Activating transcription factor (ATF) 3 plays a role in determining cell fate and generates a variety of alternatively spliced isoforms in stress response. We have reported previously that splice variant ATF3⌬Zip2, which lacks the leucine zipper region, is induced in response to various stress stimuli. However, its biological function has not been elucidated. By using cells treated with tumor necrosis factor-␣ and actinomycin D or cells overexpressing ATF3⌬Zip2, we showed that ATF3⌬Zip2 sensitizes cells to apoptotic cell death in response to tumor necrosis factor-␣, at least in part through suppressing nuclear factor (NF)-B-dependent transcription of antiapoptotic genes such as cIAP2 and XIAP. ATF3⌬Zip2 interacts with a p65 (RelA)-cofactor complex containing CBP/p300 and HDAC1 at NF-B sites of the proximal promoter region of the cIAP2 gene in vivo and down-regulates the recruitment of CBP/p300. Our study revealed that ATF3⌬Zip2 counteracts anti-apoptotic activity of NF-B, at least in part, by displacing positive cofactor CBP/p300 and provides insight into the mechanism by which ATF3 regulates cell fate through alternative splicing in stress response.

Background: Transcriptional elongation is a rate-limiting step in activation of stress response genes. Results: Optimal expression of stress response regulator ATF3 requires the elongation activity but not the ubiquitination activity of Elongin A. Conclusion: Elongin A plays a key role for the adequate expression of ATF3 in vivo. Significance: RNAPII ubiquitination and transcriptional elongation are independent activities of Elongin A.

Elongin A is a transcription elongation factor that increases the overall rate of mRNA chain elongation by RNA polymerase II. To gain more insight into the physiological functions of Elongin A, we generated Elongin A-deficient mice. Elongin A homozygous mutant (Elongin A À/À ) embryos demonstrated a severely retarded development and died at between days 10.5 and 12.5 of gestation, most likely due to extensive apoptosis. Moreover, mouse embryonic fibroblasts (MEFs) derived from Elongin A À/À embryos exhibited not only increased apoptosis but also senescence-like growth defects accompanied by the activation of p38 MAPK and p53. Knockdown of Elongin A in MEFs by RNA interference also dramatically induced the senescent phenotype. A study using inhibitors of p38 MAPK and p53 and the generation of Elongin A-deficient mice with p53-null background suggests that both the p38 MAPK and p53 pathways are responsible for the induction of senescence-like phenotypes, whereas additional signaling pathways appear to be involved in the mediation of apoptosis in Elongin A À/À cells. Taken together, our results suggest that Elongin A is required for the transcription of genes essential for early embryonic development and downregulation of its activity is tightly associated with cellular senescence. Cell Death and Differentiation (2007) Eukaryotic mRNA synthesis by RNA polymerase II (pol II) is regulated by the concerted action of a set of transcription factors that control the activity of pol II during the initiation and elongation stages of transcription. At least six general transcription factors have been identified in eukaryotic cells and found to promote the selective binding of pol II to promoters and to support the basal level of transcription. 1 In addition, a diverse collection of elongation factors that promote efficient elongation of transcripts by pol II in vitro have also been identified. 2-4 These factors fall into two broad functional classes based on their ability to either reactivate arrested pol II or suppress the transient pausing of pol II. The first class is composed of members of the SII family. 3,5 The second class comprises a collection of elongation factors, including TFIIF, 6 Elongin, 7,8 ELL 9 and CSB, 10 which increase the overall rate of mRNA chain elongation by decreasing the frequency and/or duration of transient pausing of pol II at sites along the DNA template.Elongin was identified as a heterotrimer composed of A, B and C subunits of B770, 118 and 112 amino acids, respectively. 7,8,11,12 Elongin A is the transcriptionally active subunit, whereas Elongins B and C are positive regulatory subunits that can form an isolable Elongin BC subcomplex. 8,13,14 Although the functions of Elongin A in vivo remain largely unclear, Gerber et al. 15 have recently reported that the Drosophila homolog of Elongin A (dEloA) colocalizes with pol II at sites of active transcription on polytene chromosomes, and it also plays a critical role in heat shock gene expression in vivo. 15,16 Moreover, by the RNA interference (...

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Transcriptional elongation factor Elongin A exhibits an activity to repress the temporary pause of RNA polymerase II (RNAPII) on the DNA template. The role of Elongin A in RNAPII transcription in mammalian cells has not, however, been clearly established. In this study, we investigate the function of Elongin A in RNAPII transcription. First, we examined immunoprecipitation and immunostaining. These showed that Elongin A binds to the phosphorylated form of RNAPII (IIO) at both Ser5 and Ser2 and partially colocalized with the RNAPIIO and newly transcribed RNA. Significantly, Western blotting and qRT‐PCR showed that Elongin A was required for the maximal induction of stress response gene ATF3 and p21. ChIP assay showed that Elongin A occupancy was increased on ATF3, p21, c‐Myc and c‐jun genes after doxorubicin treatment. Furthermore, we performed re‐introduction assay of various mutants of Elongin A. It indicated that expressions of ATF3 and p21 gene were dependent on elongation activity of Elongin A. By contrast, polyubiquitination of RNAPII was dependent on ubiqutination activity of Elongin A. Taken together, our data provide the evidence that mammalian Elongin A is involved in the elongation phase of transcription in vivo and plays a crucial role in response to stress stimuli. Furthermore, our data indicated that two activities of Elongin A are independent of one another in response to stress.