Abstract

The liver is the predominant organ of metabolism for many endogenous and foreign chemicals. Cytosolic sulfotransferases (SULTs) catalyze the sulfonation of drugs and other xenobiotics, as well as hormones, neurotransmitters, and sterols, with consequences that include enhanced drug elimination, hormone inactivation, and pro-carcinogen bioactivation. SULTs are classified into six gene families, but only SULT1 and SULT2 enzymes are expressed in human liver. We characterized the developmental expression patterns of SULT1 and SULT2 mRNAs and proteins in human liver samples using quantitative RT-PCR (RT-qPCR), RNA sequencing, and targeted quantitative proteomics. Using a set of prenatal, infant, and adult liver specimens, RT-qPCR analysis demonstrated that SULT1A1 (transcript variant 1) expression did not vary appreciably during development; SULT1C2, 1C4, and 1E1 mRNA levels were highest in prenatal and/or infant liver; and 1A2, 1B1, and 2A1 mRNA levels were highest in infant and/or adult. Hepatic SULT1A1 (transcript variant 5), 1C3, and 2B1 mRNA levels were low regardless of developmental stage. RNA sequencing of a different set of liver specimens (prenatal and pediatric) provided generally comparable results to those of the RT-qPCR analysis, with the additional finding that SULT1A3 expression was highest during gestation. Analysis of SULT protein content in a library of human liver cytosols demonstrated that protein levels generally corresponded with the mRNAs, with the major exception that SULT1C4 protein levels were much lower than expected based on mRNA levels. These findings further support the concept that hepatic SULTs play important metabolic roles throughout the human life-course, including early development.