The roles of the Na,K-ATPase beta 1 subunit in pump sorting and epithelial integrity.
In epithelial MDCK cells, the Na,K-ATPase is co-localized with adherens junctions in all stages of monolayer formation starting from initiation of cell-cell contact. The Na,K-ATPase and adherens junction proteins stay partially co-localized even after internalization due to disruption of intercellular contacts by Ca2+ deprivation. Similar to adherens junction proteins, the Na,K-ATPase is resistant to extraction with non-ionic detergent, suggesting pump association with the cytoskeleton. In contrast, the heterodimer formed by expressed unglycosylated Na,K-ATPase beta 1 subunit and the endogenous alpha 1 subunit is easily dissociated from the adherens junctions and cytoskeleton by detergent extraction. The MDCK cells in which half of the endogenous beta 1 subunits in the lateral membrane are substituted by unglycosylated beta 1 subunits display a slower rate of cell-to-cell contact formation and decreased ability to both spread over the surface and migrate. The lack of N-glycans in the Na,K-ATPase beta 1 subunit results in an impairment of mature cell-cell junctions as detected by an increase in the paracellular permeability of the MDCK cell monolayers and by a decrease in resistance of adherens junction proteins to extraction by a non-ionic detergent. Therefore the N-glycans of the Na,K-ATPase beta 1 subunit are important for retention of the pump at the sites of cell-cell contact. Moreover, they are important for the integrity and stability of cell-cell junctions in mature epithelia. In addition, N-glycans contribute to the formation of cell-cell contacts between surface-attached dispersed cells by mediating lamellipodia formation and stabilizing the newly formed adherens junctions.
Vagin
Olga
O
Department of Physiology, School of Medicine, UCLA, Los Angeles, CA 90073, USA. olgav@ucla.edu
Sachs
George
G
Tokhtaeva
Elmira
E
D022005:Adherens Junctions / Q000201:enzymology* / Q000502:physiology; D000818:Animals; D002460:Cell Line; D004285:Dogs; D004848:Epithelium / Q000201:enzymology / Q000502:physiology; D011134:Polysaccharides; D021122:Protein Subunits / Q000737:chemistry / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000502:physiology*
D011134:Polysaccharides; D021122:Protein Subunits; D000254:Sodium-Potassium-Exchanging ATPase