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The JNK phosphatase M3/6 is inhibited by protein-damaging stress
C Palacios1, M K Collins, G R Perkins
1The Department of Immunology, University College London Medical School, Windeyer Building, 46 Cleveland Street, London W1P6DB, United Kingdom.
Abstract:
Cells respond to stresses such as osmotic shock and heat shock by activating stress-activated protein kinases (SAPKs), including c-Jun N-terminal kinase (JNK) [1]. Activation of JNK requires phosphorylation of threonine and tyrosine residues in the TPY activation loop motif [2, 3] and can be reversed by the removal of either phosphate group. Numerous JNK phosphatases including dual-specificity phosphatases [4, 5], have been identified. Many stimuli activate JNK by increasing its rate of phosphorylation; however, JNK dephosphorylation is inhibited in cells after heat shock [6], suggesting that a JNK phosphatase(s) is inactivated. M3/6 is a dual-specificity phosphatase selective for JNK [7, 8]. We have previously expressed M3/6 in the mouse bone marrow cell line BAF3 in order to show that JNK activation by IL-3 is necessary for cell survival and proliferation [9]. Here we report that M3/6 dissociates from JNK and appears in an insoluble fraction after heat shock. These data identify M3/6 as a JNK phosphatase that is inactivated by heat shock and provide a molecular mechanism for the activation of JNK by heat shock.
Insights
Heat shock inactivates the M3/6 phosphatase, which normally deactivates stress-activated protein kinases (SAPKs) like c-Jun N-terminal kinase (JNK). This inactivation mechanism explains how JNK remains active during heat stress.
Area of Science:
- Cellular stress response
- Signal transduction pathways
- Enzymology
Background:
- Cells activate stress-activated protein kinases (SAPKs), including c-Jun N-terminal kinase (JNK), in response to environmental stresses like heat shock.
- JNK activation, a phosphorylation event, is reversible by dephosphorylation, with numerous JNK phosphatases identified.
- Heat shock inhibits JNK dephosphorylation, suggesting the inactivation of specific JNK phosphatases.
Purpose of the Study:
- To investigate the role of the dual-specificity phosphatase M3/6 in JNK regulation during heat shock.
- To elucidate the molecular mechanism underlying JNK activation following heat stress.
Main Methods:
- Utilized the mouse bone marrow cell line BAF3.
- Investigated the interaction and localization of M3/6 phosphatase with JNK under heat shock conditions.
Main Results:
- M3/6 phosphatase was found to dissociate from JNK after heat shock.
- M3/6 phosphatase translocated to an insoluble cellular fraction following heat shock.
- These findings indicate M3/6 is a JNK phosphatase inactivated by heat shock.
Conclusions:
- M3/6 is a JNK-specific phosphatase that is inactivated by heat shock.
- The dissociation and insolubilization of M3/6 provide a molecular explanation for sustained JNK activation during heat stress.