Human CD8α glycoprotein is expressed at the apical plasma membrane domain in permanently transformed MDCK II clones

Madin-Darby canine kidney cells (MDCK II) have been cotransfected with plasmids expressing the human CD8α glycoprotein and the bacterial gene which confers resistance to neomycin. Stable transformants have been isolated in the presence of G-418 in the culture medium and screened for CD8α expression by immunofluorescence. The three clones we have characterized showed: 1) high level of synthesis and efficient surface expression of glycosylated, homodimeric CD8α and 2) preferential apical deposition of CD8α in confluent monolayers. This polar distribution has been measured in cells grown on a plastic substratum as well as on nitrocellulose filter by means of EM immunocytochemistry and surface radioimmunoassay. CD8α was 6 to 11-fold enriched on the apical membrane whereas the 58 kDa protein, a basolateral marker in MDCK II cells, resulted about 9-fold enriched on the basolateral membrane of the three clones. We believe these permanently transformed clones could prove to be a useful tool with which to study cell polarity.