Association of stomatin with lipid-protein complexes in the plasma membrane and the endocytic compartment.
Membrane protein - microvilli - lipid raft - GPI-anchored protein - epithelial cell The 31 kDa integral membrane protein stomatin (protein 7.2b) has a monotopic structure and a cytofacial orientation. We have shown previously that stomatin is located in plasma membrane protruding structures and forms high-order homo-oligomers in the human epithelial cell line UAC, suggesting that this protein has a structural function in the cortical morphogenesis of the cells. It is also present in a pool of juxtanuclear vesicles. In this study, we show that stomatin colocalizes with the GPI-anchored proteins placental alkaline phosphatase (PLAP) and membrane folate receptor alpha (MFRalpha) endogenously expressed in UAC cells. This observation enabled us to demonstrate two different aspects of stomatin. First, using anti-PLAP antibody internalization, we show that the peri-centrosomal vesicles containing stomatin correspond to a subset of endosomes, which can also be labeled with the late endosomal/lysosomal marker LAMP-2. Secondly, we found that stomatin is partially present in detergent-insoluble membrane domains and co-patches with PLAP on the plasma membrane, after cross-linking of PLAP by antibodies. These data indicate that stomatin and GPI-anchored proteins are linked through lipid rafts and undergo the same sorting events. We propose that stomatin, through its affinity for lipid rafts, functions in concentrating GPI-anchored proteins in membrane microvillar structures. Consistent with this hypothesis, we found that stomatin is expressed exclusively in microvilli of the apical membrane in polarized Madin-Darby canine kidney (MDCK) cells.
Snyers
L
L
Institute of Biochemistry, University of Vienna, Vienna Biocenter, Austria.
Umlauf
E
E
Prohaska
R
R
D000469:Alkaline Phosphatase / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D001798:Blood Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D051242:Caveolin 1; D022461:Caveolins; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology; D004285:Dogs; D004705:Endocytosis; D005455:Fluorescent Antibody Technique; D058973:Folate Receptors, GPI-Anchored; D058851:GPI-Linked Proteins; D006801:Humans; D015151:Immunoblotting; D015850:Interleukin-6 / Q000378:metabolism / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism; D050356:Lipid Metabolism; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008871:Microvilli / Q000378:metabolism; D010920:Placenta / Q000187:drug effects / Q000201:enzymology; D011956:Receptors, Cell Surface; D011990:Receptors, Transferrin / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism; D015854:Up-Regulation
D001798:Blood Proteins; D002352:Carrier Proteins; D051242:Caveolin 1; D022461:Caveolins; C488964:Stom protein, mouse; D058973:Folate Receptors, GPI-Anchored; D058851:GPI-Linked Proteins; D015850:Interleukin-6; D007527:Isoenzymes; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D011990:Receptors, Transferrin; C036860:STOM protein, human; D003907:Dexamethasone; D000469:Alkaline Phosphatase; C019839:alkaline phosphatase, placental; D014357:Trypsin