title: Ligand density dramatically affects integrin alpha IIb beta 3-mediated platelet signaling and spreading.
abstract: The impact of ligand density on integrin-mediated cell adhesion and outside-in signaling is not well understood. Using total internal reflection fluorescent microscopy, conformation-specific antibodies, and Ca(2+) flux measurements, we found that the surface density of fibrinogen affects alpha II b beta 3-mediated platelet signaling, adhesion, and spreading. Adhesion to fibrinogen immobilized at low density leads to rapid increases in cytosolic Ca(2+) and sequential formation of filopodia and lamellipodia. In contrast, adhesion to high-density fibrinogen results in transient or no increases in Ca(2+) and simultaneous formation of filopodia and lamellipodia. alpha II b beta 3 receptors at the basal surface of platelets engage fibrinogen in a ringlike pattern at the cell edges under both conditions. This engagement is, however, more dynamic and easily reversed on high-density fibrinogen. Src and Rac activity and actin polymerization are important for adhesion to low-density fibrinogen, whereas PKC/PI3 kinases contribute to platelet spreading on high-density fibrinogen. We conclude that 2 fundamentally different signaling mechanisms can be initiated by a single integrin receptor interacting with the same ligand when it is immobilized at different densities.
authors.affiliation: Laboratory of Blood and Vascular Biology, Rockefeller University, New York, NY 10021, USA. marketa@rockefeller.edu
authors.forename: Markéta
authors.initials: M
authors.lastname: Jirousková
authors.forename: Jyoti K
authors.initials: JK
authors.lastname: Jaiswal
authors.forename: Barry S
authors.initials: BS
authors.lastname: Coller
mesh_terms: D001792:Blood Platelets / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D020013:Calcium Signaling; D048430:Cell Shape; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005340:Fibrinogen / Q000494:pharmacology*; D006801:Humans; D008024:Ligands; D010973:Platelet Adhesiveness; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000187:drug effects / Q000502:physiology*; D011554:Pseudopodia / Q000187:drug effects; D015398:Signal Transduction
chemical_list: D008024:Ligands; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D005340:Fibrinogen