Circular RNAs are a class of non-coding RNAs that are receiving extensive attention. Despite reports showing circular RNAs acting as microRNA sponges, the biological functions of circular RNAs remain largely unknown. We show that in patient tumor samples and in a panel of cancer cells, circ-Foxo3 was minimally expressed. Interestingly, during cancer cell apoptosis, the expression of circ-Foxo3 was found to be significantly increased. We found that silencing endogenous circ-Foxo3 enhanced cell viability, whereas ectopic expression of circ-Foxo3 triggered stress-induced apoptosis and inhibited the growth of tumor xenografts. Also, expression of circ-Foxo3 increased Foxo3 protein levels but repressed p53 levels. By binding to both, circ-Foxo3 promoted MDM2-induced p53 ubiquitination and subsequent degradation, resulting in an overall decrease of p53. With low binding affinity to Foxo3 protein, circ-Foxo3 prevented MDM2 from inducing Foxo3 ubiquitination and degradation, resulting in increased levels of Circular RNAs are a large class of non-coding RNAs that are circularized by joining free 3'-to 5'-ends, forming a circular structure. 1-4Although circular RNAs were initially characterized over 30 years ago, their functions in mammalian cells are still largely unknown. Most circular RNAs are predominantly found in the cytoplasm and contain exons, known as circRNAs.5 A relatively smaller group of circular RNAs that contain both exons and introns are known as EIciRNAs, and are predominantly found in the nucleus. 6 Recent studies have indicated that some circular RNAs contain miRNA binding sites and may function as sponges to arrest miRNA functions. 7,8 It has further been reported that EIciRNAs increase the transcription of their parental genes.9 Recently, we showed that the circular RNA circ-Foxo3 could function by binding to proteins in related signal pathways. 10,11 In the present study, we used computational approach to elucidate the interaction of circ-Foxo3 with MDM2 and p53. The RING-finger domain in the carboxyl terminal of the MDM2 is known to bind RNA specifically in a sequence-specific manner, 12 whereas p53 interacts with RNA via its C-terminal regulatory domain. 13 Our study comprised of computer-aided RNA structure modeling of circ-Foxo3 employing minimum free energy algorithm and machine translation system followed by its molecular interaction with MDM2 (RING-finger domain) and p53 (C-terminal regulatory domain) that includes docking, scoring, clustering, and refinement of the most promising models. The interaction was further confirmed by an approach of molecular experiments to explicate the biological functions of circ-Foxo3. ResultsDecreased expression of circ-Foxo3 in tumors and cancer cells. Downregulation of Foxo3 is often observed in cancer development.14,15 Both circ-Foxo3 and Foxo3 mRNA are encoded by the FOXO3 gene. 16 We found that the levels of circ-Foxo3 in tumor specimen were significantly lower than in the adjacent benign tissue (Figure 1a). We examined circ-Foxo3 expression and detected s...
Circular RNAs (circRNAs) are a subclass of noncoding RNAs widely expressed in mammalian cells. We report here the tumorigenic capacity of a circRNA derived from angiomotin-like1 (circ-Amotl1). Circ-Amotl1 is highly expressed in patient tumor samples and cancer cell lines. Single-cell inoculations using circ-Amotl1-transfected tumor cells showed a 30-fold increase in proliferative capacity relative to control. Agarose colony-formation assays similarly revealed a 142-fold increase. Tumor-take rate in nude mouse xenografts using 6-day (219 cells) and 3-day (9 cells) colonies were 100%, suggesting tumor-forming potential of every cell. Subcutaneous single-cell injections led to the formation of palpable tumors in 41% of mice, with tumor sizes >1 cm in 1 month. We further found that this potent tumorigenicity was triggered through interactions between circ-Amotl1 and c-myc. A putative binding site was identified in silico and tested experimentally. Ectopic expression of circ-Amotl1 increased retention of nuclear c-myc, appearing to promote c-myc stability and upregulate c-myc targets. Expression of circ-Amotl1 also increased the affinity of c-myc binding to a number of promoters. Our study therefore reveals a novel function of circRNAs in tumorigenesis, and this subclass of noncoding RNAs may represent a potential target in cancer therapy.
Circular RNAs are a large group of noncoding RNAs that are widely expressed in mammalian cells. Genome-wide analyses have revealed abundant and evolutionarily conserved circular RNAs across species, which suggest specific physiological roles of these species. Using a microarray approach, we detected increased expression of a circular RNA circ-Dnmt1 in eight breast cancer cell lines and in patients with breast carcinoma. Silencing circ-Dnmt1 inhibited cell proliferation and survival. Ectopic circ-Dnmt1 increased the proliferative and survival capacities of breast cancer cells by stimulating cellular autophagy. We found that circ-Dnmt1-mediated autophagy was essential in inhibiting cellular senescence and increasing tumor xenograft growth. We further found that ectopically expressed circ-Dnmt1 could interact with both p53 and AUF1, promoting the nuclear translocation of both proteins. Nuclear translocation of p53 induced cellular autophagy while AUF1 nuclear translocation reduced Dnmt1 mRNA instability, resulting in increased Dnmt1 translation. From here, functional Dnmt1 could then translocate into the nucleus, inhibiting p53 transcription. Computational algorithms revealed that both p53 and AUF1 could bind to different regions of circ-Dnmt1 RNA. Our results showed that the highly expressed circular RNA circ-Dnmt1 could bind to and regulate oncogenic proteins in breast cancer cells. Thus circ-Dnmt1 appears to be an oncogenic circular RNA with potential for further preclinical research.
The secretin/secretin receptor (SR) axis is upregulated by proliferating cholangiocytes during cholestasis. Secretin stimulates biliary proliferation by downregulation of let-7a and subsequent upregulation of the growth-promoting factor NGF. It is not know if the secretin/SR axis plays a role in subepithelial fibrosis observed during cholestasis. Our aim was to determine the role of secretin/SR axis in the activation of biliary fibrosis in animal models and human primary sclerosing cholangitis (PSC). Studies were performed in Wild-type (WT) mice with bile duct ligation (BDL), BDL SR−/− mice or Mdr2−/− mouse models of cholestatic liver injury. In selected studies, the SR antagonist (Sec 5–27) was used to block the secretin/SR axis. Biliary proliferation and fibrosis were evaluated as well as the secretion of secretin (by cholangiocytes and S cells), the expression of markers of fibrosis, TGF-β1, TGF-β1R, let-7a and downstream expression of NGF. Correlative studies were performed in human control and PSC liver tissue biopsies, serum and bile. SR antagonist reduced biliary proliferation and hepatic fibrosis in BDL WT and Mdr2−/− mice. There was decreased expression of let-7a in BDL and Mdr2−/− cholangiocytes that was associated with increased NGF expression. Inhibition of let-7a accelerated liver fibrosis due to cholestasis. There was increased expression of TGF-β1, TGF-β1R. Significantly higher expression of secretin, SR and TGF-β1 was observed in PSC patient liver samples compared to healthy controls. In addition, there was higher expression of fibrosis genes and remarkably decreased expression of let-7a and increased expression of NGF compared to the control. Conclusion The secretin/SR axis plays a key role in regulating the biliary contribution to cholestasis-induced hepatic fibrosis.
Yap is the key component of Hippo pathway which plays crucial roles in tumorigenesis. Inhibition of Yap activity could promote apoptosis, suppress proliferation, and restrain metastasis of cancer cells. However, how Yap is regulated is not fully understood. Here, we reported Yap being negatively regulated by its circular RNA (circYap) through the suppression of the assembly of Yap translation initiation machinery. Overexpression of circYap in cancer cells significantly decreased Yap protein but did not affect its mRNA levels. As a consequence, it remarkably suppressed proliferation, migration and colony formation of the cells. We found that circYap could bind with Yap mRNA and the translation initiation associated proteins, eIF4G and PABP. The complex containing overexpressed circYap abolished the interaction of PABP on the poly(A) tail with eIF4G on the 5′-cap of the Yap mRNA, which functionally led to the suppression of Yap translation initiation. Individually blocking the binding sites of circYap on Yap mRNA or respectively mutating the binding sites for PABP and eIF4G derepressed Yap translation. Significantly, breast cancer tissue from patients in the study manifested dysregulation of circYap expression. Collectively, our study uncovered a novel molecular mechanism in the regulation of Yap and implicated a new function of circular RNA, supporting the pursuit of circYap as a potential tool for future cancer intervention.
Substance P (SP) is involved in the proliferation of cholangiocytes in bile duct ligated (BDL) mice and human cholangiocarcinoma growth by interacting with the neurokinin-1 receptor (NK-1R). To identify whether SP regulates liver fibrosis during cholestasis, wild type (WT) or NK-1R knockout (NK-1R−/−) mice that received BDL or sham surgery and Mdr2−/− mice treated with either an NK-1R antagonist (L-733,060) or saline were used. Additionally, WT mice were treated with SP or saline intraperitoneally. In vivo, there was increased expression of TAC1 (coding SP) and NK-1R in both BDL and Mdr2−/− mice compared to WT mice. The expression of TAC1 and NK-1R was significantly higher in liver samples from PSC patients compared to healthy controls. Knockout of NK-1R decreased BDL-induced liver fibrosis and treatment with L-733,060 resulted in decreased liver fibrosis in Mdr2−/− mice, which was shown by decreased Sirius red staining, fibrosis gene and protein expression and reduced transforming growth factor-β1 levels in serum and cholangiocytes supernatants. Furthermore, we observed that reduced liver fibrosis in NK-1R−/− mice with BDL surgery or Mdr2−/− mice treated with L-733,060 was associated with enhanced cellular senescence of hepatic stellate cells (HSCs) and decreased senescence of cholangiocytes. In vitro, L-733,060 inhibited SP-induced expression of fibrotic genes in HSCs and cholangiocytes. Treatment with L-733,060 partially reversed SP-induced decrease of senescence genes expression in cultured HSCs and SP-induced increase of senescence-related genes expression in cultured cholangiocytes. Collectively, our results demonstrated the regulatory effects of the SP/NK-1R axis on liver fibrosis through changes in cellular senescence during cholestatic liver injury.
TP53 mutations occur in many different types of cancers that produce mutant p53 proteins. The mutant p53 proteins have lost wild-type p53 activity and gained new functions that contribute to malignant tumor progression. Different p53 mutations create distinct profiles in loss of wild-type p53 activity and gain of functions. Targeting the consequences generated by the great number of p53 mutations would be extremely complex. Therefore, in this study we used a workaround and took advantage of the fact that mutant p53 cannot bind H2AX. Using this, we developed a new approach to repress the acquisition of mutant p53 functions. We show here that the delivery of a circular RNA circ-Ccnb1 inhibited the function of three p53 mutations. By microarray analysis and real-time PCR, we detected decreased circ-Ccnb1 expression levels in patients bearing breast carcinoma. Ectopic delivery of circ-Ccnb1 inhibited tumor growth and extended mouse viability. Using proteomics, we found that circ-Ccnb1 precipitated p53 in p53 wild-type cells, but instead precipitated Bclaf1 in p53 mutant cells. Further experiments showed that H2AX serves as a bridge, linking the interaction of circ-Ccnb1 and wild-type p53, thus allowing Bclaf1 to bind Bcl2 resulting in cell survival. In the p53 mutant cells, circ-Ccnb1 formed a complex with H2AX and Bclaf1, resulting in the induction of cell death. We found that this occurred in three p53 mutations. These results shed light on the possible development of new approaches to inhibit the malignancy of p53 mutations.
Melatonin therapy or prolonged exposure to complete darkness reduces biliary hyperplasia and liver fibrosis in bile-duct-ligated (BDL) rats; however, no information exists in primary sclerosing cholangitis (PSC). Thus, we aimed to determine the therapeutic effects of prolonged dark therapy or melatonin administration on hepatic fibrosis in the multidrug resistance gene 2-knockout (Mdr2) mouse model of PSC. Melatonin levels, biliary mass, liver fibrosis, angiogenesis and miR-200b expression were evaluated in wild-type and Mdr2 mice exposed to darkness or melatonin treatment or in male patients with PSC and healthy controls. Mdr2 mice were also treated with miR-200b inhibitor or control before evaluating biliary mass, liver fibrosis, and angiogenesis. After overexpression of arylalkylamine -acetyltransferase (AANAT; the enzyme regulating melatonin synthesis) or inhibition of miR-200b in cholangiocytes and hepatic stellate cells, we evaluated angiogenesis and fibrosis gene expression. After exposure to darkness or administration of melatonin, Mdr2 mice show elevated serum melatonin levels and inhibition of biliary mass, along with reduction of liver fibrosis and angiogenesis. MicroRNA PCR analysis demonstrated that miR-200b expression increased in Mdr2 mice and patients with PSC compared with controls and decreased in Mdr2 mice subjected to dark exposure or melatonin treatment. Inhibition of miR-200b in Mdr2 ablates biliary proliferation, liver fibrosis, and angiogenesis. , overexpression of AANAT or inhibition of miR-200b in cholangiocytes and hepatic stellate cells decreased the expression of miR-200b, angiogenesis, and fibrosis genes. Dark therapy or targeting melatonin/miR-200b axis may be important in the management of biliary damage and liver fibrosis in cholangiopathies including PSC.-Wu, N., Meng, F., Zhou, T., Han, Y., Kennedy, L., Venter, J., Francis, H., DeMorrow, S., Onori, P., Invernizzi, P., Bernuzzi, F., Mancinelli, R., Gaudio, E., Franchitto, A., Glaser, S., Alpini G. Prolonged darkness reduces liver fibrosis in a mouse model of primary sclerosing cholangitis by miR-200b down-regulation.
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