Glioblastomas (GBM) are the most aggressive form of primary brain tumors in humans. A key feature of malignant gliomas is the presence of an undifferentiated cell population defined Glioblastoma Stem cells (GSCs). the high resistance cell subpopulation to drugs treatment and radiotherapy..
CSN5 and CSN6, the critical subunits of the constitutive photomorphogenesis 9 (COP9) signalosome (CSN), has received attention as a regulator of the degradation of cancer-related proteins such as p53, c-myc and c-Jun, through the ubiquitin-proteasome system, suggesting its relevance in cancerogenesis. However, the biological functions and molecular mechanisms of CSN in glioblastoma (GBM) and in particular in GSCs remain poorly understood. As reported in yeast, the deletion of the CSN5 gene causes the activation of the transcription of two autophagic genes (ATG16 and ATG33) and an increase of the vacuolar size, suggesting the autophagy activation. In cancer cells, autophagy has been recognized as an adaptive response to starvation or stress conditions. However, prolonged autophagy leads to a high turnover rate of proteins and organelles above the survival threshold, resulting in cancer cells death. This adaptation can be utilized as a therapeutic tool for the cancer treatment- The alteration of COP/ signalosome system may also be related to unfolded protein, increase, the oxidative stress and lipid metabolism alteration. The better understanding of these processes and the identification of new drugs able to alter these mechanisms appear of the great relevance for the glioma therapy
In this project we propose to test the role played by CSN in GSCs derived from human biopsies. For this aim, starting from preliminary data obtained, we will evaluate specific inhibitors of CSN activity previously tested in yeast. Moreover, selective agonist of M2 agonists, that, in preliminary data resulted able to negatively modulate the NEDD8 activity, will be also studied.
In recent years the interest on the neddylation pathway as an antitumor target is significantly increasing since the inhibitor of the activating enzyme Nedd8 (MLN4924) has reached phase 1 and 2 in clinical trials. In addition, a new molecule, CSN5i-3 was recently described as a CSN5 inhibitor with anticancer activity. Indeed, since the up regulation of the human CSN5 enzyme is present in many tumors, its inibitors may be considered a promising tool for cancer therapy. Considering that glioblastoma multiforme is the most aggressive brain tumor in human and given the high inefficacy the surgical and pharmacological therapies in the treatment of this tumor, in this project we propose to test in glioblastoma cell line U251 and in glioblastoma cancer stem cells GB7 obtained from human biopsy, two inhibitors of Csn5 previously selected from a screening performed in yeast.
Taking advantage of the phenotypes observed in yeast using the Csn5 inhibitors, we will be able to address our experiments to the analysis of the autophagic pathway and the mitochondrial function, a field still unexplored in a glioblastoma model. Moreover, we wìll also evaluate the ability of these inhibitors to modify the lipids metabolism because in yeast we observed a modulation of lipid biogenesis in absence of the CSN5 gene. In fact, the increased lipogenesis has been considered as another metabolic hallmark of cancer cells. Consistent with this, glioma was shown to have enhanced lipid synthesis. Therefore, altering the lipid metabolism could reduce the metabolic reserve used by glioma in autophagic processes; this could therefore no longer be able to promote the survival of glioblastoma cells, but on the contrary counteract it.