RICIN-RESISTANT MADIN-DARBY CANINE KIDNEY-CELLS MISSORT A MAJOR ENDOGENOUS APICAL SIALOGLYCOPROTEIN

gp114 is a major sialoglycoprotein expressed on the apical membrane of Madin-Darby canine kidney (MDCK) II cells. We investigated its distribution in two lectin-resistant mutant cell lines derived from MDCKII cells, MDCKII-RCA(r) and MDCKII-ConA(r) cells. gp114 was present on the apical membrane of MDCKII-ConA(r) cells but was predominantly basolateral in MDCKII-RCA(r) cells. No change of polarity was observed for several apical and basolateral markers in this cell line. Reversal of polarity of gp114 mainly resulted from a modification of its intracellular sorting. gp114 showed altered endocytosis in MDCKII-RCA(r) cells. In MDCKII cells gp114 was slowly endocytosed, whereas in MDCKII-RCA(r) cells endocytosis of gp114 was highly increased. Using mannosidase I and II inhibitors we found that N-glycosylation only slightly affects gp114 sorting and endocytosis. Our results suggest that gp114 or an associated component in MDCK-RCA(r) fails to express apical information or that a mutation creates a basolateral sorting signal which could be related to endocytic signals.