Disease-Associated Mutations in CEP120 Destabilize the Protein and Impair Ciliogenesis

Nimesh Joseph,Caezar Al-Jassar,Christopher M Johnson,Antonina Andreeva,Deepak D Barnabas,Stefan M.V Freund,Fanni Gergely,Mark Van Breugel

doi:10.1016/j.celrep.2018.04.100

Abstract

SummaryCiliopathies are a group of genetic disorders caused by a failure to form functional cilia. Due to a lack of structural information, it is currently poorly understood how ciliopathic mutations affect protein functionality to give rise to the underlying disease. Using X-ray crystallography, we show that the ciliopathy-associated centriolar protein CEP120 contains three C2 domains. The point mutations V194A and A199P, which cause Joubert syndrome (JS) and Jeune asphyxiating thoracic dystrophy (JATD), respectively, both reduce the thermostability of the second C2 domain by targeting residues that point toward its hydrophobic core. Genome-engineered cells homozygous for these mutations have largely normal centriole numbers but show reduced CEP120 levels, compromised recruitment of distal centriole markers, and deficient cilia formation. Our results provide insight into the disease mechanism of two ciliopathic mutations in CEP120, identify putative binding partners of CEP120 C2B, and suggest a complex genotype-phenotype relation of the CEP120 ciliopathy alleles.

Highlights

Cilia are hair-like protrusions of the plasma membrane
Joubert syndrome (JS) and Jeune asphyxiating thoracic dystrophy (JATD) Mutations in the CEP120 C2B Domain Impair Ciliogenesis Lastly, we investigated whether the CEP120 point mutant centrioles could serve as basal bodies to template the formation of cilia
We show that the ciliopathic mutations V194A and A199P within the second C2 domain (C2B) of CEP120 affect residues that point toward its hydrophobic core and lead to its reduced thermostability in vitro and decreased cellular and centrosomal CEP120 levels in vivo

Summary

Introduction

Cilia are hair-like protrusions of the plasma membrane. They are essential cellular organelles with multiple functions, such as cell motility and liquid movement, and play a crucial role in several major signaling pathways. Cilia are formed when centrioles (basal bodies) dock against the cell membrane and extend their peripheral microtubule array to form the ciliary axoneme. At the start of ciliogenesis, the mother centriole is converted into a basal body via recruitment of a Golgi-derived ciliary vesicle onto its distal end. This process, which is a prerequisite for basal body docking, is facilitated by components of the centriole distal appendages, including CEP164 (Graser et al, 2007a; Schmidt et al, 2012; Tanos et al, 2013). Distal appendages have been implicated in removing the ciliogenesis suppressor

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Discussion

Conclusion