Abstract
Ultraviolet light (UV), a strong mutagen and carcinogen, damages DNA directly and stimulates signal molecules including p38 and JNK. However, the role of UV-induced signals in DNA repair and mutagenesis remains to be elucidated. In this thesis, we investigated the effect of p38 and JNK on UV-induced cytotoxicity, mutagenicity, DNA damage and repair using cells containing dominant negative forms of p38, JNK1 or JNK2 (p38DN, JNK1DN or JNK2DN) that were derived from a human lung adenocarcinoma cell line, CL3. CL3-p38DN cells that stably expressing p38DN were less sensitive than the control CL3-pB cells to stimulate p38 phosphorylation and JNK kinase activity in response to UV, although the endogenous level of phosphorylated-p38 was higher in CL3-p38DN cells than in the control cells. The results suggest that p38DN may be associated with MKK4, the upstream activator of both p38 and JNK, thereby block these signal cascades. The level of phosphorylated-ERK was also increased slightly by UV in CL3-p38DN cells but not in the control cells. The UV-induced cytotoxicity and hprt mutations observed in CL3-p38DN cells were markedly lower than those observed in the control CL3-pB cells using assays for the colony forming ability and the resistance to 6-thioguanine, respectively. However, similar levels of UV-induced DNA damage and their repair efficiency were observed in CL3-p38DN and the control cells when determined using a quantitative polymerase-chain-reaction protocol. These results suggest that the declined cytotoxicity and mutation frequency observed in UV-treated CL3-p38DN cells are not due to a reduced amount of DNA lesions. By contrast, the JNK kinase activity, the phosphorylated-p38 and -ERK, and the cytotoxicity induced by UV were similar in CL3-JNK1DN and CL3-JNK2DN cells containing stably expressed JNK1DN and JNK2DN when compared with the control CL3-pLNCX cells. The hprt mutations induced by low dosages of UV (5-10 J/m2) in CL3-JNK2DN cells were significantly higher than those observed in the CL3-JNK1DN or the control cells. Whereas, UV at 20 J/m2 induced lower hprt mutations in CL3-JNK2DN than the CL3-JNK1DN or the control cells. The results suggest that the UV-induced JNK2 but not JNK1 may interfere mutagenesis.