Abstract

The effect of brefeldin A (BFA) on total and polarized protein secretion was examined in MDCK cells. Increasing concentrations of BFA have increasingly inhibitory effects on total protein secretion. The total protein secretion was essentially unaffected by BFA at 0.5 microgram/ml. When the BFA concentration was increased to 10 and 30 micrograms/ml, the total protein secretion was reduced to about 70 and 25%, respectively, of the control level. Consistent with this effect on total protein secretion, the Golgi structure as revealed by C6-NBD-ceramide (a fluorescent ceramide analog) staining was essentially unaltered by 0.5 microgram/ml BFA, while 10 and 30 micrograms/ml BFA significantly dispersed the Golgi apparatus. When the polarity of protein secretion was examined, it was found that the ratio of proteins secreted from the apical to those from the basolateral surface was reduced from 1.5-2.0 to 0.4-0.7 by all three BFA concentrations. Furthermore, several proteins which are preferentially released from the apical surface were found to be released without apparent surface polarity, while several other proteins which were preferentially released from the basolateral surface were unaffected. This study suggests that BFA, at 0.5 microgram/ml, can selectively inhibit protein secretion from the apical surface without affecting total protein secretion. The inhibition of apical secretion results in enhanced protein secretion from the basolateral surface.