An ion-transporting ATPase encodes multiple apical localization signals.
Epithelial cells accumulate distinct populations of membrane proteins at their two plasmalemmal domains. We have examined the molecular signals which specify the differential subcellular distributions of two closely related ion pumps. The Na,K-ATPase is normally restricted to the basolateral membranes of numerous epithelial cell types, whereas the H,K-ATPase is a component of the apical surfaces of the parietal cells of the gastric epithelium. We have expressed full length and chimeric H,K-ATPase/Na,K-ATPase cDNAs in polarized renal proximal tubular epithelial cells (LLC-PK1). We find that both the alpha and beta subunits of the H,K-ATPase encode independent signals that specify apical localization. Furthermore, the H,K-ATPase beta-subunit possesses a sequence which mediates its participation in the endocytic pathway. The interrelationship between epithelial sorting and endocytosis signals suggested by these studies supports the redefinition of apical and basolateral as functional, rather than simply topographic domains.
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
C J
CJ
Gottardi
M J
MJ
Caplan
D000595:Amino Acid Sequence; D000818:Animals; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D002478:Cells, Cultured; D004705:Endocytosis; D017506:H(+)-K(+)-Exchanging ATPase / Q000032:analysis / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010295:Parietal Cells, Gastric / Q000737:chemistry* / Q000378:metabolism; D021382:Protein Sorting Signals / Q000032:analysis / Q000737:chemistry*; D051381:Rats; D017386:Sequence Homology, Amino Acid; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis / Q000737:chemistry*
D021382:Protein Sorting Signals; D017506:H(+)-K(+)-Exchanging ATPase; D000254:Sodium-Potassium-Exchanging ATPase