Identification of two calcineurin B-binding proteins: tubulin and heat shock protein 60

Anti-secretogranin III therapy of oxygen-induced retinopathy with optimal safety

Retinopathy of prematurity (ROP) with pathological retinal neovascularization is the most common cause of blindness in children. ROP is currently treated with laser therapy or cryotherapy, both of which may adversely affect the peripheral vision with limited efficacy. Owing to the susceptibility of the developing retina and vasculatures to pharmacological intervention, there is currently no approved drug therapy for ROP in preterm infants. Secretogranin III (Scg3) was recently discovered as a highly disease-restricted angiogenic factor, and a Scg3-neutralizing monoclonal antibody (mAb) was reported with high efficacy to alleviate oxygen-induced retinopathy (OIR) in mice, a surrogate model of ROP. Herein we independently investigated the efficacy of anti-Scg3 mAb in OIR mice and characterized its safety in neonatal mice. We developed a new Scg3-neutralizing mAb recognizing a distinct epitope and independently established the therapeutic activity of anti-Scg3 therapy to alleviate OIR-induced pathological retinal neovascularization in mice. Importantly, anti-Scg3 mAb showed no detectable adverse effects on electroretinography and developing retinal vasculature. Furthermore, systemic anti-Scg3 mAb induced no renal tubular injury or abnormality in kidney vessel development and body weight gain of neonatal mice. In contrast, anti-vascular endothelial growth factor drug aflibercept showed significant side effects in neonatal mice. These results suggest that anti-Scg3 mAb may have the safety and efficacy profiles required for ROP therapy.

Genetically engineered drug rhCNB induces apoptosis and cell cycle arrest in both gastric cancer cells and hepatoma cells

Objectives

Calcineurin B (CNB) is a regulatory subunit of calcineurin, and it has antitumor activity. In this study, we aimed to investigate the effect of recombinant human calcineurin B (rhCNB) on the proliferation of gastric cancer cells and hepatoma cells both in vitro and in vivo.

Materials and methods

Cell viability and cell proliferation were detected by MTT and BrdU assay. Flow cytometry, Western blot and immunohistochemistry were performed to determine rhCNB-induced apoptosis and cell cycle arrest. The antitumor activities of rhCNB were observed in mice tumor models.

Results

We demonstrated that rhCNB inhibits the proliferation of gastric cancer cells and hepatoma cells both in vitro and in vivo. We showed that the inhibition of cell proliferation by rhCNB is associated with apoptosis and cell cycle arrest in both tumor cell lines. Furthermore, we indicated that rhCNB promotes p53 protein expression, a potent proapoptotic factor. Meanwhile, we also exhibited that rhCNB decreases the expression of both cyclin B1 and CDK1 proteins, two proteins associated with G₂/M arrest.

Conclusion

Together, these findings suggest that rhCNB markedly inhibits tumor growth and provides guidance for its drug development.

Understanding the Molecular Mechanisms Underpinning Gene by Environment Interactions in Psychiatric Disorders: The FKBP5 Model

Epidemiologic and genetic studies suggest common environmental and genetic risk factors for a number of psychiatric disorders, including depression, bipolar disorder, and schizophrenia. Genetic and environmental factors, especially adverse life events, not only have main effects on disease development but also may interact to shape risk and resilience. Such gene by adversity interactions have been described for FKBP5, an endogenous regulator of the stress-neuroendocrine system, conferring risk for a number of psychiatric disorders. In this review, we present a molecular and cellular model of the consequences of FKBP5 by early adversity interactions. We illustrate how altered genetic and epigenetic regulation of FKBP5 may contribute to disease risk by covering evidence from clinical and preclinical studies of FKBP5 dysregulation, known cell-type and tissue-type expression patterns of FKBP5 in humans and animals, and the role of FKBP5 as a stress-responsive molecular hub modulating many cellular pathways. FKBP5 presents the possibility to better understand the molecular and cellular factors contributing to a disease-relevant gene by environment interaction, with implications for the development of biomarkers and interventions for psychiatric disorders.

The genetically engineered drug rhCNB induces apoptosis via a mitochondrial route in tumor cells

The calcineurin B subunit (CNB) has antitumor activity. We showed previously that recombinant human CNB (rhCNB) also had strong anti-tumor activity in vivo, and was thus a promising candidate anti-tumor drug. It appeared to kill tumor cells via immunomodulation. Here, we show that rhCNB inhibits the proliferation of human hepatoma HepG-2 cells, resulting in their apoptosis. Exogenous CNB was found to localize to mitochondria in tumor cells and activate the mitochondrial apoptosis pathway, as indicated by a decrease of mitochondrial transmembrane potential, release of cytochrome C and activation of caspase-9, which then activates caspase-3. At the same time Bcl-2 &Bcl-xL expression decreased, Bim expression increased, and Bax was activated. Interaction between rhCNB and Bcl-xL was detected, which may inhibit the function of Bcl-xL. Long-term tumor targeting was also observed in nude mice. These data deepened our understanding of the anti-tumor mechanism of rhCNB and provided guidance for its drug development.

The protein serine/threonine phosphatases PP2A, PP1 and calcineurin: A triple threat in the regulation of the neuronal cytoskeleton

The microtubule, F-actin and neurofilament networks play a critical role in neuronal cell morphogenesis, polarity and synaptic plasticity. Significantly, the assembly/disassembly and stability of these cytoskeletal networks is crucially modulated by protein phosphorylation and dephosphorylation events. Herein, we aim to more closely examine the role played by three major neuronal Ser/Thr protein phosphatases, PP2A, PP1 and calcineurin, in the homeostasis of the neuronal cytoskeleton. There is strong evidence that these enzymes interact with and dephosphorylate a variety of cytoskeletal proteins, resulting in major regulation of neuronal cytoskeletal dynamics. Conversely, we also discuss how multi-protein cytoskeletal scaffolds can also influence the regulation of these phosphatases, with important implications for neuronal signalling and homeostasis. Not surprisingly, deregulation of these cytoskeletal scaffolds and phosphatase dysfunction are associated with many neurological diseases.

Cellular uptake of exogenous calcineurin B is dependent on TLR4/MD2/CD14 complexes, and CnB is an endogenous ligand of TLR4

Our previous research showed that recombinant calcineurin B (rhCnB) stimulates cytokine secretion by immune cells, probably through TLR4. Exogenous CnB can be incorporated into many different tumour cells in vitro, but the mode of uptake and receptors required remain unknown. Here, we report that exogenous CnB is taken up by cells in a time- and concentration-dependent manner via clathrin-dependent receptor-mediated internalization. Our findings further confirm that uptake is mediated by the TLR4/MD2 complex together with the co-receptor CD14. The MST results revealed a high affinity between CnB and the TLR4 receptor complex. No binding was detected between CnB and LPS. CnB inhibited the uptake of LPS, and LPS also inhibited the uptake of CnB. These results indicate that the uptake of exogenous CnB did not occur through LPS and that CnB was not a chaperone of LPS. Thus, we conclude that TLR4 receptor complexes were required for the recognition and internalization of exogenous CnB. CnB could be a potential endogenous ligand of TLR4 and function as an agonist of TLR4. These properties of CnB support its potential for development as an anti-cancer drug.

Hepatoma-derived growth factor-related protein-3 is a novel angiogenic factor

Hepatoma-derived growth factor-related protein-3 (Hdgfrp3 or HRP-3) was recently reported as a neurotrophic factor and is upregulated in hepatocellular carcinoma to promote cancer cell survival. Here we identified HRP-3 as a new endothelial ligand and characterized its in vitro and in vivo functional roles and molecular signaling. We combined open reading frame phage display with multi-round in vivo binding selection to enrich retinal endothelial ligands, which were systematically identified by next generation DNA sequencing. One of the identified endothelial ligands was HRP-3. HRP-3 expression in the retina and brain was characterized by Western blot and immunohistochemistry. Cell proliferation assay showed that HRP-3 stimulated the growth of human umbilical vein endothelial cells (HUVECs). HRP-3 induced tube formation of HUVECs in culture. Wound healing assay indicated that HRP-3 promoted endothelial cell migration. HRP-3 was further confirmed for its in vitro angiogenic activity by spheroid sprouting assay. HRP-3 extrinsically activated the extracellular-signal-regulated kinase ½ (ERK1/2) pathway in endothelial cells. The angiogenic activity of HRP-3 was independently verified by mouse cornea pocket assay. Furthermore, in vivo Matrigel plug assay corroborated HRP-3 activity to promote new blood vessel formation. These results demonstrated that HRP-3 is a novel angiogenic factor.

The synergistic interaction between the calcineurin B subunit and IFN-γ enhances macrophage antitumor activity

Macrophages are involved in tumor growth and progression. They infiltrate into tumors and cause inflammation, which creates a microenvironment favoring tumor growth and metastasis. However, certain stimuli may induce macrophages to act as tumor terminators. Here we report that the calcineurin B subunit (CnB) synergizes with IFN-γ to make macrophages highly cytotoxic to cancer cells. Furthermore, CnB and IFN-γ act synergistically to polarize mouse tumor-associated macrophages, as well as human monocyte-derived macrophages to an M1-like phenotype. This synergy is mediated by the crosstalk between CnB-engaged integrin αM-p38 MAPK signaling and IFN-γ-initiated p38/PKC-δ/Jak2 signaling. Interestingly, the signal transducer and activator of transcription 1 (STAT1) is a key factor that orchestrates the synergy of CnB and IFN-γ, and the phosphorylation status at Ser727 and Tyr701 of STAT1 is directly regulated by CnB and IFN-γ.

ABCF1 extrinsically regulates retinal pigment epithelial cell phagocytosis

Intracellular ABCF1 is identified and characterized as a new ligand to extrinsically stimulate retinal pigment epithelial cell phagocytosis. A new approach developed in this study is broadly applicable to many other phagocytes and will enable systematic elucidation of their ligands to broaden understanding of extrinsic regulation and cargo recognition.

Phagocytosis of shed photoreceptor outer segments (POSs) by retinal pigment epithelial (RPE) cells is critical to retinal homeostasis and shares many conserved signaling pathways with other phagocytes, including extrinsic regulations. Phagocytotic ligands are the key to cargo recognition, engulfment initiation, and activity regulation. In this study, we identified intracellular protein ATP-binding cassette subfamily F member 1 (ABCF1) as a novel RPE phagocytotic ligand by a new approach of functional screening. ABCF1 was independently verified to extrinsically promote phagocytosis of shed POSs by D407 RPE cells. This finding was further corroborated with primary RPE cells and RPE explants. Internalized POS vesicles were colocalized with a phagosome marker, suggesting that ABCF1-mediated engulfment is through a phagocytic pathway. ABCF1 was released from apoptotic cells and selectively bound to shed POS vesicles and apoptotic cells, possibly via externalized phosphatidylserine. ABCF1 is predominantly expressed in POSs and colocalized with the POS marker rhodopsin, providing geographical convenience for regulation of RPE phagocytosis. Collectively these results suggest that ABCF1 is released from and binds to shed POSs in an autocrine manner to facilitate RPE phagocytosis through a conserved pathway. Furthermore, the new approach is broadly applicable to many other phagocytes and will enable systematic elucidation of their ligands to understand extrinsic regulation and cargo recognition.

Lyar Is a New Ligand for Retinal Pigment Epithelial Phagocytosis

Phagocytosis is critical to tissue homeostasis, as highlighted by phagocytosis defect of retinal pigment epithelial (RPE) cells with debris accumulation, photoreceptor degeneration and blindness. Phagocytosis ligands are the key to delineating molecular mechanisms and functional roles of phagocytes, but are traditionally identified in individual cases with technical challenges. We recently developed open reading frame phage display (OPD) for phagocytosis-based functional cloning (PFC) to identify unknown ligands. One of the identified ligands was Ly-1 antibody reactive clone (Lyar) with functions poorly defined. Herein, we characterized Lyar as a new ligand to stimulate RPE phagocytosis. In contrast to its reported nucleolar expression, immunohistochemistry showed that Lyar was highly expressed in photoreceptor outer segments (POSs) of the retina. Cytoplasmic Lyar was released from apoptotic cells, and selectively bound to shed POSs and apoptotic cells, but not healthy cells. POS vesicles engulfed through Lyar-dependent pathway were targeted to phagosomes and colocalized with phagosome marker Rab7. These results suggest that Lyar is a genuine RPE phagocytosis ligand, which in turn supports the validity of OPD/PFC as the only available approach for unbiased identification of phagocytosis ligands with broad applicability to various phagocytes.

Identification and characterization of the cDNAs encoding the two subunits of Chinese mitten crab (Eriocheir sinensis) calcineurin: their implications in stress and immune response

Calcineurin (CN), the only Ca(2+)/calmodulin-activated serine/threonine protein phosphatase, is a key effector participating in Ca(2+)-dependent signal transduction pathways in a number of cellular processes under normal, stress and pathological conditions. However, the expression and the relevance of CN in stress and immune response have not been characterized in crustaceans. Here, we identified the cDNAs that encode the two subunits of CN (termed EsCN-A and EsCN-B, respectively) in Chinese mitten crab Eriocheir sinensis and analysed their expression patterns in response to stress and immune challenges. The catalytic subunit EsCN-A is comprised of 511 amino acids with a theoretical molecular mass of 57.5 kDa and shows 80% sequence identity with human beings CN-A alpha isoform, while the regulatory subunit EsCN-B protein is composed of 170 amino acids with an estimated molecular mass of 19.3 kDa and shares 88% sequence identity with human beings CN-B type 1. Tissue distribution analysis reveals that both EsCN-A and EsCN-B mRNA transcripts are expressed in all tested tissues with the greatest expression in hepatopancreas and the lowest expression in haemocytes. In addition, both EsCN-A and EsCN-B genes could be significantly up-regulated but with different expression patterns by ambient salinity (15‰ and 30‰ salinities) and pH (pH 6 and 8.5) stresses in gill, hepatopancreas, haemocytes, intestine and muscle. Furthermore, EsCN-A and EsCN-B were up-regulated by LPS and Poly(I:C) immune stimulations in E. sinensis haemocytes in vitro. Moreover, EsCN-A and EsCN-B mRNA were significantly up-regulated in haemocytes, gill, hepatopancreas, intestine and muscle in response to Edwardsiella tarda challenge in vivo. Finally, we revealed the importance of EsCN in LPS-induced nitric oxide production in E. sinensis haemocytes. Together our observations suggest that EsCN, the important downstream effector of CaM-mediated signalling pathway(s), may possess vital roles in stress and immune response in the Chinese mitten crab.

Infarct size reduction by cyclosporine A at reperfusion involves inhibition of the mitochondrial permeability transition pore but does not improve mitochondrial respiration

INTRODUCTION

Ischemic postconditioning (PoCo) and cyclosporine A (CysA) given prior to reperfusion reduce myocardial infarct size after ischemia/reperfusion. Ischemic postconditioning's protection is characterized by better preservation of mitochondrial respiration and calcium retention capacity. Protection by CysA is not entirely clear. Cyclosporine A inhibits not only mitochondrial permeability transition pore (mPTP) opening but also the phosphatase calcineurin. We have investigated whether CysA mediates protection not only by mPTP inhibition but also through a more upstream inhibition of calcineurin with subsequently better preserved mitochondrial respiration.

MATERIAL AND METHODS

Anesthetized pigs were subjected to 90 min ischemia and 10 min reperfusion initiated with either PoCo (6 × 20 s reperfusion/re-occlusion; n = 9), CysA infusion (5 mg/kg i.v.; 5 min before reperfusion; n = 4), or immediate full reperfusion (IFR; n = 8). Mitochondria were isolated from myocardial tissue for measurement of respiration and calcium retention capacity.

RESULTS

In mitochondria from ischemic/reperfused myocardium, ADP-stimulated complex I respiration was similar between CysA (116 ±11 nmol O2/min/mg protein) and IFR (117 ±8), but better preserved with PoCo (160 ±9; p < 0.05). Calcium retention capacity was greater with both PoCo and CysA (1096 ±45 and 1287 ±128 nmol Ca(2+)/mg protein) than with IFR (756 ±103; p < 0.05).

CONCLUSIONS

Cyclosporine A's protection is not associated with improved mitochondrial respiration. Protection is unlikely related to an upstream calcineurin inhibition, but is indeed secondary to mPTP inhibition.

Proteomic analysis for Type I interferon antagonism of Japanese encephalitis virus NS5 protein

Japanese encephalitis virus (JEV) nonstructural protein 5 (NS5) exhibits a Type I interferon (IFN) antagonistic function. This study characterizes Type I IFN antagonism mechanism of NS5 protein, using proteomic approach. In human neuroblastoma cells, NS5 expression would suppress IFNβ‐induced responses, for example, expression of IFN‐stimulated genes PKR and OAS as well as STAT1 nuclear translocation and phosphorylation. Proteomic analysis showed JEV NS5 downregulating calreticulin, while upregulating cyclophilin A, HSP 60 and stress‐induced‐phosphoprotein 1. Gene silence of calreticulin raised intracellular Ca²⁺ levels while inhibiting nuclear translocalization of STAT1 and NFAT‐1 in response to IFNβ, thus, indicating calreticulin downregulation linked with Type I IFN antagonism of JEV NS5 via activation of Ca²⁺/calicineurin. Calcineurin inhibitor cyclosporin A attenuated NS5‐mediated inhibition of IFNβ‐induced responses, for example, IFN‐sensitive response element driven luciferase, STAT1‐dependent PKR mRNA expression, as well as phosphorylation and nuclear translocation of STAT1. Transfection with calcineurin (vs. control) siRNA enhanced nuclear translocalization of STAT1 and upregulated PKR expression in NS5‐expressing cells in response to IFNβ. Results prove Ca²⁺, calreticulin, and calcineurin involvement in STAT1‐mediated signaling as well as a key role of JEV NS5 in Type I IFN antagonism. This study offers insights into the molecular mechanism of Type I interferon antagonism by JEV NS5.

Role of calcineurin and actin dynamics in regulated secretion of microneme proteins in Plasmodium falciparum merozoites during erythrocyte invasion

Plasmodium falciparum invades host erythrocytes by multiple invasion pathways. The invasion of erythrocytes by P. falciparum merozoites is a complex process that requires multiple interactions between host receptors and parasite ligands. A number of parasite proteins that mediate interaction with host receptors during invasion are localized to membrane-bound apical organelles referred to as micronemes and rhoptries. The timely release of these proteins to the merozoite surface is crucial for receptor engagement and invasion. It has been demonstrated previously that exposure of merozoites to a low potassium (K(+)) ionic environment as found in blood plasma leads to a rise in cytosolic calcium (Ca(2+)), which triggers microneme secretion. The signalling pathways that regulate microneme discharge in response to rise in cytosolic Ca(2+) are not completely understood. Here, we show that a P. falciparum Ca(2+)-dependent protein phosphatase, calcineurin (PfCN), is an essential regulator of Ca(2+)-dependent microneme exocytosis. An increase in PfCN activity was observed in merozoites following exposure to a low K(+) environment. Treatment of merozoites with calcineurin inhibitors such as FK506 and cyclosporin A prior to transfer to a low K(+) environment resulted in inhibition of secretion of microneme protein apical merozoite antigen-1 (PfAMA-1). Inhibition of PfCN was shown to result in reduced dephosphorylation and depolymerization of apical actin, which appears to be criticalfor microneme secretion. PfCN thus serves as an effector of Ca(2+)-dependent microneme exocytosis by regulating depolymerization of apical actin. Inhibitors that target PfCN block microneme exocytosis and limit growth of P. falciparum blood-stage parasites providing a novel approach towards development of new therapeutic strategies against malaria.

Calcium, calpain, and calcineurin in low-frequency depression of transmitter release

Low-frequency depression (LFD) of transmitter release occurs at phasic synapses with stimulation at 0.2 Hz in both isolated crayfish (Procambarus clarkii) neuromuscular junction (NMJ) preparations and in intact animals. LFD is regulated by presynaptic activity of the Ca(2+)-dependent phosphatase calcineurin (Silverman-Gavrila and Charlton, 2009). Since the fast Ca(2+) chelator BAPTA-AM inhibits LFD but the slow chelator EGTA-AM does not, the Ca(2+) sensor for LFD may be close to a Ca(2+) source at active zones. Calcineurin can be activated by the Ca(2+)-activated protease calpain, and immunostaining showed that both proteins are present at nerve terminals. Three calpain inhibitors, calpain inhibitor I, MDL-28170, and PD150606, but not the control compound PD145305, inhibit LFD both in the intact animal as shown by electromyograms and by intracellular recordings at neuromuscular junctions. Analysis of mini-EPSPs indicated that these inhibitors had minimal postsynaptic effects. Proteolytic activity in CNS extract, detected by a fluorescent calpain substrate, was modulated by Ca(2+) and calpain inhibitors. Western blot analysis of CNS extract showed that proteolysis of calcineurin to a fragment consistent with the constitutively active form required Ca(2+) and was blocked by calpain inhibitors. Inhibition of LFD by calpain inhibition blocks the reduction in phosphoactin and the depolymerization of tubulin that normally occurs in LFD, probably by blocking the dephosphorylation of cytoskeletal proteins by calcineurin. In contrast, high-frequency depression does not involve protein phosphorylation- or calpain-dependent mechanisms. LFD may involve a specific pathway in which local Ca(2+) signaling activates presynaptic calpain and calcineurin at active zones and causes changes of tubulin cytoskeleton.

Effect of high-load and high-volume resistance exercise on the tensiomyographic twitch response of biceps brachii

The purpose of the present study was to assess the ability of TMG in detecting mechanical fatigue induced by two different resistance exercises on biceps brachii: high-volume (HV), and high-load (HL). Sixteen healthy subjects (age 25.1±2.6years; body mass 79.9±8.9kg; height 179±7.4cm) performed arm-curl in two different protocols (HV: 8×15×10kg, HL: 5×3×30kg). Tensiomyography was used to assess muscle response to both exercise protocols. The contractile capacity of biceps brachii significantly varied by means of the effects of potentiation and fatigue mechanisms that take place at different exercise phases. The most significant changes correspond to values of maximum radial displacement of muscle belly (D(m)), sustained contraction time (T(s)), relaxation time (T(r)), and contraction velocity (V(c)). The behavior of these parameters is, in general, similar in both exercise protocols, but they show subtle differences among them. During the first set, in both protocols, values for V(c) increase, along with a decrease in T(r), T(s), and D(m) values. Fatigue onset was evident from changes in such parameters, with HL being the first in showing these mechanisms. Tensiomyography has been shown to be highly sensitive in detecting fatigue-induced changes.

Localization and activity of the calcineurin catalytic and regulatory subunit complex at the septum is essential for hyphal elongation and proper septation in Aspergillus fumigatus

Calcineurin, a heterodimer composed of the catalytic (CnaA) and regulatory (CnaB) subunits, plays key roles in growth, virulence and stress responses of fungi. To investigate the contribution of CnaA and CnaB to hyphal growth and septation, ΔcnaB and ΔcnaAΔcnaB strains of Aspergillus fumigatus were constructed. CnaA colocalizes to the contractile actin ring early during septation and remains at the centre of the mature septum. While CnaB's septal localization is CnaA-dependent, CnaA's septal localization is CnaB-independent, but CnaB is required for CnaA's function at the septum. Catalytic null mutations in CnaA caused stunted growth despite septal localization of the calcineurin complex, indicating the requirement of calcineurin activity at the septum. Compared to the ΔcnaA and ΔcnaB strains, the ΔcnaAΔcnaB strain displayed more defective growth and aberrant septation. While three Ca(2+) -binding motifs in CnaB were sufficient for its association with CnaA at the septum, the amino-terminal arginine-rich domains (16-RRRR-19 and 44-RLRKR-48) are dispensable for septal localization, yet required for complete functionality. Mutation of the 51-KLDK-54 motif in CnaB causes its mislocalization from the septum to the nucleus, suggesting it is a nuclear export signal sequence. These findings confirm a cooperative role for the calcineurin complex in regulating hyphal growth and septation.

Cardiomyocyte calcineurin signaling in subcellular domains: from the sarcolemma to the nucleus and beyond

The serine-threonine phosphatase calcineurin is activated in cardiac myocytes in the diseased heart and induces pathological hypertrophy. Calcineurin activity is mainly triggered by calcium/calmodulin binding but also through calpain mediated cleavage. How controlled calcineurin activation is possible in cardiac myocytes, which typically show a 10-fold difference in cytosolic calcium concentration with every heartbeat, has remained enigmatic. It is now emerging that calcineurin activation and signaling occur in subcellular microdomains, in which it is brought together with target proteins and exceedingly high concentrations of calcium in order to induce downstream signaling. We review current evidence of subcellular calcineurin mainly at the sarcolemma and the nucleus, but also in association with the sarcoplasmic reticulum and mitochondria. We also suggest that knowledge about subcellular signaling could help to develop inhibitors of calcineurin in specific microdomains to avoid side-effects that may arise from complete calcineurin inhibition.

CIB1 is a regulator of pathological cardiac hypertrophy

Hypertrophic heart disease is a leading health problem facing the Western world. Here we identified the small EF-hand domain-containing protein CIB1 (Ca²⁺ and integrin binding protein 1) in a screen for novel regulators of cardiomyocyte hypertrophy. Yeast two-hybrid screening for CIB1 interacting partners identified a related EF-hand domain-containing protein calcineurin B, the regulatory subunit of the pro-hypertrophic protein phosphatase calcineurin. CIB1 largely localizes to the sarcolemma in mouse and human myocardium, where it anchors calcineurin to control its activation in coordination with the L-type Ca²⁺ channel. CIB1 protein levels and membrane association were enhanced in cardiac pathological hypertrophy, but not in physiological hypertrophy. Consistent with these observations, mice lacking Cib1 show a dramatic reduction in myocardial hypertrophy, fibrosis, cardiac dysfunction, and calcineurin-NFAT activity following pressure overload, while the degree of physiologic hypertrophy after swimming was not altered. Transgenic mice with inducible and cardiac-specific overexpression of CIB1 showed enhanced cardiac hypertrophy in response to pressure overload or calcineurin signaling. Moreover, mice lacking the Ppp3cb gene showed no enhancement in cardiac hypertrophy associated with CIB1 overexpression. Thus, CIB1 functions as a novel regulator of cardiac hypertrophy through its ability to regulate calcineurin sarcolemmal association and activation.

Efficient identification of tubby-binding proteins by an improved system of T7 phage display

Mutation in the tubby gene causes adult-onset obesity, progressive retinal, and cochlear degeneration with unknown mechanism. In contrast, mutations in tubby-like protein 1 (Tulp1), whose C-terminus is highly homologous to tubby, only lead to retinal degeneration. We speculate that their diverse N-terminus may define their distinct disease profile. To elucidate the binding partners of tubby, we used tubby N-terminus (tubby-N) as bait to identify unknown binding proteins with open-reading-frame (ORF) phage display. T7 phage display was engineered with three improvements: high-quality ORF phage display cDNA library, specific phage elution by protease cleavage, and dual phage display for sensitive high throughput screening. The new system is capable of identifying unknown bait-binding proteins in as fast as approximately 4-7 days. While phage display with conventional cDNA libraries identifies high percentage of out-of-frame unnatural short peptides, all 28 tubby-N-binding clones identified by ORF phage display were ORFs. They encode 16 proteins, including 8 nuclear proteins. Fourteen proteins were analyzed by yeast two-hybrid assay and protein pull-down assay with ten of them independently verified. Comparative binding analyses revealed several proteins binding to both tubby and Tulp1 as well as one tubby-specific binding protein. These data suggest that tubby-N is capable of interacting with multiple nuclear and cytoplasmic protein binding partners. These results demonstrated that the newly-engineered ORF phage display is a powerful technology to identify unknown protein-protein interactions.

Calcineurin mediates the immune response of hemocytes through NF-kappaB signaling pathway in pearl oyster (Pinctada fucata)

Calcineurin (CN), a multifunctional protein, mediates the immune response through diverse signaling pathways in mammals, while the function of CN in the immune response of molluscan hemocytes still remains unclear. In the present study, we detected the distribution of CN in various tissues and the expression levels of Pf-CNA and Pf-CNB gene in hemocytes of Pinctada fucata. After the preparation of hemocyte monolayers, we checked the response of enzymatic activity of CN, the degradation level of IkappaBalpha, the activity of iNOS and the production of NO, and IL-2 to the challenge of lipopolysaccharide (LPS) and cyclosporin A (CsA). CN activity in hemocytes was very sensitive to both the stimulation of LPS and the inhibition of CsA. Most importantly, IkappaBalpha degradation in hemocytes was induced by LPS and attenuated by CsA. Consequently, the activity of iNOS was elevated and the production of NO was increased. Additionally, we found that the synthesis of IL-2 was increased by LPS but was apparently weakened by CsA. In vivo bacterial clearance experiments showed that CsA significantly decreased the ability of in vivo bacteria clearance in pearl oyster. All the results revealed, for the first time, that CN mediated the immune response of molluscan hemocytes via activating NF-kappaB signaling pathway.

Identification of tubby and tubby-like protein 1 as eat-me signals by phage display

Phagocytosis is an important process for the removal of apoptotic cells or cellular debris. Eat-me signals control the initiation of phagocytosis and hold the key for in-depth understanding of its molecular mechanisms. However, because of difficulties to identify unknown eat-me signals, only a limited number of them have been identified and characterized. Using a newly developed functional cloning strategy of open reading frame (ORF) phage display, we identified nine putative eat-me signals, including tubby-like protein 1 (Tulp1). This further led to the elucidation of tubby as the second eat-me signal in the same protein family. Both proteins stimulated phagocytosis of retinal pigment epithelium (RPE) cells and macrophages. Tubby-conjugated fluorescent microbeads facilitated RPE phagocytosis. Tubby and Tulp1, but not other family members, enhanced the uptake of membrane vesicles by RPE cells in synergy. Retinal membrane vesicles of Tubby mice and Tulp1(-/-) mice showed reduced activities for RPE phagocytosis, which were compensated by purified tubby and Tulp1, respectively. These data reveal a novel activity of tubby and Tulp1, and demonstrate that unbiased identification of eat-me signals by the broadly applicable strategy of ORF phage display can provide detailed insights into phagocyte biology.

Efficient identification of phosphatidylserine-binding proteins by ORF phage display

To efficiently elucidate the biological roles of phosphatidylserine (PS), we developed open-reading-frame (ORF) phage display to identify PS-binding proteins. The procedure of phage panning was optimized with a phage clone expressing MFG-E8, a well-known PS-binding protein. Three rounds of phage panning with ORF phage display cDNA library resulted in approximately 300-fold enrichment in PS-binding activity. A total of 17 PS-binding phage clones were identified. Unlike phage display with conventional cDNA libraries, all 17 PS-binding clones were ORFs encoding 13 real proteins. Sequence analysis revealed that all identified PS-specific phage clones had dimeric basic amino acid residues. GST fusion proteins were expressed for 3 PS-binding proteins and verified for their binding activity to PS liposomes, but not phosphatidylcholine liposomes. These results elucidated previously unknown PS-binding proteins and demonstrated that ORF phage display is a versatile technology capable of efficiently identifying binding proteins for non-protein molecules like PS.

Calcineurin and cytoskeleton in low-frequency depression

Transmitter release at high probability phasic synapses of crayfish neuromuscular junctions depresses by over 50% in 60 min when stimulated at 0.2 Hz. Inhibition of the protein phosphatase calcineurin by intracellular pre-synaptic injection of autoinhibitory peptide inhibited low-frequency depression (LFD) and resulted in facilitation of transmitter release. Since this inhibitor had no major effects when injected into the post-synaptic cell, only pre-synaptic calcineurin activity is necessary for LFD. To examine changes in phosphoproteins during LFD we performed a phosphoproteomic screen on proteins extracted from motor axons and nerve terminals after LFD induction or treatment with various drugs that affect kinase and phosphatase activity. Proteins separated by PAGE were stained with phospho-specific/total protein ratio stains (Pro-Q Diamond/SYPRO Ruby) to identify protein bands for analysis by mass spectrometry. Phosphorylation of actin and tubulin decreased during LFD, but increased when calcineurin was blocked. Tubulin and phosphoactin immunoreactivity in pre-synaptic terminals were also reduced after LFD. The actin depolymerizing drugs cytochalasin and latrunculin and the microtubule stabilizer taxol inhibited LFD. Therefore, dephosphorylation of pre-synaptic actin and tubulin and consequent changes in the cytoskeleton may regulate LFD. LFD is unlike long-term depression found in mammalian synapses because the latter requires in most instances post-synaptic calcineurin activity.Thus, this simpler invertebrate synapse discloses a novel pre-synaptic depression mechanism.

Overexpression of calcineurin B subunit (CnB) enhances the oncogenic potential of HEK293 cells

Calcineurin (CaN) is a Ca(2+)/calmodulin (CaM)-stimulated protein phosphatase. It is a heterodimeric enzyme consisting of a catalytic A subunit (CnA) and a Ca(2+)-binding regulatory B subunit (CnB). CaN's key role in vivo is well known, while the function of CnB keeps unclear except that it acts as a regulator of CaN. The present paper shows that CnB overexpression promotes proliferation of human embryonic kidney HEK293 cells by comparing with vector control cells in the complete or serum reduced medium. Furthermore, stable CnB transfectants showed dramatically improved growth in soft agar. And the migration ability of CnB overexpressors also was enhanced remarkably. But in the progress of transformation, the activity of CaN remained unchanged between CnB overexpressors and controls. Therefore, CnB, rather than CaN, is involved in the proliferation promotion of HEK293 cells. Subsequently, 11 proteins with different expression levels between CnB transfectants and controls were identified using two-dimensional gel electrophoresis and electrospray ionization time-of-fight mass spectrometry. Therein, the expression of heat shock protein 27 (HSP27) and protein DJ-1 increased along with CnB overexpression. The important role of CnB in cell neoplastic transformation was found and the possible mechanism was analyzed.

Studies of the anticancer effect of calcineurin B

Calcineurin (CN) is a Ca (2+)/calmodulin-stimulated protein phosphatase. It is a heterodimeric enzyme consisting of a catalytic subunit (CN A) and a Ca2+ -binding regulatory subunit (CN B), which plays an important role in the human immune system. Its regulatory subunit, CN B, on its own, was found to have a remarkable anticancer effect in mice. To clarify the basis of this action the in vivo and in vitro effect of CN B on several types of mice immunocytes was investigated. The phagocytic activity of peritoneal macrophages of both normal mice and mice bearing S 180 solid tumors increased when CN B was injected daily. In vitro examination using a modified MTT assay and an [3H] incorporation assay showed that the cytotoxicity of peritoneal macrophages was increased substantially. CN B also increased the natural killer activity of murine spleen lymphocytes in vivo and in vitro, and synergized with concanavalin A in stimulating their proliferation. Our results indicate that CN B has a significant stimulatory action on the immune system that may partially account for its anticancer activity.

Identification of tribbles homolog 2 as an autoantigen in autoimmune uveitis by phage display

Autoimmune uveitis is a group of ocular inflammatory disorders with unknown causes. As in other autoimmune diseases, identification of autoantigens from uveitis patients would markedly improve our understanding of the disease mechanism. Here, we report that a candidate autoantigen was identified by phage display in an unbiased fashion. A bacteriophage T7 display cDNA library was generated from human eye and characterized. Patient-specific phages were enriched by four rounds of phage display with purified patient IgG. Enriched phages demonstrated a 20-fold increase in binding specificity to the patient IgG compared with control IgG. Two clonal phages with particularly high relative binding specificities were isolated and characterized. The encoded genes, tribbles homolog 2 (TRB2) and an unknown protein, had 170- and 42-fold increases in their binding specificities to the patient IgG, respectively. The patient-specific immunoreactivities were further confirmed by Western blotting. Anti-TRB2 antibody activities were detected in several uveitis patients but not in control subjects, suggesting that TRB2 is a uveitis-associated candidate autoantigen. These results demonstrate that autoantigens can be identified by phage display using uveitis patient serum.

Selective prion protein binding to synaptic components is modulated by oxidative and nitrosative changes induced by copper(II) and peroxynitrite in cholinergic synaptosomes, unveiling a role for calcineurin B and thioredoxin

Choline acetyltransferase (ChAT) and choline transport are decreased after nitrosative stress. ChAT activity is altered in scrapie-infected neurons, where oxidative stress develops. Cellular prion protein (PrPc) may play a neuroprotective function in participating in the redox control of neuronal environment and regulation of copper metabolism, a role impaired when PrPc is transformed into PrPSc in prion pathologies. The complex cross-talk between PrPc and cholinergic neurons was analyzed in vitro using peroxynitrite and Cu2+ treatments on nerve endings isolated from Torpedo marmorata, a model of the motoneuron pre-synaptic element. Specific interactions between solubilized synaptic components and recombinant ovine prion protein (PrPrec) could be demonstrated by Biacore technology. Peroxynitrite abolished this interaction in a concentration-dependent way and induced significant alterations of neuronal targets. Interaction was restored by prior addition of peroxynitrite trapping agents. Cu2+ (in the form of CuSO4) treatment of synaptosomes triggered a milder oxidative effect leading to a bell-shaped increase of PrPrec binding to synaptosomal components, counteracted by the natural thiol agents, glutathione and thioredoxin. Copper(II)-induced modifications of thiols in several neuronal proteins. A positive correlation was observed between PrPrec binding and immunoreactive changes for calcineurin B and its partners, suggesting a synergy between calcineurin complex and PrP for copper regulation.

Physiological Ca2+ level and Ca2+-induced Permeability Transition Pore control protein phosphorylation in rat brain mitochondria

Phosphorylation of several low molecular mass proteins (3.5, 17, 23 and 29kDa) was observed in rat brain mitochondria (RBM) at ATP concentration close to that in the mitochondrial matrix. Furthermore, regulatory effects of Ca2+ on phosphorylation of these proteins were investigated. Protein phosphorylation was found to be modulated by Ca2+ in the physiological concentration range (10(-8) to 10(-6)M free Ca2+). Incorporation of 32P from [gamma-32P]ATP into the 17kDa protein was dramatically increased within the 10(-7) to 10(-6)M free Ca2+ range, whereas an opposite effect was observed for the 3.5kDa polypeptide. Strong de-phosphorylation of the 3.5kDa polypeptide and enhanced 32P-incorporation into the 17 and 23kDa proteins were found with supra-threshold Ca2+ loads and these effects were eliminated or reduced in the presence of cyclosporin A, an inhibitor of Permeability Transition Pore (PTP) opening. In the presence of calmidazolium (Cmz), a calmodulin antagonist, enhanced levels of phosphorylation of the 17 and 3.5kDa polypeptides were observed and the 17kDa protein phosphorylation was suppressed by H-8, a protein kinase A inhibitor. It is concluded that Ca2+ in physiological concentrations, as a second messenger, can control phosphorylation of the low molecular mass phospoproteins in RBM, in addition to well known regulation of some Krebs cycle dehydrogenases by Ca2+. The protein phosphorylation was strongly dependent on the Ca2+-induced PTP opening.