Human liver estrogen sulfotransferase: identification by cDNA cloning and expression

Sulfation is an important pathway in the biotransformation of steroid hormones such as estrogens. Human liver contains three well-characterized sulfotransferase (ST) enzymes, dehydroepiandrosterone (DHEA) ST and two forms of phenol sulfotransferase (PST). Although two of these enzymes, DHEA ST and one form of PST, can catalyze the sulfate conjugation of estrogens, our goal was to test the hypothesis that human liver might also contain a distinct estrogen ST (EST). We used the PCR to clone a human liver EST cDNA by utilizing degenerate oligonucleotide primers designed on the basis of highly conserved EST sequences in non-human species to amplify a 512 nucleotide portion of the open reading frame (ORF) with single-stranded human liver cDNA as a template. Rapid amplification of cDNA ends (RACE) was then used to obtain the 5'- and 3'-ends of the EST cDNA. The ORF of this cDNA consisted of 882 nucleotides and encoded 294 amino acids. The protein encoded by the human liver EST cDNA was 81%, 73%, and 72% identical to the amino acid sequences of guinea pig adrenocortical, bovine placental and rat liver ESTs, respectively. Human liver EST transiently expressed in COS-1 cells was capable of catalyzing the sulfation of estrone, DHEA and 4-nitrophenol, but not that of dopamine. The expressed human liver EST was also characterized with regard to thermal stability, inhibition by 2,6-dichloro-4-nitrophenol (DCNP) and response to NaCl. Identification of human liver EST by cloning and expression of its cDNA should enhance understanding of the enzymology and regulation of the biotransformation of estrogens and other steroids in humans.