FUNCTIONAL PARTITIONING OF BETA-1 INTEGRINS REVEALED BY ACTIVATING AND INHIBITORY MABS

Integrins exist in different activation states on the surfaces of cell s, Addition of the proper signal, ligand, or antibody can alter the ac tivation state of these molecules, We report here the identification o f two immunocytochemically distinct populations of beta(1) integrins o n fixed embryonic chick dermal fibroblasts. One population, recognized by the integrin activating mAb TASC, localizes to discrete regions of the cell, most likely focal contacts. These integrins co-localize wit h other proteins, such as vinculin and F-actin, and their retention at these sites is dependent on the actin cytoskeleton. The other populat ion, identified with the inhibitory mAb W1B10, is more evenly distribu ted throughout the cell surface, and its pattern remains unchanged aft er disruption of the actin cytoskeleton, Double labeling experiments u sing Fab fragments of TASC alongside whole W1B10 IgG revealed non-over lapping staining patterns, These results show that it is possible to v isualize and study discrete populations of integrins on cell surfaces using two different antibodies, We hypothesize that these antibodies r eport differences in the distribution of receptors in two different st ates, A model is proposed describing the ligand independent recruitmen t of integrins based on these findings and results from other labs.