FODRIN-ANKYRIN CYTOSKELETON OF CHOROID-PLEXUS PREFERENTIALLY COLOCALIZES WITH APICAL NA+K+-ATPASE RATHER THAN WITH BASOLATERAL ANION-EXCHANGER AE2

A unique feature of the choroid plexus as a single-layer epithelium is its localization of Na+K+-ATPase at its apical (lumenal) surface. In contrast, a band 3 (AE1)-related anion exchanger protein has been localized to the basolateral surface of the choroid plexus. Both Na+K+-ATPase and AE1 in other tissues have been shown to bind via ankyrin to the spectrin-actin-based membrane cytoskeleton. Since linkage of integral membrane proteins to the membrane cytoskeleton is important for their restriction to specialized domains of the cell surface, we investigated the polarity of the choroid plexus membrane cytoskeleton. We developed isoform-specific antibodies to confirm the identity of choroid plexus band 3-related polypeptide as AE2. We demonstrated that ankyrin, fodrin/spectrin, actin, myosin, and cr-actinin are predominantly apical in choroid plexus and preferentially colocalize with apical Na+K+-ATPase rather than with basolateral anion exchanger AE2. Colchicine administration did not alter the polarity of apical cytoskeletal and transport proteins or basolateral AE2 in choroid plexus, suggesting that biosynthetic targeting of these proteins is not microtubule dependent. In choroid plexus papilloma, Na+K+-ATPase and AE2 were decreased in amount and failed to preserve their polarized distributions.