title: Constitutive internalization of murine MHC class I molecules.
abstract: The total number of cell surface glycoprotein molecules at the plasma membrane results from a balance between their constitutive internalization and their egress to the cell surface from intracellular pools and/or biosynthetic pathway. Constitutive internalization is net result of constitutive endocytosis and endocytic recycling. In this study we have compared spontaneous internalization of murine major histocompatibility complex (MHC) class I molecules (K(d), D(d), full L(d), and empty L(d)) after depletion of their egress to the cell surface (Cycloheximide [CHX], brefeldin A [BFA]) and internalization after external binding of monoclonal antibody (mAb). MHC class I alleles differ regarding their cell surface stability, kinetics, and in the way of internalization and degradation. K(d) and D(d) molecules are more stable at the cell surface than L(d) molecules and, thus, constitutively internalized more slowly. Although the binding of mAbs to cell surface MHC class I molecules results in faster internalization than depletion of their egress, it is still slow and, thereby, can serve as a model for tracking of MHC class I endocytosis. Internalization of fully conformed MHC class I molecules (K(d), D(d), and L(d)) was neither inhibited by chlorpromazine (CP) (inhibitor of clathrin endocytosis), nor with filipin (inhibitor of lipid raft dependent endocytosis), indicating that fully conformed MHC class I molecules are internalized via the bulk pathway. In contrast, internalization of empty L(d) molecules was inhibited by filipin, indicating that non-conformed MHC class I molecules require intact cholesterol-rich membrane microdomains for their constitutive internalization. Thus, conformed and non-conformed MHC class I molecules use different endocytic pathways for constitutive internalization.
authors.affiliation: Department of Physiology and Immunology, Medical Faculty, University of Rijeka, Rijeka, Croatia.
authors.forename: Hana
authors.initials: H
authors.lastname: Mahmutefendić
authors.forename: Gordana
authors.initials: G
authors.lastname: Blagojević
authors.forename: Natalia
authors.initials: N
authors.lastname: Kucić
authors.forename: Pero
authors.initials: P
authors.lastname: Lucin
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D000935:Antifungal Agents / Q000494:pharmacology; D041702:BALB 3T3 Cells; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002966:Clathrin / Q000037:antagonists & inhibitors / Q000378:metabolism; D022163:Clathrin-Coated Vesicles / Q000187:drug effects / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D005372:Filipin; D015395:Histocompatibility Antigens Class I / Q000187:drug effects / Q000378:metabolism*; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013997:Time Factors
chemical_list: D000911:Antibodies, Monoclonal; D000935:Antifungal Agents; D002966:Clathrin; D015395:Histocompatibility Antigens Class I; D011500:Protein Synthesis Inhibitors; D005372:Filipin