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Selective suppression of stress-activated protein kinase pathway by protein phosphatase 2C in mammalian cells
M Hanada1, T Kobayashi, M Ohnishi
1Department of Biochemistry, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan.
Abstract:
Protein phosphatase 2Calpha (PP2Calpha) or PP2Cbeta-1 expressed in COS7 cells suppressed anisomycin- and NaCl-enhanced phosphorylations of p38 co-expressed in the cells. PP2Calpha or PP2Cbeta-1 expression also suppressed both basal and stress-enhanced phosphorylations of MKK3b and MKK6b, which are upstream protein kinases of p38, and of MKK4, which is one of the major upstream protein kinases of JNK. Basal activity of MKK7, another upstream protein kinase of JNK, was also suppressed by PP2Calpha or PP2Cbeta-1 expression. However, basal as well as serum-activated phosphorylation of MKK1alpha, an upstream protein kinase of ERKs, was not affected by PP2Cbeta or PP2Cbeta-1. A catalytically inactive mutant of PP2Cbeta-1 further enhanced the NaCl-stimulated phosphorylations of MMK3b, MKK4 and MKK6b, suggesting that this mutant PP2Cbeta-1 works as a dominant negative form. These results suggest that PP2C selectively inhibits the SAPK pathways through suppression of MKK3b, MKK4, MKK6b and MKK7 activities in mammalian cells.
Insights
Protein phosphatase 2C (PP2C) selectively inhibits stress-activated protein kinase (SAPK) pathways. PP2C suppresses key upstream kinases like MKK3b, MKK4, MKK6b, and MKK7, impacting p38 and JNK signaling.
Area of Science:
- Cellular signaling
- Molecular biology
- Enzymology
Background:
- Protein phosphatases play crucial roles in regulating cellular processes.
- Stress-activated protein kinase (SAPK) pathways are involved in cellular responses to stress.
- The specific roles of Protein Phosphatase 2C (PP2C) in SAPK pathway regulation require further elucidation.
Purpose of the Study:
- To investigate the inhibitory effects of Protein Phosphatase 2Calpha (PP2Calpha) and PP2Cbeta-1 on SAPK pathway components.
- To determine if PP2C isoforms selectively target specific kinases within the p38, JNK, and ERK pathways.
Main Methods:
- Expression of PP2Calpha or PP2Cbeta-1 in COS7 cells.
- Analysis of phosphorylation levels of p38, MKK3b, MKK6b, MKK4, MKK7, and MKK1alpha.
- Utilizing a catalytically inactive mutant of PP2Cbeta-1 to assess dominant-negative effects.
Main Results:
- PP2Calpha and PP2Cbeta-1 suppressed p38 phosphorylation induced by anisomycin and NaCl.
- Both PP2C isoforms inhibited basal and stress-enhanced phosphorylation of MKK3b, MKK6b, and MKK4.
- PP2C isoforms also suppressed basal MKK7 activity but did not affect MKK1alpha phosphorylation.
- A dominant-negative PP2Cbeta-1 mutant enhanced MKK3b, MKK4, and MKK6b phosphorylation.
Conclusions:
- PP2C isoforms selectively inhibit SAPK pathways.
- PP2C acts by suppressing the activities of MKK3b, MKK4, MKK6b, and MKK7.
- These findings highlight PP2C as a key negative regulator of stress signaling in mammalian cells.