Degradation of Internalized [alpha]v[beta]5 Integrin Is Controlled by uPAR Bound uPA: Effect on [beta]1 Integrin Activity and [alpha]-SMA Stress Fiber Assembly

• Published in: PloS one 2012-03, Vol.7 (3), p.e33915
• Main Authors: Wang, Lingyan, Pedroja, Benjamin S, Meyers, Erin E, Garcia, Angelo L, Twining, Sally S, Bernstein, Audrey M
• Format: Article
• Language: English
• Subjects: Collagen; Integrins; Transforming growth factors; Ubiquitin
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0033915

Myofibroblasts (Mfs) that persist in a healing wound promote extracellular matrix (ECM) accumulation and excessive tissue contraction. Increased levels of integrin [alpha]v[beta]5 promote the Mf phenotype and other fibrotic markers. Previously we reported that maintaining uPA (urokinase plasminogen activator) bound to its cell-surface receptor, uPAR prevented TGF[beta]-induced Mf differentiation. We now demonstrate that uPA/uPAR controls integrin [beta]5 protein levels and in turn, the Mf phenotype. When cell-surface uPA was increased, integrin [beta]5 levels were reduced (61%). In contrast, when uPA/uPAR was silenced, integrin [beta]5 total and cell-surface levels were increased (2-4 fold). Integrin [beta]5 accumulation resulted from a significant decrease in [beta]5 ubiquitination leading to a decrease in the degradation rate of internalized [beta]5. uPA-silencing also induced [alpha]-SMA stress fiber organization in cells that were seeded on collagen, increased cell area (1.7 fold), and increased integrin [beta]1 binding to the collagen matrix, with reduced activation of [beta]1. Elevated cell-surface integrin [beta]5 was necessary for these changes after uPA-silencing since blocking [alpha]v[beta]5 function reversed these effects. Our data support a novel mechanism by which downregulation of uPA/uPAR results in increased integrin [alpha]v[beta]5 cell-surface protein levels that regulate the activity of [beta]1 integrins, promoting characteristics of the persistent Mf.