Protein Phosphatase Activity Research Articles

Coordination of Protein Kinase and Phosphoprotein Phosphatase Activities in Mitosis.

Dynamic changes in protein phosphorylation govern the transitions between different phases of the cell division cycle. A “tug of war” between highly conserved protein kinases and the family of phosphoprotein phosphatases (PPP) establishes the phosphorylation state of proteins, which controls their function. More than three-quarters of all proteins are phosphorylated at one or more sites in human cells, with the highest occupancy of phosphorylation sites seen in mitosis. Spatial and temporal regulation of opposing kinase and PPP activities is crucial for accurate execution of the mitotic program. The role of mitotic kinases has been the focus of many studies, while the contribution of PPPs was for a long time underappreciated and is just emerging. Misconceptions regarding the specificity and activity of protein phosphatases led to the belief that protein kinases are the primary determinants of mitotic regulation, leaving PPPs out of the limelight. Recent studies have shown that protein phosphatases are specific and selective enzymes, and that their activity is tightly regulated. In this review, we discuss the emerging roles of PPPs in mitosis and their regulation of and by mitotic kinases, as well as mechanisms that determine PPP substrate recognition and specificity.

Inhibition of CREB binding protein-beta-catenin signaling down regulates CD133 expression and activates PP2A-PTEN signaling in tumor initiating liver cancer cells

BackgroundThe WNT-beta-catenin pathway is known to regulate cellular homeostasis during development and tissue regeneration. Activation of WNT signaling increases the stability of cytoplasmic beta-catenin and enhances its nuclear translocation. Nuclear beta-catenin function is regulated by transcriptional co-factors such as CREB binding protein (CBP) and p300. Hyper-activated WNT-beta-catenin signaling is associated with many cancers. However, its role in inducing stemness to liver cancer cells, its autoregulation and how it regulates tumor suppressor pathways are not well understood. Here we have investigated the role of CBP-beta-catenin signaling on the expression of CD133, a known stem cell antigen and PP2A-PTEN pathway in tumor initiating liver cancer cells.MethodsHuman hepatoblastoma cell line HepG2 and clonally expanded CD133 expressing tumor initiating liver cells (TICs) from premalignant murine liver were used in this study. CBP-beta-catenin inhibitor ICG001 was used to target CBP-beta catenin signaling in liver cancer cells in vitro. Western blotting and real time PCR (qPCR) were used to quantify protein expression/phosphorylation and mRNA levels, respectively. CBP and CD133 gene silencing was performed by siRNA transfection. Fluorescence Activated Cell Sorting (FACS) was performed to quantify CD133 positive cells. Protein Phosphatase (PP2A) activity was measured after PP2AC immunoprecipitation.ResultsCBP inhibitor ICG001 and CBP silencing significantly reduced CD133 expression and anchorage independent growth in HepG2 and murine TICs. CD133 silencing in TICs decreased cell proliferation and expression levels of cell cycle regulatory genes, CyclinD1 and CyclinA2. ICG001 treatment and CBP silencing reduced the levels of phosphoSer380/Tyr382/383PTEN, phosphoSer473-AKT, Phospho-Ser552beta-catenin in TICs. ICG001 mediated de-phosphorylation of PTEN in TICs was PP2A dependent and partly prevented by co-treatment with PP2A inhibitor okadaic acid.ConclusionsCBP-beta-catenin signaling promotes stemness via CD133 induction and cell proliferation in TICs. We found a novel functional link between CBP-beta-catenin and PP2A-PTEN-AKT pathway in liver TICs. Therefore, CBP-beta-catenin-PP2A-PTEN-AKT signaling axis could be a novel therapeutic target to prevent liver tumor initiation and cancer recurrence.

Amphetamine Neurotoxicity in PC12 Cells through the PP2A/AKT/GSK3β Pathway.

Amphetamine (AMPH) abuse can influence neuropsychiatric disorders and cell apoptosis by interfering with the protein kinase B/ glycogen synthase kinase 3 beta (AKT/GSK3β) pathway. However, the mechanisms underlying this regulation are poorly understood. Using PC12 cells, we found that AMPH inhibited AKT and GSK-3β phosphorylation levels and increased total GSK-3β levels. Furthermore, AMPH caused an increase in the activity of protein phosphatase 2 (PP2A), a signaling protein upstream of AKT, which in turn inhibited phosphorylated AKT levels. Okadaic acid, a PP2A inhibitor, protected PC12 cells against AMPH-induced apoptosis. Together, our results suggest that the PP2A/AKT/GSK3β pathway plays an important role in AMPH-induced neurotoxicity.

Caffeic acid phenethyl ester down-regulates claudin-2 expression at the transcriptional and post-translational levels and enhances chemosensitivity to doxorubicin in lung adenocarcinoma A549 cells

Claudin-2 is highly expressed in human lung adenocarcinoma cells and involved in the promotion of proliferation. Here, we searched for a compound, which can decrease claudin-2 expression using lung adenocarcinoma A549 cells. In the screening using compounds included in royal jelly and propolis, the protein level of claudin-2 was dose-dependently decreased by caffeic acid phenethyl ester (CAPE), whereas the mRNA level and promoter activity were only decreased by 50 μM CAPE. These results suggest that CAPE down-regulates claudin-2 expression mediated by two different mechanisms. CAPE (50 μM) decreased the level of p-NF-κB, whereas it increased that of IκB. The CAPE-induced decrease in promoter activity of claudin-2 was blocked by the mutation in an NF-κB-binding site. The inhibition of NF-κB may be involved in the decrease in mRNA level of claudin-2. The CAPE (10 μM)-induced decrease in claudin-2 expression was inhibited by chloroquine, a lysosomal inhibitor. CAPE increased the expression and activity of protein phosphatase (PP) 1 and 2A. The CAPE-induced decrease in claudin-2 expression was blocked by cantharidin, a potent PPs inhibitor. The cell proliferation was suppressed by CAPE, which was partially rescued by ectopic expression of claudin-2. In addition, the toxicity and accumulation of doxorubicin in 3D spheroid cells were enhanced by CAPE, which was inhibited by ectopic expression of claudin-2. Taken together, CAPE down-regulates claudin-2 expression at the transcriptional and post-translational levels, and enhances sensitivity of cells to doxorubicin in 3D culture conditions. CAPE may be a useful adjunctive compound in the treatment of lung adenocarcinoma.

Rif1 acts through Protein Phosphatase 1 but independent of replication timing to suppress telomere extension in budding yeast

The Rif1 protein negatively regulates telomeric TG repeat length in the budding yeast Saccharomyces cerevisiae, but how it prevents telomere over-extension is unknown. Rif1 was recently shown to control DNA replication by acting as a Protein Phosphatase 1 (PP1)-targeting subunit. Therefore, we investigated whether Rif1 controls telomere length by targeting PP1 activity. We find that a Rif1 mutant defective for PP1 interaction causes a long-telomere phenotype, similar to that of rif1Δ cells. Tethering PP1 at a specific telomere partially substitutes for Rif1 in limiting TG repeat length, confirming the importance of PP1 in telomere length control. Ablating Rif1–PP1 interaction is known to cause precocious activation of telomere-proximal replication origins and aberrantly early telomere replication. However, we find that Rif1 still limits telomere length even if late replication is forced through deletion of nearby replication origins, indicating that Rif1 can control telomere length independent of replication timing. Moreover we find that, even at a de novo telomere created after DNA synthesis during a mitotic block, Rif1–PP1 interaction is required to suppress telomere lengthening and prevent inappropriate recruitment of Tel1 kinase. Overall, our results show that Rif1 controls telomere length by recruiting PP1 to directly suppress telomerase-mediated TG repeat lengthening.

Aralkyl selenoglycosides and related selenosugars in acetylated form activate protein phosphatase-1 and -2A

Aralkyl and aryl selenoglycosides as well as glycosyl selenocarboxylate derivatives were assayed on the activity of protein phosphatase-1 (PP1) and -2A (PP2A) catalytic subunits (PP1c and PP2Ac) in search of compounds for PP1c and PP2Ac effectors. The majority of tested selenoglycosides activated both PP1c and PP2Ac by ∼2–4-fold in a phosphatase assay with phosphorylated myosin light chain substrate when the hydroxyl groups of the glycosyl moiety were acetylated, but they were without any effects in the non-acetylated forms. A peptide from the myosin phosphatase target subunit-1 (MYPT123–38) that included an RVxF PP1c-binding motif attenuated activation of PP1c by 2-Trifluoromethylbenzyl 2,3,4,6-tetra-O-acetyl-1-seleno-β-d-glucopyranoside (TFM-BASG) and 4-Bromobenzyl 2,3,4,6-tetra-O-acetyl-1-seleno-β-d-glucopyranoside (Br-BASG). MYPT123–38 stimulated PP2Ac and contributed to PP2Ac activation exerted by either Br-BASG or TFM-BASG. Br-BASG and TFM-BASG suppressed partially binding of PP1c to MYPT1 in surface plasmon resonance based binding experiments. Molecular docking predicted that the hydrophobic binding surfaces in PP1c for interaction with either the RVxF residues of PP1c-interactors or selenoglycosides are partially overlapped. Br-BASG and TFM-BASG caused a moderate increase in the phosphatase activity of HeLa cells in 1 h, and suppressed cell viability in 24 h incubations. In conclusion, our present study identified selenoglycosides as novel activators of PP1 and PP2A as well as provided insights into the structural background of their interactions establishing a molecular model for future design of more efficient phosphatase activator molecules.

Role of Protein Phosphatase 1 and Inhibitor of Protein Phosphatase 1 in Nitric Oxide-Dependent Inhibition of the DNA Damage Response in Pancreatic β-Cells.

Nitric oxide is produced at micromolar levels by pancreatic β-cells during exposure to proinflammatory cytokines. While classically viewed as damaging, nitric oxide also activates pathways that promote β-cell survival. We have shown that nitric oxide, in a cell type-selective manner, inhibits the DNA damage response (DDR) and, in doing so, protects β-cells from DNA damage-induced apoptosis. This study explores potential mechanisms by which nitric oxide inhibits DDR signaling. We show that inhibition of DDR signaling (measured by γH2AX formation and the phosphorylation of KAP1) is selective for nitric oxide, as other forms of reactive oxygen/nitrogen species do not impair DDR signaling. The kinetics and broad range of DDR substrates that are inhibited suggest that protein phosphatase activation may be one mechanism by which nitric oxide attenuates DDR signaling in β-cells. While protein phosphatase 1 (PP1) is a primary regulator of DDR signaling and an inhibitor of PP1 (IPP1) is selectively expressed only in β-cells, disruption of either IPP1 or PP1 does not modify the inhibitory actions of nitric oxide on DDR signaling in β-cells. These findings support a PP1-independent mechanism by which nitric oxide selectively impairs DDR signaling and protects β-cells from DNA damage-induced apoptosis.

Protein Kinase D Modulation of Cardiac Protein Phophatases

Protein Kinase D1 (PKD1) is an important stress stimuli transducer affecting myriad cellular functions. Despite a crucial role in pathological cardiac remodeling, few cardiac PKD1 targets have been identified. Recent studies suggest PKD1 could target protein phosphatases (PP) other than the well-known substrate slingshot. Here we test this by measuring phosphatase activity and expression in ventricular homogenates (n=10) from cardiac-specific PKD1 knockout mice (cKO) vs. their wildtype littermates (WT). Using the EnzChek phosphatase assay kit with the 6,8-difluoro-4-methylumbelliferyl phosphate substrate (DiFMUP), PP1, PP2a, PP2b and PP2c phosphatase activity was measured as tautomycin-, LB100-, calcineurin- and sanguinarine chloride-sensitive DiFMUP fluorescence respectively. PP1 activity was slightly higher in cKO vs. WT homogenates (1.4 ± 0.1 vs. 1.0 ± 0.1) at baseline. Inhibition of the other PKD isoforms with 25 nM CRT0066101, reduced PP1 activity in both WT and cKO (to 0.8 ± 0.4 and 0.7 ± 0.1 respectively). PP2a activity was slightly reduced in cKO homogenates (1 ± 0.2 vs. 0.7 ± 0.2) at baseline, and strongly reduced with CRT treatment in both WT and cKO (0.3 ± 0.1 vs. 0.2 ± 0.1 respectively). PP2b activity was unaltered in WT vs. cKO homogenates (1.0±0.2 vs. 1.0±0.1) but CRT strongly reduced PP2b activity (0.2±0.1 vs. 0.1±0.2 in WT and cKO respectively). PP2c activity was also similar at baseline and decreased following CRT inhibition (0.2 ± 0.1 vs. 0.1 ± 0.1 in WT and cKO). Interestingly PP2A protein expression was reduced in cKO vs. WT homogenates. Our results are a first step in defining PKD isoforms as regulators of cardiac protein phosphatase activity. Future experiments will be critical to uncover the molecular mechanisms that underlie the fine-tuning of phosphatase activity in health and disease by PKD signaling.

PTEN Inhibition in Human Disease Therapy.

The tumor suppressor PTEN is a major homeostatic regulator, by virtue of its lipid phosphatase activity against phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3], which downregulates the PI3K/AKT/mTOR prosurvival signaling, as well as by its protein phosphatase activity towards specific protein targets. PTEN catalytic activity is crucial to control cell growth under physiologic and pathologic situations, and it impacts not only in preventing tumor cell survival and proliferation, but also in restraining several cellular regeneration processes, such as those associated with nerve injury recovery, cardiac ischemia, or wound healing. In these conditions, inhibition of PTEN catalysis is being explored as a potentially beneficial therapeutic intervention. Here, an overview of human diseases and conditions in which PTEN inhibition could be beneficial is presented, together with an update on the current status of specific small molecule inhibitors of PTEN enzymatic activity, their use in experimental models, and their limitations as research or therapeutic drugs.

Distinct Roles of Protein Phosphatase 1 Bound on Neurabin and Spinophilin and Its Regulation in AMPA Receptor Trafficking and LTD Induction.

Protein phosphatase-1 (PP1) constrains learning and memory formation in part through its effects on the induction threshold of long-term potentiation (LTP) and depression (LTD). LTD induction requires both the enzymatic activity of PP1 and its proper anchoring to synaptic spines. We have shown previously that neurabin, a major synaptic scaffolding protein, targets PP1 to synapses for LTD induction. Here, we show that PP1 bound on spinophilin, a close homolog of neurabin and another major synaptic PP1 anchoring protein, does not play a role in LTD induction, which suggests that neurabin plays a privileged role in nanodomain targeting of PP1 in LTD induction. We found that protein kinase A can significantly weaken the neurabin-PP1 interaction in neurons via phosphorylation of neurabin at serine 461, a phosphorylation site adjacent to the PP1-binding motif that is not conserved in spinophilin. Finally, we found that a neurabin mutation (S461E), which mimics phosphorylation, blocked AMPA receptor endocytosis and LTD induction. The results indicate the critical importance of nanodomain targeting of PP1 within synaptic spines and its regulation in LTD induction.

Down Syndrome Critical Region 1 Gene, Rcan1, Helps Maintain a More Fused Mitochondrial Network.

The regulator of calcineurin 1 (RCAN1) inhibits CN (calcineurin), a Ca2+-activated protein phosphatase important in cardiac remodeling. In humans, RCAN1 is located on chromosome 21 in proximity to the Down syndrome critical region. The hearts and brains of Rcan1 KO mice are more susceptible to damage from ischemia/reperfusion (I/R); however, the underlying cause is not known. Mitochondria are key mediators of I/R damage. The goal of these studies was to determine the impact of RCAN1 on mitochondrial dynamics and function. Using both neonatal and isolated adult cardiomyocytes, we show that, when RCAN1 is depleted, the mitochondrial network is more fragmented because of increased CN-dependent activation of the fission protein, DRP1 (dynamin-1-like). Mitochondria in RCAN1-depleted cardiomyocytes have reduced membrane potential, O2 consumption, and generation of reactive oxygen species, as well as a reduced capacity for mitochondrial Ca2+ uptake. RCAN1-depleted cardiomyocytes were more sensitive to I/R; however, pharmacological inhibition of CN, DRP1, or CAPN (calpains; Ca2+-activated proteases) restored protection, suggesting that in the absence of RCAN1, CAPN-mediated damage after I/R is greater because of a decrease in the capacity of mitochondria to buffer cytoplasmic Ca2+. Increasing RCAN1 levels by adenoviral infection was sufficient to enhance fusion and confer protection from I/R. To examine the impact of more modest, and biologically relevant, increases in RCAN1, we compared the mitochondrial network in induced pluripotent stem cells derived from individuals with Down syndrome to that of isogenic, disomic controls. Mitochondria were more fused, and O2 consumption was greater in the trisomic induced pluripotent stem cells; however, coupling efficiency and metabolic flexibility were compromised compared with disomic induced pluripotent stem cells. Depletion of RCAN1 from trisomic induced pluripotent stem cells was sufficient to normalize mitochondrial dynamics and function. RCAN1 helps maintain a more interconnected mitochondrial network, and maintaining appropriate RCAN1 levels is important to human health and disease.

Protein phosphatases and podocyte function.

Deregulation of protecting factor signaling actions in podocytes has emerged as an alternative pathway of podocyte injury mechanisms. Here, we review recent knowledge that highlighted how podocyte protecting factors are modulated by protein phosphatases. Protein tyrosine kinases and phosphatases participate in many, if not all, aspects of cellular function by turning on or off multiple signaling cascades and podocytes are no exception. Modulation of tyrosine residue phosphorylation of podocyte factors such as nephrin, vascular endothelial growth factor, insulin receptors and substrates has been shown to promote podocyte damage and cell death that contributed to multiple glomerular diseases. Protein phosphatase activity can cause either an increase [Src homology 2 domain-containing phosphatase 2 (SHP-2)] or a decrease [Protein tyrosine phosphatase1B (PTP1B), SHP-1 and SH2 domain-containing 5'-inositol phosphatase 2 (SHIP2)] in nephrin tyrosine phosphorylation depending on which podocyte injury model was used. Insulin resistance is closely linked to the development and progression of renal disease. Expression of PTP1B, SHP-1, phosphatase and tensin homolog and SHIP2 are potential mechanisms of podocytes insulin resistance in diabetic kidney disease. Tight regulation of protein phosphatases is critical to maintain cell homeostasis and may offer new perceptive targets to restore protecting factor actions in order to prevent podocyte dysfunction and glomerular diseases.

PI3K- and PTEN-Governed PIP<sub>2</sub> and PIP<sub>3</sub> Equilibrium Regulates the Activation and Function of B Cells Through Dock2 Controlled Growth of Antigen Receptor Microclusters

The growth of B cell receptor (BCR) microclusters upon antigen stimulation is one of the most important events in B cell activation, however the underlying molecular mechanism unknown. Here, we systematically addressed this question through a combination of molecular imaging, genetic ablation, pharmacological inhibitor and mice model approaches. We showed that the earliest BCR signaling molecules, Lyn, Syk and PLCγ2 are required for B cells to initiate the growth of BCR microclusters. PI3K-mediated PIP3 production but not Akt and PDK1 activation was required for the sustained growth of the BCR microclusters. The PI3K counterpart signaling molecule, PTEN, potently inhibited the growth of the BCR microclusters, which was dependent on its membrane binding activities and on the lipid phosphatase but not protein phosphatase activity. Mechanistically, we showed that PIP3-dependent recruitment and activation of a unique guanine nucleotide exchange factor, Dock2, was required for the sustained growth of the BCR microclusters through the remodeling of the F-actin cytoskeleton. As a consequence, the formation of the antigen-induced B cell immunological synapse (IS) in Dock2 deficient B cells was drastically impaired. Moreover, Dock2 deficient B cells exhibited decreased Ca2 influx. Physiologically, we found that mice with reduced expression of PTEN in B cells showed enhanced antibody responses and a spontaneous lupus-like autoimmune phenotype. Clinically, we showed that primary B cells from lupus patients exhibited more prominent BCR and PI3K microclusters than B cells from healthy controls. Thus, these results demonstrated the importance of PI3K- and PTEN-governed PIP2 and PIP3 equilibrium in regulating the dynamic growth of BCR microclusters during the initiation of B cell activation.

In-Gel Protein Phosphatase Assay Using Fluorogenic Substrates.

Protein phosphorylation plays important roles in regulating a variety of biological processes in animals, plants, and microorganisms. Therefore, it is important to use appropriate techniques to detect and analyze protein kinases and protein phosphatases. In this chapter, we describe the method to detect protein phosphatase activities using fluorogenic substrates such as 4-methylumbelliferyl phosphate (MUP) after separating proteins by one-dimensional or two-dimensional polyacrylamide gel electrophoresis.

A Multi-season Investigation of Microbial Extracellular Enzyme Activities in Two Temperate Coastal North Carolina Rivers: Evidence of Spatial but Not Seasonal Patterns.

Riverine systems are important sites for the production, transport, and transformation of organic matter. Much of the organic matter processing is carried out by heterotrophic microbial communities, whose activities may be spatially and temporally variable. In an effort to capture and evaluate some of this variability, we sampled four sites—two upstream and two downstream—at each of two North Carolina rivers (the Neuse River and the Tar-Pamlico River) ca. twelve times over a time period of 20 months from 2010 to 2012. At all of the sites and dates, we measured the activities of extracellular enzymes used to hydrolyze polysaccharides and peptides, and thus to initiate heterotrophic carbon processing. We additionally measured bacterial abundance, bacterial production, phosphatase activities, and dissolved organic carbon (DOC) concentrations. Concurrent collection of physical data (stream flow, temperature, salinity, dissolved oxygen) enabled us to explore possible connections between physiochemical parameters and microbial activities throughout this time period. The two rivers, both of which drain into Pamlico Sound, differed somewhat in microbial activities and characteristics: the Tar-Pamlico River showed higher β-glucosidase and phosphatase activities, and frequently had higher peptidase activities at the lower reaches, than the Neuse River. The lower reaches of the Neuse River, however, had much higher DOC concentrations than any site in the Tar River. Both rivers showed activities of a broad range of polysaccharide hydrolases through all stations and seasons, suggesting that the microbial communities are well-equipped to access enzymatically a broad range of substrates. Considerable temporal and spatial variability in microbial activities was evident, variability that was not closely related to factors such as temperature and season. However, Hurricane Irene's passage through North Carolina coincided with higher concentrations of DOC at the downstream sampling sites of both rivers. This DOC maximum persisted into the month following the hurricane, when it continued to stimulate bacterial protein production and phosphatase activity in the Neuse River, but not in the Tar-Pamlico River. Microbial community activities are related to a complex array of factors, whose interactions vary considerably with time and space.

Effect of replacing inorganic zinc with a lower level of organic zinc (zinc propionate) on performance, biochemical constituents, antioxidant, immune and mineral status in buffalo calves

An experiment of 120 days was carried out to investigate the effects of replacing inorganic zinc (ZnSO4; 80 ppm) with lower level (75% of inorganic levels; 60 ppm) of organic zinc (Zn propionate; Zn-Prop) on growth, serum biochemical constituents, immune response, mineral and antioxidant status in buffalo calves. Twelve buffalo calves (193.3±19.63kg; 14-24 months) were randomly allotted to a control (80 ppm Zn) and experimental (60 ppm Zn) diets. All calves were weighed at fortnight interval. Animals were immunized against Brucella abortus (BA) and chicken RBC (CRBC) antigens on day 90 with a booster dose of 15 days interval and serum was collected on 7, 14, 21 and 28 d of post sensitization (PS) to study the antibody titres. Blood was collected on 114 d of experiment to prepare serum and haemolysate. Cell mediated immune response (CMIR) was determined against phytohemagglutinin-P (PHA-P) on day 118. The fortnightly body weights, average daily gain, dry matter intake, feed conversion ratio were comparable between the dietary groups. Similarly, serum albumin, globulin, creatinine and mineral (Zn, Cu, Mn, Fe) levels were comparable while higher (P less than 0.05) serum total protein and alkaline phosphatase activities were observed in organic Zn supplemented calves. After 7 d of PS, serum antibody titres (log2) against BA were higher (P less than 0.05) with Zn-Prop supplementation, while the titres against CRBC were not affected by Zn source and dose. Lipid peroxidation and antioxidant enzyme activities (glutathione reductase, RBC catalase and superoxide dismutase) estimated in haemolysate were comparable between groups, while glutathione peroxidase (P less than 0.05) activity increased with Zn-prop supplementation compared to ZnSO4. The CMIR was higher (P less than 0.05) with organic Zn. It can be concluded that the growth performance, antioxidant status, and immune response in calves fed lower levels of organic Zn (Zn-Propionate) (75% of inorganic mineral supplementation) was comparable to those fed 100% of inorganic zinc and the CMI response was higher in organic Zn supplemented calves.

Developmental and light regulation of tumor suppressor protein PP2A in the retina.

Protein phosphatases are a group of universal enzymes that are responsible for the dephosphorylation of various proteins and enzymes in cells. Cellular signal transduction events are largely governed by the phosphorylation of key proteins. The length of cellular response depends on the activation of protein phosphatase that dephosphorylates the phosphate groups to halt a biological response, and fine-tune the defined cellular outcome. Dysregulation of these phosphatase(s) results in various disease phenotypes. The retina is a post-mitotic tissue, and oncogenic tyrosine and serine/ threonine kinase activities are important for retinal neuron survival. Aberrant activation of protein phosphatase(s) may have a negative effect on retinal neurons. In the current study, we characterized tumor suppressor protein phosphatase 2 (PP2A), a major serine/ threonine kinase with a broad substrate specificity. Our data suggest that PP2A is developmentally regulated in the retina, localized predominantly in the inner retina, and expressed in photoreceptor inner segments. Our findings indicate that PKCα and mTOR may serve as PP2A substrates. We found that light regulates PP2A activity. Our studies also suggest that rhodopsin regulates PP2A and its substrate(s) dephosphorylation. PP2A substrate phosphorylation is increased in mice lacking the A-subunit of PP2A. However, there is no accompanying effect on retina structure and function. Together, our findings suggest that controlling the activity of PP2A in the retina may be neuroprotective.

Evidence that PP2A activity is dispensable for spindle assembly checkpoint-dependent control of Cdk1.

Progression through mitosis, the cell cycle phase deputed to segregate replicated chromosomes, is granted by a protein phosphorylation wave that follows an activation-inactivation cycle of cyclin B-dependent kinase (Cdk) 1, the major mitosis-promoting enzyme. To ensure correct chromosome segregation, the safeguard mechanism spindle assembly checkpoint (SAC) delays Cdk1 inactivation by preventing cyclin B degradation until mitotic spindle assembly. At the end of mitosis, reversal of bulk mitotic protein phosphorylation, downstream Cdk1 inactivation, is required to complete mitosis and crucially relies on the activity of major protein phosphatases like PP2A. A role for PP2A, however, has also been suggested in spindle assembly and SAC-dependent control of Cdk1. Indeed, PP2A was found in complex with SAC proteins while small interfering RNAs (siRNAs)-mediated downregulation of PP2A holoenzyme components affected mitosis completion in mammalian cells. However, whether the SAC-dependent control of Cdk1 required the catalytic activity of PP2A has never been directly assessed. Here, using two PP2A inhibitors, okadaic acid and LB-100, we provide evidence that PP2A activity is dispensable for SAC control of Cdk1 in human cells.

The effects of dietary supplement of galactooligosaccharide on innate immunity, immune related genes expression and growth performance in zebrafish (Danio rerio)

The present study investigates the effect of different levels of galactooligosaccharide (GOS) on innate immune parameters, immune related genes expression as well as growth performance in zebrafish (Danio rerio). Four hundred and twenty fish (mean weight 45 ± 0.1 mg) were supplied, randomly stocked in twelve aquaria assigned to four treatments. Zebrafish were fed with either control diet or control diet enriched with different levels (0.5, 1 and 2%) of GOS for eight weeks. At the end of feeding trial innate immune parameters (total immunoglobulin, total protein and alkaline phosphatase activity), immune related genes expression (interleukin 1 beta [il1b], Lysozyme [lyz], tumor necrosis factor alpha [tnf-alpha]) as well as growth performance were measured. Evaluation of immune parameters revealed significant (P < .05) increase of total protein and total Ig in zebrafish fed 1 or 2% GOS compared other treatments. However, in case of lysozyme activity no significant (P > .05) differences were noticed between GOS fed fish and control group. Also, in case of ALP activity, significant increase (P < .05) was observed in 2% GOS treatment. Gene expression studies revealed significant upregulation (P < .05) of tnf-alpha and lyz genes in GOS fed fish. While no significant (P > .05) difference was observed in case of il1b gene expression. Evaluation of growth performance at the end of feeding trial revealed no significant (P < .05) improvement in GOS fed groups. The present results revealed positive effects of GOS on innate immune parameters and related gene expression in zebrafish.

Biochemical and histological changes in the heart of post-partum rats exposed to Natron

BackgroundThe customary puerperal practice of Natron consumption has been identified as one of the predisposing factors in the etiology of peripartum cardiomyopathy (PPCM). This study was designed to investigate the effect of Natron in postpartum Wistar albino rats. MethodsA total of 30 postpartum Wistar rats were exposed to different doses (50mg/kg, 100mg/kg, 200mg/kg and 300mg/kg) of Natron for 28days. After the treatment, we carried out biochemical analyses and histological evaluations of kidney, liver and heart. ResultsThe study revealed that the exposure of postpartum rats to 100mg/kg of Natron and above significantly (p<0.05) increase the cardiac markers; myoglobin, creatine kinase-MB, troponin I and T as compared with control. The result of liver function indicated no significant difference in alanine aminotransferase, aspartate aminotransferase, gamma-glutamyltransferase, albumin and total protein of the Natron treated groups as compared with control. However, at higher doses, the levels of total protein, globulin and alkaline phosphatase activity were significantly increased in comparison to the control. There was no significant difference in the kidney function markers of the treatment groups as compared with control. Histological examinations revealed no changes in the kidney of the treated groups. Mild portal triaditis was observed in the liver of the treated rats. The heart of the rats administered ≥100mg/kg of Natron showed myocyte hypertrophy. ConclusionThe study demonstrated that the administration of Natron for 28days caused changes in the heart of postpartum rats and thus may contribute to the pathogenesis of PPCM.