Degradation of Internalized αvβ5 Integrin Is Controlled by uPAR Bound uPA: Effect on β1 Integrin Activity and α-SMA Stress Fiber Assembly

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 b5 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.