Inhibition of apoptosis by ATFx: a novel role for a member of the ATF/CREB family of mammalian bZIP transcription factors.

The mammalian ATF/CREB family of transcription factors comprises a large group of basic-region leucine zipper (bZIP) proteins whose members mediate diverse transcriptional regulatory functions. Here we report that expression of a specific mouse ATF gene, ATFx, is down-regulated in a variety of cells undergoing apoptosis following growth factor deprivation. When stably expressed in an interleukin 3 (IL-3)-dependent cell line, ATFx suppresses apoptosis resulting from cytokine deprivation. Conversely, a dominant-negative ATFx mutant induces apoptosis of cells cultured in the presence of growth factors. We also show that 24p3, a secreted lipocalin that induces apoptosis when added to hematopoietic cells, represses ATFx expression. However, constitutive expression of ATFx renders cells resistant to 24p3-mediated apoptosis. Collectively, our results indicate that ATFx is an anti-apoptotic factor, a novel role for an ATF protein.