Principal Investigator: Yanzhuang Wang, PhD
Grant Title: Golgi cisternal stacking is required for accurate glycosylation
Abstract
Objectives: How and why Golgi cisternae form stacks? The Golgi
apparatus is a key cellular membrane organelle in the secretory pathway thatprocesses a wide variety of proteins, including antibodies that protect us
against infections, enzymes that help digest our food, and protein factors that
help our cells to grow and even die when appropriate. To perform thesefunctions, the Golgi membranes need to form a unique, stacked structure.
However, the mechanism and significance of cisternal stacking for normal
cell physiology remains largely untested. In an increasing number of diseases,
including cancer, viral infections and multiple types of neurodegenerative
diseases, the Golgi apparatus is fragmented abnormally, although theunderlying mechanism is so far unexplored. Our research aims to understandhow the stacked Golgi structure is formed and why its formation is important Yanzhuang Wang, PhD
Associate Professor
for Golgi function under normal and disease conditions (1, 2).
University of MichiganAnn Arbor, USA
Methods: A unique multidisciplinary approach. We have developed aunique multidisciplinary approach employing biochemistry, cell biology, electron microscopy, andproteomics and glycomics, combined with a novel in vitro reconstitution assay, to provide a mechanistic
explanation for Golgi structure formation and function. This allowed us to reveal that stack formation
directly involves the Golgi stacking protein GRASP65 and GRASP55, which play complementary andessential roles in Golgi cisternal stacking by forming mitotically regulated trans-oligomers (3-5).
Results: Golgi cisternal stacking is required for accurate glycosylation. We have explored thefunctional consequences of Golgi unstacking by
the depletion of GRASP55, GRASP65 or both. We
found that Golgi cisternal unstacking stimulates
COPI vesicle budding and thus enhances proteintransport. Golgi fragmentation, however, impairs
protein sorting and alters the glycosylation of cellsurface proteins. Subsequently, cell adhesion andmigration were reduced when the Golgi wasunstacked. Furthermore, total protein synthesis andthe proliferation of cells with unstacked Golgi
were enhanced. We propose that Golgi stackformation is a flux regulator for protein trafficking Figure 1. Golgi destruction accelerates protein trafficking andand thereby functions as a quality control impairs accurate glycosylation. When Golgi cisternae are stacked
mechanism for protein sorting and modifications, (A), vesicles can only form and fuse at the rims. This slows down
trafficking, but enforces accurate glycosylation. Once the cisternae
e.g. glycosylation (Figure 1) (6, 7). This work has are unstacked (B), more membrane area becomes accessible forsignificant impact in understanding human vesicle budding and fusion, thereby increasing cargo transport. This,diseases in which the Golgi becomes abnormal. however, causes glycosylation and sorting defects.
For example, cancer cells have fragmented Golgi, which may be the reason why these cells have reduced
cell attachment, changes on cell surface glycan, and secretion of lysosomal enzymes, all of which could
be caused by Golgi dysfunction.
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G. Joshi, Y. Chi, Z. Huang, Y. Wang, Abeta-induced Golgi fragmentation in Alzheimer's disease enhances Abeta
production. Proc Natl Acad Sci U S A 111, E1230-1239 (2014).
G. Joshi, Y. Wang, Golgi defects enhance APP amyloidogenic processing in Alzheimer's disease. Bioessays 37, 240247 (2015).
D. Tang, H. Yuan, O. Vielemeyer, F. Perez, Y. Wang, Sequential phosphorylation of GRASP65 during mitotic Golgi
disassembly. Biology open 1, 1204-1214 (2012).
D. Tang, H. Yuan, Y. Wang, The Role of GRASP65 in Golgi Cisternal Stacking and Cell Cycle Progression. Traffic11, 827-842 (2010).
Y. Xiang, Y. Wang, GRASP55 and GRASP65 play complementary and essential roles in Golgi cisternal stacking. JCell Biol 188, 237-251 (2010).
Y. Wang, J. H. Wei, B. Bisel, D. Tang, J. Seemann, Golgi Cisternal Unstacking Stimulates COPI Vesicle Budding andProtein Transport. PLoS ONE 3, e1647 (2008).
Y. Xiang et al., Regulation of cargo sorting and glycosylation by the Golgi matrix proteins GRASP55/65. Nat
Commun 4, 1659 (2013).