title: Low-density-lipoprotein-receptor-related protein (LRP) interacts with a GTP-binding protein.
abstract: The low-density-lipoprotein-receptor-related protein (LRP) binds and internalizes numerous ligands, including lipoproteins, proteinase-inhibitor complexes and others. We have shown previously that LRP-mediated ligand internalization is dependent on cAMP-dependent protein kinase (PKA) activity. Here, we investigated whether ligation of LRP increases the intracellular cAMP level and PKA activity via a stimulatory GTP-binding protein. Treatment of LRP-expressing cell lines with the LRP ligands lactoferrin or urokinase-type plasminogen activator caused a significant elevation in cAMP and stimulated PKA activity in a dose-dependent manner. Addition of the 39 kDa receptor-associated protein (RAP), an antagonist for ligand interactions with LRP, blocked the lactoferrin-induced increase in PKA activity, demonstrating a requirement for ligand binding to LRP. Incubation of cell membrane fractions with lactoferrin increased GTPase activity in a time- and dose-dependent manner, and treatment with LRP ligands suppressed cholera-toxin-mediated ADP-ribosylation of the Gsalpha subunit of a heterotrimeric G-protein. Affinity precipitation of LRP with RAP resulted in co-precipitation of two isoforms of Gsalpha from detergent extracts. We thus conclude that LRP is a signalling receptor that associates directly with a stimulatory heterotrimeric G-protein and activates a downstream PKA-dependent pathway.
authors.affiliation: The Scripps Research Institute, Department of Immunology, 10550 N. Torrey Pines Road, IMM13, La Jolla, CA 92037, USA.
authors.forename: L
authors.initials: L
authors.lastname: Goretzki
authors.forename: B M
authors.initials: BM
authors.lastname: Mueller
mesh_terms: D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007781:Lactoferrin / Q000494:pharmacology; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D017395:Plasminogen Activator Inhibitor 1 / Q000494:pharmacology; D011971:Receptors, Immunologic / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D026503:Low Density Lipoprotein Receptor-Related Protein-1; D017395:Plasminogen Activator Inhibitor 1; D011971:Receptors, Immunologic; D002772:Cholera Toxin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D007781:Lactoferrin; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D019205:GTP-Binding Protein alpha Subunits, Gs