Regulation Of Phosphoproteins Research Articles

Antithrombotic Effect of Artemisinin through Phosphoprotein Regulation in U46619-induced Platelets

Antithrombotic Effect of Artemisinin through Phosphoprotein Regulation in U46619-induced Platelets

Inhibitory effects of hydroxygenkwanin on platelets aggregation via regulation of phosphoproteins in collagen-induced human platelets

Inhibitory effects of hydroxygenkwanin on platelets aggregation via regulation of phosphoproteins in collagen-induced human platelets

Erratum to: Inhibitory effects of artemether on collagen-induced platelet aggregation via regulation of phosphoprotein inducing PI3K/Akt and MAPK

Erratum to: Inhibitory effects of artemether on collagen-induced platelet aggregation via regulation of phosphoprotein inducing PI3K/Akt and MAPK

Pharmacological Actions of 5-Hydroxyindolin-2 on Modulation of Platelet Functions and Thrombus Formation via Thromboxane A2 Inhibition and cAMP Production

Platelets play a very significant role in hemostasis while simultaneously posing a risk for the development of various cardiovascular diseases. Platelet-mediated issues can occur in blood vessels and trigger various medical problems. Therefore, controlling platelet function is important in the prevention of thrombosis. In this regard, we need to find compounds that provide potent antiplatelet activity with minimum side effects. Therefore, we examined the effect of 5-hydroxyindolin-2-one isolated from Protaetia brevitarsis larvae having antiplatelet properties and investigated different pathways that mediate the antiplatelet activity. We examined the effect of 5-hydroxyindolin-2-one (5-HI) on the regulation of phosphoproteins, thromboxane A2 generation, and integrin αIIbβ3 action. Our data showed that human platelet aggregation was inhibited by 5-HI (75, 100, 150, 200 μM) without cytotoxicity, and it suppressed intracellular Ca2+ concentration through the regulation of inositol 1, 4, 5-triphosphate receptor I (Ser1756) and extracellular signal-regulated kinase (ERK). Moreover, collagen-elevated thromboxane A2 production and αIIbβ3 action were inhibited by 5-HI through the regulation of cytosolic phospholipase A2 (cPLA2), mitogen-activated protein kinase p38 (p38MAPK), vasodilator-stimulated phosphoprotein (VASP), phosphoinositide 3-kinase (PI3K), and Akt (protein kinase B). Therefore, we suggested that 5-HI could be a potential substance for the prevention of thrombosis-mediated thrombosis.

Abstract 11566: Distribution and New Function of Na, K-ATPase and Its Phosphoprotein Regulator Phospholemman in Cardiac Myocytes

Introduction: Na, K-ATPase (NKA), regulated by phosphoprotein phospholemman (PLM), contributes to excitation-contraction via the Na,Ca-exchanger at cardiac T-tubules (TTs). It is known that the intercalated discs (IDs) contain concentrated specific Na channels and K channels, that rely on ion gradients set by NKA. Yet, the coordinated trafficking and localization of NKA and PLM in cardiomyocytes (CMs) remains incompletely understood, Hypothesis: NKA and PLM are concentrated in the ID and essential for cardiac conduction. Methods: We have made five antibodies (Abs) that specifically identify PLM (B8, PLM-N-term, and PLM-C-term) or NKA (NKA-α1 and Pan-α, recognizing both α1 and α2 subunits of NKA). Confocal immunofluorescence assays were used to determine the intracellular distribution of PLM and NKA. Optical mapping studies were performed in rabbit hearts. Results: These five Abs all displayed specific fluorescence signals in dog CMs that were more intense at the IDs than TTs. These signals were eliminated by competing peptides. B8 and NKA-α1 signals highly overlapped, with similar intensity ratios between ID and TT at ~3. Immunostaining of connexin 43, γ-catenin, or N-cadherin confirmed the co-localization of NKA and PLM to the ID. PLM and NKA co-enriched with ID protein markers in sarcolemma/ID membrane preparations. To corroborate the localization of PLM at the ID, we expressed dog PLM in rat CMs. By 30h post-infection, B8 detected newly synthesized dog PLM that paralleled the pattern of its steady-state distribution in tissue, with concentrated protein apparent at IDs (B8 fluorescence intensity ratio of ID/TT = 2.6 ± 0.5, 50CMs). Nocodazole prevented newly-made dog PLM trafficking to ID. Finally, optical mapping studies showed that the NKA inhibitor ouabain and digoxin significantly increased activation times in a dose-dependent manner (n=5 and 4 rabbits, respectively). Conclusions: The α1 subunit of NKA and PLM are each expressed at a ~3X higher concentration in ID compared to TT in CMs, contributing to cardiac conduction. Mechanisms of PLM and NKA protein trafficking to the two disparate subcellular sites, and associated effects of PLM regulation by adrenergic signaling, provide important new insights into the physiology of cardiac conduction.

Trifluoperazine (TFP)-mediated fluorescence imaging approach reveals a probable calmodulin (CaM)-independent calcium signaling accompanying differential protein phosphorylation in NaCl-stressed sunflower seedlings (Helianthus annuus L. var. KBSH44)

The impact of calcium (Ca2+) under abiotic stress is manifested by both calmodulin (CaM)-dependent and calmodulin-independent pathways of signaling mechanisms in plants. Present work demonstrates the impact of NaCl (120 mM) stress on Ca2+-calmodulin activity and its spatial distribution in roots of 2d old sunflower seedlings (Helianthus annuus). NaCl stress significantly increases [Ca2+]cyt in roots (69%) which corresponds with 8% increase in activated calmodulin (Ca2+-CaM) levels. Thus, NaCl stress induced Ca2+ signaling in roots is likely to majorly operate through CaM-independent routes. Trifluoperazine-mediated fluorescence imaging reveals differential distribution of Ca2+-CaM complex in the elongation and differentiation zone of seedling roots which indicate spatial regulation of Ca2+-CaM signaling operative in the presence of NaCl stress. NaCl stress-induced CaM-independent Ca2+ signaling is further accompanied by differential protein phoshorylation of cytosolic proteins in seedling roots and cotyledons. Phosphoproteins exhibiting qualitative differences in roots in response to salt-stress were of both low and high molecular weight range (76–17.5 kDa) unlike in cotyledons where only high molecular weight (>76 kDa) phosphoproteins exhibited major differential expressions in response to 120 mM NaCl stress. Among the various polypeptides in the fraction of OB membrane proteins two polypeptides of 48 and >76 kDa exhibited increased protein phosphorylation in the presence of NaCl stress. NaCl stress for 48 h induces differences in the expression of phosphoproteins in roots and cotyledons, suggesting the long distance signaling of Na+ stress from roots to cotyledons. Roots seem to exhibit much stringent regulation of phosphoproteins in comparison with cotyledons which have lesser qualitative differences. Thus, present work provides evidence on the modulation of Ca2+-CaM signaling accompanying differential protein phosphorylation in sunflower seedling roots and cotyledons under NaCl stress.

Inhibitory effects of artemether on collagen-induced platelet aggregation via regulation of phosphoprotein inducing PI3K/Akt and MAPK

Inhibitory effects of artemether on collagen-induced platelet aggregation via regulation of phosphoprotein inducing PI3K/Akt and MAPK

Extracellular phosphoprotein regulation is affected by culture system scale-down

BackgroundPhosphorylated proteins are known to be present in multiple body fluids in normal conditions, and abnormally accumulated under some pathological conditions. The biological significance of their role in the extracellular space has started being elucidated only recently, for example in bone mineralization, neural development, and coagulation. Here, we address some criticalities of conventional culture systems for the study of the extracellular regulation of phosphorylation. MethodsWe make use of microfluidics to scale-down the culture volume to a size comparable to the interstitial spaces occurring in vivo. The phosphoprotein content of conditioned media was analyzed by a colorimetric assay that detects global phosphorylation. ResultsWe found that miniaturization of the culture system increases phosphoprotein accumulation. Moreover, we demonstrated that in conventional culture systems dilution affects the extent of the phosphorylation reactions occurring within the extracellular space. On the other hand, in microfluidics the phosphorylation status was not affected by addition of adenosine triphosphate (ATP) and FAM20C Golgi Associated Secretory Pathway Kinase (FAM20C) ectokinase, as if their concentration was already not limiting for the phosphorylation reaction to occur. ConclusionsThe volume of the extracellular environment plays a role in the process of extracellular phosphorylation due to its effect on the concentration of substrates, enzymes and co-factors. General significanceThus, the biological role of extracellular phosphoregulation may be better appreciated within a microfluidic culture system.

In Vitro Antiplatelet Activity of Mulberroside C through the Up-Regulation of Cyclic Nucleotide Signaling Pathways and Down-Regulation of Phosphoproteins.

Physiological agonists trigger signaling cascades, called “inside-out signaling”, and activated platelets facilitate adhesion, shape change, granule release, and structural change of glycoprotein IIb/IIIa (αIIb/β3). Activated αIIb/β3 interacts with fibrinogen and begins second signaling cascades called “outside-in signaling”. These two signaling pathways can lead to hemostasis or thrombosis. Thrombosis can occur in arterial and venous blood vessels and is a major medical problem. Platelet-mediated thrombosis is a major cause of cardiovascular disease (CVD). Therefore, controlling platelet activity is important for platelet-mediated thrombosis and cardiovascular diseases. In this study, focus on Morus Alba Linn, a popular medicinal plant, to inhibit the function of platelets and found the containing component mulberroside C. We examine the effect of mulberroside C on the regulation of phosphoproteins, platelet-activating factors, and binding molecules. Agonist-induced human platelet aggregation is dose-dependently inhibited by mulberroside C without cytotoxicity, and it decreased Ca2+ mobilization and p-selectin expression through the upregulation of inositol 1, 4, 5-triphosphate receptor I (Ser1756), and downregulation of extracellular signal-regulated kinase (ERK). In addition, mulberroside C inhibited thromboxane A2 production, fibrinogen binding, and clot retraction. Our results show antiplatelet effects and antithrombus formation of mulberroside C in human platelets. Thus, we confirm that mulberroside C could be a potential phytochemical for the prevention of thrombosis-mediated CVDs.

Backbone and side-chain chemical shift assignments of full-length, apo, human Pin1, a phosphoprotein regulator with interdomain allostery.

Pin1 is a human peptidyl-prolyl cis-trans isomerase important for the regulation of phosphoproteins that are implicated in many diseases including cancer and Alzheimer's. Further biophysical study of Pin1 will elucidate the importance of the two-domain system to regulate its own activity. Here, we report near-complete backbone and side-chain 1H, 13C and 15N NMR chemical shift assignments of full-length, apo Pin1 for the purpose of studying interdomain allostery and dynamics.

Abstract 5328: Protein phosphatase 2A activity is a major determinant of therapy response in cancer cells

Abstract Protein phosphatase 2A (PP2A) dephosphorylates majority of Ser/Thr phosphorylated proteins. Consequently, PP2A is an antagonist of multiple oncogenic pathways and PP2A reactivation may provide an alternative route to target these pathways. Importantly, because PP2A reactivation would result in simultaneous dephosphorylation of both collateral and downstream effectors of kinase pathways, it might circumvent commonly encountered kinase inhibitor resistance mechanisms. To systematically study the role of PP2A in cancer therapy response we used RNAi targeting against PP2A inhibitor proteins CIP2A, PME-1 and SET (PP2A reactivation), and PP2A structural subunits (PP2A inhibition), together with high throughput drug sensitivity screen covering 300 clinical cancer drugs and investigational compounds. Changes in phosphorylation status of PP2A targets in response to RNAi perturbation, was studied by LC-MS/MS-based label-free quantitative phosphoproteomics analysis. Importantly, we show that cancer cell drug sensitivity across 300 compounds correlates with PP2A activity profile so that PP2A inhibition made cells on average resistant to therapies, whereas their sensitization by PP2A inhibitor protein siRNAs correlated with changes in phosphoprotein regulation. In particular, cancer cell response to kinase inhibitors followed very closely PP2A activity regulation and PP2A reactivation resulted in increased average sensitivity to 105 kinase inhibitors. Furthermore, we show that PP2A reactivation results in convergent phosphorylation patterns with targeting of kinase pathways by RAS inhibition. We also identify novel PP2A regulated phosphorylation sites in target proteins of these kinases. As a validation study, we demonstrate that PP2A inhibitor protein PME-1 mediates resistance of glioma cells to various types of survival pathway kinase inhibitors, as well as to temozolomide. Co-treatment with PME-1 siRNA and kinase inhibitors eradicates several GBM cell lines, and glioma stem cells, in vitro, and this combination strategy shows pronounced efficacy also in in vivo models. The PME-1-elicited resistance mechanism is mediated by reactivation of specific PP2A complexes and involves regulation of PP2A target HDAC4. Together our data combines 4500 drug response profiles, and more than 5000 quantitative phosphopeptide idenitifications to draw first systemic map of relevance of PP2A biology in cancer therapy responses. In particular the data reveals an unprecedented importance of PP2A activity for kinase inhibitor responses. Based on these data we propose that in order to efficiently inhibit phosphorylation-dependent signaling in cancer cells, and thus provide better therapeutic index for the kinase inhibitors, they should be combined with emerging small molecule PP2A reactivating compounds. Citation Format: Otto Kauko, Susumu Imanishi, Amanpreet Kaur, Daniel Laajala, Evgeny Kulesskiy, Mikael Jumppanen, Garry Corthals, Tero Aittokallio, Krister Wennerberg, Jukka Westermarck. Protein phosphatase 2A activity is a major determinant of therapy response in cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5328. doi:10.1158/1538-7445.AM2015-5328

Plasmodium vivax inhibits erythroid cell growth through altered phosphorylation of the cytoskeletal protein ezrin

BackgroundThe underlying causes of severe malarial anaemia are multifactorial. In previously reports, Plasmodium vivax was found to be able to directly inhibited erythroid cell proliferation and differentiation. The molecular mechanisms underlying the suppression of erythropoiesis by P. vivax are remarkably complex and remain unclear. In this study, a phosphoproteomic approach was performed to dissect the molecular mechanism of phosphoprotein regulation, which is involved in the inhibitory effect of parasites on erythroid cell development.MethodsThis study describes the first comparative phosphoproteome analysis of growing erythroid cells (gECs), derived from human haematopoietic stem cells, exposed to lysates of infected erythrocytes (IE)/uninfected erythrocytes (UE) for 24, 48 and 72 h. This study utilized IMAC phosphoprotein isolation directly coupled with LC MS/MS analysis.ResultsLysed IE significantly inhibited gEC growth at 48 and 72 h and cell division resulting in the accumulation of cells in G0 phase. The relative levels of forty four phosphoproteins were determined from gECs exposed to IE/UE for 24-72 h and compared with the media control using the label-free quantitation technique. Interestingly, the levels of three phosphoproteins: ezrin, alpha actinin-1, and Rho kinase were significantly (p < 0.05) altered. These proteins display interactions and are involved in the regulation of the cellular cytoskeleton. Particularly affected was ezrin (phosphorylated at Thr567), which is normally localized to gEC cell extension peripheral processes. Following exposure to IE, for 48-72 h, the ezrin signal intensity was weak or absent. This result suggests that phospho-ezrin is important for actin cytoskeleton regulation during erythroid cell growth and division.ConclusionsThese findings suggest that parasite proteins are able to inhibit erythroid cell growth by down-regulation of ezrin phosphorylation, leading to ineffective erythropoiesis ultimately resulting in severe malarial anaemia. A better understanding of the mechanisms of ineffective erythropoiesis may be beneficial in the development of therapeutic strategies to prevent severe malarial anaemia.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0648-9) contains supplementary material, which is available to authorized users.

Inducing autophagy

Autophagy is a lysosomal-mediated catabolic process, which through degradation of different cytoplasmic components aids in maintaining cellular homeostasis and survival during exposure to extra- or intracellular stresses. Ammonia is a potential toxic and stress-inducing byproduct of glutamine catabolism, which has recently been found to induce autophagy in an MTOR independent way and support cancer cell survival. In this study, quantitative phosphoproteomics was applied to investigate the initial signaling events linking ammonia to the induction of autophagy. The MTOR inhibitor rapamycin was used as a reference treatment to emphasize the differences between an MTOR-dependent and -independent autophagy-induction. By this means 5901 phosphosites were identified of which 626 were treatment-specific regulated and 175 were coregulated. Investigation of the ammonia-specific regulated sites supported that MTOR activity was not affected, but indicated increased MAPK3 activity, regulation of proteins involved in Rho signal transduction, and a novel phosphorylation motif, serine-proline-threonine (SPT), which could be linked to cytoskeleton-associated proteins. MAPK3 could not be identified as the primary driver of ammonia-induced autophagy but instead the data suggested an upregulation of AMPK and the unfolded protein response (UPR), which might link ammonia to autophagy induction. Support of UPR induction was further obtained from the finding of increased protein levels of the ER stress markers DDIT3/CHOP and HSPA5 during ammonia treatment. The large-scale data set presented here comprises extensive high-quality quantitative information on phosphoprotein regulation in response to 2 very different autophagy inducers and should therefore be considered a general resource for the community.

Differential Phosphoproteome Regulation of Nucleus Accumbens in Environmentally Enriched and Isolated Rats in Response to Acute Stress

Increasing evidence shows that stress contributes to the pathogenesis of major depressive disorder which is a severe neuropsychiatric disorder and influences over 10% of the world's population. Our previous studies revealed that rats reared in an enriched environment display less depression-related behavior compared to rats raised in an isolated environment, which implies that environmental enrichment produces an antidepressant-like behavioral phenotype. However, the molecular mechanisms are not fully understood. Protein phosphorylation rapidly changes signaling pathway function and alters the function of proteins associated with the stress-induced depressive disorder. Thus, in this study, a phosphoproteomic approach was used to uncover differential phosphoprotein regulation in rat nucleus accumbens between isolated (IC) and enriched environmental conditions (EC) under basal conditions, and in response to acute stress. We found 23 phosphoproteins were regulated in EC vs. IC rats under basal conditions; 10 phosphoproteins regulated by stress in IC rats; and 15 regulated by stress in EC rats. Among all significantly regulated phosphoproteins, 11 of them were represented in at least two conditions. The regulated phosphoproteins represent signaling pathway proteins (including ERK2), enzymes, transcriptional regulators, protein translation regulators, transporters, chaperones and cytoskeletal proteins. These findings provide a global view for further understanding the contribution of protein phosphorylation in depression pathogenesis and antidepressant action.

Comprehensive Phosphoproteome Analysis of INS-1 Pancreatic Beta-Cells using Various Digestion Strategies Coupled with Liquid Chromatography–Tandem Mass Spectrometry

Type 2 diabetes results from aberrant regulation of the phosphorylation cascade in beta-cells. Phosphorylation in pancreatic beta-cells has not been examined extensively, except with regard to subcellular phosphoproteomes using mitochondria. Thus, robust, comprehensive analytical strategies are needed to characterize the many phosphorylated proteins that exist, because of their low abundance, the low stoichiometry of phosphorylation, and the dynamic regulation of phosphoproteins. In this study, we attempted to generate data on a large-scale phosphoproteome from the INS-1 rat pancreatic beta-cell line using linear ion trap MS/MS. To profile the phosphoproteome in-depth, we used comprehensive phosphoproteomic strategies, including detergent-based protein extraction (SDS and SDC), differential sample preparation (in-gel, in-solution digestion, and FASP), TiO2 enrichment, and MS replicate analyses (MS2-only and multiple-stage activation). All spectra were processed and validated by stringent multiple filtering using target and decoy databases. We identified 2467 distinct phosphorylation sites on 1419 phosphoproteins using 4 mg of INS-1 cell lysate in 24 LC-MS/MS runs, of which 683 (27.7%) were considered novel phosphorylation sites that have not been characterized in human, mouse, or rat homologues. Our informatics data constitute a rich bioinformatics resource for investigating the function of reversible phosphorylation in pancreatic beta-cells. In particular, novel phosphorylation sites on proteins that mediate the pathology of type 2 diabetes, such as Pdx-1, Nkx.2, and Srebf1, will be valuable targets in ongoing phosphoproteomics studies.

Presenilin1/gamma-secretase promotes the EphB2-induced phosphorylation of ephrinB2 by regulating phosphoprotein associated with glycosphingolipid-enriched microdomains/Csk binding protein.

Reverse signaling through the ephrinB ligands is important for several morphogenetic events, such as axon guidance, neuronal plasticity, spine maturation, and synaptogenesis. Signaling is initiated by binding of EphB receptors to ephrinB ligands, stimulating their tyrosine phosphorylation via an unclear mechanism. Here we show that this mechanism involves presenilin1 (PS1)/γ-secretase regulation of phosphoprotein associated with glycosphingolipid-enriched microdomains/Csk binding protein (PAG/Cbp), an adaptor protein that controls the activity of Src kinases. Using immunoprecipitation and Western blot of mouse primary neuronal and human embryonic kidney (HEK293) cell extracts overexpressing PAG/Cbp, we show that EphB2 induces tyrosine dephosphorylation of PAG/Cbp in a γ-secretase-dependent manner. In these cells, PAG/Cbp dephosphorylation is promoted by the PS1/γ-secretase-produced fragment of ephrinB2 cleavage (ephrinB2/CTF2), which forms complexes with PAG/Cbp when introduced exogenously. EphB2-induced tyrosine phosphorylation of ephrinB2 depends on PAG/Cbp because EphB2 cannot increase ephrinB2 phosphorylation in cells treated with anti-PAG siRNA or in PAG/Cbp-knockout (KO) cells. Furthermore, in contrast to WT PS1, familial Alzheimer disease (FAD) PS1 mutants expressed in PS1-KO mouse embryonic fibroblasts inhibited both the EphB2-induced dephosphorylation of PAG/Cbp and the phosphorylation of ephrinB2. PS1 FAD mutations may thus inhibit the function of ephrinB in the brain, promoting neurodegeneration in Alzheimer disease.

ProteoConnections: A bioinformatics platform to facilitate proteome and phosphoproteome analyses

Novel and improved computational tools are required to transform large-scale proteomics data into valuable information of biological relevance. To this end, we developed ProteoConnections, a bioinformatics platform tailored to address the pressing needs of proteomics analyses. The primary focus of this platform is to organize peptide and protein identifications, evaluate the quality of the acquired data set, profile abundance changes, and accelerate data interpretation. Peptide and protein identifications are stored into a relational database to facilitate data mining and to evaluate the quality of data sets using graphical reports. We integrated databases of known PTMs and other bioinformatics tools to facilitate the analysis of phosphoproteomics data sets and to provide insights for subsequent biological validation experiments. Phosphorylation sites are also annotated according to kinase consensus motifs, contextual environment, protein domains, binding motifs, and evolutionary conservation across different species. The practical application of ProteoConnections is further demonstrated for the analysis of the phosphoproteomics data sets from rat intestinal IEC-6 cells where we identified 9615 phosphorylation sites on 2108 phosphoproteins. Combined proteomics and bioinformatics analyses revealed valuable biological insights on the regulation of phosphoprotein functions via the introduction of new binding sites on scaffold proteins or the modulation of protein-protein, protein-DNA, or protein-RNA interactions. Quantitative proteomics data can be integrated into ProteoConnections to determine the changes in protein phosphorylation under different cell stimulation conditions or kinase inhibitors, as demonstrated here for the MEK inhibitor PD184352.

Neural phosphoproteomics of a chronic hypoxia model—Lymnaea stagnalis

Chronic hypoxia is a common clinical event that induces adaptive responses and can result in behavioral deterioration. The reduction of metabolic rate during hypoxia may limit overall protein phosphorylation owing to the lack of high energy phosphate. However, the hypoxia-induced regulation of phosphoproteins is poorly understood. Here, we characterized the CNS phosphoproteome of Lymnaea stagnalis, a freshwater snail that has been used as a model to study chronic hypoxia-induced neural depression. After hypoxia treatment for 4 days, the motor behavior of the snail was suppressed. Electrophysiological measurements from Pedal A (PeA) interneurons showed that hypoxia increased the frequency of spontaneous postsynaptic excitatory potentials (sEPSPs), but reduced the firing frequency, the amplitude, and the half-width duration (APD50) of spontaneous action potentials. Imaging with a fluorescent phosphate label, Pro-Q Diamond, revealed that the neuronal phosphoprotein level was reduced after the hypoxia treatment. The hypoxia-induced changes in the phosphoproteome of the central ganglia were quantified using one-dimensional gel-electrophoresis by comparing the fluorescence intensity ratio of phospholabeled phosphoproteins versus total proteins between the hypoxia and control groups. We analyzed 16 protein bands: eight showed decreased phosphorylation levels after hypoxia treatment, and eight did not change. Using mass spectrometry analysis and protein database matching we found three phosphoproteins that may be associated with chronic hypoxia-induced neuronal adaptive response of the snail. This is the first proteomic screening for neural phosphoproteins in chronic hypoxia.

Novel Blockade of Protein Kinase A-Mediated Phosphorylation of AMPA Receptors

The phosphorylation state of the glutamate receptor subtype 1 (GluR1) subunit of the AMPA receptor (AMPAR) plays a critical role in synaptic expression of the receptor, channel properties, and synaptic plasticity. Several Gs-coupled receptors that couple to protein kinase A (PKA) readily recruit phosphorylation of GluR1 at S845. Conversely, activation of the ionotropic glutamate NMDA receptor (NMDAR) readily recruits dephosphorylation of the same GluR1 site through Ca2+-mediated recruitment of phosphatase activity. In a physiological setting, receptor activation often overlaps and crosstalk between coactivation of multiple signaling cascades can result in differential regulation of a given substrate. After investigating the effect of coactivation of the NMDAR and the Gs-coupled beta-adrenergic receptor on GluR1 phosphorylation state, we have observed a novel signal that prevents PKA-mediated phosphorylation of GluR1 at serine site 845. This blockade of GluR1 phosphorylation is dependent on cellular depolarization recruited by either NMDAR or AMPAR activation, independent of Ca2+ and independent of calcineurin, protein phosphatase 1, and/or protein phosphatase 2A activity. Thus, in addition to the typical kinase-phosphatase rivalry mediating protein phosphorylation state, we have identified a novel form of phospho-protein regulation that occurs at GluR1 and may also occur at several other PKA substrates.

Generation and application of phospho-specific antibodies for p53 and pRB.

The functions of many proteins are likely to be regulated by phosphorylation. Thus, antibodies that can recognize specifically phosphorylated sites on proteins have a wide variety of uses for studying the function and regulation of phosphoproteins. We have improved methods for generation of phosphorylation site-specific antibodies and have successfully obtained antibodies for the analysis of most of the phosphorylation sites on p53 and RB proteins.