Vault-phagy: a phase-separation-mediated selective autophagy of vault, a non-membranous organelle

ABSTRACTSQSTM1/p62 bodies are phase-separated condensates that play a fundamental role in intracellular quality control and stress responses. Despite extensive studies investigating the mechanism of formation and degradation of SQSTM1/p62 bodies, the constituents of SQSTM1/p62 bodies remain elusive. We recently developed a purification method for intracellular SQSTM1/p62 bodies using a cell sorter and identified their constituents by mass spectrometry. Combined with mass spectrometry of tissues from selective autophagy-deficient mice, we identified vault, a ubiquitous non-membranous organelle composed of proteins and non-coding RNA, as a novel substrate for selective autophagy. Vault directly binds to NBR1, an SQSTM1/p62 binding partner recruited to SQSTM1/p62 bodies, and is subsequently degraded by selective autophagy dependent on the phase separation of SQSTM1/p62. We named this process “vault-phagy” and found that defects in vault-phagy are related to nonalcoholic steatohepatitis (NASH)-derived hepatocellular carcinoma. Our method for purifying SQSTM1/p62 bodies will contribute to elucidating the mechanisms of several stress responses and diseases mediated by SQSTM1/p62 bodies.KEYWORDS: Fluorescence-activated particle sortingliquid-liquid phase separationMallory-Denk bodiesNBR1nonalcoholic steatohepatitisselective autophagy Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThis study was supported by a Grant-in-Aid for Scientific Research on Innovative Areas [19H05706 to M.K.], a Grant-in-Aid for Scientific Research (A) [21H004771 to M.K.], a Grant- in-Aid for Scientific Research (B) [23H02441 to H.M.], and Advanced Research and Development Programs for Medical Innovation [AMED-PRIME, 21gm6410019h0001 to H.M.].