Activating transcription factor 2-derived peptides alter resistance of human tumor cell lines to ultraviolet irradiation and chemical treatment.

Activating transcription factor 2 (ATF2) and its kinase, p38, play an important role in the resistance of melanoma to radiation and chemotherapy. Whereas ATF2 up-regulates the expression of tumor necrosis factor alpha, which serves as a survival factor in late-stage melanoma cells, p38 attenuates Fas expression via inhibition of nuclear factor-kappaB. We investigated whether ATF2-derived peptides could be used to alter the sensitivity of human melanoma cells to radiation and chemical treatment. Of four 50-amino acid peptides tested, the peptide spanning amino acids 50-100 elicited the most efficient increase in the sensitivity of human melanoma cells to UV radiation or treatment by mitomycin C, Adriamycin, and verapamil, or UCN-01, as revealed by apoptosis assays. Sensitization by ATF2 peptide was also observed in the MCF7 human breast cancer cells but not in early-stage melanoma or melanocytes, or in in vitro-transformed 293T cells. When combined with an inhibitor of p38 catalytic activity, cells expressing amino acids 50-100 of ATF2 exhibited an increase in the degree of programmed cell death, indicating that combined targeting of ATF2 and p38 kinases is sufficient to induce apoptosis in late-stage melanoma cells. The ability of the peptide to increase apoptosis coincided with increased cell surface expression of Fas, which is the primary death-signaling cascade in these late-stage melanoma cells. Overall, our studies identified a critical domain of ATF2 that may be used to sensitize tumor cells to radiation and chemical treatment-induced apoptosis and that can induce apoptosis when combined with inhibition of ATF2 kinase, p38.