ATF2 confers radiation resistance to human melanoma cells

We have previously identified a U.V.-response element (URE; TGACAACA) and its bound proteins, members of the AP1 and ATF transcription factor families, in melanoma cells. Using a mutant form of cylic AMP response element binding (CREB), we found that CREB-associated-URE-bound proteins conferred characteristic melanoma phenotypes, including radiation resistance (Oncogene 12: 2223, 1996). In the present study we sought to determine which of the CREB-associated proteins confers radiation resistance on human melanoma cells. To this end we purified and identified via microsequencing ATF2 as a major URE- bound and CREB-associated protein in MeWo cells--a late stage human melanoma cell line. To determine the contribution of ATF2 to radiation resistance, MeWo cells were transfected with ATF2 cDNA lacking the trans-activation domain (ATF2(delta1-195)). MeWo cells that stably express ATF2(delta1-195) showed weaker transcriptional activities and an altered pattern of homo/hetero dimers. ATF2(delta1-195) clones exhibited up to tenfold lower resistance to irradiation by either U.V. or X-rays. The degree of resistance to radiation in the ATF2(delta1-195)-expressing clones could be increased upon transient transfection with ATF2(wt), but not with phosphorylation-defective mutant ATF2(69,71). Similarly, transfection of ATF2(wt) to WM3211, an early stage human melanoma cells line, increased resistance to radiation. Finally, changes elicited through ATF2(delta1-195) also led to reduced drug resistance, as shown for MMC, araC and cisplatinum. Our results suggest that ATF2 is a regulator of radiation and drug resistance in melanomas, and that tumor targeted ATF2 modulators may be useful sensitizers in the treatment of tumors of this type.