Ternary Complex Factor-Serum Response Factor Complex-Regulated Gene Activity Is Required for Cellular Proliferation and Inhibition of Apoptotic Cell Death

Abstract

Members of the ternary complex factor (TCF) subfamily of the ETS-domain transcription factors are activated through phosphorylation by mitogen-activated protein kinases (MAPKs) in response to a variety of mitogenic and stress stimuli. The TCFs bind and activate serum response elements (SREs) in the promoters of target genes in a ternary complex with a second transcription factor, serum response factor (SRF). The association of TCFs with SREs within immediate-early gene promoters is suggestive of a role for the ternary TCF-SRF complex in promoting cell cycle entry and proliferation in response to mitogenic signaling. Here we have investigated the downstream gene regulatory and phenotypic effects of inhibiting the activity of genes regulated by TCFs by expressing a dominantly acting repressive form of the TCF, Elk-1. Inhibition of ternary complex activity leads to the downregulation of several immediate-early genes. Furthermore, blocking TCFmediated gene expression leads to growth arrest and triggers apoptosis. By using mutant Elk-1 alleles, we demonstrated that these effects are via an SRF-dependent mechanism. The antiapoptotic gene Mcl-1 is identified as a key target for the TCF-SRF complex in this system. Thus, our data confirm a role for TCF-SRF-regulated gene activity in regulating proliferation and provide further evidence to indicate a role in protecting cells from apoptotic cell death.Elk-1 is a member of the ternary complex factor (TCF) subfamily of ETS-domain transcription factors (reviewed in references 46 and 50). In mammals there are two other TCFs, SAP-1 and SAP-2/ERP/Net. These proteins are characterized by their ability to form ternary complexes on target promoters in conjunction with the MADS-box protein serum response factor (SRF). The TCFs share four domains, the ETS DNAbinding domain, the B-box, the D-domain, and the C-domain. SAP-2/Net contains additional regions that impart repressive properties (9, 29). The D-and C-domains constitute the regulatory part of Elk-1 and other TCFs. The D-domain acts as a docking site for mitogen-activated protein kinases (MAPKs) (reviewed in references 15 and 49). These docked kinases can then phosphorylate residues in the C-domain, which constitutes the transcriptional activation domain (TAD). Phosphorylation of the TAD leads to elevation of the transactivation potential of the TCFs and also enhances ternary complex formation (reviewed in references 46, 50, 54, and 58). The TCFs can be phosphorylated by members of all three of the major MAPK pathways present in mammals: ERK, JNK, and p38 (reviewed in references 46, 50, and 58). The ERK MAPK pathway predominantly transmits mitogenic and differentiation stimuli, whereas the JNK and p38 MAPK pathways primarily transduce stress and cytokine stimuli to the nucleus (reviewed in reference 41). The TCFs therefore play a pivotal role in transducing extracellular stimuli into alterations in gene expression in the nucleus.The B-box of the TCFs is required for ternary complex formation (11,23,55) and mediates protein-prote...

Impact of Phospho-ELK-1 Expression in Enterocytes in Biodosimetry after Low-dose Irradiation

“…ELK-1 is a component of the ternary complex that binds the serum response element (SRE) in response to serum 11 . ELK-1 is inducible by pro-inflammatory cytokine cascade member Interleukine-1 beta 12 and growth factors such as vascular endothelial growth factor 13 and epidermal growth factor 14 , which are up-regulated after irradiation in vivo.…”

“…An early ELK-1 activation after radiation-induced DNA damage leads to higher cell proliferation and higher resistency to apoptosis probably via action of antiapoptotic MCL-1 11 , whereas persisting activation has link to G2/M cell cycle arrest and/or apoptosis. Suzuki 4 , et al sugested that apoptosis seen in MAPK active condition after irradiation is due to p53 accumulation, which was not detected at doses up to 0.5 Gy, while between 1.0 Gy and 6.0 Gy, the level of p53 protein increased in a dose-dependent manner.…”

Signal-induced functions of the transcription factor TFII-I

“…Lack of this constraint together with rapid signal-induced transcriptional response also necessitates an unusual specificity at the level of promoter occupancy. The promoter region contains binding sites for several transcription factors, some of which are constitutively active in the nucleus while others are signal induced (7)(8)(9)(10)(11)(12)(13)(14)(15). Despite the fact that c-fos has served as a paradigm for understanding signal-induced transcription for two decades, it is still unclear as to how various signaling pathways converge on this gene simultaneously.…”

“…Despite the fact that c-fos has served as a paradigm for understanding signal-induced transcription for two decades, it is still unclear as to how various signaling pathways converge on this gene simultaneously. For example, the transcriptional activation of c-fos is dependent on both the Ras and Rho signaling pathways (7)(8)(9)(10)(11)(12)(13)(14)(15)(16). While Ras and Rho belong to the GTP-binding protein (G-protein) super family, the Ras pathway involves Raf/Mek1/ERK activation and Rho signaling predominantly involves cytoskeletal reorganization (17)(18)(19)(20).…”

“…Growth factor induced transcriptional activation of the immediate early (IE) c-fos protooncogene is essential for quiescent cells to re-enter cell cycle and eventually undergo proliferation (7)(8)(9)(10)(11)(12). The c-fos gene expression is virtually undetectable upon serum starvation but it is elevated within minutes upon growth factor stimulation.…”