Implication of PBP74/mortalin/GRP75 in the radio-adaptive response

Purpose : To investigate the relationship between expression of the human peptide-binding protein PBP74 and the occurrence of an adaptive response to ionizing radiation. Materials and methods : Human tumour cell lines HT29 and MCF-7 were transfected with a PBP74 or PBP74 antisense construct. For demonstration of an adaptive response, cells lines were irradiated with a conditioning dose of 0.25 Gy cobalt-60 γ-rays followed by a second dose of 4.0 Gy after an interval of 4.5 h. Response was measured in terms of clonogenic survival. Results : Transfection of a PBP74 plasmid caused transient overexpression of PBP74 mRNA in both cell lines. The optimal dose for the induction of PBP74 in the cell lines investigated was 0.1-0.25Gy and PBP74 induction occurred within 30 min of irradiation. For both cell lines, the adaptive response was repressed when cells were transfected with the anti-PBP plasmid. However, the converse, an enhancement of the adaptive response in cell lines transfected with the PBP74 construct, was seen only for HT29 cells under certain experimental conditions. Conclusions : The results support the view that while PBP74 is necessary to the adaptive response, it may not by itself be sufficient for the adaptive response to occur.