Role of ER stress sensor Bip/GRP78 in protection of genome stability from DNA damaging stresses

与分子伴侣在哺乳动物细胞对dna损伤应激反应中的作用的广泛研究相比，关于内质网（ER）应激诱导的分子伴侣Bip/GRP78的作用的报道很少。为了研究Bip/GRP78是否参与了对UVC（主要是波长254 nm）的抵抗，我们通过交换含有Bip/GRP反义cDNA的人RSa细胞，建立了Bip/GRP78下调的人细胞。我们发现转染的细胞比单独转染载体的对照细胞对uvc诱导的细胞死亡表现出更高的敏感性。在反义cdna转染的细胞中，体内对两种主要类型的uvc损伤DNA（胸腺嘧啶二聚体和（6-4）光产物）的去除能力和体外修复uvc照射质粒的全细胞提取物的DNA合成活性显著降低。此外，反义cdna转染的细胞对顺铂诱导的细胞死亡的敏感性也略高于对照细胞。顺铂诱导的DNA损伤主要通过核苷酸切除修复，如uvc诱导的DNA损伤。目前的结果表明，至少在测试的人类RSa细胞中，Bip/GRP78可能通过核苷酸切除修复对uvc诱导的细胞死亡起保护作用。

In contrast to extensive studies on the roles of molecular chaperones in mammalian cell responses to DNA-damaging stresses, there are only a few reports about the roles of Bip/GRP78, an endoplasmic reticulum(ER) stress-induced molecular chaperone. To investigate whether Bip/GRP78 is involved in resistance to a DNA-damaging agent, UVC (principally 254 nm in wavelength), we established human cells with down-regulation of Bip/GRP78 by transaction of human RSa cells with antisense cDNA for Bip/GRP. We found that the transfected cells showed higher sensitivity to UVC-induced cell death than control cells transfected with the vector alone. In the antisense-cDNA transfected cells, the removal capacities of the two major types of UVC-damaged DNA (thymine dimers and (6-4) photoproducts) in vivo and DNA synthesis activity of whole cell extracts to repair UVC-irradiated plasmids in vitro were remarkably decreased compared with those in the control cells. Furthermore, the antisense-cDNA transfected cells also showed slightly higher sensitivity to cisplatin-induced cell death than the control cells. Cisplatin-induced DNA damage is primarily repaired by nucleotide excision repair, like UVC-induced DNA damage. The present results suggest that Bip/GRP78 plays a protective role against UVC-induced cell death possibly via nucleotide excision repair, at least in the human RSa cells tested.