Clathrin-coated lattices and buds on MHC class II compartments do not selectively recruit mature MHC-II.
Newly synthesized major histocompatibility complex class II molecules (MHC-II) are transported to MHC-II-containing endosomal and lysosomal compartments (MIICs) for the degradation of associated invariant chain and peptide loading. Subsequently MHC-II is transported to the plasma membrane, in part through direct fusion of MIICs with the plasma membrane. In search of potential alternative pathway(s) we studied the 3-dimensional structure of MIICs and the subcellular distribution of MHC-II by immuno electronmicroscopy on whole-mount preparations and cryosections of Mel JuSo cells. Intracellular MHC-II and invariant chain mainly localized to lamp-1 positive compartments suggesting that the majority of MHC-II exits the endocytic tract at lysosomes. Clathrin-coated lattices and buds were found to be associated with these organelles, but MHC-II was not found to be enriched in the clathrin-coated domains. Moreover, leupeptin, a drug that interferes with Ii-processing and delays delivery of newly synthesized MHC-II to the plasma membrane, was not found to decrease the relative amount of MHC-II in clathrin-coated areas. Together these data indicate clathrin-mediated exit site(s) from lysosomes but suggest that they do not selectively recruit mature MHC-II, consistent with the notion that transport to the plasma membrane occurs independently of the cytoplasmic domains of the MHC-II (&agr;) and (beta) chains.
Ramm
G
G
Department of Cell Biology, University Medical Center and Institute for Biomembranes, Utrecht University, The Netherlands.
Pond
L
L
Watts
C
C
Stoorvogel
W
W
D000944:Antigens, Differentiation, B-Lymphocyte / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D002451:Cell Compartmentation; D002460:Cell Line; D002966:Clathrin / Q000378:metabolism*; D003034:Coated Pits, Cell-Membrane / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D008247:Lysosomes / Q000276:immunology / Q000378:metabolism; D016253:Microscopy, Immunoelectron
D000944:Antigens, Differentiation, B-Lymphocyte; D002966:Clathrin; D000949:Histocompatibility Antigens Class II; D007976:Leupeptins; C045084:invariant chain; C032854:leupeptin