Effects of I domain deletion on the function of the beta2 integrin lymphocyte function-associated antigen-1.
A subset of integrin alpha subunits contain an I domain, which is important for ligand binding. We have deleted the I domain from the beta2 integrin lymphocyte function-asssociated antigen-1 (LFA-1) and expressed the resulting non-I domain-containing integrin (DeltaI-LFA-1) in an LFA-1-deficient T cell line. DeltaI-LFA-1 showed no recognition of LFA-1 ligands, confirming the essential role of the I domain in ligand binding. Except for I domain monoclonal antibodies (mAbs), DeltaI-LFA-1 was recognized by a panel of anti-LFA-1 mAbs similarly to wild-type LFA-1. However, DeltaI-LFA-1 had enhanced expression of seven mAb epitopes that are associated with beta2 integrin activation, suggesting that it exhibited an "active" conformation. In keeping with this characteristic, DeltaI-LFA-1 induced constitutive activation of alpha4beta1 and alpha5beta1, suggesting intracellular signaling to these integrins. This "cross-talk" was not due to an effect on beta1 integrin affinity. However, the enhanced activity was susceptible to inhibition by cytochalasin D, indicating a role for the cytoskeleton, and also correlated with clustering of beta1 integrins. Thus, removal of the I domain from LFA-1 created an integrin with the hallmarks of a constitutively active receptor mediating signals into the cell. These findings suggest a key role for the I domain in controlling integrin activity.
Leitinger
B
B
Leukocyte Adhesion Laboratory, Imperial Cancer Research Fund, London WC2A 3PX, United Kingdom. b.leitinger@icrf.icnet.uk
Hogg
N
N
D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology; D018821:CD18 Antigens / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D002448:Cell Adhesion / Q000187:drug effects; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D000939:Epitopes / Q000276:immunology; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D039041:Integrin alpha4beta1; D016023:Integrins / Q000378:metabolism; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D019169:Jurkat Cells; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1 / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000502:physiology; D011940:Receptor Aggregation; D017469:Receptors, Fibronectin / Q000378:metabolism; D016201:Receptors, Lymphocyte Homing / Q000378:metabolism; D017384:Sequence Deletion / Q000235:genetics*; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection; D015854:Up-Regulation / Q000187:drug effects; D019010:Vascular Cell Adhesion Molecule-1 / Q000378:metabolism
D000911:Antibodies, Monoclonal; D018821:CD18 Antigens; D000939:Epitopes; D005353:Fibronectins; D039041:Integrin alpha4beta1; D016023:Integrins; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1; D017469:Receptors, Fibronectin; D016201:Receptors, Lymphocyte Homing; D019010:Vascular Cell Adhesion Molecule-1; D018799:Intercellular Adhesion Molecule-1; D015638:Cytochalasin D