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Janice M. Burke, Feng Cao, Pamela E. Irving; High Levels of E-/P-Cadherin: Correlation with Decreased Apical Polarity of Na/K ATPase in Bovine RPE Cells In Situ. Invest. Ophthalmol. Vis. Sci. 2000;41(7):1945-1952.
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purpose. The adherens junction protein E-cadherin induces a basolateral polarity
of Na/K ATPase in most epithelial cells that express it, whereas in
retinal pigment epithelium (RPE) cells, Na/K ATPase is largely apical.
The purpose of this study was to determine whether the distribution of
Na/K ATPase differs in RPE cells in situ, that differ in levels of
methods. Bovine RPE cells in situ were immunostained with an E-cadherin antibody
(which has some cross-reactivity with the closely related epithelial
cadherin P-cadherin), and RPE cells with different levels of junctional
stain were identified. RPE cells with low and high E-/P-cadherin were
costained in various combinations with Na/K ATPase and interacting
proteins of the membrane cytoskeleton (ankyrin, fodrin, and actin) and
analyzed by confocal imaging.
results. Individual RPE cells within the same monolayer differed in amount of
Na/K ATPase, with a lower frequency of high expressing cells in the
area centralis. High expressing Na/K ATPase cells were found among
cells with both low and high E-/P-cadherin levels. In cells with low
E/P-cadherin, Na/K ATPase localized to apical microvilli, whereas in
high E-/P-cadherin cells, Na/K ATPase was on basolateral surfaces in
addition to microvilli. Actin staining showed that microvillar domains
were smaller and that lateral membrane domains were taller in
high E-/P-cadherin cells. In high but not low E-/P-cadherin cells,
ankyrin and fodrin levels varied among cells, with a subset of cells
showing distinctly higher expression. Both ankyrin and fodrin had
complex subcellular distribution patterns, although they tended to be
enriched basal to rather than apical to the adherens junction. Cells
with high Na/K ATPase did not necessarily have commensurately higher
levels of ankyrin or fodrin. Where both Na/K ATPase and ankyrin were
high, they codistributed weakly in apical microvilli but more
prominently on the basal cell surface.
conclusions. Within the same RPE monolayer, the polarity of Na/K ATPase differs
among cells, with a more basal polarity found in cells with high levels
of junctional E-/P-cadherin. The increased basal Na/K ATPase was due to
a combination of a smaller microvillar domain, a taller lateral domain,
and more basolateral staining for Na/K ATPase, perhaps because of an
enrichment of a basal ankyrin–fodrin membrane cytoskeleton with which
Na/K ATPase is known to associate.
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