Abstract
Oral clearance of lamotrigine, an antiepileptic drug commonly used in pregnant women, is increased in pregnancy by unknown mechanisms. In this study, we show that 17β-estradiol (E2) up-regulates expression of UDP glucuronosyltransferase (UGT) 1A4, the major enzyme responsible for elimination of lamotrigine. Endogenous mRNA expression levels of UGT1A4 in estrogen receptor (ER) α-negative HepG2 cells were induced 2.3-fold by E2 treatment in the presence of ERα expression. E2 enhanced transcriptional activity of UGT1A4 in a concentration-dependent manner in HepG2 cells when ERα was cotransfected. Induction of UGT1A4 transcriptional activity by E2 was also observed in ERα-positive MCF7 cells, which was abrogated by pretreatment with the antiestrogen fulvestrant (ICI 182,780). Analysis of UGT1A4 upstream regions using luciferase reporter assays identified a putative specificity protein-1 (Sp1) binding site (–1906 to –1901 base pairs) that is critical for the induction of UGT1A4 transcriptional activity by E2. Deletion of the Sp1 binding sequence abolished the UGT1A4 up-regulation by E2, and Sp1 bound to the putative Sp1 binding site as determined by a electrophoretic mobility shift assay. Analysis of ERα domains using ERα mutants revealed that the activation function (AF) 1 and AF2 domains but not the DNA binding domain of ERα are required for UGT1A4 induction by E2 in HepG2 cells. Finally, E2 treatment increased lamotrigine glucuronidation in ERα-transfected HepG2 cells. Together, our data indicate that up-regulation of UGT1A4 expression by E2 is mediated by both ERα and Sp1 and is a potential mechanism contributing to the enhanced elimination of lamotrigine in pregnancy.
Footnotes
-
This work was supported by the National Institutes of Health National Institute of Child Health and Human Development [Grant HD055313 and Fellowship K12HK055892]. The study was conducted in a facility constructed with support from the National Institutes of Health National Center for Research Resources [Grant C06-RR15482].
-
H.C. and K.Y. contributed equally to this work.
-
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
-
doi:10.1124/dmd.109.026609.
-
ABBREVIATIONS: UGT, UDP-glucuronosyltransferase; E2, 17β-estradiol; ER, estrogen receptor; ERE, estrogen response element; AP1, activation protein-1; Sp1, specificity protein-1, ICI 182,780, fulvestrant; tk, thymidine kinase; PCR, polymerase chain reaction; AF, activation function; qRT, quantitative real-time; ds, double-stranded.
-
↵1 Current affiliation: Department of Pharmacology, College of Medicine, University of Illinois at Chicago, Chicago, Illinois.
- Accepted June 18, 2009.
- Received January 7, 2009.
- The American Society for Pharmacology and Experimental Therapeutics
DMD articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|
