Initiation of attachment and generation of mature focal adhesions by integrin-containing filopodia in cell spreading.
Integrin receptors, and associated cytoplasmic proteins mediate adhesion, cell signaling and connections to the cytoskeleton. Using fluorescent protein chimeras, we analyzed initial integrin adhesion in spreading fibroblasts with Total Internal Reflection Fluorescence (TIRF) microscopy. Surprisingly, sequential radial projection of integrin and actin containing filopodia formed the initial cell-matrix contacts. These Cdc42-dependent, integrin-containing projections recruited cytoplasmic focal adhesion (FA) proteins in a hierarchical manner; initially talin with integrin and subsequently FAK and paxillin. Radial FA structures then anchored cortical actin bridges between them and subsequently cells reorganized their actin, a process promoted by Src, and characterized by lateral FA reorientation to provide anchor points for actin stress fibers. Finally, the nascent adhesions coalesced until they formed mature FAs.
Partridge
Michael A
MA
Department of Pathology and Cell Biology, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA.
Marcantonio
Eugene E
EE
D000199:Actins / Q000378:metabolism; D000818:Animals; D002448:Cell Adhesion; D005109:Extracellular Matrix / Q000378:metabolism; D051417:Focal Adhesion Kinase 1 / Q000378:metabolism*; D022001:Focal Adhesions / Q000502:physiology*; D016023:Integrins / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence / Q000379:methods; D041681:NIH 3T3 Cells; D051419:Paxillin / Q000378:metabolism; D011554:Pseudopodia / Q000378:metabolism*; D016608:Talin / Q000378:metabolism; D014162:Transfection; D020764:cdc42 GTP-Binding Protein / Q000502:physiology; D019061:src-Family Kinases / Q000502:physiology
D000199:Actins; D016023:Integrins; D051419:Paxillin; D016608:Talin; D051417:Focal Adhesion Kinase 1; C496051:Ptk2 protein, mouse; D019061:src-Family Kinases; D020764:cdc42 GTP-Binding Protein