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Lv S, Chen Z, Mi H, Yu X. Cofilin Acts as a Booster for Progression of Malignant Tumors Represented by Glioma. Cancer Manag Res 2022; 14:3245-3269. [PMID: 36452435 PMCID: PMC9703913 DOI: 10.2147/cmar.s389825] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Accepted: 11/10/2022] [Indexed: 07/20/2023] Open
Abstract
Cofilin, as a depolymerization factor of actin filaments, has been widely studied. Evidences show that cofilin has a role in actin structural reorganization and dynamic regulation. In recent years, several studies have demonstrated a regulatory role for cofilin in the migration and invasion mediated by cell dynamics and epithelial to mesenchymal transition (EMT)/EMT-like process, apoptosis, radiotherapy resistance, immune escape, and transcriptional dysregulation of malignant tumor cells, particularly glioma cells. On this basis, it is practical to evaluate cofilin as a biomarker for predicting tumor metastasis and prognosis. Targeting cofilin regulating kinases, Lin11, Isl-1 and Mec-3 kinases (LIM kinases/LIMKs) and their major upstream molecules inhibits tumor cell migration and invasion and targeting cofilin-mediated mitochondrial pathway induces apoptosis of tumor cells represent effective options for the development of novel anti-malignant tumor drug, especially anti-glioma drugs. This review explores the structure, general biological function, and regulation of cofilin, with an emphasis on the critical functions and prospects for clinical therapeutic applications of cofilin in malignant tumors represented by glioma.
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Affiliation(s)
- Shihong Lv
- Department of Gastroenterology, The Second Affiliated Hospital of Mudanjiang Medical College, Mudanjiang Medical College, Mudanjiang, 157011, People’s Republic of China
| | - Zhiye Chen
- Department of Neurosurgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, People’s Republic of China
- Department of Histology and Embryology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, People’s Republic of China
| | - Hailong Mi
- Department of Histology and Embryology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, People’s Republic of China
| | - Xingjiang Yu
- Department of Histology and Embryology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, People’s Republic of China
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2
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Kumar N, Rath PP, Aggarwal P, Maiti S, Bhavesh NS, Gourinath S. Unravelling the Biology of EhActo as the First Cofilin From Entamoeba histolytica. Front Cell Dev Biol 2022; 10:785680. [PMID: 35281106 PMCID: PMC8914023 DOI: 10.3389/fcell.2022.785680] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2021] [Accepted: 02/09/2022] [Indexed: 11/13/2022] Open
Abstract
Actin-depolymerising factors (ADF) are a known family of proteins that regulate actin dynamics. Actin regulation is critical for primitive eukaryotes since it drives their key cellular processes. Entamoeba histolytica, a protist human pathogen harbours eleven proteins within this family, however, with no actin depolymerising protein reported to date. We present here the NMR model of EhActo, the first Cofilin from E. histolytica that severs actin filaments and also participates in cellular events like phagocytosis and pseudopod formation. The model typically represents the ADF-homology domain compared to other cofilins. Uniquely, EhActo lacks the critical Serine3 residue present in all known actophorins mediating its phospho-regulation. The second mode of regulation that cofilin’s are subjected to is via their interaction with 14-3-3 proteins through the phosphorylated Serine residue and a consensus binding motif. We found a unique interaction between EhActo and 14-3-3 without the presence of the consensus motif or the phosphorylated Serine. These interesting results present unexplored newer mechanisms functional in this pathogen to regulate actophorin. Through our structural and biochemical studies we have deciphered the mechanism of action of EhActo, implicating its role in amoebic biology.
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Affiliation(s)
- Nitesh Kumar
- Department of Pathology, Indira Gandhi Institute of Medical Sciences, Patna, India
- International Centre for Genetic Engineering and Biotechnology, New Delhi, India
- *Correspondence: Nitesh Kumar, ; Samudrala Gourinath,
| | | | - Priyanka Aggarwal
- International Centre for Genetic Engineering and Biotechnology, New Delhi, India
| | - Sankar Maiti
- Indian Institute of Science, Education and Research, Kolkata, India
| | - Neel Sarovar Bhavesh
- International Centre for Genetic Engineering and Biotechnology, New Delhi, India
| | - Samudrala Gourinath
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, India
- *Correspondence: Nitesh Kumar, ; Samudrala Gourinath,
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3
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Huyck L, Van Troys M, Ampe C. Phosphosite conservation in single domain orthologs versus paralogs: a way to combine differential regulation with redundant core functions. FEBS Lett 2012; 586:296-302. [PMID: 22265693 DOI: 10.1016/j.febslet.2012.01.018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2011] [Revised: 01/04/2012] [Accepted: 01/09/2012] [Indexed: 11/19/2022]
Abstract
Evolutionary conservation for structure function relations is commonly accepted. Here we hypothesize that closely related single domain paralogous proteins, having similar expression profiles and redundant biochemical core functions, additionally evolved to allow and maintain isoform specific differential regulation by single conserved amino acid substitutions. To substantiate this, we considered two families of closely related actin binding proteins combined with data mining of phosphorylated residues in human and mouse proteins. We show that such residues are identical in other orthologs whereas paralogs have a different, but also conserved, non-phosphorylatable residue at the equivalent positions.
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Affiliation(s)
- Lynn Huyck
- Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium
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4
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Poukkula M, Kremneva E, Serlachius M, Lappalainen P. Actin-depolymerizing factor homology domain: a conserved fold performing diverse roles in cytoskeletal dynamics. Cytoskeleton (Hoboken) 2011; 68:471-90. [PMID: 21850706 DOI: 10.1002/cm.20530] [Citation(s) in RCA: 110] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2011] [Revised: 06/29/2011] [Accepted: 08/05/2011] [Indexed: 11/09/2022]
Abstract
Actin filaments form contractile and protrusive structures that play central roles in many processes such as cell migration, morphogenesis, endocytosis, and cytokinesis. During these processes, the dynamics of the actin filaments are precisely regulated by a large array of actin-binding proteins. The actin-depolymerizing factor homology (ADF-H) domain is a structurally conserved protein motif, which promotes cytoskeletal dynamics by interacting with monomeric and/or filamentous actin, and with the Arp2/3 complex. Despite their structural homology, the five classes of ADF-H domain proteins display distinct biochemical activities and cellular roles, only parts of which are currently understood. ADF/cofilin promotes disassembly of aged actin filaments, whereas twinfilin inhibits actin filament assembly via sequestering actin monomers and interacting with filament barbed ends. GMF does not interact with actin, but instead binds Arp2/3 complex and promotes dissociation of Arp2/3-mediated filament branches. Abp1 and drebrin are multidomain proteins that interact with actin filaments and regulate the activities of other proteins during various actin-dependent processes. The exact function of coactosin is currently incompletely understood. In this review article, we discuss the biochemical functions, cellular roles, and regulation of the five groups of ADF-H domain proteins.
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Affiliation(s)
- Minna Poukkula
- Program in Cell and Molecular Biology, Institute of Biotechnology, University of Helsinki, Finland
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5
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Entamoeba invadens: Identification of ADF/cofilin and their expression analysis in relation to encystation and excystation. Exp Parasitol 2011; 127:195-201. [DOI: 10.1016/j.exppara.2010.07.018] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2010] [Revised: 07/21/2010] [Accepted: 07/27/2010] [Indexed: 11/20/2022]
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6
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Zhao H, Hakala M, Lappalainen P. ADF/cofilin binds phosphoinositides in a multivalent manner to act as a PIP(2)-density sensor. Biophys J 2010; 98:2327-36. [PMID: 20483342 DOI: 10.1016/j.bpj.2010.01.046] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2009] [Revised: 01/21/2010] [Accepted: 01/22/2010] [Indexed: 11/27/2022] Open
Abstract
Actin-depolymerizing-factor (ADF)/cofilins have emerged as key regulators of cytoskeletal dynamics in cell motility, morphogenesis, endocytosis, and cytokinesis. The activities of ADF/cofilins are regulated by membrane phospholipid PI(4,5)P(2) in vitro and in cells, but the mechanism of the ADF/cofilin-PI(4,5)P(2) interaction has remained controversial. Recent studies suggested that ADF/cofilins interact with PI(4,5)P(2) through a specific binding pocket, and that this interaction is dependent on pH. Here, we combined systematic mutagenesis with biochemical and spectroscopic methods to elucidate the phosphoinositide-binding mechanism of ADF/cofilins. Our analysis revealed that cofilin does not harbor a specific PI(4,5)P(2)-binding pocket, but instead interacts with PI(4,5)P(2) through a large, positively charged surface of the molecule. Cofilin interacts simultaneously with multiple PI(4,5)P(2) headgroups in a cooperative manner. Consequently, interactions of cofilin with membranes and actin exhibit sharp sensitivity to PI(4,5)P(2) density. Finally, we show that cofilin binding to PI(4,5)P(2) is not sensitive to changes in the pH at physiological salt concentration, although the PI(4,5)P(2)-clustering activity of cofilin is moderately inhibited at elevated pH. Collectively, our data demonstrate that ADF/cofilins bind PI(4,5)P(2) headgroups through a multivalent, cooperative mechanism, and suggest that the actin filament disassembly activity of ADF/cofilin can be accurately regulated by small changes in the PI(4,5)P(2) density at cellular membranes.
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Affiliation(s)
- Hongxia Zhao
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
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7
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Brzeska H, Guag J, Remmert K, Chacko S, Korn ED. An experimentally based computer search identifies unstructured membrane-binding sites in proteins: application to class I myosins, PAKS, and CARMIL. J Biol Chem 2010; 285:5738-47. [PMID: 20018884 PMCID: PMC2820801 DOI: 10.1074/jbc.m109.066910] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2009] [Revised: 12/01/2009] [Indexed: 11/06/2022] Open
Abstract
Programs exist for searching protein sequences for potential membrane-penetrating segments (hydrophobic regions) and for lipid-binding sites with highly defined tertiary structures, such as PH, FERM, C2, ENTH, and other domains. However, a rapidly growing number of membrane-associated proteins (including cytoskeletal proteins, kinases, GTP-binding proteins, and their effectors) bind lipids through less structured regions. Here, we describe the development and testing of a simple computer search program that identifies unstructured potential membrane-binding sites. Initially, we found that both basic and hydrophobic amino acids, irrespective of sequence, contribute to the binding to acidic phospholipid vesicles of synthetic peptides that correspond to the putative membrane-binding domains of Acanthamoeba class I myosins. Based on these results, we modified a hydrophobicity scale giving Arg- and Lys-positive, rather than negative, values. Using this basic and hydrophobic scale with a standard search algorithm, we successfully identified previously determined unstructured membrane-binding sites in all 16 proteins tested. Importantly, basic and hydrophobic searches identified previously unknown potential membrane-binding sites in class I myosins, PAKs and CARMIL (capping protein, Arp2/3, myosin I linker; a membrane-associated cytoskeletal scaffold protein), and synthetic peptides and protein domains containing these newly identified sites bound to acidic phospholipids in vitro.
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Affiliation(s)
- Hanna Brzeska
- Laboratory of Cell Biology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA.
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8
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Saarikangas J, Zhao H, Lappalainen P. Regulation of the actin cytoskeleton-plasma membrane interplay by phosphoinositides. Physiol Rev 2010; 90:259-89. [PMID: 20086078 DOI: 10.1152/physrev.00036.2009] [Citation(s) in RCA: 362] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The plasma membrane and the underlying cortical actin cytoskeleton undergo continuous dynamic interplay that is responsible for many essential aspects of cell physiology. Polymerization of actin filaments against cellular membranes provides the force for a number of cellular processes such as migration, morphogenesis, and endocytosis. Plasma membrane phosphoinositides (especially phosphatidylinositol bis- and trisphosphates) play a central role in regulating the organization and dynamics of the actin cytoskeleton by acting as platforms for protein recruitment, by triggering signaling cascades, and by directly regulating the activities of actin-binding proteins. Furthermore, a number of actin-associated proteins, such as BAR domain proteins, are capable of directly deforming phosphoinositide-rich membranes to induce plasma membrane protrusions or invaginations. Recent studies have also provided evidence that the actin cytoskeleton-plasma membrane interactions are misregulated in a number of pathological conditions such as cancer and during pathogen invasion. Here, we summarize the wealth of knowledge on how the cortical actin cytoskeleton is regulated by phosphoinositides during various cell biological processes. We also discuss the mechanisms by which interplay between actin dynamics and certain membrane deforming proteins regulate the morphology of the plasma membrane.
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Affiliation(s)
- Juha Saarikangas
- Program in Cell and Molecular Biology, Institute of Biotechnology, University of Helsinki, Helsinki, Finland
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9
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Leyman S, Sidani M, Ritsma L, Waterschoot D, Eddy R, Dewitte D, Debeir O, Decaestecker C, Vandekerckhove J, van Rheenen J, Ampe C, Condeelis J, Van Troys M. Unbalancing the phosphatidylinositol-4,5-bisphosphate-cofilin interaction impairs cell steering. Mol Biol Cell 2009; 20:4509-23. [PMID: 19741095 DOI: 10.1091/mbc.e09-02-0121] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Cofilin is a key player in actin dynamics during cell migration. Its activity is regulated by (de)phosphorylation, pH, and binding to phosphatidylinositol-4,5-bisphosphate [PI(4,5)P(2)]. Here, we here use a human cofilin-1 (D122K) mutant with increased binding affinity for PI(4,5)P(2) and slower release from the plasma membrane to study the role of the PI(4,5)P(2)-cofilin interaction in migrating cells. In fibroblasts in a background of endogenous cofilin, D122K cofilin expression negatively affects cell turning frequency. In carcinoma cells with down-regulated endogenous cofilin, D122K cofilin neither rescues the drastic morphological defects nor restores the effects in cell turning capacity, unlike what has been reported for wild-type cofilin. In cofilin knockdown cells, D122K cofilin expression promotes outgrowth of an existing lamellipod in response to epidermal growth factor (EGF) but does not result in initiation of new lamellipodia. This indicates that, next to phospho- and pH regulation, the normal release kinetics of cofilin from PI(4,5)P(2) is crucial as a local activation switch for lamellipodia initiation and as a signal for migrating cells to change direction in response to external stimuli. Our results demonstrate that the PI(4,5)P(2) regulatory mechanism, that is governed by EGF-dependent phospholipase C activation, is a determinant for the spatial and temporal control of cofilin activation required for lamellipodia initiation.
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Affiliation(s)
- Shirley Leyman
- Department of Medical Protein Research, VIB, B-9000 Ghent, Belgium
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10
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Frantz C, Barreiro G, Dominguez L, Chen X, Eddy R, Condeelis J, Kelly MJS, Jacobson MP, Barber DL. Cofilin is a pH sensor for actin free barbed end formation: role of phosphoinositide binding. ACTA ACUST UNITED AC 2008; 183:865-79. [PMID: 19029335 PMCID: PMC2592832 DOI: 10.1083/jcb.200804161] [Citation(s) in RCA: 154] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Newly generated actin free barbed ends at the front of motile cells provide sites for actin filament assembly driving membrane protrusion. Growth factors induce a rapid biphasic increase in actin free barbed ends, and we found both phases absent in fibroblasts lacking H(+) efflux by the Na-H exchanger NHE1. The first phase is restored by expression of mutant cofilin-H133A but not unphosphorylated cofilin-S3A. Constant pH molecular dynamics simulations and nuclear magnetic resonance (NMR) reveal pH-sensitive structural changes in the cofilin C-terminal filamentous actin binding site dependent on His133. However, cofilin-H133A retains pH-sensitive changes in NMR spectra and severing activity in vitro, which suggests that it has a more complex behavior in cells. Cofilin activity is inhibited by phosphoinositide binding, and we found that phosphoinositide binding is pH-dependent for wild-type cofilin, with decreased binding at a higher pH. In contrast, phosphoinositide binding by cofilin-H133A is attenuated and pH insensitive. These data suggest a molecular mechanism whereby cofilin acts as a pH sensor to mediate a pH-dependent actin filament dynamics.
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Affiliation(s)
- Christian Frantz
- Department of Cell and Tissue Biology, University of California, San Francisco, CA 94143, USA
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11
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Van Troys M, Huyck L, Leyman S, Dhaese S, Vandekerkhove J, Ampe C. Ins and outs of ADF/cofilin activity and regulation. Eur J Cell Biol 2008; 87:649-67. [PMID: 18499298 DOI: 10.1016/j.ejcb.2008.04.001] [Citation(s) in RCA: 257] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2008] [Revised: 03/25/2008] [Accepted: 04/02/2008] [Indexed: 12/15/2022] Open
Abstract
The actin-binding proteins of the actin-depolymerisation factor (ADF)/cofilin family were first described more than three decades ago, but research on these proteins still occupies a front role in the actin and cell migration field. Moreover, cofilin activity is implicated in the malignant, invasive properties of cancer cells. The effects of ADF/cofilins on actin dynamics are diverse and their regulation is complex. In stimulated cells, multiple signalling pathways can be initiated resulting in different activation/deactivation switches that control ADF/cofilin activity. The output of this entire regulatory system, in combination with spatial and temporal segregation of the activation mechanisms, underlies the contribution of ADF/cofilins to various cell migration/invasion phenotypes. In this framework, we describe current views on how ADF/cofilins function in migrating and invading cells.
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12
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Ono S. Mechanism of depolymerization and severing of actin filaments and its significance in cytoskeletal dynamics. INTERNATIONAL REVIEW OF CYTOLOGY 2007; 258:1-82. [PMID: 17338919 DOI: 10.1016/s0074-7696(07)58001-0] [Citation(s) in RCA: 212] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The actin cytoskeleton is one of the major structural components of the cell. It often undergoes rapid reorganization and plays crucial roles in a number of dynamic cellular processes, including cell migration, cytokinesis, membrane trafficking, and morphogenesis. Actin monomers are polymerized into filaments under physiological conditions, but spontaneous depolymerization is too slow to maintain the fast actin filament dynamics observed in vivo. Gelsolin, actin-depolymerizing factor (ADF)/cofilin, and several other actin-severing/depolymerizing proteins can enhance disassembly of actin filaments and promote reorganization of the actin cytoskeleton. This review presents advances as well as a historical overview of studies on the biochemical activities and cellular functions of actin-severing/depolymerizing proteins.
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Affiliation(s)
- Shoichiro Ono
- Department of Pathology, Emory University, Atlanta, GA 30322, USA
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13
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Lambrechts A, Van Troys M, Ampe C. The actin cytoskeleton in normal and pathological cell motility. Int J Biochem Cell Biol 2005; 36:1890-909. [PMID: 15203104 DOI: 10.1016/j.biocel.2004.01.024] [Citation(s) in RCA: 170] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/22/2004] [Indexed: 11/20/2022]
Abstract
Cell motility is crucial for tissue formation and for development of organisms. Later on cell migration remains essential throughout the lifetime of the organism for wound healing and immune responses. The actin cytoskeleton is the cellular engine that drives cell motility downstream of a complex signal transduction cascade. The basic molecular machinery underlying the assembly and disassembly of actin filaments consists of a variety of actin binding proteins that regulate the dynamic behavior of the cytoskeleton in response to different signals. The multitude of proteins and regulatory mechanisms partaking in this system makes it vulnerable to mutations and alterations in expression levels that ultimately may cause diseases. The most familiar one is cancer that in later stages is characterized by active aberrant cell migration. Indeed tumor invasion and metastasis are increasingly being associated with deregulation of the actin system.
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Affiliation(s)
- Anja Lambrechts
- Department of Biochemistry, Faculty of Medicine and Health Sciences, Flanders Interuniversity Institute for Biotechnology (VIB), Ghent University, A. Baertsoenkaai 3, B-9000 Gent, Belgium.
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14
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Bongalon S, Dai YP, Singer CA, Yamboliev IA. PDGF and IL-1β Upregulate Cofilin and LIMK2 in Canine Cultured Pulmonary Artery Smooth Muscle Cells. J Vasc Res 2004; 41:412-21. [PMID: 15467300 DOI: 10.1159/000081247] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2004] [Accepted: 07/27/2004] [Indexed: 01/02/2023] Open
Abstract
Actin cytoskeleton reorganization is regulated by various actin-binding proteins. Cofilin is the principal filament-depolymerizing protein, whose activity is reduced upon phosphorylation by LIMK. Thus, LIMK and cofilin comprise a signal transduction module regulating actin turnover and myogenic tone in healthy vasculature. Novel functions of smooth muscle cells (SMCs) in the hypertensive pulmonary artery, such as increased motility and proliferation, are supported by the actin cytoskeleton. We therefore hypothesized that bioactive peptides that affect these SMC functions may also result in an upregulation of LIMK and cofilin expression. Semiquantitative RT-PCR and immunoblotting indicated that LIMK2 and cofilin mRNA and protein expression is upregulated in canine pulmonary artery SMCs (PASMCs) exposed to PDGF or IL-1beta (10 ng/ml). Inhibition of ERK MAPKs (U-0126, 10 muM) or p38 MAPK (PD-169316, 10 muM), but not PI3Ks (LY-294002, 50 muM), reduced LIMK2 and cofilin gene expression stimulated by PDGF or IL-1beta. Inhibition of ROCK (Y-27632, 10 muM) reduced only the IL-1beta-stimulated LIMK2 and cofilin expression. These novel observations in PASMCs indicate that LIMK2 and cofilin expression can be induced by PDGF or IL-1beta. This parallel upregulation of LIMK2 and cofilin may have potentially broad functional significance for the progress of pulmonary artery disease.
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Affiliation(s)
- Shaner Bongalon
- Department of Pharmacology, Center of Biomedical Research Excellence, University of Nevada School of Medicine, Reno, NV 89557, USA
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15
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Hilpelä P, Vartiainen MK, Lappalainen P. Regulation of the Actin Cytoskeleton by PI(4,5)P2 and PI(3,4,5)P3. Curr Top Microbiol Immunol 2004; 282:117-63. [PMID: 14594216 DOI: 10.1007/978-3-642-18805-3_5] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The actin cytoskeleton is fundamental for various motile and morphogenetic processes in cells. The structure and dynamics of the actin cytoskeleton are regulated by a wide array of actin-binding proteins, whose activities are controlled by various signal transduction pathways. Recent studies have shown that certain membrane phospholipids, especially PI(4,5)P2 and PI(3,4,5)P3, regulate actin filament assembly in cells and in cell extracts. PI(4,5)P2 appears to be a general regulator of actin polymerization at the plasma membrane or at membrane microdomains, whereas PI(3,4,5)P3 promotes the assembly of specialized actin filament structures in response to some growth factors. Biochemical studies have demonstrated that the activities of many proteins promoting actin assembly are upregulated by PI(4,5)P2, whereas proteins that inhibit actin assembly or promote filament disassembly are down-regulated by PI(4,5)P2. PI(3,4,5)P3 promotes its effects on the actin cytoskeleton mainly through activation of the Rho family of small GTPases. In addition to their effects on actin dynamics, both PI(4,5)P2 and PI(3,4,5)P3 promote the formation of specific actin filament structures through activation/inactivation of actin filament cross-linking proteins and proteins that mediate cytoskeleton-plasma membrane interactions.
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Affiliation(s)
- P Hilpelä
- Program in Cellular Biotechnology, Institute of Biotechnology, University of Helsinki, P.O. Box 56, 00014 Helsinki, Finland
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16
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Kumar N, Zhao P, Tomar A, Galea CA, Khurana S. Association of villin with phosphatidylinositol 4,5-bisphosphate regulates the actin cytoskeleton. J Biol Chem 2003; 279:3096-110. [PMID: 14594952 DOI: 10.1074/jbc.m308878200] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Villin, an epithelial cell actin-binding protein, severs actin in vitro and in vivo. Previous studies report that phosphatidylinositol 4,5-bisphosphate (PIP(2)) regulates actin severing by villin, presumably by interaction with villin. However, direct association of villin with PIP(2) has never been characterized. In this report, we presented mutational analysis to identify the PIP(2)-binding sites in villin. Villin (human) binds PIP(2) with a K(d) of 39.5 microm, a stoichiometry of 3.3, and a Hill coefficient of 1. We generated deletion mutants of villin lacking putative PIP(2)-binding sites and examined the impact of these mutations on PIP(2) binding and actin dynamics. Our analysis revealed the presence of three PIP(2)-binding sites, two in the amino-terminal core and one in the carboxyl-terminal headpiece of human villin. Synthetic peptides analogous with these sites confirmed the binding domains. Circular dichroism and quenching of intrinsic tryptophan fluorescence revealed a significant conformational change in these peptides ensuing in their association with PIP(2). By using site-directed mutagenesis (arginine 138 to alanine), we demonstrated the presence of an identical F-actin and PIP(2)-binding site in the capping and severing domain of villin. In contrast, the mutants lysine 822 and 824 to alanine demonstrated the presence of an overlapping F-actin and PIP(2)-binding site in the actin cross-linking domain of villin. Consistent with this observation, association of villin with PIP(2) inhibited the actin capping and severing functions of villin and enhanced the actin bundling function of villin. Our studies revealed that structural changes induced by association with PIP(2) could regulate the actin-modifying functions of villin. This study provided biochemical proof of the functional significance of villin association with PIP(2) and identified the molecular mechanisms involved in the regulation of actin dynamics by villin and PIP(2).
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Affiliation(s)
- Narendra Kumar
- Department of Physiology, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
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17
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Mohri K, Ono S. Actin filament disassembling activity of Caenorhabditis elegans actin-interacting protein 1 (UNC-78) is dependent on filament binding by a specific ADF/cofilin isoform. J Cell Sci 2003; 116:4107-18. [PMID: 12953066 DOI: 10.1242/jcs.00717] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Actin-interacting protein 1 (AIP1) is a conserved WD-repeat protein that enhances actin filament disassembly only in the presence of actin depolymerizing factor (ADF)/cofilin. In the nematode Caenorhabditis elegans, an AIP1 ortholog is encoded by the unc-78 gene that is required for organized assembly of muscle actin filaments. We produced bacterially expressed UNC-78 protein and found that it enhances actin filament disassembly preferentially in the presence of a specific ADF/cofilin isoform. Extensive and rapid filament disassembly by UNC-78 was observed in the presence of UNC-60B, a muscle-specific C. elegans ADF/cofilin isoform. UNC-78 also reduced the rate of spontaneous polymerization and enhanced subunit dissociation from filaments in the presence of UNC-60B. However, in the presence of UNC-60A, a non-muscle C. elegans ADF/cofilin isoform, UNC-78 only slightly enhanced filament disassembly. Interestingly, UNC-78 failed to enhance disassembly by mouse muscle-type cofilin. Using mutant forms of UNC-60B, we demonstrated that the F-actin-specific binding site of UNC-60B at the C terminus is required for filament disassembly by UNC-78. UNC-78 was expressed in body wall muscle and co-localized with actin where UNC-60B was also present. Surprisingly, UNC-78 was co-localized with actin in unc-60B null mutants, suggesting that the AIP1-actin interaction is not dependent on ADF/cofilin in muscle. These results suggest that UNC-78 closely collaborates with UNC-60B to regulate actin dynamics in muscle cells.
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Affiliation(s)
- Kurato Mohri
- Department of Pathology, Emory University, Atlanta, GA 30322, USA
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18
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Abstract
Phosphoinositides [PPIs, which collectively refer to phosphorylated derivatives of phosphatidylinositol (PI)] have a pivotal role as precursors to important second messengers and as bona fide signaling and scaffold targeting molecules. This review focuses on recent advances that elucidate how PPIs, particularly PI(4,5)P2 (PIP2), directly regulate the actin cytoskeleton in vivo by modulating the activity and targeting of actin regulatory proteins. The role of PIP2 in stimulating actin polymerization and in establishing cytoskeleton-plasma membrane linkages is emphasized. In addition, the review presents tantalizing evidence that suggests how binding of selected cytoskeletal proteins to membrane PPIs may promote PPI clustering into raft lipid microdomains, alter their accessibility to other proteins, and even distort the bilayer conformation. These actions have profound implications for many other PPI-regulated membrane functions that are beginning to be uncovered, and they suggest how PPIs can mediate crosstalk between the actin cytoskeleton and an expanding spectrum of essential cellular functions.
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Affiliation(s)
- Helen L Yin
- Department of Physiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390, USA.
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19
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Choe H, Burtnick LD, Mejillano M, Yin HL, Robinson RC, Choe S. The calcium activation of gelsolin: insights from the 3A structure of the G4-G6/actin complex. J Mol Biol 2002; 324:691-702. [PMID: 12460571 DOI: 10.1016/s0022-2836(02)01131-2] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Gelsolin participates in the reorganization of the actin cytoskeleton that is required during such phenomena as cell movement, cytokinesis, and apoptosis. It consists of six structurally similar domains, G1-G6, which are arranged at resting intracellular levels of calcium ion so as to obscure the three actin-binding surfaces. Elevation of Ca(2+) concentrations releases latches within the constrained structure and produces large shifts in the relative positioning of the domains, permitting gelsolin to bind to and sever actin filaments. How Ca(2+) is able to activate gelsolin has been a major question concerning the function of this protein. We present the improved structure of the C-terminal half of gelsolin bound to monomeric actin at 3.0 A resolution. Two classes of Ca(2+)-binding site are evident on gelsolin: type 1 sites share coordination of Ca(2+) with actin, while type 2 sites are wholly contained within gelsolin. This structure of the complex reveals the locations of two novel metal ion-binding sites in domains G5 and G6, respectively. We identify both as type 2 sites. The absolute conservation of the type 2 calcium-ligating residues across the six domains of gelsolin suggests that this site exists in each of the domains. In total, gelsolin has the potential to bind eight calcium ions, two type 1 and six type 2. The function of the type 2 sites is to facilitate structural rearrangements within gelsolin as part of the activation and actin-binding and severing processes. We propose the novel type 2 site in G6 to be the critical site that initiates overall activation of gelsolin by releasing the tail latch that locks calcium-free gelsolin in a conformation unable to bind actin.
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Affiliation(s)
- Han Choe
- Structural Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92186-5800, USA
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20
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Paavilainen VO, Merckel MC, Falck S, Ojala PJ, Pohl E, Wilmanns M, Lappalainen P. Structural conservation between the actin monomer-binding sites of twinfilin and actin-depolymerizing factor (ADF)/cofilin. J Biol Chem 2002; 277:43089-95. [PMID: 12207032 DOI: 10.1074/jbc.m208225200] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Twinfilin is an evolutionarily conserved actin monomer-binding protein that regulates cytoskeletal dynamics in organisms from yeast to mammals. It is composed of two actin-depolymerization factor homology (ADF-H) domains that show approximately 20% sequence identity to ADF/cofilin proteins. In contrast to ADF/cofilins, which bind both G-actin and F-actin and promote filament depolymerization, twinfilin interacts only with G-actin. To elucidate the molecular mechanisms of twinfilin-actin monomer interaction, we determined the crystal structure of the N-terminal ADF-H domain of twinfilin and mapped its actin-binding site by site-directed mutagenesis. This domain has similar overall structure to ADF/cofilins, and the regions important for actin monomer binding in ADF/cofilins are especially well conserved in twinfilin. Mutagenesis studies show that the N-terminal ADF-H domain of twinfilin and ADF/cofilins also interact with actin monomers through similar interfaces, although the binding surface is slightly extended in twinfilin. In contrast, the regions important for actin-filament interactions in ADF/cofilins are structurally different in twinfilin. This explains the differences in actin-interactions (monomer versus filament binding) between twinfilin and ADF/cofilins. Taken together, our data show that the ADF-H domain is a structurally conserved actin-binding motif and that relatively small structural differences at the actin interfaces of this domain are responsible for the functional variation between the different classes of ADF-H domain proteins.
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Affiliation(s)
- Ville O Paavilainen
- Program in Cellular Biotechnology, Institute of Biotechnology, P.O. Box 56, University of Helsinki, 00014 Helsinki, Finland
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21
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Lambrechts A, Jonckheere V, Dewitte D, Vandekerckhove J, Ampe C. Mutational analysis of human profilin I reveals a second PI(4,5)-P2 binding site neighbouring the poly(L-proline) binding site. BMC BIOCHEMISTRY 2002; 3:12. [PMID: 12052260 PMCID: PMC116585 DOI: 10.1186/1471-2091-3-12] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/13/2002] [Accepted: 05/28/2002] [Indexed: 11/10/2022]
Abstract
BACKGROUND Profilin is a small cytoskeletal protein which interacts with actin, proline-rich proteins and phosphatidylinositol 4,5-bisphosphate (PI(4,5)-P2). Crystallography, NMR and mutagenesis of vertebrate profilins have revealed the amino acid residues that are responsible for the interactions with actin and poly(L-proline) peptides. Although Arg88 of human profilin I was shown to be involved in PI(4,5)-P2-binding, it was suggested that carboxy terminal basic residues may be involved as well. RESULTS Using site directed mutagenesis we have refined the PI(4,5)-P2 binding site of human profilin I. For each mutant we assessed the stability and studied the interactions with actin, a proline-rich peptide and PI(4,5)-P2 micelles. We identified at least two PI(4,5)-P2-binding regions in human profilin I. As expected, one region comprises Arg88 and overlaps with the actin binding site. The second region involves Arg136 in the carboxy terminal helix and neighbours the poly(L-proline) binding site. In addition, we show that adding a small protein tag to the carboxy terminus of profilin strongly reduces binding to poly(L-proline), suggesting local conformational changes of the carboxy terminal alpha-helix may have dramatic effects on ligand binding. CONCLUSIONS The involvement of the two terminal alpha-helices of profilin in ligand binding imposes important structural constraints upon the functions of this region. Our data suggest a model in which the competitive interactions between PI(4,5)-P2 and actin and PI(4,5)-P2 and poly(L-proline) regulate profilin functions.
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Affiliation(s)
- Anja Lambrechts
- Department of Medical Protein Research (VIB09), Flanders Interuniversity Institute of Biotechnology and Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium
| | - Veronique Jonckheere
- Department of Medical Protein Research (VIB09), Flanders Interuniversity Institute of Biotechnology and Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium
| | - Daisy Dewitte
- Department of Medical Protein Research (VIB09), Flanders Interuniversity Institute of Biotechnology and Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium
| | - Joel Vandekerckhove
- Department of Medical Protein Research (VIB09), Flanders Interuniversity Institute of Biotechnology and Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium
| | - Christophe Ampe
- Department of Medical Protein Research (VIB09), Flanders Interuniversity Institute of Biotechnology and Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium
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22
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Abstract
Tropomyosin binds to actin filaments and is implicated in stabilization of actin cytoskeleton. We examined biochemical and cell biological properties of Caenorhabditis elegans tropomyosin (CeTM) and obtained evidence that CeTM is antagonistic to ADF/cofilin-dependent actin filament dynamics. We purified CeTM, actin, and UNC-60B (a muscle-specific ADF/cofilin isoform), all of which are derived from C. elegans, and showed that CeTM and UNC-60B bound to F-actin in a mutually exclusive manner. CeTM inhibited UNC-60B-induced actin depolymerization and enhancement of actin polymerization. Within isolated native thin filaments, actin and CeTM were detected as major components, whereas UNC-60B was present at a trace amount. Purified UNC-60B was unable to interact with the native thin filaments unless CeTM and other associated proteins were removed by high-salt extraction. Purified CeTM was sufficient to restore the resistance of the salt-extracted filaments from UNC-60B. In muscle cells, CeTM and UNC-60B were localized in different patterns. Suppression of CeTM by RNA interference resulted in disorganized actin filaments and paralyzed worms in wild-type background. However, in an ADF/cofilin mutant background, suppression of CeTM did not worsen actin organization and worm motility. These results suggest that tropomyosin is a physiological inhibitor of ADF/cofilin-dependent actin dynamics.
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Affiliation(s)
- Shoichiro Ono
- Department of Pathology, Emory University, Atlanta, Georgia 30322, USA.
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23
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Abstract
The ADF/cofilins are a family of actin-binding proteins expressed in all eukaryotic cells so far examined. Members of this family remodel the actin cytoskeleton, for example during cytokinesis, when the actin-rich contractile ring shrinks as it contracts through the interaction of ADF/cofilins with both monomeric and filamentous actin. The depolymerizing activity is twofold: ADF/cofilins sever actin filaments and also increase the rate at which monomers leave the filament's pointed end. The three-dimensional structure of ADF/cofilins is similar to a fold in members of the gelsolin family of actin-binding proteins in which this fold is typically repeated three or six times; although both families bind polyphosphoinositide lipids and actin in a pH-dependent manner, they share no obvious sequence similarity. Plants and animals have multiple ADF/cofilin genes, belonging in vertebrates to two types, ADF and cofilins. Other eukaryotes (such as yeast, Acanthamoeba and slime moulds) have a single ADF/cofilin gene. Phylogenetic analysis of the ADF/cofilins reveals that, with few exceptions, their relationships reflect conventional views of the relationships between the major groups of organisms.
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Affiliation(s)
- Sutherland K Maciver
- Genes and Development Interdisciplinary Group, Department of Biomedical Sciences, University of Edinburgh, George Square, Edinburgh EH8 9XD, Scotland, UK.
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24
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Vartiainen MK, Mustonen T, Mattila PK, Ojala PJ, Thesleff I, Partanen J, Lappalainen P. The three mouse actin-depolymerizing factor/cofilins evolved to fulfill cell-type-specific requirements for actin dynamics. Mol Biol Cell 2002; 13:183-94. [PMID: 11809832 PMCID: PMC65081 DOI: 10.1091/mbc.01-07-0331] [Citation(s) in RCA: 184] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Actin-depolymerizing factor (ADF)/cofilins are essential regulators of actin filament turnover. Several ADF/cofilin isoforms are found in multicellular organisms, but their biological differences have remained unclear. Herein, we show that three ADF/cofilins exist in mouse and most likely in all other mammalian species. Northern blot and in situ hybridization analyses demonstrate that cofilin-1 is expressed in most cell types of embryos and adult mice. Cofilin-2 is expressed in muscle cells and ADF is restricted to epithelia and endothelia. Although the three mouse ADF/cofilins do not show actin isoform specificity, they all depolymerize platelet actin filaments more efficiently than muscle actin. Furthermore, these ADF/cofilins are biochemically different. The epithelial-specific ADF is the most efficient in turning over actin filaments and promotes a stronger pH-dependent actin filament disassembly than the two other isoforms. The muscle-specific cofilin-2 has a weaker actin filament depolymerization activity and displays a 5-10-fold higher affinity for ATP-actin monomers than cofilin-1 and ADF. In steady-state assays, cofilin-2 also promotes filament assembly rather than disassembly. Taken together, these data suggest that the three biochemically distinct mammalian ADF/cofilin isoforms evolved to fulfill specific requirements for actin filament dynamics in different cell types.
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Affiliation(s)
- Maria K Vartiainen
- Programs in Cellular Biotechnology, Institute of Biotechnology, Viikki Biocenter, University of Helsinki, Helsinki, 00014 Finland
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25
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Pfannstiel J, Cyrklaff M, Habermann A, Stoeva S, Griffiths G, Shoeman R, Faulstich H. Human cofilin forms oligomers exhibiting actin bundling activity. J Biol Chem 2001; 276:49476-84. [PMID: 11679578 DOI: 10.1074/jbc.m104760200] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human cofilin possesses the tendency for self-association, as indicated by the rapid formation of dimers and oligomers when reacted with water-soluble carbodiimide, Ellman's reagent, or glutathione disulfide. Intermolecular disulfide bonds involve Cys(39) and probably Cys(147) of two adjacent cofilin units. The disulfide-linked dimers and oligomers exhibit a biological activity distinct from the monomer. While monomeric cofilin decreased viscosity and light-scattering of F-actin solutions, dimers and oligomers caused an increase in viscosity and light scattering. Electron microscopy revealed that cofilin oligomers induce the formation of highly ordered actin bundles with occasionally blunt ends similar to actin-cofilin rods observed in cells under oxidative stress. Bundling activity of the disulfide-linked oligomers could be completely reversed into severing activity by dithiothreitol. Formation of cofilin oligomers occurred also in the presence of actin at pH 8, but not at pH 6.6, and was significantly enhanced in the presence of phosphatidylinositol 4,5-bisphosphate. Our data are consistent with the idea that cofilin exists in two forms in vivo also: as monomers exhibiting the known severing activity and as oligomers exhibiting actin bundling activity. However, stabilization of cofilin oligomers in cytoplasm is probably achieved not by disulfide bonds but by a local increase in cofilin concentration and/or binding of regulatory proteins.
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Affiliation(s)
- J Pfannstiel
- Max-Planck-Institute for Medical Research, Heidelberg 69120, Germany.
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26
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Blondin L, Sapountzi V, Maciver SK, Renoult C, Benyamin Y, Roustan C. The second ADF/cofilin actin-binding site exists in F-actin, the cofilin-G-actin complex, but not in G-actin. EUROPEAN JOURNAL OF BIOCHEMISTRY 2001; 268:6426-34. [PMID: 11737197 DOI: 10.1046/j.0014-2956.2001.02592.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
ADF/cofilins are actin binding proteins that bind actin close to both the N- and C-termini (site 1), and we have found a second cofilin binding site (site 2) centered around helix 112-125 [Renoult, C., Ternent, D., Maciver, S.K., Fattoum, A., Astier, C., Benyamin, Y. & Roustan, C. (1999) J. Biol. Chem. 274, 28893-28899]. We proposed a model in which ADF/cofilin intercalated between subdomains 1 and 2 of two longitudinally associated actin monomers within the actin:cofilin cofilament, explaining the change in twist that ADF/cofilins induce in the filament [McGough, A. Pope, B., Chiu, W. & Weeds, A. (1998) J. Cell Biol. 138, 771-781]. Here, we have determined the fuller extent of the cofilin footprint on site 1 of actin. Site 1 is primarily the G-actin binding site. Experiments with both peptide mimetics and fluorescently labeled cofilin suggest that site 2 only becomes available for cofilin binding within the filament, possibly due to motion between subdomains 1 and 2 within an actin monomer. We have detected motion between subdomains 1 and 2 of G-actin by FRET induced by cofilin, to reveal the second cofilin-binding site. This motion may also explain how cofilins inhibit the nucleotide exchange of actin, and why the actin:cofilin complex is polymerizable without dissociation.
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Affiliation(s)
- L Blondin
- UMR 5539 (CNRS) Laboratoire de motilité cellulaire (Ecole Pratiques des Hautes Etudes), Université de Montpellier 2, France
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27
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Ching TT, Lin HP, Yang CC, Oliveira M, Lu PJ, Chen CS. Specific binding of the C-terminal Src homology 2 domain of the p85alpha subunit of phosphoinositide 3-kinase to phosphatidylinositol 3,4,5-trisphosphate. Localization and engineering of the phosphoinositide-binding motif. J Biol Chem 2001; 276:43932-8. [PMID: 11555646 DOI: 10.1074/jbc.m105159200] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphoinositide second messengers, generated from the action of phosphoinositide 3-kinase (PI3K), mediate an array of signaling pathways through the membrane recruitment and activation of downstream effector proteins. Although pleckstrin domains of many target proteins have been shown to bind phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) and/or phosphatidylinositol 3,4-bisphosphate (PI(3,4)P(2)) with high affinity, published data concerning the phosphoinositide binding specificity of Src homology 2 (SH2) domains remain conflicting. Using three independent assays, we demonstrated that the C-terminal (CT-)SH2 domain, but not the N-terminal SH2 domain, on the PI3K p85alpha subunit displayed discriminative affinity for PIP(3). However, the binding affinity diminished precipitously when the acyl chain of PIP(3) was shortened. In addition, evidence suggests that the charge density on the phosphoinositol ring represents a key factor in determining the phosphoinositide binding specificity of the CT-SH2 domain. In light of the largely shared structural features between PIP(3) and PI(4,5)P(2), we hypothesized that the PIP(3)-binding site on the CT-SH2 domain encompassed a sequence that recognized PI(4,5)P(2). Based on a consensus PI(4,5)P(2)-binding sequence (KXXXXXKXKK; K denotes Arg, Lys, and His), we proposed the sequence (18)RNKAENLLRGKR(29) as the PIP(3)-binding site. This binding motif was verified by using a synthetic peptide and site-directed mutagenesis. More importantly, neutral substitution of flanking Arg(18) and Arg(29) resulted in a switch of ligand specificity of the CT-SH2 domain to PI(4,5)P(2) and PI(3,4)P(2), respectively. Together with computer modeling, these mutagenesis data suggest a pseudosymmetrical relationship in the recognition of the phosphoinositol head group at the binding motif.
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Affiliation(s)
- T T Ching
- Division of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, Kentucky 40536, USA
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28
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Abstract
Several cytoskeletal proteins have been shown to interact in vitro with, and in some cases are regulated by, specific membrane lipids. In some cases, evidence for in situ interactions has been provided. The molecular basis for such interactions is now being unravelled. At least five structurally distinct types of lipid-binding sites in cytoskeletal proteins have been identified. However, our understanding of the physiological role of such interactions is still limited. Precise knowledge about the binding-site structures and the actual amino acid residues involved should now enable the expression of mutant proteins that specifically lack the ability to interact with lipids. The impact of these mutations on protein location and function can then be assessed.
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Affiliation(s)
- V Niggli
- Dept of Pathology, University of Bern, Murtenstrasse 31, CH-3010 Bern, Switzerland.
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