The Golgin Protein Giantin Regulates Interconnections Between Golgi Stacks.

Ayano Satoh,Kunihiko Nishino,Runa Murakami,Naomi Abe-Kanoh,Mitsuko Hayashi-Nishino,Yoshimasa Nakamura,Mayuko Koreishi,Sidney Yu,Yasuko Honjo,Junko Masuda,Toshiyuki Nakamura,Joerg Malsam,Takuto Shakuno

doi:10.3389/fcell.2019.00160

Abstract

Golgins are a family of Golgi-localized long coiled-coil proteins. The major golgin function is thought to be the tethering of vesicles, membranes, and cytoskeletal elements to the Golgi. We previously showed that knockdown of one of the longest golgins, Giantin, altered the glycosylation patterns of cell surfaces and the kinetics of cargo transport, suggesting that Giantin maintains correct glycosylation through slowing down transport within the Golgi. Giantin knockdown also altered the sizes and numbers of mini Golgi stacks generated by microtubule de-polymerization, suggesting that it maintains the independence of individual Golgi stacks. Therefore, it is presumed that Golgi stacks lose their independence following Giantin knockdown, allowing easier and possibly increased transport among stacks and abnormal glycosylation. To gain structural insights into the independence of Golgi stacks, we herein performed electron tomography and 3D modeling of Golgi stacks in Giantin knockdown cells. Compared with control cells, Giantin-knockdown cells had fewer and smaller fenestrae within each cisterna. This was supported by data showing that the diffusion rate of Golgi membrane proteins is faster in Giantin-knockdown Golgi, indicating that Giantin knockdown structurally and functionally increases connectivity among Golgi cisternae and stacks. This increased connectivity suggests that contrary to the cis-golgin tether model, Giantin instead inhibits the tether and fusion of nearby Golgi cisternae and stacks, resulting in transport difficulties between stacks that may enable the correct glycosylation of proteins and lipids passing through the Golgi.

Highlights

Eukaryotic cells have various forms of glycans on their cell surfaces that are important for cell–cell communications, development, differentiation, infection, and signaling
Golgi stacks are connected as ribbon-like structures that are dependent on the integrity of microtubules, the depolymerization of which by Nocodazole disperses the ribbon-like Golgi into mini Golgi stacks that can be observed by light microscopy
Our previous work using Nocodazole suggested that the connectivity between Golgi stacks may be altered by the loss of Giantin (Koreishi et al, 2013a)

Summary

Introduction

Eukaryotic cells have various forms of glycans on their cell surfaces that are important for cell–cell communications, development, differentiation, infection, and signaling. Most of these glycans are attached to lipids and proteins initially in the endoplasmic reticulum (ER) and are further extended and trimmed in the Golgi apparatus. The stacking of Golgi cisternae is secured by Golgi stacking proteins GRASP55/65, and their loss disrupts Golgi stacking and accelerates cargo transport without affecting the lateral linking (ribbon formation) of the stacks (Xiang et al, 2013). The authors of this study proposed that GRASP55/65 may slow cargo transport down to ensure correct glycosylation occurs through the Golgi by maintaining Golgi stacks in normal cells (Xiang et al, 2013)

Methods

Results

Conclusion