Disease relevance of CYBB

• X-Linked chronic granulomatous disease: mutations in the CYBB gene encoding the gp91-phox component of respiratory-burst oxidase [1].
• We examined CYBB gene expression in an Epstein-Barr virus (EBV)-transformed B-cell line from 1 patient in this kindred [2].
• Overexpression of TF1(phox) in myeloid leukemia cell lines increased reporter gene expression from artificial promoter constructs containing CYBB promoter sequence [3].
• Sequencing the entire coding region of the NADPH subunit CYBB (gpS1phase) disclosed that CYBB is a highly conserved gene, which does not represent a risk factor for clozapine-induced agranulocytosis [4].
• Cytochrome b558 was expressed in Sf9 insect cells coinfected with recombinant baculoviruses carrying cDNAs for p22phox and gp91phox [5].

High impact information on CYBB

• Together with the phagocyte NADPH oxidase itself (NOX2/gp91(phox)), the homologs are now referred to as the NOX family of NADPH oxidases [6].
• Although insertional influences have probably reinforced the therapeutic efficacy in this trial, our results suggest that gene therapy in combination with bone marrow conditioning can be successfully used to treat inherited diseases affecting the myeloid compartment such as CGD [7].
• The bacteriocidal capacity of phagocytic cells is impaired in X-linked chronic granulomatous disease (X-CGD), a disorder characterized by the absence of functional plasma-membrane-associated NADPH oxidase [8].
• In Western blots antisera detect a neutrophil protein of relative molecular mass in 90,000 (90K) that is absent in X-CGD patients [8].
• Based on our identification of the X-CGD protein in vivo, we propose that one of its critical roles is to interact with the 22K species to form a functional cytochrome b complex [8].

Chemical compound and disease context of CYBB

• The X-linked form of chronic granulomatous disease (CGD) is caused by mutations in the CYBB gene, which encodes the 91-kD subunit of the flavocytochrome b558, a component of the superoxide-generating nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in phagocytic leukocytes [9].
• Upon stimulation with phorbol myristate acetate, no fluorescence was seen in intracellular compartments of neutrophils isolated from patients with X-linked chronic granulomatous disease lacking gp91-phox, a membrane component of NADPH oxidase [10].
• Analyses of the O2- release and expression of NADPH oxidase components verified that he suffered from gp91-phox- chronic granulomatous disease (CGD), and that his mother was a carrier of the disease [11].
• Nox2-containing NADPH oxidase and Akt activation play a key role in angiotensin II-induced cardiomyocyte hypertrophy [12].
• No taurine-chloramine was detected in supernatants of lymphocytes and PMN from patients with an oxidative burst defect (chronic granulomatous disease, CGD) with the KI method, but Pholasin-dependent CL was consistently observed [13].

Biological context of CYBB

• The mutation was present in heterozygous form in genomic DNA from her leukocytes but was fully expressed in mRNA from these cells, indicating that in her leukocytes the X chromosome carrying the nonmutated CYBB allele had been inactivated [14].
• In four X-linked CGD patients we have identified novel missense mutations in CYBB, the gene encoding gp91-phox [15].
• Reverse transcriptase-polymerase chain reaction analysis of RNA splicing revealed a preponderance of unspliced CYBB transcripts in the patient's nuclear RNA [2].
• We conclude that IFN-gamma partially corrects a nuclear processing defect due to the intronic mutation in the CYBB gene in this kindred, most likely by augmentation of nuclear export of normal transcripts, and improvement in the fidelity of splicing at the first intron [2].
• The CYBB promoter region contains several lineage-specific cis-elements involved in the IFN-gamma response [3].

Anatomical context of CYBB

• Improved superoxide-generating ability by interferon gamma due to splicing pattern change of transcripts in neutrophils from patients with a splice site mutation in CYBB gene [16].
• Thus, this patient shows a somatic mosaic for the CYBB mutation, which probably originated during her lifetime in her bone marrow [14].
• Moreover, the CYBB mutation was not present in the DNA from her cheek cells and was barely detectable in the DNA from her memory T lymphocytes [14].
• The changes in the splicing pattern of the transcripts and the prolonged effect on superoxide-generating ability of patient neutrophils indicate that IFN-gamma induced a partial correction of the abnormal splicing of CYBB gene transcripts in myeloid progenitor cells [16].
• The CYBB gene encodes gp91Phox; a component of the phagocyte respiratory burst oxidase [17].

Associations of CYBB with chemical compounds

• In comparison to HoxA9, Nup98-hoxA9 has greater binding affinity for the CYBB cis element, but binding is not altered by HD tyrosine phosphorylation [17].
• The X-linked form of the disease (X-CGD) arises from mutations in the CYBB gene, which encodes the 91-kD glycoprotein gp91(phox), the largest component of the oxidase [18].
• This suggests that the alpha-helical loop of the C-terminal of Nox2 is probably involved in the correct assembly of the NADPH oxidase complex occurring during activation, permitting cytosolic factor translocation and electron transfer from NADPH to FAD [19].
• We therefore conclude that the large subunit of the NADPH oxidase cytochrome b (gp91-phox) is the arachidonate activable H+ channel of human neutrophils [20].
• In contrast, the D484T and D500A/R/G mutants of the alpha-helical loop of Nox2 exhibited no NADPH oxidase and INT reductase activities associated with a defective p47(phox) membrane translocation [19].

Physical interactions of CYBB

• Thus, the introduction or reversal of charge at residues 369, 408, and 568 in gp91-phox destroys the correct binding of p47-phox and p67-phox to cytochrome b(558) [15].
• We identify a sequence in the NCF2 promoter that is homologous to the HoxA10-binding CYBB cis element [21].
• On the basis of these observations we propose that while Rac2 can bind to a site distinct from either gp91phox or p22phox, it depends upon an interaction with the flavocytochrome b558 for maximal stability in the membrane [22].
• The mapping also confirmed a previously reported binding domain on gp91-phox (E554SGPRGVHFIF564) and putative Src homology 3 domain binding sites on p22-phox (P156PRPP160 and G177GPPGGP183) [23].
• Finally, a new X91(+) CGD case was detected, characterized by a missense mutation Leu505Arg in the potential NADPH-binding site of gp91 phox [24].

Co-localisations of CYBB

• In atherosclerotic arteries, there was an additional intense area of superoxide in the plaque shoulder, which is rich in macrophages and alpha-actin-positive cells. p22phox colocalized with gp91phox mainly in macrophages, whereas Nox4 was found only in nonphagocytic vascular cells [25].

Regulatory relationships of CYBB

• Interestingly, NOX4 was expressed at 100-fold higher levels compared with NOX2 [26].
• Previously, we identified a CYBB cis element, necessary for IFN-gamma-induced gp91phox expression, and also activated by this transcription factor combination [27].
• In some rare cases, the mutated gp91 phox is normally expressed but no NADPH oxidase can be detected [28].
• IQGAP1 regulates reactive oxygen species-dependent endothelial cell migration through interacting with Nox2 [29].
• We reported that IQGAP1, an actin binding scaffold protein, mediates VEGF-induced activation of gp91phox (Nox2)-dependent NAD(P)H oxidase and EC migration [29].

Other interactions of CYBB

• We conclude that residue 500 of gp91-phox resides in a region critical for stable binding of p47-phox and p67-phox [30].
• We find HoxA9-mediated CYBB-transcription requires Pbx1 but is inhibited by Meis1 [17].
• Fluorescence in situ hybridization and microsatellite analyses for 19 loci/regions on the X chromosome demonstrated that the del(Xp) chromosome was missing SHOX and had the breakpoint between DMD and CYBB [31].
• Thirty-five members of a Spanish family with X-linked RP were evaluated by linkage analysis using nine polymorphic markers (CYBB, DXS1110, M6, DXS6679, DXS1068, DXS1058, MAOA, MAOB and DXS6849) that map to the X-chromosome region Xp21.1 to Xp11.3, in an attempt to determine the carrier state of these females at risk [32].
• Rac, albeit probably dispensable to the Nox3 activity, plays an essential role in activation of gp91phox [33].

Analytical, diagnostic and therapeutic context of CYBB

• Electrophoretic mobility shift assay with nuclear proteins from a variety of cell lines demonstrated binding of a protein to the CYBB promoter that was cross-immunoreactive with TF1(phox) [3].
• In circumstances in which this is uninformative, patients should be referred to centers capable of additional testing, including Western blot analysis and CYBB mutation analysis, to clarify the disease genotype [34].
• A previous Southern blot study, using a cytochrome b heavy chain cDNA as probe, revealed a Pst I restriction fragment pattern for the cytochrome b heavy chain gene (CYBB) different to that of normal individuals [35].
• 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 [36].
• CGD, as a very well-characterized inherited affection of the hematopoietic stem cells, is predestined to be among the first diseases to profit from the advances in cutting-edge therapeutics, such as gene therapy and in utero stem cell transplantation [37].

References