Estrogen-ERα signaling and DNA hypomethylation co-regulate expression of stem cell protein PIWIL1 in ERα-positive endometrial cancer cells

Abstract

Background: We previously identified PIWIL1 as an oncogene involved in endometrial carcinogenesis. However, the mechanism of Piwil1 mediated regulation of tumorigenesis remains poorly understood. Methods: The expression levels of target genes in endometrial cancer cells were detected by quantitative reverse transcription-PCR (RT-qPCR) and western blotting. Up-or down-regulation of ERα or PIWIL1 was achieved by transient transfection with expressing plasmids or short hairpin RNA (shRNA). Dual-luciferase reporter assays and chromatin immunoprecipitation (ChIP) were used to demonstrate the ERα bound to the half estrogen response element (half-ERE) located in PIWIL1 promoter. The expression of PIWIL1 and ERα in endometrial carcinoma tissues were investigated using immunohistochemistry and RT-qPCR. The proliferation ability of cancer cells were evaluated by MTT. Methylation status of the PIWIL1 promoter was detected by bisulfite sequencing PCR (BSP). Results: In the present study, we found that PIWIL1 mediated E 2-stimulated cancer cell proliferation. In ERα-positive endometrial cancer cells, we demonstrated that estrogen-ERα signaling significantly up-regulated the expression of PIWIL1, which was mediated by binding of the ERα onto the PIWIL1 promoter. Furthermore, we found that a half-ERE in the PIWIL1 promoter was essential for ERα binding. The PIWIL1 promoter was hypomethylated in ERα-positive endometrial cancer cells. Treatment with 5-aza-deoxycytidine (5-aza-dC) could up-regulate PIWIL1 expression. Conclusions: These findings uncover a novel molecular mechanism by which estrogen-ERα signaling and DNA hypomethylation co-regulate PIWIL1 expression. These findings provide novel insights into the hormonal regulation of PIWIL1 in endometrial cancer and the PIWIL1's role in estrogen-stimulated endometrial carcinogenesis.

Critical Roles of PIWIL1 in Human Tumors: Expression, Functions, Mechanisms, and Potential Clinical Implications

“…Activation of the RASSF1C/MEK/ERK pathway has been shown to induce PIWIL1 expression in non-small cell lung cancer cells (Reeves et al, 2012). In addition, aberrant promoter DNA hypomethylation is one of the major mechanisms for PIWIL1 overexpression in lung cancer (Xie et al, 2018) and endometrial cancer (Chen et al, 2020). In endometrial cancer cells, estrogen was shown to enhance the transcription of PIWIL1 by facilitating the binding of the ERα to the PIWIL1 promoter (Chen et al, 2020).…”

“…In addition, aberrant promoter DNA hypomethylation is one of the major mechanisms for PIWIL1 overexpression in lung cancer (Xie et al, 2018) and endometrial cancer (Chen et al, 2020). In endometrial cancer cells, estrogen was shown to enhance the transcription of PIWIL1 by facilitating the binding of the ERα to the PIWIL1 promoter (Chen et al, 2020). A positive correlation between HPV16 E7 and PIWIL1 was detected in cervical cancer tissues, although the related mechanism has not yet been described (Liu et al, 2010a).…”

The interplay of sex steroid hormones and microRNAs in endometrial cancer: current understanding and future directions

“…Altered expression of hormone-regulated genes has been linked to a role for PAX2 in fine-tuning the interplay between ER alpha and PR (57,58). Inhibiting ERRa/TGF-b can suppress in vitro invasion of EC cells, and ER signaling increases the expression of the oncogene PIWIL1 in ER-positive endometrial cancer cells (59,60). Tumor suppressor genes such as CACNA2D3 are associated with EC and can exert a tumor-suppressive effect in vitro (3,61).…”

The roles of estrogen receptor alpha (ERα) in endometrial carcinoma

“…In addition to upstream and co-regulators, ERα can also promote EC through its downstream proteins or target genes, mainly re ected in three aspects: proliferation, metastasis and invasion, and anti-apoptosis (Table 4) [44][45][46]. Above all, ERα can promote proliferation by promoting or inhibiting downstream substrates.…”