Disruption of OTC promoter-enhancer interaction in a patient with symptoms of ornithine carbamoyltransferase deficiency

Abstract

In a female patient with signs of ornithine carbamoyltransferase deficiency (OTCD), the only variation found was a heterozygous single nucleotide substitution c.-366A>G. Determination of transcription start sites of human OTC 95, 119 and 169 bp upstream of the initiation codon located the variation upstream of the 5'-untranslated region. We predicted the human promoter and enhancer elements from homology with rat and mouse, performed function analysis of both regulatory regions and assessed the impact of the promoter variation in functional studies using dual luciferase reporter assay. Our data indicate that: (i) Full transcriptional activity of human OTC promoter depends on an upstream enhancer, as do the rodent promoters. (ii) The promoter variation c.-366A>G does not affect the function of the promoter alone but it disrupts the interaction of the promoter with the enhancer. (iii) The promoter-enhancer interaction contributes to tissue specific expression of OTC in the liver. We conclude that mutations in the regulatory regions of OTC can lead to OTCD and should be included in genetic testing.

Transcriptional Regulation of N-Acetylglutamate Synthase

“…While regulation of NAGS by Sp1, CREB, HNF-1, NF-Y, and factors that regulate them, requires additional study, identification of regions that regulate human NAGS and OTC have enabled diagnosis of patients with clinical symptoms of urea cycle disorders, but lacking disease causing mutations in the coding regions of the genes [93], [94]. Recently, we identified a patient with a mutation in the enhancer of NAGS and confirmed the diagnosis of NAGS deficiency by showing that the mutation significantly decreases transcription of NAGS [93].…”

Disease-causing mutations in the promoter and enhancer of the ornithine transcarbamylase gene

“…In the remaining 10%-15% of affected individuals, a molecular cause of OTCD cannot be ascertained through clinical testing. In a few such instances, mutations were ultimately identified in intronic or regulatory regions (Caldovic, Abdikarim, Narain, Tuchman, & Morizono, 2015;Engel et al, 2008;Luksan et al, 2010). Mutations in these regions may, in fact, be responsible for a large proportion of OTCD, in patients with no identified variants via current clinical methods.…”

“…OTC is expressed in the liver and intestine of humans and other mammals (Brusilow & Horwich, 2001). Transcription of the human OTC gene appears to initiate at multiple transcription start sites (Luksan et al, 2010), whereas transcription of the mouse and rat Otc genes initiate 136 and 98 bp upstream of the translation initiation codon, respectively (Takiguchi, Murakami, Miura, & Mori, 1987;Veres, Craigen, & Caskey, 1986). In the rat Otc promoter, four regions, A-D, bind transcription factors that regulate expression of the Otc gene ( Figure 1; (Murakami, Nishiyori, Takiguchi, & Mori, 1990)).…”

Characterization of the Human Ornithine Transcarbamylase 3′ Untranslated Regulatory Region

“…As recently demonstrated (Luksan et al, 2010), mutations in the OTC promoter region may have functional consequences preventing proper binding to the distal enhancer, in addition to mutations in the transcription factor binding sites that would impair gene expression. Therefore, it may be that a mutation in the 3¢ UTR sequence could affect translational efficiency and/or stability of the mRNA precursor, thus leading to a disease-associated phenotype.…”

“…Recently, the 5¢ UTR of the gene was studied, and a disruption of the enhancer-promoter binding site was found to be associated with clinical presentation (Luksan et al, 2010). This finding has reinforced the hypothesis that some uncharacterized OTCD cases may present with mutations in regulatory regions.…”