Transcriptional regulation of N-acetylglutamate synthase.
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The urea cycle converts toxic ammonia to urea within the liver of mammals. At least 6 enzymes are required for ureagenesis, which correlates with dietary protein intake. The transcription of urea cycle genes is, at least in part, regulated by glucocorticoid and glucagon hormone signaling pathways. N-acetylglutamate synthase (NAGS) produces a unique cofactor, N-acetylglutamate (NAG), that is essential for the catalytic function of the first and rate-limiting enzyme of ureagenesis, carbamyl phosphate synthetase 1 (CPS1). However, despite the important role of NAGS in ammonia removal, little is known about the mechanisms of its regulation. We identified two regions of high conservation upstream of the translation start of the NAGS gene. Reporter assays confirmed that these regions represent promoter and enhancer and that the enhancer is tissue specific. Within the promoter, we identified multiple transcription start sites that differed between liver and small intestine. Several transcription factor binding motifs were conserved within the promoter and enhancer regions while a TATA-box motif was absent. DNA-protein pull-down assays and chromatin immunoprecipitation confirmed binding of Sp1 and CREB, but not C/EBP in the promoter and HNF-1 and NF-Y, but not SMAD3 or AP-2 in the enhancer. The functional importance of these motifs was demonstrated by decreased transcription of reporter constructs following mutagenesis of each motif. The presented data strongly suggest that Sp1, CREB, HNF-1, and NF-Y, that are known to be responsive to hormones and diet, regulate NAGS transcription. This provides molecular mechanism of regulation of ureagenesis in response to hormonal and dietary changes.
Mice, Inbred C57BL
Carbamoyl-Phosphate Synthase (Ammonia)
Gene Expression Regulation, Enzymologic
Sequence Homology, Nucleic Acid
Molecular Sequence Data
Sp1 Transcription Factor
Cyclic AMP Response Element-Binding Protein
Transcription Factor AP-2
Hepatocyte Nuclear Factor 1-alpha
Enhancer Elements, Genetic
Promoter Regions, Genetic
Published Version (Please cite this version)10.1371/journal.pone.0029527
Publication InfoLopez, Giselle; Heibel, Sandra Kirsch; Panglao, Maria; Sodha, Sonal; Mariño-Ramírez, Leonardo; Tuchman, Mendel; & Caldovic, Ljubica (2012). Transcriptional regulation of N-acetylglutamate synthase. PloS one, 7(2). pp. e29527. 10.1371/journal.pone.0029527. Retrieved from https://hdl.handle.net/10161/17848.
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Assistant Professor in Pathology
I am a physician scientist with a clinical focus on neuropathology, and a research interest in brain tumors. Originally from Maryland, I completed my undergraduate training at the University of Maryland, completing degrees in Physiology and Neurobiology as well as Spanish Language and Literature. I subsequently came to Duke for my MD and PhD, and discovered a passion for brain tumor research, and quickly realized that this was my life's calling. After completing a residency and fellowship at the