Increased expression of the secretory Na+-K+-2Cl- cotransporter with differentiation of a human intestinal cell line

We studied the expression of the secretory Na(+)-K(+)- 2Cl- cotransporter during epithelial differentiation using the clonal human adenocarcinoma cell line HT29-18. Differentiation of HT29-18 cells was accompanied by up to 7-fold increases in cotransporter protein levels, approximately 3-fold increases in cotransporter mRNA levels, and approximately 2.5-fold increases in cotransporter functional expression. No apparent change in cotransporter mRNA stability was observed with differentiation, suggesting that these effects may be due to differences in mRNA transcription rate. Confocal immunofluorescence microscopy showed that undifferentiated cells grew in multilayers and exhibited a diffuse, apparently unlocalized membrane labeling by anti-Na(+)-K(+)-2Cl- cotransporter antibody. In contrast, differentiated cells grew in monolayers with strong cotransporter labeling localized to the basal and lateral membranes. Taken together with previous studies demonstrating that expression of the cystic fibrosis transmembrane regulator is also increased following HT29-18 cell differentiation, our results suggest that these cells provide a promising model for studying epithelial differentiation to a Cl- secretory phenotype.