Functional investigation of prognostic biomarkers and therapeutic targets in glioma brain tumors

Abstract: Gliomas are known to be the most prevalent primary tumors of the central nervous system, of which glioblastoma is the most aggressive type with a median survival less than 2 years and no available cure. Studies in this thesis investigated the significance of two potentially important proteins in glioma biology, the transcription factor PROX1 and the histone chaperone NPM1, and the interplay of the therapeutic targets p53 and mTOR. Study I combined dataset mining and experimental studies to elucidate the function of PROX1 in glioblastoma. PROX1 mRNA was significantly lower in tumors with a mesenchymal signature, and its modulation in cultures derived from a heterogeneous glioblastoma tumor, transitioned the cells between non-mesenchymal and mesenchymal gene expression-based profiles. Concomitant with this were changes in proliferation rate, cell cycle proteins and stem cell markers. Further, the results revealed PROX1 regulation by SOX2, a connection that could be controlled by a CDK2 small molecule inhibitor. The findings from this study highlight the value of PROX1 as a prognostic tool and the functional role of PROX1 in glioma tumor development. In study II, immunohistochemistry analysis confirmed a significant overexpression of NPM1 in human glioblastoma samples. Moreover, the subcellular localization of NPM1 was assessed in glioma cell lines. NPM1 displayed a cloudy nuclear staining compared with the more pronounced nucleolar staining observed in normal cells. Moreover, NPM1 depletion altered the nucleolar structure, but had no major effect on cell viability. Interestingly, enforced expression of NPM1 reduced apoptosis in histone H1.5 depleted cells, suggesting that NPM1 acts in a pro-survival manner in cells. In study III, the p53 response to drug-induced nucleolar stress and simultaneous inhibition of mTOR pathway by the use of various natural and synthetic compounds was analyzed. mTOR inhibition interfered with the p53 pathway stress response, as assessed by the impairment of p53 stabilization and reduced mRNA and protein levels of its downstream target p21. This provides information that may help improve combinatorial drug treatment regimens for cancer patients. Collectively, these studies provide novel insights into the biology of glioma brain tumors useful for patient diagnosis and more effective personalized therapies.