Abstract EN:

Voltage-dependent anion channel1 (VDAC1) is a porin of the mitochondrial outer membrane that plays a very important role in the regulation of cellular metabolism and apoptosis. As a consequence of hypoxia (i.e. decrease of oxygen availability), a new form of VDAC1, VDAC1-∆C, is produced from a microfusion between abnormally enlarged mitochondria and endolysosomes. Through this mechanism, the endolysosomal asparagine endopeptidase Legumain (LGMN) mediates the cleavage of VDAC1 at specific sites. Clear cell Renal Cell Carcinoma (ccRCC) is the most common form of kidney cancer characterized by loss or mutation of VHL tumor suppressor gene, occurring in both sporadic and hereditary ccRCCs. VHL inactivation is responsible for the normoxic stabilization of hypoxia-inducible transcription factors (HIFs) and thus a dysregulation of the hypoxic pathway. Moreover, ccRCC is usually characterized by loss of the primary cilium (PC) a non-motile sensory organelle of cell surface, making this cancer a model of ciliopathy. The primary cilium serves a number of key functions, among which cell signalization and cell cycle regulation are of special interest in tumorigenesis. In vitro, we demonstrated the presence of VDAC1-∆C in RCC4 cells, stabilizing both HIF1-α and HIF2-α. VDAC1-∆C was not detected in RCC4 cells re-expressing the wt pVHL (RCC4+pVHL), without HIFs stabilization. The absence of VDAC1-∆C in these cells was correlated with a low expression of LGMN and with the increase of the number of ciliated cells compared to RCC4 cell line. The silencing of VDAC1 or of LGMN in RCC4 cells abolished the presence of VDAC1-∆C and significantly increased both the number of ciliated cells and their invasive potential. In parallel, we demonstrated that a restrict group of patients, in a cohort of 19 ccRCC patients, were characterized by the absence of VDAC1-∆C, low expression of LGMN and an increase in ciliated cells.We found a gene signature based on GLI and IFT20 genes, which are markers of PC activity and formation respectively, whose overexpression (GLI1+/IFT20+) reflected the increase of PC expression. This classification, based on VDAC1, LGMN and the genes GLI1 and IFT20, was reinforced from the study of a TCGA cohort of 375 non-metastatic ccRCC. 48 patients (GLI1+/IFT20+)/375, about 12% of patients, had a poor prognosis in terms of overall survival and disease free survival. We found that an epithelial to mesenchymal transition (EMT) signature and maintenance of glycolytic metabolism were at the basis of the increase in tumor aggressiveness. Moreover, we found that patients with i) an increased expression of PC, ii) the absence of VDAC1-∆C and iii) a GLI1+/IFT20+ signature were more resistant to sunitinib, the current standard of care treatment for metastatic ccRCC, and we confirmed the same results in vitro, in ccRCC cell lines. However, since the immunophenoscore was in favor to GLI1+/IFT20+ group of patients, immunotherapy could be a particularly beneficial treatment. To understand the VDAC1-∆C -dependent restraint of PC expression, RAS-transformed mouse embryonic fibroblasts (MEF) cell lines knockout for VDAC1 (Vdac1-/-) expressing i) human VDAC1 wt (VDAC1+/+), ii) a non- cleavable form of VDAC1 (VDAC1Mut) and iii) only the truncated form of VDAC1 (VDAC1-STOP) have been engineered. We first determined that VDAC1-∆C is involved in the increase of glycolysis and respiration and that VDAC1-∆C confers the capability to metabolize more metabolites. We also demonstrated that VDAC1-∆C inhibits PC formation, thus participating to the ciliopathic phenotype of tumors. Finally, we demonstrated that the presence of VDAC1-∆C can also occur in normoxia upon silencing of the iron-sulfur biosynthetic machinery in mitochondria or with impaired iron homeostasis, attributing a new role to VDAC1 in the context of iron deprivation.Thus, my research demonstrated a new function of VDAC1 and, in particular, of VDAC1-∆C in both hypoxic and normoxic contexts.