ATF3 and stress responses

Abstract

The purpose of this review is to discuss ATF3, a member of the ATF/CREB family of transcription factors, and its roles in stress responses. In the introduction, we briefly describe the ATF/CREB family, which contains more than 10 proteins with the basic region-leucine zipper (bZip) DNA binding domain. We summarize their DNA binding and heterodimer formation with other bZip proteins, and discuss the nomenclature of these proteins. Over the years, identical or homologous cDNA clones have been isolated by different laboratories and given different names. We group these proteins into subgroups according to their amino acid similarity; we also list the alternative names for each member, and clarify some potential confusion in the nomenclature of this family of proteins. We then focus on ATF3 and its potential roles in stress responses. We review the evidence that the mRNA level of ATF3 greatly increases when the cells are exposed to stress signals. In animal experiments, the signals include ischemia, ischemia coupled with reperfusion, wounding, axotomy, toxicity, and seizure; in cultured cells, the signals include serum factors, cytokines, genotoxic agents, cell death-inducing agents, and the adenoviral protein E1A. Despite the overwhelming evidence for its induction by stress signals, not much else is known about ATF3. Preliminary results suggest that the JNK/SAPK pathway is involved in the induction of ATF3 by stress signals; in addition, IL-6 and p53 have been demonstrated to be required for the induction of ATF3 under certain conditions. The consequences of inducing ATF3 during stress responses are not clear. Transient transfection and in vitro transcription assays indicate that ATF3 represses transcription as a homodimer; however, ATF3 can activate transcription when coexpressed with its heterodimeric partners or other proteins. Therefore, it is possible that, when induced during stress responses, ATF3 activates some target genes but represses others, depending on the promoter context and cellular context. Even less is understood about the physiological significance of inducing ATF3. We will discuss our preliminary results and some reports by other investigators in this regard.

FIG. 1

Induction of ATF3 by acetaminophen and Fas antibody. (A, B) In situ hybridization assay showing induction of ATF3 in the liver by acetaminophen. Four-week-old male Sprague-Dawley rats were fasted for 42 h and IP injected with saline (A) or 500 mg/kg acetaminophen (B). Two hours later, the animals were sacrificed and the livers were analyzed by in situ hybridization using antisense ATF3 RNA as a probe as described previously (17). The pictures were produced by dark-field photography after radiographic emulsion for 10 days. (C) Reverse transcription coupled with polymerase chain reaction (RT-PCR) assay showing induction of ATF3 by Fas antibody. HL-60 cells (2 × 10⁷) treated with Fas antibody for the indicated time periods (0, 15, or 30 min) were kindly provided by Drs. K. M. Coggeshall and K. Schlottmann. Total RNA was isolated using the Trizol method according to the manufacturer’s instructions (Life Technologies), and 5 μg of RNA was analyzed by RT-PCR to amplify ATF3 mRNA (top band, indicated by arrow) and glyceraldehyde-3-phosphate dehydrogenase mRNA (GAPDH, bottom band). Twenty percent of the PCR products were resolved on a 2% agarose gel and visualized under UV after ethidium bromide staining. The primers are as follows: ATF3 N′-terminal (5′-GCTCTAGAAAAAAAGAGAAGACRGAGTCG-3′), ATF3 C′-terminal (5′-TCTCCAATGCGTTCAGGGTT-3′), GAPDH N′-terminal (5′-CATTGACCTCAACTACATGG-3′), and GAPDH C′-terminal (5′-ACCACCCTGTTGCTGTAGCC-3′). “-RT” indicates a RT-PCR reaction without reverse transcriptase.