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We investigated the 5'-flanking region of the rat angiotensinogen gene to define the DNA elements conferring inducibility by glucocorticoids and estrogens. Two putative glucocorticoid-responsive elements (GREs) based on sequence comparison were identified. Here we report the functional importance of these sequences. We constructed several deletion mutants of the 5'-region in front of the bacterial reporter gene for chloramphenicol acetyltransferase (CAT). The angiotensinogen-CAT-reporter plasmids (pRagCAT) were transiently transfected into the rat hepatoma cells FTO 2B and Fe 33. All pRagCAT constructs in which the 5'-region contained at least one of the two GRE consensus sequences were stimulated by dexamethasone. On the other hand, deletion mutants containing no GRE sequences were not inducible with dexamethasone. In additional experiments, the transcriptional functions of the two putative GREs were assessed by cloning synthetic oligonucleotides encompassing the GRE sequences directly in front of the heterologous herpes simplex virus thymidine-kinase promoter. Our results showed that each synthetic GRE was capable of stimulating the heterologous TK promoter after administration of dexamethasone and that both GREs together act synergistically. We also investigated the transcriptional control of angiotensinogen by estrogen. Although no estrogen-responsive element consensus sequences were detectable by sequence comparison, we did identify sequences between -60 to -92 which conferred estrogen inducibility to the rat angiotensinogen gene. In this region, a so-called half-palindromic estrogen-responsive element is localized at nucleotides -87 to -91.
Feldmer et al. (Fri,) studied this question.