Deglycosylation of Na+/K+-ATPase causes the basolateral protein to undergo apical targeting in polarized hepatic cells.
Polarized epithelia, such as hepatocytes, target their integral membrane proteins to specific apical or basolateral membrane domains during or after biogenesis. The roles played by protein glycosylation in this sorting process remain controversial. We report here that deglycosylation treatments in well-polarized hepatic cells by deglycosylation drugs, or by site-directed mutagenesis of the N-linked-glycosylation residues, all cause the Na+/K+-ATPase beta-subunit to traffic from the native basolateral to the apical/canalicular domain. Deglycosylated beta-subunits are still able to bind and therefore transport the catalytic alpha-subunits to the aberrant apical location. Such apical targeting is mediated via the indirect transcytosis pathway. Cells containing apical Na+/K+-ATPase appear to be defective in maintaining the ionic gradient across the plasma membrane and in executing hepatic activities that are dependent upon the ionic homeostasis such as canalicular excretion.
Lian
Wei-Nan
WN
Institute of Microbiology and Immunology, National Yang-Ming University, 155 Sec. 2 Linong Street, Taipei 112, Taiwan.
Wu
Tzu-Wei
TW
Dao
Ro-Lan
RL
Chen
Yann-Jang
YJ
Lin
Chi-Hung
CH
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002460:Cell Line; D016764:Cell Polarity; D006031:Glycosylation; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006706:Homeostasis; D006801:Humans; D016297:Mutagenesis, Site-Directed; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology*; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014415:Tunicamycin / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D021122:Protein Subunits; D014415:Tunicamycin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase