The Molecular Basis of Integrin Function
A major research focus of my laboratory is the dissection of the role of leukocyte integrins in inflammation, and an elucidation of the mechanisms that regulate the functions of these adhesion receptors in health and disease. Leukocyte integrins play pivotal roles in mediating the extravasation and homing of leukocytes under normal conditions, as part of immunosurveilance and host defense. The improper production/release of inflammatory mediators can change the kinetics of extravasation and/or misdirect normal homing, leading to the initiation and/or propagation of tissue injury. The proinflammatory profile that exists in diabetes is multifactorial, but includes upregulation of integrins and modifications of the endothelial cell phenotype favoring pathologic adhesion to leukocytes. In this pathologic condition, leukocyte integrins switch from low to high affinity states leading to tissue injury.
The dynamic nature of integrin-mediated cell migration necessitates that these receptors be able to rapidly and reversibly alter their affinity to ligands. The basic mechanisms that underlie affinity switching in integrins are poorly understood both at a cell signaling level as well as at a structural level. Deletions of integrin cytoplasmic tails alter the affinity state of integrins, suggesting that intracellular interactions are directly involved in modulating extracellular integrin-ligand interactions. In addition, ligation of integrins by ligands elicits downstream signaling events that regulate cell growth, differentiation, mobility and fate. The nature of these inside-out and outside-in signals remains obscure. Using genetic, molecular and structural biology approaches, our goal is to define the structural basis of affinity switching in integrins, elucidate the intracellular pathways that regulate these receptors and that mediate their downstream effects.
1. Xiong, J.P., Stehle, Zhang, R., Joachimiak, A., Frech, M., Goodman, S.L., and Arnaout, M.A. Crystal Structure of the Extracellular Domain of Integrin aVb3 in complex with an Arg-Gly-Asp ligand. 2002. Science.;296:151-155.
2. Arnaout MA, Goodman SL, Xiong JP. Coming to grips with integrin binding to ligands. Curr Opin Cell Biol. 2002 Oct; 14(5):641-51.
3. Xiong JP, Stehle T, Goodman SL, Arnaout MA. New insights into the structural basis of Integrin activation. Blood. 2003 102:1155-9
4. Ajroud K, Sugimori T, Goldmann WH, Fathallah DM, Xiong JP, Arnaout MA. Binding Affinity of Metal Ions to the CD11b A-domain Is Regulated by Integrin Activation and Ligands. J Biol Chem. 2004;279:25483-8.
5. Gupta V, Lindroos A, Sugimori T, Ianakiev P, Xiong JP and Arnaout MA. The b-tail domain (bTD) regulates physiologic ligand binding to integrin CD11b/CD18. 2006. Blood Apr 15;109(8):3513-20. Epub 2006 Dec 14.
6. Gupta V, Alonso, JL, Sugimori,, T, Xiong, JP and Arnaout MA. Role of the b-Subunit Arginine/Lysine Finger in Integrin Heterodimer Formation and Function. 2007. J Immunol. 180:1713-8. PMCID:
7. Jian-Ping Xiong, Bhuvaneshwari Mahalingham, Jose Luis Alonso, Laura Ann Borrelli, Xianliang Rui, Saurabh Anand, Bradley T. Hyman, Thomas Rysiok, Dirk Müller-Pompalla, Simon L. Goodman, M. Amin Arnaout. Crystal structure of the complete integrin αVβ3 ectodomain plus an α/β transmembrane fragment. J Cell Biol. 2009; 186(4): 589–600. PMCID: PMC2733745
8. Bhuvaneshwari Mahalingam, Kaouther Ajroud, Jose Luis Alonso, Saurabh Anand, Brian Adair, Alberto L Horenstein, Fabio Malavasi, Jian-Ping Xiong, M. Amin Arnaout. Stable coordination of the inhibitory Ca2+ ion at MIDAS in integrin CD11b/CD18 by an antibody-derived ligand aspartate: Implications for integrin regulation and structure-based drug design. J Immunol. 2011; 187(12): 6393–6401. PMCID: PMC3237904
9. Van Agthoven JF, Xiong JP, Alonso JL, Rui X, Adair BD, Goodman SL, Arnaout MA. Structural basis for pure antagonism of integrin αVβ3 by a high-affinity form of fibronectin. Nat Struct Mol Biol. 2014 Apr;21(4):383-8. PMID:24658351