PT  - JOURNAL ARTICLE
AU  - Sanna Siissalo
AU  - Hongbo Zhang
AU  - Eric Stilgenbauer
AU  - Ann Marie Kaukonen
AU  - Jouni Hirvonen
AU  - Moshe Finel
TI  - The Expression of Most UDP-Glucuronosyltransferases (UGTs) Is Increased Significantly during Caco-2 Cell Differentiation, whereas UGT1A6 Is Highly Expressed Also in Undifferentiated Cells
AID  - 10.1124/dmd.108.022335
DP  - 2008 Nov 01
TA  - Drug Metabolism and Disposition
PG  - 2331--2336
VI  - 36
IP  - 11
4099  - http://dmd.aspetjournals.org/content/36/11/2331.short
4100  - http://dmd.aspetjournals.org/content/36/11/2331.full
SO  - Drug Metab Dispos2008 Nov 01; 36
AB  - The human colon carcinoma cell line Caco-2 is often used as a model for intestinal drug absorption. To better understand xenobiotic glucuronidation in Caco-2 cells, we have examined the expression levels of different UDP-glucuronosyltransferases (UGTs) in them. The effects of two main factors were investigated, namely, passage number and cell differentiation. Hence, the mRNA levels of 15 human UGTs of subfamilies 1A and 2B were assessed in both undifferentiated and fully differentiated cells at four passage levels: P31, P37, P43, and P49. Quantitative reverse transcriptase-polymerase chain reaction was used to determine the mRNA levels of individual UGTs, and the values were normalized using β-actin as a reference gene. The results indicate that although passage number in the tested range exerts a mild effect on the expression level of several UGTs, the contribution of cell differentiation is much larger. The expression of nearly all the UGTs that were examined in this study was significantly, sometimes greatly, increased during cell differentiation. UGT1A6 was a distinct exception to this rule, however, because it was already highly expressed in the undifferentiated cells. The mRNA findings were confirmed at the enzyme activity level by measuring the glucuronidation of 1-naphthol, a very good substrate for UGT1A6, as well as estradiol that is not glucuronidated by this enzyme. The results revealed that 1-naphthol glucuronidation activity was high in both the differentiated and undifferentiated cells, whereas estradiol glucuronidation was only detected in the differentiated cells. Thus, Caco-2 cell differentiation plays a major role in UGT expression and ensuing metabolic reactions. The American Society for Pharmacology and Experimental Therapeutics