[Preirradiation heat shock protein induction increases cellular radioresistance]

It was studied how does the transcriptional stress response and the heat shock protein (HSP) overexpression affect cellular radioresistance. For this purpose, normal murine fibroblasts and fibroblasts devoid of HSF1-gene (HSF1 is a transcriptional factor initiating stress-responsive HSP expression) were compared. Some cell samples were infected with specific vectors for expression of the constitutively active (mutant) HSF1 or individual HSP (HSP70, HSP56, HSP27). It was found that heat stress (43 degrees C, 30 min) increased the HSP level in normal fibroblasts and improved their survival following exposure to gamma-radiation, with both the effects being suppressed by quercetin (an inhibitor of HSF1-mediated HSP induction). In the HSF1-deprived cells, heat stress caused neither the up-regulation of HSP levels nor the enhancement of radioresistance, although both the effects were well manifested following the active HSF1 expression in those cells. The vector-induced over-expression of HSP70 or/and HSP27 equally enhanced the radioresistance in both cell cultures infected.