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Sorting of H,K‐ATPase β‐Subunit in MDCK and LLC‐PK 1 Cells is Independent of μ1B Adaptin Expression
Author(s) -
Duffield Amy,
Fölsch Heike,
Mellman Ira,
Caplan Michael J.
Publication year - 2004
Publication title -
traffic
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.677
H-Index - 130
eISSN - 1600-0854
pISSN - 1398-9219
DOI - 10.1111/j.1398-9219.2004.00192.x
Subject(s) - biology , protein subunit , microbiology and biotechnology , clathrin , epithelial polarity , transferrin , transfection , transferrin receptor , receptor , cell culture , endocytosis , biochemistry , cell , gene , genetics
The cytoplasmic tail of the H,K‐ATPase β‐subunit contains a putative tyrosine‐based motif that directs the β‐subunit's basolateral sorting when it is expressed in Madin‐Darby Canine Kidney (MDCK) cells. When expressed in LLC‐PK 1 cells, however, the β‐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 μ1B subunit of the AP‐1B clathrin adaptor complex. μ1B is expressed by MDCK cells, but not LLC‐PK 1 cells, and transfection of μ1B into LLC‐PK 1 cells restores basolateral localization of low‐density lipoprotein and transferrin receptors. For the β‐subunit, however, μ1B expression in LLC‐PK 1 cells does not induce its basolateral expression. We found that the β‐subunit interacts with both μ1B and μ1A in vitro and in vivo . The capacity to participate in a μ1B interaction therefore is not sufficient to program the β‐subunit's basolateral localization in MDCK cells. Our data suggest that the H,K‐ATPase β‐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.