MODULATION OF CELL-MIGRATION BY INTEGRIN-MEDIATED CYTOSKELETAL LINKAGES AND LIGAND-BINDING AFFINITY

Integrin cell surface adhesion receptors play a central role in mediat ing cell migration. We have developed a model system consisting of CHO cells ectopically expressing the alpha IIb beta 3 integrin to study i ntegrin affinity and cytoskeletal interactions during cell migration. The alpha IIb beta 3 integrins are suited for study of integrin recept ors during cell migration because they are well characterized with res pect to ligand binding, cytoskeletal interactions, and signal transduc tion, and mutants with altered receptor function are available. The al pha IIb beta 3 receptor specifically mediates migration of alpha IIb b eta 3-transfected CHO cells. The migration of transfected CHO cells wa s studied on a fibrinogen substrate both by time lapse videomicroscopy and by random and haptotactic transwell assays. Haptotactic and rando m transwell assays measured distinct aspects of migration, with the ra ndom transwell assay correlating most closely with time lapse videomic roscopy. Mutations in the cytoplasmic domains that increase ligand aff inity or activation of the alpha IIb beta 3 receptor into a high affin ity state by the LIBS6 antibody decreased the migration rate. Likewise , mutations that increase cytoskeletal organization without affecting affinity also decreased the migration rate. In contrast, truncation of the beta chain, which alters cytoskeletal associations as assayed by absence of focal adhesions, decreased haptotactic migration while incr easing random migration. These effects on the migration rate were part ially compensated for by altering substrate concentration, demonstrati ng optimum substrate concentrations that supported maximal migration. For example, cells expressing integrins locked in the high affinity st ate showed maximal migration at lower substrate concentrations than ce lls expressing low affinity receptor. Together, these results implicat e the strength of adhesion between cell and substrate, as modulated by receptor affinity, organization of adhesive complexes, and substrate concentration, as important regulators of cell migration rate. Further , we demonstrate a dominant effect of high affinity integrin in inhibi ting migration regardless of the organization of adhesive complexes. T hese observations have potential implications for tumor metastasis and its therapy.