicine; McMaster University; Hamilton ON Canada
| | - S. K. Coleman
- Pathology and Molecular Medicine; McMaster University; Hamilton ON Canada
| | - I. A. Rebalka
- Pathology and Molecular Medicine; McMaster University; Hamilton ON Canada
| | - A. Chiang
- Pathology and Molecular Medicine; McMaster University; Hamilton ON Canada
| | - R. Wathra
- Pathology and Molecular Medicine; McMaster University; Hamilton ON Canada
| | | | - Z. Orfanos
- Institute for Cell Biology; University of Bonn; Bonn Germany
| | - T. J. Hawke
- Pathology and Molecular Medicine; McMaster University; Hamilton ON Canada
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A short splice form of Xin-actin binding repeat containing 2 (XIRP2) lacking the Xin repeats is required for maintenance of stereocilia morphology and hearing function. J Neurosci 2015; 35:1999-2014. [PMID: 25653358 DOI: 10.1523/jneurosci.3449-14.2015] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Approximately one-third of known deafness genes encode proteins located in the hair bundle, the sensory hair cell's mechanoreceptive organelle. In previous studies, we used mass spectrometry to characterize the hair bundle's proteome, resulting in the discovery of novel bundle proteins. One such protein is Xin-actin binding repeat containing 2 (XIRP2), an actin-cross-linking protein previously reported to be specifically expressed in striated muscle. Because mutations in other actin-cross-linkers result in hearing loss, we investigated the role of XIRP2 in hearing function. In the inner ear, XIRP2 is specifically expressed in hair cells, colocalizing with actin-rich structures in bundles, the underlying cuticular plate, and the circumferential actin belt. Analysis using peptide mass spectrometry revealed that the bundle harbors a previously uncharacterized XIRP2 splice variant, suggesting XIRP2's role in the hair cell differs significantly from that reported in myocytes. To determine the role of XIRP2 in hearing, we applied clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9-mediated genome-editing technology to induce targeted mutations into the mouse Xirp2 gene, resulting in the elimination of XIRP2 protein expression in the inner ear. Functional analysis of hearing in the resulting Xirp2-null mice revealed high-frequency hearing loss, and ultrastructural scanning electron microscopy analyses of hair cells demonstrated stereocilia degeneration in these mice. We thus conclude that XIRP2 is required for long-term maintenance of hair cell stereocilia, and that its dysfunction causes hearing loss in the mouse.
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8
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XIRP2, an actin-binding protein essential for inner ear hair-cell stereocilia. Cell Rep 2015; 10:1811-8. [PMID: 25772365 DOI: 10.1016/j.celrep.2015.02.042] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 01/30/2015] [Accepted: 02/14/2015] [Indexed: 01/20/2023] Open
Abstract
Hair cells of the inner ear are mechanoreceptors for hearing and balance, and proteins highly enriched in hair cells may have specific roles in the development and maintenance of the mechanotransduction apparatus. We identified XIRP2/mXinβ as an enriched protein likely to be essential for hair cells. We found that different isoforms of this protein are expressed and differentially located: short splice forms (also called XEPLIN) are targeted more to stereocilia, whereas two long isoforms containing a XIN-repeat domain are in both stereocilia and cuticular plates. Mice lacking the Xirp2 gene developed normal stereocilia bundles, but these degenerated with time: stereocilia were lost and long membranous protrusions emanated from the nearby apical surfaces. At an ultrastructural level, the paracrystalline actin filaments became disorganized. XIRP2 is apparently involved in the maintenance of actin structures in stereocilia and cuticular plates of hair cells, and perhaps in other organs where it is expressed.
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9
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Molt S, Bührdel JB, Yakovlev S, Schein P, Orfanos Z, Kirfel G, Winter L, Wiche G, van der Ven PFM, Rottbauer W, Just S, Belkin AM, Fürst DO. Aciculin interacts with filamin C and Xin and is essential for myofibril assembly, remodeling and maintenance. J Cell Sci 2014; 127:3578-92. [PMID: 24963132 DOI: 10.1242/jcs.152157] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Filamin C (FLNc) and Xin actin-binding repeat-containing proteins (XIRPs) are multi-adaptor proteins that are mainly expressed in cardiac and skeletal muscles and which play important roles in the assembly and repair of myofibrils and their attachment to the membrane. We identified the dystrophin-binding protein aciculin (also known as phosphoglucomutase-like protein 5, PGM5) as a new interaction partner of FLNc and Xin. All three proteins colocalized at intercalated discs of cardiac muscle and myotendinous junctions of skeletal muscle, whereas FLNc and aciculin also colocalized in mature Z-discs. Bimolecular fluorescence complementation experiments in developing cultured mammalian skeletal muscle cells demonstrated that Xin and aciculin also interact in FLNc-containing immature myofibrils and areas of myofibrillar remodeling and repair induced by electrical pulse stimulation (EPS). Fluorescence recovery after photobleaching (FRAP) experiments showed that aciculin is a highly dynamic and mobile protein. Aciculin knockdown in myotubes led to failure in myofibril assembly, alignment and membrane attachment, and a massive reduction in myofibril number. A highly similar phenotype was found upon depletion of aciculin in zebrafish embryos. Our results point to a thus far unappreciated, but essential, function of aciculin in myofibril formation, maintenance and remodeling.
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Affiliation(s)
- Sibylle Molt
- Institute for Cell Biology, University of Bonn, 53121 Bonn, Germany
| | - John B Bührdel
- Department of Internal Medicine II, University of Ulm, 89081 Ulm, Germany
| | - Sergiy Yakovlev
- University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Peter Schein
- Institute for Cell Biology, University of Bonn, 53121 Bonn, Germany
| | | | - Gregor Kirfel
- Institute for Cell Biology, University of Bonn, 53121 Bonn, Germany
| | - Lilli Winter
- Department of Biochemistry and Molecular Cell Biology, Max F. Perutz Laboratories, University of Vienna, 1030 Vienna, Austria
| | - Gerhard Wiche
- Department of Biochemistry and Molecular Cell Biology, Max F. Perutz Laboratories, University of Vienna, 1030 Vienna, Austria
| | | | - Wolfgang Rottbauer
- Department of Internal Medicine II, University of Ulm, 89081 Ulm, Germany
| | - Steffen Just
- Department of Internal Medicine II, University of Ulm, 89081 Ulm, Germany
| | - Alexey M Belkin
- University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Dieter O Fürst
- Institute for Cell Biology, University of Bonn, 53121 Bonn, Germany
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10
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Wang Q, Lin JLC, Erives AJ, Lin CI, Lin JJC. New insights into the roles of Xin repeat-containing proteins in cardiac development, function, and disease. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2014; 310:89-128. [PMID: 24725425 DOI: 10.1016/b978-0-12-800180-6.00003-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Since the discovery of Xin repeat-containing proteins in 1996, the importance of Xin proteins in muscle development, function, regeneration, and disease has been continuously implicated. Most Xin proteins are localized to myotendinous junctions of the skeletal muscle and also to intercalated discs (ICDs) of the heart. The Xin gene is only found in vertebrates, which are characterized by a true chambered heart. This suggests that the evolutionary origin of the Xin gene may have played a key role in vertebrate origins. Diverse vertebrates including mammals possess two paralogous genes, Xinα (or Xirp1) and Xinβ (or Xirp2), and this review focuses on the role of their encoded proteins in cardiac muscles. Complete loss of mouse Xinβ (mXinβ) results in the failure of forming ICD, severe growth retardation, and early postnatal lethality. Deletion of mouse Xinα (mXinα) leads to late-onset cardiomyopathy with conduction defects. Molecular studies have identified three classes of mXinα-interacting proteins: catenins, actin regulators/modulators, and ion-channel subunits. Thus, mXinα acts as a scaffolding protein modulating the N-cadherin-mediated adhesion and ion-channel surface expression. Xin expression is significantly upregulated in early stages of stressed hearts, whereas Xin expression is downregulated in failing hearts from various human cardiomyopathies. Thus, mutations in these Xin loci may lead to diverse cardiomyopathies and heart failure.
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Affiliation(s)
- Qinchuan Wang
- Department of Biology, University of Iowa, Iowa City, Iowa, USA
| | | | - Albert J Erives
- Department of Biology, University of Iowa, Iowa City, Iowa, USA
| | - Cheng-I Lin
- Institute of Physiology, National Defense Medical Center, Taipei, Taiwan, ROC
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Wang Q, Lu TL, Adams E, Lin JLC, Lin JJC. Intercalated disc protein, mXinα, suppresses p120-catenin-induced branching phenotype via its interactions with p120-catenin and cortactin. Arch Biochem Biophys 2013; 535:91-100. [PMID: 23296090 DOI: 10.1016/j.abb.2012.12.018] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2012] [Revised: 12/20/2012] [Accepted: 12/23/2012] [Indexed: 01/11/2023]
Abstract
The Xin repeat-containing proteins, Xinα (Xirp1) and Xinβ (Xirp2), localize to the intercalated discs (ICDs) of mammalian hearts. Mouse Xinα (mXinα) directly interacts with β-catenin and actin filaments, potentially coupling the N-cadherin/β-catenin complexes to the underlying actin cytoskeleton and modulating ICD integrity and function. Supporting this possibility, mXinα-null hearts develop ICD structural defects and cardiomyopathy with conduction defects. However, the underlying mechanisms leading to these defects remain unclear. Here, we showed that mXinα also interacted with p120-catenin and cortactin. Different from the β-catenin binding domain, there existed multiple p120-catenin binding sites on mXinα, while only the extreme N-terminus of mXinα containing a SH3-binding motif could interact with cortactin. In mouse heart, a significant fraction of cortactin was co-localized with N-cadherin to ICDs, whereas in mXinα-null heart, this fraction of cortactin was drastically reduced. Therefore, mXinα may modulate ICD integrity and function through its interactions with catenins and cortactin. Analyses of the in vivo consequence of p120-catenin and mXinα interaction revealed that force-expressed mXinα or its fragments significantly suppressed the p120-catenin-induced branching phenotypes. It is known that p120-catenin directly regulates Rho GTPases, leading to the branching phenotype. Thus, mXinα may sequester the p120-catenin from inhibiting RhoA activity and/or from activating Rac1 activity.
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Affiliation(s)
- Qinchuan Wang
- Department of Biology, University of Iowa, Iowa City, IA 52242-1324, United States
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12
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Myopodin is an F-actin bundling protein with multiple independent actin-binding regions. J Muscle Res Cell Motil 2012; 34:61-9. [PMID: 23225103 DOI: 10.1007/s10974-012-9334-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Accepted: 11/28/2012] [Indexed: 01/14/2023]
Abstract
The assembly of striated muscle myofibrils is a multistep process in which a variety of proteins is involved. One of the first and most important steps in myofibrillogenesis is the arrangement of thin myofilaments into ordered I-Z-I brushes, requiring the coordinated activity of numerous actin binding proteins. The early expression of myopodin prior to sarcomeric α-actinin, as well as its binding to actin, α-actinin and filamin indicate an important role for this protein in actin cytoskeleton remodelling with the precise function of myopodin in this process yet remaining to be resolved. While myopodin was previously described as a protein capable of cross-linking actin filaments into thick bundles upon transient transfections, it has remained unclear whether myopodin alone is capable of bundling actin, or if additional proteins are involved. We have therefore investigated the in vitro actin binding properties of myopodin. High speed cosedimentation assays with skeletal muscle actin confirmed direct binding of myopodin to F-actin and showed that this interaction is mediated by at least two independent actin binding sites, found in all myopodin isoforms identified to date. Furthermore, low-speed cosedimentation assays revealed that not only full length myopodin, but also the fragment containing only the second binding site, bundles microfilaments in the absence of accessory proteins. Ultrastructural analysis demonstrated that this bundling activity resembled that of α-actinin. Biochemical experiments revealed that bundling was not achieved by myopodin's ability to dimerize, indicating the presence of two individual F-actin binding sites within the second binding segment. Thus full length myopodin contains at least three F-actin binding sites. These data provide further understanding of the mechanisms by which myopodin contributes to actin reorganization during myofibril assembly.
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13
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Otten C, van der Ven PF, Lewrenz I, Paul S, Steinhagen A, Busch-Nentwich E, Eichhorst J, Wiesner B, Stemple D, Strähle U, Fürst DO, Abdelilah-Seyfried S. Xirp proteins mark injured skeletal muscle in zebrafish. PLoS One 2012; 7:e31041. [PMID: 22355335 PMCID: PMC3280289 DOI: 10.1371/journal.pone.0031041] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2011] [Accepted: 12/30/2011] [Indexed: 11/18/2022] Open
Abstract
Myocellular regeneration in vertebrates involves the proliferation of activated progenitor or dedifferentiated myogenic cells that have the potential to replenish lost tissue. In comparison little is known about cellular repair mechanisms within myocellular tissue in response to small injuries caused by biomechanical or cellular stress. Using a microarray analysis for genes upregulated upon myocellular injury, we identified zebrafish Xin-actin-binding repeat-containing protein1 (Xirp1) as a marker for wounded skeletal muscle cells. By combining laser-induced micro-injury with proliferation analyses, we found that Xirp1 and Xirp2a localize to nascent myofibrils within wounded skeletal muscle cells and that the repair of injuries does not involve cell proliferation or Pax7(+) cells. Through the use of Xirp1 and Xirp2a as markers, myocellular injury can now be detected, even though functional studies indicate that these proteins are not essential in this process. Previous work in chicken has implicated Xirps in cardiac looping morphogenesis. However, we found that zebrafish cardiac morphogenesis is normal in the absence of Xirp expression, and animals deficient for cardiac Xirp expression are adult viable. Although the functional involvement of Xirps in developmental and repair processes currently remains enigmatic, our findings demonstrate that skeletal muscle harbours a rapid, cell-proliferation-independent response to injury which has now become accessible to detailed molecular and cellular characterizations.
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Affiliation(s)
- Cécile Otten
- Max Delbrück Center (MDC) for Molecular Medicine, Berlin, Germany
| | - Peter F. van der Ven
- Department of Molecular Cell Biology, Institute of Cell Biology, University of Bonn, Bonn, Germany
| | - Ilka Lewrenz
- Department of Molecular Cell Biology, Institute of Cell Biology, University of Bonn, Bonn, Germany
| | - Sandeep Paul
- Institute for Toxicology and Genetics, Karlsruhe, Germany
- University of Southern California Keck School of Medicine, Los Angeles, California, United States of America
| | - Almut Steinhagen
- Department of Molecular Cell Biology, Institute of Cell Biology, University of Bonn, Bonn, Germany
| | - Elisabeth Busch-Nentwich
- Vertebrate Development and Genetics, The Wellcome Trust Sanger Institute, Cambridge, United Kingdom
| | - Jenny Eichhorst
- Leibniz Institute for Molecular Pharmacology, Berlin, Germany
| | | | - Derek Stemple
- Vertebrate Development and Genetics, The Wellcome Trust Sanger Institute, Cambridge, United Kingdom
| | - Uwe Strähle
- Institute for Toxicology and Genetics, Karlsruhe, Germany
| | - Dieter O. Fürst
- Department of Molecular Cell Biology, Institute of Cell Biology, University of Bonn, Bonn, Germany
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Hazard D, Fernandez X, Pinguet J, Chambon C, Letisse F, Portais JC, Wadih-Moussa Z, Rémignon H, Molette C. Functional genomics of the muscle response to restraint and transport in chickens. J Anim Sci 2011; 89:2717-30. [PMID: 21512117 DOI: 10.2527/jas.2010-3288] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
In the present study, we used global approaches (proteomics, transcriptomics, and metabolomics) to assess the molecular basis of the muscle response to stress in chickens. A restraint test, combined with transport for 2 h (RT test) was chosen as the potentially stressful situation. Chickens (6 wk old) were either nontreated (control chickens) or submitted to the RT test (treated chickens). The RT test induced a 6-fold increase in corticosterone concentrations, suggesting hypothalamic-pituitary-adrenal axis activation. The RT test decreased the relative abundance of several hexose phosphates [glucose-1-P (G1P), glucose-6-P (G6P), fructose-6-P (F6P), and mannose-6-P (M6P)] in thigh muscle. In addition, 55 transcripts, among which 39 corresponded to unique annotated genes, were significantly up- (12 genes) or downregulated (27 genes) by treatment. Similarly, 45 proteic spots, among which 29 corresponded to unique annotated proteins, were overexpressed (11 proteins), underexpressed (14 proteins), or only expressed in treated chickens. Integrative analysis of differentially expressed genes and proteins showed that most transcripts and proteins belong to 2 networks whose genes were mainly related with cytoskeleton structure or carbohydrate metabolism. Whereas the decrease in energetic metabolites suggested an activation of glycogenolysis and glycolysis in response to the RT test, the reduced expression of genes and proteins involved in these pathways suggested the opposite. We hypothesized that the prolonged RT test resulted in a repression of glycogenolysis and glycolysis in thigh muscle of chickens. The down-expression of genes and proteins involved in the formation of fiber stress after the RT test suggests a reinforcement of myofibrils in response to stress.
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Affiliation(s)
- D Hazard
- Université de Toulouse, INPT ENSAT, UMR1289 Tissus Animaux Nutrition Digestion Ecosystème et Métabolisme, F-31326 Castanet-Tolosan, France
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15
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Ono S. Dynamic regulation of sarcomeric actin filaments in striated muscle. Cytoskeleton (Hoboken) 2010; 67:677-92. [PMID: 20737540 PMCID: PMC2963174 DOI: 10.1002/cm.20476] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2010] [Revised: 07/21/2010] [Accepted: 07/29/2010] [Indexed: 01/08/2023]
Abstract
In striated muscle, the actin cytoskeleton is differentiated into myofibrils. Actin and myosin filaments are organized in sarcomeres and specialized for producing contractile forces. Regular arrangement of actin filaments with uniform length and polarity is critical for the contractile function. However, the mechanisms of assembly and maintenance of sarcomeric actin filaments in striated muscle are not completely understood. Live imaging of actin in striated muscle has revealed that actin subunits within sarcomeric actin filaments are dynamically exchanged without altering overall sarcomeric structures. A number of regulators for actin dynamics have been identified, and malfunction of these regulators often result in disorganization of myofibril structures or muscle diseases. Therefore, proper regulation of actin dynamics in striated muscle is critical for assembly and maintenance of functional myofibrils. Recent studies have suggested that both enhancers of actin dynamics and stabilizers of actin filaments are important for sarcomeric actin organization. Further investigation of the regulatory mechanism of actin dynamics in striated muscle should be a key to understanding how myofibrils develop and operate.
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Affiliation(s)
- Shoichiro Ono
- Department of Pathology and Department of Cell Biology, Emory University, Atlanta, Georgia 30322, USA.
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16
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Otten J, van der Ven PFM, Vakeel P, Eulitz S, Kirfel G, Brandau O, Boesl M, Schrickel JW, Linhart M, Hayess K, Naya FJ, Milting H, Meyer R, Fürst DO. Complete loss of murine Xin results in a mild cardiac phenotype with altered distribution of intercalated discs. Cardiovasc Res 2009; 85:739-50. [PMID: 19843512 DOI: 10.1093/cvr/cvp345] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
AIMS Xin is a striated muscle-specific F-actin binding protein that has been implicated in cardiomyopathies. In cardiomyocytes, Xin is localized at intercalated discs (IDs). Mice lacking only two of the three Xin isoforms (XinAB(-/-) mice) develop severe cardiac hypertrophy. To further investigate the function of Xin variants in the mammalian heart, we generated XinABC(-/-) mice deficient in all Xin isoforms. METHODS AND RESULTS XinABC(-/-) mice showed a very mild phenotype: heart weight, heart weight to tibia length ratios, and cardiac dimensions were not altered. Increased perivascular fibrosis was only observed in hearts of young XinABC(-/-) mice. Striking differences were revealed in isolated cardiomyocytes: XinABC(-/-) cells demonstrated a significantly increased number of non-terminally localized ID-like structures. Furthermore, resting sarcomere length was increased, sarcomere shortening, peak shortening at 0.5-1 Hz, and the duration of shortening were decreased, and shortening and relengthening velocities were accelerated at frequencies above 4 Hz in XinABC(-/-) cardiomyocytes. ECG showed a significantly shorter HV interval and a trend towards shorter QRS interval in XinABC(-/-) mice, suggesting a faster conduction velocity of the ventricular-specific conduction system. In human cardiac tissue, expression of XinC protein was detected solely in samples from patients with cardiac hypertrophy. CONCLUSION Total Xin deficiency leads to topographical ID alterations, premature fibrosis and subtle changes in contractile behaviour; this is a milder cardiac phenotype than that observed in XinAB(-/-) mice, which still can express XinC. Together with the finding that XinC is detected solely in cardiomyopathic human tissues, this suggests that its expression is responsible for the stronger dominant phenotype in XinAB(-/-) mice. Furthermore, it indicates that XinC may be involved in the development of human cardiac hypertrophy.
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Affiliation(s)
- Julia Otten
- Department of Molecular Cell Biology, Institute for Cell Biology, University of Bonn, Ulrich-Haberland-Str. 61a, Bonn D-53121, Germany
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17
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Sjöblom B, Ylänne J, Djinović-Carugo K. Novel structural insights into F-actin-binding and novel functions of calponin homology domains. Curr Opin Struct Biol 2008; 18:702-8. [PMID: 18952167 DOI: 10.1016/j.sbi.2008.10.003] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2008] [Revised: 10/14/2008] [Accepted: 10/14/2008] [Indexed: 12/23/2022]
Abstract
Tandem calponin homology (CH) domains are well-known actin filaments (F-actin) binding motifs. There has been a continuous debate about the details of CH domain-actin interaction, mainly because atomic level structures of F-actin are not available. A recent electron microscopy study has considerably advanced our structural understanding of CH domain:F-actin complex. On the contrary, it has recently also been shown that CH domains can bind other macromolecular systems: two CH domains from separate polypeptides Ncd80, Nuf2 can form a microtubule-binding site, as well as tandem CH domains in the EB1 dimer, while the single C-terminal CH domain of alpha-parvin has been observed to bind to a alpha-helical leucin-aspartate rich motif from paxillin.
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Affiliation(s)
- Björn Sjöblom
- Department for Biomolecular Structural Chemistry, Max F. Perutz Laboratories, University of Vienna, Campus Vienna Biocenter 5, A-1030 Vienna, Austria
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18
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Grosskurth SE, Bhattacharya D, Wang Q, Lin JJC. Emergence of Xin demarcates a key innovation in heart evolution. PLoS One 2008; 3:e2857. [PMID: 18682726 PMCID: PMC2478706 DOI: 10.1371/journal.pone.0002857] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2008] [Accepted: 07/09/2008] [Indexed: 11/22/2022] Open
Abstract
The mouse Xin repeat-containing proteins (mXinα and mXinβ) localize to the intercalated disc in the heart. mXinα is able to bundle actin filaments and to interact with β-catenin, suggesting a role in linking the actin cytoskeleton to N-cadherin/β-catenin adhesion. mXinα-null mouse hearts display progressively ultrastructural alterations at the intercalated discs, and develop cardiac hypertrophy and cardiomyopathy with conduction defects. The up-regulation of mXinβ in mXinα-deficient mice suggests a partial compensation for the loss of mXinα. To elucidate the evolutionary relationship between these proteins and to identify the origin of Xin, a phylogenetic analysis was done with 40 vertebrate Xins. Our results show that the ancestral Xin originated prior to the emergence of lamprey and subsequently underwent gene duplication early in the vertebrate lineage. A subsequent teleost-specific genome duplication resulted in most teleosts encoding at least three genes. All Xins contain a highly conserved β-catenin-binding domain within the Xin repeat region. Similar to mouse Xins, chicken, frog and zebrafish Xins also co-localized with β-catenin to structures that appear to be the intercalated disc. A putative DNA-binding domain in the N-terminus of all Xins is strongly conserved, whereas the previously characterized Mena/VASP-binding domain is a derived trait found only in Xinαs from placental mammals. In the C-terminus, Xinαs and Xinβs are more divergent relative to each other but each isoform from mammals shows a high degree of within-isoform sequence identity. This suggests different but conserved functions for mammalian Xinα and Xinβ. Interestingly, the origin of Xin ca. 550 million years ago coincides with the genesis of heart chambers with complete endothelial and myocardial layers. We postulate that the emergence of the Xin paralogs and their functional differentiation may have played a key role in the evolutionary development of the heart.
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Affiliation(s)
- Shaun E. Grosskurth
- Department of Biology, University of Iowa, Iowa City, Iowa, United States of America
| | | | - Qinchuan Wang
- Department of Biology, University of Iowa, Iowa City, Iowa, United States of America
| | - Jim Jung-Ching Lin
- Department of Biology, University of Iowa, Iowa City, Iowa, United States of America
- * E-mail:
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19
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Lai YJ, Huang EYK, Yeh HI, Chen YL, Lin JJC, Lin CI. On the mechanisms of arrhythmias in the myocardium of mXinalpha-deficient murine left atrial-pulmonary veins. Life Sci 2008; 83:272-83. [PMID: 18644388 DOI: 10.1016/j.lfs.2008.06.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2007] [Revised: 05/21/2008] [Accepted: 06/15/2008] [Indexed: 12/13/2022]
Abstract
We have previously shown that left atrial-pulmonary vein tissue (LA-PV) can generate reentrant arrhythmias (atrial fibrillation, AF) in wild-type (mXinalpha+/+) but not in mXinalpha-null (mXinalpha-/-) mice. With the present experiments, we investigated the arrhythmogenic activity and the underlying mechanisms in mXinalpha+/+ vs. mXinalpha-/- LA-PV. Electrical activity and conduction velocity (CV) were recorded in LA-PV by means of a MED64 system. CV was significantly faster in mXinalpha+/+ than in mXinalpha-/- LA-PV and it was increased by 1 muM isoproterenol (ISO). AF could be induced by fast pacing in the mXinalpha+/+ but not in mXinalpha-/- LA-PV where automatic rhythms could occur. ISO increased the incidence of AF in Xinalpha+/+ whereas it increased that of automatic rhythms in mXinalpha-/- LA-PV. In LA-PV with the right atrium attached (RA-LA-PV), automatic rhythms occurred in all preparations. In mXinalpha+/+ RA-LA-PV simultaneously treated with ISO, strophanthidin and atropine, the incidence of the automatic rhythm was about the same, but AF increased significantly. In contrast, in mXinalpha-/- RA-LA-PV under the same condition, the automatic rhythm was markedly enhanced, but still no AF occurred. Conventional microelectrode techniques showed a longer APD(90) and a less negative maximum diastolic potential (MDP) in mXinalpha-/- than mXinalpha+/+ LA-PV tissues. Whole-cell current clamp experiments also showed a less negative MDP in mXinalpha-/- vs. mXinalpha+/+ LA-PV cardiomyocytes. The fact that AF could be induced by fast pacing under several conditions in mXinalpha+/+ but not in mXinalpha-/- LA-PV preparations appears to be due to a slower CV, a prolonged APD(90), a less negative MDP and possibly larger areas of conduction block in mXinalpha-/- myocardial cells. In contrast, the non-impairment of automatic and triggered rhythms in mXinalpha-/- preparations may be due to the fact that the mechanisms underlying these rhythms do not involve cell-to-cell conduction.
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Affiliation(s)
- Yu-Jun Lai
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan
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20
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Galkin VE, Orlova A, Brieher W, Kueh HY, Mitchison TJ, Egelman EH. Coronin-1A stabilizes F-actin by bridging adjacent actin protomers and stapling opposite strands of the actin filament. J Mol Biol 2007; 376:607-13. [PMID: 18177666 DOI: 10.1016/j.jmb.2007.12.007] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2007] [Revised: 11/28/2007] [Accepted: 12/04/2007] [Indexed: 11/28/2022]
Abstract
Coronins are F-actin-binding proteins that are involved, in concert with Arp2/3, Aip1, and ADF/cofilin, in rearrangements of the actin cytoskeleton. An understanding of coronin function has been hampered by the absence of any structural data on its interaction with actin. Using electron microscopy and three-dimensional reconstruction, we show that coronin-1A binds to three protomers in F-actin simultaneously: it bridges subdomain 1 and subdomain 2 of two adjacent actin subunits along the same long-pitch strand, and it staples subdomain 1 and subdomain 4 of two actin protomers on different strands. Such a mode of binding explains how coronin can stabilize actin filaments in vitro. In addition, we show which residues of F-actin may participate in the interaction with coronin-1A. Human nebulin and Xin, as well as Salmonella invasion protein A, use a similar mechanism to stabilize actin filaments. We suggest that the stapling of subdomain 1 and subdomain 4 of two actin protomers on different strands is a common mechanism for F-actin stabilization utilized by many actin-binding proteins that have no homology.
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Affiliation(s)
- Vitold E Galkin
- Department of Biochemistry and Molecular Genetics, University of Virginia, Box 800733, Charlottesville, VA 22908-0733, USA.
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21
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Choi S, Gustafson-Wagner EA, Wang Q, Harlan SM, Sinn HW, Lin JLC, Lin JJC. The intercalated disk protein, mXinalpha, is capable of interacting with beta-catenin and bundling actin filaments [corrected]. J Biol Chem 2007; 282:36024-36. [PMID: 17925400 PMCID: PMC2394275 DOI: 10.1074/jbc.m707639200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Targeted deletion of mXinalpha results in cardiac hypertrophy and cardiomyopathy with conduction defects (Gustafson-Wagner, E., Sinn, H. W., Chen, Y.-L., Wang, D.-Z., Reiter, R. S., Lin, J. L.-C., Yang, B., Williamson, R. A., Chen, J. N., Lin, C.-I., and Lin, J. J.-C. (2007) Am. J. Physiol. 293, H2680-H2692). To understand the underlying mechanisms leading to such cardiac defects, the functional domains of mXinalpha and its interacting proteins were investigated. Interaction studies using co-immunoprecipitation, pull-down, and yeast two-hybrid assays revealed that mXinalpha directly interacts with beta-catenin. The beta-catenin-binding site on mXinalpha was mapped to amino acids 535-636, which overlaps with the known actin-binding domains composed of the Xin repeats. The overlapping nature of these domains provides insight into the molecular mechanism for mXinalpha localization and function. Purified recombinant glutathione S-transferase- or His-tagged mXinalpha proteins are capable of binding and bundling actin filaments, as determined by co-sedimentation and electron microscopic studies. The binding to actin was saturated at an approximate stoichiometry of nine actin monomers to one mXinalpha. A stronger interaction was observed between mXinalpha C-terminal deletion and actin as compared with the interaction between full-length mXinalpha and actin. Furthermore, force expression of green fluorescent protein fused to an mXinalpha C-terminal deletion in cultured cells showed greater stress fiber localization compared with force-expressed GFP-mXinalpha. These results suggest a model whereby the C terminus of mXinalpha may prevent the full-length molecule from binding to actin, until the beta-catenin-binding domain is occupied by beta-catenin. The binding of mXinalpha to beta-catenin at the adherens junction would then facilitate actin binding. In support of this model, we found that the actin binding and bundling activity of mXinalpha was enhanced in the presence of beta-catenin.
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Affiliation(s)
- Sunju Choi
- Department of Biological Sciences, University of Iowa, Iowa City, Iowa 52242-1324, USA
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22
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Gustafson-Wagner EA, Sinn HW, Chen YL, Wang DZ, Reiter RS, Lin JLC, Yang B, Williamson RA, Chen J, Lin CI, Lin JJC. Loss of mXinalpha, an intercalated disk protein, results in cardiac hypertrophy and cardiomyopathy with conduction defects. Am J Physiol Heart Circ Physiol 2007; 293:H2680-92. [PMID: 17766470 PMCID: PMC2394510 DOI: 10.1152/ajpheart.00806.2007] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The intercalated disk protein Xin was originally discovered in chicken striated muscle and implicated in cardiac morphogenesis. In the mouse, there are two homologous genes, mXinalpha and mXinbeta. The human homolog of mXinalpha, Cmya1, maps to chromosomal region 3p21.2-21.3, near a dilated cardiomyopathy with conduction defect-2 locus. Here we report that mXinalpha-null mouse hearts are hypertrophied and exhibit fibrosis, indicative of cardiomyopathy. A significant upregulation of mXinbeta likely provides partial compensation and accounts for the viability of the mXinalpha-null mice. Ultrastructural studies of mXinalpha-null mouse hearts reveal intercalated disk disruption and myofilament disarray. In mXinalpha-null mice, there is a significant decrease in the expression level of p120-catenin, beta-catenin, N-cadherin, and desmoplakin, which could compromise the integrity of the intercalated disks and functionally weaken adhesion, leading to cardiac defects. Additionally, altered localization and decreased expression of connexin 43 are observed in the mXinalpha-null mouse heart, which, together with previously observed abnormal electrophysiological properties of mXinalpha-deficient mouse ventricular myocytes, could potentially lead to conduction defects. Indeed, ECG recordings on isolated, perfused hearts (Langendorff preparations) show a significantly prolonged QT interval in mXinalpha-deficient hearts. Thus mXinalpha functions in regulating the hypertrophic response and maintaining the structural integrity of the intercalated disk in normal mice, likely through its association with adherens junctional components and actin cytoskeleton. The mXinalpha-knockout mouse line provides a novel model of cardiac hypertrophy and cardiomyopathy with conduction defects.
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23
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Egelman EH. The iterative helical real space reconstruction method: surmounting the problems posed by real polymers. J Struct Biol 2007; 157:83-94. [PMID: 16919474 DOI: 10.1016/j.jsb.2006.05.015] [Citation(s) in RCA: 186] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2006] [Revised: 05/02/2006] [Accepted: 05/16/2006] [Indexed: 11/20/2022]
Abstract
Many important biological macromolecules exist as helical polymers. Examples are actin, tubulin, myosin, RecA, Rad51, flagellin, pili, and filamentous bacteriophage. The first application of three-dimensional reconstruction from electron microscopic images was to a helical polymer, and a number of laboratories today are using helical tubes of integral membrane proteins for solving the structure of these proteins in the electron microscope at near atomic resolution. We have developed a method to analyze and reconstruct electron microscopic images of macromolecular helical polymers, the iterative helical real space reconstruction (IHRSR) algorithm. We can show that when there is disorder or heterogeneity, when the specimens diffract weakly, or when Bessel functions overlap, we can do far better with our method than can be done using traditional Fourier-Bessel approaches. In many cases, structures that were not even amenable to analysis can be solved at fairly high resolution using our method. The problems inherent in the traditional approach are discussed, and examples are presented illustrating how the IHRSR approach surmounts these problems.
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Affiliation(s)
- Edward H Egelman
- Department of Biochemistry and Molecular Genetics, University of Virginia Health Sciences, P.O. Box 800733, Charlottesville, VA 22908-0733, USA.
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