Ciliary membrane proteins traffic through the Golgi via a Rabep1/GGA1/Arl3-dependent mechanism.

Hyunho Kim,Hangxue Xu,Klaus Piontek,Feng Qian,Edward J Weinman,Alessandra Boletta,Qiong Huang,Gregory G Germino,Qin Yao,Patricia Outeda,Valeriu Cebotaru,Terry Watnick,Marco Chiaravalli,Weizhe Li

doi:10.1038/ncomms6482

Abstract

Primary cilia contain specific receptors and channel proteins that sense the extracellular milieu. Defective ciliary function causes ciliopathies such as autosomal dominant polycystic kidney disease (ADPKD). However, little is known about how large ciliary transmembrane proteins traffic to the cilia. Polycystin-1 (PC1) and -2 (PC2), the two ADPKD gene products, are large transmembrane proteins that co-localize to cilia where they act to control proper tubular diameter. Here we describe that PC1 and PC2 must interact and form a complex to reach the trans-Golgi network (TGN) for subsequent ciliary targeting. PC1 must also be proteolytically cleaved at a GPS site for this to occur. Using yeast two-hybrid screening coupled with a candidate approach, we identify a Rabep1/GGA1/Arl3-dependent ciliary targeting mechanism, whereby Rabep1 couples the polycystin complex to a GGA1/Arl3-based ciliary trafficking module at the TGN. This study provides novel insights into the ciliary trafficking mechanism of membrane proteins.

Highlights

Primary cilia contain specific receptors and channel proteins that sense the extracellular milieu
We demonstrate that PC1–PC2 interaction and G-proteincoupled receptor cleavage site (GPS) cleavage of PC1 are both required for the polycystin complex to reach the trans-Golgi network (TGN) and for subsequent ciliary targeting
We found that PC1 localizes to cilia in wild-type mouse embryonic fibroblasts (MEFs), but not in Pkd[2] À / À MEFs (Fig. 1a,c)

Summary

Introduction

Primary cilia contain specific receptors and channel proteins that sense the extracellular milieu. Primary cilia are microtubule-based non-motile projections on the apical surface of cells, which organize important signalling pathways mediated by specific receptors and channel proteins at the ciliary membrane in response to mechanical and chemical stimuli[1]. They are the key organelle for controlling correct tubular diameter, and defective ciliary function causes a variety of ciliopathies[1], including autosomal dominant polycystic kidney disease (ADPKD)[2,3]. We demonstrate that PC1–PC2 interaction and GPS cleavage of PC1 are both required for the polycystin complex to reach the TGN and for subsequent ciliary targeting. Our study provides novel insights into the ciliary trafficking mechanism of transmembrane proteins, with implications for ADPKD, the most common human ciliopathy

Methods

Results

Conclusion