Key proteins involved in αIIbβ3 outside-in signaling in platelets
| Protein . | Knockout mouse platelet phenotype (unless otherwise stated) . | Reference . |
|---|---|---|
| Positive regulators | ||
| ADAP | Reduced attachment and spreading on fibrinogen under shear flow. Unstable thrombi. Increased tail rebleeding. | 48, 52 |
| c-Cbl | Impaired spreading on fibrinogen. Delayed clot retraction. | 98 |
| CD148 | Reduced spreading on fibrinogen. Compromised thrombus formation and stability. Increased tail bleeding. | 64 |
| Cdc42 | Conflicting reports regarding role in filopodia formation on fibrinogen. Accelerated arterial occlusive thrombus formation but prolonged bleeding times. | 113, 114 |
| CIB1 | Reduced spreading on fibrinogen. Impaired arterial occlusion associated with unstable thrombus formation. Increased tail-bleeding time. | 87, 155 |
| Dab2 | Impaired spreading on fibrinogen. Impaired thrombus formation. Impaired clot retraction. Prolonged bleeding time. | 156 |
| FAK | Impaired spreading on fibrinogen. Increased tail rebleeding. | 82 |
| Gα13 | Impaired stable thrombus formation. Increased tail-bleeding time. Contrasting reports regarding role in spreading on fibrinogen. Mutation of the Gα13-binding β3 ExE motif, or peptide-mediated inhibition of the β3-Gα13 interaction, inhibited platelet spreading on fibrinogen and thrombus formation, whereas the peptide did not affect tail bleeding. | 43, 63, 102, 157 |
| ILK | Impaired thrombus stability. Increased tail bleeding time and volume. | 135, 136 |
| Kindlin-3 | Severe bleeding during development. Loss of spreading on fibrinogen. Loss of thrombus formation. Increased tail bleeding. | 133 |
| Lnk | Impaired spreading on fibrinogen. Reduced thrombus stability. Impaired clot retraction. Increased tail bleeding. | 137 |
| PDK1 | Reduced spreading on fibrinogen. Reduced thrombus formation. Delayed clot retraction. | 101 |
| PECAM-1 | Reduced spreading on fibrinogen. Delayed clot retraction. | 158 |
| PI3Kβ | p110β KO, kinase-dead, and pharmacological inhibition: reduced spreading on fibrinogen. Almost complete inability to adhere to fibrinogen under flow. Unstable thrombi. Delayed clot retraction. No effect on rodent tail-bleeding time. | 91,-93, 95 |
| PKC | PKCθ; reduced spreading on fibrinogen yet enhanced thrombus formation due to enhanced secretion. PKCα; reduced thrombus formation due to reduced secretion. PKCβ; reduced spreading. | 78, 79, 159, 160 |
| PLCγ2 | Defective spreading on fibrinogen. | 76 |
| Pyk2 | Defective spreading on fibrinogen. Impaired thrombus formation. Slightly prolonged tail-bleeding time. | 97, 161 |
| Rac1 | Defective spreading on fibrinogen. Reduced thrombus formation and stability. Prolonged tail bleeding. | 109,-111 |
| Rasa3 | Rasa3 RapGAP activity restrains Rap1-driven cell spreading on fibrinogen. | 47 |
| RhoA | Normal extent of spreading on fibrinogen but with slightly altered morphology. Required for thrombus stability. Essential for clot retraction. Increased tail bleeding. | 102 |
| ROCK2 | Impaired thrombus formation. Prolonged tail-bleeding time. | 162 |
| SLP-76 | Fetal hemorrhage and platelet dysfunction including impaired spreading on fibrinogen. | 75, 84, 85 |
| SFKs | Deletion of the c-Src–docking sequence in β3 impacts platelet spreading on fibrinogen and impairs thrombus formation and stability. These mice also show increased tail bleeding. Mouse platelets deficient in c-Src display impaired spreading on fibrinogen. Some redundancy with other SFKs such as Fyn and Lyn occurs, whereas Lyn is important for thrombus formation. However, Lyn also holds a negative regulatory role in cell spreading. Loss of SFKs does not affect tail bleeding. Mutation of Tyr 747 and Tyr 759 residues in the β3-integrin tail, which are phosphorylated by SFKs, leads to unstable platelet aggregates, impaired clot retraction, and increased tail rebleeding. | 55,-57, 65, 69 |
| Syk | Impaired spreading on fibrinogen. | 55 |
| Tetraspanin CD151 | Impaired spreading on fibrinogen. Delayed clot retraction. Moderate in vivo bleeding defect. | 143 |
| Tetraspanin TSSC6 | Impaired spreading on fibrinogen. Impaired thrombus stability. Impaired clot retraction. Increased tail bleeding. | 142 |
| Vav1/3 | Impaired spreading on fibrinogen. | 77 |
| VPS33B | Impaired spreading on fibrinogen. Impaired stable thrombus formation. Impaired clot retraction. Increased tail bleeding. | 106 |
| WASP | WAS patients and WASP KO mice: Decreased spreading on fibrinogen. Impaired clot retraction. Increased tail rebleeding. | 117 |
| Negative regulators | ||
| Dok-1 | Increased spreading on fibrinogen after thrombin stimulation. Accelerated thrombus formation. Increased clot retraction. Shortened bleeding time. | 138 |
| Dok-2 | Shear-dependent increase in αIIbβ3 adhesive function with accelerated thrombus growth in vivo. | 139 |
| JAM-A | Enhanced spreading on fibrinogen. Enhanced thrombus formation. Enhanced clot retraction. Shortened tail-bleeding time. | 163 |
| Paxillin | Knock down: Increased spreading on fibrinogen. Enhanced thrombus formation. Enhanced clot retraction. Reduced tail-bleeding time. | 131 |
| SHIP1 | Conflicting reports from 2 mouse lines. One study reports enhanced spreading on fibrinogen, and enhanced adhesion and spreading on fibrinogen under flow due to enhanced stability of adhesive contacts. In contrast, another study reports defects in thrombus formation, increased tail-bleeding time, and impaired clot retraction due to a role for SHIP1 in platelet contractility and thrombus organization. | 11, 164 |
| Tetraspanin CD82 | Enhanced clot retraction. Reduced bleeding time. | 165 |
| Protein . | Knockout mouse platelet phenotype (unless otherwise stated) . | Reference . |
|---|---|---|
| Positive regulators | ||
| ADAP | Reduced attachment and spreading on fibrinogen under shear flow. Unstable thrombi. Increased tail rebleeding. | 48, 52 |
| c-Cbl | Impaired spreading on fibrinogen. Delayed clot retraction. | 98 |
| CD148 | Reduced spreading on fibrinogen. Compromised thrombus formation and stability. Increased tail bleeding. | 64 |
| Cdc42 | Conflicting reports regarding role in filopodia formation on fibrinogen. Accelerated arterial occlusive thrombus formation but prolonged bleeding times. | 113, 114 |
| CIB1 | Reduced spreading on fibrinogen. Impaired arterial occlusion associated with unstable thrombus formation. Increased tail-bleeding time. | 87, 155 |
| Dab2 | Impaired spreading on fibrinogen. Impaired thrombus formation. Impaired clot retraction. Prolonged bleeding time. | 156 |
| FAK | Impaired spreading on fibrinogen. Increased tail rebleeding. | 82 |
| Gα13 | Impaired stable thrombus formation. Increased tail-bleeding time. Contrasting reports regarding role in spreading on fibrinogen. Mutation of the Gα13-binding β3 ExE motif, or peptide-mediated inhibition of the β3-Gα13 interaction, inhibited platelet spreading on fibrinogen and thrombus formation, whereas the peptide did not affect tail bleeding. | 43, 63, 102, 157 |
| ILK | Impaired thrombus stability. Increased tail bleeding time and volume. | 135, 136 |
| Kindlin-3 | Severe bleeding during development. Loss of spreading on fibrinogen. Loss of thrombus formation. Increased tail bleeding. | 133 |
| Lnk | Impaired spreading on fibrinogen. Reduced thrombus stability. Impaired clot retraction. Increased tail bleeding. | 137 |
| PDK1 | Reduced spreading on fibrinogen. Reduced thrombus formation. Delayed clot retraction. | 101 |
| PECAM-1 | Reduced spreading on fibrinogen. Delayed clot retraction. | 158 |
| PI3Kβ | p110β KO, kinase-dead, and pharmacological inhibition: reduced spreading on fibrinogen. Almost complete inability to adhere to fibrinogen under flow. Unstable thrombi. Delayed clot retraction. No effect on rodent tail-bleeding time. | 91,-93, 95 |
| PKC | PKCθ; reduced spreading on fibrinogen yet enhanced thrombus formation due to enhanced secretion. PKCα; reduced thrombus formation due to reduced secretion. PKCβ; reduced spreading. | 78, 79, 159, 160 |
| PLCγ2 | Defective spreading on fibrinogen. | 76 |
| Pyk2 | Defective spreading on fibrinogen. Impaired thrombus formation. Slightly prolonged tail-bleeding time. | 97, 161 |
| Rac1 | Defective spreading on fibrinogen. Reduced thrombus formation and stability. Prolonged tail bleeding. | 109,-111 |
| Rasa3 | Rasa3 RapGAP activity restrains Rap1-driven cell spreading on fibrinogen. | 47 |
| RhoA | Normal extent of spreading on fibrinogen but with slightly altered morphology. Required for thrombus stability. Essential for clot retraction. Increased tail bleeding. | 102 |
| ROCK2 | Impaired thrombus formation. Prolonged tail-bleeding time. | 162 |
| SLP-76 | Fetal hemorrhage and platelet dysfunction including impaired spreading on fibrinogen. | 75, 84, 85 |
| SFKs | Deletion of the c-Src–docking sequence in β3 impacts platelet spreading on fibrinogen and impairs thrombus formation and stability. These mice also show increased tail bleeding. Mouse platelets deficient in c-Src display impaired spreading on fibrinogen. Some redundancy with other SFKs such as Fyn and Lyn occurs, whereas Lyn is important for thrombus formation. However, Lyn also holds a negative regulatory role in cell spreading. Loss of SFKs does not affect tail bleeding. Mutation of Tyr 747 and Tyr 759 residues in the β3-integrin tail, which are phosphorylated by SFKs, leads to unstable platelet aggregates, impaired clot retraction, and increased tail rebleeding. | 55,-57, 65, 69 |
| Syk | Impaired spreading on fibrinogen. | 55 |
| Tetraspanin CD151 | Impaired spreading on fibrinogen. Delayed clot retraction. Moderate in vivo bleeding defect. | 143 |
| Tetraspanin TSSC6 | Impaired spreading on fibrinogen. Impaired thrombus stability. Impaired clot retraction. Increased tail bleeding. | 142 |
| Vav1/3 | Impaired spreading on fibrinogen. | 77 |
| VPS33B | Impaired spreading on fibrinogen. Impaired stable thrombus formation. Impaired clot retraction. Increased tail bleeding. | 106 |
| WASP | WAS patients and WASP KO mice: Decreased spreading on fibrinogen. Impaired clot retraction. Increased tail rebleeding. | 117 |
| Negative regulators | ||
| Dok-1 | Increased spreading on fibrinogen after thrombin stimulation. Accelerated thrombus formation. Increased clot retraction. Shortened bleeding time. | 138 |
| Dok-2 | Shear-dependent increase in αIIbβ3 adhesive function with accelerated thrombus growth in vivo. | 139 |
| JAM-A | Enhanced spreading on fibrinogen. Enhanced thrombus formation. Enhanced clot retraction. Shortened tail-bleeding time. | 163 |
| Paxillin | Knock down: Increased spreading on fibrinogen. Enhanced thrombus formation. Enhanced clot retraction. Reduced tail-bleeding time. | 131 |
| SHIP1 | Conflicting reports from 2 mouse lines. One study reports enhanced spreading on fibrinogen, and enhanced adhesion and spreading on fibrinogen under flow due to enhanced stability of adhesive contacts. In contrast, another study reports defects in thrombus formation, increased tail-bleeding time, and impaired clot retraction due to a role for SHIP1 in platelet contractility and thrombus organization. | 11, 164 |
| Tetraspanin CD82 | Enhanced clot retraction. Reduced bleeding time. | 165 |
Presented are the phenotypes of platelets with deficiency or inhibition of a range of proteins involved in the αIIbβ3 outside-in signaling pathway, with a focus on the key outside-in driven processes of platelet spreading, stable thrombus formation, and clot retraction. Bleeding is also included for consideration of whether proteins may be potential candidates for the therapeutic targeting of the αIIbβ3 outside-in signaling pathway to prevent unwanted thrombosis, while avoiding unwanted bleeding.
JAM-A, junctional adhesion molecule-A; PECAM-1, platelet endothelial cell adhesion molecule-1.