by
Rongjuan Mi;
Lina Song;
Yingchun Wang;
Xiaokun Ding;
Junwei Zeng;
Sylvain Lehoux;
Rajindra P. Aryal;
Jianmei Wang;
Vanja K. Crew;
Irma van Die;
Arlene B Chapman;
Richard D. Cummings;
Tongzhong Ju
Background: Tn4 B cells from a patient with Tn antigen-positive leukocytes lack transcripts of Cosmc.
Results: The Cosmc promoter in Tn4 cells is methylated and 5-aza-2′-deoxycytidine treatment restores Cosmc transcription and normal O-glycans.
Conclusion: Methylation-dependent epigenetic silencing of Cosmc occurs in Tn4 cells and results in Tn antigen expression.
Significance: These findings provide a novel mechanism underlying aberrant expression of Tn antigen in human diseases.
The UT-A1 urea transporter is a glycoprotein with two different glycosylated forms of 97 and 117 kDa. In this study, we found the 117-kDa UT-A1 preferentially resides in lipid rafts, suggesting that the glycosylation status may interfere with UT-A1 lipid raft trafficking. This was confirmed by a site-directed mutagenesis study in MDCK cells. The nonglycosylated UT-A1 showed reduced localization in lipid rafts. By using sugar-specific binding lectins, we further found that the UT-A1 in nonlipid rafts contained a high amount of mannose, as detected by concanavalin A, while the UT-A1 in lipid rafts was the mature N-acetylglucosamine-containing form, as detected by wheat germ agglutinin. In the inner medulla (IM) of diabetic rats, the more abundant 117-kDa UT-A1 in lipid rafts was the mature glycosylation form, with high amounts of N-acetylglucosamine and sialic acid. In contrast, in the IM of normal rats, the predominant 97-kDa UT-A1 was the form enriched in mannose. Functionally, inhibition of glycosylation by tunicamycin or elimination of the glycosylation sites by mutation significantly reduced UT-A1 activity in oocytes. Taken together, our study reveals a new role of N-linked glycosylation in regulating UT-A1 activity by promoting UT-A1 trafficking into membrane lipid raft subdomains.—Chen, G., Howe, A. G., Xu, G., Fröhlich, O., Klein, J. D., Sands, J. M. Mature N-linked glycans facilitate UT-A1 urea transporter lipid raft compartmentalization.