Spatial regulation of Golgi phosphatidylinositol-4-phosphate is required for enzyme localization and glycosylation fidelity.
The enrichment of phosphatidylinositol-4-phosphate (PI(4)P) at the trans Golgi network (TGN) is instrumental for proper protein and lipid sorting, yet how the restricted distribution of PI(4)P is achieved remains unknown. Here, we show that lipid phosphatase Suppressor of actin mutations 1 (SAC1) is crucial for the spatial regulation of Golgi PI(4)P. Ultrastructural analysis revealed that SAC1 is predominantly located at cisternal Golgi membranes but is absent from the TGN, thus confining PI(4)P to the TGN. RNAi-mediated knockdown of SAC1 caused changes in Golgi morphology and mislocalization of Golgi enzymes. Enzymes involved in glycan processing such as mannosidase-II (Man-II) and N-acetylglucosamine transferase-I (GnT-I) redistributed to aberrant intracellular structures and to the cell surface in SAC1 knockdown cells. SAC1 depletion also induced a unique pattern of Golgi-specific defects in N-and O-linked glycosylation. These results indicate that SAC1 organizes PI(4)P distribution between the Golgi complex and the TGN, which is instrumental for resident enzyme partitioning and Golgi morphology.
Cheong
Fei Ying
FY
Division of Nephrology & Hypertension, Department of Medicine Oregon Health & Science University, Portland, OR 97239, USA.
Sharma
Vandana
V
Blagoveshchenskaya
Anastasia
A
Oorschot
Viola M J
VM
Brankatschk
Ben
B
Klumperman
Judith
J
Freeze
Hudson H
HH
Mayinger
Peter
P
D015536:Down-Regulation; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000648:ultrastructure*; D018129:Phosphatidylinositol Phosphates / Q000737:chemistry / Q000378:metabolism*; D021381:Protein Transport; D021601:trans-Golgi Network / Q000737:chemistry
D008565:Membrane Proteins; D018129:Phosphatidylinositol Phosphates; C416669:Sac1 protein, mammalian; C037178:phosphatidylinositol 4-phosphate