| dc.description.abstract | Cancer is the second leading cause of death worldwide. In Norwegian men, prostate cancer (PCa) was the most commonly diagnosed cancer and second most frequent cause of cancer death in 2017. The tumor microenvironment (TME), that is the local environment around cancer cells, is a very hostile and nutrient-deprived area. In order to adapt to the TME, cancer cells activate stress signaling pathways such as the integrated stress response (ISR) and the unfolded protein response (UPR). General control non-derepressible 2 (GCN2), heme-regulated eIF2α kinase (HRI), double-stranded RNA-dependent protein kinase (PKR), and the PKR-like endoplasmic reticulum (ER) kinase (PERK) constitute the regulators of the ISR, where PERK is also included in the UPR. These four stress-sensing kinases phosphorylate the alpha subunit of eukaryotic translation initiation factor 2 (eIF2α) upon activation. This activates translation of the common effector activating transcription factor 4 (ATF4), which activates expression of genes that aim to restore cellular homeostasis. Dysregulation of the ISR and UPR has been associated with various diseases, including cancers, and targeting such pathways has previously shown potential as a treatment option. In this study, we assessed the regulation of three of the eIF2α kinases by androgens and, in two different PCa cell lines, by ER stress. In addition, the effect on cell viability, survival, and apoptosis was investigated upon siRNA-mediated knockdown of three of the eIF2α kinases. Finally, localization of GCN2 and a novel ATF4-target identified in our group, FAM129A, was evaluated using immunofluorescence microscopy. Results showed that androgens differentially affected the ISR-regulators and that they were all upregulated by various ER stressors in both PCa cell lines. siRNA-mediated knockdown studies revealed that both PERK and GCN2 are important for viability and survival of PCa cells, but only knockdown of GCN2 induced apoptosis. Furthermore, in a model of metastatic PCa, GCN2 was most critical for cell viability and survival, and knockdown lead to induction of apoptosis and upregulated the downstream ATF4-target FAM129A. Lastly, GCN2 showed a cytosolic localization, but did not appear to localize to the same organelles as FAM129A. The data presented in this thesis suggest an important role for GCN2 in PCa cells and provide initial results to further evaluate the role of eIF2α kinases in ER stress signaling and in PCa. | eng |