Evidence for regulation of UDP-glucuronosyltransferase (UGT) 1A1 protein expression and activity via DNA methylation in healthy human livers

<jats:title>Abstract</jats:title><jats:sec><jats:title>Objectives</jats:title><jats:p>Interindividual variability in glucuronidation of bilirubin and drugs by UDP-glucuronosyltransferase 1A1 (UGT1A1) is considerable and only partially explained by genetic polymorphisms and enzyme inducers. Here we determined whether a well-known epigenetic modification, cytosine methylation, explains a proportion of this variability in human liver.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>UGT1A1 phenotypes, including UGT1A1 protein and bilirubin glucuronidation, and UGT1A1*28 genotype were determined using a human liver bank (n = 46). Methylation levels were quantified at 5 CpG sites associated with known transcription factor response elements in the UGT1A1 promoter and distal enhancer, as well as a CpG-rich island 1.5 kb further upstream.</jats:p></jats:sec><jats:sec><jats:title>Key findings</jats:title><jats:p>Individual CpG sites showed considerable methylation variability between livers, ranging from 10- to 29-fold variation with average methylation levels from 25 to 41%. Multivariate regression analysis identified *28/*28 genotype, −4 CpG site methylation and alcohol history as significant predictors of UGT1A1 protein content. Exclusion of livers with *28/*28 genotype or alcohol history revealed positive correlations of −4 CpG methylation with bilirubin glucuronidation (R = 0.73, P &lt; 0.00001) and UGT1A1 protein content (R = 0.54, P = 0.008).</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>These results suggest that differential methylation of the −4 CpG site located within a known USF response element may explain a proportion of interindividual variability in hepatic glucuronidation by UGT1A1.</jats:p></jats:sec>