Disease relevance of HGD

• Alkaptonuria is a rare metabolic disorder resulting from loss of homogentisate 1,2 dioxygenase (HGO) activity [1].
• AKU patients are deficient for homogentisate 1,2 dioxygenase (HGO); this deficiency causes homogentisic aciduria, ochronosis, and arthritis [2].
• Recombinant expression of mutated HGO enzymes in E. coli demonstrates the inactivating effect of three of these mutations [3].
• Alkaptonuria, a rare autosomal-recessive disorder caused by mutations in the HGD gene and a deficiency of homogentisate 1,2-dioxygenase, is characterized by accumulation of homogentisic acid (HGA), ochronosis, and destruction of connective tissue resulting in joint disease [4].
• RESULTS: In Barrett's esophagus (BE; P = 0.001), high-grade dysplasia (HGD; P = 0.001), and esophageal adenocarcinoma (EAC; P = 0.00003), the level and frequency of Reprimo methylation were significantly higher than in normal esophagus (NE) [5].

High impact information on HGD

• We show that HGO maps to the same location described for AKU, illustrate that HGO harbours missense mutations that cosegregate with the disease, and provide biochemical evidence that at least one of these missense mutations is a loss-of-function mutation [1].
• Glucose production (HGO), glucose utilization (Rd) [3-3H]glucose, and glucose oxidation and lipid oxidation (LO) (indirect calorimetry) were determined [6].
• We conclude that, in a late phase of hypoglycemia, the indirect effects of catecholamines (lipolysis mediated) account for at least approximately 50% of the adrenergic contribution to increased HGO, and approximately 85% of suppressed Rd [6].
• Homogentisate dioxygenase (HGO) cleaves the aromatic ring during the metabolic degradation of Phe and Tyr [7].
• The active site iron ion is coordinated near the interface between subunits in the HGO trimer by a Glu and two His side chains [7].

Chemical compound and disease context of HGD

• Analysis of alkaptonuria (AKU) mutations and polymorphisms reveals that the CCC sequence motif is a mutational hot spot in the homogentisate 1,2 dioxygenase gene (HGO) [8].
• Alkaptonuria (AKU; McKusick No. 203500), a rare hereditary disorder of the phenylalanine catabolism, was the first disease to be interpreted as an inborn error of metabolism (A. E. Garrod, 1902, Lancet 2: 1616-1620) [9].
• Alkaptonuria (AKU) is caused by lack of homogentisate 1, 2 dioxygenase (HGO) activity [10].
• We have expressed recombinant wild-type human gammaD crystallin (HGD) and its Arg-14 to Cys mutant (R14C) in Escherichia coli and show that R14C forms disulfide-linked oligomers, which markedly raise the phase separation temperature of the protein solution [11].
• Alkaptonuria (endogenous ochronosis) is a rare metabolic disorder caused by a deficiency of homogentisic acid oxidase, an enzyme responsible for the metabolic degradation of tyrosine [12].

Biological context of HGD

• Herein we describe haplotype and mutational analyses of HGO in seven new AKU pedigrees [8].
• We also report characterization of five polymorphic sites in HGO and describe the haplotypic associations of alleles at these sites in normal and AKU chromosomes [2].
• We identified 12 novel mutations: 8 (E42A, W97G, D153G, S189I, I216T, R225H, F227S, and M368V) missense mutations that result in amino acid substitutions at positions conserved in HGO in different species, 1 (F10fs) frameshift mutation, 2 intronic mutations (IVS9-56G-->A, IVS9-17G-->A), and 1 splice-site mutation (IVS5+1G-->T) [2].
• The human HGO gene spans 54,363 bp and codes for a 1715-nt-long transcript that is split into 14 exons ranging from 35 to 360 bp [9].
• The HGO transcription start site was determined by primer extension [9].

Anatomical context of HGD

• We report that sequences from -1074 to +89 bp (relative to the HGO transcription start site) are sufficient to promote transcription of a CAT reporter gene in human liver cells and that this fragment contains putative binding sites for liver-enriched transcription factors that might be involved in the regulation of HGO expression in liver [9].
• AIMS: To assess the involvement of the recently identified human homogentisate 1,2-dioxygenase gene (HGO) in alkaptonuria (AKU) in two unrelated patients with ochronosis of the conjunctiva, sclera, and cornea [13].
• To elucidate the role of COX-2 in esophageal carcinogenesis, we examined the expression of this enzyme in normal squamous epithelium (n = 42), squamous dysplasia [high-grade dysplasia (HGD, n = 41; low-grade dysplasia (LGD, n = 33)]; carcinoma in situ (n = 16), mucosal invasive carcinoma (n = 18), and advanced SCC (n = 45) [14].
• Gastric dysplasia (high-grade, HGD, and low-grade, LGD) and normal mucosa were tested for anti-p53, anti-Ki-67 and anti-PCNA monoclonal antibodies on paraffin sections, and for relative AgNOR area and number on semithin Epon-Araldite sections [15].
• Statistical analysis of our data shows that the intensity of the immunohistochemical stain, as reflected in the nuclear scores of p53, is a reliable parameter that can differentiate between LGD and HGD of the oral mucosa [16].

Associations of HGD with chemical compounds

• Reexamination of all 29 mutations and polymorphisms thus far described in HGO shows that these nucleotide changes are not randomly distributed; the CCC sequence motif and its inverted complement, GGG, are preferentially mutated [8].
• These analyses also demonstrated that the nucleotide substitutions in HGO do not involve CpG dinucleotides, which illustrates important differences between HGO and other genes for the occurrence of mutation at specific short-sequence motifs [8].
• Homogentisate 1,2-dioxygenase (HGD) is a mononuclear Fe(II)-dependent oxygenase that catalyzes the third step in the pathway for the catabolism of tyrosine, the conversion of homogentisate (HG) to maleylacetoacetate (MAA) [17].
• In addition, in SE, LGD, and HGD samples, the pattern of cyclin B1 expression was assessed by determination of the presence of positive cells in four mucosal compartments: the deep glandular zone, the lower crypt zone, the upper crypt zone, and the luminal surface [18].
• Because of the deficient activity of the enzyme homogentisic acid oxidase, homogentisic acid accumulates in plasma, is deposited in various tissues and is excreted in large amounts in urine [19].

Regulatory relationships of HGD

• More importantly, although 0 of 6 biopsies with HGD (0%) expressed Glut1, 9 of 13 biopsies with adenocarcinoma (69%) were Glut1 positive (P = 0.0108, Fisher's exact test) [20].

Other interactions of HGD

• The results show complete cosegregation (Z = 6.32; theta = 0) between a C-->T transition at position 817 of the human HGO cDNA and AKU [10].
• METHODS: A mutation screen of the entire coding region of the HGO gene was performed using single stranded conformational analysis after polymerase chain reaction with oligonucleotide primers flanking all 14 exons of the HGO gene [13].
• All hyperplastic components expressed HGM, 5 (22.7%) of which were accompanied by focal intestinal metaplasia demonstrated by MUC2 expression, whereas intestinalization frequently occurred in neoplastic components (93% of LGD, 53% of HGD, and 64% of CA components) [21].
• E-cad decreases from NM to EGC, although not significantly from LGD to HGD; MMP2 is significantly more expressed only in EGC [22].
• CONCLUSIONS: Reprimo methylation occurs significantly more frequently in BE, HGD, and EAC than in NE or ESCC, suggesting that this epigenetic alteration is a specialized columnar, cell-specific early event with potential as a biomarker for the early detection of esophageal neoplasia [5].

Analytical, diagnostic and therapeutic context of HGD

• The gene for HGO seems to be expressed in various tissues, as shown by RT-PCR on different cDNAs [23].
• Immunohistochemistry showed a significantly high COX-2 expression in HGD compared with other lesions [14].
• For HGD, esophagectomy is still recommended for healthy surgical candidates, but more patients will be followed, particularly those with "focal" HGD [24].
• BACKGROUND: Photodynamic therapy (PDT) may be used to ablate high-grade dysplasia/early stage cancer (HGD/T1) in patients with Barrett's esophagus [25].
• Complete remission was defined as the absence of HGD/EC in biopsies taken in two consecutive follow-up endoscopies [26].

References