PROJECT TITLE: Ubiquitylation of BBSome is required for ciliary assembly and signaling.
Francesco Chiuso, Rossella delle Donne, Giuliana Giamundo, Laura Rinaldi, Domenica Borzacchiello, Federica Moraca, Daniela Intartaglia, Rosa Iannuci, Emanuela Senatore, Luca Lignitto, Carrodo Garbi, Paolo Conflitti, Bruno Catalanotti, Ivan Conte, & Antonio Feliciello
ABSTRACT: Bardet-Biedl syndrome (BBS) is a ciliopathy characterized by retinal degeneration, obesity, renal abnormalities, postaxial polydactyly, and developmental defects. Genes mutated in BBS encode for components and regulators of the BBSome, an octomeric complex that controls the trafficking of cargos and receptors within the primary cilium. Although both structure and function of the BBSome have been extensively studied, the impact of ubiquitin signaling on BBSome is largely unknown. We identify the E3 ubiquitin ligase PJA2 as a novel resident of the ciliary compartment and regulator of the BBSome. Upon GPCR-cAMP stimulation, PJA2 ubiquitylates BBSome subunits. We demonstrate that ubiquitylation of BBS1 at lysine 143 increases the stability of the BBSome and promotes its binding to BBS3, an Arf-like GTPase protein controlling the targeting of the BBSome to the ciliary membrane. Downregulation of PJA2 or expression of a ubiquitylation-defective BBS1 mutant (BBS1K143R) affects the trafficking of G-protein-coupled receptors (GPCRs) and Shh-dependent gene transcription. Expression of BBS1K143R in vivo impairs cilium formation, embryonic development, and photoreceptors’ morphogenesis, thus recapitulating the BBS phenotype in the medaka fish model.
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Author Contributions: Ivan Conte, PhD: Supervision, funding acquisition; investigation; writing – original draft; writing – review and editing.
This study was conducted with IRRF Funds: Ivan Conte, PhD