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Growth factor-induced p42/p44 MAPK nuclear translocation and retention requires both MAPK activation and neosynthesis
P Lenormand1, J M Brondello, A Brunet
1Centre de Biochimie-Centre National de la Recherche Scientifique (CNRS) UMR 6543, Université de Nice, 06108 Nice, France. lenorman@unice.fr
Abstract:
Mitogen-activated protein kinases (p42/p44 MAPK, also called Erk2 and Erk1) are key mediators of signal transduction from the cell surface to the nucleus. We have previously shown that the activation of p42/p44 MAPK required for transduction of mitogenic signaling is associated with a rapid nuclear translocation of these kinases. However, the means by which p42 and p44 MAPK translocate into the nucleus after cytoplasmic activation is still not understood and cannot simply be deduced from their protein sequences. In this study, we have demonstrated that activation of the p42/ p44 MAPK pathway was necessary and sufficient for triggering nuclear translocation of p42 and p44 MAPK. First, addition of the MEK inhibitor PD 98059, which blocks activation of the p42/p44 MAPK pathway, impedes the nuclear accumulation, whereas direct activation of the p42/p44 MAPK pathway by the chimera DeltaRaf-1:ER is sufficient to promote nuclear accumulation of p42/p44 MAPK. In addition, we have shown that this nuclear accumulation of p42/p44 MAPK required the neosynthesis of short-lived proteins. Indeed, inhibitors of protein synthesis abrogate nuclear accumulation in response to serum and accelerate p42/p44 MAPK nuclear efflux under conditions of persistent p42/p44 MAPK activation. In contrast, inhibition of targeted proteolysis by the proteasome synergistically potentiated p42/p44 MAPK nuclear localization by nonmitogenic agonists and markedly prolonged nuclear localization of p42/p44 MAPK after mitogenic stimulation. We therefore conclude that the MAPK nuclear translocation requires both activation of the p42/p44 MAPK module and neosynthesis of short-lived proteins that we postulate to be nuclear anchors.
Insights
Nuclear translocation of mitogen-activated protein kinases (MAPK) requires pathway activation and new protein synthesis. This process is regulated by protein synthesis and degradation, suggesting short-lived proteins act as nuclear anchors for MAPK signaling.
Area of Science:
- Cellular Biology
- Molecular Biology
- Signal Transduction
Background:
- Mitogen-activated protein kinases (MAPK), specifically p42/p44 MAPK (Erk1/Erk2), are crucial for relaying signals from the cell surface to the nucleus.
- Previous studies indicated that activated p42/p44 MAPK rapidly moves into the nucleus during mitogenic signaling.
- The precise mechanism governing this nuclear translocation following cytoplasmic activation remained unclear.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying the nuclear translocation of p42/p44 MAPK.
- To determine the necessity and sufficiency of p42/p44 MAPK pathway activation for nuclear import.
- To investigate the role of protein synthesis and degradation in regulating MAPK nuclear localization.
Main Methods:
- Utilized the MEK inhibitor PD 98059 to block p42/p44 MAPK pathway activation.
- Employed a DeltaRaf-1:ER chimera to directly activate the p42/p44 MAPK pathway.
- Assessed the impact of protein synthesis inhibitors and proteasome inhibitors on nuclear accumulation of p42/p44 MAPK.
Main Results:
- p42/p44 MAPK pathway activation was both necessary and sufficient for triggering nuclear translocation.
- Inhibition of MEK blocked nuclear accumulation, while DeltaRaf-1:ER induced it.
- Inhibitors of protein synthesis prevented nuclear accumulation and accelerated nuclear efflux, while proteasome inhibitors enhanced and prolonged nuclear localization.
Conclusions:
- MAPK nuclear translocation is dependent on both the activation of the p42/p44 MAPK module and the synthesis of short-lived proteins.
- These short-lived proteins are hypothesized to function as nuclear anchors, facilitating MAPK nuclear localization.
- The findings reveal a dynamic regulatory mechanism involving protein synthesis and degradation for MAPK signaling in the nucleus.