title: Constitutive and UV-induced fibronectin degradation is a ubiquitination-dependent process controlled by beta-TrCP.
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.
authors.affiliation: Department of Molecular Pharmacology and Biological Chemistry, Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, Illinois 60611, USA. dipankar-ray@northwestern.edu
authors.forename: Dipankar
authors.initials: D
authors.lastname: Ray
authors.forename: Evan C
authors.initials: EC
authors.lastname: Osmundson
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kiyokawa
mesh_terms: D000818:Animals; D051242:Caveolin 1 / Q000737:chemistry; D045744:Cell Line, Tumor; D005353:Fibronectins / Q000737:chemistry / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008247:Lysosomes / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D011499:Protein Processing, Post-Translational; D051381:Rats; D025801:Ubiquitin / Q000737:chemistry*; D014466:Ultraviolet Rays; D044844:beta-Transducin Repeat-Containing Proteins / Q000737:chemistry*
chemical_list: D051242:Caveolin 1; D005353:Fibronectins; D025801:Ubiquitin; D044844:beta-Transducin Repeat-Containing Proteins