AQP4 and glioblastoma: In GBM, AQP4 colocalizes with chloride and potassium channels at the leading edges of motile tumor cells to enhance locomotion [19,20], promoting cell volume regulation, integrin trafficking and metalloproteinase (MMP) secretion in response to protein kinase C [19,68,93,97], which also reduces osmotic water permeability by inducing AQP4 internalization [98].