title: Glucocorticoid-regulated and constitutive trafficking of proteolytically processed cell surface-associated glycoproteins in wild type and variant rat hepatoma cells.
abstract: Glucocorticoids regulate the trafficking of mouse mammary tumor virus (MMTV) glycoproteins to the cell surface in the rat hepatoma cell line M1.54, but not in the immunoselected sorting variant CR4. To compare the localization of MMTV glycoproteins to another proteolytically processed glycoprotein, both wild type M1.54 cells and variant CR4 cells were transfected with a human insulin receptor (hIR) expression vector, pRSVhIR. The production of cell surface hIR was monitored in dexamethasone-treated and -untreated wild type M1.54 and variant CR4 cells by indirect immunofluorescence, direct plasma membrane immunoprecipitation, and by [125I] insulin binding. In both wild type and variant rat hepatoma cells, hIR were localized at the cell surface in the presence or in the absence of 1 microM dexamethasone. In contrast, the glucocorticoid-regulated trafficking of cell surface MMTV glycoproteins occurred only in wild type M1.54 cells. We conclude that the hIR, which undergoes posttranslational processing reactions similar to MMTV glycoproteins, does not require glucocorticoids to be transported to the plasma membrane and is representative of a subset of cell surface glycoproteins whose trafficking is constitutive in rat hepatoma cells. Thus, MMTV glycoproteins and hIR provide specific cell surface markers to characterize the glucocorticoid-regulated and constitutive sorting pathways.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley 94720.
authors.forename: S L
authors.initials: SL
authors.lastname: Amacher
authors.forename: L J
authors.initials: LJ
authors.lastname: Goodman
authors.forename: D A
authors.initials: DA
authors.lastname: Bravo
authors.forename: K Y
authors.initials: KY
authors.lastname: Wong
authors.forename: I D
authors.initials: ID
authors.lastname: Goldfine
authors.forename: D M
authors.initials: DM
authors.lastname: Hawley
authors.forename: G L
authors.initials: GL
authors.lastname: Firestone
mesh_terms: D000818:Animals; D003907:Dexamethasone / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D005938:Glucocorticoids / Q000502:physiology*; D006801:Humans; D007457:Iodine Radioisotopes; D008114:Liver Neoplasms, Experimental / Q000235:genetics / Q000378:metabolism*; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics; D008562:Membrane Glycoproteins / Q000235:genetics*; D051379:Mice; D051381:Rats; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism; D013462:Sulfur Radioisotopes; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D005938:Glucocorticoids; D007457:Iodine Radioisotopes; D008562:Membrane Glycoproteins; D013462:Sulfur Radioisotopes; D003907:Dexamethasone; D011972:Receptor, Insulin