Low cytoplasmic pH causes fragmentation and dispersal of the Golgi apparatus in human hepatoma cells

The centrosomal localization of the Golgi apparatus in interphase cells is thought to be maintained by retrograde microtubule-based motility. It is well established that, when intracellular pH is lowered, lysosomes and endosomes, also showing pericentrosomal localization, translocate towards the plus ends of microtubules within 15 min. In this study, we found that prolonged incubation in low pH medium (pH 6.6) with 20 mM Na acetate induced the fragmentation and dispersal of the Golgi apparatus in the human hepatoma cell line PLC/PRF/5. The fraction of Golgi-dispersed cells increased in a time-dependent manner, and reached over 60% after the 16-h incubation. The cytoplasmic pH was dropped to approximately 7.10. Replacement with normal pH medium restored the structure and localization of the apparatus within 30 min. In the low pH condition, the microtubular network and endoplasmic reticulum appeared normal, and cytoplasmic dynein was still bound to the fragmented Golgi membranes. These findings suggest that low cytoplasmic pH suppresses the retrograde movement of the Golgi apparatus as well as that of lysosomes and endosomes.