IMPDH2Genetic Polymorphism: A Promoter Single-Nucleotide Polymorphism Disrupts a Cyclic Adenosine Monophosphate Responsive Element

Abstract

Inosine 5'-monophosphate dehydrogenase (IMPDH), which catalyzes a key step in the de novo biosynthesis of guanine nucleotide, is mediated by two highly conserved isoforms, IMPDH1 and IMPDH2. In this study, IMPDH2 genetic polymorphism was investigated in 96 individuals of Caucasian origin. Four single-nucleotide polymorphisms were identified, comprising one previously described single base-pair substitution in the close vicinity of the consensus donor splice site of intron 7 (IVS7+10T>C), and three novel polymorphisms, one silent substitution in exon 9 (c.915C>G), one single base-pair insertion (g.6971_6972insT) within the 3'-untranslated region of the gene, and one substitution located in the promoter region (c.-95T>G) in a transcription factor binding site CRE(A) (cyclic adenosine monophosphate [cAMP] response element). Considering the nature and location of this latter polymorphism, its functional relevance was examined by transfecting HEK293 and Jurkat cell lines with constructs of the related region of IMPDH2/luciferase reporter gene. The c.-95T>G mutation leads to a significant decrease of luciferase activity (HEK293: 55% decrease, p < 0.05; Jurkat: 65% decrease, p < 0.05) compared with the wild-type promoter sequence and, therefore, is likely to determine interindividual differences in IMPDH2 transcriptional regulation. These results might contribute to a better understanding of the variability in clinical outcome and dose adjustments of certain immunosuppressors that are metabolized through the IMPDH pathway or that are IMPDH inhibitors.

Defects in purine nucleotide metabolism lead to substantial incorporation of xanthine and hypoxanthine into DNA and RNA

“…For example, a T-to-G substitution in the promoter region of the human IMPDH2 gene, a homolog of E. coli purA encoding SAMP synthetase (Fig. 1), reduced gene expression by 50-60% (15). While the present studies focused on a complete loss of this gene, it is reasonable to assume that a 50-60% decrease in SAMP synthetase activity could cause measurable increases in hypoxanthine incorporation into DNA and RNA in human cells affected with the genetic polymorphism.…”

“…These synergies suggest that even modest changes in the activities of pairs of these enzymes caused by genetic polymorphisms could result in increased misincorporation of hypoxanthine into nucleic acids in humans. Given the large reductions in activity caused by common genetic polymorphisms in the human homologs of purA and rdgB (15,16), a substantial number of humans could possess polymorphisms that affect two or more purine metabolism genes, with the consequence of increased incorporation of deaminated nucleotides into DNA and RNA.…”

“…GMP is also derived from IMP but via xanthosine monophosphate (XMP) through the action of IMP dehydrogenase (guaB) and GMP synthetase (guaA). Xanthine and hypoxanthine thus play significant roles in purine metabolism as components of the cellular nucleotide pool.The concentrations of purine nucleotide pool components are highly regulated (11,12), with many human diseases caused by imbalances arising from genetic polymorphisms and mutations in purine metabolism (13)(14)(15)(16)(17). For example, loss of adenosine deaminase results in severe combined immunodeficiency (18), while loss of hypoxanthine-guanine phosphoribosyltransferase leads to the hyperuricemia and neurological symptoms of LeschNyhan syndrome (14), and increases in the activity of purine nucleotide metabolic enzymes, such as IMP dehydrogenase, are associated with several types of cancer (19).…”

IMP dehydrogenase deficiency in Leishmania donovani causes a restrictive growth phenotype in promastigotes but is not essential for infection in mice

“…The null genotype and restrictive growth phenotype of cultured Δ impdh parasites authenticates a single IMPDH encoding locus in L. donovani . In contrast, mammalian cells have two similar but distinct IMPDH genes [15]. …”

Risk given byAGTpolymorphisms in inducing susceptibility to essential hypertension among isolated populations from a remote region of China: A case-control study among the isolated populations

“…Our findings about the Hani minority were in accordance with the reports of Gu et al 24,30,96,97 However, our research about the Yi minority showed no association in -532T/C (rs5046), which was in accordance with the finding of Zhu et al 33 This inconsistency could be attributed to the different genetic backgrounds, living habits, and environmental factors among different populations. Since the previous studies revealed that the variants localized near the 5′ region of a gene might be associated with the regulation of this gene expression level, 100–102 the functional effect of rs5046 polymorphism localized at the promoter region of AGT gene on the expression level of this gene was predicted by p -match. The result revealed that the sequence (TGTGTTTTCC) containing the C allele of rs5046 could be captured by the TF c-Rel, suggesting that the C→T single nucleotide substitution of rs5046 would change the sequence structure of the TF binding site, thereby affecting the binding affinity between this TF c-Rel and its binding site.…”