Rat liver UDP-glucuronosyltransferase. cDNA sequence and expression of a form glucuronidating 3-hydroxyandrogens

A cDNA clone, pUDPGT(r)-4, encoding a form of rat UDP-glucuronosyltransferase has been isolated from a SV40 expression library. Sequence analysis revealed that the cDNA is 1970 base pairs in length and encodes a protein of 530 amino acids, which has amino- and carboxyl-terminal sequences characteristic of signal peptide and transmembrane segments, respectively. There is one potential asparagine-linked glycosylation site. Transfection of UDPGT(r)-4 cDNA into COS cells resulted in the glucuronidation of etiocholanolone, androsterone, and lithocholic acid in a transient expression assay. Several other common substrates of UDP-glucuronosyltransferase were not conjugated by the UDPGT(r)-4 enzyme. UDPGT(r)-4 cDNA is identical in sequence over a common 1.7 kilobase-region of overlap to UDPGT(r)-1, a cDNA previously isolated in this laboratory (Mackenzie, P.I., Gonzalez, F.J., and Owens, I.S. (1984) J. Biol. Chem. 259, 12153-12160). UDPGT(r)-4 cDNA, however, contains a shorter 3'-untranslated region. Northern analysis showed that the poly(A) RNA counterparts of UDPGT(r)-4 and UDPGT(r)-1 cDNAs are approximately 2.3 and 3.0 kilobases in length, respectively. The steady-state level of UDPGT(r)-4 poly(A) RNA in the liver is 20-fold higher than that of UDPGT(r)-1 poly(A) RNA. These data indicate that the UDPGT(r)-4 enzyme is a 3-hydroxyandrogen UDP-glucuronosyltransferase which is encoded by two distinct species of mRNA transcribed from the same gene.