Cytosolic Ca²⁺modulates Golgi structure through PKC-mediated GRASP55 phosphorylation

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 Ca 2+ 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 Ca 2+ modulates Golgi structure and function.antibodies against CHOP, p-eIF2a, eIF2a and p115 (Cell Signaling, Danvers, MA), GRASP55 and GRASP65 (Proteintech), Bip (Santa Cruz), GM130 ("N73" from J. Seemann), and TGN46 (Bio-Rad).

SARS-CoV-2 remodels the Golgi apparatus to facilitate viral assembly and secretion

“…SARS-CoV-2 infection down-regulates GRASP55 but not its homolog GRASP65. GRASP55 has been shown to play a crucial role in various stress responses (Ireland et al, 2020b;Nüchel et al, 2021;Wang, 2018, 2020), while GRASP65 functions more in cell migration and apoptosis (Ahat et al, 2019;Bisel et al, 2008;Lane et al, 2002). In this study, we found that GRASP55 plays a vital role in viral infection, most likely related to its function in Golgi structure 13 formation.…”