title: Sorting of H,K-ATPase beta-subunit in MDCK and LLC-PK cells is independent of mu 1B adaptin expression.
abstract: The cytoplasmic tail of the H,K-ATPase beta-subunit contains a putative tyrosine-based motif that directs the beta-subunit's basolateral sorting when it is expressed in Madin-Darby Canine Kidney (MDCK) cells. When expressed in LLC-PK(1) cells, however, the beta-subunit is localized to the apical membrane. Several proteins that contain tyrosine-based motifs, including the low-density lipoprotein and transferrin receptors, show a similar sorting 'defect' when expressed in LLC-PK(1) cells. For low-density lipoprotein and transferrin receptors, this behavior is due to the differential expression of the mu 1B subunit of the AP-1B clathrin adaptor complex. mu 1B is expressed by MDCK cells, but not LLC-PK(1) cells, and transfection of mu 1B into LLC-PK(1) cells restores basolateral localization of low-density lipoprotein and transferrin receptors. For the beta-subunit, however, mu B expression in LLC-PK(1) cells does not induce its basolateral expression. We found that the beta-subunit interacts with both mu 1B and mu 1A in vitro and in vivo. The capacity to participate in a mu 1B interaction therefore is not sufficient to program the beta-subunit's basolateral localization in MDCK cells. Our data suggest that the H,K-ATPase beta-subunit's basolateral sorting signal is either masked in certain epithelial cells, or requires an interaction with sorting machinery other than AP-1B for delivery to the basolateral plasma membrane.
authors.affiliation: Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06510, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Duffield
authors.forename: Heike
authors.initials: H
authors.lastname: Fölsch
authors.forename: Ira
authors.initials: I
authors.lastname: Mellman
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Caplan
mesh_terms: D033983:Adaptor Protein Complex mu Subunits / Q000378:metabolism*; D033942:Adaptor Proteins, Vesicular Transport / Q000737:chemistry / Q000378:metabolism; D020816:Amino Acid Motifs; D000818:Animals; D002460:Cell Line; D003593:Cytoplasm / Q000737:chemistry; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D017506:H(+)-K(+)-Exchanging ATPase / Q000737:chemistry / Q000378:metabolism; D018374:LLC-PK1 Cells; D008565:Membrane Proteins / Q000378:metabolism; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D011973:Receptors, LDL / Q000378:metabolism; D011990:Receptors, Transferrin / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013552:Swine; D014162:Transfection; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism*
chemical_list: D033983:Adaptor Protein Complex mu Subunits; D033942:Adaptor Proteins, Vesicular Transport; D008565:Membrane Proteins; D021122:Protein Subunits; D011973:Receptors, LDL; D011990:Receptors, Transferrin; D011993:Recombinant Fusion Proteins; D014443:Tyrosine; D005982:Glutathione Transferase; D017506:H(+)-K(+)-Exchanging ATPase