Accumulation of aquaporin-1 during hemolysin-induced necrotic cell death

Altered tissue water homeostasis may contribute to edema formation during various stresses including bacterial infection. We observed induction of aquaporin-1 (AQP1) during Staphylococcus aureus infection of cultured cells indicating a potential mechanism underlying altered water homeostasis during infection. To investigate mechanisms of AQP1 induction, we examined the effects of the S. aureus alpha-hemolysin on AQP1 abundance in Balb/c fibroblasts. Fibroblasts incubated with 30 microg/ml hemolysin exhibited a 5-10 fold increase in AQP1 protein within 4-6 hours of exposure. The use of multiple signaling cascade inhibitors failed to affect hemolysin-mediated accumulation of AQP1. However, immunoprecipitation revealed an initial accumulation of ubiquitinated AQP1 followed by a decrease to baseline levels after 4 hours. Immunofluorescence indicated that following hemolysin exposure, AQP1 was no longer on the plasma membrane, but was found in a population of submembrane vacuoles. AQP1 redistribution was further indicated by surface biotinylation experiments suggesting diminished AQP1 abundance on the plasma membrane as well as redistribution out of lipid raft fractions. Live cell confocal microscopy revealed that the pattern of cell volume change observed following hemolysin exposure was altered in cells in which AQP1 was silenced. We conclude that alpha-toxin alters proteasomal processing and leads to intracellular accumulation of AQP1, which may likely contribute to disrupted cell volume homeostasis in infection.