Targeting the estrogen receptor alpha (ERα)-mediated circ-SMG1.72/miR-141-3p/Gelsolin signaling to better suppress the HCC cell invasion

It has recently been shown that the upregulation of a pseudogene specific to a protein-coding gene could function as a sponge to bind multiple potential targeting microRNAs (miRNAs), resulting in increased gene expression. Similarly, it was recently demonstrated that circular RNAs can function as sponges for miRNAs, and could upregulate expression of mRNAs containing an identical sequence. Furthermore, some mRNAs are now known to not only translate protein, but also function to sponge miRNA binding, facilitating gene expression. Collectively, these appear to be effective mechanisms to ensure gene expression and protein activity. Here we show that expression of a member of the forkhead family of transcription factors, Foxo3, is regulated by the Foxo3 pseudogene (Foxo3P), and Foxo3 circular RNA, both of which bind to eight miRNAs. We found that the ectopic expression of the Foxo3P, Foxo3 circular RNA and Foxo3 mRNA could all suppress tumor growth and cancer cell proliferation and survival. Our results showed that at least three mechanisms are used to ensure protein translation of Foxo3, which reflects an essential role of Foxo3 and its corresponding non-coding RNAs.

Hepatocellular carcinoma (HCC) is sexually dimorphic in both rodents and humans, with significantly higher incidence in males, an effect that is dependent on sex hormones. The molecular mechanisms by which estrogens prevent and androgens promote liver cancer remain unclear. Here, we discover that sexually dimorphic HCC is completely reversed in Foxa1- and Foxa2-deficient mice after diethylnitrosamine-induced hepatocarcinogenesis. Coregulation of target genes by Foxa1/a2 and either the estrogen receptor (ERα) or the androgen receptor (AR) was increased during hepatocarcinogenesis in normal female or male mice, respectively, but was lost in Foxa1/2-deficient mice. Thus, both estrogen-dependent resistance to and androgen-mediated facilitation of HCC depend on Foxa1/2. Strikingly, single nucleotide polymorphisms at FOXA2 binding sites reduce binding of both FOXA2 and ERα to their targets in human liver and correlate with HCC development in women. Thus, Foxa factors and their targets are central for the sexual dimorphism of HCC. Copyright © 2012 Elsevier Inc. All rights reserved.

Men have a higher incidence of hepatocellular carcinoma (HCC) than women, which is believed to partly be because of protective effects of estrogen. We sought to determine whether there were differences in levels of microRNA (miRNA) molecules between male and female HCC samples. The expression profiles of a panel of candidate miRNAs were compared between male and female HCC tissues using the TaqMan miRNA assay. A luciferase reporter assay was used to identify mRNA targets recognized by specific miRNAs. The levels of pri- and pre-miRNA for each specific miRNA were assayed by quantitative reverse-transcription polymerase chain reaction to delineate the step deregulated in the biogenesis process. Finally, a colorimetric assay was used to determine the effect of specific miRNAs on hepatoma cell proliferation. The miR-18a miRNA increased specifically in samples from female HCC patients (female/male ratio, 4.58; P = .0023). The gene ESR1, which encodes the estrogen receptor-alpha (ERalpha), was identified as a target of miR-18a. miR-18a can repress ERalpha translation by binding to its mRNA at the 3' untranslated region. Increased levels of miR-18a in female HCC tissues correlated with reduced ERalpha expression; the level of pre-miR-18a changed in concordance with that of mature miR-18a in these tissues. Overexpression of miR-18a decreased ERalpha levels but stimulated the proliferation of hepatoma cells. This study provides a novel miRNA-mediated regulatory mechanism for controlling ERalpha expression in hepatocytes. miR-18a prevents translation of ERalpha, potentially blocking the protective effects of estrogen and promoting the development of HCC in women.