title: Low density lipoprotein receptor-related protein-1 promotes beta1 integrin maturation and transport to the cell surface.
abstract: Low density lipoprotein receptor-related protein-1 (LRP-1) mediates the endocytosis of multiple plasma membrane proteins and thereby models the composition of the cell surface. LRP-1 also functions as a catabolic receptor for fibronectin, limiting fibronectin accumulation in association with cells. The goal of the present study was to determine whether LRP-1 regulates cell surface levels of the beta(1) integrin subunit. We hypothesized that LRP-1 may down-regulate cell surface beta(1) by promoting its internalization; however, unexpectedly, LRP-1 expression was associated with a substantial increase in cell surface beta(1) integrin in two separate cell lines, murine embryonic fibroblasts (MEFs) and CHO cells. The total amount of beta(1) integrin was unchanged because LRP-1-deficient cells retained increased amounts of beta(1) in the endoplasmic reticulum (ER). Expression of human LRP-1 in LRP-1-deficient MEFs reversed the shift in subcellular beta(1) integrin distribution. Metabolic labeling experiments demonstrated that the precursor form of newly synthesized beta(1) integrin (p105) is converted into mature beta(1) (p125) more slowly in LRP-1-deficient cells. Although low levels of cell surface beta(1) integrin, in LRP-1-deficient MEFs, were associated with decreased adhesion to fibronectin, the subcellular distribution of beta(1) integrin was most profoundly dependent on LRP-1 only after the cell cultures became confluent. A mutagen-treated CHO cell line, in which LRP-1 is expressed but retained in the secretory pathway, also demonstrated nearly complete ER retention of beta(1) integrin. These studies support a model in which LRP-1 either directly or indirectly promotes maturation of beta(1) integrin precursor and thereby increases the level of beta(1) integrin at the cell surface.
authors.affiliation: Department of Pathology, University of Virginia School of Medicine, Charlottesville 22908, USA.
authors.forename: Ana María
authors.initials: AM
authors.lastname: Salicioni
authors.forename: Alban
authors.initials: A
authors.lastname: Gaultier
authors.forename: Cristina
authors.initials: C
authors.lastname: Brownlee
authors.forename: Michael K
authors.initials: MK
authors.lastname: Cheezum
authors.forename: Steven L
authors.initials: SL
authors.lastname: Gonias
mesh_terms: D000818:Animals; D001692:Biological Transport; D016466:CHO Cells; D002448:Cell Adhesion; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D006224:Cricetinae; D003720:Densitometry; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D004705:Endocytosis; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D019012:Integrin beta1 / Q000378:metabolism*; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000737:chemistry*; D051379:Mice; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase / Q000378:metabolism; D013997:Time Factors
chemical_list: D005353:Fibronectins; D019012:Integrin beta1; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D006026:Glycoside Hydrolases; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase