Heat shock-induced acquisition of thermotolerance at the levels of cell survival and translation in Xenopus A6 kidney epithelial cells

In this study we have investigated the acquisition of thermotolerance in a Xenopus laevis kidney A6 epithelial cell line at both the level of cell sur vival and translation. In cell survival studies, A6 cells were incubated at temperatures ranging from 22 to 35 degrees C for 2 h followed by a thermal challenge at 39 degrees C for 2 h and a recovery period at 22 degrees C fo r 24 h. Optimal acquisition of thermotolerance occurred at 33 degrees C. Fo r example, exposure of A6 cells to 39 degrees C for 2 h resulted in only 3. 4% survival of the cells whereas prior exposure to 33 degrees C for 2 h enh anced the survival rate to 69%. This state of thermotolerance in A6 cells w as detectable after 1 h at 33 degrees C and was maintained even after 18 h of incubation. Cycloheximide inhibited the acquisition of thermotolerance a t 33 degrees C suggesting the requirement for ongoing protein synthesis. Th e optimal temperature for the acquisition of translational thermotolerance also occurred at 33 degrees C. Treatment of A6 cells at 39 degrees C for 2 h resulted in an inhibition of labeled amino acid incorporation into protei n which recovered to approximately 14% of control after 19 h at 22 degrees C whereas cells treated at 33 degrees C for 2 h prior to the thermal challe nge recovered to 58% of control levels. These translationally thermotoleran t cells displayed relatively high levels of the heat shock proteins hsp30, hsp70, and hsp90 compared to pretreatment at 22, 28, 30, or 35 degrees C. T hese studies demonstrate that Xenopus A6 cells can acquire a state of therm otolerance and that it is correlated with the synthesis of heat shock prote ins.