1. Introduction
Human SULT1E1 cDNA was first isolated, cloned, and characterized from the liver, and its localization was mapped to human chromosome 4
[20][1]. SULT1E1 is expressed in the human embryo, and is also highly expressed in a wide range of fetal tissues, such as the liver, lung, kidney, and hormone-dependent tissues—such as the testis or endometrium—but its expression in adults with normal status is much lower than in the fetus and placenta
[21,22][2][3]. The expression of SULT1E1 varies widely in the human population, although it is not known whether this is under genetic control or not
[23][4]. Thus, it is possible that the variability in SULT1E1 expression results from different chemical influences.
Two agonists of peroxisome-proliferator-activated receptor α (PPARα), WY14643 and IGF-1, show different regulatory effects on the SULT1E1 promoter activity. While WY14643 suppressed SULT1E1 activity, IGF-1 upregulated it, as measured by estrogen levels in endothelial cells and smooth muscle cells
[24][5]. Interestingly, SULT1E1 was attenuated by both transfection with PPARγ small interfering RNA (siRNA) and exposure to GW9662, the PPARγ antagonist
[25][6].
SULT1E1 regulation was observed when hepatocyte nuclear factor 4α (HNF4α) was silenced. The significant suppression of both mRNA and protein levels of SULT1E1 occurred via Farnesoid X receptor (FXR) agonists in HepG2 cells
[26][7]. This finding confirmed that the effect of FXR on E
2 was SULT1E1-dependent. In patients with obstructive cholestasis, the accumulation of bile acids (activator of FXR) led to reduced mRNA and protein expression of hepatic SULT1E1, increased serum E
2 levels, and decreased serum estrone sulfate concentration
[27][8]. Phosphorylated RORα takes a regulatory signal to HNF4α, and then activates the
SULT1E1 promoter in human liver cells
[28][9].
Basal expression of SULT1E1 in the liver is relatively low
[29][10], but its expression and role could be impacted in response to ligands/substrates for nuclear receptors, such as the liver X receptor (LXR)
[29][10], the glucocorticoid receptor (GR)
[30][11], the constitutive androstane receptor (CAR)
[31][12], the estrogen receptor α (ERα)
[32][13], the pregnane X receptor (PXR)
[33][14], and the RAR-related orphan receptor α (RORα)
[34][15] ().
Table 1.
Sult1e1 regulation.