Non-canonical Caspase-8 Activation on Autophagosomal Membranes

Project Summary/Abstract This project aims to address a significant knowledge gap regarding the mechanism by which VPS37A deficiency provides a survival advantage for cancer cells, particularly in the context of accumulated intracellular Death- Inducing Signaling Complexes (iDISC) and impaired autophagic flux. The VPS37A gene, located on 8p22, is frequently lost in major solid cancers. Our recent findings have highlighted VPS37A as a crucial regulator of phagophore closure, a pivotal step in the formation of double membrane autophagosomes during autophagy. Notably, the depletion of VPS37A inhibits phagophore closure, leading to the upregulation of the NF-κB signaling pathway. This upregulation is dependent on the LC3-conjugation machinery and the autophagy adaptor p62. Moreover, the inhibition of NF-κB activation through the blockade of IKK or TAK1 induces iDISC-mediated apoptosis in 8p/VPS37A-deleted cancer cells. Additionally, our analysis of the Cancer Dependency Map portal revealed that TAK1, along with its cofactor TAB2, demonstrates a strong functional connection with VPS37A in cancer cell survival. TAK1 and TAB2 are known to localize on autophagosomal membranes. Based on these compelling observations, we propose that the TAK1/TAB2/NF-κB axis associated with the phagophore serves as a gatekeeper, suppressing iDISC activation and promoting cancer cell survival. We are in an ideal position to test this hypothesis in the following Specific Aims: 1) define the phagophore-associated regulators of the TAK1/NF-κB pathway; 2) define the regulators of iDISC activation upon phagophore closure inhibition; 3) explore the roles of phagophore-mediated TAK1/NF-kB signaling in tumor development and progression. Successful implementation of this research will provide valuable insights into the interplay between the TAK1/NF-κB signaling and iDISC/CASP8 cascade on phagophores to control cell death and survival and pave the way for future development of new strategies to treat cancers, especially those with 8p/VPS37A deletion.