Samoylenko A. HIF-1-dependent signaling networks in normal and tumor cells

The aim of the study was to assess the role of transcription factor HIF-1 as a regulator of intracellular processes at the molecular level using several genes, expression of which is enhanced by hypoxia, as well as to explore possible mechanisms linking hypoxia with malignant transformation of cells. The study of signaling networks involved in the regulation of PAI-1 expression by hypoxia, hyperinsulinemia and oxidative stress, revealed that transcription factor HIF-1? and hypoxia response element (HRE) in the promoter of PAI-1 mediate expression of this gene not only by hypoxia but also by the action of insulin. For the first time it was found that enhanced expression of PAI-1 upon oxidative stress induced by hydrogen peroxide is mediated by activation of the transcription factor FOXO4. Activation of FOXO4, in turn, leads to the downregulation of transcription factor HIF-1?, while stimulating transcription factor CREB. Finally, it was shown for the first time that adaptor protein Ruk/CIN85 enhances the expression of PAI-1 by modulating HIF-1? levels, affecting the degradation of the protein. Since it is known that PAI-1 and HIF-1? play a role in the development of cancer, it has been suggested that enhanced expression of Ruk/CIN85 promotes malignant transformation of cells both in vivo and in vitro. Indeed, it was found that expression of Ruk/CIN85 is enhanced in breast cancer samples. It was also found that enhanced expression of Ruk/CIN85 promotes malignant transformation of human breast adenocarcinoma MCF-7 cells. The thesis has shown that transcription factor USF2, involved in the modulation of HIF-1?-dependent gene expression, may act as an inhibitor or activator depending on the malignant transformation. In general, the thesis proposes the model showing an integral role of hypoxia response elements (HRE) in the signal transduction not only by hypoxia but also by other stimuli, such as insulin and ROS, using PAI-1 regulation as example. It is demonstrated that action of these stimuli is mediated via transcription factors HIF-1, USF-2 and CREB, that compete for binding with HRE. At the same time, we found novel roles of individual components of hypoxia-dependent signaling pathways during carcinogenesis.