Mutational evidence for control of cell adhesion through integrin diffusion/clustering, independent of ligand binding.
Previous studies have shown that integrin alpha chain tails make strong positive contributions to integrin-mediated cell adhesion. We now show here that integrin alpha4 tail deletion markedly impairs static cell adhesion by a mechanism that does not involve altered binding of soluble vascular cell adhesion molecule 1 ligand. Instead, truncation of the alpha4 cytoplasmic domain caused a severe deficiency in integrin accumulation into cell surface clusters, as induced by ligand and/ or antibodies. Furthermore, alpha4 tail deletion also significantly decreased the membrane diffusivity of alpha4beta1, as determined by a single particle tracking technique. Notably, low doses of cytochalasin D partially restored the deficiency in cell adhesion seen upon alpha4 tail deletion. Together, these results suggest that alpha4 tail deletion exposes the beta1 cytoplasmic domain, leading to cytoskeletal associations that apparently restrict integrin lateral diffusion and accumulation into clusters, thus causing reduced static cell adhesion. Our demonstration of integrin adhesive activity regulated through receptor diffusion/clustering (rather than through altered ligand binding affinity) may be highly relevant towards the understanding of inside-out signaling mechanisms for beta1 integrins.
Yauch
R L
RL
Division of Tumor Virology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA.
Felsenfeld
D P
DP
Kraeft
S K
SK
Chen
L B
LB
Sheetz
M P
MP
Hemler
M E
ME
D000818:Animals; D016466:CHO Cells; D002448:Cell Adhesion / Q000235:genetics; D006224:Cricetinae; D000939:Epitopes / Q000096:biosynthesis; D006801:Humans; D039041:Integrin alpha4beta1; D016023:Integrins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D004915:Leukemia, Erythroblastic, Acute; D008024:Ligands; D008345:Manganese; D016296:Mutagenesis; D011485:Protein Binding / Q000235:genetics; D011487:Protein Conformation; D016201:Receptors, Lymphocyte Homing / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016029:Receptors, Very Late Antigen / Q000187:drug effects; D017384:Sequence Deletion; D019810:Sodium Azide; D014162:Transfection; D014407:Tumor Cells, Cultured; D019010:Vascular Cell Adhesion Molecule-1 / Q000378:metabolism
D000939:Epitopes; D039041:Integrin alpha4beta1; D016023:Integrins; D008024:Ligands; D016201:Receptors, Lymphocyte Homing; D016029:Receptors, Very Late Antigen; D019010:Vascular Cell Adhesion Molecule-1; D008345:Manganese; D019810:Sodium Azide