Cell spreading was controlled independently of the amount and density of immobilized integrin ligand by culturing cells on single adhesive islands of different sizes (100-2500 mum(2)) and shapes (squares, circles, and lines) or on many smaller (3-5 mum diameter) circular islands that were coated with a saturating density of fibronectin and separated by non-adhesive regions. The amount of focal adhesions (FAs) containing vinculin and phosphotyrosine increased in direct proportion to cell spreading under all conditions. FAs localized asymmetrically along the periphery of the small islands that experienced highest tensional stress, and FA staining increased when cytoskeletal tension was stimulated with thrombin, whereas inhibitors of contractility promoted FA disassembly. Thus, these findings demonstrate the existence of an "inside-out" mechanism whereby global cell distortion produces increases in cytoskeletal tension that feed back to drive local changes in FA assembly. This complex interplay between cell morphology, mechanics, and adhesion may be critical to how cells integrate from and function in living tissues. (C) 2003 Elsevier Inc. All rights reserved.