Circular RNAs regulate many processes in cells and many of them play a role in pathophysiological processes such as cancer development. They have very diverse functions from binding miRNA and proteins and regulating their role to transcription into proteins. In cancer, circular RNAs have altered expression and act as oncogenes or tumor suppressors. The thesis focuses on the role of circular RNAs in primary liver cancer, the most common type of which is hepatocellular carcinoma (HCC). Due to its limited symptoms and lack of effective biomarkers for early diagnosis, it is one of the leading causes of cancer death in the world. The purpose of the thesis was to use various bioinformatics tools and databases to predict the functions of circular RNAs that have altered expression in liver cancer tumors and the experimental validation of their expression in model cell lines for liver cancer. Following functional annotation, exosomal circular RNAs were selected as candidates and their expression in model liver cancer cell lines (HepG2, Huh-7, SNU-449) and a liver pericyte line (LX-2) was successfully confirmed using the RT-qPCR method. Expression was expressed relative to the THLE-5b control line, and it was found that certain circular RNAs in the cell lines used were upregulated and others downregulated. We found that the data in most of the databases used did not overlap, as they are mostly experimentally unconfirmed de novo predictions with different algorithms rather than experimentally obtained data, and that the levels of circular RNA expression in different liver cancer lines is variable.
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