GRP78 confers radioresistance by increasing radiation-induced DNA double-strand break repair and cell autophagy and the subsequent inhibition of apoptosis.

<p>(A) Silencing GRP78 inhibited the radiation-induced (5 Gy, 12 h) expression of the DNA double-strand break repair protein DNA-PK and increased the phosphorylation level of ATM. Silencing GRP78 also inhibited the radiation-induced expression of the autophagy-related proteins LC3B (LC3B-II/β-actin) and Atg16L1 and increased the expression of the apoptosis marker protein cleaved caspase-3 and cleaved PARP. (B) Immunofluorescence studies showed that after oropharyngeal carcinoma cells received 5 Gy radiation for 1 h, the γ-H2AX foci in nucleus increased (the blue background indicates the cell nucleus, and light red dots indicate γ-H2AX foci). In addition, the effect of radiation after GRP78 silencing was more evident than that of simple radiation. (C) Immunofluorescence studies by LC3B staining also showed autophagy regions in the nucleus after 5 Gy radiation for 1 h (the blue background indicates the cell nucleus, and light green dots indicate LC3B foci), which was reversed after GRP78 silencing. The oropharyngeal carcinoma cells were pretreated with 20 μmol/L Ly294002 or 5 mmol/L 3-MA for 12 h. The cells were then treated with 5 Gy of radiation. Compared with the IR group, *P < 0.05. For (A), bands were quantified using ImageJ software and were normalized to a loading control. Fold changes are shown compared with the negative control lane without radiation. N/A = not applicable.