Cholesterol depletion reduces epical transport capacity in epithelial Madin-Darby canine kidney cells

Reduction of the cholesterol level in membranes of epithelial Madin-Darby c anine kidney (MDCK) cells reverses the apical-to-basolateral transport rati o of the apical membrane marker protein influenza virus haemagglutinin and the secreted glycoprotein gp80. At the same time, basolateral transport of the vesicular stomatitis virus G protein is unaffected [Keller and Simons ( 1998) J. Cell Biol. 140, 1357-1367]. To investigate whether cholesterol dep letion influences apical sorting mechanisms specifically, or apical transpo rt capacity more generally, we studied the effect of. cholesterol depletion on the secretion of three different classes of molecules from the apical a nd basolateral surfaces of MDCK cell layers: glycoprotein gp80, sulphated p roteoglycans and proteins, and non-glycosylated rat growth hormone. In each case, cholesterol depletion reduced the fraction secreted to the apical me dium and increased the fraction secreted basolaterally. The fact that this was observed for all sulphated proteins and proteoglycans and for the nongl ycosylated rat growth hormone, which is randomly secreted in untreated cell s. indicates that cholesterol depletion reduces the apical transport capaci ty, rather than interfering with specific recognition and sorting processes .