Ciliogenesis is regulated by TRIM37 through ubiquitinating p62 and controlling the autophagy pathway

Primary cilia are microtubule-based structures that project from the cell surface and play critical roles in signal transduction and the maintenance of cellular homeostasis. Their assembly is precisely regulated by multiple cellular processes. TRIM37 is an E3 ubiquitin ligase of the class VIII subfamily of TRIM proteins, which is involved in multiple cellular processes, including tumorigenesis and centriole homeostasis; however, its biological function in ciliogenesis remains elusive. This study aimed to elucidate how the E3 ubiquitin ligase TRIM37 regulates autophagy to affect primary ciliogenesis in mammalian cells and the underlying molecular mechanism. The data indicated that TRIM37 was localized in the basal body, and its knockdown led to a significant reduction in ciliogenesis rate and cilium length in both RPE1 and HK2 cells, an effect that was independent of cell cycle alterations. Moreover, TRIM37 knockdown resulted in accumulation of LC3-II and p62, downregulation of Beclin1 and WIPI2, and suppression of autophagic initiation. By means of bafilomycin A1-mediated autophagic flux blockade and LC3-LAMP2 immunofluorescence colocalization analysis, we further confirmed that TRIM37-knockdown cells exhibited marked autophagic flux impairment, characterized by decreased autophagosome formation and defective fusion between autophagosomes and lysosomes. Functional complementation experiments showed that TRIM37’s E3 ubiquitin ligase activity (required for its function) is essential for maintaining normal ciliogenesis and autophagic homeostasis. TRIM37 mediates the ubiquitination and turnover of SQSTM1/p62, thus regulating autophagic activity and ciliogenesis. Furthermore, simultaneous knockdown of TRIM37 and SQSTM1/p62 alleviated the ciliogenesis defects and autophagic abnormalities induced by TRIM37 deficiency. This study identified a novel TRIM37-SQSTM1/p62-autophagy regulatory axis that modulates mammalian ciliogenesis. This regulatory axis provides novel insights into the molecular regulatory network of ciliogenesis.