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Shen P, Xie ZJ, Li H, Sanchez ER: Glucocorticoid receptor conversion to high affinity nuclear binding and transcription enhancement activity in Chinese hamster ovary cells subjected to heat and chemical stress. J Steroid Biochem Mol Biol. 1993 Dec;47(1-6):55-64.
The untransformed glucocorticoid receptor (GR) is a heteromeric complex containing two molecules of the 90-kDa heat shock protein (hsp90) and one molecule of the 56-kDa heat shock protein (hsp56). In the absence of hormone, this complex is found in the cytosolic fraction of cells, and upon hormone-binding the complex dissociates and the GR is recovered in the nuclear pellet fraction. Given the association of heat shock proteins with the cytosolic form of the GR, we have examined the effects of heat shock on GR subcellular localization and transcription enhancement activity in a series of Chinese hamster ovary (CHO) cells which express either low levels of endogenous GR (CHOd cells), high levels of the mouse GR (WCL2 cells), or high levels of mutated mouse GR unable to bind DNA (NB cells). It was found that heat shock treatment of WCL2 cells results in wild-type mouse GR that is recovered almost entirely within the nuclear pellet fraction, a response similar to that seen in hormone-treated cells. In contrast, heat shock treatment of NB cells results in complete loss of GR from the cytosolic fraction, but almost no shift of GR to the nuclear nuclear pellet. These results indicate that heat shock-mediated conversion to high-affinity nuclear binding by the wild-type GR requires a functional DNA-binding domain, and that heat shock will result in loss of GR to proteolysis in the absence of nuclear sequestration. Analysis of MMTV-CAT reporter gene expression in these cells revealed that heat or chemical shock, in comparison to hormone-treatment, results in a small induction of MMTV-CAT expression in the WCL2 cells, but not in the CHOd or NB cells. These results indicate that cellular stress can cause at least a partial induction of hormone-independent GR-mediated gene expression. |
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