Dual oxidases (Duox1 and Duox2) are plasma membrane-targeted hydrogen peroxide generators that support extracellular hemoperoxidases. Duox activator 2 (Duoxa2), initially described as an endoplasmic reticulum resident protein, functions as a maturation factor needed to deliver active Duox2 to the cell surface. However, less is known about the Duox1/Duoxa1 homologues. We identified four alternatively spliced Duoxa1 variants and explored their roles in Duox subcellular targeting and reconstitution. Duox1 and Duox2 are functionally rescued by Duoxa2 or the Duoxa1 variants that contain the third coding exon. All active maturation factors are cotransported to the cell surface when coexpressed with either Duox1 or Duox2, consistent with detection of endogenous Duoxa1 on apical plasma membranes of the airway epithelium. In contrast, the Duoxa proteins are retained in the endoplasmic reticulum when expressed without Duox. Duox1/Duoxa1alpha and Duox2/Duoxa2 pairs produce the highest levels of hydrogen peroxide, as they undergo Golgi-based carbohydrate modifications and form stable cell surface complexes. Cross-functioning pairs that do not form stable complexes produce less hydrogen peroxide and leak superoxide. These findings suggest Duox activators not only promote Duox maturation, but they function as part of the hydrogen peroxide-generating enzyme.

In the phagocytic cell, NADPH oxidase (Nox2) system, cytoplasmic regulators (p47 phox , p67 phox , p40 phox , and Rac) translocate and associate with the membrane-spanning flavocytochrome b 558 , leading to activation of superoxide production. We examined membrane targeting of phox proteins and explored conformational changes in p40 phox that regulate its translocation to membranes upon stimulation. GFP-p40 phox translocates to early endosomes, whereas GFP-p47 phox translocates to the plasma membrane in response to arachidonic acid. In contrast, GFP-p67 phox does not translocate to membranes when expressed alone, but it is dependent on p40 phox and p47 phox for its translocation to early endosomes or the plasma membrane, respectively. Translocation of GFP-p40 phox or GFP-p47 phox to their respective membrane-targeting sites is abolished by mutations in their phox (PX) domains that disrupt their interactions with their cognate phospholipid ligands. Furthermore, GFP-p67 phox translocation to either membrane is abolished by mutations that disrupt its interaction with p40 phox or p47 phox . Finally, we detected a head-to-tail (PX-Phox and Bem1 [PB1] domain) intramolecular interaction within p40 phox in its resting state by deletion mutagenesis, cell localization, and binding experiments, suggesting that its PX domain is inaccessible to interact with phosphatidylinositol 3-phosphate without cell stimulation. Thus, both p40 phox and p47 phox function as diverse p67 phox "carrier proteins" regulated by the unmasking of membrane-targeting domains in distinct mechanisms. INTRODUCTIONIn phagocytic cells, reactive oxygen species (ROS) are produced by NADPH oxidase (Nox2 system). The enzyme is a multiprotein complex assembled from a membrane-spanning flavocytochrome b 558 (composed of gp91 phox [Nox2] and p22 phox ) and four cytoplasmic components (p47 phox , p67 phox , p40 phox , and Rac) (Leto, 1999;Nauseef, 2004;Quinn and Gauss, 2004). In unstimulated phagocytes, the oxidase is dissociated and inactive: the flavocytochrome b 558 is stored on the membranes of intracellular granules (Jesaitis et al., 1990), Rac is maintained in a GDP-bound cytoplasmic complex dimerized with Rho-guanine nucleotide dissociation inhibitor (GDI) , and the other phox proteins associate in a separate ternary cytoplasmic complex (p47 phox -p67 phox -p40 phox ) in a dephosphorylated state (Bolscher et al., 1989;Rotrosen and Leto, 1990;Kuribayashi et al., 2002;Lapouge et al., 2002). During phagocyte activation, intracellular granules containing flavocytochrome b 558 fuse with phagosomes; p47 phox is phosphorylated, thereby inducing conformational changes in p47 phox that promote the interaction of the cytoplasmic complex with the flavocytochrome b 558 ; and Rac dissociates from Rho-GDI and translocates independently to the membrane after exchange of GDP for GTP (Heyworth et al., 1994;Zhao et al., 2003), resulting in generation of superoxide anion by the transfer of electrons from cytoplasmic NADPH to molecular oxygen.Chronic granulomatous disease...

Phagocytes such as dendritic cells and macrophages, which are distributed in the small intestinal mucosa, play a crucial role in maintaining mucosal homeostasis by sampling the luminal gut microbiota. However, there is limited information regarding microbial uptake in a steady state. We investigated the composition of murine gut microbiota that is engulfed by phagocytes of specific subsets in the small intestinal lamina propria (SILP) and Peyer’s patches (PP). Analysis of bacterial 16S rRNA gene amplicon sequences revealed that: 1) all the phagocyte subsets in the SILP primarily engulfed Lactobacillus (the most abundant microbe in the small intestine), whereas CD11bhi and CD11bhiCD11chi cell subsets in PP mostly engulfed segmented filamentous bacteria (indigenous bacteria in rodents that are reported to adhere to intestinal epithelial cells); and 2) among the Lactobacillus species engulfed by the SILP cell subsets, L. murinus was engulfed more frequently than L. taiwanensis, although both these Lactobacillus species were abundant in the small intestine under physiological conditions. These results suggest that small intestinal microbiota is selectively engulfed by phagocytes that localize in the adjacent intestinal mucosa in a steady state. These observations may provide insight into the crucial role of phagocytes in immune surveillance of the small intestinal mucosa.

Nox organizer 1 (Noxo1), a p47 phox homolog, is produced as four isoforms with unique N-terminal PX domains derived by alternative mRNA splicing. We compared the subcellular distribution of these isoforms or their isolated PX domains produced as GFP fusion proteins, as well as their ability to support Nox1 activity in several transfected models. Noxo1α, β, γ, and δ show different subcellular localization patterns, determined by their PX domains. In HEK293 cells, Noxo1β exhibits prominent plasma membrane binding, Noxo1γ shows plasma membrane and nuclear associations, Noxo1α and δ localize primarily on intracellular vesicles or cytoplasmic aggregates, but not the plasma membrane. Nox1 activity correlates with Noxo1 plasma membrane binding in HEK293 cells, since Noxo1β supports the highest activity and Noxo1γ and Noxo1α support moderate or low activities, respectively. In COS-7 cells, where Noxo1α localizes on the plasma membrane, the activities supported by the three isoforms (α, β, and γ) do not differ significantly. The PX domains of β and γ bind the same phospholipids, including phosphatidic acid. These results indicate the variant PX domains are unique determinants of Noxo1 localization and Nox1 function. Finally, the overexpressed Noxo1 isoforms do not affect p22 phox localization, although Nox1 is needed to transport p22 phox to the plasma membrane.

Probiotic lactobacilli stimulate macrophages and dendritic cells to secrete cytokines and thereby regulate the immune responses of the host. The balance of the IL-10 and IL-12 production induced by a probiotic is crucial for determining the direction of the immune response. In the present study, we examined the ability of microbial components to modify IL-10 and IL-12 production induced by a popular probiotic strain, Lactobacillus casei strain Shirota (LcS), which itself predominantly induces IL-12 production. Microbial ligands for toll-like receptor (TLR)3 and TLR5 further enhanced the IL-12 induction by LcS, whereas ligands for TLR2, TLR4, TLR7, and TLR9 converted the cytokine production pattern from IL-12 predominant to IL-10 predominant. These results indicate that the probiotic induction of IL-10 and IL-12 production can be flexibly modified by co-stimulation with microbial components. This could explain the variety of immunomodulatory functions (immunoactivation or anti-inflammation) exerted by this probiotic strain.