STEROID RECEPTOR TRANSLOCATION AND HEAT SHOCK

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The long-term objective of this proposal is to study the mechanism by which glucocorticoid hormone causes transformation of its receptor from an inactive state to one which can actively regulate specific gene expression. The proposed research is composed of two approaches. In the first, an experimental system will be developed to examine glucocorticoid receptor (GR) transport from the cytoplasm to the nucleus. In the second, the relationship of the cellular heat shock response to glucocorticoid receptor function will be studied. During my post-doctoral tenure with Dr. William Pratt, we showed that GR exists in a complex with the 90-kDa heat shock protein (J.Biol.Chem. 260:13810, 1985 and J.Biol. Chem. 260:12398, 1985), that hormone-dependent dissociation of hsp9O from GR precedes conversion of GR to the DNA-state (J.Biol.Chem. 262:6986, 1987), and that deletion of a short, conserved region within the GR will cause loss of hsp9O binding (J.Biol.Chem. 265:12778, 1990). Our reports that hsp9O within intact cells may be bound to microtubules (Mol.Endocrinol. 2:756, 1988 and Euro.J.Cell Biol. 58:66, 1989), suggests a role for cellular elements in GR movement. In this proposal, a system is described by which GR in intact cells is slowly driven into the nucleus in response to hormone to identify receptor-associated proteins involved in: 1) transport to the nucleus, 2) transport across nuclear pores, and 3) localization of the GR to its ultimate site of specific gene transcription. We have shown that transfected mouse GR in CHO cells is localized to the nucleus in association with hsp7O, while GR of L cells is cytoplasmic and not associated with hsp7O (J.Biol.Chem. 265:20123, 1990). The proposed GR transport system may serve to determine if the GR in the CHO cells represents an intermediate state in the translocation pathway. We have shown that the GR complex of IM-9 cells contains a 56kDa protein of unique amino acid sequence (Biochemistry 29:5145, 1990). Since arriving at MCO, I have shown that this protein is also a novel heat shock protein, hsp56 (J. Biol. Chem. 265:22067, 1990). This has led me to speculate that the stress response and glucocorticoid hormone action are functionally related. In a letter submitted to Nature, I show that heat shock treatment of L cells will induce nuclear localization of the unliganded GR. This proposal seeks to expand on the cellular and molecular significance of this observation.