Protein phosphatase 2A (PP2A) represents a conserved family of important protein serine/threonine phosphatases in species ranging from yeast to human. The PP2A core enzyme comprises a scaffold subunit and a catalytic ...Protein phosphatase 2A (PP2A) represents a conserved family of important protein serine/threonine phosphatases in species ranging from yeast to human. The PP2A core enzyme comprises a scaffold subunit and a catalytic subunit. The heterotrimeric PP2A holoenzyme consists of the core enzyme and a variable regulatory subunit. The catalytic subunit of PP2A is subject to reversible methylation, medi-ated by two conserved enzymes. Both the PP2A core and holoenzymes are regulated through interac-tion with a large number of cellular cofactors. Recent biochemical and structural investigation reveals critical insights into the assembly and function of the PP2A core enzyme as well as two families of holoenzyme. This review focuses on the molecular mechanisms revealed by these latest advances.展开更多
Phospholipase D （PLD） exerts broad biological functions in eukaryotes through regulating downstream effectors by its product, phosphatidic acid （PA）. Protein kinases and phosphatases, such as mammalian target of r...Phospholipase D （PLD） exerts broad biological functions in eukaryotes through regulating downstream effectors by its product, phosphatidic acid （PA）. Protein kinases and phosphatases, such as mammalian target of rapa- mycin （mTOR）, Protein Phosphatase 1 （PP1） and Protein Phosphatase 2C （PP2C）, are PA-binding proteins that execute crucial regulatory functions in both animals and plants. PA participates in many signaling pathways by modulating the enzymatic activity and/or subcellular localization of bound proteins. In this study, we demonstrated that PLD-derived PA interacts with the scaffolding A1 subunit of Protein Phosphatase 2A （PP2A） and regulates PP2A-mediated PIN1 dephos- phorylation in Arabidopsis. Genetic and pharmacological studies showed that both PA and PP2A participate in the regu- lation of auxin distribution. In addition, both the phosphorylation status and polar localization of PIN1 protein were affected by PLD inhibitors, Exogenous PA triggered the membrane accumulation of PP2AA1 and enhanced the PP2A activity at membrane, while PLD inhibition resulted in the reduced endosomal localization and perinuclear aggregation of PP2AA1. These results demonstrate the important role of PLD-derived PA in normal PP2A-mediated PIN dephosphoryl- ation and reveal a novel mechanism, in which PA recruits PP2AA1 to the membrane system and regulates PP2A function on membrane-targeted proteins. As PA and PP2A are conserved among eukaryotes, other organisms might use similar mechanisms to mediate multiple biological processes.展开更多
Brassinosteroid （BR） binding activates the receptor kinase BRI1 by inducing heterodimerization with its co- receptor kinase BAK1; however, the mechanisms that reversibly inactivate BRI1 remain unclear. Here we show ...Brassinosteroid （BR） binding activates the receptor kinase BRI1 by inducing heterodimerization with its co- receptor kinase BAK1; however, the mechanisms that reversibly inactivate BRI1 remain unclear. Here we show that cytoplasm-localized protein phosphatase 2A （PP2A） B＇ regulatory subunits interact with BRI1 to mediate its dephosphorylation and inactivation. Loss-of-function and overexpression experiments showed that a group of PP2A B＇ regulatory subunits, represented by B＇η, negatively regulate BR signaling by decreasing BRI1 phosphorylation. BR increases the expression levels of these B＇ subunits, and B/TI interacts preferentially with phosphorylated BRI1, suggesting that the dynamics of BR signaling are modu- lated by the PP2A-mediated feedback inactivation of BRI1. Compared with PP2A B＇α and B＇β, which promote BR responses by dephosphorylating the downstream transcription factor BZR1, the BRI1- inactivating B＇ subunits showed similar binding to BRI1 and BZR1 but distinct subcellular localization. Alteration of the nuclear/cytoplasmic localization of the B＇ subunits revealed that cytoplasmic PP2A de- phosphorylates BRI1 and inhibits the BR response, whereas nuclear PP2A dephosphorylates BZR1 and ac- tivates the BR response. Our findings not only identify the PP2A regulatory B subunits that mediate the binding and dephosphorylation of BRI1, but also demonstrate that the subcellular localization of PP2A specifies its substrate selection and distinct effects on BR signaling.展开更多
Decreased expression of brain-derived neurotrophic factor（BDNF） plays an important role in the pathogenesis of Alzheimer＇s disease, and a typical pathological change in Alzheimer＇s disease is neurofibrillary tangl...Decreased expression of brain-derived neurotrophic factor（BDNF） plays an important role in the pathogenesis of Alzheimer＇s disease, and a typical pathological change in Alzheimer＇s disease is neurofibrillary tangles caused by hyperphosphorylation of tau. An in vivo model of Alzheimer＇s disease was developed by injecting okadaic acid（2 μL） and exogenous BDNF（2 μL） into the hippocampi of adult male Wister rats. Spatial learning and memory abilities were assessed using the Morris water maze. The expression levels of protein phosphatase 2 A（PP2 A）, PP2 Ac-Yp307, p-tau（Thr231）, and p-tau（Ser396/404） were detected by western blot assay. The expression levels of BDNF, TrkB, and synaptophysin mRNA were measured by quantitative real-time polymerase chain reaction. Our results indicated that BDNF expression was suppressed in the hippocampus of OA-treated rats, which resulted in learning and memory deficits. Intra-hippocampal injection of BDNF attenuated this OA-induced cognitive impairment. Finally, our findings indicated an involvement of the PI3 K/GSK-3β/AKT pathway in the mechanism of BDNF in regulating cognitive function. These results indicate that BDNF has beneficial effect on Alzheimer＇s disease, and highlight the potential of BDNF as a drug target for treatment of Alzheimer＇s disease.展开更多
The Two-dimensional Quantitative Structure-activity Relationship （2D-QSAR） of a series of novel norcantharidin analogues, which exhibit hnhibitory activities of protein phosphatase 1 and 2A （PP1 and PP2A）, has bee...The Two-dimensional Quantitative Structure-activity Relationship （2D-QSAR） of a series of novel norcantharidin analogues, which exhibit hnhibitory activities of protein phosphatase 1 and 2A （PP1 and PP2A）, has been studied with a combined method of ab initio （I/F）, molecular mechanics （MM＋） and statistics. The established 2D-QSAR model （Eq. 1） for PP1 shows a reasonable regressive performance （R2= 0.749）, and the hydrophobic property of this molecule plays a decisive role in determining the inhibitory activity of PP1. In addition, the established 2D-QSAR model （Eq. 2） for PP2A also shows an acceptable regressive performance （R2= 0.701）, and the dipole moment of the molecule determines the inhibitory activity of PP2A.展开更多
It is well established that the protein serine/threonine phosphatase 2A(PP2A) plays very important roles in many different cellular processes,including cell proliferation and differentiation,gene expression,neurotrans...It is well established that the protein serine/threonine phosphatase 2A(PP2A) plays very important roles in many different cellular processes,including cell proliferation and differentiation,gene expression,neurotransmission,apoptosis,and aging.PP2A consists of three heterogenic subunits:the scaffold subunit A,the catalytic subunit C,and the regulatory subunit B.While both the scaffold and the catalytic subunits contain only two forms,at least four families of the regulatory subunits,B,B',B'',and B''' have been identified.These regulatory subunits from different families are encoded by different genes and bear other functions besides directing the specificity of PP2A.To study the functions of the regulatory subunits of PP2A in lower vertebrates,we have cloned the full-length cDNA sequence of the gene encoding the regulatory subunit B'δ of PP2A from gold fish,Carassius auratus using 3'-RACE and 5'-RACE cloning strategies.Our results revealed that the full-length B'δ cDNA contains 2415 bp and encodes a protein of 555 amino acids.The B'δ protein displays a very high level of sequence identity with the B'δ regulatory subunit from other species of vertebrates.Regarding its expression pattern,RT-PCR revealed that the highest level of mRNA was detected in brain,a less level detected in liver,spermary,ovary,kidney and gill,and the lowest level detected in the fin.During different developmental stages of gold fish,the highest level of mRNA expression was detected at the stages of two-cell,multiple-cell,blastula and gastrula,and a decreased level of B'δ mRNA was detected in other developmental stages.At the protein level,the highest expression level of B'δ protein was found in spermary,ovary,brain and heart,a less amount found in liver and the lowest level detected in kidney,gill and fin.Developmentally,B'δ protein was strongly expressed at the stages of two-cell,multiple-cell,blastula,gastrula,neurula,and optic vesicle,and then decreased at the stages of brain differentiation and eye pigmentation.These results sugg展开更多
基金Supported by NIH grant R01 CA123155Start-up Funds from Tsinghua Univer-sity
文摘Protein phosphatase 2A (PP2A) represents a conserved family of important protein serine/threonine phosphatases in species ranging from yeast to human. The PP2A core enzyme comprises a scaffold subunit and a catalytic subunit. The heterotrimeric PP2A holoenzyme consists of the core enzyme and a variable regulatory subunit. The catalytic subunit of PP2A is subject to reversible methylation, medi-ated by two conserved enzymes. Both the PP2A core and holoenzymes are regulated through interac-tion with a large number of cellular cofactors. Recent biochemical and structural investigation reveals critical insights into the assembly and function of the PP2A core enzyme as well as two families of holoenzyme. This review focuses on the molecular mechanisms revealed by these latest advances.
文摘Phospholipase D （PLD） exerts broad biological functions in eukaryotes through regulating downstream effectors by its product, phosphatidic acid （PA）. Protein kinases and phosphatases, such as mammalian target of rapa- mycin （mTOR）, Protein Phosphatase 1 （PP1） and Protein Phosphatase 2C （PP2C）, are PA-binding proteins that execute crucial regulatory functions in both animals and plants. PA participates in many signaling pathways by modulating the enzymatic activity and/or subcellular localization of bound proteins. In this study, we demonstrated that PLD-derived PA interacts with the scaffolding A1 subunit of Protein Phosphatase 2A （PP2A） and regulates PP2A-mediated PIN1 dephos- phorylation in Arabidopsis. Genetic and pharmacological studies showed that both PA and PP2A participate in the regu- lation of auxin distribution. In addition, both the phosphorylation status and polar localization of PIN1 protein were affected by PLD inhibitors, Exogenous PA triggered the membrane accumulation of PP2AA1 and enhanced the PP2A activity at membrane, while PLD inhibition resulted in the reduced endosomal localization and perinuclear aggregation of PP2AA1. These results demonstrate the important role of PLD-derived PA in normal PP2A-mediated PIN dephosphoryl- ation and reveal a novel mechanism, in which PA recruits PP2AA1 to the membrane system and regulates PP2A function on membrane-targeted proteins. As PA and PP2A are conserved among eukaryotes, other organisms might use similar mechanisms to mediate multiple biological processes.
文摘Brassinosteroid （BR） binding activates the receptor kinase BRI1 by inducing heterodimerization with its co- receptor kinase BAK1; however, the mechanisms that reversibly inactivate BRI1 remain unclear. Here we show that cytoplasm-localized protein phosphatase 2A （PP2A） B＇ regulatory subunits interact with BRI1 to mediate its dephosphorylation and inactivation. Loss-of-function and overexpression experiments showed that a group of PP2A B＇ regulatory subunits, represented by B＇η, negatively regulate BR signaling by decreasing BRI1 phosphorylation. BR increases the expression levels of these B＇ subunits, and B/TI interacts preferentially with phosphorylated BRI1, suggesting that the dynamics of BR signaling are modu- lated by the PP2A-mediated feedback inactivation of BRI1. Compared with PP2A B＇α and B＇β, which promote BR responses by dephosphorylating the downstream transcription factor BZR1, the BRI1- inactivating B＇ subunits showed similar binding to BRI1 and BZR1 but distinct subcellular localization. Alteration of the nuclear/cytoplasmic localization of the B＇ subunits revealed that cytoplasmic PP2A de- phosphorylates BRI1 and inhibits the BR response, whereas nuclear PP2A dephosphorylates BZR1 and ac- tivates the BR response. Our findings not only identify the PP2A regulatory B subunits that mediate the binding and dephosphorylation of BRI1, but also demonstrate that the subcellular localization of PP2A specifies its substrate selection and distinct effects on BR signaling.
文摘Decreased expression of brain-derived neurotrophic factor（BDNF） plays an important role in the pathogenesis of Alzheimer＇s disease, and a typical pathological change in Alzheimer＇s disease is neurofibrillary tangles caused by hyperphosphorylation of tau. An in vivo model of Alzheimer＇s disease was developed by injecting okadaic acid（2 μL） and exogenous BDNF（2 μL） into the hippocampi of adult male Wister rats. Spatial learning and memory abilities were assessed using the Morris water maze. The expression levels of protein phosphatase 2 A（PP2 A）, PP2 Ac-Yp307, p-tau（Thr231）, and p-tau（Ser396/404） were detected by western blot assay. The expression levels of BDNF, TrkB, and synaptophysin mRNA were measured by quantitative real-time polymerase chain reaction. Our results indicated that BDNF expression was suppressed in the hippocampus of OA-treated rats, which resulted in learning and memory deficits. Intra-hippocampal injection of BDNF attenuated this OA-induced cognitive impairment. Finally, our findings indicated an involvement of the PI3 K/GSK-3β/AKT pathway in the mechanism of BDNF in regulating cognitive function. These results indicate that BDNF has beneficial effect on Alzheimer＇s disease, and highlight the potential of BDNF as a drug target for treatment of Alzheimer＇s disease.
基金supported by the China Scholarship Council (CSC [2006] No. 3085)
文摘The Two-dimensional Quantitative Structure-activity Relationship （2D-QSAR） of a series of novel norcantharidin analogues, which exhibit hnhibitory activities of protein phosphatase 1 and 2A （PP1 and PP2A）, has been studied with a combined method of ab initio （I/F）, molecular mechanics （MM＋） and statistics. The established 2D-QSAR model （Eq. 1） for PP1 shows a reasonable regressive performance （R2= 0.749）, and the hydrophobic property of this molecule plays a decisive role in determining the inhibitory activity of PP1. In addition, the established 2D-QSAR model （Eq. 2） for PP2A also shows an acceptable regressive performance （R2= 0.701）, and the dipole moment of the molecule determines the inhibitory activity of PP2A.
基金Supported by US NIH GRANT 1R01 EY 015765the Changjiang Scholar Team Award (Grant No. IRT0045)Fu-rong Scholar Professorship Funds (Grant No. 24030604)
文摘It is well established that the protein serine/threonine phosphatase 2A(PP2A) plays very important roles in many different cellular processes,including cell proliferation and differentiation,gene expression,neurotransmission,apoptosis,and aging.PP2A consists of three heterogenic subunits:the scaffold subunit A,the catalytic subunit C,and the regulatory subunit B.While both the scaffold and the catalytic subunits contain only two forms,at least four families of the regulatory subunits,B,B',B'',and B''' have been identified.These regulatory subunits from different families are encoded by different genes and bear other functions besides directing the specificity of PP2A.To study the functions of the regulatory subunits of PP2A in lower vertebrates,we have cloned the full-length cDNA sequence of the gene encoding the regulatory subunit B'δ of PP2A from gold fish,Carassius auratus using 3'-RACE and 5'-RACE cloning strategies.Our results revealed that the full-length B'δ cDNA contains 2415 bp and encodes a protein of 555 amino acids.The B'δ protein displays a very high level of sequence identity with the B'δ regulatory subunit from other species of vertebrates.Regarding its expression pattern,RT-PCR revealed that the highest level of mRNA was detected in brain,a less level detected in liver,spermary,ovary,kidney and gill,and the lowest level detected in the fin.During different developmental stages of gold fish,the highest level of mRNA expression was detected at the stages of two-cell,multiple-cell,blastula and gastrula,and a decreased level of B'δ mRNA was detected in other developmental stages.At the protein level,the highest expression level of B'δ protein was found in spermary,ovary,brain and heart,a less amount found in liver and the lowest level detected in kidney,gill and fin.Developmentally,B'δ protein was strongly expressed at the stages of two-cell,multiple-cell,blastula,gastrula,neurula,and optic vesicle,and then decreased at the stages of brain differentiation and eye pigmentation.These results sugg
