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Nuclear translocation of p42/p44 mitogen-activated protein kinase is required for growth factor-induced gene
A Brunet1, D Roux, P Lenormand
1CNRS-UMR 6543 Centre de Biochimie, Université de Nice, Parc Valrose, 06108 Nice, France.
Abstract:
Mitogen-activated protein kinase (MAPK) modules, composed of three protein kinases activated by successive phosphorylation, are involved in the signal transduction of a wide range of extracellular agents. In mammalian cells, mitogenic stimulation triggers the translocation of p42/p44MAPK from the cytoplasm to the nucleus, whereas the other protein kinases of the module remain cytosolic. Since MAPK has been shown to phosphorylate and activate nuclear targets, such as the transcription factor Elk1, it has been proposed, but not yet demonstrated, that MAPK nuclear translocation could represent a critical step in signal transduction. In this study, we sequestered p42/p44MAPK in the cytoplasm by the expression of a catalytically inactive form of cytoplasmic MAP kinase phosphatase (MKP-3/Pyst-1). Sequestering MAPK in the cytoplasm did not alter its activation or its ability to phosphorylate cytoplasmic substrates of MAPK (p90RSK1 or an engineered cytoplasmic form of Elk1). In contrast, prevention of MAPK nuclear translocation strongly inhibited Elk1-dependent gene transcription and the ability of cells to reinitiate DNA replication in response to growth factors. Thus the relocalization of MAPK to the nucleus appears to be an important regulatory step for mitogen-induced gene expression and cell cycle re-entry.
Insights
Mitogen-activated protein kinase (MAPK) nuclear translocation is crucial for gene expression and cell cycle re-entry. Preventing MAPK from entering the nucleus blocks growth factor-induced DNA replication and transcription.
Area of Science:
- Cellular signaling
- Molecular biology
- Signal transduction pathways
Background:
- Mitogen-activated protein kinase (MAPK) modules are key in signal transduction.
- Mitogenic stimulation causes p42/p44MAPK to move from the cytoplasm to the nucleus in mammalian cells.
- MAPK's nuclear translocation is proposed as a critical signaling step but lacks direct evidence.
Purpose of the Study:
- To investigate the role of p42/p44MAPK nuclear translocation in signal transduction.
- To determine if MAPK nuclear localization is essential for gene transcription and DNA replication.
Main Methods:
- Utilized a catalytically inactive form of cytoplasmic MAP kinase phosphatase (MKP-3/Pyst-1) to sequester p42/p44MAPK in the cytoplasm.
- Assessed MAPK activation and phosphorylation of cytoplasmic substrates (p90RSK1, cytoplasmic Elk1).
- Measured Elk1-dependent gene transcription and DNA replication initiation upon growth factor stimulation.
Main Results:
- Cytoplasmic sequestration of MAPK did not affect its activation or cytoplasmic substrate phosphorylation.
- Inhibition of MAPK nuclear translocation significantly reduced Elk1-dependent gene transcription.
- Preventing MAPK nuclear entry impaired the cells' ability to reinitiate DNA replication.
Conclusions:
- The nuclear relocalization of MAPK is a critical regulatory step for mitogen-induced gene expression.
- MAPK's translocation to the nucleus is essential for growth factor-stimulated cell cycle re-entry and DNA replication.