Ultraviolet light-induced DNA damage triggers apoptosis in nucleotide excision repair-deficient cells via Bcl-2 decline and caspase-3/-8 activation

Ultraviolet (UV) light is a potent mutagenic and genotoxic agent. Whereas D NA damage induced by UV light is known to be responsible for UV-induced gen otoxicity, its role in triggering apoptosis is still unclear. We addressed this issue by comparing nucleotide excision repair (NER) deficient 27-1 and 43-3B Chinese hamster (CHO) cells with the corresponding wild-type and ERC C-1 complemented cells. It is shown that NER deficient cells are dramatical ly hypersensitive to UV-C induced apoptosis, indicating that DNA damage is the major stimulus for the apoptotic response. Apoptosis triggered by UV-C induced DNA damage is related to caspase- and proteosome-dependent degradat ion of Bcl-2 protein. The expression of other members of the Bcl-2 family s uch as Bax, Bcl-x(L) and Bak were not affected. Bcl-2 decline is causally i nvolved in UV-C induced apoptosis since overexpression of Bcl-2 protected N ER deficient cells against apoptosis. We also demonstrate that caspase-8, c aspase-9 and caspase-3 are activated and PARP is cleaved in response to unr epaired UV-C induced DNA damage. Caspase-8 activation occurred independentl y of CD95 receptor activation since CD95R/ FasR and CD95L/FasL were not alt ered in expression, and transfection of transdominant negative FADD failed to block apoptosis. Overall, the data demonstrate that UV-C induced non-rep aired DNA damage triggers apoptosis in NER deficient fibroblasts involving components of the intrinsic mitochondrial damage pathway.