HEAT INACTIVATION OF KU AUTOANTIGEN - POSSIBLE ROLE IN HYPERTHERMIC RADIOSENSITIZATION

Heat shock prior, during, or immediately after ionizing radiation syne rgistically increases cell killing, a phenomenon termed hyperthermic r adiosensitization, Recently, we have shown a constitutive DNA-binding factor in rodent cells that is inactivated by heat shock to be identic al to Ku autoantigen. Ku, consisting of an M-r 70,000 (Ku70) and an M- r 86,000 (Ku80) subunit, is a heterodimeric nuclear protein and is the DNA-binding regulatory component of the mammalian DNA-dependent prote in kinase DNA-PK. Recent genetic and biochemical studies indicate the involvement of Ku and DNA-PK in DNA double-strand break repair and V(D )J recombination. On the basis of these findings, we propose that heat -induced loss of the DNA-binding activity of Ku may lead to hypertherm ic radiosensitization, To test this hypothesis, we examined and compar ed the DNA-binding activity of Ku, the DNA-PK kinase activity, and hyp erthermic radiosensitization in rodent cells immediately after heat sh ock and during post-heat shock recovery at 37 degrees C. Our results s how that the heat-induced loss of Ku-DNA binding activity correlates w ell with an increased radiosensitivity of the heat-shocked cells, and furthermore, the loss of synergistic interaction between heat and radi ation parallels the recovery of the DNA-binding activity of Ku. On the other hand, the heat-induced decrease of DNA-PK activity did not corr elate with hyperthermic radiosensitization. Our data, for the first ti me, provide evidence for a role of Ku protein in modulating the cellul ar response to combined treatments of heat shock and ionizing radiatio n.