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Protein kinase C mu selectively activates the mitogen-activated protein kinase (MAPK) p42 pathway
1Institute of Cell Biology and Immunology, University of Stuttgart, Germany.
Abstract:
Here we show that human protein kinase C mu (PKC mu) activates the mitogen-activated protein kinase (MAPK). Transient expression of constitutive active PKC mu leads to an activation of Raf-1 kinase as demonstrated by in vitro phosphorylation of MAPK. PKC mu enhances transcriptional activity of a basal thymidine kinase promotor containing serum response elements (SREs) as shown by luciferase reporter gene assays. SRE driven gene activation by PKC mu is triggered by the Elk-1 ternary complex factor. PKC mu-mediated activation of SRE driven transcription can be inhibited by the MEK1 inhibitor PD98059. In contrast to the activation of the p42/ERK1 MAPK cascade, transient expression of constitutive active PKC mu does neither affect c-jun N-terminal kinase nor p38 MAPK.
Insights
Human protein kinase C mu (PKC mu) activates the mitogen-activated protein kinase (MAPK) pathway, specifically the p42/ERK1 cascade. This activation enhances gene transcription via serum response elements, independent of other MAPK pathways.
Area of Science:
- Cellular signaling pathways
- Molecular biology
- Signal transduction
Background:
- Protein kinase C mu (PKC mu) is a signaling enzyme implicated in various cellular processes.
- Mitogen-activated protein kinases (MAPKs) are crucial regulators of cell proliferation, differentiation, and survival.
- Understanding the cross-talk between different signaling pathways is essential for deciphering complex cellular functions.
Purpose of the Study:
- To investigate the role of human protein kinase C mu (PKC mu) in the activation of mitogen-activated protein kinase (MAPK).
- To elucidate the downstream targets and mechanisms by which PKC mu influences gene transcription.
- To determine the specificity of PKC mu-mediated MAPK activation within the broader MAPK family.
Main Methods:
- Transient expression of constitutively active PKC mu in cultured cells.
- In vitro kinase assays to assess Raf-1 and MAPK phosphorylation.
- Luciferase reporter gene assays to measure transcriptional activity driven by serum response elements (SREs).
- Inhibition studies using the MEK1 inhibitor PD98059.
Main Results:
- Constitutively active PKC mu activated Raf-1 kinase and subsequently MAPK.
- PKC mu enhanced transcriptional activity of an SRE-containing thymidine kinase promoter.
- Elk-1, a ternary complex factor, was identified as a key mediator of PKC mu-induced SRE transcriptional activation.
- PKC mu-mediated SRE-driven transcription was inhibited by PD98059, confirming MEK1 involvement.
- PKC mu specifically activated the p42/ERK1 MAPK cascade, without affecting c-jun N-terminal kinase or p38 MAPK.
Conclusions:
- Human PKC mu is an upstream activator of the p42/ERK1 MAPK cascade.
- PKC mu regulates gene transcription through the Elk-1 transcription factor and SRE elements.
- The findings highlight a specific role for PKC mu in regulating the ERK MAPK pathway, distinct from other MAPK family members.