The Roles of CircRNAs in Bladder Cancer: Biomarkers, Tumorigenesis Drivers, and Therapeutic Targets

Circular RNAs: driving forces behind chemoresistance and immune evasion in bladder cancer

Bladder cancer (BCa) is characterized by recurring relapses and the emergence of chemoresistance, especially against standard treatments like cisplatin and gemcitabine. Despite its significance, the molecular mechanisms underlying chemoresistance in BCa remain elusive. Recent studies have revealed that circular RNAs (circRNAs) are pivotal regulators of cancer progression and chemoresistance. Through their function as miRNA sponges and protein sequesters, circRNAs modulate the expression of key genes, ultimately driving either drug resistance or sensitivity in BCa. The complex interplay between circRNAs and chemoresistance suggests that they may represent promising therapeutic targets for overcoming treatment resistance in patients with BCa. This review aims to summarize the current understanding of circRNAs' regulatory roles in chemoresistance and provide insights into their potential as therapeutic targets, particularly in the context of cisplatin and gemcitabine resistance. Furthermore, we explore how chemoresistance can also impact tumor immune evasion, thereby affecting the tumor microenvironment. Our findings may pave the way for the advancement of innovative treatment approaches for bladder cancer.

CircACTR2 promotes bladder cancer progression through IKBKB-mediated NF-κB signaling pathway activation

Background

Circular RNAs (circRNAs) have significant roles in tumor progression. The role of circRNA derived from ARP2 actin-related protein 2 homolog (circACTR2) has been reported in various human diseases. However, the functions and regulatory mechanisms of circACTR2 in Bladder Cancer (BCa) remain unknown.

Objectives

This study aims to explore the biological role and regulatory mechanism of circACTR2 in BCa.

Methods

We analyzed the effects of circACTR2 on BCa through bioinformatics analyses, RT-qPCR, and cell function assays.

Results

We observed the upregulation of circACTR2 in BCa tissues and validated its circular structure. Loss-of-function assays demonstrated that silencing circACTR2 suppressed the proliferation, invasion, and migration of BCa cells. Mechanistic investigation revealed that circACTR2 sponges miR-219a-2-3p to elevate the expression of the inhibitor of nuclear factor kappa B kinase subunit beta (IKBKB). This induced upregulation of IKKβ protein promoted the nuclear translocation of p65, thereby activating the NF-κB signaling pathway.

Conclusions

Our findings indicate that circACTR2 promotes BCa cell proliferation, migration, and invasion by activating the NF-κB signaling pathway via the miR-219a-2-3p/IKBKB axis, potentially unveiling a new therapeutic target for BCa.

Non-coding RNA transcripts, incredible modulators of cisplatin chemo-resistance in bladder cancer through operating a broad spectrum of cellular processes and signaling mechanism

Bladder cancer (BC) is a highly frequent neoplasm in correlation with significant rate of morbidity, mortality, and cost. The onset of BC is predominantly triggered by environmental and/or occupational exposures to carcinogens, such as tobacco. There are two distinct pathways by which BC can be developed, including non-muscle-invasive papillary tumors (NMIBC) and non-papillary (or solid) muscle-invasive tumors (MIBC). The Cancer Genome Atlas project has further recognized key genetic drivers of MIBC along with its subtypes with particular properties and therapeutic responses; nonetheless, NMIBC is the predominant BC presentation among the suffering individuals. Radical cystoprostatectomy, radiotherapy, and chemotherapy have been verified to be the common therapeutic interventions in metastatic tumors, among which chemotherapeutics are more conventionally utilized. Although multiple chemo drugs have been broadly administered for BC treatment, cisplatin is reportedly the most effective chemo drug against the corresponding malignancy. Notwithstanding, tumor recurrence is usually occurred following the consumption of cisplatin regimens, particularly due to the progression of chemo-resistant trait. In this framework, non-coding RNAs (ncRNAs), as abundant RNA transcripts arise from the human genome, are introduced to serve as crucial contributors to tumor expansion and cisplatin chemo-resistance in bladder neoplasm. In the current review, we first investigated the best-known ncRNAs, i.e. microRNAs (miRNAs), long ncRNAs (lncRNAs), and circular RNAs (circRNAs), correlated with cisplatin chemo-resistance in BC cells and tissues. We noticed that these ncRNAs could mediate the BC-related cisplatin-resistant phenotype through diverse cellular processes and signaling mechanisms, reviewed here. Eventually, diagnostic and prognostic potential of ncRNAs, as well as their therapeutic capabilities were highlighted in regard to BC management.

circCD2AP promotes epithelial mesenchymal transition and stemness in bladder cancer by regulating FOXQ1/USP21 axis

Bladder cancer (BC) is a prevalent and deadly disease. circCD2AP was suggested to be highly expressed in BC. However, the exact mechanism needs further investigation. In this study, circCD2AP was observed to be upregulated in BC and linked to poor prognosis in individuals. Functionally, circCD2AP or USP21 knockdown inhibited BC cell EMT and stemness both in vitro and in vivo. Mechanistically, circCD2AP interacted with ELAVL1 to enhance the stability of USP21 mRNA, which, in turn, inhibited the ubiquitination degradation of FOXQ1. Through rescue assay, USP21 or FOXQ1 knockdown was found to abolish the promoting effects of circCD2AP or USP21 overexpression on BC cell EMT and stemness. Overall, this study has unveiled the role of circCD2AP/ELAVL1/USP21/FOXQ1 axis in BC EMT and stemness regulation, offering insights into the mechanisms underlying BC progression, with potential implications for therapeutic strategies.

Role of circular RNA and its delivery strategies to cancer - An overview

With the passage of years and the progress of research on ribonucleic acids, the range of forms in which these molecules have been observed grows. One of them, discovered relatively recently, is circular RNA - covalently closed circles (circRNA). In recent years, there has been a huge increase in the interest of researchers in this group of molecules. It entailed a significant increase in the state of knowledge about them, which in turn caused a dramatic change in their perception. Rather than seeing circular RNAs as curiosities that represent a minor information noise in a cell or a result of RNA misprocessing, they came to be regarded as a common, essential, and potentially extremely useful group of molecules. Nevertheless, the current state of the art of circRNA is full of white cards. A lot of valuable information has been obtained from high-throughput methods to study whole transcriptomes, but many issues related to circular RNAs still need to be clarified. Presumably, each answer obtained will raise several new questions. However, circRNAs have a wealth of potential applications, including therapeutic applications.

Emerging landscape of circFNDC3B and its role in human malignancies

In recent years, more attention has been paid to expanding the abundance of Circular RNAs (circRNAs), while the circRNAs that have been found to have significant functions have not been studied in different diseases. CircFNDC3B is one of the most researched circRNAs generated from fibronectin type III domain-containing protein 3B (FNDC3B) gene. Accumulating researches have reported the multiple functions of circFNDC3B in different cancer types and other non-neoplastic diseases, and predicted that circFNDC3B might be a potential biomarker. Notably, circFNDC3B can play roles in different diseases by binding to various microRNAs (miRNAs), binding to RNA-binding proteins (RBPs), or encoding functional peptides. This paper systematically summarizes the biogenesis and function of circRNAs, reviews and discusses the roles and molecular mechanisms of circFNDC3B and its target genes in different cancers and non-neoplastic diseases, which will do favor to broaden our comprehension of the function of circRNAs and facilitate subsequent research on circFNDC3B.

Ferroptosis-associated circular RNAs: Opportunities and challenges in the diagnosis and treatment of cancer

Ferroptosis is an emerging form of non-apoptotic regulated cell death which is different from cell death mechanisms such as autophagy, apoptosis and necrosis. It is characterized by iron-dependent lipid peroxide accumulation. Circular RNA (circRNA) is a newly studied evolutionarily conserved type of non-coding RNA with a covalent closed-loop structure. It exhibits universality, conservatism, stability and particularity. At present, the functions that have been studied and found include microRNA sponge, protein scaffold, transcription regulation, translation and production of peptides, etc. CircRNA can be used as a biomarker of tumors and is a hotspot in RNA biology research. Studies have shown that ferroptosis can participate in tumor regulation through the circRNA molecular pathway and then affect cancer progression, which may become a direction of cancer diagnosis and treatment in the future. This paper reviews the molecular biological mechanism of ferroptosis and the role of circular RNA in tumors and summarizes the circRNA related to ferroptosis in tumors, which may inspire research prospects for the precise prevention and treatment of cancer in the future.

Biomarkers of Bladder Cancer: Cell-Free DNA, Epigenetic Modifications and Non-Coding RNAs

Bladder cancer (BC) is the 10th most frequent cancer in the world. The initial diagnosis and surveillance of BC require a combination of invasive and non-invasive methods, which are costly and suffer from several limitations. Cystoscopy with urine cytology and histological examination presents the standard diagnostic approach. Various biomarkers (e.g., proteins, genes, and RNAs) have been extensively studied in relation to BC. However, the new trend of liquid biopsy slowly proves to be almost equally effective. Cell-free DNA, non-coding RNA, and other subcellular structures are now being tested for the best predictive and diagnostic value. In this review, we focused on published gene mutations, especially in DNA fragments, but also epigenetic modifications, and non-coding RNA (ncRNA) molecules acquired by liquid biopsy. We performed an online search in PubMed/Medline, Scopus, and Web of Science databases using the terms "bladder cancer", in combination with "markers" or "biomarkers" published until August 2022. If applicable, we set the sensitivity and specificity threshold to 80%. In the era of precision medicine, the development of complex laboratory techniques fuels the search and development of more sensitive and specific biomarkers for diagnosis, follow-up, and screening of BC. Future efforts will be focused on the validation of their sensitivity, specificity, predictive value, and their utility in everyday clinical practice.

The interplay between non-coding RNAs and Wnt/ß-catenin signaling pathway in urinary tract cancers: from tumorigenesis to metastasis

Non-coding RNAs (ncRNAs) are emerging as important regulators in various pathological conditions including tumorigenesis, metastasis, and drug resistance in human cancers. Oncogenic or tumor suppressor ncRNAs exert prominent effects on cell proliferation, migration and invasion in cancer cells through modulating various signaling pathways including Wnt/β-catenin. Upregulation of the oncogenic Wnt/β-catenin pathway was reported to be implicated in multiple human cancers including breast, liver, colorectal, and urothelial cancers. Therefore, identifying interactions between ncRNAs and canonical Wnt signaling components may represent novel therapeutic targets for better treatment and management of cancer. In this review, we summarized the recent findings about miRNA/lncRNA-dependent mechanisms that regulate Wnt/β-catenin signaling involved in tumorigenesis and metastasis of urinary tract cancers.

The Role of Circular RNAs in the Drug Resistance of Cancers

Cancer is a major threat to human health and longevity. Chemotherapy is an effective approach to inhibit cancer cell proliferation, but a growing number of cancer patients are prone to develop resistance to various chemotherapeutics, including platinum, paclitaxel, adriamycin, and 5-fluorouracil, among others. Significant progress has been made in the research and development of chemotherapeutic drugs over the last few decades, including targeted therapy drugs and immune checkpoint inhibitors; however, drug resistance still severely limits the application and efficacy of these drugs in cancer treatment. Recently, emerging studies have emphasized the role of circular RNAs (circRNAs) in the proliferation, migration, invasion, and especially chemoresistance of cancer cells by regulating the expression of related miRNAs and targeted genes. In this review, we comprehensively summarized the potential roles and mechanisms of circRNAs in cancer drug resistance including the efflux of drugs, apoptosis, intervention with the TME (tumor microenvironment), autophagy, and dysfunction of DNA damage repair, among others. Furthermore, we highlighted the potential value of circRNAs as new therapeutic targets and prognostic biomarkers for cancer.

Circular RNA-Is the Circle Perfect?

Circular RNA (circRNA) is a distinct class of non-coding RNA produced, in principle, using a back-splicing mechanism, conserved during evolution, with increased stability and a tissue-dependent expression. Circular RNA represents a functional molecule with roles in the regulation of transcription and splicing, microRNA sponge, and the modulation of protein–protein interaction. CircRNAs are involved in essential processes of life such as apoptosis, cell cycle, and proliferation. Due to the regulatory role (upregulation/downregulation) in pathogenic mechanisms of some diseases (including cancer), its potential roles as a biomarker or therapeutic target in these diseases were studied. This review focuses on the importance of circular RNA in cancer.