Disease relevance of ALAS2

• Absent phenotypic expression of X-linked sideroblastic anemia in one of 2 brothers with a novel ALAS2 mutation [1].
• Thus, the reported linkage of acquired sideroblastic anemia and sideroblastic anemia with ataxia to Xq13 presumably results from genes other than ALAS2 [2].
• This late-onset form of XLSA can be distinguished from refractory anemia and ringed sideroblasts by microcytosis, pyridoxine-responsiveness, and ALAS2 mutations [3].
• The proband's brother, an ALAS2 R452H hemizygote, had mild anemia and mild iron overload [4].
• A fragment of the ALAS2 promoter ranging from -716 to +1 conveyed hypoxia responsiveness to a heterologous luciferase reporter gene construct in transiently transfected HeLa cells [5].

High impact information on ALAS2

• Using transient expression and coimmunoprecipitation, we verified that mitochodrially expressed SCS-betaA associates specifically with ALAS-E and not with ALAS-N [6].
• Interaction between succinyl CoA synthetase and the heme-biosynthetic enzyme ALAS-E is disrupted in sideroblastic anemia [6].
• To identify possible mitochondrial factors that modulate ALAS-E function, we screened a human bone marrow cDNA library, using the mitochondrial form of human ALAS-E as a bait protein in the yeast 2-hybrid system [6].
• The first and the rate-limiting enzyme of heme biosynthesis is delta-aminolevulinate synthase (ALAS), which is localized in mitochondria [6].
• X-linked sideroblastic anemia (XLSA) is caused by mutations of the erythroid-specific delta-aminolevulinate synthase gene (ALAS2) resulting in deficient heme synthesis [3].

Chemical compound and disease context of ALAS2

• A novel missense mutation, G663A, in exon 5 of the erythroid-specific delta-aminolevulinate synthase gene (ALAS2) was identified in a Japanese male with pyridoxine-responsive sideroblastic anemia [7].
• A promoter mutation in the erythroid-specific 5-aminolevulinate synthase (ALAS2) gene causes X-linked sideroblastic anemia [8].
• Hypoxia (1% O2) and inhibition of the proteasome increased both the stability and the specific activity of ALAS2 (greater than 2- and 7-fold, respectively, over 72 h of treatment) [9].
• We examined the effect of hemin, TGF-beta1 and cytosine arabinoside (Ara-C) on the levels of mRNAs for the erythroid-specific 5-aminolevulinate synthase (ALAS-E) and gamma-globin in various human myelogenous leukemia cell lines [10].

Biological context of ALAS2

• A 38-year-old male presented with this phenotype (hemoglobin [Hb] 7.6 g/dL, mean corpuscular volume [MCV] 64 fL, serum ferritin 859 microg/L), and molecular analysis of ALAS2 showed a mutation 1731G>A predicting an Arg560His amino acid change [1].
• We have investigated whether introns 1, 3, and 8, which correspond to DNase I-hypersensitivity sites in the structurally related mouse ALAS2 gene, affect expression of the human ALAS2 promoter in transient expression assays [11].
• Furthermore, the mapping of the ALAS2 gene to the X chromosome and the observed reduction in ALAS activity in X-linked sideroblastic anemia suggest that this disorder may be due to a mutation in the erythroid-specific gene [12].
• The ALAS2 gene segregated with the human X chromosome in all 30 hybrid cell lines analyzed and was discordant with all other chromosomes in at least 8 of the 30 hybrids [12].
• These studies localized the ALAS2 gene to the distal subregion of Xp11.21 in Interval 5 indicating the following gene order: Xpter-OATL2-[L62-3A, Xp11.21; A62-1A-4b, Xp11.21]-(ALAS2, DXS323)-[B13-3, Xp11.21; C9-5, Xp11.21]-(DXS14, DXS429)-DXS422-(DXZ1, Xcen) [2].

Anatomical context of ALAS2

• A 36-year-old brother was hemizygous for this mutation and expressed the mutated ALAS2 mRNA in his reticulocytes, but showed almost no phenotypic expression [1].
• Erythroid-specific 5-aminolevulinate synthase (ALAS2) catalyzes the rate-limiting step in heme biosynthesis of erythroid cells [13].
• Here, we show that treatment of erythroid K562 cells with HDAC inhibitors sodium butyrate or Trichostatin A gave rise to a significant increase in ALAS2 gene transcripts, with a concurrent increase in acetylation level of histone H4 at the ALAS2 gene promoter [13].
• This suggests that cis-acting elements present in the 5'-flanking region are not responsible for maintenance of transcriptional silencing in non-erythroid cell lines and that tissue-specific regulation of ALAS2 depends on other regions of the gene or on chromatin remodeling [14].
• Differentiation of embryonic stem cells with a disrupted ALAS2 gene has established that expression of this gene is critical for erythropoiesis and cannot be compensated by expression of the ubiquitous isoform of the enzyme (ALAS1) [15].

Associations of ALAS2 with chemical compounds

• This is the first study to delimit the cis-acting region responsible for activation of the ALAS2 promoter upon dimethyl-sulfoxide induction in MEL cells [14].
• R411C mutation of the ALAS2 gene encodes a pyridoxine-responsive enzyme with low activity [16].
• The mutation predicted the substitution of leucine for phenylalanine at residue 165 (F165L) in the first highly conserved domain of the ALAS2 catalytic core shared by all species [17].
• We identified a novel point mutation in the fifth exon of this patient's ALAS2 gene, which resulted in an amino acid change at residue 159 from aspartic acid to asparagine (Asp159Asn) [18].
• Consistent with this finding, activity of a bacterially expressed ALAS2 mutant protein harbouring this mutation was 19.5% compared with the normal control, but was increased up to 31.6% by the addition of pyridoxal 5'-phosphate (PLP) in vitro [19].

Physical interactions of ALAS2

• Histone acetyltransferase p300 bound withALAS2 promoter and overexpression of p300 increased both the promoter reporter expression and endogenous mRNA level of ALAS2 [13].

Regulatory relationships of ALAS2

• In contrast, iron depletion, known to induce HIF-1 activity but inhibit ALAS2 translation, did not increase ALAS2 promoter activity [5].

Other interactions of ALAS2

• Using these different cDNAs, the human ALAS housekeeping gene (ALAS1) and the human erythroid-specific (ALAS2) gene have been localized to chromosomes 3p21 and X, respectively, by somatic cell hybrid and in situ hybridization techniques [12].
• Tight linkage of MRX81 to DNA markers ALAS2, DXS991, and DXS7132 was observed with a maximum LOD score of 3.43 [20].
• Both of the GATA-1 sites and all the Sp1 sites at the ALAS2 promoter contributed to the transcription synergistic action with p300 [13].
• ALAS2 was placed on the multipoint linkage map of the X chromosome in the pericentromeric region with the locus order: pter-(DXS255, TFE3, DXS146)-(DXS14, ALAS2, DXZ1)-AR-(DXS153, DXS159)-qter [21].
• No recombination between the WWS locus and ALAS2 or with AR (z = 4.890 at theta = 0.0) was found [22].

Analytical, diagnostic and therapeutic context of ALAS2

• Assignment of human erythroid delta-aminolevulinate synthase (ALAS2) to a distal subregion of band Xp11.21 by PCR analysis of somatic cell hybrids containing X; autosome translocations [2].
• Sequence analysis identified an A to C transversion in exon 7 (K299Q) of the ALAS2 gene in the male proband and his daughter [3].
• Four new mutations in the erythroid-specific 5-aminolevulinate synthase (ALAS2) gene causing X-linked sideroblastic anemia: increased pyridoxine responsiveness after removal of iron overload by phlebotomy and coinheritance of hereditary hemochromatosis [23].
• As mutations in ALAS2 cause congenital sideroblastic anaemia (CSA) in humans, sau represents the first animal model of this disease [24].
• A case-control study has been made on smoking habits in women who, during 1975, gave birth to infants with closure defects of the central nervous system (ASB) or with cleft lip or cleft palate (CLP) [25].

References