Glucocorticoids, a major subclass of steroid hormones, modulate a large number of metabolic, cardiovascular, immune, and behavioral functions. The intracellular effects of glucocorticoids are mediated by the glucocorticoid receptor (GR), a 94-kDa intracellular protein belonging to the phylogenetically conserved nuclear hormone receptor superfamily. In the absence of glucocorticoid, the GR is maintained predominantly in the cytoplasm as part of an inactive multiprotein complex that consists of the receptor, two Hsp90 molecules, one molecule each of Hsp70 and Hsp56, and an immunophilin of the FK506- and rapamycin-binding class. When glucocorticoid binds to GR, the receptor undergoes a change in conformation, dissociates from regulatory heat shock proteins, and is hyperphosphorylated. The activated receptor rapidly translocates to the cell nucleus, where it is able to initiate transcriptional regulation.
Cells will undergo genotypic changes resulting in reduced responsiveness over time in normal cell culture conditions. Genetic instability is a biological phenomenon that occurs in all stably transfected cells. Therefore, it is critical to prepare an adequate number of frozen stocks at early passages.