Abstract 155: An endosomal type Igamma PIP 5-kinase controls endosome maturation, lysosome function, and autophagy by modulating Rab7a

Abstract Endosomes are major protein-sorting stations in cells. Defects in endosomal sorting are implicated in various human pathologies, such as cancer and neurodegenerative disorders. The small GTPase Ras-related protein Rab-7a (Rab7a) serves as a key organizer of the endosomal-lysosomal system. However, molecular mechanisms controlling Rab7a activation levels and subcellular translocation are still poorly defined. Here, we demonstrate that type Igamma phosphatidylinositol phosphate 5-kinase i5 (PIPKIgammai5), an endosome-localized enzyme that produces phosphatidylinositol 4,5-bisphosphate (PI4,5P2), directly interacts with Rab7a and plays critical roles in the control of endosomal-lysosomal system. The loss of PIPKIgammai5 blocks Rab7a recruitment to early endosomes, which prevents the maturation of early to late endosomes. In this way, PIPKIgammai5 is required for Epidermal Growth Factor Receptor (EGFR) sorting from endosomes to lysosomes, which controls the down-regulation of EGFR signaling. Furthermore, PIPKIgammai5 loss disturbs retromer complex connection with Rab7a, which blocks the retrograde sorting of Cation-independent Mannose 6-Phosphate Receptor (CI-MPR) from late endosomes. This leads to the decreased sorting of hydrolases to lysosomes. Thus, loss of PIPKIgammai5 causes lysosome dysfunction and reduces the autophagic degradation. By modulating retromer-Rab7a connection, PIPKIgammai5 is also required for the recruitment of the GTPase-activating protein (GAP) TBC1 domain family member 5 (TBC1D5) to late endosomes, which controls the conversion of Rab7a from the active state to the inactive state. Altogether, PIPKIgammai5 is critical for the modulation of Rab7a activity, localization, and function in the endosomal-lysosomal system. Citation Format: Ming Sun, Gary Luong, Faiz Plastikwala, Yue Sun. An endosomal type Igamma PIP 5-kinase controls endosome maturation, lysosome function, and autophagy by modulating Rab7a [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 155.