Received for publication August 27, 2007.
Revised October 25, 2007.
Accepted for publication October 25, 2007.

Sulfotransferase forms expressed in human intestinal Caco-2 and TC7 cells at varying stages of differentiation and role in benzo[a]pyrene metabolism

Abstract

The Caco-2 cell line and its sub-clone TC7, are frequently used for studying human intestinal transport and metabolism of xenobiotics. We have investigated the expression of soluble sulfotransferases (SULT) in parental Caco-2 and TC7 cells by immunoblotting. SULT1A1, 1A2, 1A3, 1B1, 1C1, 1C2 and 2A1 were expressed in both cell lines. SULT2B1a, 2B1b and 4A1 were absent. SULT1E1 protein was found in TC7, but not in Caco-2, cells. Other differences in SULT between the lines were minor. More important was the influence of differentiation. Expression of the various SULT forms was low, or not detectable, in cultures just reaching confluence, but then increased strongly. Likewise, the rate of sulfation of the model substrate 3-hydroxybenzo[a]pyrene was increased with increasing culture duration. Benzo[a]pyrene-1-sulfate and -3-sulfate were formed in both cell lines, when benzo[a]pyrene was used as a substrate. A further metabolite, 3-hydroxybenzo[a]pyrene-glucuronide, was detected in TC7, but not in parental Caco-2, cells. Cytochrome P450 inducers enhanced the conversion of benzo[a]pyrene to these metabolites, without altering mRNA levels of major phenol-conjugating SULT forms (1A1, 1A3 and 1B1). Overall, differentiated Caco-2 and TC7 cells are rich sources of SULT, as is human intestinal mucosa. The SULT pattern is most similar to that found in small intestine, although levels of SULT1A1 and 1B1 are lower, and those of SULT1C1 are higher in Caco-2 and TC7 cells than previously found in intestinal samples. The differentiation-dependent expression of SULT in the cultured cells reflects the in vivo situation, where SULT expression is focused to differentiated enterocytes.

Key words: extrahepatic drug metabolism, sulfate conjugation, sulfotransferases, UDP glucuronyltransferases