Sorting of H, K-ATPase [beta]-Subunit in MDCK and LLC-PK1 Cells is Independent of [mu]1B Adaptin Expression.
Duffield, Amy 1; Folsch, Heike 2; Mellman, Ira 2; Caplan, Michael J. 1,2,*
[Article] Traffic. 5(6):449-461, June 2004.

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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-PK1 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-PK1 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-PK1 cells, and transfection of [mu]1B into LLC-PK1 cells restores basolateral localization of low-density lipoprotein and transferrin receptors. For the [beta]-subunit, however, [mu]1B expression in LLC-PK1 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.

Copyright (C) 2004 Blackwell Publishing Ltd.