Transcription Factor EB regulates phosphatidylinositol-3-phosphate levels on endomembranes and alters lysosome positioning in the bladder cancer model

Abstract

Late endosomes/lysosomes (endolysosomes) emerge as a potential regulatory hub during cancer. Here, we investigate the intracellular landscape of this organelle in a collection of bladder cancer cell lines and normal human urothelium cells under standardized culture conditions. We find that high-grade bladder cancer cells are characterized by scattered endolysosomes that are accompanied by an altered cellular pH homeostasis and major changes of mTORC1 regulation. Mechanistically, we reveal that mTORC1 substrate specificity is altered, and mTORC1 responsiveness to endolysosome positioning is lost in high-grade cancer cells compared to low-grade cells, highlighting unexpected mechanisms of mTORC1 deregulation in the bladder cancer model. Because endolysosome positioning was critical for invasion from 3D spheroids, our results indicate that changes in their cellular positioning and ability to support signaling, strongly impact cancer cell behavior. Thus, monitoring detailed changes of endolysosomes at different steps of cancer disease reveals intricate spatial and temporal dimensions of tumorigenesis.Statement of significanceOur study reveals significant changes of endolysosomes in bladder cancer progression, highlighting endolysosome dysfunction as a fundamental driving progress in malignancies. The identified alterations in endolysosome positioning and associated mTORC1 signaling regulation could help to stratify emerging therapeutic strategies targeting the endolysosomal compartment.