Non-coding sequence variants define a novel regulatory element in the first intron of the N-acetylglutamate synthase gene.

N-acetylglutamate synthase deficiency (NAGSD, MIM #237310) is an autosomal recessive urea cycle disorder caused either by decreased expression of the NAGS gene or defective NAGS enzyme resulting in decreased production of N-acetylglutamate (NAG), an allosteric activator of carbamylphosphate synthetase 1 (CPS1). NAGSD is the only urea cycle disorder that can be effectively treated with a single drug, N-carbamylglutamate (NCG), a stable NAG analog, which activates CPS1 to restore ureagenesis. We describe three patients with NAGSD due to four novel sequence variants in the NAGS regulatory regions. All three patients had hyperammonemia that resolved upon treatment with NCG. Sequence variants NM_153006.2:c.-3065A>C and NM_153006.2:c-3098C>T reside in the NAGS enhancer, within known HNF1 and predicted glucocorticoid receptor binding sites, respectively. Sequence variants NM_153006.2:c.426+326G>A and NM_153006.2:c.427-218A>C reside in the first intron of NAGS and define a novel NAGS regulatory element that binds retinoic X receptor α. Reporter gene assays in HepG2 and HuH-7 cells demonstrated that all four substitutions could result in reduced expression of NAGS. These findings show that analyzing non-coding regions of NAGS and other urea cycle genes can reveal molecular causes of disease and identify novel regulators of ureagenesis.

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Noncoding sequence variants define a novel regulatory element in the first intron of the N ‐acetylglutamate synthase gene

Human Mutation ◽

10.1002/humu.24281 ◽

2021 ◽

Author(s):

Johannes Häberle ◽

Marvin B. Moore ◽

Nantaporn Haskins ◽

Véronique Rüfenacht ◽

Dariusz Rokicki ◽

...

Keyword(s):

Regulatory Element ◽

Sequence Variants ◽

Noncoding Sequence ◽

First Intron ◽

Acetylglutamate Synthase

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Identification, cloning and expression of the mouse N-acetylglutamate synthase gene

Biochemical Journal ◽

10.1042/bj20020161 ◽

2002 ◽

Vol 364 (3) ◽

pp. 825-831 ◽

Cited By ~ 38

Author(s):

Ljubica CALDOVIC ◽

Hiroki MORIZONO ◽

Xiaolin YU ◽

Mark THOMPSON ◽

Dashuang SHI ◽

...

Keyword(s):

Coli Strain ◽

Cloning And Expression ◽

Affinity Column ◽

E Coli ◽

Apparent Homogeneity ◽

Liver Cdna Library ◽

Targeting Signal ◽

Acetylglutamate Synthase ◽

Carbamylphosphate Synthetase ◽

Allosteric Activator

In ureotelic animals, N-acetylglutamate (NAG) is an essential allosteric activator of carbamylphosphate synthetase I (CPSI), the first enzyme in the urea cycle. NAG synthase (NAGS; EC 2.3.1.1) catalyses the formation of NAG from glutamate and acetyl-CoA in liver and intestinal mitochondria. This enzyme is supposed to regulate ureagenesis by producing variable amounts of NAG, thus modulating CPSI activity. Moreover, inherited deficiencies in NAGS have been associated with hyperammonaemia, probably due to the loss of CPSI activity. Although the existence of the NAGS protein in mammals has been known for decades, the gene has remained elusive. We identified the mouse (Mus musculus) and human NAGS genes using their similarity to the respective Neurospora crassa gene. NAGS was cloned from a mouse liver cDNA library and was found to encode a 2.3kb message, highly expressed in liver and small intestine with lower expression levels in kidney, spleen and testis. The deduced amino acid sequence contains a putative mitochondrial targeting signal at the N-terminus. The cDNA sequence complements an argA (NAGS)-deficient Escherichia coli strain, reversing its arginine auxotrophy. His-tagged versions of the pre-protein and two putative mature proteins were each overexpressed in E. coli, and purified to apparent homogeneity by using a nickel-affinity column. The pre-protein and the two putative mature proteins catalysed the NAGS reaction but one of the putative mature enzymes had significantly higher activity than the pre-protein. The addition of l-arginine increased the catalytic activity of the purified recombinant NAGS enzymes by approx. 2–6-fold.

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Impaired ureagenesis due to arginine-insensitive N-acetylglutamate synthase

10.1101/425959 ◽

2018 ◽

Author(s):

Parthasarathy Sonaimuthu ◽

Emilee Senkevitch ◽

Nantaporn Haskins ◽

Prech Uapinyoying ◽

Markey McNutt ◽

...

Keyword(s):

Urea Cycle ◽

Ammonia Concentration ◽

Ammonia Toxicity ◽

Wild Type ◽

Adeno Associated Virus ◽

The Central Nervous System ◽

Acetylglutamate Synthase ◽

And Control ◽

Carbamylphosphate Synthetase

AbstractThe urea cycle protects the central nervous system from ammonia toxicity by converting ammonia to non-toxic urea. N-acetylglutamate synthase (NAGS) is an enzyme that catalyzes the formation of N-acetylglutamate (NAG), an allosteric activator of carbamylphosphate synthetase 1 (CPS1), the rate limiting enzyme of the urea cycle. Enzymatic activity of mammalian NAGS doubles in the presence of L-arginine but the physiological significance of NAGS activation by L-arginine is unknown. Previously, we have described the creation of a NAGS knockout (Nags−/−) mouse, which develops hyperammonemia without N-carbamylglutamate and L-citrulline supplementation (NCG+Cit). In order to investigate the effect of L-arginine on ureagenesis in vivo, we used adeno associated virus (AAV) mediated gene transfer to deliver either wild-type or E354A mutant mouse NAGS (mNAGS), which is not activated by L-arginine, to Nags−/− mice. The ability of the E354A mNAGS mutant protein to rescue Nags−/− mice was determined by measuring their activity on the voluntary wheel following NCG+Cit withdrawal. The Nags−/− mice that received E354A mNAGS remained apparently healthy and active but had elevated plasma ammonia concentration despite similar expression levels of the E354A mNAGS and control wild-type NAGS proteins. The corresponding mutation in human NAGS (NP 694551.1:p.E360D) that abolishes binding and activation by L-arginine was also identified in a patient with hyperammonemia due to NAGS deficiency. Taken together, our results suggest that L-arginine binding to the NAGS enzyme is essential for normal ureagenesis.

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Gene delivery corrects N-acetylglutamate synthase deficiency and enables insights in the physiological impact of L-arginine activation of N-acetylglutamate synthase

Scientific Reports ◽

10.1038/s41598-021-82994-8 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

P. Sonaimuthu ◽

E. Senkevitch ◽

N. Haskins ◽

P. Uapinyoying ◽

M. McNutt ◽

...

Keyword(s):

Ammonia Concentration ◽

Ammonia Toxicity ◽

Wild Type ◽

Adeno Associated Virus ◽

The Central Nervous System ◽

Acetylglutamate Synthase ◽

Physiological Impact ◽

Carbamylphosphate Synthetase ◽

Allosteric Activator

AbstractThe urea cycle protects the central nervous system from ammonia toxicity by converting ammonia to urea. N-acetylglutamate synthase (NAGS) catalyzes formation of N-acetylglutamate, an essential allosteric activator of carbamylphosphate synthetase 1. Enzymatic activity of mammalian NAGS doubles in the presence of L-arginine, but the physiological significance of NAGS activation by L-arginine has been unknown. The NAGS knockout (Nags−/−) mouse is an animal model of inducible hyperammonemia, which develops hyperammonemia without N-carbamylglutamate and L-citrulline supplementation (NCG + Cit). We used adeno associated virus (AAV) based gene transfer to correct NAGS deficiency in the Nags−/− mice, established the dose of the vector needed to rescue Nags−/− mice from hyperammonemia and measured expression levels of Nags mRNA and NAGS protein in the livers of rescued animals. This methodology was used to investigate the effect of L-arginine on ureagenesis in vivo by treating Nags−/− mice with AAV vectors encoding either wild-type or E354A mutant mouse NAGS (mNAGS), which is not activated by L-arginine. The Nags−/− mice expressing E354A mNAGS were viable but had elevated plasma ammonia concentration despite similar levels of the E354A and wild-type mNAGS proteins. The corresponding mutation in human NAGS (NP_694551.1:p.E360D) that abolishes binding and activation by L-arginine was identified in a patient with NAGS deficiency. Our results show that NAGS deficiency can be rescued by gene therapy, and suggest that L-arginine binding to the NAGS enzyme is essential for normal ureagenesis.

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Phosphorylation-dependent binding of a 138-kDa myc intron factor to a regulatory element in the first intron of the c-myc gene.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(19)39597-3 ◽

1990 ◽

Vol 265 (8) ◽

pp. 4547-4551

Author(s):

M Zajac-Kaye ◽

D Levens

Keyword(s):

Regulatory Element ◽

First Intron ◽

Myc Gene

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The transcriptional tissue specificity of the human proα1(I) collagen gene is determined by a negative cis-regulatory element in the promoter

Biochemical Journal ◽

10.1042/bj2860179 ◽

1992 ◽

Vol 286 (1) ◽

pp. 179-185 ◽

Cited By ~ 24

Author(s):

C P Simkevich ◽

J P Thompson ◽

H Poppleton ◽

R Raghow

Keyword(s):

Tissue Specificity ◽

Regulatory Element ◽

Mesenchymal Cell ◽

Cell Types ◽

Regulatory Elements ◽

Negative Influence ◽

Collagen Gene ◽

Specific Expression ◽

Cis Acting ◽

First Intron

The transcriptional activity of plasmid pCOL-KT, in which human pro alpha 1 (I) collagen gene upstream sequences up to -804 and most of the first intron (+474 to +1440) drive expression of the chloramphenicol acetyltransferase (CAT) gene [Thompson, Simkevich, Holness, Kang & Raghow (1991) J. Biol. Chem. 266, 2549-2556], was tested in a number of mesenchymal and non-mesenchymal cells. We observed that pCOL-KT was readily expressed in fibroblasts of human (IMR-90 and HFL-1), murine (NIH 3T3) and avian (SL-29) origin and in a human rhabdomyosarcoma cell line (A204), but failed to be expressed in human erythroleukaemia (K562) and rat pheochromocytoma (PC12) cells, indicating that the regulatory elements required for appropriate tissue-specific expression of the human pro alpha 1 (I) collagen gene were present in pCOL-KT. To delineate the nature of cis-acting sequences which determine the tissue specificity of pro alpha 1 (I) collagen gene expression, functional consequences of deletions in the promoter and first intron of pCOL-KT were tested in various cell types by transient expression assays. Cis elements in the promoter-proximal and intronic sequences displayed either a positive or a negative influence depending on the cell type. Thus deletion of fragments using EcoRV (nt -625 to -442 deleted), XbaI (-804 to -331) or SstII (+670 to +1440) resulted in 2-10-fold decreased expression in A204 and HFL-1 cells. The negative influences of deletions in the promoter-proximal sequences was apparently considerably relieved by deleting sequences in the first intron, and the constructs containing the EcoRV/SstII or XbaI/SstII double deletions were expressed to a much greater extent than either of the single deletion constructs. In contrast, the XbaI* deletion (nt -804 to -609), either alone or in combination with the intronic deletion, resulted in very high expression in all cells regardless of their collagen phenotype; the XbaI*/(-SstII) construct, which contained the intronic SstII fragment (+670 to +1440) in the reverse orientation, was not expressed in either mesenchymal or nonmesenchymal cells. Based on these results, we conclude that orientation-dependent interactions between negatively acting 5′-upstream sequences and the first intron determine the mesenchymal cell specificity of human pro alpha 1 (I) collagen gene transcription.

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