Role of aquaporin isoforms on Nox-dependent redox signalling involved in proliferation of leukaemia cells

NAD(P)H oxidases (Nox) are a family of membrane-associated enzymatic complexes that, transferring electrons from NAD(P)H inside the cell to molecular oxygen across the membrane, generate superoxide anion (O2-) and/or hydrogen peroxide (H2O2) outside the cell [1]. Nox-produced ROS can act as messengers in redox signalling and hydrogen peroxide is considered the main effector due to its relative stability. Although it is now confirmed the involvement of ROS in biosignalling, it still remains unclear whether the ROS generated extracellularly by Nox can permeate through the plasma membrane by simple diffusion or mediated by transport proteins. Recent experimental evidence suggest that two isoforms of aquaporins (AQP3 and AQP8) have the ability to channel H2O2 across the membranes and that they may have an important role in redox signalling [2]. Our attention has been focused on ROS involved in signalling transduction pathways contributing to cancer development. In particular, we have previously demonstrated that Nox-generated ROS sustain glucose uptake and cellular proliferation in leukaemia cell lines [3]. In this study, we assess whether specific aquaporin isoforms play a role in facilitating Nox-produced H2O2 transport through the plasma membrane affecting downstream pathways linked to cell proliferation in leukaemia cells. We demonstrated that the treatment with AgNO3, a potent aquaporin inhibitor, causes a decrease in intracellular ROS level both when H2O2 is produced by Nox enzymes and when it is added exogenously to the medium; on the contrary, overexpression of AQP8 and AQP3 causes an increase in the intracellular ROS level when hydrogen peroxide is added. Furthermore, aquaporin inhibition causes a significant decrease in glucose transport in HL60 and B1647 cells and VEGF-induced intracellular ROS accumulation is augmented when AQP3 or AQP8 are overexpressed. In conclusion, our data suggest that AQP3 and AQP8, but not AQP1, are able to transport Nox-generated H2O2 across the plasma membrane supporting leukaemia cells proliferation.