Function And Regulation Of Estrogen Sulfotransferase SULT1E1

Estrogen plays a critical role in the functions of target organs and tissues. It regulates physiologic functions including secretion, metabolism, reproduction and development via binding to estrogen receptors in the cell nucleus or membrane.Estrogen levels are maintained by synthesis and metabolism in vivo. Estrogens are synthesized by the catalysis of aromatase,17β-HSD type I and sulfatase. Sulfation is the main pathway of estrogen metabolism, which involved in the inactivation of estrogen. Estrogen sulfotransferase SULT1E1is the key enzyme in estrogen sulfation. So far, the study on SULT1E1was focus on the relationship between SULT1E1and estrogen sensitive tumors, the mechanisms were not yet clear; moreover, there was no report about SULT1E1expression and its function on endothelium. Therefore, three parts were involved in our present study on SULT1E1functions and regulations as follows:Part1Estrogens are involved in the complex regulation of cell proliferation and apoptosis of hormone sensitive tumors including breast and endometrial cancers. Sulfation is the main pathway for estrogen metabolism, which is believed to be involved in the inactivation of estrogens in target tissues. SULT1E1and PAPSS (PAPSS1and PAPSS2) are responsible for the estrogen sulfation by providing catalyzing enzyme and universal sulfate donor.The expression patterns of SULT1E1and PAPSS were detected in the breast and endometrial tissues by tissue array analysis and the assessment of clinical samples.The estrogen sulfation enzymes were comparatively higher in the tumorous tissues than their adjacent normal tissues. SULT1E1overexpression inhibited the tumorigenesis in subcutaneous xenograft model. By CCK-8assay and flow cytometry assay, overexpression of SULT1E1and PAPSS1by adenovirus blocked the estrogen pro-proliferating effect and promoted cell apoptosis induced by H2O2in MCF-7cells. By Real-time RT-PCR and Western-blot assays, overexpression of SULT1E1and PAPSS1suppressed cell growth and triggered apoptosis by downregulating the levels of c-myc, cyclin D1and bcl-2, meanwhile, upregulating bax expression. These data suggested that overexpression of SULT1E1and PAPSS inhibited MCF-7cells growth and induced apoptosis by regulating the expression of proliferation and apoptosis related genes/proteins. Part217β-estradiol (E2) plays a pivotal role in cardiovascular system by attenuating endothelial dysfunction. E2could be sulfated to estradiol sulfate (E2S) by human estrogen sulfotransferase (hSULT1E1). However, to date, there is no report about the expression and function of SULT1E1in endothelium. We hypothesize that SULT1E1may regulate the functions of endothelial cells. We identified that SULT1E1was highly expressed in human umbilical vein endothelial cells (HUVECs) and stably existed during early passages by immunofluorescence microscopic detection, Realtime RT-PCR and Western-blot. The synthesized siRNA targeting SULT1E1was used to suppress the expression, activity of SULT1E1and estrogen sulfation in HUVECs, which were confirmed by SULT1E1enzyme activity assay in vitro and estrogen sulfation assay in vivo etc.SULT1E1could maximally sulfate80nM E2, while only40nM E2was sulfated by SULT1E1siRNA treatment. Knock-down of SULT1E1regulated inflammatory factors, cholesterol contents, cell migration and their related genes in HUVECs, which could be attenuated by PPARy siRNA or PPARy antagonist GW9662. To further explore the underlying mechanism, we figured that whether estrogen was involved in the SULT1E1reulation on the functions of HUVECs. Compared with the cell responses in the absence of estrogen, the effects of SULT1E1interference on the inflammatory response and lipid metabolism related genes in the presence of80nM estrogen were completely conversed, which could be resisted by the ERβ siRNA or ER antagonist ICI182780. Exogenous estrogen and sulfated estrogen were added in the HUVECs to explain the phenomenon. It was showed that E2S upregulated the expressions of PPARy, IL-4and Iipid metabolism related genes, which was converse to E2. These data suggested that when exogenous estrogen existed, estrogen regulated the functions of HUVECs in control group, while regulation of both E2and E2S were exsited in SULT1E1siRNA group. The study demonstrated that SULT1E1regulated the cell responses depended on the ratio of E2to E2S, because E2and E2S sulfated by SULT1E1could regulate the inflammation and lipid metabolism of endothelial cells via PPARy in different manners.Part3Based on the importance of SULT1E1on the estrogen functions,the regulation on SULT1E1expression was so critical. At present, researches on the regulation of SULT1E1were so little. It was reported that IGF-1could increase the estrogen sulfatase activity of STS in breast cancer cells; PPARa on the regulation of the aminotransferase was still controversial. So, we hypothesis that IGF-1and PPARa may regulate SULT1E1expressions. SULT1E1expressions were identified in HUVECs and HUASMCs by immumofluoresence and western blot assays. IGF-1upregulated SULT1E1expressions, while PPARa agonist WY14643downregulated SULT1E1regulations. By enzyme activity assays, produced sulfated estrogen was increased due to enhanced SULT1E1enzyme activity by IGF-1; sulfated estrogen was reduced due to decreased SULT1E1enzyme activity by WY14643. Luciferase report vector containing SULT1E1promoter was constructed. By luciferase activity assay, the activity of SULT1E1promoter was increased by IGF-1and decreased by WY14643treatment.In summary, overexpression of SULT1E1and PAPSS retarded MCF-7cells growth in vivo and in vitro by arresting cell cycles and inducing apoptosis; knock-down of SULT1E1regulated inflammatory factors, cholesterol content and cell migration via regulating PPARy in endothelial cells; IGF-1and PPARa agonist WY14643regulated SULT1E1expressions in transcription levels and influenced SULT1E1enzyme activity. Our present study provided new insight into SULT1E1functions.