Heat shock response and thermal resistance in cultured human retinal pigment epithelium

The heat shock response was examined in cultured human retinal pigment epithelium (RPE) using indirect immunofluorescence. Mild head shock (39.5-40 degrees C for 1 hr) caused no changes in cell morphology and cells continued to produce the intermediate filament proteins, cytokeratin (keratin) and vimentin. In addition, cells subjected to mild heat shock demonstrated the presence of a heat shock protein (HSP-90). After severe heat shock (45.5-46 degrees C for 1 hr) most cells showed marked morphological changes and, in addition, HSP-90 and/or stress-induced 40 kDa protein production was significantly enhanced. The expression of vimentin was relatively well preserved whereas that of keratin was markedly reduced. When the more severe grade of heat shock was preceded by mild heat shock 20-24 hr earlier, the subsequent severe heat shock resulted in less marked morphological change than in cells not preconditioned and, in addition, the expression of both vimentin and keratin was relatively well preserved. Mildly heat shocked cells appeared to gain thermal resistance supporting the theory that the concomitant synthetic capacity for HSP and normal cellular proteins contributes to thermal resistance. In doubly heat shocked cells, however, HSP-90 expression was not enhanced. The discrepancy between the expression of HSP and thermal resistance is discussed.