Definition:

Mediates the transport of steroid sulfate conjugates and other specific organic anions. Responsible for the transport of estrone 3-sulfate (E1S) through the basal membrane of syncytiotrophoblast, highlighting a potential role in the placental absorption of fetal-derived sulfated steroids including the steroid hormone precursor dehydroepiandrosterone sulfate (DHEA-S). Mediates the intestinal absorption of sulfated steroids across the apical/luminal membrane of intestinal enterocytes. Also facilitates the uptake of sulfated steroids at the basal/sinusoidal membrane of hepatocytes, therefore accounting for the major part of organic anions clearance of liver. Mediates the uptake of the neurosteroids DHEA-S and pregnenolone sulfate (PregS) into the endothelial cells of the blood-brain barrier as the first step to enter the brain. Also plays a role in the reuptake of neuropeptides such as substance P/TAC1 and vasoactive intestinal peptide/VIP released from retinal neurons. Transports coproporphyrin III (CPIII), a by-product of heme synthesis, and may be involved in the hepatic disposition of CPIII. Also mediates the uptake of prostaglandins D2 (PGD2), E1 (PGE1) and E2 (PGE2), taurocholate, leukotriene C4 and thromboxane B2. Shows a pH-sensitive substrate specificity which may be ascribed to the effect of proton gradient as a driving force of transport, thereby resulting in different transport activities depending on the cell membrane pH. Cytoplasmic glutamate acts as the probable exchanging organic anion in the placenta. Most likely contributes to the oral absorption and the disposition of a wide range of drugs in the intestine and the liver.; [Isoform 3]: Has estrone 3-sulfate (E1S) transport activity comparable with the full-length isoform 1.