CircRHOT1 restricts gastric cancer cell ferroptosis by epigenetically regulating GPX4

Background

Gastric cancer (GC) is a malignant form of cancer that severely threatens human health. Despite developments on treatment, the prognosis of patients with advanced GC remains poor. Hence, the identification of detailed molecular mechanisms and potential therapeutic targets is of great importance for GC study. In recent years, circular RNAs have been widely reported to be important regulators in cancer initiation and progression. This study sought to evaluate the function of circRHOT1 in GC development.

Methods

Clinical specimens were collected from patients with GC to detect the level of circRHOT1. The expression of circRHOT1 in several GC cell lines was detected by quantitative real-time polymerase chain reaction. Cell Counting Kit 8 (CCK-8), colony formation, and xenograft tumor growth experiments were performed to check cell proliferation. Cell ferroptosis was determined by the levels of intracellular iron, Fe2+ (Divalent iron ion), lipid reactive oxygen species, malondialdehyde, and glutathione. The protein levels of SLC7A11 and glutathione peroxidase-4 (GPX4) were detected by western blot assays. The epigenetic regulation of the GPX4 gene was analyzed by chromatin immunoprecipitation assays.

Results

CircRHOT1 was more highly expressed in the GC tumors than the adjacent non-tumor tissues. The knockdown of circRHOT1 significantly suppressed cell growth (P<0.05) and stimulated the ferroptosis of the GC cells (P<0.05). CircRHOT1 recruited KAT5 (Acetyltransferase Tip60) to promote the acetylation of lysine 27 on histone H3 protein subunit (H3k27Ac) of the GPX4 gene and stimulated gene transcription. The overexpression of KAT5 and GPX4 notably reversed the anti-proliferation effect of circRHOT1 depletion (P<0.05).

Conclusions

CircRHOT1 promoted GC progression and suppressed ferroptosis by recruiting KAT5 to initiate GPX4 transcription. Our findings showed that cirRHOT1 is a promising target for GC treatment.

Circular RNA circRHOT1 contributes to pathogenesis of non-small cell lung cancer by epigenetically enhancing C-MYC expression through recruiting KAT5

Non-small cell lung cancer (NSCLC) one of the most prevalent and severe malignancies globally and the molecular mechanisms of NSCLC are poor understood, limiting the development of diagnostic biomarkers and targeted therapies. Circular RNAs (circRNAs) have been identified as a sort of critical regulator in cancer progression. In this study, we identities the epigenetic regulation function of circular RNA circRHOT1 in promoting NSCLC cell proliferation. We found that circRHOT1 were elevated in the clinical tumor tissues relative to that in the peritumor tissues from NSCLC patients. circRHOT1 was up-regulated in human lung cancer cell lines compared with normal human lung epithelial cell line. MTT assays revealed that the silencing of circRHOT1 by siRNA suppressed cell viabilities of NSCLC cells. Colony formation and Edu assays confirmed that circRHOT1 knockdown attenuated NSCLC cell proliferation in vitro. Meanwhile, the depletion of circRHOT1 induced NSCLC cell apoptosis and cell cycle arrest in vitro. Mechanically, the depletion of circRHOT1 remarkably reduced c-MYC mRNA and protein expression in NSCLC cells. Inhibition of circRHOT1 reduced the enrichment of transcription active marker histone H3 lysine 27 acetylation (H3K27ac) and RNA polymerase II on the promoter of c-MYC. RNA pull down analysis showed that circRHOT1 was able to directly interact with acetyltransferase KAT5 in NSCLC cells. In summary, we concluded that circRHOT1 contributed to pathogenesis of NSCLC by epigenetically enhancing c-MYC expression through recruiting KAT5. CircRHOT1 and KAT5 may be used as the potential targets for NSCLC therapy.

Circular RNA RHOT1 promotes progression and inhibits ferroptosis via mir-106a-5p/STAT3 axis in breast cancer

To explore the effect of circRHOT1 on breast cancer progression and the underlying mechanism. Significantly, our data revealed that the depletion of circRHOT1 was able to repress the proliferation and induce the apoptosis of breast cancer cells. CircRHOT1 knockdown could remarkably inhibit the invasion and migration in the breast cancer cells. Meanwhile, the depletion of circRHOT1 enhanced the erastin-induced inhibition effect on cell growth of breast cancer cells. The circRHOT1 knockdown notably increased the levels of reactive oxygen species (ROS), iron, and Fe²⁺ in breast cancer cells. Mechanically, circRHOT1 was able to sponge microRNA-106a-5p (miR-106a-5p) and inhibited ferroptosis by down-regulating miR-106a-5p in breast cancer cells. Besides, miR-106a-5p induced ferroptosis by targeting signal transducer and activator of transcription 3 (STAT3) in the system. Moreover, the overexpression of STAT3 and miR-106a-5p inhibitor could reverse circRHOT1 knockdown-mediated breast cancer progression. Functionally, circRHOT1 promoted the tumor growth of breast cancer in vivo. In conclusion, we discovered that circRHOT1 contributed to malignant progression and attenuated ferroptosis in breast cancer by the miR-106a-5p/STAT3 axis. Our finding provides new insights into the mechanism by which circRHOT1 promotes the development of breast cancer. CircRHOT1 and miR-106a-5p may serve as potential targets for breast cancer therapy.

CircRHOT1 mediated cell proliferation, apoptosis and invasion of pancreatic cancer cells by sponging miR-125a-3p

Pancreatic cancer patients are asymptomatic at early stages and leading to late diagnoses. Additionally, pancreatic cancer easily metastasizes and is resistant to radiotherapy and chemotherapy. Therefore, it is critical to understand the underlying molecular mechanisms involved in pancreatic cancer to develop more efficient diagnostic and treatment strategies. In this study, we demonstrated that circRHOT1 was overexpressed in pancreatic cancer tissues and cell lines, and it was found to directly bind to miR-125a-3p, acting as an endogenous sponge to inhibit its activity. Knockdown of circRHOT1 expression significantly inhibited proliferation as well as invasion, and it promoted apoptosis of pancreatic cancer cells via the regulation of E2F3 through the targeting of miR-125a-3p. Taken together, our results showed that circRHOT1 plays critical roles in regulating the biological functions of pancreatic cancer cells, suggesting that circRHOT1 may serve as a potential diagnostic marker and therapeutic target for patients with pancreatic cancer.

Circular RNA circRHOT1 promotes hepatocellular carcinoma progression by initiation of NR2F6 expression

Background

Increasing evidence has revealed a close relationship between non-coding RNAs and cancer progression. Circular RNAs (circRNAs), a recently identified new member of non-coding RNAs, are demonstrated to participate in diverse biological processes, such as development, homeostatic maintenance and pathological responses. The functions of circRNAs in cancer have drawn wide attention recently. Until now, the expression patterns and roles of circRNAs in hepatocellular carcinoma (HCC) have remained largely unknown.

Methods

Bioinformatics method was used to screen differentially expressed novel circRNAs in HCC. Northern blotting, qRT-PCR, in situ hybridization (ISH) and RNA-FISH were utilized to analyzed the expression of circRHOT1 in HCC tisues.CCK8, colony formation, EdU assays were used to analyze proliferation of HCC cells. Transwell assay was utilized to analyze HCC cell migration and invasion. FACS was used for apoptosis analysis. Xenograft experiments were used to analyze tumor growth in vivo. Mass spectrum, RNA pulldown, RIP and EMSA was utilized to test the interaction between circRHOT1 and TIP60. RNA-sequencing method was used to analyze the downstream target gene of circRHOT1.

Results

We identified circRHOT1 (hsa_circRNA_102034) as a conserved and dramatically upregulated circRNA in HCC tissues. HCC patients displaying high circRHOT1 level possessed poor prognosis. Through in vitro and in vivo experiments, we demonstrated circRHOT1 significantly promoted HCC growth and metastasis. Regarding the mechanism, we conducted a RNA pulldown with a biotin-labeled circRHOT1-specific probe and found that circRHOT1 recruited TIP60 to the NR2F6 promoter and initiated NR2F6 transcription. Moreover, NR2F6 knockout inhibited growth, migration and invasion, whereas rescuing NR2F6 in circRHOT1-knockout HCC cells rescued the proliferation and metastasis abilities of HCC cells.

Conclusion

Taken together, circRHOT1 inhibits HCC development and progression via recruiting TIP60 to initiate NR2F6 expression, indicating that circRHOT1 and NR2F6 may be potential biomarkers for HCC prognosis.

Electronic supplementary material

The online version of this article (10.1186/s12943-019-1046-7) contains supplementary material, which is available to authorized users.