BINDING-ACTIVITY OF GLUCOCORTICOID RECEPTORS AFTER HEAT-SHOCK

The response of glucocorticoid receptors (GR) to heat was measured by the change in ligand binding activity both in control cells and in cells made tolerant to heat by a prior mild heat exposure. The study was prompted by earlier data showing that one of the heat shock proteins (HSP90) is an essential component of the GR complex [1-3] and that treatment of mammalian cells with hydrocortisone induces resistance to heat damage [4]. The GR rapidly loses binding activity after commencement of heating. There is a 50% loss of activity after 4 min at 45 °C, 8 min at 44 °C, or 17 min at 43 °C. The reduction in binding is due mainly to a reduction in affinity of binding to the ligand. The ability to bind glucocorticoid recovers quickly after heat treatment. Activity returns to levels 60-80% of normal by 2 h after a heat treatment that initially reduces binding to less than 20% of normal. However, complete restoration of binding activity takes approximately 3 days. The recovery of binding activity does not require protein synthesis. Pretreatment of cells with hydrocortisone, using conditions that induce heat resistance, reduces the activity to 10-20% of control, but residual receptors display a heat sensitivity similar to that of control cells. There was evidence for a limited degree of protection of GR from heat damage in thermotolerant cells. © 1991 Academic Press, Inc. All rights of reproduction in any form reserved.