Distinct Roles of TRAPPC8 and TRAPPC12 in Ciliogenesis via Their Interactions With OFD1.

Caiyun Zhang,Gavin Ka Yu Siu,Xiaomin Luo,Sidney Yu,Chunman Li

doi:10.3389/fcell.2020.00148

Abstract

The transport protein particle (TRAPP) complex was initially identified as a tethering factor for COPII vesicle. Subsequently, three forms (TRAPPI, II, and III) have been found and TRAPPIII has been reported to serve as a regulator in autophagy. This study investigates a new role of mammalian TRAPPIII in ciliogenesis. We found a ciliopathy protein, oral-facial-digital syndrome 1 (OFD1), interacting with the TRAPPIII-specific subunits TRAPPC8 and TRAPPC12. TRAPPC8 is necessary for the association of OFD1 with pericentriolar material 1 (PCM1). Its depletion reduces the extent of colocalized signals between OFD1 and PCM1, but does not compromise the structural integrity of centriolar satellites. The interaction between TRAPPC8 and OFD1 inhibits that between OFD1 and TRAPPC12, suggesting different roles of TRAPPIII-specific subunits in ciliogenesis and explaining the differences in cilium lengths in TRAPPC8-depleted and TRAPPC12-depleted hTERT-RPE1 cells. On the other hand, TRAPPC12 depletion causes increased ciliary length because TRAPPC12 is required for the disassembly of primary cilia. Overall, this study has revealed different roles of TRAPPC8 and TRAPPC12 in the assembly of centriolar satellites and demonstrated a possible tethering role of TRAPPIII during ciliogenesis.

Highlights

Primary cilia are microtubule-based sensory organelles that project from the surface of most mammalian cells (Malicki and Johnson, 2017)
BBS9 was transported to the cilium of TRAPPC12 depleted cells (Figures S6E,F). This suggests that molecular trafficking still could occur in spite of the mislocalization of pericentriolar material 1 (PCM1). We identified both TRAPPC8 and TRAPPC12 interact with a ciliopathy-related protein orofaciodigital syndrome 1 (OFD1)
We cannot rule out the possibility that the increased interaction between TRAPPC12 and OFD1 in the absence of TRAPPC8 might have been solely responsible for the defects in ciliogenesis in the TRAPPC8 depletion

Summary

Introduction

Primary cilia are microtubule-based sensory organelles that project from the surface of most mammalian cells (Malicki and Johnson, 2017). Centriolar satellites are the membrane-free granules with a diameter ranging from 70 to 100 nm and move along microtubules in the vicinity of the centrosome (Balczon et al, 1994; Kubo et al, 1999; Dammermann and Merdes, 2002; Kubo and Tsukita, 2003) These structures, as TRAPPIII-OFD1 in Ciliogenesis dynamic protein complexes, are responsible for proteins trafficking from the cytoplasm toward the centrosome and ciliary complex, or vice versa (Barenz et al, 2011; Lopes et al, 2011; Tollenaere et al, 2015; Hori and Toda, 2017). The population of OFD1 at centriolar satellites promotes the regular growth of the primary cilium via its degradation by autophagy under serum starvation conditions (Tang et al, 2013)

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Conclusion