Transcriptional regulation of N-acetylglutamate synthase.

Abstract

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.

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Citation

Published Version (Please cite this version)

10.1371/journal.pone.0029527

Publication Info

Heibel, Sandra Kirsch, Giselle Yvette Lopez, Maria Panglao, Sonal Sodha, Leonardo Mariño-Ramírez, Mendel Tuchman and Ljubica Caldovic (2012). Transcriptional regulation of N-acetylglutamate synthase. PloS one, 7(2). p. e29527. 10.1371/journal.pone.0029527 Retrieved from https://hdl.handle.net/10161/17848.

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Scholars@Duke

López

Giselle Yvette López

Associate 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. Clinically, I specialize in neuropathology. While I have active projects and collaborations on many kinds of brain tumors, my lab's primary focus is oligodendroglioma, a kind of infiltrative brain tumor that impacts adults. Our goal is to identify new ways to treat these tumors and improve the lives of patients with oligodendrogliomas and other kinds of brain tumors. By blending together computational approaches with wet lab approaches, we use the strengths inherent in different research modalities to excel in identifying unexplored pathways and thinking outside the box to identify new ways to target this brain tumor.  We do this through research in an inclusive, multidisciplinary lab environment that strives for excellence in research while creating well-rounded, thriving scientists ready for the next step in their careers.

Research Opportunities
We currently have opportunities in the laboratory for one-year projects (ideal for post-bac fellows or third year med student research experiences), as well as more extensive projects (graduate student-level). These projects are centered on identifying and testing novel therapeutic approaches for oligodendroglioma using in vitro and in vivo model systems. Please reach out if you are interested and would like to hear more about my mentoring philosophy, lab culture, and opportunities to be at the cutting edge of science.


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