Novel Human Homologues of p47 and p67 Participate in Activation of Superoxide-producing NADPH Oxidases

Abstract

The catalytic core of a superoxide-producing NADPH oxidase (Nox) in phagocytes is gp91 phox /Nox2, a membrane-integrated protein that forms a heterodimer with p22 phox to constitute flavocytochrome b 558 . The cytochrome becomes activated by interacting with the adaptor proteins p47 phox and p67 phox as well as the small GTPase Rac. Here we describe the cloning of human cDNAs for novel proteins homologous to p47 phox and p67 phox , designated p41 nox and p51 nox , respectively; the former is encoded by NOXO1 (Nox organizer 1), and the latter is encoded by NOXA1 (Nox activator 1). The novel homologue p41 nox interacts with p22 phox via the two tandem SH3 domains, as does p47 phox . The protein p51 nox as well as p67 phox can form a complex with p47 phox and with p41 nox via the C-terminal SH3 domain and binds to GTPbound Rac via the N-terminal domain containing four tetratricopeptide repeat motifs. These bindings seem to play important roles, since p47 phox and p67 phox activate the phagocyte oxidase via the same interactions. Indeed, p41 nox and p51 nox are capable of replacing the corresponding classical homologue in activation of gp91 phox . Nox1, a homologue of gp91 phox , also can be activated in cells, when it is coexpressed with p41 nox and p51 nox , with p41 nox and p67 phox , or with p47 phox and p51 nox ; in the former two cases, Nox1 is partially activated without any stimulants added, suggesting that p41 nox is normally in an active state. Thus, the novel homologues p41 nox and p51 nox likely function together or in combination with a classical one, thereby activating the two Nox family oxidases.

Subcellular localization and function of alternatively spliced Noxo1 isoforms

“…Recent evidence suggests that Rac1 also regulates Nox1 most likely through GTP-dependent interactions with the Nox activator, Noxa1 [16][17][18][19] We showed that the association of Noxa1 with the plasma membrane depends on its interaction with Noxo1 [17]. These structural and functional similarities between the Nox and phox regulators may explain why Noxo1 and Noxa1 can function in partially compensating for p47 phox and p67 phox in supporting Nox2 activity [8,[13][14][15]. Noxo1, Noxa1, and Rac1 also support Nox3 activity, which appears to function critically in the inner ear [17,[20][21][22]; mice with lesions in either the NOX3 or NOXO1 gene have defects in sensing gravity resulting from impaired otoconia formation [23,24].…”

“…Based on recent observations in Nox1 knockout mice, Nox1 is also thought to act in the cardiovascular system in the pressor response to Angiotensin II [11,12]. Nox1 expressed alone produces little superoxide, although its activity is significantly enhanced in the presence of two co-factors, Noxo1 and Noxa1, detected in colon epithelium that are homologous to p47 phox and p67 phox , respectively [13][14][15]. Noxo1 was proposed to act as a "Nox organizer" based on structural and functional similarities with p47 phox , which is a multi-modular "adaptor" protein that bridges interactions between the membrane (flavocytochrome b 558 and lipid) and p67 phox .…”

“…Several groups described structural variants of human Noxo1, which were proposed to result from alternative splicing of mRNA sequences encoding their PX domains [14,15,25,26]. We characterized Noxo1α and showed that it supports Nox1 activity in several transfected cell models (Genbank™ accession no.…”

Ionizing irradiation induces apoptotic damage of salivary gland acinar cells via NADPH oxidase 1-dependent superoxide generation

“…Nox1 can function even in the absence of p22 phox , although p22 phox is required for the full activity of Nox1 [36]. Furthermore, Nox1 but not Nox2 can also be activated by the p47 phox homologue Noxo1 (Nox organizer 1) and the p67 phox homologue Noxa1 (Nox activator 1) [37].…”

Regulation of smooth muscle by inducible nitric oxide synthase and NADPH oxidase in vascular proliferative diseases

“…The proteins NOXO1 (Nox organizer 1) and NOXA1 (Nox activator 1) are novel homologs of p47phox and p67phox, respectively, that regulate the activity of Nox1 and Nox3 [7,24,44,151]. NOXO1 contains tandem SH3 domains that interact with p22phox like p47phox, but has no autoinhibitory domain like p47phox.…”