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 apparatus 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 resulted in 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 Golgi fragmentation was 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.Support or Funding InformationThis work was supported by the National Institutes of Health (Grants GM112786, GM105920, and GM130331), MCubed and the Fastforward Protein Folding Disease Initiative of the University of Michigan to Y. Wang. S. Ireland is a graduate student who has been partially supported by the Mary Sue and Kenneth Coleman Endowed Fellowship Fund from the University of Michigan.