Abstract
Loss of fibronectin (FN) assembly in the extracellular matrix has long been recognized as a feature of cellular transformation. However, such assembly is regulated not only by FN synthesis but also by its post-translational modifications. The mechanism controlling FN protein stability has remained unclear so far. Recently it was demonstrated that FN matrix turnover occurs intracellularly at the lysosome following caveolin-1-dependent endocytosis. Although FN was reported to undergo ubiquitindependent degradation, the ubiquitin ligase responsible for FN ubiquitination is unknown. In this study, we have identified beta-TrCP as the ubiquitin ligase for lysosomal degradation of FN. We found two conserved beta-TrCP recognition motif (DSGVVYS and DSGSIVVS) in the primary amino acid sequence of human, mouse, and rat FN. Down-regulation of either beta-TrCP1 or beta-TrCP2 by small interference (siRNA) caused significant accumulation of FN. Immunolocalization studies showed intracellular accumulation of FN in beta-TrCP siRNA-treated cells without showing much alteration in its matrix association. We also observed that exposure of cells to UV irradiation effectively down-regulated FN following increased ubiquitination, which was significantly inhibited either by lysosomal inhibitor or by siRNA-mediated down-regulation of beta-TrCP. Taken together, constitutive FN degradation, as well as UV-induced degradation, is ubiquitination dependent and controlled by beta-TrCP.
Highlights
Fibronectin (FN),2 a matrix glycoprotein, plays important roles in cell adhesion, migration, growth, and differentiation [1]
UV-mediated Degradation of Fibronectin Is Mediated by Lysosomes—As it was previously demonstrated that FN undergoes continuous turnover through a lysosome-dependent pathway, we examined whether UV-dependent FN down-regulation was mediated by either lysosomal or proteasomal degradation
FN matrix polymerization is a key regulator of extracellular matrix (ECM) remodeling [26]
Summary
Fibronectin (FN),2 a matrix glycoprotein, plays important roles in cell adhesion, migration, growth, and differentiation [1]. Immunolocalization studies showed intracellular accumulation of FN in -TrCP siRNA-treated cells without showing much alteration in its matrix association. We observed that exposure of cells to UV irradiation effectively down-regulated FN following increased ubiquitination, which was significantly inhibited either by lysosomal inhibitor or by siRNA-mediated down-regulation of -TrCP.
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