The human gene for xanthine dehydrogenase (XDH) is localized on chromosome band 2q22

Differentially accessible, single copy sequences form contiguous domains along metaphase chromosomes that are conserved among multiple tissues

BACKGROUND

During mitosis, chromatin engages in a dynamic cycle of condensation and decondensation. Condensation into distinct units to ensure high fidelity segregation is followed by rapid and reproducible decondensation to produce functional daughter cells. Factors contributing to the reproducibility of chromatin structure between cell generations are not well understood. We investigated local metaphase chromosome condensation along mitotic chromosomes within genomic intervals showing differential accessibility (DA) between homologs. DA was originally identified using short sequence-defined single copy (sc) DNA probes of < 5 kb in length by fluorescence in situ hybridization (scFISH) in peripheral lymphocytes. These structural differences between metaphase homologs are non-random, stable, and heritable epigenetic marks which have led to the proposed function of DA as a marker of chromatin memory. Here, we characterize the organization of DA intervals into chromosomal domains by identifying multiple DA loci in close proximity to each other and examine the conservation of DA between tissues.

RESULTS

We evaluated multiple adjacent scFISH probes at 6 different DA loci from chromosomal regions 2p23, 3p24, 12p12, 15q22, 15q24 and 20q13 within peripheral blood T-lymphocytes. DA was organized within domains that extend beyond the defined boundaries of individual scFISH probes. Based on hybridizations of 2 to 4 scFISH probes per domain, domains ranged in length from 16.0 kb to 129.6 kb. Transcriptionally inert chromosomal DA regions in T-lymphocytes also demonstrated conservation of DA in bone marrow and fibroblast cells.

CONCLUSIONS

We identified novel chromosomal regions with allelic differences in metaphase chromosome accessibility and demonstrated that these accessibility differences appear to be aggregated into contiguous domains extending beyond individual scFISH probes. These domains are encompassed by previously established topologically associated domain (TAD) boundaries. DA appears to be a conserved feature of human metaphase chromosomes across different stages of lymphocyte differentiation and germ cell origin, consistent with its proposed role in maintenance of intergenerational cellular chromosome memory.

Genetic variants in XDH are associated with prognosis for gastric cancer in a Chinese population

OBJECTIVE

We explored the association between single nucleotide polymorphisms (SNPs) rs207454 and rs494852 located in xanthine dehydrogenase (XDH) and gastric cancer (GC) survival.

METHODS

A total of 940 patients with gastric cancer were enrolled and genotyped using TaqMan allelic discrimination method. The Kaplan-Meier test and log-rank examine were used to assess the effect of genetic variation.

RESULTS

Patients carrying rs207454 CC genotype had a longer survival time than those with the AA genotype (P = 0.042). The similar association was detected in the recessive model (P = 0.017). We conducted expression quantitative trait loci (eQTL) analysis and found that gastric cancer patients carrying rs207454 CC genotype had significant lower XDH levels than those with AA/AC genotype, suggesting that rs207454 polymorphism effected the expression of XDH. Additionally, the Kaplan-Meier curves showed that gastric cancer patients with high expression of XDH had remarkably poor survival outcome than those with low expression (hazard ratio [HR] = 1.53, 95% confidence interval [CI] = 1.29-1.82).

CONCLUSIONS

Genetic variants in XDH were associated with the survival of gastric cancer and may act as prognostic markers for individual suffered from gastric cancer.

Xanthine oxidoreductase - clinical significance in colorectal cancer and in vitro expression of the protein in human colon cancer cells

Xanthine oxidoreductase (XOR) is a key enzyme in degradation of DNA and RNA, and has previously been shown to be decreased in aggressive breast and gastric cancer. In this study, XOR expression was assessed in tissue microarray specimens of 478 patients with colorectal cancer and related to clinical parameters. In addition, we performed in vitro studies of XOR activity, protein and mRNA in colon cancer cells (Caco-2). Results from the tissue expression analyses show that XOR was decreased in 62% and undetectable in 22% of the tumours as compared to normal tissue. Loss of XOR was associated with poor grade of differentiation (p=0.006) and advanced Dukes stage (p=0.03). In multivariate survival analysis, XOR was a prognostic factor (p=0.008), independent of Dukes stage, histological grade, age and tumour location. The in vitro analyses show that XOR is not measurable in undifferentiated Caco-2 cells, but appears and increases with differentiation. We conclude that XOR expression is associated with histological grade of differentiation and extent of disease in colorectal cancer, and it provides significant prognostic information independently of established factors.

Decreased xanthine oxidoreductase is a predictor of poor prognosis in early-stage gastric cancer

BACKGROUND

Xanthine oxidoreductase (XOR) is a key enzyme in the degradation of DNA, RNA and high-energy phosphates. About half of the patients with breast cancer have a decrease in XOR expression. Patients with breast cancer with unfavourable prognosis are independently identified by the loss of XOR.

AIM

To assess the clinical relevance of XOR expression in gastric cancer.

METHODS

XOR levels were studied by immunohistochemistry in tissue microarray specimens of 337 patients with gastric cancer and the relation between XOR expression and a series of clinicopathological variables, as well as disease-specific survival, was assessed.

RESULTS

XOR was moderately decreased in 41% and was undetectable in another 14% of the tumours compared with the corresponding normal tissue. Decreased XOR was associated with advanced stage, deep tumour penetration, diffusely spread tumour location, positive lymph node status, large tumour size, non-curative disease, cellular aneuploidy, high S-phase fraction and high cyclooxygenase-2 expression, but not with p53 expression or Borrmann classification. Down regulation of XOR was associated with unfavourable outcome, and the cumulative 5-year gastric cancer-specific survival in patients with strong XOR expression was 47%, compared with 22% in those with moderate to negative expression (p<0.001). This was also true in patients with stage I-II (p = 0.01) and lymph node-negative (p = 0.02) disease, as well as in patients with smaller (< or =5 cm) tumours (p = 0.02).

CONCLUSION

XOR expression in gastric cancer may be a new marker for a more aggressive gastric cancer biology, similar to that previously reported for breast cancer.

Down-regulated xanthine oxidoreductase is a feature of aggressive breast cancer

PURPOSE

Xanthine oxidoreductase (XOR) is a key enzyme in the degradation of DNA, RNA, and high-energy phosphates and also plays a role in milk lipid globule secretion. Given the strong and regulated expression of XOR in normal breast epithelium, and the previously shown alterations of its expression in experimental tumorigenesis, we hypothesized that XOR may be differentially expressed in breast cancer.

EXPERIMENTAL DESIGN

XOR expression was analyzed by immunohistochemistry in tissue microarray specimens of 1,262 breast cancer patients with a median follow-up of 9.5 years.

RESULTS

Expression of XOR was moderately decreased in 50% and undetectable in another 7% of the tumors. Decreased XOR expression was associated with poor histologic grade of differentiation, ductal and lobular histologic types, large tumor size, high number of positive axillary lymph nodes, and high cyclooxygenase-2 expression, but not with estrogen or progesterone receptor status, Ki-67, p53, or ERBB2 amplification. Absence of XOR expression was associated with unfavorable outcome, and patients with no XOR expression had more than twice the risk of distant recurrence as compared with those with a moderately decreased or normal expression (hazard ratio, 2.21; P < 0.0001). This was also true in patients with node-negative disease (hazard ratio, 2.75; P < 0.0001) as well as in patients with small (< or = 1 cm) tumors (hazard ratio, 3.09; P = 0.027). In a multivariate survival analysis, negative XOR emerged as an independent prognostic factor both in the entire series (P = 0.01) and among patients with node-negative disease (P = 0.0009).

CONCLUSION

Loss of XOR identifies breast cancer patients with unfavorable prognosis.

The aldehyde oxidase gene cluster in mice and rats. Aldehyde oxidase homologue 3, a novel member of the molybdo-flavoenzyme family with selective expression in the olfactory mucosa

Mammalian molybdo-flavoenzymes are oxidases requiring FAD and molybdopterin (molybdenum cofactor) for their catalytic activity. This family of proteins was thought to consist of four members, xanthine oxidoreductase, aldehyde oxidase 1 (AOX1), and the aldehyde oxidase homologues 1 and 2 (AOH1 and AOH2, respectively). Whereas the first two enzymes are present in humans and various other mammalian species, the last two proteins have been described only in mice. Here, we report on the identification, in both mice and rats, of a novel molybdo-flavoenzyme, AOH3. In addition, we have cloned the cDNAs coding for rat AOH1 and AOH2, demonstrating that this animal species has the same complement of molybdo-flavoproteins as the mouse. The AOH3 cDNA is characterized by remarkable similarity to AOX1, AOH1, AOH2, and xanthine oxidoreductase cDNAs. Mouse AOH3 is selectively expressed in Bowman's glands of the olfactory mucosa, although small amounts of the corresponding mRNA are present also in the skin. In the former location, two alternatively spliced forms of the AOH3 transcript with different 3'-untranslated regions were identified. The general properties of AOH3 were determined by purification of mouse AOH3 from the olfactory mucosa. The enzyme possesses aldehyde oxidase activity and oxidizes, albeit with low efficiency, exogenous substrates that are recognized by AOH1 and AOX1. The Aoh3 gene maps to mouse chromosome 1 band c1 and rat chromosome 7 in close proximity to the Aox1, Aoh1, and Aoh2 loci and has an exon/intron structure almost identical to that of the other molybdo-flavoenzyme genes in the two species.

Cellular distribution, metabolism and regulation of the xanthine oxidoreductase enzyme system

Xanthine oxidase (EC 1.1.3.22) and xanthine dehydrogenase (EC 1.1.1. 204) are both members of the molybdenum hydroxylase flavoprotein family and represent different forms of the same gene product. The two enzyme forms and their reactions are often referred to as xanthine oxidoreductase (XOR) activity. Physiologically, XOR is known as the rate-limiting enzyme in purine catabolism but has also been shown to be able to metabolize a number of other physiological compounds. Recent studies have also demonstrated its ability to metabolize xenobiotics, including a number of anticancer compounds, to their active metabolites. During the past 10 years, evidence has mounted to support a role for XOR in the pathophysiology of inflammatory diseases and atherosclerosis as well as its previously determined role in ischemia-reperfusion injury. While significant progress has recently been made in our understanding of the physiological and biochemical nature of this enzyme system, considerable work still needs to be done. This paper will review some of the more recent work characterizing the interactions and the factors that influence the interactions of XOR with various physiological and xenobiotic compounds.

Nuclear factor Y activates the human xanthine oxidoreductase gene promoter

To study the regulation of the human xanthine oxidoreductase (XOR) gene, we cloned 1.9 kb of the promoter region. In reporter gene assays, a construct encompassing nucleotides between 142 to +42 conferred maximal basal activity of the XOR promoter in 293T cells, in comparison with shorter (-92 to +42) or longer (up to -1937 to +42) constructs. The promoter activity was low in NIH-3T3 cells. The most active construct contained a putative CCAAT motif at -119 to -123. Electrophoretic mobility shift assays showed that this sequence binds the ubiquitous nuclear factor Y (NF-Y). Mutation of the CCAAT motif (CTGAT) abolished the NF-Y binding and considerably reduced the promoter activity. Our data suggest an important functional role for NF-Y in the transcriptional activation of the human XOR gene.

Genetic disorders and urolithiasis

A recent analysis of the McKusick's On-Line Mendelian Inheritance in Man (OMIM) database revealed over 30 genetic or putatively genetic conditions in which urolithiasis contributes to the disease pathology at least to some extent. There is wide clinical, biochemical, and genetic heterogeneity in many of these conditions.

Xanthinuria in a family of Cavalier King Charles spaniels

Xanthine calculi were found in a 7-month-old male Cavalier King Charles spaniel with urethral obstruction and renal insufficiency. Because the only two other reported cases of naturally occurring xanthine urolithiasis concerned a Cavalier King Charles and a King Charles spaniel the urine of the littermates and parents of the patient were also examined for xanthinuria. Semi-quantitative analysis revealed high urine concentrations of hypoxanthine and xanthine in the patient and his female littermate. Quantitative analysis by high-pressure liquid chromatography (HPLC) of the urine samples from the family of this Cavalier King Charles spaniel and nine control dogs revealed that hypoxanthine and xanthine excretion was 30 and 60 times higher in the affected patient and the female littermate than in the others dogs. The pattern of xanthinuria, which is caused by a deficiency of the enzyme xanthine oxidase, in the relation diagram of this family of Cavalier King Charles Spaniels was consistent with an autosomal recessive mode of inheritance.

Cloning and expression in vitro of human xanthine dehydrogenase/oxidase

To study the expression of human xanthine dehydrogenase/oxidase (hXDH/XO), we cloned the cDNA covering its complete coding sequence and characterized it by translation in vitro in rabbit reticulocyte lysates and by transient expression in COS-1 cells. Two specific protein products with approximate molecular masses of 150 and 130 kDa were detected in both expression systems. These products are compatible with the molecular sizes of XDH/XO, and these peptides also showed immunoreactivity with polyclonal anti-hXDH antibodies. Significant XDH/XO enzyme activity (277 +/- 54 pmol/min per mg of protein) was measured in lysates of transfected COS cells, whereas in control transfections the activities were below the detection limit of our assay (0.2 pmol/min per mg of protein). The COS cells expressed the enzyme predominantly (89.8 +/- 0.3%) in the dehydrogenase form.

Novel human vascular endothelial growth factor genes VEGF-B and VEGF-C localize to chromosomes 11q13 and 4q34, respectively

BACKGROUND

Vascular endothelial growth factor (VEGF) is an important regulator of endothelial cell proliferation, migration, and permeability during embryonic vasculogenesis as well as in physiological and pathological angiogenesis. The recently isolated VEGF-B and VEGF-C cDNAs encode novel growth factor genes of the VEGF family.

METHODS AND RESULTS

Southern blotting and polymerase chain reaction analysis of somatic cell hybrids and fluorescence in situ hybridization (FISH) of metaphase chromosomes were used to assess the chromosomal localization of VEGF-B and VEGF-C genes. The VEGF-B gene was found on chromosome 11q13, proximal to the cyclin D1 gene, which is amplified in a number of human carcinomas. However, VEGF-B was not amplified in several mammary carcinoma cell lines containing amplified cyclin D1. The VEGF-C gene was located on chromosome 4q34, close to the human aspartylglucosaminidase gene previously mapped to 4q34-35.

CONCLUSIONS

The VEGF-B locus in 11q13 and the VEGF-C locus in 4q34 are candidate targets for mutations that lead to vascular malformations or cardiovascular diseases.