Transcytosis of immunoglobulin A in the mouse enterocyte occurs through glycolipid raft- and rab17-containing compartments.
OBJECTIVE
Glycolipid "rafts" have been shown to play a role in apical membrane trafficking in the enterocyte. The present study characterized the membrane compartments of the enterocyte involved in transepithelial transport of small intestinal immunoglobulin A (IgA).


METHODS
Immunogold electron microscopy and radioactive labeling of mouse small intestinal explants were performed.


RESULTS
IgA and the polymeric immunoglobulin receptor/secretory component were present in a raft compartment. Raft association occurred posttranslationally within 30 minutes, preceding secretion into the culture medium. IgA labeling was seen primarily in enterocytes along the basolateral plasma membrane and over endosomes and small vesicles in the basolateral and apical regions of the cytoplasm. IgA and a brush border enzyme, aminopeptidase N, were colocalized in apical endosomes and small vesicles and were also frequently seen associated with the same vesicular profiles of glycolipid rafts. Colocalization of IgA and rab17, a small guanosine triphosphatase involved in transcytosis, was seen mainly along the basolateral plasma membrane and over basolateral endosomes and vesicles, but also in the apical region of the cytoplasm.


CONCLUSIONS
IgA is transcytosed through a raft-containing compartment, most likely the apical endosomes. Our data also support the notion that rab17 is involved in transcytotic membrane traffic.
Department of Medical Biochemistry and Genetics, Biochemistry Laboratory C, the Panum Institute, University of Copenhagen, Copenhagen, Denmark.
G H
GH
Hansen
L L
LL
Niels-Christiansen
L
L
Immerdal
W
W
Hunziker
A J
AJ
Kenny
E M
EM
Danielsen
D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000276:immunology; D004705:Endocytosis; D051418:Focal Adhesion Kinase 2; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000378:metabolism*; D006017:Glycolipids / Q000378:metabolism; D007070:Immunoglobulin A / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000276:immunology*; D007421:Intestine, Small / Q000276:immunology*; D051379:Mice; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D009924:Organ Culture Techniques; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011961:Receptors, Fc / Q000378:metabolism*; D020691:rab GTP-Binding Proteins
D006017:Glycolipids; C045281:IgA receptor; D007070:Immunoglobulin A; D011961:Receptors, Fc; C081073:rab17 protein, epithelial; D011505:Protein-Tyrosine Kinases; D051418:Focal Adhesion Kinase 2; D020558:GTP Phosphohydrolases; D020691:rab GTP-Binding Proteins