title: Distinct pathways for constitutive endocytosis of fully conformed and non-conformed L(d) molecules.
abstract: OBJECTIVE
  To characterize the constitutive internalization of major histocompatibility complex (MHC) class I molecules, we have studied the expression of completely conformed (full) and unconformed (empty) L(d) molecules on non-polarized murine P815 cells.
  
  
  METHODS
  Spontaneous endocytosis of L(d) molecules was induced by cycloheximide, an inhibitor of protein synthesis, and their disappearance from the cell surface was determined by flow cytometry. In order to investigate the mechanism of internalization, a palette of inhibitors of endocytosis and vesicular transport was used.
  
  
  RESULTS
  Inhibitors of clathrine endocytosis did not influence the internalization of L(d) molecules. Inhibitors of caveolar endocytosis and inhibitors of endolysosomal degradation prevented down-regulation of empty, but not of full L(d) molecules.
  
  
  CONCLUSIONS
  Empty L(d) molecules are internalized mostly by caveolar endocytosis and full L(d) molecules use a different pathway, neither clathrine-mediated nor caveolar. After internalization, full L(d) molecules are probably degraded and empty L(d) molecules recycle between endosomal compartment and the cell surface before they enter into the degradation compartment.
authors.affiliation: Department of Physiology and Immunology, Medical Faculty, University of Rijeka, Croatia.
authors.forename: Hana
authors.initials: H
authors.lastname: Mahmutefendić
authors.forename: Natalia
authors.initials: N
authors.lastname: Kucić
authors.forename: Pero
authors.initials: P
authors.lastname: Lucin
mesh_terms: D000818:Animals; D004705:Endocytosis / Q000276:immunology*; D005434:Flow Cytometry; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D007739:L Cells; D051379:Mice
chemical_list: D015395:Histocompatibility Antigens Class I