Project 1: Integrins are a family of ubiquitous transmembrane heterodimers that mediate fundamental processes requiring cell-matrix and cell-cell interactions and reside on cell surfaces in an equilibrium between resting inactive molecules and active ligand-binding molecules. Like other proteins, integrins are "soft" amino acid polymers that continuously sample ensembles of conformational states. Conversion from their resting to active states occurs when allosteric modulators such the divalent cation Mn[2+] or the cytoskeletal protein talin shift the distribution of conformations from one pre-existing population to another. The resting integrin conformation is enforced by non-convalent interactions involving their membraneproximal cytoplasmic, transmembrane, and juxtamembrane extracellular domains;these interactions are disrupted when an integrin shifts to its active conformation. This project is focused on the platelet integrin allbB3 , a receptor for macromolecular ligands such as fibrinogen and von Willebr and factor (VWF) following platelet stimulation. Binding of these ligands to allbp3 is responsible for platelet aggregation and is a critical step in the formation of hemostatic platelet plugs and pathologic arterial thrombi. The overall goals of the project are gain a thermodynamic understanding of allbp3 regulation and to use this understanding to develop novel allosteric modulators to attenuate allbp3 function.
In Aim 1, we will generate a thermodynamic model for allbp3 activation, testing the hypothesis that topographically-distinct interactions between allb and B3 differentially regulate allbp3 activation. The relative contribution of the membrane-proximal cytoplasmic, transmembrane, and juxtamembrane extracellular domains of allb or B3 to maintaining allbB3 in its resting conformation will be quantitated using a novel AraC-based bacterial transcriptional reporter system, as well as optical tweezers-based force spectroscopy. The data will be used to derive a thermodynamic model of allbB3 activation. Chemical libraries and molecular databases will then be screened for potential allbB3 inhibitors that bind to the relevant extracellular hot spot regions of either allb or B3.
In Aim 2, we will use soluble anti-transmembrane domain peptides to modify the activation state of individual allbB3 molecules in situ. By destabilizing the allbB3 heterodimer, we found that an anti-allb transmembrane domain peptide causes ligand binding-independent transactivation of B3-bound c-Src, implying that allbB3 activation alone is sufficient to cause rapid allbB3 oligomerization. Conversely, by stabilizing the allbB3 heterodimer, transmembrane-domain targeted peptides would act as novel allbB3 antagonists. Thus, we propose using computational methods to design peptides that stabilize the allbB3 TM domain heterodimer, preventing allbB3 activation and serving as lead compounds for the development of novel antithrombotic agents.

Public Health Relevance

Fibrinogen and von Willebr and factor binding to the active form of the integrin allbB3 is responsible for the platelet stickiness that quenches bleeding after trauma and causes the thrombi that complicate atherosclerosis. However, current intravenous allbB3 inhibitors have limited clinical applicability and oral inhibitors were associated with excess mortality. The goals of this project are to determine how platelets regulate allbB3 function and to use this information to design novel, effective, and safer allbB3 inhibitors.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Program Projects (P01)
Project #
Application #
Study Section
Heart, Lung, and Blood Initial Review Group (HLBP)
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Pennsylvania
United States
Zip Code
Tomaiuolo, Maurizio; Stalker, Timothy J; Welsh, John D et al. (2014) A systems approach to hemostasis: 2. Computational analysis of molecular transport in the thrombus microenvironment. Blood 124:1816-23
Welsh, John D; Stalker, Timothy J; Voronov, Roman et al. (2014) A systems approach to hemostasis: 1. The interdependence of thrombus architecture and agonist movements in the gaps between platelets. Blood 124:1808-15
Lian, Lurong; Suzuki, Aae; Hayes, Vincent et al. (2014) Loss of ATE1-mediated arginylation leads to impaired platelet myosin phosphorylation, clot retraction, and in vivo thrombosis formation. Haematologica 99:554-60
Stalker, Timothy J; Welsh, John D; Tomaiuolo, Maurizio et al. (2014) A systems approach to hemostasis: 3. Thrombus consolidation regulates intrathrombus solute transport and local thrombin activity. Blood 124:1824-31
Stalker, Timothy J; Welsh, John D; Brass, Lawrence F (2014) Shaping the platelet response to vascular injury. Curr Opin Hematol 21:410-7
Kowalska, M Anna; Zhao, Guohua; Zhai, Li et al. (2014) Modulation of protein C activation by histones, platelet factor 4, and heparinoids: new insights into activated protein C formation. Arterioscler Thromb Vasc Biol 34:120-6
Min, Sang H; Suzuki, Aae; Stalker, Timothy J et al. (2014) Loss of PIKfyve in platelets causes a lysosomal disease leading to inflammation and thrombosis in mice. Nat Commun 5:4691
Brass, Lawrence F; Tomaiuolo, Maurizio; Stalker, Timothy J (2013) Harnessing the platelet signaling network to produce an optimal hemostatic response. Hematol Oncol Clin North Am 27:381-409
Lu, Qiongyu; Dong, Ningzheng; Wang, Qi et al. (2013) Increased levels of plasma soluble Sema4D in patients with heart failure. PLoS One 8:e64265
Stalker, Timothy J; Traxler, Elizabeth A; Wu, Jie et al. (2013) Hierarchical organization in the hemostatic response and its relationship to the platelet-signaling network. Blood 121:1875-85

Showing the most recent 10 out of 238 publications