Protein Phosphatase Methyl-Esterase PME-1 Protects Protein Phosphatase 2A from Ubiquitin/Proteasome Degradation
0
Citation
0
Reference
20
Related Paper
Abstract:
Protein phosphatase 2A (PP2A) is a conserved essential enzyme that is implicated as a tumor suppressor based on its central role in phosphorylation-dependent signaling pathways. Protein phosphatase methyl esterase (PME-1) catalyzes specifically the demethylation of the C-terminal Leu309 residue of PP2A catalytic subunit (PP2Ac). It has been shown that PME-1 affects the activity of PP2A by demethylating PP2Ac, but also by directly binding to the phosphatase active site, suggesting loss of PME-1 in cells would enhance PP2A activity. However, here we show that PME-1 knockout mouse embryonic fibroblasts (MEFs) exhibit lower PP2A activity than wild type MEFs. Loss of PME-1 enhanced poly-ubiquitination of PP2Ac and shortened the half-life of PP2Ac protein resulting in reduced PP2Ac levels. Chemical inhibition of PME-1 and rescue experiments with wild type and mutated PME-1 revealed methyl-esterase activity was necessary to maintain PP2Ac protein levels. Our data demonstrate that PME-1 methyl-esterase activity protects PP2Ac from ubiquitin/proteasome degradation.Keywords:
Dephosphorylation
Esterase
Protein Degradation
Cite
Transcriptional coactivator p300 is required for embryonic development and cell proliferation. Valproic acid, a histone deacetylase inhibitor, is widely used in the therapy of epilepsy and bipolar disorder. However, it has intrinsic teratogenic activity through unidentified mechanisms. We report that valproic acid stimulates proteasome-dependent p300 degradation through augmentation of gene expression of the B56gamma regulatory subunits of protein phosphatase 2A. The B56gamma3 regulatory and catalytic subunits of protein phosphatase 2A interact with p300. Overexpression of the B56gamma3 subunit leads to proteasome-mediated p300 degradation and represses p300-dependent transcriptional activation, which requires the B56gamma3 interaction domain of p300. Conversely, silencing of the B56gamma subunit expression by RNA interference increases the stability and transcriptional activity of the coactivator. Our study establishes the functional interaction between protein phosphatase 2A and p300 activity and provides direct evidence for signal-dependent control of p300 function.
Protein phosphatase 1
Protein Degradation
Cite
Citations (39)
Protein phosphatase 2A and GSK–3β are important factors involved in tau hyperphosphorylation. PP–2A is able to dephosphorylate GSK–3β in vitro and has been proposed to regulate GSK–3β activity in vivo. From the finding that lithium can block ceramide induced activation of a protein phosphatase with characteristics similar to PP–2A, it could imply that GSK–3 regulates PP–2A in a manner similar to the regulation of PP–1. The mechanism of glycogen synthase kinase–3β regulating protein phosphatase 2A's activity was investigated. GSK–3β was found to be co–precipitated with I2PP–2A. I2PP–2A and PP–2A C subunit protein levels were detected by Western blots after inhibition or activation of GSK–3β. I2PP–2A immunoreactivity was decreased while treated with LiCl and SB216763, two GSK–3 inhibitors. And PP–2A C subunit protein level was decreased after treated with LiCl for 24 hours, but increased after treated with SB216763 for one hour. On the contrary, while increase activity of GSK–3β by wortmannin for one hour or transient transfection with GSK–3β plasmid, I2PP–2A protein level was found to decrease and PP–2A C subunit protein level was increased. These results indicated that I2PP–2A could form a stable complex with GSK–3β in vivo. And GSK–3β may possibly regulate PP–2A activity by changing the expression of PP–2A C subunit protein and I2PP–2A protein.
Wortmannin
Protein phosphatase 1
Hyperphosphorylation
GSK3B
Cite
Citations (0)
DUSP6
Protein phosphatase 1
Cite
Citations (75)
Human protein phosphatase‐2C α (PP2C α ) was purified to homogeneity after expression in Escherichia coli . AMP inhibited the dephosphorylation of AMP‐activated protein kinase (AMPK), but not phosphocasein, by PP2C α . The concentration dependence and the effects of other nucleotides (ATP and formycin A‐5′‐monophosphate) suggest that AMP acts by binding to the same site which causes direct allosteric activation of AMPK. A similar, although less pronounced, effect was observed with another protein phosphatase (PP2A c ). We have now shown that AMPK activates the AMPK cascade by four mechanisms, which should make the system exquisitely sensitive to changes in AMP concentration.
Dephosphorylation
AMP-Activated Protein Kinase
Adenosine monophosphate
Cite
Citations (582)
Phosphoprotein phosphatase 2A (PP2A) is one of the four major protein serine/threonine phosphatases found in all eukaryotic cells. We have shown that the 36-kDa catalytic subunit of PP2A is carboxyl methylated in eukaryotic cells, and we have previously identified and purified a novel methyltransferase (MTase) that is responsible for this modification. Here, we describe a novel protein carboxyl methyl-esterase (MEase) from bovine brain that demethylates PP2A. The enzyme has been purified to homogeneity as a monomeric 46-kDa soluble protein. The MEase is highly specific for PP2A. It does not catalyze the demethylation of other protein or peptide methylesters. Moreover, MEase activity is dramatically inhibited by nanomolar concentrations of okadaic acid, a specific inhibitor of PP2A. From these results, we conclude that PP2A methylation is controlled by two specific enzymes, a MTase and a MEase. Since PP2A methylation is highly conserved in eukaryotes ranging from human to yeast, it is likely that this system plays an important role in phosphatase regulation.
Dephosphorylation
DUSP6
Phosphoprotein
Protein phosphatase 1
Cite
Citations (137)
Dual-specificity phosphatase
Dithiothreitol
DUSP6
Cite
Citations (55)
Demethylation
Alanine
Residue (chemistry)
Cite
Citations (31)
Dephosphorylation
Cite
Citations (15)
The catalytic activity of the C subunit of serine/threonine phosphatase 2A is regulated by the association with A (PR65) and B subunits. It has been reported that the alpha4 protein, a yeast homolog of the Tap42 protein, binds the C subunit of serine/threonine phosphatase 2A and protein phosphatase 2A‐related protein phosphatases such as protein phosphatase 4 and protein phosphatase 6. In the present study, we showed that alpha4 binds these three phosphatases and the association of alpha4 reduces the activities of these phosphatases in vitro. In contrast, PR65 binds to the C subunit of serine/threonine phosphatase 2A but not to protein phosphatase 4 and protein phosphatase 6. These results suggest that the alpha4 protein is a common regulator of the C subunit of serine/threonine phosphatase 2A and protein phosphatase 2A‐related protein phosphatases.
DUSP6
AKT3
Protein phosphatase 1
Cite
Citations (65)
We have expressed the catalytic domain of Chinese hamster HMG‐CoA reductase, and 13 point mutations involving the region around the single phosphorylation site for AMP‐activated protein kinase. After phosphorylation, these were used to test the specificity of isoforms of protein phosphatase‐2A [bovine PP2A C (catalytic subunit) and PP2A 1 (ABC heterotrimer)] and protein phosphatase‐2C (human α; mouse α, β1, β2, β3, β4, β5). PP2A 1 had >50‐fold higher activity for HMG‐CoA reductase variants than PP2A C , but their relative selectivity for different variants was similar. Although the specificities of PP2A and PP2C were distinct, no dramatic differences in selectivity were observed between different PP2C isoforms.
Cite
Citations (11)