N‐LINKED GLYCOSYLATION IS REQUIRED FOR UT‐A1 UREA TRANSPORTER TRAFFICKING INTO THE MEMBRANE LIPID RAFT SUBDOMAINS

Abstract

UT-A1 urea transporter is a glycoprotein with two differently glycosylated forms of 97 and 117 kDa. In the cell membrane, UT-A1 is associated with lipid rafts. Interestingly, the 117 kDa UT-A1 is preferentially distributed in the lower density fractions after centrifugation, suggesting that the glycosylation may regulate UT-A1 membrane lipid raft trafficking. This was confirmed by a site-directed mutagenesis study. The nonglycosylated UT-A1 mutant lost its ability to traffic into lipid raft subdomains. In addition, the UT-A1 in lipid rafts is the mature glycosylation form which is insensitive to Endo H digestion. In diabetic rat inner medulla, the increased 117 kDa UT-A1 is expressed in lipid rafts and shifted to lower sucrose density fractions. Inhibition of glycosylation by tunicamycin significantly reduced UT-A1 urea transport activity in oocytes. Taken together, our study revealed a new role of N-linked glycosylation in regulating UT-A1 urea transport activity by promoting UT-A1 trafficking into membrane lipid raft subdomains.