As a key regulator of development, organ size, tissue homeostasis and cancer, the Hippo pathway is tightly regulated by various growth-related signaling events. Among them, energy stress activates the Hippo pathway to inhibit its downstream effector YAP1. Our recent work reported a YAP1-independent role of the Hippo pathway in promoting macroautophagy/autophagy and cell survival in response to energy stress, a process mediated by Hippo kinase MAP4K2. MAP4K2 interacts with and phosphorylates MAP1LC3A/LC3A at S87, which in turn drives autophagosome-lysosome fusion via the RAB3GAP-RAB18 axis. Energy stress activates MAP4K2 by reducing its association with the Hippo phosphatase complex STRIPAK component STRN4. Moreover, MAP4K2 is highly expressed in head and neck cancer, while MAP4K2 and its mediated autophagy are required for head and neck cancer development. Taken together, our study not only reveals a noncanonical role of the Hippo pathway in energy stress response, but also suggests Hippo kinase MAP4K2 as a potential therapeutic target for head and neck cancer treatment.Abbreviation: AMPK: 5'-AMP-activated protein kinase; Atg8: autophagy related 8; LATS1: large tumor suppressor 1; LIR: microtubule-associated protein 1 light chain 3-interacting region; MAP1LC3A/LC3A: microtubule-associated protein 1 light chain 3 alpha; MAP4K2: mitogen-activated protein kinase kinase kinase kinase 2; PPP2/PP2A: protein phosphatase 2; RAB3GAP: RAB3 GTPase activating protein; RAB18: RAB18, member RAS oncogene family; SLMAP: sarcolemma associated protein; STK3/MST2: serine/threonine kinase 3; STK4/MST1: serine/threonine kinase 4; STRIPAK: striatin-interacting phosphatase and kinase; STRN4: striatin, calmodulin binding protein 4; SQSTM1/p62: sequestosome 1; TEAD: TEA domain family member; ULK1: unc-51 like kinase 1; WWTR1/TAZ: WW domain containing transcription regulator 1; YAP1: yes-associated protein 1.
Keywords: Autophagy; Energy stress; Hippo pathway; LC3; MAP4K2; STRIPAK.