Aquaporin 9 phosphorylation mediates membrane localization and neutrophil polarization.

Abstract

Neutrophils are of prime importance in the host innate defence against invading microorganisms by employing two primary mechanisms, locomotion towards and phagocytosis of the prey. Recent research points to pivotal roles for water channels known as aquaporins in cell motility. Here, we focused on the role of aquaporin 9 (AQP9) in chemoattractant-induced polarization and migration of primary mouse neutrophils and neutrophil-like HL60 cells. We found that AQP9 is phosphorylated downstream of the fMLF receptor or PMA stimulation in primary human neutrophils. The dynamics of AQP9 was assessed using GFP-tagged AQP9 constructs and other fluorescent markers through various live-cell imaging techniques. Expression of wild-type or the phosphomimic S11D AQP9 changed cell volume regulation as a response to hyperosmotic changes and enhanced neutrophil polarization and chemotaxis. Wt AQP9 and S11D AQP9 displayed a very dynamic distribution at the cell membrane, whereas the phosphorylation-deficient S11A AQP9 failed to localize to the plasma membrane. Furthermore, we found that Rac1 regulated the translocation of AQP9 to the plasma membrane. Our results show that AQP9 plays an active role in neutrophil volume regulation and migration. The display of AQP9 at the plasma membrane depends on AQP9 phosphorylation, which appeared to be regulated through a Rac1-dependent pathway.