Structural insights into Nox4 and Nox2: motifs involved in function and cellular localization.

Regulated generation of reactive oxygen species (ROS) is primarily accomplished by NADPH oxidases (Nox). Nox1 to Nox4 form a membrane-associated heterodimer with p22(phox), creating the docking site for assembly of the activated oxidase. Signaling specificity is achieved by interaction with a complex network of cytosolic components. Nox4, an oxidase linked to cardiovascular disease, carcinogenesis, and pulmonary fibrosis, deviates from this model by displaying constitutive H(2)O(2) production without requiring known regulators. Extensive Nox4/Nox2 chimera screening was initiated to pinpoint structural motifs essential for ROS generation and Nox subcellular localization. In summary, a matching B loop was crucial for catalytic activity of both Nox enzymes. Substitution of the carboxyl terminus was sufficient for converting Nox4 into a phorbol myristate acetate (PMA)-inducible phenotype, while Nox2-based chimeras never gained constitutive activity. Changing the Nox2 but not the Nox4 amino terminus abolished ROS generation. The unique heterodimerization of a functional Nox4/p22(phox) Y121H complex was dependent on the D loop. Nox4, Nox2, and functional Nox chimeras translocated to the plasma membrane. Cell surface localization of Nox4 or PMA-inducible Nox4 did not correlate with O(2)(-) generation. In contrast, Nox4 released H(2)O(2) and promoted cell migration. Our work provides insights into Nox structure, regulation, and ROS output that will aid inhibitor design.

Heterodimerization controls localization of Duox-DuoxA NADPH oxidases in airway cells.

Duox NADPH oxidases generate hydrogen peroxide at the air-liquid interface of the respiratory tract and at apical membranes of thyroid follicular cells. Inactivating mutations of Duox2 have been linked to congenital hypothyroidism, and epigenetic silencing of Duox is frequently observed in lung cancer. To study Duox regulation by maturation factors in detail, its association with these factors, differential use of subunits and localization was analyzed in a lung cancer cell line and undifferentiated or polarized lung epithelial cells. We show here that Duox proteins form functional heterodimers with their respective DuoxA subunits, in close analogy to the phagocyte NADPH oxidase. Characterization of novel DuoxA1 isoforms and mispaired Duox-DuoxA complexes revealed that heterodimerization is a prerequisite for reactive oxygen species production. Functional Duox1 and Duox2 localize to the leading edge of migrating cells, augmenting motility and wound healing. DuoxA subunits are responsible for targeting functional oxidases to distinct cellular compartments in lung epithelial cells, including Duox2 expression in ciliated cells in an ex vivo differentiated lung epithelium. As these locations probably define signaling specificity of Duox1 versus Duox2, these findings will facilitate monitoring Duox isoform expression in lung disease, a first step for early screening procedures and rational drug development.

Lung epithelial injury by B. anthracis lethal toxin is caused by MKK-dependent loss of cytoskeletal integrity.

Bacillus anthracis lethal toxin (LT) is a key virulence factor of anthrax and contributes significantly to the in vivo pathology. The enzymatically active component is a Zn(2+)-dependent metalloprotease that cleaves most isoforms of mitogen-activated protein kinase kinases (MKKs). Using ex vivo differentiated human lung epithelium we report that LT destroys lung epithelial barrier function and wound healing responses by immobilizing the actin and microtubule network. Long-term exposure to the toxin generated a unique cellular phenotype characterized by increased actin filament assembly, microtubule stabilization, and changes in junction complexes and focal adhesions. LT-exposed cells displayed randomly oriented, highly dynamic protrusions, polarization defects and impaired cell migration. Reconstitution of MAPK pathways revealed that this LT-induced phenotype was primarily dependent on the coordinated loss of MKK1 and MKK2 signaling. Thus, MKKs control fundamental aspects of cytoskeletal dynamics and cell motility. Even though LT disabled repair mechanisms, agents such as keratinocyte growth factor or dexamethasone improved epithelial barrier integrity by reducing cell death. These results suggest that co-administration of anti-cytotoxic drugs may be of benefit when treating inhalational anthrax.

Mutational analysis reveals distinct features of the Nox4-p22 phox complex.

The integral membrane protein p22(phox) forms a heterodimeric enzyme complex with NADPH oxidases (Noxs) and is required for their catalytic activity. Nox4, a Nox linked to cardiovascular disease, angiogenesis, and insulin signaling, is unique in its ability to produce hydrogen peroxide constitutively. To date, p22(phox) constitutes the only identified regulatory component for Nox4 function. To delineate structural elements in p22(phox) essential for formation and localization of the Nox4-p22(phox) complex and its enzymatic function, truncation and point mutagenesis was used. Human lung carcinoma cells served as a heterologous expression system, since this cell type is p22(phox)-deficient and promotes cell surface expression of the Nox4-p22(phox) heterodimer. Expression of p22(phox) truncation mutants indicates that the dual tryptophan motif contained in the N-terminal amino acids 6-11 is essential, whereas the C terminus (amino acids 130-195) is dispensable for Nox4 activity. Introduction of charged residues in domains predicted to be extracellular by topology modeling was mostly tolerated, whereas the exchange of amino acids in predicted membrane-spanning domains caused loss of function or showed distinct differences in p22(phox) interaction with various Noxs. For example, the substitution of tyrosine 121 with histidine in p22(phox), which abolished Nox2 and Nox3 function in vivo, preserved Nox4 activity when expressed in lung cancer cells. Many of the examined p22(phox) mutations inhibiting Nox1 to -3 maturation did not alter Nox4-p22(phox) association, further accenting the differences between Noxs. These studies highlight the distinct interaction of the key regulatory p22(phox) subunit with Nox4, a feature which could provide the basis for selective inhibitor development.

A novel mutation of the CYBB gene resulting in severe form of X-linked chronic granulomatous disease.

We evaluated a boy who had multiple Salmonella septicemia, Aspergillus pneumonia and brain abscesses. His nitroblue tetrazolium (NBT) test was reportedly abnormal. The dihydrorhodamine (DHR) flow cytometry assay was compatible with typical X-linked chronic granulomatous disease (X-CGD). CYBB analysis revealed a novel complex mutation atggacg --> ttca in exon 12 (base pairs 1532-1538). As a result, 3 amino acids Tyr 511, Gly 512 and Arg 513 were deleted and replaced by 2 amino acids, Phe and Gln. The DHR and mutation analysis of his mother showed normal DHR pattern and no mutations in exon 12 of CYBB gene. In conclusion, any children with multiple Salmonella and Aspergillus infection should be suspected of CGD. NBT test, DHR assay and gene analysis are helpful toolsto confirm the diagnosis e v en i n the case of de novo mutation.

The Rab27a-binding protein, JFC1, regulates androgen-dependent secretion of prostate-specific antigen and prostatic-specific acid phosphatase.

Two of the major proteins secreted by the prostate epithelium secretory cells are PSA (prostate-specific antigen) and PSAP (prostatic-specific acid phosphatase). The molecules involved in the secretory machinery of PSA and PSAP, and the regulation of this machinery, remain unknown. In the present paper, we provide evidence that JFC1 [synaptotagmin-like protein (slp1)], a Rab27a- and PtdIns(3,4,5)P3-binding protein, regulates the androgen-dependent secretion of PSAP and PSA in human LNCaP prostate carcinoma cells. Androgen-dependent PSAP secretion was significantly inhibited in cells that expressed the C2A domain of JFC1 [PtdIns(3,4,5)P3-binding-domain], but was unaffected by JFC1 overexpression. Conversely, PSA secretion was not inhibited by the C2A domain of JFC1. We show, using immunofluorescence analysis, that JFC1 co-localizes with PSAP, but rarely with PSA, in prostate granules, suggesting that JFC1 is part of the PSAP secretory machinery. However, PSA secretion was significantly increased in LNCaP cells that overexpressed JFC1, indicating that the secretion of PSA is susceptible to variations in the intracellular concentration of JFC1. Both PSAP and PSA secretion was increased by overexpression of wild-type Rab27a or the constitutively active Rab27aQ78L. The secretion of PSA was partially inhibited in the presence of LY294002, while the secretion of PSAP was completely abolished by the PI3K (phosphoinositide 3-kinase) inhibitor. This supports the view that PI3K plays a differential role in the secretion of prostate secretory markers. In conclusion, we present evidence that JFC1 differentially regulates the secretion of PSAP and PSA, and that Rab27a and PI3K play a central role in the exocytosis of prostate-specific markers.

Long polymerase chain reaction-based fluorescence in situ hybridization analysis of female carriers of X-linked chronic granulomatous disease deletions.

Chronic granulomatous disease (CGD) is a rare inherited disorder in which antimicrobial activity of phagocytes is impaired due to the lack of reactive oxygen species, or oxidative burst, produced by NADPH oxidase. The X-linked form of CGD, representing approximately 70% of all cases, is caused by mutations in the cytochrome b beta subunit (CYBB) gene, which maps to chromosome Xp21.1. CYBB encodes the gp91-phox protein, a necessary component in the NADPH oxidase pathway. A wide variety of mutations have been identified in X-linked CGD patients, all of which lead to deletion of the functional protein and no oxidative burst activity. The mutations vary from single nucleotide substitutions to deletions of the entire gene. In this article, we report a mutation detection method for probands of female relatives at risk for carrier status of large deletions of the CYBB gene. Through fluorescent in situ hybridization of metaphase chromosomes, we were able to consistently distinguish carriers from noncarriers using polymerase chain reaction-derived, labeled DNA specific for exons 2 to 13 of the CYBB region at Xp21.1.

Chronic granulomatous disease caused by a deficiency in p47(phox) mimicking Crohn's disease.

We describe 2 cases of autosomal recessive chronic granulomatous disease (CGD) in 2 sisters presenting with a picture consistent with inflammatory bowel disease. The index case is a 10-year-old girl with a history of refractory Crohn's colitis treated with aggressive immunosuppressive therapy whose course subsequently was complicated by central nervous system aspergillosis. Additional evaluation showed a diagnosis of CGD, an underlying immunodeficiency in which phagocytes fail to produce microbicidal reactive oxygen intermediates because of inherited defects in the reduced form of nicotinamide-adenine phosphate dinucleotide (NADPH) oxidase. The diagnosis of a typically X-linked inherited disease in our female patient suggested that she had 1 of the 3 less common autosomal recessive forms of the disease. This was confirmed by studies showing the absence of the p47(phox) subunit of NADPH oxidase in her neutrophils and the presence of a homozygous dinucleotide deletion in the neutrophil cytosolic factor 1 gene that encodes p47(phox). Additional analyses of members of the patient's immediate family showed the same homozygous mutation in 2 siblings, 1 of whom also developed chronic colitis consistent with a diagnosis of Crohn's disease. These 2 cases emphasize the importance of high clinical suspicion for an alternative diagnosis of immune deficiency in the setting of presumed inflammatory bowel disease and opportunistic infection.

Identification of a novel NCF-1 (p47-phox) pseudogene not containing the signature GT deletion: significance for A47 degrees chronic granulomatous disease carrier detection.

The p47-phox gene, NCF-1, has 2 nearly identical pseudogenes (psiNCF-1) in proximity at chromosomal locus 7q11.23. A dinucleotide deletion (DeltaGT) at the beginning of exon 2 that leads to a frameshift and premature stop codon is considered the signature sequence of the pseudogenes. It is also the most prevalent mutation in p47-phox-deficient (A47 degrees ) chronic granulomatous disease (CGD) as a result of the insertion of a DeltaGT-containing fragment of pseudogene into NCF-1. Extending our study of the relationship between NCF-1 and psiNCF-1 to 53 unaffected control individuals, we found that although in most (n = 44), the ratio of pseudogene (DeltaGT) to functional gene (GTGT) sequence in amplicons spanning exon 2 was 2:1, as previously observed, surprisingly, in 7 persons the ratio was 1:1, and in 2 persons the ratio was 1:2. The lowered ratios are explained by the presence, in a heterozygous or homozygous state, respectively, of a pseudogene that contains GTGT rather than DeltaGT. It is possible that this pseudogene has not undergone deletion of GT, but more likely, based on analysis of additional NCF-1/psiNCF-1 markers, it represents the previously unidentified product of the reciprocal crossover of DNA fragments between the functional gene and one of its pseudogenes. The mutated NCF-1 resulting from this event is the predominant A47 degrees CGD allele. The existence of 2 extended haplotypes encompassing NCF-1/psiNCF-1 further complicates the detection of A47 degrees CGD carriers. Although most have a DeltaGT/GTGT ratio of 5:1, some have a ratio of 2:1 and are indistinguishable by this means from unaffected individuals.

Molecular quality control machinery contributes to the leukocyte NADPH oxidase deficiency in chronic granulomatous disease.

Chronic granulomatous disease (CGD) is an inherited immunodeficiency disease caused by defects in leukocyte NADPH oxidase. Various inherited defects in one of the membrane-bound components of NADPH oxidase, gp91-phox, cause X-linked (X91) CGD. Analysis of three patients with X91 CGD revealed that different mechanisms of molecular quality control lead to the common phenotype of absence of mature membrane-bound NADPH oxidase complex in leukocytes. In the first patient, aberrant intron splicing created a premature stop codon. However, the mutant mRNA was degraded prematurely, which prevented the production of truncated protein. In the second patient, a frameshift mutation with the potential to generate a gp91-phox polypeptide, with an aberrant and elongated C-terminus, led to barely detectable levels of gp91-phox, even though the reported functional domains of the protein appeared unaffected. In the third patient, a point mutation created a single amino acid change in the predicted FAD-binding site of gp91-phox. Although gp91-phox was detectable with Western blotting, no cytochrome b(558) was expressed on the cell surface. These analyses showed that molecular quality control machinery plays an important role in the pathogenesis of CGD, not only in the X910 but also in the X91- form of this X-linked disease.