Actin-related protein (Arp) 2/3 complex plays a critical role in the aquaporin-2 exocytotic pathway.

Liu, Chen-Chung Steven; Cheung, Pui W; Dinesh, Anupama; Baylor, Noah; Paunescu, Theodor C; Nair, Anil V; Bouley, Richard; Brown, Dennis

The trafficking of proteins such as aquaporin-2 (AQP2) in the exocytotic pathway requires an active actin cytoskeleton network, but the mechanism is incompletely understood. Here, we show that the actin-related protein (Arp) 2/3 complex, a key factor in actin filament branching and polymerization, is involved in the shuttling of aquaporin-2 (AQP2) between the trans Golgi network (TGN) and the plasma membrane. Arp2/3 inhibition (using CK-666) or siRNA knockdown blocks vasopressin induced AQP2 membrane accumulation, and induces the formation of distinct AQP2 perinuclear patches positive for markers of TGN-derived clathrin coated vesicles. After a 20oC cold block, AQP2 formed perinuclear patches due continuous endocytosis coupled with inhibition of exit from the TGN-associated vesicles. Upon rewarming, AQP2 normally leaves the TGN, and redistributes into the cytoplasm, entering the exocytotic pathway. Inhibition of Arp2/3 blocked this process, and trapped AQP2 in clathrin positive vesicles. Taken together, these results suggest that Arp2/3 is essential for AQP2 trafficking, specifically for its delivery into the post-TGN exocytotic pathway to the plasma membrane.