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Am J Physiol Gastrointest Liver Physiol 274: G599-G606, 1998;
0193-1857/98 $5.00
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Vol. 274, Issue 3, G599-G606, March 1998

Downregulation of a human colonic sialyltransferase by a secondary bile acid and a phorbol ester

Ming Li1, Ravi Vemulapalli1, Asad Ullah1, Leighton Izu2, Michael E. Duffey2, and Peter Lance1

1 Department of Medicine, Division of Gastroenterology, Buffalo Veterans Affairs Medical Center; and 2 Department of Physiology, State University of New York at Buffalo, Buffalo, New York 14215

Fecal constituents such as bile acids and increased sialylation of membrane glycoproteins by alpha -2,6-sialyltransferase (HST6N-1) may contribute to colorectal tumorigenesis. We hypothesized that bile acids and phorbol ester [12-O-tetradecanoylphorbol-13-acetate (TPA)] would upregulate HST6N-1 in colonic cells. However, deoxycholate (DOC) (300 µmol/l), a secondary bile acid, and TPA (20 ng/ml) decreased expression of an ~100-kDa glycoprotein bearing alpha -2,6-linked sialic acid in a colon cancer cell line (T84) in vitro. HST6N-1 mRNA levels were reduced ~80% by treatment (<= 24 h) with DOC or TPA but not by cholate, a primary bile acid. Treatment (24 h) with DOC or TPA decreased activity of this enzyme to 30% and 13% of control, respectively. These effects of DOC and TPA were transcriptional and were mediated by Ca2+ and protein kinase C, respectively. Thus DOC and TPA both downregulated, and did not upregulate, alpha -2,6-sialyltransferase expression in vitro, but by different transduction pathways. As colorectal tumors grow, their progressive removal from the fecal milieu that normally downregulates this enzyme may favor invasion and metastasis.

glycosyltransferase expression; gene expression regulation; colorectal neoplasia


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