Cell Biology

Promoting the Apoptotic Activity of c-Jun

Science Signaling  06 Nov 2012:
Vol. 5, Issue 249, pp. ec288
DOI: 10.1126/scisignal.2003753

The transcription factors c-Jun and AATF (apoptosis-antagonizing transcription factor) both function in responding to cellular stress, and both have diverse functions and can promote responses ranging from cell survival to cell death. Ferraris et al. identified AATF as promoting the apoptotic activity of c-Jun. Compared with controls, overexpression of AATF in mouse embryonic fibroblasts (MEFs) and human embryonic kidney (HEK) 293 cells increased the number of detached and dead cells in response to ultraviolet (UV) irradiation and increased the abundance of transcripts of genes, such as the one encoding tumor necrosis factor–α (TNF-α), that are targeted by c-Jun. Flow cytometry revealed an increase in the number of annexin V-positive wild-type MEFs, but not c-Jun knockouts, and an increase in the amount of activated caspase-3 in wild-type MEFs, in response to irradiation when AATF was overexpressed. Western blots of lysates from UV-irradiated HEK293 cells revealed that overexpression of AATF, but not the AP-1 transcription factor ATF-2, increased the abundance of phosphorylated c-Jun, a posttranslational event that is required for activity; this persisted for up to 3 days, which may enable prolonged c-Jun activation or poise c-Jun for a rapid response. Knockdown of AATF decreased the abundance of phosphorylated c-Jun in lysates from irradiated HEK293 cells and reduced the abundance of TNF-α transcripts. In nonirradiated HEK293 cells, AATF was localized to the nucleolus and c-Jun was in the nucleoplasm, but upon irradiation, AATF and c-Jun colocalized in the nucleoplasm. AATF and c-Jun were also coimmunoprecipitated in lysates from irradiated cells. Thus, AATF appears to promote the apoptotic response to DNA damage by associating with and enhancing c-Jun activity.

S. E. Ferraris, K. Isoniemi, E. Torvaldson, J. Anckar, J. Westermarck, J. E. Eriksson, Nucleolar AATF regulates c-Jun–mediated apoptosis. Mol. Biol. Cell 23, 4323–4332 (2012). [Abstract] [Full Text]