Regulation of γ-glutamylcysteine synthetase regulatory subunit (GLCLR) gene expression:: Identification of the major transcriptional start site in HT29 cells

gamma-Glutamylcysteine synthetase (GCS) is of major importance in glutathione homeostasis. The GCS heterodimer is composed of catalytic (heavy subunit, GCS(h)) and regulatory (light subunit, GCS(l)) subunits. Regulation of the human GCS(l) subunit gene (GLCLR) expression was studied as GCS(l) has a critical role in glutathione synthesis. The minimal basal expression of GLCLR was found to be mediated by a region between nt -205 and -318. The major transcriptional start site in HT29 cells was located within this region at nt -283. A region between nt -411 and -447 was identified as having a potential involvement in the negative regulation of GLCLR expression. In order to study the transcriptional regulation of GCS(l) by oxidant stress, HepG2 cells were treated with sodium nitroprusside (SNP). SNP (1.5 mM) was found to increase glutathione levels by 2-fold, as well as GCS activity by 6-fold. This is accompanied by a co-ordinate increase in the levels of the both the GCS(l) and GCSh subunits, each by approximately 2-fold. The transcriptional activity of the GLCLR gene was increased by approximately 2.5-fold in SNP-treated cells. (C) 1999 Elsevier Science B.V. All rights reserved.