| Licorice root has been used as a hepatoprotective herbal medicine. Its biological activities have been widely studied. However, the mechanism of its actions remains unknown. In the present study, the effect of an aqueous extract of licorice root (LE) on the expression of UDP-glucuronosyltransferase (UGT) 1A isozymes including UGT 1A6, 1A7 and 1A8 was investigated.; In vitro study was carried out in which rat liver cells (Clone 9) treated with different concentrations (25000–3000 mg/mL) of LE. With the use of semi-quantitative RT-PCR, UGT 1A6, 1A7 and 1A8 were identified and found to be inducible by the LE. UGT 1A6 and 1A7 reached the maximal level after treatment for 16 h while UGT 1A8 was maximally induced after 24 h treatment. Moreover, their expression levels increased gradually with the increase of LE dosage. This induction was suppressed by actinomycin D, indicating that LE was not involved in the stabilization of UGT1A6, 1A7 and 1A8 mRNAs. Transcription of the UGT isozymes was only partially affected after prolonged treatment (16 h) with cycloheximide. The results implied that de novo protein synthesis was not required for the induction. Similar effects were observed in the 3-methylcholanthrene induction experiment. Further analysis of the proximal promoter region of UGT1A isozymes suggests that a normal Xenobiotic Responsive Element (XRE) in UGT1A6 and two non-coding strand XREs in both UGT1A7 and UGT1A8 may be the prime targets for LE-mediated induction. The results reflect the non-directional binding of Ah receptor to the XREs. On the basis of the sequence analysis of the promoter region, UGT1A8 may participate in both cellular differentiation and hormonal regulation.; Comparing the gene expression profile of LE treatment, at least seven candidates were identified to be differentially regulated. IGFBP-2 and TIMP-3 were potently repressed while GSTp, DT diaphorase, PAI-1, fosl-1 and uPAR were up-regulated 3–4 fold by LE. The results were confirmed by Northern blot analysis. Induction of fosl-1 could result in promoting the expression of GSTp, DT diaphorase, uPAR and PAI-1 as AP-1 or ARE, the interacting elements were previously found in their promoter regions. Activation of uPAR and PAM together with down-regulation of TEMP-3 may imply a role of LE in the regulation of cell mobility. |
