Na,K-ATPase β-subunit cis homo-oligomerization is necessary for epithelial lumen formation in mammalian cells.
Na,K-ATPase is a hetero-oligomer of an α- and a β-subunit. The α-subunit (Na,K-α) possesses the catalytic function, whereas the β-subunit (Na,K-β) has cell-cell adhesion function and is localized to the apical junctional complex in polarized epithelial cells. Earlier, we identified two distinct conserved motifs on the Na,K-β(1) transmembrane domain that mediate protein-protein interactions: a glycine zipper motif involved in the cis homo-oligomerization of Na,K-β(1) and a heptad repeat motif that is involved in the hetero-oligomeric interaction with Na,K-α(1). We now provide evidence that knockdown of Na,K-β(1) prevents lumen formation and induces activation of extracellular regulated kinases 1 and 2 (ERK1/2) mediated by phosphatidylinositol 3-kinase in MDCK cells grown in three-dimensional collagen cultures. These cells sustained cell proliferation in an ERK1/2-dependent manner and did not show contact inhibition at high cell densities, as revealed by parental MDCK cells. This phenotype could be rescued by wild-type Na,K-β(1) or heptad repeat motif mutant of Na,K-β(1), but not by the glycine zipper motif mutant that abrogates Na,K-β(1) cis homo-oligomerization. These studies suggest that Na,K-β(1) cis homo-oligomerization rather than hetero-oligomerization with Na,K-α(1) is involved in epithelial lumen formation. The relevance of these findings to pre-neoplastic lumen filling in epithelial cancer is discussed.
Nemours Center for Childhood Cancer Research, Alfred I. duPont Hospital for Children, Wilmington, DE 19803,  USA.
Sonali P
SP
Barwe
Anna
A
Skay
Ryan
R
McSpadden
Thu P
TP
Huynh
Sigrid A
SA
Langhans
Landon J
LJ
Inge
Ayyappan K
AK
Rajasekaran
D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation; D004285:Dogs; D015151:Immunoblotting; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization / Q000235:genetics / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000378:metabolism*
D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D000254:Sodium-Potassium-Exchanging ATPase