Abstract
Colon cancer cells express the carbohydrate determinant sialyl Lewis(x), while they exhibit markedly decreased the expression of its sulfated derivative, sialyl 6-sulfo Lewis(x). In contrast, normal colonic epithelial cells strongly express sialyl 6-sulfo Lewis(x), but they virtually do not express sialyl Lewis(x). Impaired sulfation was therefore suggested to occur during the course of malignant transformation of colonic epithelial cells and was assumed to be responsible for the increased sialyl Lewis(x) expression in cancers. To elucidate the molecular biological background of the impaired sulfation in cancers, we studied the expression levels of mRNA for 6-O-sulfotransferase isoenzymes, PAPS synthases and transporters, and a cell membrane sulfate transporter, DTDST, in cancer tissues. The most striking decrease in cancer cells compared with nonmalignant epithelial cells was noted in the transcription of the DTDST gene (P = 0.0000014; n = 20). Most cultured colon cancer cells had a diminished DTDST transcription, which was restored when cultured with histone deacetylase inhibitors. Suppression of DTDST transcription under the control of a tet-off inducible promoter resulted in increased sialyl Lewis(x) expression and reduced sialyl 6-sulfo Lewis(x) expression. Unexpectedly, the growth rate of the cancer cells was markedly enhanced when transcription of DTDST was suppressed. These results show that the decrease in the transcription of the sulfate transporter gene is the major cause of decreased expression of sialyl 6-sulfo Lewis(x) and increased expression of sialyl Lewis(x) in colon cancers. The results also suggest that the diminished DTDST expression is closely related to enhanced proliferation of cancer cells.
Highlights
Malignant transformation is frequently associated with a drastic alteration in the surface expression of carbohydrate determinants [1,2,3,4]
Colon cancer cells strongly express sialyl Lewisx, while they exhibit markedly decreased sialyl 6-sulfo Lewisx expression compared with normal colonic epithelial cells
From the comparison of the structures of the two glycans, impaired sulfation at the C6 position of the N-acetylglucosamine moiety was assumed to have occurred during the course of malignant transformation of colonic epithelial cells, and this was thought to be responsible for the increased expression of sialyl Lewisx in cancers
Summary
Malignant transformation is frequently associated with a drastic alteration in the surface expression of carbohydrate determinants [1,2,3,4]. The sialyl Lewisx determinant is a typical cancer-associated glycan [1,2,3, 7,8,9], but the molecular mechanism responsible for preferential expression of the determinant in cancer has not been fully elucidated. Colon cancer cells strongly express sialyl Lewisx, while they exhibit markedly decreased sialyl 6-sulfo Lewisx expression compared with normal colonic epithelial cells. Impaired 6-sulfation was suggested to occur during the course of malignant transformation of colonic epithelial cells and to be responsible for the preferential expression of sialyl Lewisx in cancers [8,9,10]. It has long been known that carbohydrate sulfation is generally suppressed in colon cancers compared with nonmalignant colonic epithelial cells [12,13,14] with a few exceptions [15], and this was expected to be related to the decreased 6-sulfation in cancers
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