Down‐regulation of Gal 3–O‐sulfotransferase‐2 (Gal3ST‐2) Expression in Human Colonic Non‐mucinous Adenocarcinoma

Expression levels of sulfomucin in human colonic adenocarcinomas are lower than those in normal colonic mucosa; this should be in part caused by down‐regulation of expression of sulfotransferases, but it remains unclear which Gal 3‐O‐sulfotransferase (Gal3ST) is responsible for the bio‐ synthesis of sulfomucin. In this study, we first examined the substrate specificities of four Gal3STs cloned so far, and found that Galβ1→3GlcNAcβl→3Galβ1→4Glc (LNT) can be utilized only by Gal3ST‐2 as an acceptor substrate. The substrate specificity of Gal3ST‐2 is closely similar to those of Gal3ST activities present in human normal mucosa and adenocarcinomas, suggesting that Gal3ST‐2 is the dominant Gal3ST in colon and colonic cancer. Secondly, using LNT as a substrate, we comparatively analyzed levels of Gal3ST‐2 activities in non‐mucinous adenocarcinoma, mucinous adenocarcinomas, and the adjacent normal mucosa. We found that levels of Gal3ST‐2 activities in non‐mucinous adenocarcinoma are significantly lower than those in the adjacent normal mucosa, while those in mucinous adenocarcinomas are not significantly different from those in the adjacent normal mucosa. Moreover, we showed by a competitive RT‐PCR method that expression levels of transcript for Gal3ST‐2 in non‐mucinous adenocarcinoma are lower than those in normal mucosa. These results suggest that Gal3ST‐2 is one of the enzymes responsible for biosynthesis of sulfomucin, and that expression levels of Gal3ST‐2 are down‐regulated in non‐mucinous adenocarcinoma.