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Abstract
The β3 cytoplasmic domain of the αvβ3 integrin is essential for intracellular signals required for cytoskeletal rearrangements. Expression of β3Ser752Pro mutation in heterologous cells profoundly affects cell spreading and β3 localization into focal contacts. However, the β3Ser752A1a substitution mostly restores normal integrin functions, suggesting that the presence of Pro is responsible for the receptor's loss of function. To further assess the role of the Ser752 of the β3 cytoplasmic domain in the cytoskeletal organization of adherent cells, we developed a computer-assisted method of image analysis allowing the automatic classification of spread cells according to the quantitative analysis of their cell morphology. We compared adhesion and spreading to von Willebrand factor (vWF) or fibrinogen (Fg) of cells expressing β3 wild type, β3Ser752Pro or β3Ser752A1a mutated integrin subunit as a chimeric αvβ3 receptor. The β3Ser752A1a substitution did not impair the general ability of cells to spread, but resulted in a delayed and reduced spreading on both vWF and Fg. Moreover, the β3Ser752A1a mutation produced modifications of the morphology of spread cells, suggesting a disorganization of their cytoskeleton. Attachment studies showed that the β3Ser752A1a mutation did not modify the capacity of cells to attach to the substrate, indicating no change in the ligand binding affinity of the αvβ3 integrin. Furthermore, we identified a slight defect of β3Ser752Pro cell attachment to vWF and Fg, beside their impairment of spreading. Taken together, these results suggest a role of Ser752 of the β3 cytoplasmic domain in the optimal cytoskeletal organization of adherent cells.