Ubiquitin-proteasome system controls ciliogenesis at the initial step of axoneme extension.

Kousuke Kasahara,Masaki Inagaki,Yoshifumi Kawamura,Yoshitaka Kawakami,Shigenobu Yonemura,Tohru Kiyono,Naoki Goshima,Fumio Matsuzaki,Saho Era

doi:10.1038/ncomms6081

Abstract

Primary cilia are microtubule-based sensory organelles that organize numerous key signals during developments and tissue homeostasis. Ciliary microtubule doublet, named axoneme, is grown directly from the distal end of mother centrioles through a multistep process upon cell cycle exit; however, the instructive signals that initiate these events are poorly understood. Here we show that ubiquitin-proteasome machinery removes trichoplein, a negative regulator of ciliogenesis, from mother centrioles and thereby causes Aurora-A inactivation, leading to ciliogenesis. Ciliogenesis is blocked if centriolar trichoplein is stabilized by treatment with proteasome inhibitors or by expression of non-ubiquitylatable trichoplein mutant (K50/57R). Started from two-stepped global E3 screening, we have identified KCTD17 as a substrate-adaptor for Cul3-RING E3 ligases (CRL3s) that polyubiquitylates trichoplein. Depletion of KCTD17 specifically arrests ciliogenesis at the initial step of axoneme extension through aberrant trichoplein-Aurora-A activity. Thus, CRL3-KCTD17 targets trichoplein to proteolysis to initiate the axoneme extension during ciliogenesis.

Highlights

Primary cilia are microtubule-based sensory organelles that organize numerous key signals during developments and tissue homeostasis
CP110 disappears from the mother centrioles during ciliogenesis[8,15], but its protein level was not regulated by proteasomal degradation after serum starvation (Fig. 1c)
Considering that trichoplein was strikingly polyubiquitylated upon serum starvation (Fig. 1d), the trichoplein removal from mother centriole depends upon the ubiquitin-proteasome system (UPS)

Summary

Introduction

Primary cilia are microtubule-based sensory organelles that organize numerous key signals during developments and tissue homeostasis. Ciliary microtubule doublet, named axoneme, is grown directly from the distal end of mother centrioles through a multistep process upon cell cycle exit; the instructive signals that initiate these events are poorly understood. We show that ubiquitin-proteasome machinery removes trichoplein, a negative regulator of ciliogenesis, from mother centrioles and thereby causes Aurora-A inactivation, leading to ciliogenesis. Depletion of KCTD17 arrests ciliogenesis at the initial step of axoneme extension through aberrant trichoplein-Aurora-A activity. The primary cilium is a membrane-bound, microtubulebased sensory organelle that is composed of nine doublet microtubules, called ciliary axoneme, elongated directly from the distal end of mother centriole or basal body. We have previously shown that trichoplein, originally identified as a keratin-binding protein[28], is concentrated at the subdistal/medial zone of both mother and daughter centrioles and activates centriolar Aurora-A kinase in growing cells[29]. A mitochondrial protein VDAC3 is shown to negatively regulate ciliogenesis at the mother centrioles[17]

Methods

Results

Conclusion