Gastric cancer is a multifactorial disease characterized by intense heterogeneity among patients and is categorized into many subtypes based on its histological and molecular background. The main problem of the disease lies in the delayed diagnosis, because in the early stages it is asymptomatic, resulting in high incidence and high mortality rates worldwide. Therefore, it is necessary to develop sensitive and specialized molecular biomarkers, as well as effective therapeutic approaches. More

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... d more research is focusing on the molecular and genetic background of gastric cancer, discovering genes that exhibit genetic diversity in the number of copies in cancer and are characterized by oncogenic activity. This category includes the transcription factors GATA4/GATA6/KLF5, which normally act as regulators of cell lineage (lineage-survival factors) since they are involved in the maintenance of specific cell types in the developmental stages of the stomach. In addition, intestinal cell line regulators CDX2/HNF4α have been associated with the most common intestinal gastric subtype due to their contribution to the phenomenon of differentiation in gastric identity that usually precedes malignant transformation. Due to the action of the above transcription factors on normal and cancerous tissues, their therapeutic targeting is not possible. Therefore, the target genes of these oncogenic transcription factors are of interest, such as lncRNAs, which show tissue-specific and cancer-specific expression. This dissertation aims to study the regulation of lncRNA by the transcription factors GATA4/GATA6/KLF5/CDX2/HNF4α in gastric cancer. The regulation of GREAT4-1 and GREAT6-2 lncRNAs by transcription factors was checked at the transcriptional level when each of them was overexpressed as well as in the suppression of GATA4/ GATA6/KLF5 only. The results showed the possible regulatory role of the latter and mainly through their collaborative action. In addition, chromatin immunoprecipitation showed that GATA4 is a direct regulator of these lncRNAs, something that could not be confirmed for GATA6. At the same time, under the overexpression of CDX2/HNF4α, their potential regulatory role in cRENA and cRENA2 was studied. As in the case of GREAT4-1 and GREAT6-2, it appeared that these factors probably act as a complex due to their common pattern in altering lncRNA expression. In the future, it remains to be tested whether transcription factors create transcription networks to regulate the expression of lncRNA targets by performing combined experiments, both overexpression, and repression. Finally, the ultimate targets include chromatin immunoprecipitation experiments to confirm which transcription factors directly or indirectly regulate lncRNAs.