ABSTRACT
It has been well documented that the endoplasmic reticulum (ER) responds to cellular stresses through the unfolded protein response (UPR), but it is unknown how the Golgi responds to similar stresses. In this study, we treated HeLa cells with ER stress inducers, thapsigargin (TG), tunicamycin (Tu) and Dithiothreitol (DTT), and found that only TG treatment caused Golgi fragmentation. TG induced Golgi fragmentation at a low dose and short time when UPR was undetectable, demonstrating that Golgi fragmentation occurs independently of ER stress. Further experiments demonstrated that TG induces Golgi fragmentation through elevated intracellular Ca2+ and protein kinase Cα (PKCα) activity, which phosphorylates the Golgi stacking protein GRASP55. Significantly, activation of PKCα with other activating or inflammatory agents, including Phorbol 12-myristate 13-acetate (PMA) and histamine, modulates the Golgi structure in a similar fashion. Hence, our study revealed a novel mechanism through which increased cytosolic Ca2+ modulates Golgi structure and function.
ABBREVIATIONS
- B/AM
- BAPTA-AM
- CAMKII
- Ca2+/calmodulin-dependent protein kinase II
- DTT
- dithiothreitol
- EM
- electron microscopy
- ER
- endoplasmic reticulum
- Endo H
- Endoglycosidase H
- GFP
- green fluorescent protein
- GORASP1
- Golgi reassembly stacking protein 1
- GORASP2
- Golgi reassembly stacking protein 2
- GRASP55
- Golgi reassembly stacking protein of 55 kDa
- GRASP65
- Golgi reassembly stacking protein of 65 kDa
- PBS
- phosphate-buffered saline
- PEI
- polyethylenimine
- PFA
- paraformaldehyde
- SPR domain
- serine/proline-rich domain
- TGN
- trans-Golgi network
- PKA
- Protein Kinase A
- PKC
- Protein Kinase C
- SNARE
- SNAP receptor protein
- PMA
- phorbol 12-myristate 13-acetate
- TG
- thapsigargin
- TGN
- trans-Golgi network
- Tu
- tunicamycin
- VSV-G
- vesicular stomatitis virus glycoprotein