AQP8 transports NOX2-generated H2O2 across the plasma membrane to promote signaling in B cells

Abstract

HO acts as a second messenger in key signaling circuits, transiently modulating tyrosine phosphatases and kinases. We investigated its origin, membrane transport, and functional role during B cell activation and differentiation. Our data identified NADPH-oxidase 2 as the main source of HO and aquaporin 8 as a transport facilitator across the plasma membrane. On aquaporin 8 silencing, inducible B lymphoma cells responded poorly to TLR and BCR stimulation. Their differentiation was severely impaired, as demonstrated by retarded onset of IgM polymerization, low amounts of IgM secretion, and prolonged BCR expression on the cell surface. A silencing-resistant aquaporin 8 rescued responsiveness, confirming that the import of HO across the membrane is essential for B cell activation. The addition of exogenous catalase to primary B splenocytes severely impaired the tyrosine phosphorylation induced by BCR cross-linking, as did the absence of NOX2 in a murine model of chronic granulomatous disease. Importantly, re-expression of gp91 through gene therapy restored the specific B cell signaling deficiency in NOX2 cells. Thus, efficient induction of B cell activation and differentiation requires intact HO fluxes across the plasma membrane for signal amplification.

Dual oxidase: a novel therapeutic target in allergic disease

“…Another issue with respect to the proposed involvement of DUOX or other NOX isozymes in cellular redox signalling is the fact that NOX‐derived ROS are generated extracellularly or within phagosomes/endosomes and are thus segregated from their putative cytoplasmic redox‐sensitive targets by a lipid membrane. The recent discovery of aquaporins as selective channels for H 2 O 2 resolves this issue, and aquaporin‐dependent transmembrane H 2 O 2 transfer likely helps confine the oxidative potential of H 2 O 2 to assure specificity in redox signalling (Bertolotti et al ., ; Thiagarajah et al ., ).…”

Bicarbonate is essential for protein-tyrosine phosphatase 1B (PTP1B) oxidation and cellular signaling through EGF-triggered phosphorylation cascades

“…NOXs are membrane-localized (typically on the plasma, endosomal, or endoplasmic reticulum membrane) and use cytoplasmic NADPH to produce superoxide and H 2 O 2 on the opposing membrane surface. The H 2 O 2 must then enter the cell, facilitated through aquaporins (7,8), to exert its signaling actions. During stimulation of platelet-derived growth factor and epidermal growth factor (EGF) receptor pathways, the catalytic Cys residue of PTP1B becomes reversibly oxidized and thus inhibited (4,9).…”

Oxidation Impacts the Intracellular Signaling Machinery in Hematological Disorders

“…•− . This latter ROS is produced by NADPH oxidase 2 (NOX2) and released, where it is subsequently taken up by the activated B cell through a transmembrane channel, identified as aquaporin 8 [64]. The role of NOX2 and the downstream generation of ROS as secondary messengers has been shown to be essential for amplifying kinase-mediated signals [65,66], and is especially requireds for B cell proliferation [67].…”

“…A crucial pathway being the Keap1-Nrf2-ARE pathway, which upregulates heme-oxygenase-1 (HO-1) and catalase, among others. Whereas catalase directly detoxifies H 2 O 2 to water and oxygen, HO-1 acts as a positive regulator of TFAM, a mitochondrial transcription factor, in turn stimulating de novo mitochondrial biogenesis, which is aimed at compensating for the damage induced by ROS and the consequent decrease in energy production [63][64][65][66][67][68]. Moreover, the ROS-scavenging capacity of CLL cells is also to be ascribed to thiols, which are significantly more abundant than in normal B cells [68].…”