Disease relevance of UROS

• Congenital erythropoietic porphyria (CEP) is an inherited disease due to a deficiency in the uroporphyrinogen III synthase (UROS), the fourth enzyme of the heme pathway [1].
• Notably, the MFG-UROS-wt vector expressed UROS activity in CEP fibroblasts at these high levels for over 6 months without cell toxicity [2].
• Transduction of K562 erythroleukemia cells by cocultivation with the MFG-UROS-wt producer cells increased their high endogenous UROS activity by 1.6-fold without selection [2].
• The patient was homoallelic for a novel URO-synthase missense mutation, G188R, that expressed less than 5% of mean normal activity in Escherichia coli, consistent with her transfusion dependency [3].
• Uroporphyrinogen III cosynthetase in liver and blood in the Dubin-Johnson syndrome [4].

High impact information on UROS

• Congenital erythropoietic porphyria, an autosomal recessive inborn error of heme biosynthesis, results from the markedly deficient activity of uroporphyrinogen III synthase [5].
• To investigate this phenotypic heterogeneity, exonic point mutations in the URO-synthase gene were identified in unrelated CEP patients [6].
• Congenital erythropoietic porphyria, a disorder of haem synthesis, is caused by uroporphyrinogen III synthase deficiency in bone-marrow normoblasts [7].
• Uroporphyrinogen III synthase, U3S, the fourth enzyme in the porphyrin biosynthetic pathway, catalyzes cyclization of the linear tetrapyrrole, hydroxymethylbilane, to the macrocyclic uroporphyrino gen III, which is used in several different pathways to form heme, siroheme, chlorophyll, F(430) and vitamin B(12) [8].
• Uroporphyrinogen III synthase knock-in mice have the human congenital erythropoietic porphyria phenotype, including the characteristic light-induced cutaneous lesions [9].

Chemical compound and disease context of UROS

• Additional modifications of the heme pathway involved induction of the activity of ALAS and, at least in HCB-induced porphyria after iron pretreatment, may have involved reduced activity of uroporphyrinogen III cosynthetase [10].

Biological context of UROS

• For each of the other chromosomes, there was 19%-53% discordance with human UROS [11].
• There was 100% concordance for the presence of the human UROS PCR product and human chromosome 10 [11].
• Toward this goal, two retroviral MFG vectors containing the UROS cDNA were constructed, one with the wild-type sequence (MFG-UROS-wt) and a second with an optimized Kozak consensus sequence (MFG-UROS-K) [2].
• Addition of either delta-aminolevulinic acid (ALA) or ferric chloride did not affect expression of the transduced UROS gene nor did the increased concentrations of uroporphyrin isomers or porphyrin intermediates affect cell viability [2].
• Both patients were homoallelic for a novel mutation of the UROS gene, the missense mutation A69T [12].

Anatomical context of UROS

• The chromosomal assignment was confirmed by Southern hybridization analysis of DNA from somatic cell hybrids with the full-length UROS cDNA [11].
• The UROS values in the erythroid colonies from SA marrow were at the lowere end of the normal range (median values: 6.7 +/- 0.3 and 14.4 +/- 3.8 pmol uroporphyrinogen/h in CFU-E and BFU-E-derived colonies respectively versus 17.4 +/- 7.3 and 25 +/- 7.2 pmol/h in CFU-E and BFU-E colonies from normal subjects [13].
• We evaluated in vitro differentiation by biochemical microassay of a cytosol enzyme involved in the haem pathway: uroporphyrinogen I synthase (UROS) [13].
• Clonally isolated K562 cells expressed UROS for over 4 months at mean levels 4.7-fold greater than the endogenous activity without cell toxicity [2].
• The correction of the enzyme deficiency was confirmed by measuring erythrocyte UROS activity and urinary porphyrin excretion [12].

Associations of UROS with chemical compounds

• A new mutation of the uroporphyrinogen III synthase (UROS) gene was evidenced by systematic sequencing of the UROS gene: the substitution of serine by proline at the amino acid residue 47 (S47P) was present at the homozygous state in the four patients [14].
• Uroporphyrinogen III synthase [UROS; hydroxymethylbilane hydro-lyase (cyclizing), EC 4.2.1.75] is the fourth enzyme in the human heme biosynthetic pathway [11].
• Chronic exposure to methyl mercury results in increased urinary excretion of uro- and coproporphyrins in rats, mediated via inhibition of ferrochelatase and UROS and stimulation of ALAS [15].
• In an attempt to predict the clinical response to androgens in two children with Fanconi anaemia (FA) and two children with Diamond-Blackfan syndrome (DB), we tested the hormonal stimulation of testosterone, nortestosterone and etiocholanolone on CFU-E, BFU-E and uroporphyrinogen I synthase activity (UROS) [16].
• PBG was the substrate for the simultaneous assay of hydroxymethylbilane synthase and uroporphyrinogen III synthase [17].

Other interactions of UROS

• After acute treatment of rats with lead, no effects on ALAD or UROS and mild, transitory effects on ALAS and ferrochelatase are observed [15].
• Androgen-induced growth of erythroid progenitors was quantified by directly scoring colonies and by a biochemical determination of the uroporphyrinogen I synthase activity (UROS) [18].
• Despite extensive mutation analysis, no other potential disease-causing genetic alterations could be detected in the PPOX gene or the uroporphyrinogen III synthase gene [19].
• Although massive coproporphyrinuria and coproporphyrinemia initially suggested a coproporphyrinogen oxidase deficiency disorder, excess porphyrins were chiefly of the isomer I series, implicating a uroporphyrinogen III synthase defect [20].
• A hitherto undescribed dual deficiency of uroporphyrinogen III synthase and uroporphyrinogen decarboxylase was observed in the erythrocytes in a 14 year-old patient who had presented with congenital erythropoietic porphyria since early childhood [21].

Analytical, diagnostic and therapeutic context of UROS

• Human uroporphyrinogen III synthase: molecular cloning, nucleotide sequence, and expression of a full-length cDNA [22].
• As a step toward the development of an effective gene therapy, we have constructed two retroviral vectors, LUSN and pMFG-US (with and without the selectable marker Neo), containing a full-length human cDNA for UROIIIS [23].
• Simultaneous determination of hydroxymethylbilane synthase and uroporphyrinogen III synthase in erythrocytes by high-performance liquid chromatography [24].
• URO-III-S concentration in erythrocytes was determined by ELISA [25].
• Furthermore, specificity of immune sera is demonstrated by immunoprecipitation of URO-III-S activity which caused a 33% reduction of enzyme activity [25].

References