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Regulation of stress-responsive mitogen-activated protein (MAP) kinase pathways by TAO2
1Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9041, USA.
Abstract:
Previous studies demonstrated that in vitro the protein kinase TAO2 activates MAP/ERK kinases (MEKs) 3, 4, and 6 toward their substrates p38 MAP kinase and c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK). In this study, we examined the ability of TAO2 to activate stress-sensitive MAP kinase pathways in cells and the relationship between activation of TAO2 and potential downstream pathways. Over-expression of TAO2 activated endogenous JNK/SAPK and p38 but not ERK1/2. Cotransfection experiments suggested that TAO2 selectively activates MEK3 and MEK6 but not MEKs 1, 4, or 7. Coimmunoprecipitation demonstrated that endogenous TAO2 specifically associates with MEK3 and MEK6 providing one mechanism for preferential recognition of MEKs upstream of p38. Sorbitol, and to a lesser extent, sodium chloride, Taxol, and nocodazole increased TAO2 activity toward itself and kinase-dead MEKs 3 and 6. Activation of endogenous TAO2 during differentiation of C2C12 myoblasts paralleled activation of p38 but not JNK/SAPK, consistent with the idea that TAO2 is a physiological regulator of p38 under certain circumstances.
Insights
The protein kinase TAO2 activates stress-sensitive pathways, specifically MEK3 and MEK6, leading to p38 MAP kinase activation in cells. TAO2
Area of Science:
- Cellular signaling pathways
- Protein kinase regulation
- Stress-activated protein kinases
Background:
- Previous in vitro studies showed TAO2 activates MEK3, MEK4, and MEK6.
- These kinases phosphorylate p38 MAP kinase and JNK/SAPK.
- The in-cell activity and regulation of TAO2 remained unclear.
Purpose of the Study:
- To investigate TAO2's ability to activate stress-sensitive MAP kinase pathways within cells.
- To explore the relationship between TAO2 activation and downstream signaling.
- To identify specific MEK activators and regulators of TAO2.
Main Methods:
- Over-expression of TAO2 in cellular systems.
- Cotransfection experiments to assess MEK activation.
- Coimmunoprecipitation to determine protein associations.
- Treatment with stress-inducing agents (sorbitol, NaCl, Taxol, nocodazole).
- Analysis of TAO2 activation during C2C12 myoblast differentiation.
Main Results:
- TAO2 over-expression activated endogenous JNK/SAPK and p38, but not ERK1/2.
- TAO2 selectively activated MEK3 and MEK6, but not MEK1, MEK4, or MEK7.
- Endogenous TAO2 specifically associated with MEK3 and MEK6.
- Stress-related agents increased TAO2 activity.
- TAO2 activation during myoblast differentiation paralleled p38 activation.
Conclusions:
- TAO2 functions as an activator of p38 MAP kinase and JNK/SAPK pathways in cells.
- TAO2 exhibits selectivity for MEK3 and MEK6, providing a mechanism for p38 regulation.
- TAO2 activity is modulated by cellular stress and it plays a physiological role in p38 activation during myogenesis.