Relationship between heat-shock protein synthesis and thermotolerance in rainbow trout fibroblasts

The role of heat-shock protein synthesis in the development of thermotolerance by rainbow trout fibroblasts was examined. During the first 6 h after being shifted from 22 degrees C to 28 degrees C, cells of the rainbow trout fibroblast line, RTG-2, rapidly synthesized the major heat-shock proteins (hsps), hsps 87, 70 and 27, and developed tolerance to 32 degrees C. After 24 h at 28 degrees C hsp synthesis was drastically reduced but thermotolerance was maintained. If these thermotolerant cells were shifted to 32 degrees C, hsp synthesis continued at a very low level, but if they were subsequently returned to 22 degrees C, synthesis of hsps 70 and 27 was induced again. The addition of actinomycin D during the first 6 h at 28 degrees C prevented hsp synthesis and the development of thermotolerance. The presence of actinomycin D during the incubation of thermotolerant cultures at 32 degrees C blocked the reinitiation of hsps synthesis at 22 degrees C but had no effect on survival. Therefore, the hsps that accumulated at 28 degrees C were sufficient to allow cells to survive a subsequent thermal stress at 32 degrees C.