Cancerous inhibitor of protein phosphatase 2A enhances chemoresistance of gastric cancer cells to oxaliplatin

BACKGROUND Cancerous inhibitor of protein phosphatase 2A(CIP2A)is a newly discovered oncogene.It is an active cell proliferation regulatory factor that inhibits tumor apoptosis in gastric cancer(GC)cells.CIP2A is functionally related to chemoresistance in various types of tumors according to recent studies.The underlying mechanism,however,is unknown.Further,the primary treatment regimen for GC is oxaliplatin-based chemotherapy.Nonetheless,it often fails due to chemoresistance of GC cells to oxaliplatin.AIM The goal of this study was to examine CIP2A expression and its association with oxaliplatin resistance in human GC cells.METHODS Immunohistochemistry was used to examine CIP2A expression in GC tissues and adjacent normal tissues.CIP2A expression in GC cell lines was reduced using small interfering RNA.After confirming the silencing efficiency,3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide tetrazolium and flow cytometry assays were used to evaluate cell proliferation and apoptosis caused by oxaliplatin treatment.Further,the key genes and protein changes were verified using realtime quantitative reverse transcription PCR and Western blotting,respectively,before and after intervention.For bioinformatics analysis,we used the R software and Bioconductor project.For statistical analysis,we used GraphPad Prism 6.0 and the Statistical Package for the Social Sciences software version 20.0(IBM,Armonk,United States).RESULTS A high level of CIP2A expression was associated with tumor size,T stage,lymph node metastasis,Tumor Node Metastasis stage,and a poor prognosis.Further,CIP2A expression was higher in GC cells than in normal human gastric epithelial cells.Using small interfering RNA against CIP2A,we discovered that CIP2A knockdown inhibited cell proliferation and significantly increased GC cell sensitivity to oxaliplatin.Moreover,CIP2A knockdown enhanced oxaliplatin-induced apoptosis in GC cells.Hence,high CIP2A levels in GC may be a factor in chemoresistance to oxaliplatin.In human GC cells,CIP2A regulated protein kinase B phosphorylation,and chemical inhibition of the protein kinase B signaling pathway was significantly associated with increased sensitivity to oxaliplatin.Therefore,the protein kinase B signaling pathway was correlated with CIP2Aenhanced chemoresistance of human GC cells to oxaliplatin.CONCLUSION CIP2A expression could be a novel therapeutic strategy for chemoresistance in GC.

Cantharidin and Its Analogues:Anticancer and Ser/Thr Protein Phosphatase Inhibitory Activities

This paper mainly describes the anticancer activities and Ser/Thr protein phosphatase inhibitory activities of cantharidin and its analogues.

Phosphoprotein phosphatase 1-interacting proteins as therapeutic targets in prostate cancer

Prostate cancer is a major public health concern world-wide, being one of the most prevalent cancers in men. Great improvements have been made both in terms of early diagnosis and therapeutics. However, there is still an urgent need for reliable biomarkers that could overcome the lack of cancer-specifcity of prostate-specifc antigen, as well as alternative therapeutic targets for advanced metastatic cases. Reversible phosphorylation of proteins is a post-translational modifcation critical to the regulation of numerous cellular processes. Phosphoprotein phosphatase 1 （PPP1） is a major serine/threonine phos-phatase, whose specifcity is determined by its interacting proteins. These interactors can be PPP1 substrates, regulators, or even both. Deregulation of this protein-protein interaction network alters cell dynamics and underlies the development of several cancer hallmarks. Therefore, the identification of PPP1 interactome in specific cellular context is of crucial importance. The knowledge on PPP1 complexes in prostate cancer remains scarce, with only 4 holoenzymes characterized in human prostate cancer models. However, an increasing number of PPP1 interactors have been identifed as expressed in human prostate tissue, including the tumor suppressors TP53 and RB1. Efforts should be made in order to identify the role of such proteins in prostate carcinogenesis, since only 26 have yet well-recognized roles. Here, we revise literature and human protein databases to provide an in-depth knowledge on the biological significance of PPP1 complexes in human prostate carcinogenesis and their potential use as therapeutic targets for the development of new therapies for prostate cancer.

Protein phosphatase PP1γ2 in sperm morphogenesis and epididymal initiation of sperm motility

The serine/threonine phosphatase （PP1） isoform PP1γ2, predominantly expressed in the testis, is a key enzyme in spermatozoa. High PP1γ2 catalytic activity holds motility in check in immature spermatozoa. Inhibition of PP1γ2 causes motility initiation in immature spermatozoa and motility stimulation and changes in flagellar beat parameters in mature spermatozoa. The PP1γ2 isoform is present in all mammalian spermatozoa studied： mouse, rat, hamster, bovine, non-human primate and man. We have now identified at least four of its regulatory proteins that regulate distinct pools of PP1γ2 within spermatozoa. Our studies provide new insights into biochemical mechanisms underlying development and regulation of sperm motility. We hypothesize that changes in sperm PP1γ2 activity as a result of phosphorylation and reversible binding of the regulatory proteins to the catalytic subunit are critical in the development and regulation of motility and the ability of sperm to fertilize eggs. Targeted disruption of the Ppplcc gene, which encodes the PP1γ1 or PP1γ2 isoforms, causes male infertility in mice as a result of impaired spermiogenesis. Our observations suggest that, in addition to motility, the protein phosphatase PP1γ2 might play an isoform-specific function in the development of specialized flagellar structures of mammalian spermatozoa. （Asian J Androl 2007 July; 9： 445--452）

Protein Phosphatase 2A as a Drug Target in the Treatment of Cancer and Alzheimer's Disease

Protein phosphatase 2A(PP2A)is a major serine/threonine phosphatase which participates in the regulation of multiple cellular processes.As a confirmed tumor suppressor,PP2A activity is downregulated in tumors and its re-activation can induce apoptosis of cancer cells.In the brains of Alzheimer's disease(AD)patients,decreased PP2A activity also plays a key role in promoting tau hyperphosphorylation and A0 generation.In this review,we discussed compounds aiming at modulating PP2A activity in the treatment of cancer or AD.The upstream factors that inactivate PP2A in diseases have not been fully elucidated and further studies are needed.It will help for the refinement and development of novel and clinically tractable PP2A-targeted compounds or therapies for the treatment of tumor and AD.

High expression of protein phosphatase 2 regulatory subunit B''alpha predicts poor outcome in hepatocellular carcinoma patients after liver transplantation

BACKGROUND Protein phosphatase 2 regulatory subunit B''alpha(PPP2R3A)gene has been reported in other tumors,but the influence of PPP2R3A gene expression on the occurrence,development,and prognosis of hepatocellular carcinoma(HCC)remains unclear.AIM To investigate whether the PPP2R3A gene could be used to predict tumor recurrence and survival of HCC patients after liver transplantation(LT).METHODS Diseased liver tissues of HCC patients after LT were collected as well as their clinical data and follow-up information.The immunohistochemical method was used to detect the expression of PPP2R3A protein in the tissues of 108 patients with primary liver cancer.Theχ2 test was used to analyze the relationship between PPP2R3A protein expression levels and the clinicopathological features of tumors.The Kaplan-Meier method was used to analyze overall postoperative survival.The COX proportional hazard model was used to analyze adverse prognostic factors.RESULTS Immunohistochemistry showed that the PPP2R3A protein was mainly expressed in the cytoplasm of HCC cells.Compared to corresponding peritumoral tissues,expression was higher in HCC tissues(P≤0.001).Correlation analysis showed that high PPP2R3A expression was correlated with preoperative serum alphafetoprotein(AFP)levels(P=0.003),tumor-node-metastasis-t stage(P≤0.001),and envelope invasion(P=0.001).Univariate analysis showed that overall survival(P≤0.001)and recurrence-free survival(P=0.025)of patients with high PPP2R3A expression(≥4 points)were poor compared to those with low expression(<4 points).The overall survival rates or recurrence-free survival rates at 1,2,and 3 years with high PPP2R3A expression were 73%,38%,and 23%or 31%,23%,and 23%,respectively.Multivariate analysis showed that high PPP2R3A expression(hazard ratio=2.900,95%confidence interval:1.411–5.960,P=0.004)was an independent survival risk factor of HCC patients after LT,and it was also an independent predictor of postoperative tumor recurrence.This study also showed in patients with AFP≥400 ng/mL,the overall survival(P≤0.001)and recurrencefree survival(P=0.023)of those with high PPP2R3A expression were significantly worse compared to those with low PPP2R3A expression.When PPP2R3A expression was low,the overall survival rate(P=0.461)or recurrence-free survival rate(P=0.072)after LT in patients with AFP<400 ng/mL and≥400 ng/mL was not significantly difference.The 1,2,and 3 year survival rate of patients with low PPP2R3A expression and AFP<400 ng/mL were 98%,80%,and 69%,respectively,while patients who met Hangzhou criteria had a posttransplant 1,2,and 3 years overall survival rate of 89%,66%,and 55%,respectively.CONCLUSION High expression of PPP2R3A might be a potential marker for predicting poor prognosis of HCC after LT.Combined with serum AFP levels,PPP2R3A might enhance the accuracy of predicting HCC outcome in patients after LT and supplement the efficacy of the Hangzhou criteria.

Cloning and sequence analysis of a full-length cDNA of SmPP1cb encoding turbot protein phosphatase 1 beta catalytic subunit

Reversible protein phosphorylation, catalyzed by protein kinases and phosphatases, is an important and versatile mechanism by which eukaryotic cells regulate almost all the signaling processes. Protein phosphatase 1 （PP1） is the first and well-characterized member of the protein serine/threonine phosphatase family. In the present study, a full-length cDNA encoding the beta isoform of the catalytic subunit of protein phosphatase l（PPlcb）, was for the first time isolated and sequenced from the skin tissue of flatfish turbot Scophthalmus maximus, designated SmPPlcb, by the rapid amplification of cDNA ends （RACE） technique. The cDNA sequence of SmPPlcb we obtained contains a 984 bp open reading frame （ORF）, flanked by a complete 39 bp 5＇ untranslated region and 462 bp 3＇ untranslated region. The ORF encodes a putative 327 amino acid protein, and the N-terminal section of this protein is highly acidic, Met-Ala-Glu-Gly-Glu-Leu-Asp-Val-Asp, a common feature for PP1 catalytic subunit but absent in protein phosphatase 2B （PP2B）. And its calculated molecular mass is 37 193 Da and pI 5.8. Sequence analysis indicated that, SmPPlcb is extremely conserved in both amino acid and nucleotide acid levels compared with the PPlcb of other vertebrates and invertebrates, and its Kozak motif contained in the 5＇UTR around ATG start codon is GXXAXXGXXATGG, which is different from mammalian in two positions A6 and G3, indicating the possibility of different initiation of translation in turbot, and also the 3＇UTR of SmPPlcb is highly diverse in the sequence similarity and length compared with other animals, especially zebraf＇lsh. The cloning and sequencing of SmPPlcb gene lays a good foundation for the future work on the biological functions of PP1 in the flatfish turbot.

The expression and localization of a novel protein phosphatase inhibitor 2810408A11Rik in mouse testis and sperm

This study investigated the expression and distribution of 2810408A11Rik in mouse testis and sperm, and explored its role in sperrnatogenesis and sperm function. The expression levels of 2810408A11Rik mRNA in multiple tissue samples were analyzed using bioinformatic resources and RT-PCR technique. A specific rabbit polyclonal antibody was prepared by prokaryotic expression of 2810408A11Rik recombinant protein and utilized for animal immunization. Western blotting, immunohistochemistry and immunofluorescence were used to detect the expression and distribution of 2810408A11Rik. The results of the bioinformatic analysi and RT-PCR showed that 2810408A11Rik mRNA was specifically expressed in mouse testis, and 2810408AllRik protein included a protein phosphatase inhibitor domain. Western blotting assays, immunohistochemistry and immunofluorescence confirmed the expression of 2810408A11Rik protein in mouse testis, especially in post-meiosis round and long spermatids, and that it is localized in the acrosome and the post-nucleus area of sperm. Our findings suggest that 2810408A11Rik may play an important role in spermatogenesis, sperm capacitation and fertilization.

COMPARATIVE STUDY OF PHOSPHOTYROSYL PROTEIN PHOSPHATASE OF MICE NORMAL LIVER, REGENERATING LIVER, AND MICE H22A HEPATOMA ASCITES CELL

In regenerating liver of mice, marked increase of the activity of phosphotyrosyl protein phosphatase (PTPP) in cytosol was observed. The PTPP activity varied with time and reached the highest level between 24 to 48 hours after partial hepatectomy. In H22a cells the PTPP activity found in every subcellular fraction was lower than that of the normal liver. The PTPP activity was mostly concentrated in lysosomes of normal liver, but mainly distributed in nucleus, cytosol and microsome of regenerating liver. In H22a cells PTPP activity seemed distribute evenly. Five similar major PTPP peaks (I-V) were obtained on DEAE cellulose chromatography of cytosols from all three of liver cells studied. However, two additional PTPP peaks, a and b, were also obtained from cytosol of liver.

Protein tyrosine phosphatase non-receptor Ⅱ:A possible biomarker of poor prognosis and mediator of immune evasion in hepatocellular carcinoma

BACKGROUND The incidence of primary liver cancer is increasing year by year.In 2022 alone,more than 900000 people were diagnosed with liver cancer worldwide,with hepatocellular carcinoma(HCC)accounting for 75%-85%of cases.HCC is the most common primary liver cancer.China has the highest incidence and mortality rate of HCC in the world,and it is one of the malignant tumors that seriously threaten the health of Chinese people.The onset of liver cancer is occult,the early cases lack typical clinical symptoms,and most of the patients are already in the middle and late stage when diagnosed.Therefore,it is very important to find new markers for the early detection and diagnosis of liver cancer,improve the therapeutic effect,and improve the prognosis of patients.Protein tyrosine phosphatase non-receptor 2(PTPN2)has been shown to be associated with colorectal cancer,triple-negative breast cancer,non-small cell lung cancer,and prostate cancer,but its biological role and function in tumors remain to be further studied.AIM To combine the results of relevant data obtained from The Cancer Genome Atlas(TCGA)to provide the first in-depth analysis of the biological role of PTPN2 in HCC.METHODS The expression of PTPN2 in HCC was first analyzed based on the TCGA database,and the findings were then verified by immunohistochemical staining,quantitative real-time polymerase chain reaction(qRT-PCR),and immunoblotting.The value of PTPN2 in predicting the survival of patients with HCC was assessed by analyzing the relationship between PTPN2 expression in HCC tissues and clinicopathological features.Finally,the potential of PTPN2 affecting immune escape of liver cancer was evaluated by tumor immune dysfunction and exclusion and immunohistochemical staining.RESULTS The results of immunohistochemical staining,qRT-PCR,and immunoblotting in combination with TCGA database analysis showed that PTPN2 was highly expressed and associated with a poor prognosis in HCC patients.Kyoto Encyclopedia of Genes and Genomes enrichment analysis showed that PTPN2 was associated with various pathways,including cancer-related pathways,the Notch signaling pathway,and the MAPK signaling pathway.Gene Set Enrichment Analysis showed that PTPN2 was highly expressed in various immune-related pathways,such as the epithelial mesenchymal transition process.A risk model score based on PTPN2 showed that immune escape was significantly enhanced in the high-risk group compared with the low-risk group.CONCLUSION This study investigated PTPN2 from multiple biological perspectives,revealing that PTPN2 can function as a biomarker of poor prognosis and mediate immune evasion in HCC.

Overexpression of mitogen-activated protein kinase phosphatase-1 in endothelial cells reduces blood-brain barrier injury in a mouse model of ischemic stroke

Ischemic stroke can cause blood-brain barrier(BBB)injury,which worsens brain damage induced by stroke.Abnormal expression of tight junction proteins in endothelial cells(ECs)can increase intracellular space and BBB leakage.Selective inhibition of mitogen-activated protein kinase,the negative regulatory substrate of mitogen-activated protein kinase phosphatase(MKP)-1,improves tight junction protein function in ECs,and genetic deletion of MKP-1 aggravates ischemic brain injury.However,whether the latter affects BBB integrity,and the cell type-specific mechanism underlying this process,remain unclear.In this study,we established an adult male mouse model of ischemic stroke by occluding the middle cerebral artery for 60 minutes and overexpressed MKP-1 in ECs on the injured side via lentiviral transfection before stroke.We found that overexpression of MKP-1 in ECs reduced infarct volume,reduced the level of inflammatory factors interleukin-1β,interleukin-6,and chemokine C-C motif ligand-2,inhibited vascular injury,and promoted the recovery of sensorimotor and memory/cognitive function.Overexpression of MKP-1 in ECs also inhibited the activation of cerebral ischemia-induced extracellular signal-regulated kinase(ERK)1/2 and the downregulation of occludin expression.Finally,to investigate the mechanism by which MKP-1 exerted these functions in ECs,we established an ischemic stroke model in vitro by depriving the primary endothelial cell of oxygen and glucose,and pharmacologically inhibited the activity of MKP-1 and ERK1/2.Our findings suggest that MKP-1 inhibition aggravates oxygen and glucose deprivation-induced cell death,cell monolayer leakage,and downregulation of occludin expression,and that inhibiting ERK1/2 can reverse these effects.In addition,co-inhibition of MKP-1 and ERK1/2 exhibited similar effects to inhibition of ERK1/2.These findings suggest that overexpression of MKP-1 in ECs can prevent ischemia-induced occludin downregulation and cell death via deactivating ERK1/2,thereby protecting the integrity of BBB,alleviating brain injury,and improving post-stroke prognosis.

Protein phosphatase 2A,a key player in Alzheimer’s disease

Protein phosphatase 2A(PP2A)is the pre-dominant serine/threonine phosphatase in eukaryotic cells.In the brains of patients with Alzheimer’s disease(AD),decreased PP2A activities were observed,which is suggested to be involved in neurofibrillary tangle(NFT)formation,disturbed amyloid precursor protein(APP)secretion and neurodegeneration in AD brain.Based on our research and other previousfindings,decreased PP2Ac level,decreased PP2A holoenzyme composition,increased level of PP2A inhibitors,increased PP2Ac Leu309 demethylation and Tyr307 phosphorylation underlie PP2A inactivation in AD.β-amyloid(Aβ)over-production,estrogen deficiency and impaired homocys-teine metabolism are the possible up-stream factors that inactivate PP2A in AD neurons.Further studies are required to disclose the role of PP2A in Alzheimer’s disease.

A Kelch Motif-Containing Serine/Threonine Protein Phosphatase Determines the Large Grain QTL Trait in Rice

A thorough understanding of the genetic basis of rice grain traits is critical for the improvement of rice （Oryza sativa L.） varieties. In this study, we generated an F2 population by crossing the large-grain japonica cultivar CW23 with Peiai 64 （PA64）, an elite indica small-grain cultivar. Using QTL analysis, 17 QTLs for five grain traits were detected on four different chromosomes. Eight of the QTLs were newly-identified in this study. In particular, qGL3-1, a newly-identified grain length QTL with the highest LOD value and largest phenotypic variation, was fine-mapped to the 17 kb region of chromosome 3. A serine/threonine protein phosphatase gene encoding a repeat domain containing two Kelch motifs was identified as the unique candidate gene corresponding to this QTL. A comparison of PA64 and CW23 sequences revealed a single nucleotide substitution （C→A） at position 1092 in exon 10, resulting in replacement of Asp （D） in PA64 with Glu （E） in CW23 for the 364th amino acid. This variation is located at the D position of the conserved sequence motif AVLDT of the Kelch repeat. Genetic analysis of a near-isogenic line （NIL） for qGL3-1 revealed that the allele qGL3-1 from CW23 has an additive or partly dominant effect, and is suitable for use in molecular marker-assisted selection.

Effect of microcystin-LR on protein phosphatase 2A and its function in human amniotic epithelial cells

Due to their toxicity,the increased distribution of microcystins(MCs) has become an important worldwide problem.MCs have been recognized as inhibitors of protein phosphatase 2A(PP2A) through their binding to the PP2A catalytic subunit.However,the exact mechanism of MC toxicity has not been elucidated,especially concerning the cellular response and its autoregulation.To further dissect the role of PP2A in MC-induced toxicity,the present study was undertaken to determine the response of PP2A in human amniotic epithelial(FL) cells treated with microcystin-LR(MCLR),one of the MC congeners.The results show that a low-dose treatment of MCLR in FL cells for 6 h induced an increase in PP2A activity,and a high-dose treatment of MCLR for 24 h decreased the activity of PP2A,as expected.The increased mRNA and protein levels of the PP2A C subunit may explain the increased activity of PP2A.Furthermore,MCLR altered microtubule post-translational modifications through PP2A.These results further clarify the underlying mechanism how MCLR affects PP2A and may be helpful for elucidating the complex toxicity of MCLR.

Zinc binds to and directly inhibits protein phosphatase 2A in vitro

Zinc induces protein phosphatase 2A （PP2A） inactivation and tau hyperphosphorylation through PP2A （tyrosine 307） phosphorylation in cells and the brain, but whether Zn2＋ has a direct inhibitory effect on PP2A is not clear. Here we explored the effect of Zn2＋ on PP2A and their direct interaction in vitro. The results showed that Zn2＋ mimicked the inhibitory effect of okadaic acid on protein phosphatase and prevented tau dephosphorylation in N2a cell lysates. PP2A activity assays indicated that a low concentration （10 pmol/L） of Zn2＋ inhibited PP2A directly. Further Zn2＋-IDA-agarose affinity binding assays showed that Zn2＋ bound to and inhibited PP2Ac（51l-270） but not PP2Ac（1.50） or PP2Ac（27.309）. Taken together, Zn2＋ inhibits PP2A directly through binding to PP2Ac（51-270） in vitro.

Functional repertoire of protein kinases and phosphatases in synaptic plasticity and associated neurological disorders

Protein phosphorylation and dephosphorylation are two essential and vital cellular mechanisms that regulate many receptors and enzymes through kinases and phosphatases.Ca^2+- dependent kinases and phosphatases are responsible for controlling neuronal processing;balance is achieved through opposition.During molecular mechanisms of learning and memory,kinases generally modulate positively while phosphatases modulate negatively.This review outlines some of the critical physiological and structural aspects of kinases and phosphatases involved in maintaining postsynaptic structural plasticity.It also explores the link between neuronal disorders and the deregulation of phosphatases and kinases.

Effect of inhibiting tyrosine kinase Src expression on protein phosphatase 2A and tau phosphorylation

The aim of this study is to investigate the effect of tyrosine kinase Src on Tyrosine 307(Y307)phosphor-ylation,protein phosphatase 2A(PP2A)activity,and on tau phosphorylation.Specific Src siRNA was transfected into cultured mouse neuroblastoma N2a cells to inhibit the expression of Src protein,and the phosphorylation levels of PP2A Y307 and tau at different sites,as well as PP2A activity were detected at different time points after siRNA transfection.Twelve hours after siRNA transfec-tion,the protein level of Src was dramatically decreased,with decreased PP2A Y307 phosphorylation.However,the total PP2A protein level was also decreased,together with a decreased PP2A activity.Tau was hyperpho-sphorylated at the Ser198/199/202 sites.Multiple factors may be involved in the cellular regulation of PP2A activ-ity.Inhibiting Src expression could induce inactivation of PP2A and tau hyperphosphorylation.

Protein phosphatase 6 (Pp6) is crucial for regulatory T cell function and stability in autoimmunity

Regulatory T(T_(reg))cells constitute a dynamic population that is critical in autoimmunity.T_(reg) cell therapies for autoimmune diseases are mainly focused on enhancing their suppressive activities.However,recent studies demonstrated that certain inflammatory conditions induce T_(reg) cell instability with diminished FoxP3 expression and convert them into pathogenic effector cells.Therefore,the identification of novel targets crucial to both T_(reg) cell function and plasticity is of vital importance to the development of therapeutic approaches in autoimmunity.In this study,we found that conditional Pp6 knockout(cKO)in T_(reg) cells led to spontaneous autoinflammation,immune cell activation,and diminished levels of FoxP3 in CD4^(+)T cells in mice.Loss of Pp6 in T_(reg) cells exacerbated two classical mouse models of T_(reg)-related autoinflammation.Mechanistically,Pp6 deficiency increased CpG motif methylation of the FoxP3 locus by dephosphorylating Dnmt1 and enhancing Akt phosphorylation at Ser473/Thr308,leading to impaired FoxP3 expression in T_(reg) cells.In summary,our study proposes Pp6 as a critical positive regulator of FoxP3 that acts by decreasing DNA methylation of the FoxP3 gene enhancer and inhibiting Akt signaling,thus maintaining T_(reg) cell stability and preventing autoimmune diseases.

RNAi screen to identify protein phosphatases that regulate the NF-kappaB signaling

NF-kappaB plays a critical role in cell survival,apoptosis,and inflammatory responses.Serine/threoninespecific phosphatases(PPs)represent the second major class of enzymes that catalyze the dephosphorylation of proteins.The roles of PPs regulating NF-kappaB activities are poorly understood.Here we describe an RNAi-based screen to identify the PPs that involve in regulating NFkappaB signaling.Thirty-four candidate PPs siRNAs were synthesized and primarily screened by NF-kappaB reporter gene assay in HeLa cells.PHLPP,one of the protein phosphatase type 2C family members(PP2C),was identified as a positive regulator of NF-kappaB signaling.Knock-down of PHLPP dramatically attenuated TNFα-stimulated NF-kappaB transcriptional activation.Knockdown of PHLPP led to enhancement of NF-kappaB/p65 nuclear import and retention,but decreased TNFα-induced phosphorylation at Ser276 on p65.This critical phosphorylation was also drastically reduced by knock-down of PKCalpha and Akt1,two important serine/threonine kinases dephosphorylated by PHLPP.The results together suggest that PHLPP-Akt-PKC may represent an important signaling loop that activates NF-kappaB/p65 signaling through critical serine phosphorylation.

Mitogen-activated protein kinase phosphatase 1 protects PC12 cells from amyloid beta-induced neurotoxicity

The mitogen-activated protein kinase（MAPK） signaling pathway plays an important role in the regulation of cell growth, proliferation, differentiation, transformation and death. Mitogen-activated protein kinase phosphatase 1（MKP1） has an inhibitory effect on the p38 MAPK and JNK pathways, but it is unknown whether it plays a role in Aβ-induced oxidative stress and neuronal inflammation. In this study, PC12 cells were infected with MKP1 sh RNA, MKP1 lentivirus or control lentivirus for 12 hours, and then treated with 0.1, 1, 10 or 100 μM amyloid beta 42（Aβ42）. The cell survival rate was measured using the cell counting kit-8 assay. MKP1, tumor necrosis factor-alpha（TNF-α） and interleukin-1β（IL-1β） m RNA expression levels were analyzed using quantitative real time-polymerase chain reaction. MKP1 and phospho-c-Jun N-terminal kinase（JNK） expression levels were assessed using western blot assay. Reactive oxygen species（ROS） levels were detected using 2′,7′-dichlorofluorescein diacetate. Mitochondrial membrane potential was measured using flow cytometry. Superoxide dismutase activity and malondialdehyde levels were evaluated using the colorimetric method. Lactate dehydrogenase activity was measured using a microplate reader. Caspase-3 expression levels were assessed by enzyme-linked immunosorbent assay. Apoptosis was evaluated using the terminal deoxynucleotidyl transferase d UTP nick end labeling method. MKP1 overexpression inhibited Aβ-induced JNK phosphorylation and the increase in ROS levels. It also suppressed the Aβ-induced increase in TNF-α and IL-1β levels as well as apoptosis in PC12 cells. In contrast, MKP1 knockdown by RNA interference aggravated Aβ-induced oxidative stress, inflammation and cell damage in PC12 cells. Furthermore, the JNK-specific inhibitor SP600125 abolished this effect of MKP1 knockdown on Aβ-induced neurotoxicity. Collectively, these results show that MKP1 mitigates Aβ-induced apoptosis, oxidative stress and neuroinflammation by inhibiting the JNK signaling pathway, thereby playing a neuroprotective role.