Pharmacological induction of heat shock protein 68 synthesis in cultured rat astrocytes.

The induction of the highly inducible 70-kDa heat shock protein (HSP 70) is associated with thermotolerance and survival from many other types of stress. This investigation studied the pharmacological induction of HSP 68 (HSP 68 is the rat homolog of human HSP 70) by 1,10-phenanthroline in cultured rat astrocytes under conditions that activated heat shock transcription factor-1 without inducing HSP 68 synthesis. Two conditions that activate heat shock transcription factor-1 and promote its binding to the heat shock element without subsequent transcription of HSP 68 mRNA, intracellular acidosis and exposure to salicylate, showed synthesis of HSP 68 when 1,10-phenanthroline was added to culture medium after the activation of heat shock transcription factor-1. 1,10-phenanthroline mimicked heat shock by inducing HSP 68 mRNA and protein under both conditions. 1,10-phenanthroline added alone to culture medium did not induce the synthesis of HSP 68 or activate heat shock transcription factor-1. These findings strongly suggest a multistep activation for HSP 68 synthesis and also demonstrate that the synthesis of HSP 68 can be pharmacologically regulated.