Trends in Biochemical Sciences
NADPH oxidases: not just for leukocytes anymore!
Section snippets
Components and regulation of the phagocyte NADPH oxidase
The Nox system of stimulated phagocytic leukocytes catalyzes the one-electron reduction of oxygen to produce superoxide anion using NADPH as substrate. When the phagocyte is activated through the action of soluble chemoattractants and chemokines, or phagocytic particles, the cytosolic components (Rac2, p47phox and p67phox) of the oxidase are induced to assemble at the level of the membrane-associated flavocytochrome b558 (cyt b) to form the active enzyme. Cyt b has two subunits, gp91phox (Nox2)
Rac GTPase function in Nox regulation
As indicated earlier, Rac2 GTPase is also a required component of the active phagocyte Nox. Upon cell activation, Rac2 dissociates from a pre-existing cytosolic complex with GDI by an as-yet undetermined mechanism. GDP is exchanged for GTP through the action of membrane-localized GEFs [31] possibly including P-Rex1, a leukocyte-specific PtdIns(3,4,5)P3- and G-protein βγ subunit-regulated Rac GEF [32] and Vav1 [16]. Rac – now in its GTP-bound active form – becomes membrane-associated. Rac
Mechanisms of Rac action in Nox regulation
Currently, there are three major molecular models describing how Rac GTPase regulates Nox activity (see [46] for a more complete discussion of the data for each). Both Lambeth et al. and Pick et al. (Fig. 2a,b) suggest that p67phox, which contains the defined activation domain for cyt b, is the only protein influencing the rate-limiting electron-transfer step (step1) of Nox. Rac is considered to act solely as an adaptor molecule that binds to p67phox through the switch I region and aids in the
Identification of non-phagocyte Nox homologs
Earlier observations describing stimulus-dependent ROS formation at modest levels in non-phagocytic cells, as well as the presence of the known Nox component p22phox in almost all cell types examined, prompted a search for gp91phox (also known as Nox2) homologs. Within the past three years, multiple mammalian Nox2 homologs have been identified in various tissues and can be classified into three groups. (1) Nox1, Nox3, Nox4, and a short form of Nox5 resemble Nox2 in that they consist of six
Biological functions of Nox proteins
The biological functions of ROS generated by Nox/Duox proteins are currently based on many hypotheses and little solid data. Their roles might vary depending on the Nox/Duox isoform and the cell type involved. The tissue distribution of the mammalian Nox homologs appears to be restricted, perhaps reflecting specific biological roles of these enzymes. The expression of Nox3 is limited to fetal tissues, where it might play a role in developmental signaling [54]. Nox4 (also known as Renox) has
Regulation of non-phagocyte Nox isoforms
Although the regulation of the phagocyte Nox2 is well-documented, very little is known about the molecular mechanisms involved in Nox isoform regulation. Although the Nox homologs resemble gp91phox (Nox2) in their basic overall structure, the formation of physical and/or functional complexes with p22phox for ROS production has not yet been established. Indirect evidence indicates that for Nox4 – the only Nox protein constitutively active in various epithelial cell types – p22phox is essential
GTPase-mediated regulation of Nox isoforms
It has been known for some time that Ras and Rac GTPases regulate oxidant-signaling pathways that are crucial for mitogenesis and oncogenesis. Transient expression of a constitutively activated form of Ras in NIH3T3 cells induced a significant increase in intracellular ROS that could be inhibited by expression of a dominant negative allele of Rac1 68, 69. Reactive oxygen species production was suppressed by treatment with the flavoprotein inhibitor diphenylene iodonium, suggesting that a Nox
Concluding remarks
Although the observations outlined here strongly indicate a regulatory role for Rac GTPase in Nox function, unfortunately there are little data at this time that directly link Rac to regulation of the activity of the non-phagocytic Nox proteins. Observations from several laboratories, mainly based upon yeast two-hybrid studies and in vitro binding assays using recombinant proteins, point to the potential association of active Rac with Nox carboxyl-terminal residues and with p51, presumably
References (71)
NADPH oxidase: an update
Blood
(1999)Potential drug targets: small GTPases that regulate leukocyte function
Trends Pharmacol. Sci.
(1999)Rac translocates independently of the neutrophil NADPH oxidase components p47phox and p67phox
J. Biol. Chem.
(1994)Inhibition of superoxide in B lymphocytes by Rac antisense oligonucleotides
J. Biol. Chem.
(1992)Deficiency of the hematopoietic cell-specific Rho family GTPase Rac2 is characterized by abnormalities in neutrophil function and host defense
Immunity
(1999)Architecture of the p40–p47–p67phox complex in the resting state of the NADPH oxidase. A central role for p67phox
J. Biol. Chem.
(2002)Molecular basis of phosphorylation-induced activation of the NADPH oxidase
Cell
(2003)Rac activation induces NADPH oxidase activity in transgenic COSphox cells, and the level of superoxide production is exchange factor-dependent
J. Biol. Chem.
(2002)Translocation of Rac correlates with NADPH oxidase activation
J. Biol. Chem.
(1993)Two signaling mechanisms for activation of αM β2 avidity in polymorphonuclear neutrophils
J. Biol. Chem.
(1998)
Mechanism for phosphorylation-induced activation of the phagocyte NADPH oxidase protein p47(phox). Triple replacement of serines 303, 304, and 328 with aspartates disrupts the SH3 domain-mediated intramolecular interaction in p47(phox), thereby activating the oxidase
J. Biol. Chem.
NADPH oxidase activity is independent of p47-phox in vitro
J. Biol. Chem.
The cytosolic component p47phox is not a sine qua non participant in the activation of NADPH oxidase, but is required for optimal superoxide production
J. Biol. Chem.
The p40phox and p47phox PX domains of NADPH oxidase target cell membranes via direct and indirect recruitment by phosphoinositides
J. Biol. Chem.
Regulation of the neutrophil respiratory burst oxidase: identification of an activation domain in p67phox
J. Biol. Chem.
The active N terminal region of p67phox
J. Biol. Chem.
Guanine nucleotide exchange regulates membrane translocation of Rac/Rho GTP-binding proteins
J. Biol. Chem.
P-Rex1, a PtdIns(3,4,5)P3- and Gβγ-regulated guanine nucleotide exchange factor for Rac
Cell
Tetratricopeptide repeat (TPR) motifs of p67phox participate in interaction with the small GTPase Rac and activation of the phagocyte NADPH oxidase
J. Biol. Chem.
Structure of the TPR domain of p67phox in complex with Rac-GTP
Mol. Cell
Peptide walking is a novel method for mapping functional domains in proteins
J. Biol. Chem.
Rac ‘insert region’ is a novel effector region that is implicated in the activation of NADPH oxidase, but not PAK65
J. Biol. Chem.
A Rac1 effector site controlling mitogenesis through superoxide production
J. Biol. Chem.
Current molecular models for NADPH oxidase regulation by Rac GTPase
Blood
Novel homologs of gp91phox
Trends Biochem. Sci.
A Ca(2+)-activated NADPH oxidase in testis, spleen and lymph nodes
J. Biol. Chem.
Purification of a novel flavoprotein involved in the thyroid NADPH oxidase
J. Biol. Chem.
Cloning of two human thyroid cDNAs encoding new members of the NADPH oxidase family
J. Biol. Chem.
Homologs of gp91phox: cloning and tissue distribution of Nox3, Nox4, and Nox5
Gene
A novel superoxide-producing NAD(P)H oxidase in kidney
J. Biol. Chem.
Novel human homologyes of p47phox and p67phox participate in activation of superoxide-producing NADPH oxidases
J. Biol. Chem.
Two novel proteins activate superoxide generation by the NADPH oxidase NOX1
J. Biol. Chem.
Proteins homologous to p47phox and p67phox support superoxide production by NAD(P)H oxidase 1 in colon epithelial cells
J. Biol. Chem.
Regulation of the phagocyte respiratory burst oxidase by protein interactions
Biochem. Mol. Biol. Int.
Activation of the NADPH oxidase involves the small GTP-binding protein p21rac1
Nature
Cited by (356)
Ethyl vinyl ketone activates oxidative and calcium burst and CML8-ACA8 participates in calcium recovery in Arabidopsis leaves
2024, Plant Physiology and BiochemistryAge-related insult of cochlear ribbon synapses: An early-onset contributor to D-galactose-induced aging in mice
2020, Neurochemistry International