Functional interactions between the Forkhead transcription factor FOXK1 and the MADS-box protein SRF

The combinatorial control of gene expression by the association of members of different families of transcription factors is a common theme in eukaryotic transcriptional control. The MADS-box transcription factors SRF and Mcm1 represent paradigms for such regulation through their interaction with numerous partner proteins. For example, in Saccharomyces cerevisiae, Mcm1 interacts with the forkhead transcription factor Fkh2. Here, we identify a novel interaction between SRF and the Forkhead transcription factor FOXK1 in human cells. The importance of this interaction is shown for the regulation of the SRF target genes SM α-actin and PPGB. The binding of FOXK1 to the SM α-actin and PPGB promoters requires the presence of SRF on the promoter. FOXK1 acts as a transcriptional repressor and it represses SM α-actin and PPGB expression. Thus FOXK1 represents an additional member of the growing repertoire of transcription factors that can interact with SRF and modulate the transcriptional output from SRF-regulated promoters

The ERK MAP kinase-PEA3/ETV4-MMP-1 axis is operative in oesophageal adenocarcinoma

<p>Abstract</p> <p>Background</p> <p>Many members of the ETS-domain transcription factor family are important drivers of tumourigenesis. In this context, their activation by Ras-ERK pathway signaling is particularly relevant to the tumourigenic properties of many ETS-domain transcription factors. The PEA3 subfamily of ETS-domain transcription factors have been implicated in tumour metastasis in several different cancers.</p> <p>Results</p> <p>Here, we have studied the expression of the PEA3 subfamily members PEA3/ETV4 and ER81/ETV1 in oesophageal adenocarcinomas and determined their role in oesophageal adenocarcinoma cell function. PEA3 plays an important role in controlling both the proliferation and invasive properties of OE33 oesophageal adenocarcinoma cells. A key target gene is <it>MMP-1</it>. The ERK MAP kinase pathway activates PEA3 subfamily members and also plays a role in these PEA3 controlled events, establishing the ERK-PEA3-MMP-1 axis as important in OE33 cells. PEA3 subfamily members are upregulated in human adenocarcinomas and expression correlates with <it>MMP-1 </it>expression and late stage metastatic disease. Enhanced ERK signaling is also more prevalent in late stage oesophageal adenocarcinomas.</p> <p>Conclusions</p> <p>This study shows that the ERK-PEA3-MMP-1 axis is upregulated in oesophageal adenocarcinoma cells and is a potentially important driver of the metastatic progression of oesophageal adenocarcinomas.</p

A Role for Non-Covalent SUMO Interaction Motifs in Pc2/CBX4 E3 Activity

Background: Modification of proteins by the small ubiquitin like modifier (SUMO) is an essential process in mammalian cells. SUMO is covalently attached to lysines in target proteins via an enzymatic cascade which consists of E1 and E2, SUMO activating and conjugating enzymes. There is also a variable requirement for non-enzymatic E3 adapter like proteins, which can increase the efficiency and specificity of the sumoylation process. In addition to covalent attachment of SUMO to target proteins, specific non-covalent SUMO interaction motifs (SIMs) that are generally short hydrophobic peptide motifs have been identified. Methodology/Principal Findings: Intriguingly, consensus SIMs are present in most SUMO E3s, including the polycomb protein, Pc2/Cbx4. However, a role for SIMs in SUMO E3 activity remains to be shown. We show that Pc2 contains two functional SIMs, both of which contribute to full E3 activity in mammalian cells, and are also required for sumoylation of Pc2 itself. Pc2 forms distinct sub-nuclear foci, termed polycomb bodies, and can recruit partner proteins, such as the corepressor CtBP. We demonstrate that mutation of the SIMs in Pc2 prevents Pc2-dependent CtBP sumoylation, and decreases enrichment of SUMO1 and SUMO2 at polycomb foci. Furthermore, mutational analysis of both SUMO1 and SUMO2 reveals that the SIM-interacting residues of both SUMO isoforms are required for Pc2-mediated sumoylation and localization to polycomb foci

Transcription factors Elk-1 and SRF are engaged in IL1-dependent regulation of ZC3H12A expression

<p>Abstract</p> <p>Background</p> <p>MCPIP is a novel CCCH zinc finger protein described as an RNase engaged in the regulation of immune responses. The regulation of expression of the gene coding for MCPIP - <it>ZC3H12A </it>is poorly explored.</p> <p>Results</p> <p>Here we report that the proinflammatory cytokine IL-1β rapidly induces the synthesis of MCPIP in primary monocyte-derived macrophages and HepG2 cells. This up-regulation takes place through the MAP kinase pathway and following activation of the transcription factor Elk-1. Using a <it>ZC3H12A </it>reporter construct we have shown that a <it>ZC3H12A </it>promoter region, stretching from -76 to +60, mediates activation by IL-1β. This region contains binding sites for Elk-1 and its partner SRF. Chromatin immunoprecipitation analysis confirms <it>in vivo </it>binding of both transcription factors to this region of the <it>ZC3H12A </it>promoter.</p> <p>Conclusions</p> <p>We conclude that the transcription factor Elk-1 plays an important role in the activation of <it>ZC3H12A </it>expression in response to IL-1β stimulation.</p

Overlapping promoter targeting by Elk-1 and other divergent ETS-domain transcription factor family members

ETS-domain transcription factors play important roles in controlling gene expression in a variety of different contexts; however, these proteins bind to very similar sites and it is unclear how in vivo specificity is achieved. In silico analysis is unlikely to reveal specific targets for individual family members and direct experimental approaches are therefore required. Here, we take advantage of an inducible dominant-negative expression system to identify a group of novel target genes for the ETS-domain transcription factor Elk-1. Elk-1 is thought to mainly function through cooperation with a second transcription factor SRF, but the targets we identify are largely SRF-independent. Furthermore, we demonstrate that there is a high degree of overlapping, cell type-specific, target gene binding by Elk-1 and other ETS-domain transcription factors. Our results are therefore consistent with the notion that there is a high degree of functional redundancy in target gene regulation by ETS-domain transcription factors in addition to the specific target gene regulation that can be dictated through heterotypic interactions exemplified by the Elk-1-SRF complex

The forkhead transcription factor FOXK2 acts as a chromatin targeting factor for the BAP1-containing histone deubiquitinase complex.

There are numerous forkhead transcription factors in mammalian cells but we know little about the molecular functions of the majority of these. FOXK2 is a ubiquitously expressed family member suggesting an important function across multiple cell types. Here, we show that FOXK2 binds to the SIN3A and PR-DUB complexes. The PR-DUB complex contains the important tumour suppressor protein, the deubiquitinase BAP1. FOXK2 recruits BAP1 to DNA, promotes local histone deubiquitination and causes changes in target gene activity. Our results therefore provide an important link between BAP1 and the transcription factor FOXK2 and demonstrate how BAP1 can be recruited to specific regulatory loci