ABSTRACT:To determine whether the dexamethasone (DEX)-inducible hepatic sulfotransferase gene expression that has been described in the rat is conserved in humans, the effects of DEX treatment on hydroxysteroid sulfotransferase (SULT2A1) and aryl sulfotransferase (SULT1A1) gene expression were investigated in primary cultured human hepatocytes. Hepatocytes were prepared from nontransplantable human livers by collagenase perfusion of the left hepatic lobe, and cultured in Williams' medium E that was supplemented with 0.25 U/ml insulin. As reported in the rat, DEX treatment produced concentration-dependent increases in SULT2A1 mRNA and protein expression, with maximum increases observed at concentrations of DEX that would be expected to activate the pregnane X receptor (PXR) transcription factor. In contrast to the rat, in which DEX-inducible SULT1A1 expression has been demonstrated, SULT1A1 expression in primary cultured human hepatocytes was not measurably increased by DEX. In transient transfections conducted in primary cultured rat hepatocytes, the PXR ligands DEX and pregnenolone-16␣-carbonitrile significantly induced transcription of human and rat SULT2A reporter gene constructs. Cotransfection of either the human or rat SULT2A reporter gene with a PXR dominant negative construct significantly reduced DEX-inducible transcription. These results underscore that while certain features of rat hepatic sulfotransferase gene regulation are conserved in humans, important differences exist across species. The findings also implicate a role for the PXR transcription factor in DEXinducible rat and human SULT2A gene expression.The cytosolic aryl sulfotransferase (SULT1A1 2 ) and hydroxysteroid sulfotransferase (SULT2A1) conjugating enzymes catalyze the transfer of a ϪSO 3 H moiety from the physiological sulfate donor 3Ј-phosphoadenosine-5Ј-phosphosulfate to the appropriate phenolic or hydroxysteroid substrates, respectively (Jakoby et al., 1980). In drug metabolism, sulfate conjugation is recognized as a double-edged sword. As a rule, sulfate conjugates are more polar than the parent substrate and hence, more amenable to excretion and elimination. However, the production of unstable sulfate conjugates can lead to the focused generation of genotoxic species and carcinogen activation.In both rats and humans, SULT1A1 and SULT2A1 enzymes are abundantly expressed in the liver, which is the seat of drug metabolism in mammalian species Falany et al., 1995). Human SULT2A1 is also expressed in the fetal (Parker et al., 1994) and adult adrenal gland (Comer and Falany, 1992), the adult small intestine (Her et al., 1996), and gastric mucosa (Tashiro et al., 2000). Relative to SULT2A1, human SULT1A1 is more extensively expressed in extra-hepatic tissues. SULT1A1 detoxifies common phenolic pharmaceuticals, such as acetaminophen (Larrey et al., 1986) and troglitazone (Honma et al., 2001), and metabolizes the hypotensive and hypertrichotic drug minoxidil to its pharmacologically active form (Falany and Kerl, 1990). The well described g...
