Jlr. Roti et N. Turkel, HEAT-SHOCK-INDUCED CHANGES IN NUCLEAR-PROTEIN AND CELL-KILLING IN THERMOTOLERANT HELA-CELLS, Radiation research, 138(2), 1994, pp. 286-290
The correlation between the protein content of nuclei and heat-induced
cell killing was determined for HeLa cells with various levels of the
rmotolerance. Thermotolerance was induced by heating cells at 45 degre
es C for 15 or 30 min and then incubating them at 37 degrees C for 5 o
r 24 h. This procedure resulted in four different levels of thermotole
rance requiring up to 5 h of heat at 45 degrees C to kill more than 90
% of the most resistant cells. Upon exposure to 45 degrees C, the incr
ease in the protein content of isolated nuclei was proportionally less
for thermotolerant cells. The difference between the initial increase
in nuclear protein content for normal and thermotolerant cells was re
latively small for shorter heating times but became clearly evident fo
r longer heating exposures. The correlations between cell killing and
nuclear protein content were not statistically different from controls
for any of the various levels of thermotolerance. The correlation was
measured over survival levels below 0.1 in thermotolerant cells. Beca
use thermotolerant HeLa cells are very resistant to heat, previous stu
dies had not tested the correlation to survival levels below a half-de
cade of cell killing. These results should resolve some of the conflic
ting observations reported in the literature and are consistent with t
he suggestion that heat-induced changes in binding of nuclear protein
play a key role in the lethal effects of hyperthermia.