Sorting of H,K-ATPase β-subunit in MDCK and LLC-PK1 cells is independent of μ1B adaptin expression
Sorting of H,K-ATPase β-subunit in MDCK and LLC-PK1 cells is independent of μ1B adaptin expression
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DOI：
10.1111/j.1398-9219.2004.00192.x
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发表时间：
2004-06-01
期刊：
影响因子：
4.5
通讯作者：
Caplan, MJ
中科院分区：
文献类型：
--
作者：
Duffield, A;Fölsch, H;Caplan, MJ
H，K-ATP酶β亚基的胞质尾区含有一个假定的基于酪氨酸的基序，当β亚基在Madin-Darby犬肾（MDCK）细胞中表达时，该基序指导β亚基的基底外侧分选。然而，当在LLC-PK 1细胞中表达时，β亚基定位于顶膜。几种含有酪氨酸基序的蛋白质，包括低密度脂蛋白和转铁蛋白受体，在LLC-PK 1细胞中表达时显示出类似的分选“缺陷”。对于低密度脂蛋白和转铁蛋白受体，这种行为是由于AP-1B网格蛋白衔接子复合物的mu 1B亚基的差异表达造成的。mu 1B由MDCK细胞表达，而不是LLC-PK 1细胞，mu 1B转染到LLC-PK 1细胞中恢复低密度脂蛋白和转铁蛋白受体的基底外侧定位。然而，对于β亚基，LLC-PK 1细胞中的mu 1B表达不诱导其基底外侧表达。我们发现，β-亚基相互作用与mu 1B和mu 1A在体外和体内。因此，参与mu 1B相互作用的能力不足以编程β亚基在MDCK细胞中的基底外侧定位。我们的数据表明，H，K-ATP酶β亚基的基底外侧分选信号要么在某些上皮细胞中被掩盖，要么需要与AP-1B以外的分选机制相互作用，以传递到基底外侧质膜。
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 mu1B subunit of the AP-1B clathrin adaptor complex. mu1B is expressed by MDCK cells, but not LLC-PK1 cells, and transfection of mu1B into LLC-PK1 cells restores basolateral localization of low-density lipoprotein and transferrin receptors. For the beta-subunit, however, mu1B expression in LLC-PK1 cells does not induce its basolateral expression. We found that the beta-subunit interacts with both mu1B and mu1A in vitro and in vivo. The capacity to participate in a mu1B 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.