1
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Sever S. Role of actin cytoskeleton in podocytes. Pediatr Nephrol 2021; 36:2607-2614. [PMID: 33188449 PMCID: PMC8116355 DOI: 10.1007/s00467-020-04812-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 09/14/2020] [Accepted: 10/05/2020] [Indexed: 12/11/2022]
Abstract
The selectivity of the glomerular filter is established by physical, chemical, and signaling interplay among its three core constituents: glomerular endothelial cells, the glomerular basement membrane, and podocytes. Functional impairment or injury of any of these three components can lead to proteinuria. Podocytes are injured in many forms of human and experimental glomerular disease, including minimal change disease, focal segmental glomerulosclerosis, and diabetes mellitus. One of the earliest signs of podocyte injury is loss of their distinct structure, which is driven by dysregulated dynamics of the actin cytoskeleton. The status of the actin cytoskeleton in podocytes depends on a set of actin binding proteins, nucleators and inhibitors of actin polymerization, and regulatory GTPases. Mutations that alter protein function in each category have been implicated in glomerular diseases in humans and animal models. In addition, a growing body of studies suggest that pharmacological modifications of the actin cytoskeleton have the potential to become novel therapeutics for podocyte-dependent chronic kidney diseases. This review presents an overview of the essential proteins that establish actin cytoskeleton in podocytes and studies demonstrating the feasibility of drugging actin cytoskeleton in kidney diseases.
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Affiliation(s)
- Sanja Sever
- Harvard Medical School and Massachusetts General Hospital, Boston, MA, USA.
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2
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Abstract
Formin homology proteins (formins) are a highly conserved family of cytoskeletal remodeling proteins that are involved in a diverse array of cellular functions. Formins are best known for their ability to regulate actin dynamics, but the same functional domains also govern stability and organization of microtubules. It is thought that this dual activity allows them to coordinate the activity of these two major cytoskeletal networks and thereby influence cellular architecture. Golgi ribbon assembly is dependent upon cooperative interactions between actin filaments and cytoplasmic microtubules originating both at the Golgi itself and from the centrosome. Similarly, centrosome assembly, centriole duplication, and centrosome positioning are also reliant on a dialogue between both cytoskeletal networks. As presented in this chapter, a growing body of evidence suggests that multiple formin proteins play essential roles in these central cellular processes.
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Affiliation(s)
- John Copeland
- Faculty of Medicine, Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON, Canada.
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3
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Watanabe N, Tohyama K, Yamashiro S. Mechanostress resistance involving formin homology proteins: G- and F-actin homeostasis-driven filament nucleation and helical polymerization-mediated actin polymer stabilization. Biochem Biophys Res Commun 2018; 506:323-329. [PMID: 30309655 DOI: 10.1016/j.bbrc.2018.09.189] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Accepted: 09/30/2018] [Indexed: 01/28/2023]
Abstract
The actin cytoskeleton has two faces. One side provides the relatively stable scaffold to maintain the shape of cell cortex fit to the organs. The other side rapidly changes morphology in response to extracellular stimuli including chemical signal and physical strain. Our series of studies employing single-molecule speckle analysis of actin have revealed diverse F-actin lifetimes spanning a range of seconds to minutes in live cells. The dynamic part of the actin turnover is tightly coupled with actin nucleation activities of formin homology proteins (formins), which serve as rapid and efficient F-actin restoration mechanisms in cells under physical stress. More recently, our two studies revealed stabilization of F-actin either by actomyosin contractile force or by helical rotation of processively-actin polymerizing diaphanous-related formin mDia1. These findings quantitatively explain our proposed anti-mechanostress cascade in that G-actin released from F-actin upon loss of tension triggers frequent nucleation and subsequent fast elongation of F-actin by formins. This formin-restored F-actin may become specifically stabilized over long distance by helical polymerization-mediated filament untwisting. In this review, we discuss how and to what extent formins-mediated F-actin restoration might confer mechanostress resistance to the cell. We also give thought to the possible involvement of helical polymerization-mediated filament untwisting in the formation of diverse actin architectures including chirality control.
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Affiliation(s)
- Naoki Watanabe
- Laboratory of Single-Molecule Cell Biology, Kyoto University Graduate School of Biostudies, Japan; Department of Pharmacology, Kyoto University Graduate School of Medicine, Japan.
| | - Kiyoshi Tohyama
- Department of Pharmacology, Kyoto University Graduate School of Medicine, Japan
| | - Sawako Yamashiro
- Laboratory of Single-Molecule Cell Biology, Kyoto University Graduate School of Biostudies, Japan
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4
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Sakamoto S, Thumkeo D, Ohta H, Zhang Z, Huang S, Kanchanawong P, Fuu T, Watanabe S, Shimada K, Fujihara Y, Yoshida S, Ikawa M, Watanabe N, Saitou M, Narumiya S. mDia1/3 generate cortical F-actin meshwork in Sertoli cells that is continuous with contractile F-actin bundles and indispensable for spermatogenesis and male fertility. PLoS Biol 2018; 16:e2004874. [PMID: 30256801 PMCID: PMC6175529 DOI: 10.1371/journal.pbio.2004874] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 10/08/2018] [Accepted: 09/10/2018] [Indexed: 11/19/2022] Open
Abstract
Formin is one of the two major classes of actin binding proteins (ABPs) with nucleation and polymerization activity. However, despite advances in our understanding of its biochemical activity, whether and how formins generate specific architecture of the actin cytoskeleton and function in a physiological context in vivo remain largely obscure. It is also unknown how actin filaments generated by formins interact with other ABPs in the cell. Here, we combine genetic manipulation of formins mammalian diaphanous homolog1 (mDia1) and 3 (mDia3) with superresolution microscopy and single-molecule imaging, and show that the formins mDia1 and mDia3 are dominantly expressed in Sertoli cells of mouse seminiferous tubule and together generate a highly dynamic cortical filamentous actin (F-actin) meshwork that is continuous with the contractile actomyosin bundles. Loss of mDia1/3 impaired these F-actin architectures, induced ectopic noncontractile espin1-containing F-actin bundles, and disrupted Sertoli cell-germ cell interaction, resulting in impaired spermatogenesis. These results together demonstrate the previously unsuspected mDia-dependent regulatory mechanism of cortical F-actin that is indispensable for mammalian sperm development and male fertility.
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Affiliation(s)
- Satoko Sakamoto
- Medical Innovation Center, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Dean Thumkeo
- Medical Innovation Center, Kyoto University Graduate School of Medicine, Kyoto, Japan
- Department of Drug Discovery Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
- * E-mail: (DT); (SN)
| | - Hiroshi Ohta
- Department of Anatomy and Cell Biology, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Zhen Zhang
- Mechanobiology Institute, National University of Singapore, Singapore
| | - Shuangru Huang
- Mechanobiology Institute, National University of Singapore, Singapore
| | - Pakorn Kanchanawong
- Mechanobiology Institute, National University of Singapore, Singapore
- Department of Biomedical Engineering, National University of Singapore, Singapore
| | - Takayoshi Fuu
- Medical Innovation Center, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Sadanori Watanabe
- Medical Innovation Center, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Kentaro Shimada
- Research Institute for Microbial Disease, Osaka University, Osaka, Japan
| | - Yoshitaka Fujihara
- Research Institute for Microbial Disease, Osaka University, Osaka, Japan
| | | | - Masahito Ikawa
- Research Institute for Microbial Disease, Osaka University, Osaka, Japan
| | - Naoki Watanabe
- Department of Pharmacology, Kyoto University Graduate School of Medicine, Kyoto, Japan
- Laboratory of Single-Molecule Cell Biology, Kyoto University Graduate School of Biostudies, Kyoto, Japan
| | - Mitinori Saitou
- Department of Anatomy and Cell Biology, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Shuh Narumiya
- Medical Innovation Center, Kyoto University Graduate School of Medicine, Kyoto, Japan
- Department of Drug Discovery Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
- * E-mail: (DT); (SN)
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5
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Helical rotation of the diaphanous-related formin mDia1 generates actin filaments resistant to cofilin. Proc Natl Acad Sci U S A 2018; 115:E5000-E5007. [PMID: 29760064 PMCID: PMC5984536 DOI: 10.1073/pnas.1803415115] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The complex interplay between actin regulatory proteins facilitates the formation of diverse cellular actin structures. Formin homology proteins (formins) play an essential role in the formation of actin stress fibers and yeast actin cables, to which the major actin depolymerizing factor cofilin barely associates. In vitro, F-actin decorated with cofilin exhibits a marked increase in the filament twist. On the other hand, a mammalian formin mDia1 rotates along the long-pitch actin helix during processive actin elongation (helical rotation). Helical rotation may impose torsional force on F-actin in the opposite direction of the cofilin-induced twisting. Here, we show that helical rotation of mDia1 converts F-actin resistant to cofilin both in vivo and in vitro. F-actin assembled by mDia1 without rotational freedom became more resistant to the severing and binding activities of cofilin than freely rotatable F-actin. Electron micrographic analysis revealed untwisting of the long-pitch helix of F-actin elongating from mDia1 on tethering of both mDia1 and the pointed end side of the filament. In cells, single molecules of mDia1ΔC63, an activated mutant containing N-terminal regulatory domains, showed tethering to cell structures more frequently than autoinhibited wild-type mDia1 and mDia1 devoid of N-terminal domains. Overexpression of mDia1ΔC63 induced the formation of F-actin, which has prolonged lifetime and accelerates dissociation of cofilin. Helical rotation of formins may thus serve as an F-actin stabilizing mechanism by which a barbed end-bound molecule can enhance the stability of a filament over a long range.
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Hua K, Ferland RJ. Primary cilia proteins: ciliary and extraciliary sites and functions. Cell Mol Life Sci 2018; 75:1521-1540. [PMID: 29305615 PMCID: PMC5899021 DOI: 10.1007/s00018-017-2740-5] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Revised: 12/21/2017] [Accepted: 12/27/2017] [Indexed: 02/07/2023]
Abstract
Primary cilia are immotile organelles known for their roles in development and cell signaling. Defects in primary cilia result in a range of disorders named ciliopathies. Because this organelle can be found singularly on almost all cell types, its importance extends to most organ systems. As such, elucidating the importance of the primary cilium has attracted researchers from all biological disciplines. As the primary cilia field expands, caution is warranted in attributing biological defects solely to the function of this organelle, since many of these "ciliary" proteins are found at other sites in cells and likely have non-ciliary functions. Indeed, many, if not all, cilia proteins have locations and functions outside the primary cilium. Extraciliary functions are known to include cell cycle regulation, cytoskeletal regulation, and trafficking. Cilia proteins have been observed in the nucleus, at the Golgi apparatus, and even in immune synapses of T cells (interestingly, a non-ciliated cell). Given the abundance of extraciliary sites and functions, it can be difficult to definitively attribute an observed phenotype solely to defective cilia rather than to some defective extraciliary function or a combination of both. Thus, extraciliary sites and functions of cilia proteins need to be considered, as well as experimentally determined. Through such consideration, we will understand the true role of the primary cilium in disease as compared to other cellular processes' influences in mediating disease (or through a combination of both). Here, we review a compilation of known extraciliary sites and functions of "cilia" proteins as a means to demonstrate the potential non-ciliary roles for these proteins.
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Affiliation(s)
- Kiet Hua
- Department of Neuroscience and Experimental Therapeutics, Albany Medical College, 47 New Scotland Avenue, MC-136, Albany, NY, 12208, USA.
| | - Russell J Ferland
- Department of Neuroscience and Experimental Therapeutics, Albany Medical College, 47 New Scotland Avenue, MC-136, Albany, NY, 12208, USA.
- Department of Neurology, Albany Medical College, Albany, NY, 12208, USA.
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7
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Reimer M, Denby E, Zustiak SP, Schober JM. Ras GAP-related and C-terminal domain-dependent localization and tumorigenic activities of IQGAP1 in melanoma cells. PLoS One 2017; 12:e0189589. [PMID: 29240845 PMCID: PMC5730206 DOI: 10.1371/journal.pone.0189589] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Accepted: 11/29/2017] [Indexed: 12/19/2022] Open
Abstract
IQGAP1 interacts with a number of binding partners through a calponin homology domain (CHD), a WW motif, IQ repeats, a Ras GAP-related domain (GRD), and a conserved C-terminal (CT) domain. Among various biological and cellular functions, IQGAP1 is known to play a role in actin cytoskeleton dynamics during membrane ruffling and lamellipodium protrusion. In addition, phosphorylation near the CT domain is thought to control IQGAP1 activity through regulation of intramolecular interaction. In a previous study, we discovered that IQGAP1 preferentially localizes to retracting areas in B16F10 mouse melanoma cells, not areas of membrane ruffling and lamellipodium protrusion. Nothing is known of the domains needed for retraction localization and very little is known of IQGAP1 function in the actin cytoskeleton of melanoma cells. Thus, we examined localization of IQGAP1 mutants to retracting areas, and characterized knock down phenotypes on tissue culture plastic and physiologic-stiffness hydrogels. Localization of IQGAP1 mutants (S1441E/S1443D, S1441A/S1443A, ΔCHD, ΔGRD or ΔCT) to retracting and protruding cell edges were measured. In retracting areas there was a decrease in S1441A/S1443A, ΔGRD and ΔCT localization, a minor decrease in ΔCHD localization, and normal localization of the S1441E/S1443D mutant. In areas of cell protrusion just behind the lamellipodium leading edge, we surprisingly observed both ΔGRD and ΔCT localization, and increased number of microtubules. IQGAP1 knock down caused loss of cell polarity on laminin-coated glass, decreased proliferation on tissue culture polystyrene, and abnormal spheroid growth on laminin-coated hydrogels. We propose that the GRD and CT domains regulate IQGAP1 localization to retracting actin networks to promote a tumorigenic role in melanoma cells.
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Affiliation(s)
- Michael Reimer
- Department of Pharmaceutical Sciences, Southern Illinois University Edwardsville, Edwardsville, Illinois, United States of America
| | - Elisabeth Denby
- Department of Pharmaceutical Sciences, Southern Illinois University Edwardsville, Edwardsville, Illinois, United States of America
| | - Silviya P. Zustiak
- Department of Biomedical Engineering, Saint Louis University, Saint Louis, Missouri, United States of America
| | - Joseph M. Schober
- Department of Pharmaceutical Sciences, Southern Illinois University Edwardsville, Edwardsville, Illinois, United States of America
- * E-mail:
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8
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Ngo KX, Kodera N, Katayama E, Ando T, Uyeda TQP. Cofilin-induced unidirectional cooperative conformational changes in actin filaments revealed by high-speed atomic force microscopy. eLife 2015; 4. [PMID: 25642645 PMCID: PMC4337605 DOI: 10.7554/elife.04806] [Citation(s) in RCA: 90] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Accepted: 01/02/2015] [Indexed: 01/12/2023] Open
Abstract
High-speed atomic force microscopy was employed to observe structural changes in actin filaments induced by cofilin binding. Consistent with previous electron and fluorescence microscopic studies, cofilin formed clusters along actin filaments, where the filaments were 2-nm thicker and the helical pitch was ∼25% shorter, compared to control filaments. Interestingly, the shortened helical pitch was propagated to the neighboring bare zone on the pointed-end side of the cluster, while the pitch on the barbed-end side was similar to the control. Thus, cofilin clusters induce distinctively asymmetric conformational changes in filaments. Consistent with the idea that cofilin favors actin structures with a shorter helical pitch, cofilin clusters grew unidirectionally toward the pointed-end of the filament. Severing was often observed near the boundaries between bare zones and clusters, but not necessarily at the boundaries. DOI:http://dx.doi.org/10.7554/eLife.04806.001 Actin is one of the most abundant proteins found inside all eukaryotic cells including plant, animal, and fungal cells. This protein is involved in a wide range of biological processes that are essential for an organism's survival. Actin proteins form long filaments that help cells to maintain their shape and also provide the force required for cells to divide and/or move. Actin filaments are helical in shape and are made up of many actin subunits joined together. Actin filaments are changeable structures that continuously grow and shrink as new actin subunits are added to or removed from the ends of the filaments. One end of an actin filament grows faster than the other; the fast-growing end is known as the barbed-end, while the slow-growing end is referred to as the pointed-end. Over 100 other proteins are known to bind to and work with actin to regulate its roles in cells and how it forms into filaments. Cofilin is one such protein that binds to and forms clusters on actin filaments and it can also sever actin filaments. Severing an actin filament can encourage the filament to disassemble, or it can help produce new barbed ends that can then grow into new filaments. Previous work had suggested that cofilin severs actin filaments at the junction between regions on the filament that are coated with cofilin and those that are not. It was also known that cofilin binding to a filament causes the filament to change shape, and that the shape change is propagated to neighboring sections of the filaments not coated with cofilin. However, the details of where cofilin binds and how changes in shape are propagated along an actin filament were not known. Furthermore, the findings of these previous studies were largely based on examining still images of actin filaments, which are unlike the constantly changing filaments of living cells. Ngo, Kodera et al. have now analyzed what happens when cofilin binds to and forms clusters along actin filaments using a recently developed imaging technique called high-speed atomic force microscopy. This technique can be used to directly visualize individual proteins in action. Consistent with previous findings, Ngo, Kodera et al. observed that filaments coated with cofilin are thicker than those filaments without cofilin; and that cofilin binding also substantially reduces the helical twist of the filament. Ngo, Kodera et al. also found that these changes in shape are propagated along the filament but in only one direction—towards the pointed-end. Moreover, cofilin clusters also only grew towards the pointed-end of the actin filament—and the filaments were often severed near, but not exactly at, the junctions between cofilin-coated and uncoated regions. Such one-directional changes in shape of the actin filaments presumably help to regulate how other actin binding proteins can interact with the filament and consequently regulate the roles of the filaments themselves. DOI:http://dx.doi.org/10.7554/eLife.04806.002
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Affiliation(s)
- Kien Xuan Ngo
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
| | - Noriyuki Kodera
- Department of Physics and Bio-AFM Frontier Research Center, Kanazawa University, Kanazawa, Japan
| | - Eisaku Katayama
- Department of Biology, Graduate School of Science, Osaka City University, Osaka, Japan
| | - Toshio Ando
- Department of Physics and Bio-AFM Frontier Research Center, Kanazawa University, Kanazawa, Japan
| | - Taro Q P Uyeda
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
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9
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Mizuno H, Watanabe N. Rotational movement of formins evaluated by using single-molecule fluorescence polarization. Methods Enzymol 2014; 540:73-94. [PMID: 24630102 DOI: 10.1016/b978-0-12-397924-7.00005-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Formin homology proteins (formins) are responsible for the formation of actin structures such as actin stress fibers, actin cables, and cytokinetic contractile rings. Formins are the major actin filament (F-actin) nucleators in the cell. Because formins remain bound to the barbed end after nucleating an actin filament, it was expected that formins might rotate along the double-helical structure of F-actin during processive actin elongation (helical rotation). Here, we describe a method to detect the rotational movement of F-actin elongating from immobilized formins using single-molecule fluorescence polarization (FLP). Tetramethylrhodamine (TMR) attached to Cys-374 of actin emits polarized fluorescence at ≈45° with respect to the filament axis. When the TMR-labeled F-actin laying at 45° in the visual field rotates, the vertical- and horizontal-polarized fluorescence (FLV and FLH, respectively) of TMR alternately become bright. This technique allowed us to demonstrate the helical rotation of mDia1, a mammalian formin. Adenosine triphosphate (ATP) hydrolysis in actin subunits is not required for helical rotation; however, ATP appears to contribute to accelerating actin elongation by mDia1. When helical rotation is limited by trapping both mDia1 and the pointed-end side, the processive filament elongation is blocked. Thus, mDia1 faithfully rotates along the long-pitch helix of F-actin. In this chapter, we introduce the theoretical concept of single-molecule FLP, the optical setup, the preparation of adenosine diphosphate-bound actin, and the procedure to observe the rotational movement of F-actin elongating from immobilized formins.
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Affiliation(s)
- Hiroaki Mizuno
- Laboratory of Single-Molecule Cell Biology, Tohoku University Graduate School of Life Sciences, Sendai, Miyagi, Japan
| | - Naoki Watanabe
- Laboratory of Single-Molecule Cell Biology, Tohoku University Graduate School of Life Sciences, Sendai, Miyagi, Japan.
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Higashida C, Kiuchi T, Akiba Y, Mizuno H, Maruoka M, Narumiya S, Mizuno K, Watanabe N. F- and G-actin homeostasis regulates mechanosensitive actin nucleation by formins. Nat Cell Biol 2013; 15:395-405. [DOI: 10.1038/ncb2693] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2012] [Accepted: 01/14/2013] [Indexed: 12/12/2022]
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