The Circular RNA circZFR Phosphorylates Rb Promoting Cervical Cancer Progression by Regulating the SSBP1/CDK2/cyclin E1 Complex

Abstract

Background: As a novel type of non-coding RNA, circular RNAs (circRNAs) play a critical role in the initiation and development of various diseases, including cancer. However, the exact function of circRNAs in human cervical cancer remains largely unknown. Methods: We identified the circRNA signature of upregulated circRNAs between cervical cancer and paired adjacent normal tissues. Using two different cohorts and GEO database, a total of six upregulated circRNAs were identified with a fold change >2, and P <0.05. Among these six circRNAs, hsa_circ_0072088 (circZFR) was the only exonic circRNA significantly overexpressed in cervical cancer. Functional experiments were performed to investigate the biological function of circZFR. CircRNA pull-down, circRNA immunoprecipitation (circRIP) and Co-immunoprecipitation (Co-IP) assays were executed to investigate the molecular mechanism underlying the function of circZFR.Results: Functionally, circZFR knockdown represses the proliferation, invasion, and tumor growth. Furthermore, circRNA pull-down experiments combined with mass spectrometry unveil the interactions of circZFR with Single-Stranded DNA Binding Protein 1 (SSBP1). Mechanistically, circZFR bound with SSBP1, thereby promoting the assembly of CDK2/cyclin E1 complexes. The activation of CDK2/cyclin E1 complexes induced p-Rb phosphorylation, thus releasing activated E2F1 leading to cell cycle progression and cell proliferation. Conclusion: Our findings provide the first evidence that circZFR is a novel onco-circRNA and might be a potential biomarker and therapeutic target for cervical cancer patients.

CircRNAs and their regulatory roles in cancers

“…The activated complex phosphorylates p-Rb and interrupts its pairing with E2F1. Subsequently, the released E2F1 transcription factor promotes the G1/S transition and the proliferation of CC cells after it triggers the transcription of genes associated with target DNA replication (Zhou et al 2021).…”

Investigating the Underlying Mechanisms of Circular RNAs and Their Application in Clinical Research of Cervical Cancer

“…They can form an SSBP1-circZFR complex that activates the CDK2/cyclin-E1 complex to induce p-Rb phosphorylation, thereby releasing the E2F1 transcription factor. Therefore, this promotes the progression of the CC cell cycle and induces the proliferation of CC cells ( Zhou et al, 2021 ). In another study, circCDKN2B-AS1 promoted the aerobic glycolysis of CC cells by recruiting IM3 protein, which is also a kind of RBP, to regulate the stability of the rate-limiting enzyme Hexokinase 2 (HK2) mRNA in the aerobic glycolysis pathway.…”

“…ROC analysis showed that the AUC of circ_0018289 was 0.907 ( He et al, 2020 ), the AUC of hsa_circ_0107593 was 0.869 ( Liao et al, 2020 ), and the AUC of circZFR was 0.88, which could significantly separate tumor tissue from ANT. Moreover, the clinical pathological features of 40 patients with CC revealed a positive correlation between circZFR expression and lymphatic metastasis, Ki67 values, and squamous cell carcinoma antigen (SCC Ag) value ( Zhou et al, 2021 ). So circ_0018289, hsa_circ_0107593, and circZFR can also serve as potential disease monitoring biomarkers of CC.…”

Circular non‐coding RNA circ_0072088 serves as a ceRNA, targeting the miR‐1225‐5p/WT1 axis to regulate non‐small cell lung cancer cell malignant behavior

“…Analogously, circ_0000376 has also been found to serve as a competitive endogenous RNA (ceRNA) of miR‐1182 to accelerate migration, invasion, and glycolysis through upregulating NOVA2 in NSCLC 13 . Circ_0072088, a well‐known circRNA originating from zinc finger RNA binding protein (ZFR), has been verified to be a carcinogenic factor in cervical and esophageal squamous cell cancers 14,15 . It has also been reported that the upregulation of circ_0072088 might contribute to pancreatic ductal adenocarcinoma cell glycolysis in vitro 16 .…”

“…13 Circ_0072088, a well-known circRNA originating from zinc finger RNA binding protein (ZFR), has been verified to be a carcinogenic factor in cervical and esophageal squamous cell cancers. 14,15 It has also been reported that the upregulation of circ_0072088 might contribute to pancreatic ductal adenocarcinoma cell glycolysis in vitro. 16 Furthermore, recent evidence indicated that circ_0072088 could facilitate NSCLC development by increasing cell growth and metastasis.…”