Cancer Genetics and Epigenetics 2024, Vol.12, No.6, 329-345 http://medscipublisher.com/index.php/cge 331 Figure 1 Functions and degradation of circRNAs (Adopted from Tao et al., 2021) Image caption: A Functions of circRNAs (a). CircRNAs play a regulatory role by binding to miRNAs (b). CircRNAs bind to proteins to act as a protein sponge or a protein scaffold (c). CircRNAs can be translated into proteins or peptides in cap-independent way, during which IRES or other initial elements are necessary (d). CircRNAs can be regulators of mRNA, including regulating translation of mRNA (up) and stability of mRNA (down). B Degradation of circRNAs (a). miR-671 is located in nucleus and directs the Ago2-slicer-dependent cleavage of circCDR1 (b). A middle region (Mid) in GW182 functions as a molecular scaffold to recruit decay factors, resulting in degradation of circRNAs (c). Highly structured circRNAs can be degraded by UPF1 and G3BP1. Both proteins are indispensable in this progress (d). RNase L can be activated once cells are invaded by virus. Subsequently, activated RNase L mediates the global degradation of circRNAs, which is essential to activate PKR in the early stage of the innate immune response (e). Cell excretion of circRNAs into the extracellular space through extracellular vesicles (EVs) may be a mechanism for cell clearance of circRNAs (Adopted from Tao et al., 2021) In ovarian cancer, circRNAs have been shown to play significant roles in tumorigenesis and cancer progression. They can function as molecular sponges for miRNAs, thereby modulating the availability of miRNAs to their target mRNAs. This sponging activity can lead to the upregulation of oncogenes or the downregulation of tumor suppressors, contributing to cancer progression. For example, circRNAs can regulate mRNA translation and stability, act as scaffolds for protein interactions, and even serve as templates for translation (Tao et al., 2021). Recent studies have also highlighted the dynamic modifications of circRNAs, such as N6-methyladenosine (m6A) methylation, which can influence their biogenesis, nuclear export, translation, and degradation. These modifications add another layer of complexity to the regulatory roles of circRNAs in cancer biology (Tao et al., 2021). ncRNAs, including miRNAs, lncRNAs, and circRNAs, play critical roles in the regulation of gene expression and the progression of ovarian cancer. Understanding the intricate networks involving these ncRNAs can provide valuable insights into the molecular mechanisms underlying ovarian cancer and potentially lead to the development of novel therapeutic strategies. 3 Mechanisms of Epigenetic Regulation by ncRNAs 3.1 DNA methylation: impact on miRNAs and lncRNAs DNA methylation, a key epigenetic modification, involves the addition of a methyl group to the 5-carbon of
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