Characterizing ambulatory function in children with PPP2R5D-related neurodevelopmental disorder

BACKGROUND

Individuals with PPP2R5D-related neurodevelopmental disorder have an atypical gait pattern characterized by ataxia and incoordination. Structured, quantitative assessments are needed to further understand the impact of these impairments on function.

RESEARCH QUESTION

How do gait parameters and ambulatory function of individuals with PPP2R5D-related neurodevelopmental disorder compare to age and sex matched healthy norms?

METHODS

Twenty-six individuals with PPP2R5D pathogenic genetic variants participated in this observational, single visit study. Participants completed at least one of the following gait assessments: quantitative gait analysis at three different speeds (preferred pace walking (PPW), fast paced walking (FPW) and running, six-minute walk test (6MWT), 10-meter walk run (10MWR), and timed up and go (TUG). Descriptive statistics were used to summarize gait variables. Percent of predicted values were calculated using published norms. Paired t-tests and regression analyses were used to compare gait variables.

RESULTS

The median age of the participants was 8 years (range 4-27) and eighteen (69.2 %) were female. Individuals with PPP2R5D-related neurodevelopmental disorder walked slower and with a wider base of support than predicted for their age and sex. Stride velocity ranged from 48.9 % to 70.1 % and stride distance from 58.5 % to 81.9 % of predicted during PPW. Percent of predicted distance walked on the 6MWT ranged from 30.6 % to 71.1 % representing varied walking impairment. Increases in stride distance, not cadence, were associated with changes in stride velocity in FPW (R2 = 0.675, p =< 0.001) and running conditions (R2 = 0.918, p =< 0.001).

SIGNIFICANCE

We quantitatively assessed the abnormal gait in individuals with PPP2R5D-related neurodevelopmental disorder. These impairments may affect ability to adapt to environmental changes and participation in daily life. Rehabilitative interventions targeting gait speed and balance may improve function and safety for individuals with PPP2R5D-related neurodevelopmental disorder.

Sit4 Genetically Interacts with Vps27 to Regulate Mitochondrial Function and Lifespan in Saccharomyces cerevisiae

The Sit4 protein phosphatase plays a key role in orchestrating various cellular processes essential for maintaining cell viability during aging. We have previously shown that SIT4 deletion promotes vacuolar acidification, mitochondrial derepression, and oxidative stress resistance, increasing yeast chronological lifespan. In this study, we performed a proteomic analysis of isolated vacuoles and yeast genetic interaction analysis to unravel how Sit4 influences vacuolar and mitochondrial function. By employing high-resolution mass spectrometry, we show that sit4Δ vacuolar membranes were enriched in Vps27 and Hse1, two proteins that are part of the endosomal sorting complex required for transport-0. In addition, SIT4 exhibited a negative genetic interaction with VPS27, as sit4∆vps27∆ double mutants had a shortened lifespan compared to sit4∆ and vps27∆ single mutants. Our results also show that Vps27 did not increase sit4∆ lifespan by improving protein trafficking or vacuolar sorting pathways. However, Vps27 was critical for iron homeostasis and mitochondrial function in sit4∆ cells, as sit4∆vps27∆ double mutants exhibited high iron levels and impaired mitochondrial respiration. These findings show, for the first time, cross-talk between Sit4 and Vps27, providing new insights into the mechanisms governing chronological lifespan.

Non-negligible inhibition effect of microcystin-LR biodegradation products target to protein phosphatase 2A

Though biodegradation is an important regulation pathway for microcystins (MCs) pollution, more consideration needs to be given to the potential risk associated with related biodegradation products (MC-BDPs). In this work, typical MCLR-BDPs were prepared and their toxicity was evaluated by protein phosphatases (PPs) inhibition assay. Results showed the initial ring opening of MCLR played a crucial role in detoxification. However, partial MCLR-BDPs still retained the critical structures and thus exhibited certain toxicity (2.8-43.5% of MCLR). With the aid of molecular simulation, the mechanism for the potential toxicity of BDPs targeting PP2A was elucidated. The initial ring opening made the loss of hydrogen bond Leu2←Arg89, and pi-H bond Adda5-His191, which was responsible for the significant reduction in the toxicity of MCLR-BDP. However, the key hydrogen bonds MeAsp3←Arg89, Glu6←Arg89, Adda5←Asn117, Adda5←His118, Arg4→Pro213, Arg4←Arg214, Ala1←Arg268, and Mdha7←Arg268, metal bond Glu6-Mn12+, and ionic bonds Glu6-Arg89, and Glu6-Mn22+ were preserved in varying degrees. Above preserved interactions maintained the interactions between PP2A and Mn2+ ions (reducing the exposure of Mn2+ ions). Above preserved interactions also hindered the combination of phosphate groups to Arg214 residual and thus exhibited potential toxicity.

Caregiver-reported dental manifestations in individuals with genetic neurodevelopmental disorders

BACKGROUND

Children with neurodevelopmental disorders (NDDs) often have poor oral health and dental abnormalities. An increasing number of genes have been associated with neurodevelopmental conditions affecting the oral cavity, but the specific dental features associated with many genes remain unknown.

AIM

To report the types and frequencies of dental manifestations in children with neurodevelopmental conditions of known genetic cause.

DESIGN

A 30-question survey assesing ectodermal and dental features was administered through Simons Searchlight, with which formed a recontactable cohort of individuals with genetic NDDs often associated with autism spectrum disorder (ASD).

RESULTS

Data were collected from a largely paediatric population with 620 affected individuals across 39 genetic conditions and 145 unaffected siblings without NDDs for comparison. Drooling, difficulty accessing dental care, late primary teeth eruption, abnormal primary and permanent teeth formation, misshapen nails, and hair loss were more frequent in individuals with NDDs. Additionally, we evidenced an association between three new pathogenic gene variant/oral manifestation pairs: CSNK2A1/unusual primary teeth, DYRK1A/late primary teeth eruption, and PPP2R5D/sialorrhea.

CONCLUSION

Our results demonstrate that genetic NDDs caused by mutations in CSNK2A1, DYRK1A, and PP2R5D are associated with unique dental manifestations, and knowledge of these features can be helpful to personalize dental care.

Pharmacogenomics of intravenous immunoglobulin response in Kawasaki disease

Introduction

Kawasaki disease (KD) is a diffuse vasculitis in children. Response to high dose intravenous gamma globulin (IVIG), the primary treatment, varies according to genetic background. We sought to identify genetic loci, which associate with treatment response using whole genome sequencing (WGS).

Method

We performed WGS in 472 KD patients with 305 IVIG responders and 167 non-responders defined by AHA clinical criteria. We conducted logistic regression models to test additive genetic effect in the entire cohort and in four subgroups defined by ancestry information markers (Whites, African Americans, Asians, and Hispanics). We performed functional mapping and annotation using FUMA to examine genetic variants that are potentially involved IVIG non-response. Further, we conducted SNP-set [Sequence] Kernel Association Test (SKAT) for all rare and common variants.

Results

Of the 43,288,336 SNPs (23,660,970 in intergenic regions, 16,764,594 in introns and 556,814 in the exons) identified, the top ten hits associated with IVIG non-response were in FANK1, MAP2K3:KCNJ12, CA10, FRG1DP, CWH43 regions. When analyzed separately in ancestry-based racial subgroups, SNPs in several novel genes were associated. A total of 23 possible causal genes were pinpointed by positional and chromatin mapping. SKAT analysis demonstrated association in the entire MANIA2, EDN1, SFMBT2, and PPP2R5E genes and segments of CSMD2, LINC01317, HIVEPI, HSP90AB1, and TTLL11 genes.

Conclusions

This WGS study identified multiple predominantly novel understudied genes associated with IVIG response. These data can serve to inform regarding pathogenesis of KD, as well as lay ground work for developing treatment response predictors.

Fly clock, my clock, and lamin B receptor

In the fruit fly Drosophila melanogaster, circadian rhythm was disrupted when the inner nuclear membrane protein lamin B receptor (LBR) was depleted from its clock neurons (Proc. Natl. Acad. Sci. USA 118, e2019756118. 2021; https://doi.org/10. 1073/pnas.2019756118 and Research 6, 0139, 2023; https://doi.org/10.34133/research.0139). Ordinarily, the clock proteinPERIOD (PER) forms foci close to the inner nuclear membrane in the circadian clock's repression phase. The size, number, and location of foci near the nuclear membrane oscillate with a 24-h rhythm. When LBR was absent the foci did not form. The PER foci bring per and other clock genes close to the nuclear envelope, where their transcription is silenced. Then, in the circadian clock's activation phase, the PER protein gradually gets degraded and the foci disappear. The clock genes, including per, relocate to the nucleus interior where they resume transcription. Rhythmic re-positioning of clock genes between nucleus periphery and interior, correlates with their repression and activation in the circadian cycle. Absence of LBR disrupted this rhythm. Phosphorylation of PER promoted the formation of foci whereas dephosphorylation by protein phosphatase 2A causedthem to disappear. LBR promoted focus formation by destabilizing the catalytic subunit of protein phosphatase 2A. The lbr gene is no stranger to this journal. The first hint that vertebrate LBR is also a sterol biosynthesis enzyme, specifically, a sterol C14 reductase, was reported here (J. Genet. 73, 33-41, 1994; https://www.ias.ac.in/article/fulltext/jgen/073/01/0033-0041). Mutations in the human Lbr gene cause a range of phenotypes--from the relatively benign Pelger-Huet anomaly to the perinatally lethal Greenberg skeletal dysplasia.Drosophila, like all insects, is a sterol auxotroph. The fly orthologue of vertebrate lbr genes encodes a protein (dLBR) that shares several properties with vertebrate LBR proteins, with one notable exception. While human LBR complemented theyeast Saccharomyces cerevisiae erg24 mutant which lacks sterol C14 reductase activity, dLBR did not (J. Cell. Sci. 117, 2015-28, 2004; https://doi.org/10.1242/jcs.01052). Despite not possessing sterol reductase activity, dLBR retains significant sequence homology with vertebrate LBRs which have this activity. An undergraduate summer trainee in my laboratory obtained early (unpublished) evidence that dLBR lost sterol reductase activity during evolution. She transferred adult drosophila flies to vials containing a medium made of agar, dextrose, and dried and powdered mycelium of the filamentous fungus Neurospora crassa. On medium made with wild-type mycelium, theflies mated, laid eggs, hatched larvae, and developed pupae which eclosed progeny adult flies. The life cycle was no different than on 'regular' fly food composed of agar, dextrose and yeast extract. However, on a medium made with mycelium from a sterol C14 reductase null mutant, the flies laid eggs which hatched and released larvae, but the larvae failed to pupate, and no adult progeny flies emerged. This was because the fly lacks a sterol C14 reductase. The wild-type sterol, ergosterol, is a precursor of the steroid hormone ecdysone needed for molting and metamorphosis. Can expression of vertebrate LBR in dLBR-depleted fly clock neurons restore circadian rhythm? Can expression of vertebrate LBR enable flies to complete their life cycle on mutant Neurospora medium? Does LBR regulate the vertebrate clock in a like manner? If yes, then is the sterol reductase activity dispensable in this role? These are some questions that came to my mind on a recent morning walk. The walk itself was a much-cherished outcome of my circadian clock.

White spot syndrome virus hijacks host PP2A-FOXO axes to promote its propagation

Viruses have developed superior strategies to escape host defenses or exploit host components and enable their infection. The forkhead box transcription factor O family proteins (FOXOs) are reportedly utilized by human cytomegalovirus during their reactivation in mammals, but if FOXOs are exploited by viruses during their infection remains unclear. In the present study, we found that the FOXO of kuruma shrimp (Marsupenaeus japonicus) was hijacked by white spot syndrome virus (WSSV) during infection. Mechanistically, the expression of leucine carboxyl methyl transferase 1 (LCMT1) was up-regulated during the early stages of WSSV infection, which activated the protein phosphatase 2A (PP2A) by methylation, leading to dephosphorylation of FOXO and translocation into the nucleus. The FOXO directly promoted transcription of the immediate early gene, wsv079 of WSSV, which functioned as a transcriptional activator to initiate the expression of viral early and late genes. Thus, WSSV utilized the host LCMT1-PP2A-FOXO axis to promote its replication during the early infection stage. We also found that, during the late stages of WSSV infection, the envelope protein of WSSV (VP26) promoted PP2A activity by directly binding to FOXO and the regulatory subunit of PP2A (B55), which further facilitated FOXO dephosphorylation and WSSV replication via the VP26-PP2A-FOXO axis in shrimp. Overall, this study reveals novel viral strategies by which WSSV hijacks host LCMT1-PP2A-FOXO or VP26-PP2A-FOXO axes to promote its propagation, and provides clinical targets for WSSV control in shrimp aquaculture.

RNF149 confers cisplatin resistance in esophageal squamous cell carcinoma via destabilization of PHLPP2 and activating PI3K/AKT signalling

Chemo-resistance has been identified as a crucial factor contributing to tumor recurrence and a leading cause of worse prognosis in patients with ESCC. Therefore, unravel the critical regulators and effective strategies to overcome drug resistance will have a significant clinical impact on the disease. In our study we found that RNF149 was upregulated in ESCC and high RNF149 expression was associated with poor prognosis with ESCC patients. Functionally, we have demonstrated that overexpression of RNF149 confers CDDP resistance to ESCC; however, inhibition of RNF149 reversed this phenomenon both in vitro and in vivo. Mechanistically, we demonstrated that RNF149 interacts with PH domain and leucine rich repeat protein phosphatase 2 (PHLPP2) and induces E3 ligase-dependent protein degradation of PHLPP2, substantially activating the PI3K/AKT signalling pathway in ESCC. Additionally, we found that inhibition of PI3K/AKT signalling pathway by AKT siRNA or small molecule inhibitor significantly suppressed RNF149-induced CDDP resistance. Importantly, RNF149 locus was also found to be amplified not only in ESCC but also in various human cancer types. Our data suggest that RNF149 might function as an oncogenic gene. Targeting the RNF149/PHLPP2/PI3K/Akt axis may be a promising prognostic factor and valuable therapeutic target for malignant tumours.

Protein Phosphatase 2A as a Therapeutic Target in Pulmonary Diseases

New disease targets and medicinal chemistry approaches are urgently needed to develop novel therapeutic strategies for treating pulmonary diseases. Emerging evidence suggests that reduced activity of protein phosphatase 2A (PP2A), a complex heterotrimeric enzyme that regulates dephosphorylation of serine and threonine residues from many proteins, is observed in multiple pulmonary diseases, including lung cancer, smoke-induced chronic obstructive pulmonary disease, alpha-1 antitrypsin deficiency, asthma, and idiopathic pulmonary fibrosis. Loss of PP2A responses is linked to many mechanisms associated with disease progressions, such as senescence, proliferation, inflammation, corticosteroid resistance, enhanced protease responses, and mRNA stability. Therefore, chemical restoration of PP2A may represent a novel treatment for these diseases. This review outlines the potential impact of reduced PP2A activity in pulmonary diseases, endogenous and exogenous inhibitors of PP2A, details the possible PP2A-dependent mechanisms observed in these conditions, and outlines potential therapeutic strategies for treatment. Substantial medicinal chemistry efforts are underway to develop therapeutics targeting PP2A activity. The development of specific activators of PP2A that selectively target PP2A holoenzymes could improve our understanding of the function of PP2A in pulmonary diseases. This may lead to the development of therapeutics for restoring normal PP2A responses within the lung.

Does modulation of tau hyperphosphorylation represent a reasonable therapeutic strategy for Alzheimer's disease? From preclinical studies to the clinical trials

Protein kinases (PKs) have emerged as one of the most intensively investigated drug targets in current pharmacological research, with indications ranging from oncology to neurodegeneration. Tau protein hyperphosphorylation was the first pathological post-translational modification of tau protein described in Alzheimer's disease (AD), highlighting the role of PKs in neurodegeneration. The therapeutic potential of protein kinase inhibitors (PKIs)) and protein phosphatase 2 A (PP2A) activators in AD has recently been explored in several preclinical and clinical studies with variable outcomes. Where a number of preclinical studies demonstrate a visible reduction in the levels of phospho-tau in transgenic tauopathy models, no reduction in neurofibrillary lesions is observed. Amongst the few PKIs and PP2A activators that progressed to clinical trials, most failed on the efficacy front, with only a few still unconfirmed and potential positive trends. This suggests that robust preclinical and clinical data is needed to unequivocally evaluate their efficacy. To this end, we take a systematic look at the results of preclinical and clinical studies of PKIs and PP2A activators, and the evidence they provide regarding the utility of this approach to evaluate the potential of targeting tau hyperphosphorylation as a disease modifying therapy.

Activation of the PP2A-B56α heterocomplex synergizes with venetoclax therapies in AML through BCL2 and MCL1 modulation

Venetoclax combination therapies are becoming the standard of care in acute myeloid leukemia (AML). However, the therapeutic benefit of these drugs in older/unfit patients is limited to only a few months, highlighting the need for more effective therapies. Protein phosphatase 2A (PP2A) is a tumor suppressor phosphatase with pleiotropic functions that becomes inactivated in ∼70% of AML cases. PP2A promotes cancer cell death by modulating the phosphorylation state in a variety of proteins along the mitochondrial apoptotic pathway. We therefore hypothesized that pharmacological PP2A reactivation could increase BCL2 dependency in AML cells and, thus, potentiate venetoclax-induced cell death. Here, by using 3 structurally distinct PP2A-activating drugs, we show that PP2A reactivation synergistically enhances venetoclax activity in AML cell lines, primary cells, and xenograft models. Through the use of gene editing tools and pharmacological approaches, we demonstrate that the observed therapeutic synergy relies on PP2A complexes containing the B56α regulatory subunit, of which expression dictates response to the combination therapy. Mechanistically, PP2A reactivation enhances venetoclax-driven apoptosis through simultaneous inhibition of antiapoptotic BCL2 and extracellular signal-regulated kinase signaling, with the latter decreasing MCL1 protein stability. Finally, PP2A targeting increases the efficacy of the clinically approved venetoclax and azacitidine combination in vitro, in primary cells, and in an AML patient-derived xenograft model. These preclinical results provide a scientific rationale for testing PP2A-activating drugs with venetoclax combinations in AML.

PP1, PP2A and PP2B Interplay in the Regulation of Sperm Motility: Lessons from Protein Phosphatase Inhibitors

Male fertility relies on the ability of spermatozoa to fertilize the egg in the female reproductive tract (FRT). Spermatozoa acquire activated motility during epididymal maturation; however, to be capable of fertilization, they must achieve hyperactivated motility in the FRT. Extensive research found that three protein phosphatases (PPs) are crucial to sperm motility regulation, the sperm-specific protein phosphatase type 1 (PP1) isoform gamma 2 (PP1γ2), protein phosphatase type 2A (PP2A) and protein phosphatase type 2B (PP2B). Studies have reported that PP activity decreases during epididymal maturation, whereas protein kinase activity increases, which appears to be a requirement for motility acquisition. An interplay between these PPs has been extensively investigated; however, many specific interactions and some inconsistencies remain to be elucidated. The study of PPs significantly advanced following the identification of naturally occurring toxins, including calyculin A, okadaic acid, cyclosporin, endothall and deltamethrin, which are powerful and specific PP inhibitors. This review aims to overview the protein phosphorylation-dependent biochemical pathways underlying sperm motility acquisition and hyperactivation, followed by a discussion of the PP inhibitors that allowed advances in the current knowledge of these pathways. Since male infertility cases still attain alarming numbers, additional research on the topic is required, particularly using other PP inhibitors.

PP2ARts1 antagonizes Rck2-mediated hyperosmotic stress signaling in yeast

In Saccharomyces cerevisiae, impairment of protein phosphatase PP2ARts1 leads to temperature and hyperosmotic stress sensitivity, yet the underlying mechanism and the scope of action of the phosphatase in the stress response remain elusive. Using a quantitative mass spectrometry-based approach we have identified a set of putative substrate proteins that show both hyperosmotic stress- and PP2ARts1-dependent changes in their phosphorylation pattern. A comparative analysis with published MS-shotgun data revealed that the phosphorylation status of many of these sites is regulated by the MAPKAP kinase Rck2, suggesting that the phosphatase antagonizes Rck2 signaling. Detailed gel mobility shift assays and protein-protein interaction analysis strongly indicate that Rck2 activity is directly regulated by PP2ARts1 via a SLiM B56-family interaction motif, revealing how PP2ARts1 influences the response to hyperosmotic stress in Yeast.

Hypoglycemia due to PI3K/AKT/mTOR signaling pathway defects: two novel cases and review of the literature

INTRODUCTION

The PI3K/AKT/mTOR signaling pathway is important for the regulation of multiple biological processes, including cellular growth and glucose metabolism. Defects of the PI3K/AKT/mTOR signaling pathway are not usually considered among the genetic causes of recurrent hypoglycemia in childhood. However, accumulating evidence links hypoglycemia with defects of this pathway.

CASE REPORTS AND REVIEW

We describe here two cases of macrocephaly and hypoglycemia bearing genetic defects in genes involved in the PI3K/AKT/mTOR pathway. The first patient was diagnosed with a PTEN hamartoma tumour syndrome (PTHS) due to the de novo germline missense mutation c.[492 + 1G > A] of the PTEN gene. The second patient presented the autosomal dominant mental retardation-35 (MDR35) due to the heterozygous missense mutation c.592G > A in the PPP2R5D gene. A review of the literature on hypoglycemia and PI3K/AKT/mTOR signaling pathway defects, with a special focus on the metabolic characterization of hypoglycemia, is included.

CONCLUSIONS

PI3K/AKT/mTOR pathway defects should be included in the differential diagnosis of patients with hypoglycemia and macrocephaly. Clinical suspicion and molecular confirmation are important, not just for an accurate genetic counselling but also for defining the follow-up management, including cancer surveillance. The biochemical profile of hypoglycemia varies among patients. While most patients are characterized by low plasmatic insulin levels, hyperinsulinemia has also been observed. Large patient cohorts are needed to gain a comprehensive profile of the biochemical patterns of hypoglycemia in such defects and eventually guide targeted therapeutic interventions.

Relationship between osteoporosis and benign paroxysmal positional vertigo based on evidence-based medicine and bioinformatics

It has been reported that osteoporosis is a possible risk factor of benign paroxysmal positional vertigo (BPPV).

PURPOSE

We analyzed the correlation between osteoporosis and BPPV and the possible mechanism by performing evidence-based medicine meta-analysis and bioinformatics analysis.

METHODS

Initially, English articles related to osteoporosis and BPPV were obtained through PubMed and EMBASE databases. Stata12.0 software was used for meta-analysis to calculate the odd ratio (OR) and 95% confidence interval (CI) of outcome indicators, and the heterogeneity was evaluated by subgroup analysis, publication bias evaluation, and sensitivity analysis. In addition, microarray datasets related to BPPV and osteoporosis were obtained from gene expression omnibus (GEO) database to screen differentially expressed genes. At last, a mouse model of osteoporosis was established by bilateral oophorectomy for validation. RT-qPCR and Western blot analysis were performed to determine expression of related factors in mouse tissues.

RESULTS

Osteoporosis was suggested as an important risk factor for BPPV through meta-analysis of these 12 articles. It was found that PPP2CA was upregulated in BPPV and low bone mineral density (BMD) samples. Moreover, PPP2CA induced dephosphorylation of BCL2, which may be involved in BPPV through regulation of BMD. Through this mechanism, silencing of PPP2CA could elevate the incidence of BPPV by promoting bone remodeling and reducing the density of otoconia around the macula.

CONCLUSIONS

PPP2CA reduces BMD expression by inducing dephosphorylation of BCL2, which may be one of the mechanisms responsible for the onset of BPPV in osteoporosis.

1HN, 13C, and 15N backbone resonance assignments of the SET/TAF-1β/I2PP2A oncoprotein (residues 23-225)

SET (TAF-1β/I2PP2A) is a ubiquitously expressed, multifunctional protein that plays a role in regulating diverse cellular processes, including cell cycle progression, migration, apoptosis, transcription, and DNA repair. SET expression is ubiquitous across all cell types. However, it is overexpressed or post-translationally modified in several solid tumors and blood cancers, where expression levels are correlated with worsening clinical outcomes. SET exerts its oncogenic effects primarily through the formation of antagonistic protein complexes with the tumor suppressor, protein phosphatase 2A (PP2A), and the well-known metastasis suppressor, nm23-H1. PP2A inhibition is often observed as a secondary driver of tumorigenesis and metastasis in human cancers. Preclinical studies have shown that the pharmacological reactivation of PP2A combined with potent inhibitors of the primary driver oncogene produces synergistic cell death and decreased drug resistance. Therefore, the development of novel inhibitors of the SET-PP2A interaction presents an attractive approach to reactivation of PP2A, and thereby, tumor suppression. NMR provides a unique platform to investigate protein targets in their natively folded state to identify protein and small-molecule ligands and report on the protein internal dynamics. The backbone ¹H^N, ¹³C, and ¹⁵N NMR resonance assignments were completed for the 204 amino acid nucleosome assembly protein-1 (NAP-1) domain of the human SET oncoprotein (residues 23-225). These assignments provide a vital first step toward the development of novel PP2A reactivators via SET-selective inhibition.

Survival-associated alternative splicing events interact with the immune microenvironment in stomach adenocarcinoma

BACKGROUND

Alternative splicing (AS) increases the diversity of mRNA during transcription; it might play a role in alteration of the immune microenvironment, which could influence the development of immunotherapeutic strategies against cancer.

AIM

To obtain the transcriptomic and clinical features and AS events in stomach adenocarcinoma (STAD) from the database. The overall survival data associated with AS events were used to construct a signature prognostic model for STAD.

METHODS

Differentially expressed immune-related genes were identified between subtypes on the basis of the prognostic model. In STAD, 2042 overall-survival-related AS events were significantly enriched in various pathways and influenced several cellular functions. Furthermore, the network of splicing factors and overall-survival-associated AS events indicated potential regulatory mechanisms underlying the AS events in STAD.

RESULTS

An eleven-AS-signature prognostic model (CD44|14986|ES, PPHLN1|21214|AT, RASSF4|11351|ES, KIAA1147|82046|AP, PPP2R5D|76200|ES, LOH12CR1|20507|ES, CDKN3|27569|AP, UBA52|48486|AD, CADPS|65499|AT, SRSF7| 53276|RI, and WEE1|14328|AP) was constructed and significantly related to STAD overall survival, immune cells, and cancer-related pathways. The differentially expressed immune-related genes between the high- and low-risk score groups were significantly enriched in cancer-related pathways.

CONCLUSION

This study provided an AS-related prognostic model, potential mechanisms for AS, and alterations in the immune microenvironment (immune cells, genes, and pathways) for future research in STAD.

Deciphering the Influence of Cigarette Smoke Carcinogens on CNS Associated Biomolecules: A Computational Synergistic Approach

BACKGROUND

Human health issues caused by Cigarette Smoke Carcinogens (CSC) are increasing rapidly every day and challenging the scientific community to provide a better understanding in order to avoid its impact on communities. Cigarette smoke also contains tobacco-based chemical compounds harmful to human beings, either smokers or non-smokers.

OBJECTIVE

We have tested 7H-Dibenzo[c,g]carbazole (7H-DBC) and Dibenz[a,h]acridine (DBAD) derivatives of Asz-arenes along with N'-Nitrosoanabasine (NAB) and N-Nitrosoanatabine (NAT) derivatives of N-Nitrosamines molecular interaction with CNS biomolecules.

METHODS

Computational synergistic approaches like system biology and molecular interaction techniques were implemented to conduct the analysis.

RESULTS

CSC efficiently interacted with NRAS, KRAS, CDH1, and RAC1 molecular targets in CNS. We have also performed the interactome analysis followed by system biology approaches and found that HSPA8 is the most important hub protein for the network generated for CSC-hampered genes of CNS. We have also identified 6 connector proteins, namely TP53, HSP90AA1, PPP2CA, CDH1, CTNNB1, and ARRB1. Further analysis revealed that NRAS and CDH1 have maximum interactions with all the selected CSC.

CONCLUSION

The obtained structural analysis data could be utilized to assess the carcinogenic effect of CSC and could be useful in the treatment of CNS diseases and disorders induced, especially by tobacco-specific carcinogens, or it could also be used in vivo/ in vitro experimentation model designing.

Microcystin-leucine arginine exhibits immunomodulatory roles in testicular cells resulting in orchitis

Microcystin-leucine arginine (MC-LR) causes testicular inflammation and hinders spermatogenesis. However, the molecular mechanisms underlying the immune responses to MC-LR in the testis have not been elucidated in detail. In this study, we show that MC-LR induced immune responses in Sertoli cells (SC), germ cells (GC), and Leydig cells (LC) via activating phosphatidylinositol 3-kinase (PI3K)/AKT/nuclear factor kappa B (NF-κB), resulting in the production of pro-inflammatory cytokines and chemokines including tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), and chemokine (C-X-C motif) ligand 10 (CXCL10). The observed effects were attributed to reduced activity of protein phosphatases 2A (PP2A) as a result of binding of MC-LR to the catalytic subunit of PP2A in SC and GC. By contrast, innate immune responses were triggered by Toll-like receptor 2 (TLR2) in LC because MC-LR could not enter into the LC and subsequently inhibit the PP2A activity. PI3K/AKT/NF-κB were also activated in SC, GC, and LC in vivo, with the enrichment of TNF-α, IL-6, MCP-1, and CXCL10 in the testis. Following chronic exposure, MC-LR-treated mice exhibited decreased sperm counts and abnormal sperm morphology. Our data demonstrate that MC-LR can activate innate immune responses in testicular cells, which provides novel insights to explore the mechanism associated with MC-LR-induced orchitis.

Interrelationship between Protein Phosphatase-2A and Cytoskeletal Architecture during the Endothelial Cell Response to Soluble Products Produced by Human Head and Neck Cancer

Tumor neovascularization is necessary for the progressive development of all solid tumors, including head and neck squamous cell carcinomas (HNSCCs). The angiogenic process includes increased endothelial cell motility. Our prior studies have shown the importance of protein phos-phatase-2A (PP-2A) in restricting endothelial cell motility. Because motility is regulated by the polymerization/depolymerization of the cellular cytoskeleton, the present study defined the interrelationship between PP-2A and the cytoskeleton during endothelial cell responses to HNSCC-derived angiogenic factors. PP-2A was shown to colocalize with microtubules of unstimulated endothelial cells. However, exposure to HNSCC-derived products resulted in a more diffuse distribution of PP-2A staining and a loss of filamentous tubulin. The feasibility of pharmacologically preventing this cytoskeletal disorganization as a means of blocking tumor-induced angiogenesis was tested. This was accomplished by use of 1α,25-dihydroxyvitamin D3[1,25 (OH)2D3] and all- trans-retinoic acid to indirectly stimulate PP-2A activity through their capacity to elevated intracellular levels of the second messenger ceramide. Pretreatment of endothelial cells with either 1,25(OH)2D3or retinoic acid prevented the cytoskeletal disorganization that otherwise occurs in endothelial cells on exposure to HNSCC-derived products. These studies support the feasibility of using elevation of PP-2A to prevent the mor-phogenic component of the angiogenic process that is stimulated by HNSCC-derived factors.

[The role of protein phosphatase 2A B56β holoenzyme in the regulation of heavy metal CdCl2 induced cytotoxicity]

OBJECTIVE

To investigate the role of holoenzyme containing Protein Phosphatase 2A B56β in regulating CdCl2 induced cytotoxicity.

METHOD

CdCl2-induced cytotoxicity in normal human cell line L-02, AFB1-transformed hepatic cell line L-02 RT-AFB1 and tumor cell line Bel7402 was measured by modified MTT assay. Stable cell lines L-02 SHAKT, L-02 SHB56β, L-02 RT-AFB1-B56β and Bel7402-B56β were generated by infecting L-02 cells or Bel7402 cells with retroviral vectors encoding lentiviral AKT shRNA, lentiviral B56β shRNA and B56β. The relative cell viability was measured in normal human cell line AFB1-transformed hepatic cell line and tumor cell line when treated by CdCl2 (0, 20, 40, 80, 160 µmol/L). After treated by wortmannin (2.5, 5.0 µmol/L) combined with 40 µmol/L CdCl2, Western blot was applied to measure the expression of associated protein in L-02.Western blot was applied to measure the expression of B56β, MT (metallothionein), AKT, and p-AKT in these cell lines treated by CdCl2.

RESULTS

The levels of MT were 0.12 ± 0.02, 0.06 ± 0.06 in L-02 RT-AFB1 and Bel7402, which were lower than L02 (0.92 ± 0.14) (F = 1 148.16, P < 0.001) when treated by 40 µmol/L CdCl2. When treated by 40 µmol/L CdCl2, the expression of p-AKT in L-02 SHAKT-1 and L-02 SHAKT-2 were 0.08 ± 0.02, 0.08 ± 0.05, which levels were lower than L-02 SHGFP (0.18 ± 0.15) (F = 724.70, P < 0.001); and the expression of MT were both 0.62 ± 0.16 in L-02 SHAKT-1 and L-02 SHAKT-2, which levels were higher than L-02 SHGFP (0.22 ± 0.14) (F = 94.73, P < 0.001). After treated by wortmannin (2.5, 5.0 µmol/L) combined with 40 µmol/L CdCl2, the expression of p-AKT in L-02 were 0.28 ± 0.07, 0.15 ± 0.11, which levels were lower than wortmannin untreated cells (0.52 ± 0.11) (F = 578.57, P < 0.001); and the expreesion of MT were 1.62 ± 0.80, 1.08 ± 0.15, which levels were higher than wortmannin untreated cells (0.69 ± 0.18) (F = 12.34, P < 0.001). When treated by 40 µmol/L CdCl2, the levels of p-AKT in L-02 SHB56β-1 and L-02 SHB56β-2 were 0.57 ± 0.13, 0.59 ± 0.02, which were higher than L-02 SHGFP (0.32 ± 0.02) (F = 87.16, P < 0.001); and the levels of MT were 0.35 ± 0.07, 0.20 ± 0.03 in L-02 SHB56β-1 and L-02 SHB56β-2, which were lower than L-02 SHGFP (1.51 ± 0.13) (F = 2 457.10, P < 0.001). After treated by 40 µmol/L CdCl2, the expression of p-AKT in L-02 RT-AFB1-B56β and Bel7402-B56β were 0.10 ± 0.11, 0.09 ± 0.01, which were lower than L-02 RT-AFB1 (0.36 ± 0.01) and Bel7402 (0.43 ± 0.11) (F = 877.62, P < 0.001); and the levels of MT were 0.92 ± 0.13, 0.95 ± 0.08 in L-02 RT-AFB1-B56β and Bel7402-B56β,which were higher than L-02 RT-AFB1 (0.44 ± 0.12) and Bel7402 (0.77 ± 0.06) (F = 51.97, P < 0.001).

CONCLUSION

Protein phosphatase 2A complexes containing B56β participated in the regulation of MT expression through direct dephosphorylation of AKT, finally affected the cytotoxicity responding to CdCl2. Our study revealed a key signaling pathways of PP2A involved in heavy metals induced cytotoxicity.

Characterization of Protein Phosphatase 2A Acting on Phosphorylated Plasma Membrane Aquaporin of Tulip Petals

A protein phosphatase holo-type enzyme (38, 65, and 75 kDa) preparation and a free catalytic subunit (38 kDa) purified from tulip petals were characterized as protein phosphatase 2A (PP2A) by immunological and biochemical approaches. The plasma membrane containing the putative plasma membrane aquaporin (PM-AQP) was prepared from tulip petals, phosphorylated in vitro, and used as the substrate for both of the purified PP2A preparations. Although both preparations dephosphorylated the phosphorylated PM-AQP at 20 degrees C, only the holo-type enzyme preparation acted at 5 degrees C on the phosphorylated PM-AQP with higher substrate specificity, suggesting that regulatory subunits are required for low temperature-dependent dephosphorylation of PM-AQP in tulip petals.

Factor VIII is a positive regulator of platelet function

FVIII is an important cofactor in the tenase coagulation factor complex, lack of FVIII causes severe bleeding, whereas high FVIII levels seem to be associated with venous and arterial thromboembolism. Resting platelets do not bind FVIII, but activated platelets bind unactivated FVIII if vWF is not present. We investigated a possible influence of platelet bound FVIII on platelet function itself as it is unclear if there is a direct effect of FVIII on platelet function. The influence of FVIII on platelet function was investigated by flow cytometric analysis of P-selectin expression (CD62P) and PAC-1 binding before and after submaximal stimulation with TRAP-6 (5 microM final concentration), by confocal microscopy and by platelet aggregometry. For flow cytometry and confocal microscopy, washed platelets were incubated with human recombinant FVIII for 5 min at 37 degrees C. Analysis of platelet surface area was measured by computerized image analysis. Treatment with FVIII only caused no changes in P-selectin expression or PAC-1 binding, respectively. Stimulation of platelets with TRAP-6 increased the expression of P-selectin (445%) and PAC-1 binding (934%) as expected. These effects were further increased when platelets were stimulated with TRAP-6 and FVIII (P-selectin 499%, difference not significant; PAC-1 1626%, P < 0.05. Values were expressed in%, related to unstimulated, buffer treated platelets). Platelet spreading on fibrinogen was significantly increased when platelets were treated with FVIII and TRAP-6 compared to TRAP-6 alone (368 vs. 307 average pixel/platelet, P<0.05). In addition platelet aggregation was enhanced when platelets were stimulated with FVIII and TRAP-6 compared to TRAP-6 alone. FVIII can act as a positive regulator of platelet function in TRAP-co-stimulated platelets. We hypothesize that FVIII induced increase in platelet activation might contribute to venous and even arterial thrombus formation in patients with high FVIII levels.

The formation of platelet–leukocyte aggregates varies during the menstrual cycle

Platelet-leukocyte aggregates are considered to play a significant role in blood coagulation and inflammatory processes. We hypothesized that hormonal changes during the menstrual cycle affect the formation of heterotypic aggregates and therefore may constitute cycle-dependent variations of the susceptibility for thromboembolic events and inflammatory disease. We therefore measured platelet-leukocyte interaction by the determination of platelet-leukocyte aggregates (PLA), platelet P-Selectin expression, and platelet fibrinogen receptor activation by PAC-1 binding in 20 healthy women during their menstrual cycle by flow cytometry. The number of platelet-granulocyte aggregates (PGA) and platelet-monocyte aggregates (PMA) was higher at ovulation compared to any other time-point of the menstrual cycle (p = 0.005, p = 0.022, respectively). Likewise, P-Selectin expression peaked on day 14 (p = 0.040). The course of PLA formation during the menstrual cycle followed the course of estrogen levels, strongly suggesting direct effects of estrogen on platelet-leukocyte interaction. The susceptibility to form platelet-leukocyte aggregates that are inducible in vitro by a suboptimal concentration of thrombin receptor activating peptide-6 decreased slightly during the transition from day 1 to 14 (p = 0.040). These data indicate that platelet function varies during particular phases of the normal menstrual cycle.

Gi protein-mediated translocation of serine/threonine phosphatase to the plasma membrane and apoptosis of ovarian cancer cell in response to gonadotropin-releasing hormone antagonist cetrorelix

Serine/threonine protein phosphatase 2A (PP2A), a crucial enzyme in apoptosis control, has been demonstrated within the plasma membrane as well as in the soluble fraction. This study aimed to examine hormonal translocation of PP2A to the plasma membrane in gonadotropin-releasing hormone (GnRH)-responsive ovarian cancer cells. Apoptosis of ovarian cancer cell lines Caov-3 and SK-Ov-3 was quantified by nuclear morphology after staining with Hoechst 33342 dye. PP2A protein and activity in plasma membrane were assessed by immunohistochemical staining with PP2A-specific antibodies and by the measurement of the dephosphorylation of phosphopeptide highly selective for the PP2A, respectively. Incubation for 48 h with a GnRH antagonist cetrorelix caused parallel increases in the percentage of cells undergoing apoptosis and the membrane-associated PP2A activity; half-maximal effects occurred with 5 nmol/l cetrorelix. PP2A protein was also localised to the plasma membrane when the cell lines were exposed to cetrorelix. Pretreatment of the cells with pertussis toxin, but not cholera toxin, completely inhibited cetrorelix-stimulated apoptotic cell death and PP2A redistribution. These findings demonstrate that translocation of PP2A to plasma membrane is closely coupled to the onset of apoptosis in ovarian cancer cells exposed to GnRH antagonist. These GnRH-induced cellular events may be mediated through pertussis toxin-sensitive Gi protein-linked GnRH receptor.

Normal function of the yeast TOR pathway requires the type 2C protein phosphatase Ptc1

Yeast ptc1 mutants are rapamycin and caffeine sensitive, suggesting a functional connection between Ptc1 and the TOR pathway that is not shared by most members of the type 2C phosphatase family. Genome-wide profiling revealed that the ptc1 mutation largely attenuates the transcriptional response to rapamycin. The lack of Ptc1 significantly prevents the nuclear translocation of Gln3 and Msn2 transcription factors to the nucleus, as well as the dephosphorylation of the Npr1 kinase, in response to rapamycin. This could explain the observed decrease in both the basal and rapamycin-induced expression of several genes subjected to nitrogen catabolite repression (GAT1, MEP1, and GLN1) and stress response element (STRE)-driven promoters. Interestingly, this decrease is abolished in the absence of the Sit4 phosphatase. Epitasis analysis indicates that the mutation of SIT4 or TIP41, encoding a Tap42-interacting protein, abolishes the sensitivity of the ptc1 strain to rapamycin and caffeine. All of these results suggest that Ptc1 is required for normal TOR signaling, possibly by regulating a step upstream of Sit4 function. According to this hypothesis, we observe that the mutation of PTC1 drastically diminishes the rapamycin-induced interaction between Tap42 and Tip41, and this can be explained by lower-than-normal levels of Tip41 in ptc1 cells. Ptc1 is not necessary for the normal expression of the TIP41 gene; instead, its absence dramatically affects the stability of Tip41. The lack of Ptc1 partially abolishes the rapamycin-induced dephosphorylation of Tip41, which may further decrease Tap42 binding. Reduced Tip41 levels contribute to the ptc1 phenotypes, although additional Ptc1 targets must exist. All of these results provide the first evidence showing that a type 2C protein phosphatase is required for the normal functioning of the TOR pathway.

PTC1 is required for vacuole inheritance and promotes the association of the myosin-V vacuole-specific receptor complex

Organelle inheritance occurs during cell division. In Saccharomyces cerevisiae, inheritance of the vacuole, and the distribution of mitochondria and cortical endoplasmic reticulum are regulated by Ptc1p, a type 2C protein phosphatase. Here we show that PTC1/VAC10 controls the distribution of additional cargoes moved by a myosin-V motor. These include peroxisomes, secretory vesicles, cargoes of Myo2p, and ASH1 mRNA, a cargo of Myo4p. We find that Ptc1p is required for the proper distribution of both Myo2p and Myo4p. Surprisingly, PTC1 is also required to maintain the steady-state levels of organelle-specific receptors, including Vac17p, Inp2p, and Mmr1p, which attach Myo2p to the vacuole, peroxisomes, and mitochondria, respectively. Furthermore, Vac17p fused to the cargo-binding domain of Myo2p suppressed the vacuole inheritance defect in ptc1Delta cells. These findings suggest that PTC1 promotes the association of myosin-V with its organelle-specific adaptor proteins. Moreover, these observations suggest that despite the existence of organelle-specific receptors, there is a higher order regulation that coordinates the movement of diverse cellular components.

Generation of active protein phosphatase 2A is coupled to holoenzyme assembly

Protein phosphatase 2A (PP2A) is a prime example of the multisubunit architecture of protein serine/threonine phosphatases. Until substrate-specific PP2A holoenzymes assemble, a constitutively active, but nonspecific, catalytic C subunit would constitute a risk to the cell. While it has been assumed that the severe proliferation impairment of yeast lacking the structural PP2A subunit, TPD3, is due to the unrestricted activity of the C subunit, we recently obtained evidence for the existence of the C subunit in a low-activity conformation that requires the RRD/PTPA proteins for the switch into the active conformation. To study whether and how maturation of the C subunit is coupled with holoenzyme assembly, we analyzed PP2A biogenesis in yeast. Here we show that the generation of the catalytically active C subunit depends on the physical and functional interaction between RRD2 and the structural subunit, TPD3. The phenotype of the tpd3Δ strain is therefore caused by impaired, rather than increased, PP2A activity. TPD3/RRD2-dependent C subunit maturation is under the surveillance of the PP2A methylesterase, PPE1, which upon malfunction of PP2A biogenesis, prevents premature generation of the active C subunit and holoenzyme assembly by counteracting the untimely methylation of the C subunit. We propose a novel model of PP2A biogenesis in which a tightly controlled activation cascade protects cells from untargeted activity of the free catalytic PP2A subunit.

Multisubunit enzymes, such as protein phosphatase 2A, consist of a catalytic subunit and one of several regulatory subunits that are responsible for substrate specificity. Whereas this molecular architecture enables the assembly of a few components into many different substrate-specific enzymes, it possesses an inherent danger in the form of the uncomplexed catalytic subunit with its unspecific phosphatase activity. Until substrate-specific complexes assemble, the catalytic subunit would constitute a risk to the cell if no control mechanisms existed. We recently obtained evidence for the existence of the catalytic subunit in a low-activity conformation that requires an activator for the switch into the active conformation. This requirement suggested that the existing model of protein phosphatase 2A biogenesis was incomplete, because it could not explain how the activity of the catalytic subunit is kept in check until it is assembled with the substrate-targeting subunits. In this study, we provide evidence that the generation of the active catalytic subunit is coupled with and regulated by holoenzyme assembly. We propose a novel model of protein phosphatase biogenesis in which a tightly controlled activation cascade protects cells from the potential risk of unspecific dephosphorylation events.

Analysis of protein phosphatase 2A (PP2A) biogenesis in yeast suggests that a tightly controlled activation cascade, involving an interaction between the protein RRD2 and the structural subunit TPD3, protects cells from untargeted activity of the free catalytic PP2A subunit.

IFN-gamma-induced IDO and WRS expression in microglia is differentially regulated by IL-4

Indoleamine 2,3-dioxygenase (IDO), a tryptophan catabolizing enzyme, has been implicated in the pathogenesis of various neurological disorders. IDO expression is induced by IFN-gamma and leads to neurotoxicity by generating quinolinic acid. Additionally, it inhibits the immune response through both tryptophan depletion and generating other tryptophan catabolites. IL-4 and IL-13 have been shown to control IDO expression by antagonizing the effects of IFN-gamma in different cell types. Here, we investigated the effects of these cytokines on IDO expression in microglia. Interestingly, we observed that both IL-4 and IL-13 greatly enhanced IFN-gamma-induced IDO expression. However, tryptophanyl-tRNA synthetase (WRS), which is coinduced with IDO by IFN-gamma, is downregulated by IL-4 and IL-13. The effect of IL-4 and IL-13 was independent of STAT-6. Modulation of IDO but not WRS was eliminated by inhibition of protein phosphatase 2A (PP2A) activity. The phosphatidylinositol 3-kinase (PI3K) pathway further differentiated the regulation of these two enzymes, as inhibiting the PI3K pathway eliminated IFN-gamma induction of IDO, whereas such inhibition greatly enhanced WRS expression. These findings show discordance between modulations of expression of two distinct enzymes utilizing tryptophan as a common substrate, and raise the possibility of their involvement in regulating immune responses in various neurological disorders.

Clonal divergence in lung cancer development is associated with allelic loss on chromosome 4

Patients who receive curative treatment for lung cancer can develop additional lung tumors that may or may not be related to the original tumor and thus require different clinical management. If a subsequent tumor has a pattern of allele loss, revealed by allelotype analysis, overlapping that of the first tumor, it is believed to be a local recurrence or metastasis. In this case history, we present loss of heterozygosity analyses of the original primary tumor, and two second primary tumors occurring in the ipsilateral and the contra-lateral lungs. The allelotyping suggests that these tumors are all clonally related but concordance is not complete. Our interpretation is that the original primary tumor and the two new primary tumors have developed to full malignancy independently, but are clonally related, possibly via a clone of motile progenitor cells. Deletion mapping of DNA from biopsies of this patient delineated a region in 4p16 that we had previously shown to be lost in the transition from carcinoma in situ to invasive tumor. We identified a minimally deleted region encompassing six genes including two candidate tumor suppressor genes, CRMP1 a lung cancer metastasis-suppressing gene and PPP2R2C a gene for a regulatory subunit of the PP2 complex known to suppress tumorigenesis, particularly viral induced transformation.

FTY720, a new alternative for treating blast crisis chronic myelogenous leukemia and Philadelphia chromosome-positive acute lymphocytic leukemia

Blast crisis chronic myelogenous leukemia (CML-BC) and Philadelphia chromosome-positive (Ph1-positive) acute lymphocytic leukemia (ALL) are 2 fatal BCR/ABL-driven leukemias against which Abl kinase inhibitors fail to induce a long-term response. We recently reported that functional loss of protein phosphatase 2A (PP2A) activity is important for CML blastic transformation. We assessed the therapeutic potential of the PP2A activator FTY720 (2-amino-2-[2-(4-octylphenyl)ethyl]-1,3-propanediol hydrochloride), an immunomodulator in Phase III trials for patients with multiple sclerosis or undergoing organ transplantation, in CML-BC and Ph1 ALL patient cells and in in vitro and in vivo models of these BCR/ABL+ leukemias. Our data indicate that FTY720 induces apoptosis and impairs clonogenicity of imatinib/dasatinib-sensitive and -resistant p210/p190(BCR/ABL) myeloid and lymphoid cell lines and CML-BC(CD34+) and Ph1 ALL(CD34+/CD19+) progenitors but not of normal CD34+ and CD34+/CD19+ bone marrow cells. Furthermore, pharmacologic doses of FTY720 remarkably suppress in vivo p210/p190(BCR/ABL)-driven [including p210/p190(BCR/ABL)(T315I)] leukemogenesis without exerting any toxicity. Altogether, these results highlight the therapeutic relevance of rescuing PP2A tumor suppressor activity in Ph1 leukemias and strongly support the introduction of the PP2A activator FTY720 in the treatment of CML-BC and Ph1 ALL patients.

Inhibition of endothelial barrier dysfunction by P21-activated kinase-1

We investigated the activity of P21-activated kinase-1 (Pak1) on myosin light chain phosphorylation and on thrombin-induced barrier dysfunction in human endothelial cells (HMEC). HMEC were infected with recombinant adenoviruses that express constitutively active Pak1, LacZ, wild-type, and a mutant myosin regulatory light chain, mMLC20 (Thr18Ala, Ser19Ala). Expression of the recombinant Pak1 mediated by adenovirus in HMEC was regulated. Active Pak1 induced dephosphorylation of MLC20 in HMEC, but not in smooth muscle cells. Active Pak1 significantly inhibited thrombin-induced endothelial barrier dysfunction. Expression of the unphosphorylatable MLC20 also inhibited thrombin-induced endothelial barrier dysfunction. Constitutively active Pak1 associated with phosphatase 2A and induced a post-translational modification of the phosphatase. Our data provide novel evidence indicating that Pak1 regulates endothelial barrier function through activation of phosphatase 2A.

Mediating ERK 1/2 signaling rescues congenital heart defects in a mouse model of Noonan syndrome

Noonan syndrome (NS) is an autosomal dominant disorder characterized by a wide spectrum of defects, which most frequently include proportionate short stature, craniofacial anomalies, and congenital heart disease (CHD). NS is the most common nonchromosomal cause of CHD, and 80%-90% of NS patients have cardiac involvement. Mutations within the protein tyrosine phosphatase Src homology region 2, phosphatase 2 (SHP2) are responsible for approximately 50% of the cases of NS with cardiac involvement. To understand the developmental stage- and cell type-specific consequences of the NS SHP2 gain-of-function mutation, Q79R, we generated transgenic mice in which the mutated protein was expressed during gestation or following birth in cardiomyocytes. Q79R SHP2 embryonic hearts showed altered cardiomyocyte cell cycling, ventricular noncompaction, and ventricular septal defects, while, in the postnatal cardiomyocyte, Q79R SHP2 expression was completely benign. Fetal expression of Q79R led to the specific activation of the ERK1/2 pathway, and breeding of the Q79R transgenics into ERK1/2-null backgrounds confirmed the pathway's necessity and sufficiency in mediating mutant SHP2's effects. Our data establish the developmental stage-specific effects of Q79R cardiac expression in NS; show that ablation of subsequent ERK1/2 activation prevents the development of cardiac abnormalities; and suggest that ERK1/2 modulation could have important implications for developing therapeutic strategies in CHD.

Nucleolar release of Hand1 acts as a molecular switch to determine cell fate

The bHLH transcription factor Hand1 is essential for placentation and cardiac morphogenesis in the developing embryo. Here we implicate Hand1 as a molecular switch that determines whether a trophoblast stem cell continues to proliferate or commits to differentiation. We identify a novel interaction of Hand1 with a protein that contains an I-mfa (inhibitor of myogenic factor) domain that anchors Hand1 in the nucleolus where it negatively regulates Hand1 activity. In the trophoblast stem-cell line Rcho-1, nucleolar sequestration of Hand1 accompanies sustained cell proliferation and renewal, whereas release of Hand1 into the nucleus leads to its activation, thus committing cells to a differentiated giant-cell fate. Site-specific phosphorylation is required for nucleolar release of Hand1, for its dimerization and biological function, and this is mediated by the non-canonical polo-like kinase Plk4 (Sak). Sak is co-expressed in Rcho-1 cells, localizes to the nucleolus during G2 and phosphorylates Hand1 as a requirement for trophoblast stem-cell commitment to a giant-cell fate. This study defines a novel cellular mechanism for regulating Hand1 that is a crucial step in the stem-cell differentiation pathway.

14-3-3 proteins and protein phosphatases are not reduced in tau-deficient mice

Tau is an axonal microtubule-associated protein, whose dysfunction causes neurodegenerative diseases such as Alzheimer's disease and other tauopathies. Earlier studies have shown the interactions of tau with glycogen synthase kinase-3beta, 14-3-3zeta, protein phosphatase 1 and protein phosphatase 2A. In this study, we compared the amounts of these tau-interacting proteins in brain microtubule-enriched fractions from wild-type and tau-deficient mice. Contrary to our expectation, we detected no difference in the amount of these proteins between wild-type and tau-deficient mice. Our findings indicate that only a small portion of tau-interacting proteins are bound to tau in vivo, and suggest the existence of other scaffolding proteins. We propose that tau-deficient mice are an ideal system for confirming the function of tau-interacting proteins.

An endogenous serine/threonine protein phosphatase inhibitor, G-substrate, reduces vulnerability in models of Parkinson's disease

Relative neuronal vulnerability is a universal yet poorly understood feature of neurodegenerative diseases. In Parkinson's disease, dopaminergic (DA) neurons in the substantia nigra (SN) (A9) are particularly vulnerable, whereas adjacent DA neurons within the ventral tegmental area (A10) are essentially spared. Our previous laser capture microdissection and microarray study (Chung et al., 2005) demonstrated that molecular differences between these DA neurons may underlie their differential vulnerability. Here we show that G-substrate, an endogenous inhibitor of Ser/Thr protein phosphatases, exhibits higher expression in A10 compared with A9 DA neurons in both rodent and human midbrain. Overexpression of G-substrate protected dopaminergic BE(2)-M17 cells against toxins, including 6-OHDA and MG-132 (carbobenzoxy-L-leucyl- L-leucyl-L-leucinal), whereas RNA interference (RNAi)-mediated knockdown of endogenous G-substrate increased their vulnerability to these toxins. G-substrate reduced 6-OHDA-mediated protein phosphatase 2A (PP2A) activation in vitro and increased phosphorylated levels of PP2A targets including Akt, glycogen synthase kinase 3beta, and extracellular signal-regulated kinase 2 but not p38. RNAi to Akt diminished the protective effect of G-substrate against 6-OHDA. In vivo, lentiviral delivery of G-substrate to the rat SN increased baseline levels of phosphorylated Akt and protected A9 DA neurons from 6-OHDA-induced toxicity. These results suggest that inherent differences in the levels of G-substrate contribute to the differential vulnerability of DA neurons and that enhancing G-substrate levels may be a neuroprotective strategy for the vulnerable A9 (SN) DA neurons in Parkinson's disease.

Identification of the PP2A-interacting region of heat shock transcription factor 2

Previous work in our laboratory demonstrated the existence of an association between heat shock transcription factor 2 (HSF2) and the serine/threonine phosphatase 2A, which is mediated by interaction between HSF2 and the A subunit (also called PR65) of this protein phosphatase. In light of the importance of HSF2-PP2A association for HSF2 cellular function, in this study, we have sought to dissect the sequences within HSF2 that are important for interaction with the A subunit of PP2A. The results of these experiments indicate that the HSF2 region comprising amino acids 343-363 is important for A subunit interaction. This region includes part of the C-terminal leucine zipper motif of HSF2 called heptad repeat C (HR-C). The results of transfection/immunoprecipitation experiments also show that deletion of the 6 amino acids from 343 to 348 from HSF2 (HSF2 (delta343-348)), is sufficient to prevent HSF2 from interacting with PP2A. These data provide insight into a new functional domain of HSF2, the PP2A A subunit-interacting region.

ER stress triggers apoptosis by activating BH3-only protein Bim

Endoplasmic reticulum (ER) stress caused by misfolded proteins or cytotoxic drugs can kill cells and although activation of this pathway has been implicated in the etiology of certain degenerative disorders its mechanism remains unresolved. Bim, a proapoptotic BH3-only member of the Bcl-2 family is required for initiation of apoptosis induced by cytokine deprivation or certain stress stimuli. Its proapoptotic activity can be regulated by several transcriptional or posttranslational mechanisms, such as ERK-mediated phosphorylation, promoting its ubiquitination and proteasomal degradation. We found that Bim is essential for ER stress-induced apoptosis in a diverse range of cell types both in culture and within the whole animal. ER stress activates Bim through two novel pathways, involving protein phosphatase 2A-mediated dephosphorylation, which prevents its ubiquitination and proteasomal degradation and CHOP-C/EBPalpha-mediated direct transcriptional induction. These results define the molecular mechanisms of ER stress-induced apoptosis and identify targets for therapeutic intervention in ER stress-related diseases.

Activation of endoplasmic reticulum stress response by hepatitis viruses up-regulates protein phosphatase 2A

The up-regulation of protein phosphatase 2 A (PP2A) is an important factor leading to an inhibition of IFNalpha signaling caused by viral protein expression. Here, we describe the molecular mechanism involved in PP2Ac up-regulation by HCV and HBV. HCV and HBV protein expression in cells induces an ER stress response leading to calcium release from the ER. HCV protein expression induces CREB activation, probably through calcium/calmodulin-dependent protein kinase. CREB binds to a CRE element in the promoter of PP2Ac and induces its transcriptional up-regulation. Because PP2Ac is involved in many important cellular processes including cell-cycle regulation, apoptosis, cell morphology, development, signal transduction and translation, its up-regulation during ER stress has potentially important implications.

Protein Phosphatase 2A and Separase Form a Complex Regulated by Separase Autocleavage

The onset of anaphase is triggered by the activation of a site-specific protease called separase. Separase cleaves the chromosomal cohesins holding the duplicated sister chromatids together, allowing sisters to simultaneously separate and segregate to opposite ends of the cell before division. Activated separase cleaves not only cohesin, but also itself; however, the biological significance of separase self-cleavage has remained elusive. Before anaphase, separase is inhibited by at least two mechanisms. The first involves the binding of securin, whereas the second requires the phosphorylation-dependent binding of cyclin-dependent kinase 1 (Cdk1)/cyclin B1. Because securin and Cdk1/cyclin B1 interact with separase in a mutually exclusive manner, the degradation of both these inhibitors plays an important role in activating separase at anaphase. Here we identify a new separase interacting partner, a specific subtype of the heterotrimeric protein phosphatase 2A (PP2A). PP2A associates with separase through the B' (B56) regulatory subunit and does so independently of securin and cyclin B1 binding. The association of PP2A with separase requires a 55-amino acid domain closely juxtaposed to separase autocleavage sites. Strikingly, mutation of these cleavage sites increases PP2A binding, suggesting that separase cleavage disrupts the interaction of PP2A with separase. Furthermore, expression of a non-cleavable separase, but not a non-cleavable mutant that cannot bind PP2A, causes a premature loss of centromeric cohesion. Together these observations provide a new mechanistic insight into a physiological function for separase self-cleavage.

Proteomic Studies of PP2A-B56γ1 Phosphatase Complexes Reveal Phosphorylation-Regulated Partners in Cardiac Local Signaling

Defects of kinase-phosphatase signaling in cardiac myocytes contribute to human heart disease. The activity of one phosphatase, PP2A, is governed by B targeting subunits, including B56gamma1, expressed in heart cells. As the role of PP2A/B56gamma1 on the heart function remains largely unknown, this study sought to identify protein partners through unbiased, affinity purification-based proteomics combined with the functional validation. The results reveal multiple interactors that are localized in strategic cardiac sites to participate in Ca2+ homeostasis and gene expression, exemplified by the Ca pump, SERCA2a, and the splicing factor ASF/SF2. These results are corroborated by confocal imaging where adenovirally overexpressed B56gamma1 is found in z-line/t-tubule region and nuclear speckles. Importantly, overexpression of B56gamma1 in cultured myocytes dramatically impairs cell contractility. These results provide a global view of B56gamma1-regulated local signaling and heart function.

Augmented Protein Kinase C-α–Induced Myofilament Protein Phosphorylation Contributes to Myofilament Dysfunction in Experimental Congestive Heart Failure

It is becoming clear that upregulated protein kinase C (PKC) signaling plays a role in reduced ventricular myofilament contractility observed in congestive heart failure. However, data are scant regarding which PKC isozymes are involved. There is evidence that PKC-alpha may be of particular importance. Here, we examined PKC-alpha quantity, activity, and signaling to myofilaments in chronically remodeled myocytes obtained from rats in either early heart failure or end-stage congestive heart failure. Immunoblotting revealed that PKC-alpha expression and activation was unaltered in early heart failure but increased in end-stage congestive heart failure. Left ventricular myocytes were isolated by mechanical homogenization, Triton-skinned, and attached to micropipettes that projected from a force transducer and motor. Myofilament function was characterized by an active force-[Ca(2+)] relation to obtain Ca(2+)-saturated maximal force (F(max)) and myofilament Ca(2+) sensitivity (indexed by EC(50)) before and after incubation with PKC-alpha, protein phosphatase type 1 (PP1), or PP2a. PKC-alpha treatment induced a 30% decline in F(max) and 55% increase in the EC(50) in control cells but had no impact on myofilament function in failing cells. PP1-mediated dephosphorylation increased F(max) (15%) and decreased EC(50) ( approximately 20%) in failing myofilaments but had no effect in control cells. PP2a-dependent dephosphorylation had no effect on myofilament function in either group. Lastly, PP1 dephosphorylation restored myofilament function in control cells hyperphosphorylated with PKC-alpha. Collectively, our results suggest that in end-stage congestive heart failure, the myofilament proteins exist in a hyperphosphorylated state attributable, in part, to increased activity and signaling of PKC-alpha.

The tumor suppressor PP2A Abeta regulates the RalA GTPase

The serine-threonine protein phosphatase 2A (PP2A) is a heterotrimeric enzyme family that regulates numerous signaling pathways. Biallelic mutations of the structural PP2A Abeta subunit occur in several types of human tumors; however, the functional consequences of these cancer-associated PP2A Abeta mutations in cell transformation remain undefined. Here we show that suppression of PP2A Abeta expression permits immortalized human cells to achieve a tumorigenic state. Cancer-associated Abeta mutants fail to reverse tumorigenic phenotype induced by PP2A Abeta suppression, indicating that these mutants function as null alleles. Wild-type PP2A Abeta but not cancer-derived Abeta mutants form a complex with the small GTPase RalA. PP2A Abeta-containing complexes dephosphorylate RalA at Ser183 and Ser194, inactivating RalA and abolishing its transforming function. These observations identify PP2A Abeta as a tumor suppressor gene that transforms immortalized human cells by regulating the function of RalA.

Selection of protein phosphatase 2A regulatory subunits is mediated by the C terminus of the catalytic Subunit

Protein phosphatase 2A (PP2A) is a family of multifunctional serine/threonine phosphatases all composed of a catalytic C, a structural A, and a regulatory B subunit. Assembly of the complex with the appropriate B subunit forms the key to the functional specificity and regulation of PP2A. Emerging evidence suggests a crucial role for methylation and phosphorylation of the PP2A C subunit in this process. In this study, we show that PP2A C subunit methylation was not absolutely required for binding the PR61/B' and PR72/B'' subunit families, whereas binding of the PR55/B subunit family was determined by methylation and the nature of the C-terminal amino acid side chain. Moreover mutation of the phosphorylatable Tyr(307) or Thr(304) residues differentially affected binding of distinct B subunit family members. Down-regulation of the PP2A methyltransferase LCMT1 by RNA interference gradually reduced the cellular amount of methylated C subunit and induced a dynamic redistribution of the remaining methylated PP2A(C) between different PP2A trimers consistent with their methylation requirements. Persistent knockdown of LCMT1 eventually resulted in specific degradation of the PR55/B subunit and apoptotic cell death. Together these results establish a crucial foundation for understanding PP2A regulatory subunit selection.

An in vivo assay to quantify stable protein phosphatase 2A (PP2A) heterotrimeric species

Protein phosphatase 2A (PP2A) regulates a broad spectrum of cellular processes. The enzyme is, in fact, largely a collection of varied heterotrimeric species composed of a catalytic (C) subunit and regulatory (B-type) subunit bound together by a structural (A) subunit. One important feature of the C subunit is that its carboxy-terminus can be modified by phosphorylation and methylation. The mechanisms that trigger such posttranslational modifications, as well as their consequences, are still under investigation. However, data collected thus far indicate that these modifications alter the binding to B subunits for an AC dimer, thereby affecting the makeup of the PP2A species in the cell. In this chapter, we describe an in vivo assay for assessing stable PP2A heterotrimer formation that is based on specific subcellular localizations of PP2A heterotrimers. This assay can be used to study the impact of a wide variety of alterations (such as mutations and covalent modifications) on PP2A heterotrimer formation. We specifically describe the use of this assay to quantify the effects of methylation on the stable formation of PP2ARts1p and PP2ACdc55p heterotrimers.

Mutagenesis and expression of the scaffolding Aalpha and Abeta subunits of PP2A: assays for measuring defects in binding of cancer-related Aalpha and Abeta mutants to the regulatory B and catalytic C subunits

Protein phosphatase 2A (PP2A) holoenzymes are composed of three subunits: one scaffolding A subunit, one regulatory B subunit, and one catalytic C subunit. The A subunit exists as two isoforms: Aalpha and Abeta. The C subunit also exists as two isoforms (Calpha and Cbeta) and B subunits fall into three families (B, B', and B") comprising over 15 members. The Aalpha and Abeta subunits consist of 15 nonidentical repeats, which are composed of two amphipathic alpha helices that are connected by a loop (intrarepeat loop). These loops are instrumental in binding regulatory B and catalytic C subunits. The genes encoding the Aalpha and Abeta subunits are relatively frequent targets for mutation in human cancer. The mutations often affect the intrarepeat loops and cause defects in the binding of specific B subunits or of B and C subunits. Here, we describe in vitro and in vivo binding assays for measuring these defects. Knowing which B subunits are affected in binding to the mutant A subunits sheds light on which holoenzymes might be involved in growth control and cancer.