Abstract A04: Interaction of VRK2 with Akt at lysosomes controls induction of autophagy

Serine–threonine kinase Akt (also known as PKB, protein kinase B), a core intracellular mediator of survival, is involved in various human cancers and has been suggested to play an important role in the regulation of autophagy in mammalian cells. Nonetheless, the physiologic function of Akt at the lysosomes is currently unknown. We have reported previously that PtdIns(3)P-dependent lysosomal accumulation of the Akt–Phafin2 complex is a critical step for autophagy induction. Here, to characterize the molecular function of activated Akt at the lysosomes in the process of autophagy, we searched for the molecules that interact with the Akt complex at the lysosomes after induction of autophagy. By time-of-flight mass spectrometry (TOF/MS) analysis, kinases of the VRK family, a unique serine–threonine family of kinases in the human kinome, were identified. VRK2 interacts with Akt1 and Akt2, but not with Akt3; the C terminus of Akt and the N terminus of VRK2 facilitate the interaction of Akt and VRK2 in mammalian cells. The kinase-dead form of VRK2A (KD VRK2A) failed to interact with Akt in co-immunoprecipitation assays. Bimolecular fluorescence complementation (BiFC) experiments showed that at the lysosomes, Akt interacted with VRK2A, but not with VRK2B or KD VRK2A. Immunofluorescent assays revealed that VRK2 and phosphorylated Akt accumulated at the lysosomes after autophagy induction. WT VRK2A, but not KD VRK2A or VRK2B, facilitated accumulation of phosphorylated Akt at the lysosomes. Downregulation of VRK2 abrogated the lysosomal accumulation of phosphorylated Akt and impaired nuclear localization of TFEB; these events coincided with inhibition of autophagy induction. The VRK2–Akt complex is required for control of lysosomal size, acidification, bacterial degradation, and for viral replication. Moreover, lysosomal VRK2–Akt controls cellular proliferation and mitochondrial outer-membrane stabilization. Given the roles of autophagy in the pathogenesis of human cancer, the current study provides a novel insight into the oncogenic activity of VRK2–Akt complexes at the lysosomes via the modulation of autophagy. Citation Format: Masayuki Noguchi, Noriyuki Hirata, Futoshi Suizu. Interaction of VRK2 with Akt at lysosomes controls induction of autophagy [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr A04.