Affinity and Avidity of the LFA-1 Integrin is Regulated by Phosphorylation

Academic Dissertation To be present for public criticism, with the permission of 1. LEUKOCYTE FUNCTION-ASSOCIATED ANTIGEN-1 1.1 Introduction 9 1.2 LFA-1 binds to ICAMs 10 1.3 Biology of LFA-1 11 LFA-1 is involved in several fundamental biological processes 11 Leukocyte adhesion deficiency and LFA-1-deficient mice 13 1.4 LFA-1 as a signalling receptor 14 Two-way signalling through LFA-1 14 Intracellular signalling controlling LFA-1 activation 15 2. INTEGRIN STRUCTURE AND AFFINITY CHANGES 2.1 Structure of the integrin ectodomain 17 The α-subunit 17 The β-subunit 18 2.2 Structure of the cytoplasmic tails 19 2.3. Models for LFA-1 ligand binding and activation 21 Structural basis of LFA-1 ligand-binding 21 Global conformational changes in the integrin ectodomain 23 3. CYTOPLASMIC DOMAINS AND REGULATION OF AVIDITY 3.1. Important motifs in the integrin cytoplasmic tails 24 3.2. LFA-1 interacts with a variety of intracellular proteins 26 Actin-binding proteins 26 Cell signalling proteins 28 3.3. Regulation of avidity 29 4. PHOSPHORYLATION OF THE INTEGRIN CYTOPLASMIC TAILS 4.1 Integrin β-chain phosphorylation 30 Serine/threonine phosphorylation 30 Tyrosine phosphorylation 32 4.2. Integrin α-chain phosphorylation 33 SUMMARY OF THE STUDY 5. AIMS OF THE STUDY 35 6. EXPERIMENTAL PROCEDURES 36 7. RESULTS 7.1. The role of the tyrosine kinase Lck in the regulation of the LFA-1 activation in human T lymphocyte 37 7.2. Characteristics of LFA-1 β chain phosphorylation 37 7.3. Identification of the phosphorylation site and stoichiometry in the αL chain 38 7.4. LFA-1 phosphorylation in the regulation of integrin activation 39 8. DISCUSSION 8.1. Lck is important for activation of LFA-1 41 8.2. Threonine phosphorylation of the β2 chain regulates LFA-1 activation through affinity-independent mechanisms 42 8.3. Serine phosphorylation of αL regulates LFA-1 activation through affinity-dependent mechanisms 44 CONCLUDING REMARKS 46 ACKNOWLEDGEMENTS 47