Transcriptional Regulation of N‐Acetyl Glutamate Synthase

Abstract

The urea cycle converts ammonia, a toxic product of protein metabolism, to urea in mammalian livers. N‐acetyl glutamate synthetase (NAGS) catalyzes the formation of N‐acetyl glutamate, an essential cofactor of carbamylphosphate synthetase I (CPSI). By providing an essential activator of CPSI, the first and rate‐limiting enzyme in the urea cycle, NAGS helps regulate urea production and may function as a nitrogen load sensor.Methods to identify transcription start sites, conserved regulatory regions, and cis‐acting regulatory motifs for NAGS included 5' RACE, multiple sequence alignment of several mammalian species upstream non‐coding sequences, Cis‐element OVERrepresentation software & Chromatin Immunoprecipitation (ChIP). Regions of high conservation were identified immediately upstream and 3kb upstream of the translation start codon. Several transcription factor binding motifs, including Sp1, AR & CREB, were conserved within the putative promoter while a TATA box motif was absent. ChIP analysis verified binding of Sp1 to the NAGS promoter. These data indicate NAGS transcription is regulated through Sp1 and hormone signalling pathways including glucocorticoids and cAMP, similar to regulation of urea cycle enzymes ASS, ASL & arginase I. These finding suggest regulation of NAGS occurs through metabolite sensing pathways and that NAGS could be the first nitrogen load sensor.NIH # 2R01DK064913‐05A1