Platelet Integrin Adhesive Functions and Signaling

C H A P T E R

S I X

Platelet Integrin Adhesive Functions and Signaling Nicolas Pre´vost, Hisashi Kato, Laurent Bodin, and Sanford J. Shattil Contents 104 104 104 106 107 107 107 108 108 110 110 111 111 111 112 114

1. Introduction 2. Cell Models 2.1. Platelets 2.2. Cell lines 3. Microscopy 3.1. Cell spreading assay 3.2. Immunostaining 4. Assaying Integrin Adhesive Responses 4.1. Flow cytometry analysis of integrin function 4.2. Adhesion assay 4.3. Platelet aggregation 4.4. Clot retraction 5. Biochemical Analysis of Integrin-Based Signaling 5.1. Initiation of integrin aIIbb3 ‘‘outside-in’’ signaling 5.2. Immunoprecipitation and co-immunoprecipitation References

Abstract Integrin-mediated cellular events affect all cell types and functions, in physiological as well as pathological settings. Blood platelets, because of their unique nature, have proven to be a powerful cell model with which to study the adhesive and signaling properties of integrins. The characterization of the structural and molecular mechanisms regulating the main platelet integrin, aIIbb3, has provided some essential clues as to how integrins are regulated in general. The present chapter details the various protocols and reagents currently in use in our laboratory to study aIIbb3 adhesive responses and signaling in both human and murine cell models.

Division of Hematology-Oncology, Department of Medicine, University of California, San Diego, La Jolla, California Methods in Enzymology, Volume 426 ISSN 0076-6879, DOI: 10.1016/S0076-6879(07)26006-9

#

2007 Elsevier Inc. All rights reserved.

103

104

Nicolas Pre´vost et al.

1. Introduction The preservation of the vascular system integrity in case of hemorrhage is primarily mediated by the formation of a platelet aggregate, or thrombus, at the site of injury. At the molecular level, platelet aggregation is mediated by integrin aIIbb3, a receptor for adhesive macromolecules such as fibrinogen and von Willebrand factor. aIIbb3 undergoes highly regulated structural changes during platelet activation, leading to its transition from a low- to a high-affinity state (Adair et al., 2002; Takagi et al., 2002; Vinogradova et al., 2002). The molecular mechanisms regulating integrin activation have recently become a topic of growing interest in fields such as cardiovascular and cancer biology (Pauhle et al., 2005). Platelets have proven a good model in which to study integrin-mediated adhesion and signaling. Platelets are readily available, easily separated from other blood cells, and contain a signaling apparatus similar to other cells. Using human and murine platelets and aIIbb3-expressing cell lines as models, it has been established that biochemical signaling pathways interacting with aIIbb3 can be grouped into two categories: ‘‘inside-out’’ signals leading to the activation of the integrin and ‘‘outside-in’’ signals leading to rearrangements of the platelet actin cytoskeleton and changes in platelet morphology. The aim of the present chapter is to introduce the techniques commonly used in our laboratory for the study of integrin aIIbb3 adhesive and signaling functions.

2. Cell Models 2.1. Platelets 2.1.1. Preparation of washed platelets from human blood Using a 19-G butterfly needle, venous blood is taken from healthy donors who have not taken any medication for at least 10 days and anticoagulated 5:1 with acid-citrate-dextrose (ACD) (65 mM trisodium citrate, 70 mM citric acid, 100 mM dextrose, pH 4.4). Red and white blood cells are removed by centrifugation at 100g for 20 min at room temperature. After collection, the platelet-rich plasma (PRP) is centrifuged at 220g for 10 min at room temperature. Platelets are then resuspended in wash buffer (150 mM NaCl, 20 mM HEPES, pH 6.5) and centrifuged at 220g for 10 min at room temperature in the presence of 1 U/ml apyrase and 1 mM prostaglandin E1 (PGE1). Finally, the platelet pellet is resuspended in Walsh’s buffer (137 mM NaCl, 20 mM PIPES, 5.6 mM dextrose, 1 g/liter BSA, 1 mM MgCl2, 2.7 mM KCl, 3.3 mM NaH2PO4, pH 7.4). Prior to any experimental procedure, platelets are typically left at room temperature for 30 min; after 30 min, most of the PGE1 has become inactive.

Platelet Integrins

105

2.1.2. Preparation of washed platelets from mouse blood Two methods are routinely being used for the isolation of blood from mice: cardiac puncture and venepuncture. The main appeal to cardiac punctures is that they are not time consuming and do not require the use of anesthetics, because animals are euthanized through CO2 asphyxiation. On the other hand, because of the loss of vasculature tonus in dead animals, blood has to be collected swiftly before platelets become activated. Cardiac punctures also present the disadvantage of yielding smaller blood volumes than venepunctures do. Blood collection through cardiac puncture is performed by the insertion of a 25-G needle through the diaphragm of the animal, immediately beneath its sternum. For venepunctures, mice are anesthetized with 1 mg of pentobarbital per 10 g of weight. After dissection of the abdomen, blood is drawn from the hepatic portal vein in heparin (15 U/ml of blood) using a 22-G needle. The blood is then diluted with one volume of wash buffer (150 mM NaCl, 20 mM PIPES, pH 6.5) and centrifuged at 60g for 7 min. After collection, the PRP is centrifuged at 240g for 10 min at room temperature. Platelets are resuspended in Walsh’s buffer as described in Section 2.1.1. Alternative anticoagulants, such as sodium citrate, are used when platelets will subsequently be exposed to thrombin (see Sections 4.3 and 4.4) or for aggregation studies. For mouse platelet aggregation studies, blood is collected into 1/9 volume 147 mM sodium citrate, pH 6.5. One volume of Walsh’s buffer is then added to the sample before centrifugation at 60g for 7 min at room temperature. After PRP recovery, the platelet concentration is adjusted to 2 to 4  108 platelets per milliliter with Walsh buffer. The platelet suspension is supplemented with 1 mM CaCl2 before aggregations are performed. 2.1.3. Preparation of gel-filtered platelets from human blood An alternative to the washed platelet protocol is gel filtration of the PRP through a sepharose column. Gel-filtered platelets are typically more responsive to adenosine diphosphate stimulation than washed platelets, especially in the context of aggregation studies. PRP is prepared as described in paragraph 2.1.1. The sepharose 2B column is prepared as follows: sepharose 2B (GE Healthcare, Cat# 17-0130-01) is poured into a 60-ml syringe containing a nylon mesh disc with a pore size less than 50 mm (seven to eight volumes of gel for each volume of PRP). The column is then carefully degassed and washed with four gel volumes of Walsh’s buffer. PRP is deposited drop by drop on the column without disturbing the gel–PRP interface. The PRP is then allowed to enter the column by gravity and the platelets are eluted in Walsh’s buffer. The platelet eluate is collected in 1-ml fractions. After use, the column is washed with four volumes of Walsh’s buffer and one volume of ddH2O, and stored at 4 in 0.05% sodium azide. Columns can be re-used up to 10 times.

106

Nicolas Pre´vost et al.

2.2. Cell lines 2.2.1. Integrin-expressing cell lines Because of the limitations anucleate platelets present as a cell model for studies of protein overexpression or knockdown, alternate model systems have been developed for studies of platelet integrin function. These include Chinese hamster ovary (CHO) cells, ‘‘SYF’’ murine fibroblasts deficient for the Src family kinases Src, Yes, and Fyn (Klinghoffer et al., 1999), and murine megakaryocytes. Integrin aIIbb3–expressing CHO and SYF cells were established as described by Diaz-Gonzalez et al. (1996) and O’Toole et al. (1990). As discussed in detail elsewhere, megakaryocytes are produced ex vivo through the differentiation of murine bone marrow (Shiraga et al., 1999) or embryonic stem cells (Eto et al., 2003). 2.2.2. Cell culture and transfection Cell culture CHO and SYF cells stably expressing integrin aIIbb3 are maintained in Dulbecco’s Modified Eagle’s Medium (DMEM) supplemented with 10% fetal calf serum (FCS), 100 U/ml of penicillin, 0.1 mg/ml of streptomycin, 2 mM of L-glutamine, and 1% nonessential amino acids at 37 in 6% CO2. Cells are never grown beyond 80 to 90% confluency. Cell reseeding is performed as follows: cells are first washed in phosphate-buffered saline (PBS) and then detached by 0.5-mM EDTA–0.05% trypsin treatment for 2 to 3 min at 37 . Trypsin is immediately neutralized by the addition of at least three volumes of culture medium. Cells are collected by centrifugation at 150g for 3 min, resuspended in medium, and replated at a confluency of approximately 40 to 50%. Typically, cells are split every 2 to 4 days, and experiments are always carried out with cells that have been passaged no more than five times. Transfection Transfection is usually carried out to test the effects of overexpression of specific recombinant proteins on aIIbb3 function. Twelve to 16 h before transfection, cells are seeded at 1  106 cells per 100-mm cell culture dish. The next day, upon reaching 50 to 80% confluency, cells are washed twice with unsupplemented DMEM. A transfection mix is prepared by mixing 300 ml of DMEM, 1 to 5 mg of DNA, and 15 ml of lipofectamine (Invitrogen, Cat# 18324-020) per 100-mm culture dish, followed by a 20-min incubation at room temperature. Four milliliters of DMEM are then added back to the mixture before incubation with the cells. After 6 h at 37 , the transfection medium is removed and replaced with complete DMEM. Transfected cells are typically ready for assaying integrin functions after 24 to 48 h.

Platelet Integrins

107

3. Microscopy 3.1. Cell spreading assay On the eve of the assay, coverslips are flamed in ethanol and then coated overnight at 4 with 100 mg/ml of fibrinogen (Enzyme Research Laboratories, Cat# FIB-1) in PBS, pH 8.0. The next morning, coverslips are washed three times in PBS and blocked with 5 mg/ml of heat-denatured bovine serum albumin (BSA) for 2 h at room temperature and then washed three times in PBS. Platelets are prepared (described in Section 2.1) and resuspended at 107 platelets/ml in Walsh’s buffer supplemented with 1 mM CaCl2. When working with cells in culture, the final concentration is adjusted to 106 cells/ml in Walsh’s buffer or Tyrode’s buffer (137 mM NaCl, 2.68 mM KCl, 11.9 mM NaHCO3, 3.3 nM NaH2PO4, 2 mM CaCl2, 1 mM MgCl2, 5.5 mM glucose, 5 mM HEPES, 0.35% BSA, pH 7.4). Cells are incubated on fibrinogen coated coverslips at 37 for 15 to 60 min in the absence or presence of agonist. After removal of unbound cells by three PBS washes, adherent cells are fixed with 3.7% of methanol-free formaldehyde (Polysciences, Inc. Cat# 04018) for 10 min at room temperature. Adherent cells are then washed three times with PBS, permeabilized with 0.2% Triton X-100 for 5 min at room temperature, and washed another three times in PBS. Cells are then ready for immunostaining.

3.2. Immunostaining Coverslips are blocked in 10% serum/PBS for 30 min at room temperature. The serum is preferentially from the same animal species as the one that the primary detecting antibody was raised in. Coverslips are then incubated with the primary antibody (at 1/100 to 1/1000 in 10% serum-PBS) for 45 min at 37 , washed three times with PBS, and incubated for 45 min at 37 with fluorophore-labeled secondary antibody (Invitrogen and Jackson Immunochemicals) at 1/500 to 1/1000 in 10% serum-PBS. For staining of intracellular actin, coverslips are incubated with 10 U/ml rhodamine-phalloidin (Invitrogen, Cat# R415) in 5% BSA/TBST (50 mM Tris/HCl, 150 mM NaCl, 0.1 % [v/v] Tween 20, pH 7.5) for 30 min at room temperature, and then washed three times with PBS. Negative controls include cells stained with an irrelevant primary immunoglobulin and cells stained with secondary antibody. After mounting in Citifluor (Ted Pella, Inc. Cat# 19470), coverslips are stored at 4 in the dark.

108

Nicolas Pre´vost et al.

4. Assaying Integrin Adhesive Responses 4.1. Flow cytometry analysis of integrin function 4.1.1. Introduction to ligands and antibodies used The affinity of integrin aIIbb3 for fibrinogen and other ligands is modulated through conformational changes of the integrin on the surface of platelets. The unmasking of specific epitopes in the extracellular domain of the integrin is one of the defining structural changes that allow its transition from a resting state to a high-affinity state. Therefore, it is possible to monitor the binding of fluorophore-labeled soluble fibrinogen as a function of integrin activation on the cell surface. Because fibrinogen is a polyvalent ligand, more discriminating tools have also been developed in order to monitor the changes in integrin affinity at the single molecule level. One such tool is PAC-1 Fab, an RGD-containing antibody Fab fragment specific for high-affinity human aIIbb3 (Abrams et al., 1994), derived from the pentameric IgM PAC-1 (Shattil et al., 1985). Because PAC-1 is specific for human aIIbb3, POW-2, a re-engineered version of PAC-1 capable of recognizing both human and mouse highaffinity aIIbb3 (and aVb3), was subsequently produced (Bertoni et al., 2002). Other antibodies routinely used in the laboratory include A2A9 and 1B5, blocking antibodies that prevent fibrinogen binding to human and mouse aIIbb3, respectively (Bennett et al., 1983; Lengweiler et al., 1999). SSA6 and D57 are function-independent antibodies used for the detection of b3 integrins and aIIbb3 on the surface of cells, respectively (O’Toole et al., 1994; Silver et al., 1987). General information regarding the aforementioned antibodies has been summarized in Table 6.1. 4.1.2. Platelets Platelets are prepared (described in Section 2.1) and adjusted to a final concentration of 108 platelets/milliliter in Walsh’s buffer. Fifty to 100 ml of the platelet suspension are used for each reaction carried out in a polystyrene tube suitable for flow cytometry (Becton Dickinson, Cat# 352008). Platelets are incubated with the detection reagent with or without a platelet agonist or inhibitor for 30 min at room temperature, away from light. For a soluble fibrinogen-binding assay, platelets are incubated with either FITC- or Alexa-Fluor488–conjugated fibrinogen (Invitrogen, Cat# F13191) at a concentration of 200 mg/ml of fibrinogen in the presence of 1 mM CaCl2. For the detection of Alexa Fluor488–conjugated PAC-1 binding to the platelet surface, an antibody concentration of 150 mg/ml is used. A secondary antibody is used to detect binding of POW-2 Fab (Bertoni et al., 2002). Four hundred microliters of PBS are added to the

109

Platelet Integrins

Table 6.1 Antibodies commonly used to study integrin aIIbb3 Antigen

Antibody name

Species/isotype

Application

Human aIIbb3

PAC-1

Mouse IgMk

Human/murine aIIbb3

POW-2 Fab

Human aIIbb3 Murine aIIbb3

A2A9 1B5

Human aIIbb3 Human b3

D57 SSA6

Re-engineered from mouse IgG1k Mouse IgG2ak Hamster IgG3k Mouse Mouse IgG1

Ligand mimetic; FACS Ligand mimetic; FACS Blocking; FACS Blocking; FACS FACS, IF IP, FACS, IF

FACS, fluorescence assisted cell sorting; IF, immunofluorescence; IP, immunoprecipitation.

platelets and samples are analyzed by flow cytometry (Shattil et al., 1987). Changes in the F-actin content of platelets can be assessed by flow cytometry using BODIPY FL-phallacidin (Invitrogen, Cat# B607) as described in Shattil et al. (1994). 4.1.3. Cell lines PAC-1/POW-2 binding Each reaction is performed on 0.5 to 7  106 cells in Walsh’s buffer. For each sample, 50 ml of cell suspension are incubated with or without 5 ml of an agonist and/or inhibitor for 10 min at room temperature. Control samples are treated with 5 ml of 100 mM EDTA, pH 7.35, or a specific aIIbb3 antagonist, such as 10 of mM integrilin or 2 mM of RGDS (to estimate nonspecific binding), or with 5 ml of 10 mM MnCl2 to stimulate aIIbb3 extrinsically. PAC-1 or POW-2 is added to each sample at a final concentration of 150 mg/ml, followed by a 20-min incubation at room temperature. Cells are then washed with 1 ml of Walsh’s buffer, collected by centrifugation at 115g for 5 min, and resuspended in 50 ml of secondary antibody solution (FITC-labeled anti-IgM 1/400 in Walsh’s buffer for PAC-1, AlexaFluor488-labeled antimurine IgG1 for POW-2) (Biosource, Cat# AMI3608; Invitrogen, Cat# A11068). Cells are then incubated for 20 min on ice in the dark, after which time 1 ml of ice-cold Walsh’s buffer is added to the cells. Finally cells are centrifuged at 115g for 5 min in the dark, at 4 and resuspended in 400 ml of 1-mg/ml propidium iodide (PI) in Walsh’s buffer. Ligand binding is assessed on single, living cells by flow cytometry, as described by O’Toole et al. (1990).

110

Nicolas Pre´vost et al.

Soluble fibrinogen binding Fibrinogen-binding assays are per- formed with FITC-, Alexa-Fluor488-, or biotin-labeled soluble fibrinogen. Cells are resuspended in Walsh’s or Tyrode’s buffer in the presence of 1 mM of CaCl2 at a final concentration of 0.5 to 3  106 cells/ml. Twenty-five microliters of cell suspension are added to a FACS tube containing 200 mg/ml fibrinogen in the presence or absence of an agonist or inhibitor. Samples incubated with 1 mM of MnCl2 serve as a positive control and/or 10 mM of EDTA or a specific aIIbb3 antagonist serves as a control for nonspecific binding. For biotin-labeled fibrinogen, cells are incubated for another 25 min with 100 mg/ml of fluorophore-labeled streptavidin at room temperature. Cells are then washed with 500 ml of ice-cold Walsh’s or Tyrode’s buffer, collected by centrifugation at 150g for 3 min at 4 , and resuspended in 400 ml of ice-cold PBS containing 2 mg/ml of PI for flow cytometry analysis.

4.2. Adhesion assay The number of platelets adhering to immobilized fibrinogen can be quantified in a colorimetric assay by measuring the activity of the platelet lysosomal enzyme acid phosphatase through the release of a p-nitrophenyl phosphate enzymatic product. One day before the experiment, a 96-well plate (Fisher #14-245-61) is coated with fibrinogen (150 ml per well of a 200 mg/ml PBS solution), or, as a negative control, heat-inactivated BSA (at 4 mg/ml in PBS) overnight at 4 . The following day the plate is blocked with 5 mg/ml of heat-inactivated BSA for 1 h at room temperature and washed twice with PBS before adding platelets. Platelets are prepared as described in Section 2.1 and adjusted to a final concentration of 108 platelets/ml in Walsh’s buffer. After adding 50 ml of platelet suspension per well, the plate is pre-incubated for 5 min at 37 . Twenty-five microliters of Walsh’s buffer (containing 3 mM of CaCl2, with or without agonist) are subsequently added to each well. The plate is incubated at room temperature for 20 to 60 min, after which it is washed four times with PBS. The substrate solution (5 mM p-nitrophenyl phosphate in 0.1 M citrate/0.1% Triton, pH 5.4) is then added at 150 ml per well. After a 1-h incubation at room temperature in the dark, the enzymatic reaction is stopped by the addition of 100 ml of a 2 N NaOH solution to each well. The plate is read immediately at 405 nm. Values for platelet adhesion are typically expressed as a percentage of platelets added to the well. The latter is estimated by subjecting all the platelets (adherent and nonadherent) in a control well to the enzyme reaction.

4.3. Platelet aggregation Human platelets are prepared by gel filtration. Platelets are resuspended at a final concentration of 1 to 4  108 platelets/milliliter in the presence of 1 mM of CaCl2 and 300 mg/ml of fibrinogen. Mouse platelets are isolated as

Platelet Integrins

111

described in Section 2.1.2. Aggregation studies are performed at 37 in a Chrono-Log optical aggregometer using siliconized glass cuvettes, under constant stirring (900 rpm) after the platelets are allowed to sit at 37 for 1 to 5 min.

4.4. Clot retraction Blood is drawn into 1/9 volume of 147 mM sodium citrate, pH 6.5. To each milliliter of blood, 500 ml of Walsh’s buffer are added. After centrifugation at 60g for 7 min, the PRP is supplemented with 1 mM of CaCl2 and adjusted to 2  108 platelets/ml with Walsh’s buffer containing 1 mM CaCl2 and 300 mg/ml fibrinogen. (For slower clot retraction kinetics, lower platelet concentrations may be used. The final platelet concentration shall not be lower than 6  105 platelets/ml.) In the event of platelet count disparities between mice of different genetic backgrounds, blood collections are to be performed in ACD. Each blood sample is then diluted with one volume of wash buffer (150 mM NaCl, 20 mM PIPES, pH6.5) and centrifuged at 60g for 7 min. The platelets are then isolated by centrifugation at 240g for 10 min at room temperature and resuspended to matching platelet concentrations in the sodium citrate-anticoagulated platelet-free plasma of a normal mouse sacrificed simultaneously. The platelet suspension is then supplemented with 1 mM of CaCl2. Clot retraction assays are performed at 37 in siliconized glass cuvettes on 200-ml platelet suspension samples in the presence of 2 U of thrombin. Clots are photographed at 5, 15, 30, 45, and 60 min. At each time point, the clot exudate is collected and weighed for quantification purposes. The greater the volume of exudate, the more the clot has retracted.

5. Biochemical Analysis of Integrin-Based Signaling 5.1. Initiation of integrin aIIbb3 ‘‘outside-in’’ signaling Ligand binding to integrin aIIbb3 initiates a variety of signaling events immediately downstream of the integrin. These responses are commonly referred to as ‘‘outside-in signaling’’ and result in the recruitment of signaling molecules and cytoskeletal proteins directly or indirectly to the cytoplasmic tails of the integrin (Arias-Salgado et al., 2005a,b; Han et al., 2006. Tadokoro et al., 2003). It is possible to artificially trigger these responses independently of agonistinduced integrin activation. Cell adhesion to immobilized fibrinogen under static conditions offers one of two experimental settings in which to study outside-in signaling downstream of aIIbb3. Alternatively, cells can be treated by a combination of soluble fibrinogen and MnCl2 while in suspension.

112

Nicolas Pre´vost et al.

After fibrinogen ligation to aIIbb3 has been achieved by either means, cells are lysed in ice-cold NP40 buffer (1% NP40, 150 mM NaCl, 50 mM Tris-HCl pH 7.4), or ice-cold RIPA buffer (1% Triton X100, 1% deoxycholate, 0.1% sodium dodecyl sulfate, 5 mM Na2EDTA, 158 mM NaCl, 10 mM Tris-HCl pH 7.2), in the presence of 1 mM of Na3VO4, 0.1 mM of NaF, and a protease inhibitor cocktail (Roche, Cat# 11873580001). For western blotting studies, cells will preferentially be lysed in RIPA buffer. Cell adhesion is carried out in 100 mm of non-tissue culture–treated Petri dishes after overnight coating with 100 mg/ml fibrinogen in PBS, pH 8.0, at 4 and 1 h blocking with 5 mg/ml BSA in PBS, pH 7.4, at room temperature. Control plates that do not support adhesion are coated overnight with 5 mg/ml BSA in PBS, pH 7.4, at 4 . For each 100-mm dish, 2 ml of either 2  108 platelets/ml or a 106 CHO or SYF cells/ml cell suspension are incubated for 5 to 30 min at room temperature. After incubation, control suspension cells not adhering to BSA plates are collected by centrifugation at 11,000g for 1 sec (platelets) or 300g for 3 min (cell lines) and lysed. For fibrinogen-coated dishes, nonadherent cells are removed with a single gentle washing in PBS, and adherent cells are lysed on ice by adding 200 ml of lysis buffer. Typically, lysates from three to five individual plates are pooled for each immunoprecipitation for a final lysate volume of 0.6 to 1 ml. The activation of integrin aIIbb3 in a cell suspension is performed on a 0.5- to 1-ml aliquot of 4  108 platelets/ml or a 3-ml aliquot of 2  106 nucleated cells/ml. All incubations are performed in Walsh’s buffer in the presence of 0.5 to 1 mM of MnCl2 and 250 mg/ml of fibrinogen, at 37 for 2 to 30 min. Cells are collected by centrifugation at 11,000g for 1 sec (platelets) or 300g for 3 min (cell lines) and lysed immediately in 0.6 to 1 ml of lysis buffer.

5.2. Immunoprecipitation and co-immunoprecipitation Typically, RIPA buffer is used for cell lysis in immunoprecipitation studies and NP40 buffer in co-immunoprecipitation studies (Table 6.2). Cell lysates are incubated on ice for 10 min with repeated vortexing. Insoluble material is pelleted by centrifugation at 21,000g for 10 min at 4 ; the protein content of the recovered soluble fraction is determined by colorimetric quantification, through the use of a bicinchoninic acid-based kit (Pierce, Cat# 23225). Each immunoprecipitation is performed on 0.3 to 1 mg of total protein, typically in a final volume of 0.5 ml (see Table 6.2 for details). The lysates are precleared for 2 to 3 h at 4 with 50 ml of protein A- or G-sepharose slurry (50% beads, 50% lysis buffer). The immunoprecipitating antibody is then added to the precleared lysate, and immunoprecipitations are carried out overnight at 4 , unless otherwise stated (Table 6.2). The next morning, the immunoprecipitate is isolated from the lysate with 50 ml of

Table 6.2

Examples of antibodies used to detect co-immunoprecipitation of proteins with integrin aIIbb3 Lysate amount

IP antibody

IB antibody (antigen)

HRP-conjugate

Lysis buffer

Platelets

Cell line

IP time

SSA6 (human b3)

Santa Cruz sc-6627 (b3) Santa Cruz sc-19 (Src) Cell signaling #2107S (pY529 c-Src) Biosource #44–660G (pY418 c-Src) Santa Cruz sc-14021 (human PTP-1B) Santa Cruz sc-209 (PKC-b) Santa Cruz sc-286 (Csk)

Anti-Goat-HRP Protein A-HRP Protein A-HRP

RIPA/NP40 NP40 NP40

300 mg 600 mg 900 mg

500 mg 1 mg 1 mg

8 h 8 h 8 h

Protein A-HRP

NP40

900 mg

1 mg

8 h

Protein A-HRP

NP40

900 mg

1 mg

8 h

Protein A-HRP

NP40

900 mg

1 mg

4h

Protein A-HRP

NP40

600 mg

1 mg

8 h

Santa Cruz sc-6627 (mouse b3)

114

Nicolas Pre´vost et al.

a 50%-protein A- or G-sepharose slurry (GE Healthcare, Cat# 17-0780-01 and Cat#17-0618–01), for 3 h at 4 . The beads are then washed three times in PBS containing 1 mM of NaVO4, 0.1 mM of NaF and protease inhibitor cocktail (Roche, Cat# 11873580001) After the washing step, the beads are boiled for 5 to 10 min at 100 in 80 ml of 2 Laemmli buffer (62.5 mM TrisHCl, pH 6.8, 2% sodium dodecyl sulfate [SDS], 25% glycerol, 0.01% bromophenol blue) plus 5% b-mercaptoethanol (v/v). Samples are then separated by SDS polyacrylamide gel electrophoresis (SDS-PAGE) and transferred to nitrocellulose or polyvinylidene difluoride (PVDF) membranes (Biorad, Cat# 162-0112 and Cat# 162-0181). For the detection of phosphorylated tyrosine residues, PVDF membranes and BSA (MP Biomedicals, Cat# 103700) are used; in the absence of such residues, nitrocellulose membranes and non-fat dry milk are used. Membranes are first blocked for 30 min in 5% blocking agent-TBST, and then incubated for 1 h at room temperature with the primary antibody in 1% blocking agent-TBST. After three 15-min washes in TBST, membranes are incubated with the secondary reagent (Protein A-HRP, Upstate, Cat# 18-160; HRP-conjugated antibodies are from Jackson Immunochemicals) in 1% blocking agent-TBST for 1 h at room temperature. Finally, membranes are washed three times for 15 min in TBST, and incubated for 1 min with a peroxidase chemiluminescent substrate (Pierce, Cat# 34080).

REFERENCES Abrams, C., Deng, Y. J., Steiner, B., O’Toole, T., and Shattil, S. J. (1994). Determinants of specificity of a baculovirus-expressed antibody Fab fragment that binds selectively to the activated form of integrin alpha IIb beta 3. J. Biol. Chem. 269, 18781–18788. Adair, B. D., and Yeager, M. (2002). Three-dimensional model of the human platelet integrin alpha IIbbeta 3 based on electron cryomicroscopy and x-ray crystallography. Proc. Natl. Acad. Sci. USA 99, 14059–14064. Arias-Salgado, E. G., Haj, F., Dubois, C., Moran, B., Kasirer-Friede, A., Furie, B. C., Furie, B., Neel, B. G., and Shattil, S. J. (2005a). PTP-1B is an essential positive regulator of platelet integrin signaling. J. Cell Biol. 170, 837–845. Arias-Salgado, E. G., Lizano, S., Shattil, S. J., and Ginsberg, M. H. (2005b). Specification of the direction of adhesive signaling by the integrin beta cytoplasmic domain. J. Biol. Chem. 280, 29699–29707. Bennett, J. S., Hoxie, J. A., Leitman, S. F., Vilaire, G., and Cines, D. B. (1983). Inhibition of fibrinogen binding to stimulated human platelets by a monoclonal antibody. Proc. Natl. Acad. Sci. USA 80, 2417–2421. Bertoni, A., Tadokoro, S., Eto, K., Pampori, N., Parise, L. V., White, G. C., and Shattil, S. J. (2002). Relationships between Rap1b, affinity modulation of integrin alpha IIbbeta 3, and the actin cytoskeleton. J. Biol. Chem. 277, 25715–25721. Diaz-Gonzalez, F., Forsyth, J., Steiner, B., and Ginsberg, M. H. (1996). Trans-dominant inhibition of integrin function. Mol. Biol. Cell 7, 1939–1951. Eto, K., Leavitt, A. L., Nakano, T., and Shattil, S. J. (2003). Development and analysis of megakaryocytes from murine embryonic stem cells. Methods Enzymol. 365, 142–158.

Platelet Integrins

115

Han, J., Lim, C. J., Watanabe, N., Soriani, A., Ratnikov, B., Calderwood, D. A., PuzonMcLaughlin, W., Lafuente, E. M., Boussiotis, V. A., Shattil, S. J., and Ginsberg, M. H. (2006). Reconstructing and deconstructing agonist-induced activation of integrin alphaIIbbeta3. Curr. Biol. 16, 1796–1806. Klinghoffer, R. A., Sachsenmaier, C., Cooper, J. A., and Soriano, P. (1999). Src family kinases are required for integrin but not PDGFR signal transduction. EMBO J. 18, 2459–2471. Lengweiler, S., Smyth, S. S., Jirouskova, M., Scudder, L. E., Park, H., Moran, T., and Coller, B. S. (1999). Preparation of monoclonal antibodies to murine platelet glycoprotein IIb/IIIa (alphaIIbbeta3) and other proteins from hamster–mouse interspecies hybridomas. Biochem. Biophys. Res. Commun. 262, 167–173. O’Toole, T. E., Loftus, J. C., Du, X. P., Glass, A. A., Ruggeri, Z. M., Shattil, S. J., Plow, E. F., and Ginsberg, M. H. (1990). Affinity modulation of the alpha IIb beta 3 integrin (platelet GPIIb-IIIa) is an intrinsic property of the receptor. Cell Regul. 1, 883–893. O’Toole, T. E., Katagiri, Y., Faull, R. J., Peter, K., Tamura, R., Quaranta, V., Loftus, J. C., Shattil, S. J., and Ginsberg, M. H. (1994). Integrin cytoplasmic domains mediate insideout signal transduction. J. Cell Biol. 124, 1047–1059. Paulhe, F., Manenti, S., Ysebaert, L., Betous, R., Sultan, P., and Racaud-Sultan, C. (2005). Integrin function and signaling as pharmacological targets in cardiovascular diseases and in cancer. Curr. Pharm. Des. 11, 2119–2134. Shattil, S. J., Hoxie, J. A., Cunningham, M., and Brass, L. F. (1985). Changes in the platelet membrane glycoprotein IIb.IIIa complex during platelet activation. J. Biol. Chem. 260, 11107–11114. Shattil, S. J., Cunningham, M., and Hoxie, J. A. (1987). Detection of activated platelets in whole blood using activation-dependent monoclonal antibodies and flow cytometry. Blood 70, 307–315. Shattil, S. J., Haimovich, B., Cunningham, M., Lipfert, L., Parsons, J. T., Ginsberg, M. H., and Brugge, J. S. (1994). Tyrosine phosphorylation of pp125FAK in platelets requires coordinated signaling through integrin and agonist receptors. J. Biol. Chem. 269, 14738–14745. Shiraga, M., Ritchie, A., Aidoudi, S., Baron, V., Wilcox, D., White, G., Ybarrondo, B., Murphy, G., Leavitt, A., and Shattil, S. (1999). Primary megakaryocytes reveal a role for transcription factor NF-E2 in integrin alpha IIb beta 3 signaling. J. Cell Biol. 147, 1419–1430. Silver, S. M., McDonough, M. M., Vilaire, G., and Bennett, J. S. (1987). The in vitro synthesis of polypeptides for the platelet membrane glycoproteins IIb and IIIa. Blood 69, 1031–1037. Tadokoro, S., Shattil, S. J., Eto, K., Tai, V., Liddington, R. C., de Pereda, J. M., Ginsberg, M. H., and Calderwood, D. A. (2003). Talin binding to integrin beta tails: A final common step in integrin activation. Science 302, 103–106. Takagi, J., Petre, B. M., Walz, T., and Springer, T. A. (2002). Global conformational rearrangements in integrin extracellular domains in outside-in and inside-out signaling. Cell 110, 599–611. Vinogradova, O., Velyvis, A., Velyviene, A., Hu, B., Haas, T., Plow, E., and Qin, J. (2002). A structural mechanism of integrin alpha(IIb)beta(3) ‘‘inside-out’’ activation as regulated by its cytoplasmic face. Cell 110, 587–597.