Ectopic expression of a GlcNAc 6-O-sulfotransferase, GlcNAc6ST-2, in colonic mucinous adenocarcinoma

The content of sulfated glycans having 6-O-sulfated GlcNAc residues alters in the course of colonic carcinogenesis. We previously characterized two GlcNAc 6-O-sulfotransferases (SulTs), SulT-a and -b, expressed in colonic normal tissues and adenocarcinomas [Seko et al. (2000) Glycobiology, 10, 919-929]. Levels of the enzymatic activities of SulT-a in normal colonic mucosa are higher than those in colonic adenocarcinomas, and the enzymatic activities of SulT-b are detected only in mucinous adenocarcinomas. To determine which GlcNAc 6-O-SulTs cloned so far correspond to SulT-a and -b, we expressed seven enzymes of a Gal/GalNAc/GlcNAc 6-O-SulT family in COS-7 cells and examined their substrate specificities in comparison with those of SulT-a and -b. GlcNAc6ST-2 (HEC-GlcNAc6ST, LSST, or GST-3) can recognize GlcNAcbeta1-->3GalNAcalpha1-O-pNP as a good acceptor as well as other O-linked- and N-linked-type oligosaccharides, and its substrate specificity was similar to that of SulT-b. GlcNAc6ST-3(I-GlcNAc6ST or GST-4alpha) preferred Galbeta1-->3(GlcNAcbeta1-->6)GalNAcalpha1-O-pNP as an acceptor to the other oligosaccharides examined, and its specificity was similar to that of SulT-a. To confirm these correspondences, we further performed quantitative analyses of transcripts for GlcNAc6ST-2 and -3 genes by competitive RT-PCR. As a result, GlcNAc6ST-2 gene was expressed in almost all the mucinous adenocarcinomas examined and hardly expressed in normal colonic mucosa and nonmucinous adenocarcinoma. Expression levels of transcript for GlcNAc6ST-3 in normal mucosa were significantly higher than those in adenocarcinomas. From these results, it was indicated that GlcNAc6ST-2 corresponds to mucinous adenocarcinoma-specific SulT-b and that expression of GlcNAc6ST-3 is down-regulated in colonic adenocarcinomas.