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Mitogen-activated protein kinase kinase 1 (MKK1) is negatively regulated by threonine phosphorylation
A J Rossomando1, P Dent, T W Sturgill
1W. M. Keck Structural Biology Laboratory, Beckman Neuroscience Center, Cold Spring Harbor Laboratory, New York 11724.
Abstract:
Mitogen-activated protein kinase kinase 1 (MKK1), a dual-specificity tyrosine/threonine protein kinase, has been shown to be phosphorylated and activated by the raf oncogene product as part of the mitogen-activated protein kinase cascade. Here we report the phosphorylation and inactivation of MKK1 by phosphorylation on threonine 286 and threonine 292. MKK1 contains a consensus phosphorylation site for p34cdc2, a serine/threonine protein kinase that regulates the cell division cycle, at Thr-286 and a related site at Thr-292. p34cdc2 catalyzes the in vitro phosphorylation of MKK1 on both of these threonine residues and inactivates MKK1 enzymatic activity. Both sites are phosphorylated in vivo as well. The data presented in this report provide evidence that MKK1 is negatively regulated by threonine phosphorylation.
Insights
Mitogen-activated protein kinase kinase 1 (MKK1) is inactivated by phosphorylation at specific threonine sites. This discovery reveals a novel negative regulatory mechanism for MKK1 in the cell division cycle.
Area of Science:
- Molecular Biology
- Cell Signaling
- Biochemistry
Background:
- Mitogen-activated protein kinase kinase 1 (MKK1) is a key enzyme in the mitogen-activated protein kinase cascade.
- MKK1 is typically activated through phosphorylation by the raf oncogene product.
- The regulation of MKK1 activity is crucial for cellular processes, including cell division.
Purpose of the Study:
- To investigate the phosphorylation and regulation of MKK1.
- To identify specific sites and kinases involved in MKK1 inactivation.
- To elucidate the role of p34cdc2 in MKK1 regulation.
Main Methods:
- In vitro kinase assays using purified p34cdc2 and MKK1.
- Phosphorylation site analysis at Threonine 286 and Threonine 292.
- In vivo phosphorylation studies to confirm regulatory sites.
Main Results:
- p34cdc2 phosphorylates MKK1 at Threonine 286 and Threonine 292.
- Phosphorylation at these sites leads to the inactivation of MKK1 enzymatic activity.
- Both Threonine 286 and Threonine 292 are phosphorylated in vivo.
Conclusions:
- MKK1 is negatively regulated by threonine phosphorylation.
- p34cdc2 acts as an inhibitory kinase for MKK1.
- This finding reveals a novel mechanism controlling the mitogen-activated protein kinase cascade.