Supplementary Figure Legends 1-4 from Epigenetic Silencing of the Sulfate Transporter Gene DTDST Induces Sialyl Lewisx Expression and Accelerates Proliferation of Colon Cancer Cells
ARTICLE ABSTRACTColon cancer cells express the carbohydrate determinant sialyl Lewisx, while they exhibit markedly decreased the expression of its sulfated derivative, sialyl 6-sulfo Lewisx. In contrast, normal colonic epithelial cells strongly express sialyl 6-sulfo Lewisx, but they virtually do not express sialyl Lewisx. 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 Lewisx 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 Lewisx expression and reduced sialyl 6-sulfo Lewisx 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 Lewisx and increased expression of sialyl Lewisx in colon cancers. The results also suggest that the diminished DTDST expression is closely related to enhanced proliferation of cancer cells. Cancer Res; 70(10); 4064–73. ©2010 AACR.