BADERC- M. Amin Arnaout

M. Amin Arnaout, M.D.

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.

References:

1. Michishita, M., Videm, V. and Arnaout, M.A. A novel divalent cation-binding site in the A-domain of the b2 integrin CR3 (CD11b/CD18) is essential for ligand binding. 1993, Cell 72:857-867.

2. Lee, J-O., Rieu, P., Arnaout, M.A. (Corresp. Author), Liddington, R. Crystal structure of the A-domain of the a-subunit of integrin CR3 (CD11b/CD18). 1995. Cell; 80:631-638.

3. Lee, J-O, Arnaout, M. A. (Corresp. Author), Liddington, R. Two conformations of the integrin A-domain (I-domain): a pathway for activation? Structure, 1995, 3:1333-1340.

4. Rui. L., Rieu, P., Griffith, D.L, Scott, D and Arnaout, M.A. Two functional states of the CD11b A-domain: Correlations with key features of two Mn²⁺-complexed crystal structures. 1998. J. Cell Biol. 143:1-12.

5. Xiong J-P, Li R, Essafi M, Stehle T, and Arnaout, MA. An isoleucine-based allosteric switch controls affinity and shape shifting in integrin CD11b A-domain. J. Biol. Chem. (Accelerated Publication) Electronic Pub. Date Oct. 16, 2000.

6. Xiong, J.P., Stehle, S., Diefenbach, B., Zhang, R., Dunker, R., Scott, D.L., Joachimiak, A., Goodman, S.L., and Arnaout, M.A. 2001. Crystal Structure of the Extracellular Segment of Integrin aVb3. Science. Published online September 6, 2001; 10.1126/science.1064535 (Science Express). 294(5541):339-45.

7. 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. Apr 5;296 (5565):151-155. (Published online ahead of print on March 7, 2002).

8. Alonso, J.L., Essafi, M., Xiong, J.-P., Stehle, T., and Arnaout, M.A. 2002. Does the integrin aA domain act as a ligand for its bA domain? Current Biology. 2002 May

9. Arnaout MA, Goodman SL, Xiong JP. Coming to grips with integrin binding to ligands. Curr Opin Cell Biol. 2002 Oct; 14(5):641-51.

10. Xiong JP, Stehle T, Goodman SL, Arnaout MA. New insights into the structural basis of Integrin activation. Blood. 2003 102:1155-9

11. 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.






			M. Amin Arnaout, M.D. 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. References: 1. Michishita, M., Videm, V. and Arnaout, M.A. A novel divalent cation-binding site in the A-domain of the b2 integrin CR3 (CD11b/CD18) is essential for ligand binding. 1993, Cell 72:857-867. 2. Lee, J-O., Rieu, P., Arnaout, M.A. (Corresp. Author), Liddington, R. Crystal structure of the A-domain of the a-subunit of integrin CR3 (CD11b/CD18). 1995. Cell; 80:631-638. 3. Lee, J-O, Arnaout, M. A. (Corresp. Author), Liddington, R. Two conformations of the integrin A-domain (I-domain): a pathway for activation? Structure, 1995, 3:1333-1340. 4. Rui. L., Rieu, P., Griffith, D.L, Scott, D and Arnaout, M.A. Two functional states of the CD11b A-domain: Correlations with key features of two Mn²⁺-complexed crystal structures. 1998. J. Cell Biol. 143:1-12. 5. Xiong J-P, Li R, Essafi M, Stehle T, and Arnaout, MA. An isoleucine-based allosteric switch controls affinity and shape shifting in integrin CD11b A-domain. J. Biol. Chem. (Accelerated Publication) Electronic Pub. Date Oct. 16, 2000. 6. Xiong, J.P., Stehle, S., Diefenbach, B., Zhang, R., Dunker, R., Scott, D.L., Joachimiak, A., Goodman, S.L., and Arnaout, M.A. 2001. Crystal Structure of the Extracellular Segment of Integrin aVb3. Science. Published online September 6, 2001; 10.1126/science.1064535 (Science Express). 294(5541):339-45. 7. 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. Apr 5;296 (5565):151-155. (Published online ahead of print on March 7, 2002). 8. Alonso, J.L., Essafi, M., Xiong, J.-P., Stehle, T., and Arnaout, M.A. 2002. Does the integrin aA domain act as a ligand for its bA domain? Current Biology. 2002 May 9. Arnaout MA, Goodman SL, Xiong JP. Coming to grips with integrin binding to ligands. Curr Opin Cell Biol. 2002 Oct; 14(5):641-51. 10. Xiong JP, Stehle T, Goodman SL, Arnaout MA. New insights into the structural basis of Integrin activation. Blood. 2003 102:1155-9 11. 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.