Abstract
The 78-kDa glucose-regulated protein (GRP78) is known as an ER stress-induced molecular chaperone. There has been little information about the roles of GRP78 in response to UVC in mammalian cells. In this annual meeting last year, we found that GRP78 is involved in the resistance of human cells to UVC using RSa cells with down-regulation of GRP78 expression by transfection of antisense cDNA for GRP78. In the present study, we investigated the mechanisms underlying the GRP78-involved UVC resistance. To estimate the DNA repair capacity of cells, the amounts of damaged DNAs in vivo were measured in the transfected cells after UVC irradiation with the specific antibodies against the damages. In addition, repair activities in whole cell extracts from the cells were measured by in vitro repair synthesis assay using UVC-irradiated plasmid as a substrate. We found that the cells with down-regulation of GRP78 expression showed lower ability to repair the damaged DNA in vivo and in vitro than the vector control cells. Furthermore, the antisense-cDNA transfected cells also showed higher sensitivity to cisplatin, by which the DNA damage induced is primarily repaired by nucleotide excision repair, like UVC-induced DNA damage. These results suggest that GRP78 has a protective role against UVC-induced cell death possibly via functioning in nucleotide excision repair, at least in the human RSa cells tested.
