Test No. 454A: Human Glucocorticoid Receptor Transactivation Assay

The Test Guideline describes a transactivation assay of the glucocorticoid receptor (GR), which is a hormone-activated transcription factor belonging to the nuclear receptor superfamily of steroid hormone receptors, and different forms are ubiquitously expressed in almost every cell in the body. The GR is involved in a wide range of key physiological processes, including the regulation of stress response, immune function, inflammation, and metabolism. A cell line (HMLN-hGR) stably transfected with a luciferase reporter gene under the control of the ligand/chemical bound GR was developed, forming the basis for a human GR transactivation (TA) assay that enables detection of both GR agonists (activation) and antagonists (inhibition). Ligand activation of GR leads to transcription of the luciferase gene which subsequently can be measured by light emission when its substrate luciferin is converted to oxyluciferin by the expressed luciferase. Transcriptional activation is measured by evaluating the concentration–response relationship of the test chemicals under agonist conditions. Antagonists can be detected in antagonist mode, where the chemicals are tested in the presence of an agonist.