Osmotically Induced Cell Volume Changes Alter Anterograde and Retrograde Transport, Golgi Structure, and COPI Dissociation

Abstract

Physiological conditions that impinge on constitutive traffic and affect organelle structure are not known. We report that osmotically induced cell volume changes, which are known to occur under a variety of conditions, rapidly inhibited endoplasmic reticulum (ER)-to-Golgi transport in mammalian cells. Both ER export and ER Golgi intermediate compartment (ERGIC)-to-Golgi trafficking steps were blocked, but retrograde transport was active, and it mediated ERGIC and Golgi collapse into the ER. Extensive tubulation and relatively rapid Golgi resident redistribution were observed under hypo-osmotic conditions, whereas a slower redistribution of the same markers, without apparent tubulation, was observed under hyperosmotic conditions. The osmotic stress response correlated with the perturbation of COPI function, because both hypo- and hyperosmotic conditions slowed brefeldin A-induced dissociation of betaCOP from Golgi membranes. Remarkably, Golgi residents reemerged after several hours of sustained incubation in hypotonic or hypertonic medium. Reemergence was independent of new protein synthesis but required PKC, an activity known to mediate cell volume recovery. Taken together these results indicate the existence of a coupling between cell volume and constitutive traffic that impacts organelle structure through independent effects on anterograde and retrograde flow and that involves, in part, modulation of COPI function.

Herpes Simplex Virus Type 1 Glycoprotein K and the UL20 Protein Are Interdependent for Intracellular Trafficking andtrans-Golgi Network Localization

“…In this regard, our group's recent observations that overexpression of gK severely inhibited virion morphogenesis and intracellular trafficking of gK by collapsing Golgi into the ER (26) may be due to the lack of sufficient amounts of UL20p to transport gK from the ER to cell surfaces and TGN. The accumulation of gK within the ER, due to its inability to be transported to subsequent compartments, could mediate a cellular ER stress response and subsequent Golgi collapse (15,47). Additional biochemical experiments are needed to more accurately define gK/UL20p stoichiometric relationships and test whether these two proteins directly interact.…”

The Cargo Receptors Surf4, Endoplasmic Reticulum-Golgi Intermediate Compartment (ERGIC)-53, and p25 Are Required to Maintain the Architecture of ERGIC and Golgi

“…Together with the partial resistance of the cis-Golgi to BFA after cargo receptor silencing, the lack of tubules implies that cargo receptors are required for efficient tubulation. The role of cargo receptors in promoting tubulation of the cis-Golgi indicated by GM130 was assessed by subjecting cells depleted of cargo receptors to hypotonic stress known to cause tubulation of the Golgi (Lee and Linstedt, 1999). Cells depleted of Surf4/ERGIC-53 or p25 showed no tubulation of the cis-Golgi, whereas in control cells the cis-Golgi was extensively tubulated after hypotonic stress (Figure 10).…”

Ionic imbalance, in addition to molecular crowding, abates cytoskeletal dynamics and vesicle motility during hypertonic stress

“…Membrane trafficking is a major process affected by hypertonicity that probably contributes significantly to the change incurred upon challenge. Indeed, we and others have observed that endocytosis, exocytosis, and vesicular trafficking are reduced from the onset of challenge, and that the reduction can persist hours after challenge (14)(15)(16)(17)(18)(19). However, how immediate changes in the cell's biophysical parameters influence these events is unclear.…”