MODULATING TFEB ACTIVITY IN THE BIRT-HOGG-DUBE' SYNDROME BY TARGETING THE VACUOLAR ATPASE

The transcription factor EB (TFEB) is a master regulator of lysosome biogenesis and autophagy, and its activity is primarily controlled by the kinase complex mTORC1. In the Birt-Hogg-Dubé (BHD) syndrome, a genetic disease caused by germline mutations in FLCN gene, TFEB was found to be constitutively active and to promote the development of kidney cysts and cancer. Therefore, inhibition of TFEB activity represents a challenging opportunity for the treatment of the BHD syndrome. We performed a high content siRNA screening to identify correctors of TFEB activation in FLCN-KO cells. Interestingly, top hits were genes encoding subunits of the vacuolar ATPase (V-ATPase). The V-ATPase is a proton-pump protein complex responsible for maintaining the low pH of lysosomes, and it has been described as a positive regulator of mTORC1 signaling, although the exact contribute of the V-ATPase to the amino acid sensing has not been fully elucidated. Our results indicate that the V-ATPase inhibition promotes a mTORC1-dependent TFEB cytosolic re-localization in FLCN-KO cells, thus pointing to a novel mechanism of regulation of TFEB activity in BHD cellular models mediated by the V-ATPase. Besides, our data suggest that the Ragulator-Rag GTPases complex plays a crucial role in controlling TFEB subcellular localization, even in absence of FLCN, through its interaction with the V-ATPase. This study aims at dissecting how the V-ATPase regulates mTORC1 signaling and TFEB activity, while searching for compounds able to target this axis, with the purpose to identify novel and effective therapeutic approaches to limit kidney pathologies associated with BHD syndrome.