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The ETS-related transcription factor ERM is a nuclear target of signaling cascades involving MAPK and PKA
R Janknecht1, D Monté, J L Baert
1Institute for Molecular Biology, Hannover Medical School, Hannover-Germany.
Abstract:
Recent studies support a model for signal transduction from activated receptor tyrosine kinases to Ras which, in turn, activates the pathway of the mitogen-activated protein kinase (MAPK). Although some members of the Ets transcription factor family have been shown to be activated by this signaling pathway, no data are available on the activation of the PEA3 group of Ets proteins. This group is composed of three members -- PEA3, ER81 and ERM -- which are very similar in the DNA-binding domain, the ETS domain, in the 32 residue amino-terminal acidic domain and in the 61 residue carboxy-terminal domain. First of all we demonstrated that ERM-transfected cells contain a positive labeling in the nucleus, and we concluded that a nuclear localization signal might be situated in the ETS domain. We then showed that of four putative reporter plasmids, ERM activated the artificial 3 x TORU plasmid which contains an Ets binding site contiguous to an AP1 one. This transactivation enhancement requires the presence of the ERM amino-terminal domain. In contrast, although the lack of the carboxy-terminal domain induced a decrease in transactivation, this latter domain is not crucial. By using the E74-reporter plasmid system which is not basically activated by ERM, we showed that the activation of the Ras/Raf-1/MAPK pathway significantly enhanced ERM-mediated transactivation. The deletion of the amino-terminal transactivation domain abolished the capacity of stimulated MAPK to activate ERM. We also demonstrated that ERM can also be activated through the protein kinase A (PKA), another signaling pathway. Nevertheless, the MAPK and PKA activation of ERM are not synergistic. Finally, we showed that this Ets transcription factor is in vitro phosphorylated by both activated ERK-2 and activated PKA. ERM has thus been identified as a transcription factor which is a target for two different signaling pathways and might therefore be involved in the mitogenic response of cells.
Insights
The ERM transcription factor is activated by both MAPK and PKA signaling pathways. This activation involves phosphorylation and suggests ERM
Area of Science:
- Molecular Biology
- Cell Signaling
- Transcription Factors
Background:
- Receptor tyrosine kinases activate Ras and MAPK pathways.
- Some Ets transcription factors are activated by MAPK.
- The PEA3 group of Ets proteins (PEA3, ER81, ERM) activation is unknown.
Purpose of the Study:
- Investigate the activation of the ERM transcription factor.
- Determine if ERM is activated by the Ras/Raf-1/MAPK pathway.
- Identify signaling pathways that regulate ERM activity.
Main Methods:
- Transfection of ERM into cells.
- Reporter plasmid assays (3xTORU, E74).
- Analysis of ERM domain requirements for transactivation.
- In vitro phosphorylation assays.
Main Results:
- ERM contains a nuclear localization signal within its ETS domain.
- ERM transactivation is enhanced by the MAPK pathway, requiring the N-terminal domain.
- ERM is also activated by Protein Kinase A (PKA).
- ERM is phosphorylated in vitro by ERK-2 and PKA.
- MAPK and PKA activation of ERM are not synergistic.
Conclusions:
- ERM is a transcription factor targeted by both MAPK and PKA signaling pathways.
- ERM's dual activation suggests a role in cellular mitogenic responses.