INDUCTION OF 72-KDA INDUCIBLE HEAT-SHOCK-PROTEIN (HSP72) IN CULTURED RAT ASTROCYTES AFTER ENERGY DEPLETION

Protein synthesis is important in the readaptive processes for culture d astrocytes after hypoxia and subsequent reoxygenation. We have ident ified 72-kDa inducible heat shock protein (HSP72) as a major stress pr otein in reoxygenated astrocytes. To assess the mechanism for reoxygen ation-mediated induction of HSP72, a reporter gene that consists of a human HSP promoter fused to the luciferase gene was transfected into c ultured astrocytes. Analysis of cellular energy nucleotides showed an increase of the ADP/ATP ratio after reoxygenation, which synchronized with activation of the HSP promoter. Activation of the HSP promoter wa s also observed after an addition of iodoacetic acid to hypoxic astroc ytes, which reached the maximum when the ADP/ATP ratio reached 50%, bu t further decline in the energy profile caused inactivation of this pr omoter. Inhibition of protein synthesis after reoxygenation resulted i n temporary restoration of the energy profile and suppression of the D NA binding activity of the heat shock factor. Addition of quercetin gr eatly decreased the [H-3]leucine incorporation in the polysome fractio n without any effect on the mature mRNA formation. These data suggest that the energy depletion in reoxygenation triggers induction of HSP72 after reoxygenation, which may act as a pivotal mediator in the stres s response of reoxygenated astrocytes by facilitating protein synthesi s.