Contribution of cubilin and amnionless to processing and membrane targeting of cubilin-amnionless complex.
Cubilin is a peripheral apical membrane receptor for multiple ligands that are taken up in several absorptive epithelia. Recently, amnionless (AMN) was identified to form a functional receptor complex with cubilin. By expression in transfected polarized MDCK cells of AMN and several cubilin fragments, including a functional "mini" version of cubilin, the processing, sorting, and membrane anchoring of the complex to the apical membrane were investigated. The results show that truncation mutants, including the N-terminal domain of cubilin, did not appear at the plasma membrane but instead were retained in the endoplasmic reticulum or partially secreted into the medium. Coexpression with AMN led to efficient transport to the apical cell surface of the cubilin constructs, which included the EGF domains, and prevented release into the medium. AMN co-precipitated with cubilin and co-localized with cubilin at the apical cell surface. Apical sorting was observed for a broad set of nonoverlapping cubilin fragments without the N-terminal region, in the absence of AMN. The preference for apical sorting disappeared when glycosylation was inhibited by tunicamycin. In conclusion, it is shown that both units contribute to the processing of the cubilin-AMN complex to the apical membrane: AMN interacts with the EGF domains of cubilin and is responsible for membrane attachment and export of the complex from the endoplasmic reticulum, whereas the extracellular cubilin molecule is responsible for apical sorting of the complex in a carbohydrate-dependent manner.
Address correspondence to: Dr. Pierre J. Verroust, INSERM U538, Centre Hospitalier Universitaire Saint Antoine, 27 Rue Chaligny, 75012 Paris, France.
Gwénaëlle
G
Coudroy
Jakub
J
Gburek
Renata
R
Kozyraki
Mette
M
Madsen
Germain
G
Trugnan
Søren K
SK
Moestrup
Pierre J
PJ
Verroust
Michèle
M
Maurice
D000818:Animals; D015153:Blotting, Western; D002241:Carbohydrates / Q000737:chemistry; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D004285:Dogs; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000737:chemistry / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology; D004848:Epithelium / Q000378:metabolism; D006031:Glycosylation; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007668:Kidney / Q000166:cytology; D008024:Ligands; D008565:Membrane Proteins / Q000378:metabolism / Q000502:physiology*; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D014162:Transfection
C424167:Amn protein, mouse; D002241:Carbohydrates; D018076:DNA, Complementary; D008024:Ligands; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; C029486:intrinsic factor-cobalamin receptor; D049452:Green Fluorescent Proteins; D004815:Epidermal Growth Factor