ANALYSIS OF THE PROMOTER OF HUMAN BILIRUBIN UDP-GLUCURONOSYLTRANSFERASE GENE (UGT1-ASTERISK-1) IN RELEVANCE TO GILBERTS-SYNDROME

Bilirubin UDP-glucuronosyltransferase 1 (B-UGT(1)) is an enzyme respon sible for hepatic bilirubin glucuronidation and in Gilbert's syndrome, its activity is decreased to 30% of normal. About one third of the pa tients we analyzed with the syndrome had a homozygous TATA box mutatio n in UGT11 coding for B-UGT(1), i.e. (TA)(7)TAA instead of (TA)(6)TAA . Since the frequency was much higher than in the normal Japanese popu lation (approximate to 1%), the mutation was considered to be closely associated with the etiology of the syndrome. Since these patients did not have any structural mutations in UGT11, we suspected a transcrip tional defect of the gene. We analyzed the promoter region !up to - 31 90) of UGT11 by transient transfection assay to identify transcriptio nally regulatory sequences and found two elements: one was between - 1 362 and - 1220 and the other between - 113 and - 70. The proximal one (PE) consisted of two elements, E-box (-104 to -95) and an HNF-1 site (-91 to -79). The two TATA boxes were compared in promoter activity, b ut no substantial difference was observed. Distal element (DE) and PE were then analyzed in these patients' DNA (n = 6) by PCR and direct se quencing. The same homozygous mutation (C-1353A) was found in two of t hem, but the reduction in promoter activity was only 15%. These result s suggest that the TATA box mutation itself is not the major cause of the syndrome and may be genetically linked to an, as yet, unidentified defect in the further upstream or in the intronic region of UGT11. ( C) 1997 Elsevier Science Ireland Ltd.