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Carbamoylphosphate synthetase-I is the flux-determining enzyme of the ornithine cycle, and neutralizes toxic ammonia by converting it to urea. An 80 bp glucocorticoid response unit located 6.3 kb upstream of the trans-cription start site mediates hormone responsiveness and liver-specific expression of carbamoylphosphate synthetase-I. | ỊFEBS Journal Hepatocyte-specific interplay of transcription factors at the far-upstream enhancer of the carbamoylphosphate synthetase gene upon glucocorticoid induction Maarten Hoogenkamp1 Ingrid C. Gaemers1 Onard J. L. M. Schoneveld1 Atze T. Das1 Thierry Grange2 and Wouter H. Lamers1 1 AMC Liver Center Academic MedicalCenter University of Amsterdam the Netherlands 2 Institut Jacques Monod du CNRS Universites Paris 6-7 Paris France Keywords carbamoylphosphate synthetase-I FoxA glucocorticoid receptor in vivo footprinting liver Correspondence W. H. Lamers AMC Liver Center Academic MedicalCenter University of Amsterdam Meibergdreef 69-71 1105 BK Amsterdam the Netherlands Fax 31 205669190 Tel 31 205665405 E-mail w.h.lamers@amc.uva.nl Received 26 July 2006 revised 12 October 2006 accepted 27 October 2006 doi 10.1111 j.1742-4658.2006.05561.x Carbamoylphosphate synthetase-I is the flux-determining enzyme of the ornithine cycle and neutralizes toxic ammonia by converting it to urea. An 80 bp glucocorticoid response unit located 6.3 kb upstream of the transcription start site mediates hormone responsiveness and liver-specific expression of carbamoylphosphate synthetase-I. The glucocorticoid response unit consists of response elements for the glucocorticoid receptor forkhead box A CCAAT enhancer-binding protein and an unidentified protein. With only four transcription factor response elements the carbamoylphosphate synthetase-I glucocorticoid response unit is a relatively simple unit. The relationship between carbamoylphosphate synthetase-I expression and in vivo occupancy of the response elements was examined by comparing a carbamoylphosphate synthetase-I-expressing hepatoma cell line with a carbamoylphosphate synthetase-I-negative fibroblast cell line. DNaseI hypersensitivity assays revealed an open chromatin configuration of the carbamoylphosphate synthetase-I enhancer in hepatoma cells only. In vivo footprinting assays showed that the accessory transcription factors of
