1
|
Structural analysis of receptors and actin polarity in platelet protrusions. Proc Natl Acad Sci U S A 2021; 118:2105004118. [PMID: 34504018 PMCID: PMC8449362 DOI: 10.1073/pnas.2105004118] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/04/2021] [Indexed: 11/18/2022] Open
Abstract
During activation the platelet cytoskeleton is reorganized, inducing adhesion to the extracellular matrix and cell spreading. These processes are critical for wound healing and clot formation. Initially, this task relies on the formation of strong cellular-extracellular matrix interactions, exposed in subendothelial lesions. Despite the medical relevance of these processes, there is a lack of high-resolution structural information on the platelet cytoskeleton controlling cell spreading and adhesion. Here, we present in situ structural analysis of membrane receptors and the underlying cytoskeleton in platelet protrusions by applying cryoelectron tomography to intact platelets. We utilized three-dimensional averaging procedures to study receptors at the plasma membrane. Analysis of substrate interaction-free receptors yielded one main structural class resolved to 26 Å, resembling the αIIbβ3 integrin folded conformation. Furthermore, structural analysis of the actin network in pseudopodia indicates a nonuniform polarity of filaments. This organization would allow generation of the contractile forces required for integrin-mediated cell adhesion.
Collapse
|
2
|
|
3
|
Thinn AMM, Wang Z, Zhu J. The membrane-distal regions of integrin α cytoplasmic domains contribute differently to integrin inside-out activation. Sci Rep 2018; 8:5067. [PMID: 29568062 PMCID: PMC5864728 DOI: 10.1038/s41598-018-23444-w] [Citation(s) in RCA: 7] [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: 11/21/2017] [Accepted: 03/13/2018] [Indexed: 12/20/2022] Open
Abstract
Functioning as signal receivers and transmitters, the integrin α/β cytoplasmic tails (CT) are pivotal in integrin activation and signaling. 18 α integrin subunits share a conserved membrane-proximal region but have a highly diverse membrane-distal (MD) region at their CTs. Recent studies demonstrated that the presence of α CTMD region is essential for talin-induced integrin inside-out activation. However, it remains unknown whether the non-conserved α CTMD regions differently regulate the inside-out activation of integrin. Using αIIbβ3, αLβ2, and α5β1 as model integrins and by replacing their α CTMD regions with those of α subunits that pair with β3, β2, and β1 subunits, we analyzed the function of CTMD regions of 17 α subunits in talin-mediated integrin activation. We found that the α CTMD regions play two roles on integrin, which are activation-supportive and activation-regulatory. The regulatory but not the supportive function depends on the sequence identity of α CTMD region. A membrane-proximal tyrosine residue present in the CTMD regions of a subset of α integrins was identified to negatively regulate integrin inside-out activation. Our study provides a useful resource for investigating the function of α integrin CTMD regions.
Collapse
Affiliation(s)
- Aye Myat Myat Thinn
- Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI, 53226, USA
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Zhengli Wang
- Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI, 53226, USA
| | - Jieqing Zhu
- Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI, 53226, USA.
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI, 53226, USA.
| |
Collapse
|
4
|
Liu J, Wang Z, Thinn AMM, Ma YQ, Zhu J. The dual structural roles of the membrane distal region of the α-integrin cytoplasmic tail during integrin inside-out activation. J Cell Sci 2015; 128:1718-31. [PMID: 25749862 DOI: 10.1242/jcs.160663] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Accepted: 03/02/2015] [Indexed: 12/22/2022] Open
Abstract
Studies on the mechanism of integrin inside-out activation have been focused on the role of β-integrin cytoplasmic tails, which are relatively conserved and bear binding sites for the intracellular activators including talin and kindlin. Cytoplasmic tails for α-integrins share a conserved GFFKR motif at the membrane-proximal region and this forms a specific interface with the β-integrin membrane-proximal region to keep the integrin inactive. The α-integrin membrane-distal regions, after the GFFKR motif, are diverse both in length and sequence and their roles in integrin activation have not been well-defined. In this study, we report that the α-integrin cytoplasmic membrane-distal region contributes to maintaining integrin in the resting state and to integrin inside-out activation. Complete deletion of the α-integrin membrane-distal region diminished talin- and kindlin-mediated integrin ligand binding and conformational change. A proper length and suitable amino acids in α-integrin membrane-distal region was found to be important for integrin inside-out activation. Our data establish an essential role for the α-integrin cytoplasmic membrane-distal region in integrin activation and provide new insights into how talin and kindlin induce the high-affinity integrin conformation that is required for fully functional integrins.
Collapse
Affiliation(s)
- Jiafu Liu
- Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI 53226, USA
| | - Zhengli Wang
- Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI 53226, USA College of Marine Science and Engineering, Qingdao Agricultural University, Qingdao 266109, China
| | - Aye Myat Myat Thinn
- Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI 53226, USA Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Yan-Qing Ma
- Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI 53226, USA Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Jieqing Zhu
- Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI 53226, USA Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| |
Collapse
|
5
|
Koloka V, Christofidou ED, Vaxevanelis S, Dimitriou AA, Tsikaris V, Tselepis AD, Panou-Pomonis E, Sakarellos-Daitsiotis M, Tsoukatos DC. A palmitoylated peptide, derived from the acidic carboxyl-terminal segment of the integrin alphaIIb cytoplasmic domain, inhibits platelet activation. Platelets 2009; 19:502-11. [PMID: 18979362 DOI: 10.1080/09537100802266875] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Platelet integrin alpha(IIb)beta(3) contains an acidic membrane distal motif, 1000LEEDDEEGE1008, in the cytoplasmic domain of the alpha(IIb) subunit. We showed that a lipid-modified peptide corresponding to the above region, palmitoyl-K-LEEDDEEGE (pal-K-1000-1008), is platelet permeable and has inhibited platelet aggregation induced by 0.4 U/ml of thrombin (IC50 = 164 microM). Moreover the peptide inhibited both Fibrinogen and PAC-1, binding to activated platelets. The non palmitoylated analog was inactive. A modified, scrambled acidic peptide (palmitoyl-K-GDDEELEEE), showed significant lower inhibitory activity than pal-K-1000-1008. A palmitoylated peptide corresponding to the membrane proximal cytoplasmic domain of alpha(IIb), 989KGVFFKR995 (pal-989-995), is known to specifically induce platelet aggregation. Pal-K-1000-1008 was an inhibitor of human washed platelet aggregation induced by pal-K-989-995 (IC50 = 15 microM). Moreover, pal-K-1000-1008 inhibited phosphorylation of ERK and FAK, two protein kinases involved in platelet activation and aggregation. Our results favour the assumption that the interaction of the membrane proximal sequence 989KGVFFKR995 of the cytoplasmic domain of alpha(IIb) with the acidic terminal 1000LEEDDEEGE1008 motif may be an important structural factor in platelet signaling, leading to platelet activation and aggregation.
Collapse
Affiliation(s)
- Vassiliki Koloka
- Sector of Organic Chemistry and Biochemistry, Department of Chemistry, University of Ioannina, Ioannina 45110, Greece
| | | | | | | | | | | | | | | | | |
Collapse
|
6
|
Group IVA cytosolic phospholipase A2 (cPLA2alpha) and integrin alphaIIbbeta3 reinforce each other's functions during alphaIIbbeta3 signaling in platelets. Blood 2008; 113:447-57. [PMID: 18840708 DOI: 10.1182/blood-2008-06-162032] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Group IVA cytosolic phospholipase A(2) (cPLA(2)alpha) catalyzes release of arachidonic acid from glycerophospholipids, leading to thromboxane A(2) (TxA(2)) production. Some platelet agonists stimulate cPLA(2)alpha, but others require fibrinogen binding to alphaIIbbeta3 to elicit TxA(2). Therefore, relationships between cPLA(2)alpha and alphaIIbbeta3 were examined. cPLA(2)alpha and a cPLA(2)alpha binding partner, vimentin, coimmunoprecipitated with alphaIIbbeta3 from platelets, independent of fibrinogen binding. Studies with purified proteins and with recombinant proteins expressed in CHO cells determined that the interaction between cPLA(2)alpha and alphaIIbbeta3 was indirect and was dependent on the alphaIIb and beta3 cytoplasmic tails. Fibrinogen binding to alphaIIbbeta3 caused an increase in integrin-associated cPLA(2)alpha activity in normal platelets, but not in cPLA(2)alpha-deficient mouse platelets or in human platelets treated with pyrrophenone, a cPLA(2)alpha inhibitor. cPLA(2)alpha activation downstream of alphaIIbbeta3 had functional consequences for platelets in that it was required for fibrinogen-dependent recruitment of activated protein kinase Cbeta to the alphaIIbbeta3 complex and for platelet spreading. Thus, cPLA(2)alpha and alphaIIbbeta3 interact to reinforce each other's functions during alphaIIbbeta3 signaling. This provides a plausible explanation for the role of alphaIIbbeta3 in TxA(2) formation and in the defective hemostatic function of mouse or human platelets deficient in cPLA(2)alpha.
Collapse
|
7
|
Haas TA, Taherian A, Berry T, Ma X. Identification of residues of functional importance within the central turn motifs present in the cytoplasmic tails of integrin alphaIIb and alphaV subunits. Thromb Res 2008; 122:507-16. [PMID: 18328539 DOI: 10.1016/j.thromres.2008.01.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Revised: 12/17/2007] [Accepted: 01/15/2008] [Indexed: 12/24/2022]
Abstract
INTRODUCTION Previous studies demonstrated that cell-permeable alphaIIb cytoplasmic peptides can modulate the activation of alphaIIbbeta3. An integrin activation motif was mapped to its membrane proximal region and a double proline mutant peptide and receptor indicated that its central turn motif had inhibitory capacity. However, the residues critical for inhibition of alphaIIbbeta3 activation were not identified. Using central turn peptides derived from alphaIIb and alphaV, residues critical for suppression of integrin activation were identified and the importance of these residues in protein-protein interactions was assessed. MATERIALS AND METHODS Cell-permeable peptides were used to determine the capacity of the central turn peptides to suppress alphaIIbbeta3 and alphaVbeta3 activation. Far Western analysis was used to characterize the capacity of the peptides to interact with CIB1 and surface plasmon resonance was used to characterize the binding of an antibody to the cytoplasmic tails of alphaIIb and alphaV. RESULTS AND CONCLUSIONS The central turn peptide from alphaV, alphaV(993-1001), has full inhibitory capacity while that derived from alphaIIb requires additional residues located adjacent to alphaIIb(995-1003). Within these two sequences there is a switch in the position of an asparaginine and leucine residue for a valine and glutamine (alphaIIb, RNRPPLEED; alphaV, RVRPPQEEQ). This switch had a dramatic effect on their inhibitory capacity and on protein-protein interactions. The two arginine and glutamic residues, juxtapositioned at identical locations in both subunits, appeared to be important in specifying the orientation by which proteins can dock to this region in alphaIIb and alphaV.
Collapse
Affiliation(s)
- Thomas A Haas
- Department of Anatomy and Cell Biology, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5.
| | | | | | | |
Collapse
|
8
|
Chen JJ, Su XY, Xi XD, Lin LP, Ding J, Lu H. Fibrinogen interaction of CHO cells expressing chimeric alphaIIb/alphavbeta3 integrin. Acta Pharmacol Sin 2008; 29:204-10. [PMID: 18215349 DOI: 10.1111/j.1745-7254.2008.00723.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
AIM The molecular mechanisms of the affinity regulation of alphavbeta3 integrin are important in tumor development, wound repairing, and angiogenesis. It has been established that the cytoplasmic domains of alphavbeta3 integrin play an important role in integrin-ligand affinity regulation. However, the relationship of structure-function within these domains remains unclear. METHODS The extracellular and transmembrane domain of alphaIIb was fused to the alphav integrin cytoplasmic domain, and the chimeric alpha subunit was coexpressed in Chinese hamster ovary (CHO) cells with the wild-type beta3 subunit or with 3 mutant beta3 sequences bearing truncations at the positions of T741, Y747, and F754, respectively. The CHO cells expressing these recombinant integrins were tested for soluble fibrinogen binding and the cell adhesion and spreading on immobilized fibrinogen. RESULTS All 4 types of integrins bound soluble fibrinogen in the absence of agonist stimulation, and only the cells expressing the chimeric alpha subunit with the wild-type beta3 subunit, but not those with truncated beta3, could adhere to and spread on immobilized fibrinogen. CONCLUSION The substitution alphaIIb at the cytoplasmic domain with the alphav cytoplasmic sequence rendered the extracellular alphaIIbbeta3 a constitutively activated conformation for ligands without the need of pinside-outq signals. Our results also indicated that the COOH-terminal sequence of beta3 might play a key role in integrin alphaIIb/alphavbeta3-mediated cell adhesion and spreading on immobilized fibrinogen. The cells expressing alphaIIb/alphavbeta3 have enormous potential for facilitating drug screening for antagonists either to alphavbeta3 intracellular interactions or to alphaIIbbeta3 receptor functions.
Collapse
Affiliation(s)
- Juan-juan Chen
- Division of Antitumor Pharmacology, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | | | | | | | | | | |
Collapse
|
9
|
Hato T, Yamanouchi J, Tamura T, Yakushijin Y, Sakai I, Yasukawa M. Cooperative role of the membrane-proximal and -distal residues of the integrin beta3 cytoplasmic domain in regulation of talin-mediated alpha IIb beta3 activation. J Biol Chem 2008; 283:5662-8. [PMID: 18174155 DOI: 10.1074/jbc.m707246200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Integrin cytoplasmic tails regulate integrin activation that is required for high affinity binding with ligands. The interaction of the integrin beta subunit tail with a cytoplasmic protein, talin, largely contributes to integrin activation. Here we report the cooperative interaction of the beta3 membrane-proximal and -distal residues in regulation of talin-mediated alpha IIb beta3 activation. Because a chimeric integrin, alpha IIb beta3/beta1, in which the beta3 tail was replaced with the beta1 tail was constitutively active, we searched for the residues responsible for integrin activation among the residues that differed between the beta3 and beta1 tails. Single amino acid substitutions of Ile-719 and Glu-749 in the beta3 membrane-proximal and -distal regions, respectively, with the corresponding beta1 residues or alanine rendered alphaIIbbeta3 constitutively active. The I719M/E749S double mutant had the same ligand binding activity as alpha IIb beta3/beta1. These beta3 mutations also induced alphaVbeta3 activation. Conversely, substitution of Met-719 or Ser-749 in the beta1 tail with the corresponding beta3 tail residue (M719I or S749E) inhibited alpha IIb beta3/beta1 activation, and the M719I/S749E double mutant inhibited ligand binding to a level comparable with that of the wild-type alpha IIb beta3. Knock down of talin by short hairpin RNA inhibited the I719M- and E749S-induced alpha IIb beta3 activation. These results suggest that the beta3 membrane-proximal and -distal residues cooperatively regulate talin-mediated alpha IIb beta3 activation.
Collapse
Affiliation(s)
- Takaaki Hato
- Division of Blood Transfusion, Ehime University Graduate School of Medicine, Ehime 791-0295, Japan.
| | | | | | | | | | | |
Collapse
|
10
|
Abstract
Integrin alpha(IIb)beta(3) plays a critical role in platelet aggregation, a central response in hemostasis and thrombosis. This function of alpha(IIb)beta(3) depends upon a transition from a resting to an activated state such that it acquires the capacity to bind soluble ligands. Diverse platelet agonists alter the cytoplasmic domain of alpha(IIb)beta(3) and initiate a conformational change that traverses the transmembrane region and ultimately triggers rearrangements in the extracellular domain to permit ligand binding. The membrane-proximal regions of alpha(IIb) and beta(3) cytoplasmic tails, together with the transmembrane segments of the subunits, contact each other to form a complex which restrains the integrin in the resting state. It is unclasping of this complex that induces integrin activation. This clasping/unclasping process is influenced by multiple cytoplasmic tail binding partners. Among them, talin appears to be a critical trigger of alpha(IIb)beta(3) activation, but other binding partners, which function as activators or suppressors, are likely to act as co-regulators of integrin activation.
Collapse
Affiliation(s)
- Y-Q Ma
- Department of Molecular Cardiology, Joseph J. Jacobs Center for Thrombosis and Vascular Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA
| | | | | |
Collapse
|
11
|
Abstract
Integrin adhesion receptors mediate cell-cell and cell-substratum adhesion and provide a continuous link for the bidirectional transmission of mechanical force and biochemical signals across the plasma membrane. Integrin-dependent cellular activities such as adhesion, migration, proliferation, and survival rely upon the dynamic interaction of integrin cytoplasmic tails with intracellular integrin-binding proteins. In this review, we describe some of the methods that we have used to identify and characterize the interactions between integrin cytoplasmic tails and cytoskeletal proteins, as well as highlight methods to decipher the regulation of integrin tail interactions with intracellular ligands. Specifically, we describe recombinant models of integrin cytoplasmic tails and their use in protein-protein interaction studies.
Collapse
Affiliation(s)
- Yatish Lad
- Department of Pharmacology, Interdepartmental Program in Vascular Biology and Transplantation, Yale University School of Medicine, New Haven, Connecticut, USA
| | | | | |
Collapse
|
12
|
Knoblauch A, Will C, Goncharenko G, Ludwig S, Wixler V. The binding of Mss4 to alpha-integrin subunits regulates matrix metalloproteinase activation and fibronectin remodeling. FASEB J 2006; 21:497-510. [PMID: 17172637 DOI: 10.1096/fj.06-7022com] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
In four independent yeast two-hybrid screens with the integrin alpha-subunits alpha3A, alpha6A, alpha7A, and alpha7B, we identified the Mss4 protein, a nucleotide exchange factor for exocytic Rab GTPases, as a novel integrin interacting protein. We have previously shown that it binds to the conserved KXGFFKR region of integrin alpha-subunits located directly beneath the cell membrane. Here we show that the binding site for integrins on Mss4 is overlapping with those for Rab GTPases. Functional analysis of the Mss4/integrin interaction revealed its importance for activation of matrix metalloproteinases (MMPs) and remodeling of secreted extracellular matrix (ECM) proteins. The exocytosis of all the proteins analyzed, however, was unaffected. Furthermore, our data suggest that Mss4 drives the coordinated action of the MT1-MMP/integrin protein complex, thus regulating the presence and activation of MT1-MMP at newly formed filopodia and lamellipodia. This in turn facilitates the conversion of pro-MMPs to MMPs, resulting in cleavage and remodeling of ECM proteins. C2C12 myoblasts with stably down-regulated Mss4 showed a disturbed fibronectin remodeling during differentiation, resulting in malfunctioned myotube formation.
Collapse
Affiliation(s)
- Alexander Knoblauch
- Institute of Molecular Virology, Muenster University Hospital Medical School, Von-Esmarch-Str. 56, 48149 Muenster, Germany
| | | | | | | | | |
Collapse
|
13
|
Aylward K, Meade G, Ahrens I, Devocelle M, Moran N. A novel functional role for the highly conserved alpha-subunit KVGFFKR motif distinct from integrin alphaIIbbeta3 activation processes. J Thromb Haemost 2006; 4:1804-12. [PMID: 16879224 DOI: 10.1111/j.1538-7836.2006.02041.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND The highly conserved integrin alpha-subunit membrane-proximal motif KVGFFKR plays a decisive role in modulating the activation of integrin alphaIIbbeta3. Previously, we have shown that a platelet permeable palmityl (pal)-peptide with this seven amino acid sequence can directly activate alphaIIbbeta3 leading to platelet aggregation. OBJECTIVES To investigate further the role of the KVGFFKR motif in integrin alphaIIbbeta3 function. METHODS We used two sequence-specific complementary model systems, palmityl pal-peptides in platelets, and mutant alphaIIbbeta3-expressing Chinese Hamster Ovary (CHO) cell lines. RESULTS In platelets we show that the two phenylalanine amino acids in pal-KVGFFKR (pal-FF) peptide are critical for stimulating platelet aggregation. Pal-FF peptide treatment of platelets also gives rise to a tyrosine phosphorylation signal despite the presence of inhibitors of fibrinogen binding. In CHO cells, a double alanine substitution, alphaIIb(F992A, F993A)beta3, induces constitutive integrin activation but prevents actin stress fiber formation upon adhesion to fibrinogen, suggesting that alphaIIbbeta3-mediated cytoskeletal reorganization is also dependent on F992 and F993. This further highlights a critical role for the two phenylalanine residues in both of these alphaIIbbeta3-mediated processes. CONCLUSION In addition to regulating integrin alphaIIbbeta3 activation state, the KVGFFKR motif also influences cytoskeletal reorganization. This activity is critically determined by F992 and F993 within the seven amino acid sequence.
Collapse
Affiliation(s)
- K Aylward
- Department of Clinical Pharmacology, Royal College of Surgeons in Ireland, Dublin, Ireland
| | | | | | | | | |
Collapse
|
14
|
Yamodo IH, Blystone SD. Integrin alphaIIb-subunit cytoplasmic domain mutations demonstrate a requirement for tyrosine phosphorylation of beta3-subunits in actin cytoskeletal organization. ACTA ACUST UNITED AC 2005; 11:121-35. [PMID: 16194880 DOI: 10.1080/15419060500212508] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Using truncated or mutated alphaIIb integrin cytoplasmic domains fused to the alphaV extracellular domain and expressed with the beta3 integrin subunit, we demonstrate that the double mutation of proline residues 998 and 999 to alanine (PP998/999AA), previously shown to disturb the C-terminal conformation of the alphaIIb integrin cytoplasmic domain, prevents tyrosine phosphorylation of beta3 integrin induced by Arg-Gly-Asp peptide ligation. This mutation also inhibits integrin mediated actin assembly and cell adhesion to vitronectin. In contrast, progressive truncation of the alphaIIb-subunit cytoplasmic domain did not reproduce these effects. Interestingly, the PP998/999AA mutations of alphaIIb did not affect beta3 tyrosine phosphorylation, cell adhesion, or actin polymerization induced by manganese. Exogenous addition of manganese was sufficient to rescue beta3 phosphorylation, cell adhesion, and actin assembly in cells expressing the PP998/999AA mutation when presented with a vitronectin substrate. Further, induction of the high affinity conformation of this mutant beta3 integrin by incubation with either Arg-Gly-Asp peptide or exogenous manganese was equivalent. These results suggest that the extracellular structure of beta3 integrins in the high affinity conformation is not directly related to the structure of the cytoplasmic face of the integrin. Moreover, the requirement for beta3 phosphorylation is demonstrated without mutation of the beta3 subunit. In support of our previous hypothesis of a role for beta3 phosphorylation in adhesion, these studies demonstrate a strong correlation between beta3 tyrosine phosphorylation and assembly of a cytoskeleton competent to support firm cell adhesion.
Collapse
Affiliation(s)
- Innocent H Yamodo
- Department of Cell and Developmental Biology, SUNY Upstate Medical University, Syracuse, New York 13210, USA
| | | |
Collapse
|
15
|
Abstract
The development and integrity of the cardiovascular system depends on integrins, a family of adhesion receptors, vitally important for homeostasis of animal species from fruit fly to man. Integrins are critical players in cell migration, cell adhesion, cell cycle progression, differentiation, and apoptosis. Consequently, integrins have a major impact on the patterning and functions of the blood and cardiovascular system. Integrins undergo conformational changes, which alter their affinity for ligands through a process operationally defined as integrin activation. Integrin activation is important for platelet aggregation, leukocyte extravasation, and cell adhesion and migration, thus influencing such processes as hemostasis, inflammation and angiogenesis. Recently, a series of studies have begun to define the mechanism of integrin activation by demonstrating that binding of a cytoskeletal protein, talin, to integrin beta subunit cytoplasmic tail is a last common step in integrin activation. These findings indicate that talin is likely to be at the center of converging signaling pathways regulating integrin activation.
Collapse
Affiliation(s)
- B I Ratnikov
- Department of Medicine, University of California San Diego, La Jolla, CA 92093-0726, USA
| | | | | |
Collapse
|
16
|
Liu J, Jackson CW, Gruppo RA, Jennings LK, Gartner TK. The beta3 subunit of the integrin alphaIIbbeta3 regulates alphaIIb-mediated outside-in signaling. Blood 2005; 105:4345-52. [PMID: 15701721 PMCID: PMC1895035 DOI: 10.1182/blood-2004-07-2718] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bidirectional signaling is an essential feature of alphaIIbbeta3 function. The alphaIIb cytoplasmic domain negatively regulates beta3-mediated inside-out signaling, but little is known about the regulation of alphaIIb-mediated outside-in signaling. We show that alphaIIb-mediated outside-in signaling is enhanced in platelets of a patient lacking the terminal 39 residues of the beta3 cytoplasmic tail. This enhanced signaling was detected as thromboxane A(2) (TxA(2)) production and granule secretion, and required ligand cross-linking of alphaIIbbeta3 and platelet aggregation. This outside-in signaling was specifically inhibited by a palmitoylated version of a beta3 peptide corresponding to cytoplasmic domain residues R724-R734. Unlike the palmitoylated peptide, the nonpalmitoylated beta3 peptide could not cross the platelet membrane and did not inhibit this outside-in signaling. The physiologic relevance of this beta3-mediated negative regulation of alphaIIb outside-in signaling was demonstrated in normal platelets treated with the palmitoylated peptide and a physiologic agonist. Binding of alphaIIbbeta3 complexes to immobilized peptides demonstrated that a peptide corresponding to beta3 residues R724-R734 appears to bind to an alphaIIb cytoplasmic domain peptide containing residues K989-D1002, but not to control peptides. These results demonstrate that alphaIIb-mediated outside-in signaling resulting in TxA(2) production and granule secretion is negatively regulated by a sequence of residues in the membrane distal beta3 cytoplasmic domain sequence RKEFAKFEEER.
Collapse
Affiliation(s)
- Junling Liu
- Department of Microbiology and Molecular Cell Sciences, University of Memphis, Memphis, TN 38152, USA
| | | | | | | | | |
Collapse
|
17
|
Abstract
The ability of cells to regulate dynamically their adhesion to one another and to the extracellular matrix (ECM) that surrounds them is essential in multicellular organisms. The integrin family of transmembrane adhesion receptors mediates both cell-cell and cell-ECM adhesion. One important, rapid and reversible mechanism for regulating adhesion is by increasing the affinity of integrin receptors for their extracellular ligands (integrin activation). This is controlled by intracellular signals that, through their action on integrin cytoplasmic domains, induce conformational changes in integrin extracellular domains that result in increased affinity for ligand. Recent studies have shed light on the final intracellular steps in this process and have revealed a vital role for the cytoskeletal protein talin.
Collapse
Affiliation(s)
- David A Calderwood
- Department of Pharmacology, Yale University School of Medicine, Sterling Hall of Medicine, New Haven, CT 06520, USA.
| |
Collapse
|
18
|
Campbell ID, Ginsberg MH. The talin-tail interaction places integrin activation on FERM ground. Trends Biochem Sci 2004; 29:429-35. [PMID: 15362227 DOI: 10.1016/j.tibs.2004.06.005] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Integrins are essential receptors for the development and functioning of multicellular animals because they mediate cell migration and cell adhesion, and regulate cell proliferation and apoptosis. Cellular regulation of the affinity of integrins for ligands - so-called 'integrin activation' - is a central property of these receptors. Integrin activation controls cell adhesion, migration and extracellular matrix assembly, thereby contributing to processes such as angiogenesis, tumor cell metastasis, inflammation, the immune response and hemostasis. Recent studies indicate that a crucial, final step in integrin activation is the binding of talin, a cytoskeletal protein, to the cytoplasmic domain of the integrin beta subunit. These results provide a focus for unraveling the many biochemical pathways implicated in integrin activation and suggest a general structural model for the connections between integrins and diverse cellular signal transduction pathways.
Collapse
Affiliation(s)
- Iain D Campbell
- Department of Biochemistry, University of Oxford, Oxford, UK OX1 3QU.
| | | |
Collapse
|
19
|
Yamanouchi J, Hato T, Tamura T, Fujita S. Suppression of integrin activation by the membrane-distal sequence of the integrin alphaIIb cytoplasmic tail. Biochem J 2004; 379:317-23. [PMID: 14723599 PMCID: PMC1224082 DOI: 10.1042/bj20031753] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2003] [Revised: 01/05/2004] [Accepted: 01/15/2004] [Indexed: 01/14/2023]
Abstract
Integrin cytoplasmic tails regulate integrin activation including an increase in integrin affinity for ligands. Although there is ample evidence that the membrane-proximal regions of the alpha and beta tails interact with each other to maintain integrins in a low-affinity state, little is known about the role of the membrane-distal region of the alpha tail in regulation of integrin activation. We report a critical sequence for regulation of integrin activation in the membrane-distal region of the alphaIIb tail. Alanine substitution of the RPP residues in the alphaIIb tail rendered alphaIIbbeta3 constitutively active in a metabolic energy-dependent manner. Although an alphaIIb/alpha6Abeta3 chimaeric integrin, in which the alphaIIb tail was replaced by the alpha6A tail, was in an energy-dependent active state to bind soluble ligands, introduction of the RPP sequence into the alpha6A tail inhibited binding of an activation-dependent antibody PAC1. In alphaIIb/alpha6Abeta3, deleting the TSDA sequence from the alpha6A tail or single amino acid substitutions of the TSDA residues inhibited alphaIIb/alpha6Abeta3 activation and replacing the membrane-distal region of the alphaIIb tail with TSDA rendered alphaIIbbeta3 active, suggesting a stimulatory role of TSDA in energy-dependent integrin activation. However, adding TSDA to the alphaIIb tail containing the RPP sequence of the membrane-distal region failed to activate alphaIIbbeta3. These results suggest that the RPP sequence after the GFFKR motif of the alphaIIb tail suppresses energy-dependent alphaIIbbeta3 activation. These findings provide a molecular basis for the regulation of energy-dependent integrin activation by alpha subunit tails.
Collapse
Affiliation(s)
- Jun Yamanouchi
- Department of Internal Medicine 1, Ehime University School of Medicine, Shigenobu, Ehime 791-0295, Japan
| | | | | | | |
Collapse
|
20
|
Calderwood DA, Tai V, Di Paolo G, De Camilli P, Ginsberg MH. Competition for talin results in trans-dominant inhibition of integrin activation. J Biol Chem 2004; 279:28889-95. [PMID: 15143061 DOI: 10.1074/jbc.m402161200] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The ability of integrin adhesion receptors to undergo rapid changes in affinity for their extracellular ligands (integrin activation) is essential for the development and function of multicellular animals and is dependent on interactions between the integrin beta subunit-cytoplasmic tail and the cytoskeletal protein talin. Cross-talk among different integrins and between integrins and other receptors impacts many cellular processes including adhesion, spreading, migration, clot retraction, proliferation, and differentiation. One form of integrin cross-talk, transdominant inhibition of integrin activation, occurs when ligand binding to one integrin inhibits the activation of a second integrin. This may be relevant clinically in a number of settings such as during platelet adhesion, leukocyte trans-migration, and angiogenesis. Here we report that competition for talin underlies the trans-dominant inhibition of integrin activation. This conclusion is based on our observations that (i). beta tails selectively defective in talin binding are unable to mediate trans-dominant inhibition, (ii). trans-dominant inhibition can be reversed by overexpression of integrin binding and activating fragments of talin, and (iii). expression of another non-integrin talin-binding protein, phosphatidylinositol phosphate kinase type Igamma-90, also inhibits integrin activation. Thus, the sequestration of talin by the suppressive species is both necessary and sufficient for trans-dominant inhibition of integrin activation.
Collapse
Affiliation(s)
- David A Calderwood
- Deptartment of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
| | | | | | | | | |
Collapse
|
21
|
Abstract
Integrins are cell adhesion receptors that couple extracellular divalent cation-dependent recognition events with intracellular mechanical and biochemical responses and vice versa, thus affecting every function of nucleated cells. The structural basis of this bidirectional signaling and its dependency on cations has been the focus of intensive study over the past three decades. Significant progress made recently in elucidating the three-dimensional structure of the extracellular and cytoplasmic segments of integrins is giving valuable new insights into the tertiary and quaternary changes that underlie activation, ligand recognition and signaling by these receptors.
Collapse
Affiliation(s)
- J-P Xiong
- Renal Unit, Leukocyte Biology & Inflammation Program, Structural Biology Program, Massachusetts General Hospital, Charlestown, MA 02129, USA
| | | | | | | |
Collapse
|
22
|
Abstract
AlphaIIbbeta3, the major membrane protein on the surface of platelets, is a member of the integrin family of heterodimeric adhesion receptors. The alphaIIb and beta3 subunits are each composed of a short cytoplasmic tail, a single transmembrane domain, and a large, extracellular region that consists of a series of linked domains. Recent structural analyses have provided insights into the organization of this and other integrins and how a signal is initiated at its cytoplasmic tail to transform the extracellular domain of alphaIIbbeta3 into a functional receptor for fibrinogen or von Willebrand factor to support platelet aggregation and thrombus formation. These functions of alphaIIbbeta3 have been targeted for antithrombotic therapy, and intravenous alphaIIbbeta3 antagonists have been remarkably effective in the setting of percutaneous coronary interventions, showing both short-term and long-term mortality benefits. However, the development of oral antagonists has been abandoned on the basis of excess of mortality in clinical trials, and the extension of therapy with existing alphaIIbbeta3 antagonists to broadly treat acute coronary syndromes has not fully met expectations. An in-depth understanding of how antagonists engage and influence the function of alphaIIbbeta3 and platelets in the context of the new structural insights may explain its salutary and potential deleterious effects.
Collapse
Affiliation(s)
- Martin J Quinn
- Joseph J. Jacobs Center for Thrombosis and Vascular Biology, Department of Molecular Cardiology/NB50, Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, Ohio 44195, USA
| | | | | | | | | |
Collapse
|
23
|
Travis MA, Humphries JD, Humphries MJ. An unraveling tale of how integrins are activated from within. Trends Pharmacol Sci 2003; 24:192-7. [PMID: 12707006 DOI: 10.1016/s0165-6147(03)00069-5] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Integrin cytoplasmic tail domains are short, but are essential for normal receptor function because of their key role in relaying bidirectional signals across the plasma membrane. Although it is well established that the cytoplasmic tails both initiate signalling pathways inside the cell and control the transition of integrins from a resting to a ligand-binding competent state, until recently the structural basis of these changes has been unclear. In the past year, however, a series of structural studies has revealed certain features of cytoplasmic domain function, and in this review we focus on how these advances have enlightened our understanding of integrin tail structure and function.
Collapse
Affiliation(s)
- Mark A Travis
- Wellcome Trust Centre for Cell-Matrix Research, School of Biological Sciences, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester M13 9PT, UK
| | | | | |
Collapse
|
24
|
Abstract
Integrins are cell surface adhesion receptors that are essential for the development and function of multicellular animals. Here we summarize recent findings on the regulation of integrin affinity for ligand (activation), one mechanism by which cells modulate integrin function. The focus is on the structural basis of integrin activation, the role of the cytoplasmic domain in integrin affinity regulation, and potential mechanisms by which activation signals are propagated from integrin cytoplasmic domains to the extracellular ligand-binding domain.
Collapse
Affiliation(s)
- R C Liddington
- Program in Cell Adhesion, The Burnham Institute, La Jolla, CA 92037, USA.
| | | |
Collapse
|
25
|
Weljie AM, Hwang PM, Vogel HJ. Solution structures of the cytoplasmic tail complex from platelet integrin alpha IIb- and beta 3-subunits. Proc Natl Acad Sci U S A 2002; 99:5878-83. [PMID: 11983888 PMCID: PMC122870 DOI: 10.1073/pnas.092515799] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2001] [Indexed: 11/18/2022] Open
Abstract
Integrin adhesion receptors constitute a cell-signaling system whereby interactions in the small cytoplasmic domains of the heterodimeric alpha- and beta-subunits provoke major functional alterations in the large extracellular domains. With two-dimensional NMR spectroscopy, we examined two synthetic peptides [alphaIIb((987)MWKVGFFKRNR) and beta3((716)KLLITIHDRKEFAKFEEERARAKWD)] encompassing the membrane-proximal regions of the cytoplasmic domain motifs from the platelet integrin complex alphaIotaIotabbeta3. These membrane-proximal regions contain two conserved motifs, represented by (989)KVGFFKR in the alphaIIb-subunit, and (716)KLLITIHDR in the beta3-subunit. The dimer interaction consists of two adjacent helices with residues V990 and F993 of the alphaIotaIotab-subunit heavily implicated in the dimer interfacial region, as is I719 of beta3. These residues are situated within the conserved motifs of their respective proteins. Further structural analysis of this unique peptide heterodimer suggests that two distinct conformers are present. The major structural difference between the two conformers is a bend in the beta3-peptide between D723 and A728, whereas the helical character in the other regions remains intact. Earlier mutational analysis has shown that a salt bridge between the side chains of alphaIotaIotab(R955) and beta3(D723) is formed. When this ion pair was modeled into both conformers, increased nuclear Overhauser effect violations suggested that the more bent structure was less able to accommodate this interaction. These results provide a molecular level rationalization for previously reported biochemical studies, as well as a basis for an atomic level understanding of the intermolecular interactions that regulate integrin activity.
Collapse
Affiliation(s)
- Aalim M Weljie
- Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, AB, Canada
| | | | | |
Collapse
|
26
|
Jannuzi AL, Bunch TA, Brabant MC, Miller SW, Mukai L, Zavortink M, Brower DL. Disruption of C-terminal cytoplasmic domain of betaPS integrin subunit has dominant negative properties in developing Drosophila. Mol Biol Cell 2002; 13:1352-65. [PMID: 11950944 PMCID: PMC102274 DOI: 10.1091/mbc.01-08-0429] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
We have analyzed a set of new and existing strong mutations in the myospheroid gene, which encodes the betaPS integrin subunit of Drosophila. In addition to missense and other null mutations, three mutants behave as antimorphic alleles, indicative of dominant negative properties. Unlike null alleles, the three antimorphic mutants are synthetically lethal in double heterozygotes with an inflated (alphaPS2) null allele, and they fail to complement very weak, otherwise viable alleles of myospheroid. Two of the antimorphs result from identical splice site lesions, which create a frameshift in the C-terminal half of the cytoplasmic domain of betaPS. The third antimorphic mutation is caused by a stop codon just before the cytoplasmic splice site. These mutant betaPS proteins can support cell spreading in culture, especially under conditions that appear to promote integrin activation. Analyses of developing animals indicate that the dominant negative properties are not a result of inefficient surface expression, or simple competition between functional and nonfunctional proteins. These data indicate that mutations disrupting the C-terminal cytoplasmic domain of integrin beta subunits can have dominant negative effects in situ, at normal levels of expression, and that this property does not necessarily depend on a specific new protein sequence or structure. The results are discussed with respect to similar vertebrate beta subunit cytoplasmic mutations.
Collapse
Affiliation(s)
- Alison L Jannuzi
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, AZ 85721, USA
| | | | | | | | | | | | | |
Collapse
|