THE JUN KINASE STRESS-ACTIVATED PROTEIN-KINASE PATHWAY FUNCTIONS TO REGULATE DNA-REPAIR AND INHIBITION OF THE PATHWAY SENSITIZES TUMOR-CELLS TO CISPLATIN

We have studied the role of Jun/stress-activated protein kinase (JNK/S APK) pathway in DNA repair and cisplatin resistance in T98G glioblasto ma cells. JUN/SAPK is activated by DNA damage and phosphorylates serin es 63 and 73 in the N-terminal domain of c-Jun, which is known to incr ease its transactivation properties, We show that treatment of T98G gl ioblastoma cells with cisplatin but not the transplatin isomer activat es JNK/SAPK about 10-fold, T98G cells, which are highly resistent to c isplatin (IC50 = 140 +/- 13 mu M), modified to express a nonphosphoryl atable dominant negative c-Jun (termed dnJun) exhibit decreased viabil ity following treatment with cisplatin, but not transplatin, in propor tion (r(Pearson) = 0.98) to the level of dnJun expressed leading to a 7-fold decreased IC50. Similar effects are observed in U87 cells, PC-3 cells, and MCF-7 cells, as well as in T98G cells modified to express TAM-67, a known inhibitor of c-Jun function. In contrast, no sensitiza tion effect was observed in cells modified to express wildtype c-Jun, Furthermore, through quantitative polymerase chain reaction-stop assay s, we show that dnJun expressing cells were inhibited in repair of cis platin adducts (p = 0.55), whereas repair is readily detectable (p = 0 .003) in parental cells. These observations indicate that the JNK/SAPK pathway is activated by cisplatin-induced DNA damage and that this re sponse is required for DNA repair and viability following cisplatin tr eatment, Regulation of DNA repair following genotoxic stress may be a normal physiological role of the JNK/SAPK pathway.