HSP27 and HSP70 increase the survival of WEHI-S cells exposed to hyperthermia.

Exposure of cells to hyperthermia and various other stress conditions induces synthesis of a small group of proteins, the heat shock proteins (HSPs). Synthesis of HSPs correlates with the development of thermotolerance, but little is known about the role of individual HSPs in this phenomenon. Using stably transfected WEHI-S murine fibrosarcoma cells we show that overexpression of either HSP27 or HSP70 clearly protects these cells from the toxic effect of elevated temperatures. Moreover, a clone expressing HSP70 mRNA in antisense orientation, and thereby reduced levels of endogenous HSP70 protein, is more thermosensitive than transfection control cells. Using indirect immunofluorescence we show that following heat treatment exogeneous HSP27 and HSP70 are relocated from the cytoplasm to the nucleus and nucleoli respectively. A similar pattern of localization was seen for the endogenous HSPs. Taken together, these results indicate that both HSP27 and HSP70 protect cells from heat mediated killing.