TISSUE-SPECIFIC EXPRESSION OF RAT SULFOTRANSFERASE MESSENGER-RNAS

The present study examined the tissue distribution of rat sulfotransfe rase (SULT) mRNAs to assess the relative contribution of each tissue t o the process of sulfation. The SULT isoforms examined were male-domin ant SULTs (SULT1A1, SULT1C1, and SULT1E2), female-dominant SULTs (SULT 20/21, SULT40/41, and SULT60), and the recently cloned, nora sex-depen dent SULT (SULT1B1). SULTs fall into two distinct classes based on sub strate preference: phenol SULTs (SULT1A1, SULT1B1, SULT1C1, and SULT1E 2) and hydroxysteroid SULTs (SULT20/21, SULT40/41, and SULT60). The fo llowing tissues were analyzed for SULT mRNA expression: liver, brain, lung, heart, intestine, kidney, adrenal, prostate, testes, ovary, uter us, and spleen by Northern blot analysis with [alpha-P-32]dATP-labeled oligonucleotide probes specific for individual SULT mRNAs. Tissue exp ression levels of each SULT were quantified and compared with liver ex pression by phosphorautoradiographic analysis. Male-dominant SULT expr ession was observed in many organs, where SULT1A1 was expressed in liv er, brain, lung, heart, intestine, kidney, adrenal, testes, and spleen ; SULT1C1 expression was observed in liver, kidney, and spleen; and SU LT1E2 expression was observed only in liver and heart. The female-domi nant SULTs exhibited a more limited tissue distribution. Expression of SULT20/21 and SULT60 was observed only in liver and adrenal gland, wh ereas SULT40/41 expression was observed only in liver. SULT1B1 was exp ressed to a similar extent in tissues of male and female rats and was detected in liver, intestine, and kidney. Expression of SULT mRNAs in liver was much higher than in other tissues, except for SULT1A1, which exhibited substantial expression in lung, and SULT1B1, which was expr essed at relatively high levels in intestine. These studies indicate t hat liver is the most diverse organ with respect to expression of mult iple SULT enzymes and is therefore the most significant organ involved in sulfation. in contrast to liver, extrahepatic tissues express spec ific SULT mRNAs, and this may be important for the physiological role of each tissue.