Water flux in cell motility: expanding the mechanisms of membrane protrusion.

Transmembrane water fluxes through aquaporins (AQPs) are suggested to play pivotal roles in cell polarization and directional cell motility. Local dilution by water influences the dynamics of the subcortical actin polymerization and directs the formation of nascent membrane protrusions. In this paper, recent evidence is discussed in support of such a central role of AQP in membrane protrusion formation and cell migration as a basis for our understanding of the underlying molecular mechanisms of directional motility. Specifically, AQP9 in a physiological context controls transmembrane water fluxes driving membrane protrusion formation, as an initial cellular response to a chemoattractant or other migratory signals. The importance of AQP-facilitated water fluxes in directional cell motility is underscored by the observation that blocking or modifying specific sites in AQP9 also interferes with the molecular machinery that govern actin-mediated cellular shape changes.