N-glycans are not the signal for apical sorting of corticosteroid binding globulin in MDCK cells

It has been suggested that N-glycans act as a general sorting signal for secretory proteins in MDCK cells [Scheiffele et al. (1995) Nature 378, 96–98]. Human corticosteroid binding globulin contains six consensus sites for N-glycosylation and is known to be secreted to the apical side of MDCK cells. Our results show that wild-type corticosteroid binding globulin is N-glycosylated when it is recombinantly expressed in MDCK cells. Six mutants, each lacking one of the N-glycosylation sites, and a mutant lacking all six N-glycosylation sites were also secreted to the apical side of MDCK cells in a polarized manner. Thus, the N-glycans on corticosteroid binding globulin do not act as an apical sorting signal in MDCK cells.