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Transcriptional repressor ERF is a Ras/mitogen-activated protein kinase target that regulates cellular proliferation
L Le Gallic1, D Sgouras, G Beal
1IMBB-FORTH, University of Crete, Voutes, Heraklion, Crete 714-09, Greece.
Abstract:
A limited number of transcription factors have been suggested to be regulated directly by Erks within the Ras/mitogen-activated protein kinase signaling pathway. In this paper we demonstrate that ERF, a ubiquitously expressed transcriptional repressor that belongs to the Ets family, is physically associated with and phosphorylated in vitro and in vivo by Erks. This phosphorylation determines the ERF subcellular localization. Upon mitogenic stimulation, ERF is immediately phosphorylated and exported to the cytoplasm. The export is blocked by specific Erk inhibitors and is abolished when residues undergoing phosphorylation are mutated to alanine. Upon growth factor deprivation, ERF is rapidly dephosphorylated and transported back into the nucleus. Phosphorylation-defective ERF mutations suppress Ras-induced tumorigenicity and arrest the cells at the G0/G1 phase of the cell cycle. Our findings strongly suggest that ERF may be important in the control of cellular proliferation during the G0/G1 transition and that it may be one of the effectors in the mammalian Ras signaling pathway.
Insights
The study reveals that Erk phosphorylation controls the ERF protein
Area of Science:
- Molecular Biology
- Cell Signaling
- Cancer Research
Background:
- The Ras/mitogen-activated protein kinase (MAPK) pathway regulates crucial cellular processes.
- Limited transcription factors are known to be directly regulated by Extracellular signal-Regulated Kinases (Erks).
Purpose of the Study:
- To investigate the role of ERF, an Ets family transcriptional repressor, in the Ras/MAPK pathway.
- To determine if Erks directly regulate ERF activity and localization.
Main Methods:
- In vitro and in vivo phosphorylation assays using Erks and ERF.
- Subcellular localization studies upon mitogenic stimulation and growth factor deprivation.
- Analysis of ERF phosphorylation site mutants.
- Assessment of Ras-induced tumorigenicity and cell cycle progression in cells with phosphorylation-defective ERF.
Main Results:
- ERF physically associates with and is phosphorylated by Erks.
- Erk-mediated phosphorylation of ERF dictates its nuclear-cytoplasmic shuttling.
- Mitogenic stimulation causes ERF phosphorylation and cytoplasmic export, reversible by Erk inhibitors or alanine mutation of phosphorylation sites.
- Growth factor deprivation leads to ERF dephosphorylation and nuclear import.
- Phosphorylation-defective ERF mutants inhibit Ras-induced tumorigenicity and arrest cells in G0/G1 phase.
Conclusions:
- ERF is a direct substrate of Erks within the Ras signaling pathway.
- ERF phosphorylation by Erks is critical for regulating its subcellular localization and cellular proliferation.
- ERF acts as a key effector in the Ras/MAPK pathway, influencing G0/G1 cell cycle transition and potentially tumorigenesis.