Polarized secretion of the regulated secretory protein chromogranin A

Bovine chromogranin A (CgA), together with secreted alkaline phosphatase (S EAP) as an external control for apical secretion were expressed in MDCK cel ls to test if CgA contains sorting signals for polarized secretion. CgA, SE AP, and the endogenous apical marker GP80 were secreted 75-80% apically, Ba solateral secretion of SEAP was inhibited 40% by ammonium chloride. Sulfate labeling and digestion with chondroitinase ABC revealed a 120 kDa proteoff lycan-CgA and 75 kDa CgA, Inhibition of proteoglycan synthesis did not affe ct apical secretion of CgA, As CgA is not N-glycosylated, we used tunicamyc in to test if cellular N-glycosylation is required for apical sorting. Tuni camycin reversed the polarity of secretion of CgA to the basolateral side. These results suggest that CgA contains dominant apical and recessive basol ateral sorting information. (C) 2000 Academic Press.