Thermosensitization of murine FM3A cells by transient incubation at low culture temperatures.

We show that when murine FM3A cells maintained at 37 degrees C were incubated at low culture temperatures between 24 degrees and 33 degrees C for 12-24 h, they became thermosensitive as compared to those incubated at 37 degrees C. The synthesis and accumulation of inducible HSP70 and constitutive HSC70 by heat shock decreased in cells incubated at 33 degrees C, whereas no such decreases were found in cells incubated at 37 degrees C. The accumulation of HSP105 because of heat shock also decreased in cells incubated at 33 degrees C. The decreased inducibility of HSP70, HSC70, and HSP105 by heat shock may in part be responsible for the increase seen in the thermosensitivity of the cells. Furthermore, the cellular concentration of HSP105 decreased in cells incubated at 33 degrees C but not in those incubated at 37 degrees C, whereas the concentration of HSC70 did not change at all in cells incubated at either temperature. The cellular content of HSP105, but not of HSC70, therefore may be a good indicator of the thermoresistant state of cells.