Transcriptional switch by activating transcription factor 2-derived peptide sensitizes melanoma cells to apoptosis and inhibits their tumorigenicity

The notorious resistance of melanoma cells to drug treatment can be overcome by expression of a 50-aa peptide derived from activating transcription factor 2 (ATF2^50-100). Here we demonstrate that ATF2 ^50-100 induced apoptosis by sequestering ATF2 to the cytoplasm, thereby inhibiting its transcriptional activities. Furthermore, ATF2 ^50-100 binds to c-Jun N-terminal kinase (JNK) and increases its activity. Mutation within ATF2^50-100 that impairs association with JNK and the inhibition of JNK or c-Jun expression by RNA interference (RNAi) reduces the degree of ATF2^50-100-induced apoptosis. In contrast, TAM67, a dominant negative of the Jun family of transcription factors, or JunD RNAi attenuates sensitization of melanoma cells expressing ATF2 ^50-100 to apoptosis after treatment with anisomycin, which is used as a model drug. Mutations within the JNK binding region of ATF2 ^50-100 or expression of TAM67 or JunD RNAi attenuates inhibition of melanoma's tumorigenicity by ATF2^50-100. We conclude that inhibition of ATF2 in concert with increased JNK/Jun and JunD activities is central for the sensitization of melanoma cells to apoptosis and inhibition of their tumorigenicity.