Circular ribonucleic acids (circRNAs) are a group of endogenic ribonucleic acids with a single-stranded covalently closed structure. With the development of high throughput RNA-sequencing methods and bioinformatic tools it has been found that circRNAs are abundant, diverse and conserved, and that their expression patterns are spatiotemporal specific. Their diverse molecular functions result in numerous physiological processes (on a cell as well as on a systemic level) and, consequently, also in pathological processes. Numerous studies have showed that certain circRNAs are associated with the development of the hepatocellular carcinoma (HCC), which is the most common liver cancer type. The modulated circRNA expression level in HCC is not simply a consequence of changes in cells or tissue (on account for what they are considered as potential biomarkers), but rather that circRNA on their own play a salient role in the pathologies development by effecting diverse processes, e.g. cell cycle, angiogenesis, apoptosis, metabolism and epithelial-mesenchymal transition. We studied the role of the heterogenous nuclear ribonucleoprotein K (hnRNPK) and the RNA binding protein 4 (RBM4) in the expression regulation of selected circRNAs. These proteins exhibit an essential role in the precursor RNA processing. For hnRNPK it has been proved that it is overexpressed in HCC, whereas for RBM4 it has been discovered that the higher expression level in HCC patients positively correlates with a higher survival rate. During the course of the bachelor’s thesis, we succeeded to prepare a vector for RBM4 overexpression in a mammal system. With this vector and a vector for hnRNPK overexpression we transfected cell cultures of the HCC model cell line Huh-7 and with the means of western blot and immunodetection proved the overexpression of the two proteins. With the method of quantitative polymerase chain reaction, we measured the expression level of selected mRNAs and circRNAs in cell cultures. Our results indicate that the overexpression of hnRNPK increases the expression level of circRNAs hsa_circ_0040921 and hsa_circ_0062682 and that the overexpression of RBM4 increases the expression level of circRNAs RNA hsa_circ_0048492 and hsa_circ_0028196. For our findings to be statistically significant a bigger number of experiment repeats would be needed.
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