title: Membrane glycoprotein PC-1 inhibition of insulin receptor function occurs via direct interaction with the receptor alpha-subunit.
abstract: Plasma cell membrane glycoprotein-1 (PC-1) inhibits insulin receptor (IR) tyrosine kinase activity and subsequent cellular signaling. PC-1 content is elevated in fibroblasts, muscle, and adipose tissue from insulin-resistant subjects, and its elevation correlates with in vivo insulin resistance. In vitro, when PC-1 is transfected and overexpressed in cultured cells, it inhibits IR tyrosine kinase activity. To determine the mechanism whereby PC-1 regulates the IR, we studied how PC-1 interacts with this protein. Overexpression of PC-1 in MCF-7 cells inhibited tyrosine kinase activity of the IR, but not of the IGF-I receptor. When the IR was immunocaptured by specific IR monoclonal antibodies, PC-1 was associated with this receptor. In contrast, after specific immunocapture, PC-1 was not associated with the IGF-I receptor. We next studied HTC cells that were overexpressing an IR alpha-subunit mutant. This IR mutant binds insulin but has a deletion in the tyrosine kinase regulatory domain located in amino acids 485-599. In contrast to normal IRs, PC-1 did not associate with this mutant and did not affect tyrosine kinase activity. To determine whether decreasing PC-1 expression would reverse the inhibition of tyrosine kinase activity, we treated MCF-7 cells overexpressing PC-1 with a monoclonal antibody to PC-1. This treatment decreased PC-1 levels; concomitantly, IR tyrosine kinase activity increased. In contrast, IGF-I receptor tyrosine kinase activity was not increased. These studies indicate, therefore, that PC-1 may inhibit the IR by interacting directly with a specific region in the IR alpha-subunit. These studies also raise the possibility that monoclonal antibodies to PC-1 could be a new treatment for insulin resistance.
authors.affiliation: Department of Medicine, Mount Zion Medical Center, University of California San Francisco, USA.
authors.forename: B A
authors.initials: BA
authors.lastname: Maddux
authors.forename: I D
authors.initials: ID
authors.lastname: Goldfine
mesh_terms: D002460:Cell Line / Q000378:metabolism; D015536:Down-Regulation / Q000502:physiology; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007158:Immunologic Techniques; D007333:Insulin Resistance / Q000502:physiology; D008562:Membrane Glycoproteins / Q000502:physiology*; D009154:Mutation; D010727:Phosphoric Diester Hydrolases; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000235:genetics; D011755:Pyrophosphatases; D011972:Receptor, Insulin / Q000037:antagonists & inhibitors* / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology; D014162:Transfection
chemical_list: D008562:Membrane Glycoproteins; D020033:Protein Isoforms; D011972:Receptor, Insulin; D010727:Phosphoric Diester Hydrolases; C065962:ectonucleotide pyrophosphatase phosphodiesterase 1; D011755:Pyrophosphatases