Immunosuppressive drugs prevent a rapid dephosphorylation of transcription factor NFAT1 in stimulated immune cells

NFATc2 Modulates Microglial Activation in the AβPP/PS1 Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) brains are characterized by fibrillar amyloid-β (Aβ) peptide containing plaques and associated reactive microglia. The proinflammatory phenotype of the microglia suggests that they may negatively affect disease course and contribute to behavioral decline. This hypothesis predicts that attenuating microglial activation may provide benefit against disease. Prior work from our laboratory and others has characterized a role for the transcription factor, nuclear factor of activated T cells (NFAT), in regulating microglial phenotype in response to different stimuli, including Aβ peptide. We observed that the NFATc2 isoform was the most highly expressed in murine microglia cultures, and inhibition or deletion of NFATc2 was sufficient to attenuate the ability of the microglia to secrete cytokines. In order to determine whether the NFATc2 isoform, in particular, was a valid immunomodulatory target in vivo, we crossed an NFATc2-/- line to a well-known AD mouse model, an AβPP/PS1 mouse line. As expected, the AβPP/PS1 x NFATc2-/- mice had attenuated cytokine levels compared to AβPP/PS1 mice as well as reduced microgliosis and astrogliosis with no effect on plaque load. Although some species differences in relative isoform expression may exist between murine and human microglia, it appears that microglial NFAT activity is a viable target for modulating the proinflammatory changes that occur during AD.

Systemic Immunomodulatory Strategies in High-risk Corneal Transplantation

The cornea is the most commonly transplanted tissue in the body. Although corneal grafts generally have high success rates, transplantation onto inflamed and vascularized host beds, or so-called high-risk corneal transplantation, has a high rate of graft rejection. The management of this high-risk corneal transplantation is challenging and involves numerous measures. One of the key measures to prevent graft rejection in these cases is the use of systemic immunosuppressive agents. In this article, we will review the systemic immunosuppressive agents most commonly used for high-risk corneal transplantation, which include corticosteroids, cysclosporine A, tacrolimus, mycophenolate mofetil, and rapamycin. Benefits, risks, and published data on the use of these medications for high-risk corneal transplantation will be detailed. We will also summarize novel immunoregulatory approaches that may be used to prevent graft rejection in high-risk corneal transplantation.

Management of high-risk corneal transplantation

The cornea is the most commonly transplanted tissue in medicine. The main cause of corneal graft failure is allograft rejection. The incidence of graft rejection depends on the presence of high-risk characteristics, most notably corneal neovascularization. Although corneal grafting has high success rates in the absence of these risk factors, high-risk keratoplasty is associated with low success rates because of a high incidence of immune-mediated graft rejection. To improve the survival of high-risk corneal transplantation, various preoperative, intraoperative, and postoperative measures can be considered; however, the key step in the management of these grafts is the long-term use of local and/or systemic immunosuppressive agents. Although a number of immunosuppressive agents have been used for this purpose, the results vary significantly across different studies. This is partly due to the lack of an optimized method for their use, as well as the lack of a precise stratification of the degree of risk in each individual patient. New targeted biologic treatments, as well as tolerance-inducing methods, show promising horizons in the management of high-risk corneal transplantation in near future.

Taurine Transport Into Fetal Cord Blood Cells: Inhibition by Cyclosporine A

OBJECTIVES

Pregnant women undergoing long-term organ transplant treatment have an increased incidence of delivering infants with intrauterine growth restriction (IUGR). Cyclosporine A is used as an immunosuppressant in such women and indirect evidence suggests that IUGR might result from an effect of cyclosporine A on amino acid transport by the placenta. In this study we tested the hypothesis that the transport of an essential amino acid, taurine, by fetal tissue other than the placenta is modulated by cyclosporine A.

METHODS

Cord blood cells (CBCs) were used to test this hypothesis as an easily obtainable fetal tissue. Transport of taurine into CBCs was measured using standard tracer flux assays.

RESULTS

Uptake of [(3)H] taurine by CBCs was linear over 15 minutes (76.2 +/- 16.6 fmol/10(6) cells/min, mean +/- SEM, n = 6) and inhibitable by 10 mM beta-alanine, a substrate of the system-beta taurine transport protein (6.7 +/- 1.0 fmol/10(6) cells/min, n = 6, P <.05, paired Student t test). Pre-incubation with cyclosporine A (5 microM) inhibited [(3)H] taurine uptake by 29.3%-5.3% (n = 8, P <.05, paired Student t test).

CONCLUSIONS

These data show that amino acid transport via system-beta can be measured in CBCs and may be a useful model for amino acid transport studies in fetal cells. We also show that system-beta was inhibited by the immunosuppressant, cyclosporine A. This suggests that the increased incidence of IUGR reported in mothers treated with cyclosporine A may be due partially to effects on taurine uptake into fetal cells outside the placenta.

NFAT1 transcription factor regulates cell cycle progression and cyclin E expression in B lymphocytes

The NFAT family of transcription factors has been primarily related to T cell development, activation, and differentiation. Further studies have shown that these ubiquitous proteins are observed in many cell types inside and outside the immune system, and are involved in several biological processes, including tumor growth, angiogenesis, and invasiveness. However, the specific role of the NFAT1 family member in naive B cell proliferation remains elusive. Here, we demonstrate that NFAT1 transcription factor controls Cyclin E expression, cell proliferation, and tumor growth in vivo. Specifically, we show that inducible expression of NFAT1 inhibits cell cycle progression, reduces colony formation, and controls tumor growth in nude mice. We also demonstrate that NFAT1-deficient naive B lymphocytes show a hyperproliferative phenotype and high levels of Cyclin E1 and E2 upon BCR stimulation when compared to wild-type B lymphocytes. NFAT1 transcription factor directly regulates Cyclin E expression in B cells, inhibiting the G1/S cell cycle phase transition. Bioinformatics analysis indicates that low levels of NFAT1 correlate with high expression of Cyclin E1 in different human cancers, including Diffuse Large B-cell Lymphomas (DLBCL). Together, our results demonstrate a repressor role for NFAT1 in cell cycle progression and Cyclin E expression in B lymphocytes, and suggest a potential function for NFAT1 protein in B cell malignancies.

Tanshinone IIA Prevents Leu27IGF-II-Induced Cardiomyocyte Hypertrophy Mediated by Estrogen Receptor and Subsequent Akt Activation

IGF-IIR plays important roles as a key regulator in myocardial pathological hypertrophy and apoptosis, which subsequently lead to heart failure. Salvia miltiorrhiza Bunge (Danshen) is a traditional Chinese medicinal herb used to treat cardiovascular diseases. Tanshinone IIA is an active compound in Danshen and is structurally similar to 17[Formula: see text]-estradiol (E[Formula: see text]. However, whether tanshinone IIA improves cardiomyocyte survival in pathological hypertrophy through estrogen receptor (ER) regulation remains unclear. This study investigates the role of ER signaling in mediating the protective effects of tanshinone IIA on IGF-IIR-induced myocardial hypertrophy. Leu27IGF-II (IGF-II analog) was shown in this study to specifically activate IGF-IIR expression and ICI 182,780 (ICI), an ER antagonist used to investigate tanshinone IIA estrogenic activity. We demonstrated that tanshinone IIA significantly enhanced Akt phosphorylation through ER activation to inhibit Leu27IGF-II-induced calcineurin expression and subsequent NFATc3 nuclear translocation to suppress myocardial hypertrophy. Tanshinone IIA reduced the cell size and suppressed ANP and BNP, inhibiting antihypertrophic effects induced by Leu27IGF-II. The cardioprotective properties of tanshinone IIA that inhibit Leu27IGF-II-induced cell hypertrophy and promote cell survival were reversed by ICI. Furthermore, ICI significantly reduced phospho-Akt, Ly294002 (PI3K inhibitor), and PI3K siRNA significantly reduced the tanshinone IIA-induced protective effect. The above results suggest that tanshinone IIA inhibited cardiomyocyte hypertrophy, which was mediated through ER, by activating the PI3K/Akt pathway and inhibiting Leu27IGF-II-induced calcineurin and NFATC3. Tanshinone IIA exerted strong estrogenic activity and therefore represented a novel selective ER modulator that inhibits IGF-IIR signaling to block cardiac hypertrophy.

Attenuation of microglial activation in a mouse model of Alzheimer's disease via NFAT inhibition

Background

Amyloid β (Aβ) peptide is hypothesized to stimulate microglia to acquire their characteristic proinflammatory phenotype in Alzheimer’s disease (AD) brains. The specific mechanisms by which Aβ leads to microglial activation remain an area of interest for identifying attractive molecular targets for intervention. Based upon the fact that microglia express the proinflammatory transcription factor, nuclear factor of activated T cells (NFAT), we hypothesized that NFAT activity is required for the Aβ-stimulated microgliosis that occurs during disease.

Methods

Primary murine microglia cultures were stimulated with Aβ in the absence or presence of NFAT inhibitors, FK506 and tat-VIVIT peptide, to quantify secretion of cytokines, neurotoxins, or Aβ phagocytosis. A transgenic mouse model of AD, APP/PS1, was treated subcutaneously via mini-osmotic pumps with FK506 or tat-VIVIT to quantify effects on cytokines, microgliosis, plaque load, and memory.

Results

Expression of various NFAT isoforms was verified in primary murine microglia through Western blot analysis. Microglial cultures were stimulated with Aβ fibrils in the absence or presence of the NFAT inhibitors, FK506 and tat-VIVIT, to demonstrate that NFAT activity regulated Aβ phagocytosis, neurotoxin secretion, and cytokine secretion. Delivery of FK506 and tat-VIVIT to transgenic APP/PS1 mice attenuated spleen but not brain cytokine levels. However, FK506 and tat-VIVIT significantly attenuated both microgliosis and Aβ plaque load in treated mice compared to controls. Surprisingly, this did not correlate with changes in memory performance via T-maze testing.

Conclusions

Our findings suggest that development of specific NFAT inhibitors may offer promise as an effective strategy for attenuating the microgliosis and Aβ plaque deposition that occur in AD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0255-2) contains supplementary material, which is available to authorized users.

Modulation of GABAA receptor signaling increases neurogenesis and suppresses anxiety through NFATc4

Correlative evidence suggests that GABAergic signaling plays an important role in the regulation of activity-dependent hippocampal neurogenesis and emotional behavior in adult mice. However, whether these are causally linked at the molecular level remains elusive. Nuclear factor of activated T cell (NFAT) proteins are activity-dependent transcription factors that respond to environmental stimuli in different cell types, including hippocampal newborn neurons. Here, we identify NFATc4 as a key activity-dependent transcriptional regulator of GABA signaling in hippocampal progenitor cells via an unbiased high-throughput genome-wide study. Next, we demonstrate that GABAA receptor (GABAAR) signaling modulates hippocampal neurogenesis through NFATc4 activity, which in turn regulates GABRA2 and GABRA4 subunit expression via binding to specific promoter responsive elements, as assessed by ChIP and luciferase assays. Furthermore, we show that selective pharmacological enhancement of GABAAR activity promotes hippocampal neurogenesis via the calcineurin/NFATc4 axis. Importantly, the NFATc4-dependent increase in hippocampal neurogenesis after GABAAR stimulation is required for the suppression of the anxiety response in mice. Together, these data provide a novel molecular insight into the regulation of the anxiety response in mice, suggesting that the GABAAR/NFATc4 axis is a druggable target for the therapy of emotional disorders.

Use of antioxidants to prevent cyclosporine a toxicity

Cyclosporine A (CsA) is a potent immunosuppressor that is widely used in transplant surgery and the treatment of several autoimmune diseases. However, major side effects of CsA such as nephrotoxicity, hepatotoxicity, neurotoxicity and cardiovascular diseases have substantially limited its usage. Although molecular mechanisms underlying these adverse effects are not clearly understood, there is some evidence that suggests involvement of reactive oxygen species (ROS) . In parallel, protective effects of various antioxidants have been demonstrated by many research groups. Extensive studies of CsA-induced nephrotoxcity have confirmed that the antioxidants can restore the damaged function and structure of kidney. Subsequently, there have appeared numerous reports to demonstrate the positive antioxidant effects on liver and other organ damages by CsA. It may be timely to review the ideas to envisage the relationship between ROS and the CsA-induced toxicity. This review is comprised of a brief description of the immunosuppressive action and the secondary effects of CsA, and a synopsis of reports regarding the antioxidant treatments against the ROS-linked CsA toxicity. A plethora of recent reports suggest that antioxidants can help reduce many CsA’s adverse effects and therefore might help develop more effective CsA treatment regimens.

The role of the NFAT signaling pathway in retinal neovascularization

PURPOSE

The purpose of the present study was to investigate the role of nuclear factor of activated T cells (NFAT), a transcription factor downstream of VEGF, in angiogenic cell behaviors of human retinal microvascular endothelial cells (HRMEC), and to assess the efficacy of NFAT signaling inhibitors in a rat model of oxygen-induced retinopathy (OIR).

METHODS

Human retinal microvascular endothelial cells were treated with VEGF in the presence or absence of the NFAT inhibitor of NFAT-calcineurin association-6 (INCA-6), and NFAT translocation was evaluated using immunocytochemistry (ICC). Human retinal microvascular endothelial cells were treated with increasing doses of INCA-6, and cell proliferation and tube formation were assessed. Rats subjected to OIR were administered increasing doses of INCA-6 or the CN inhibitor FK-506, and the retinal neovascular area was measured.

RESULTS

Nuclear factor of activated T-cells c1 was translocated to the nucleus of HRMEC treated with VEGF, and INCA-6 treatment blocked translocation. Inhibitor of NFAT-calcineurin association-6inhibited HRMEC proliferation and tube formation in a dose-dependent manner. Both INCA-6 and FK-506 treatment significantly reduced pathologic neovascularization in OIR.

CONCLUSIONS

This investigation has demonstrated that in HRMEC, NFATc1 is activated downstream of VEGF signaling and NFAT signaling plays a key role in angiogenic cell behaviors. In addition, NFAT inhibition is shown to be highly efficacious in an OIR model. These findings indicate that the NFAT signaling pathway may serve as a suitable therapeutic target for the treatment of neovascular eye disease.

Calcineurin-dependent ion channel regulation in heart

Calcineurin, a serine-threonine-specific, Ca(2+)-calmodulin-activated protein phosphatase, conserved from yeast to humans, plays a key role in regulating cardiac development, hypertrophy, and pathological remodeling. Recent studies demonstrate that calcineurin regulates cardiomyocyte ion channels and receptors in a manner which often entails direct interaction with these target proteins. Here, we review the current state of knowledge of calcineurin-mediated regulation of ion channels in the myocardium with emphasis on the transient outward potassium current (Ito) and L-type calcium current (ICa,L). We go on to discuss unanswered questions that surround these observations and provide perspective on future directions in this exciting field.

The role of the paracrine/autocrine mediator endothelin-1 in regulation of cardiac contractility and growth

Endothelin-1 (ET-1) is a critical autocrine and paracrine regulator of cardiac physiology and pathology. Produced locally within the myocardium in response to diverse mechanical and neurohormonal stimuli, ET-1 acutely modulates cardiac contractility. During pathological cardiovascular conditions such as ischaemia, left ventricular hypertrophy and heart failure, myocyte expression and activity of the entire ET-1 system is enhanced, allowing the peptide to both initiate and maintain maladaptive cellular responses. Both the acute and chronic effects of ET-1 are dependent on the activation of intracellular signalling pathways, regulated by the inositol-trisphosphate and diacylglycerol produced upon activation of the ET(A) receptor. Subsequent stimulation of protein kinases C and D, calmodulin-dependent kinase II, calcineurin and MAPKs modifies the systolic calcium transient, myofibril function and the activity of transcription factors that coordinate cellular remodelling. The precise nature of the cellular response to ET-1 is governed by the timing, localization and context of such signals, allowing the peptide to regulate both cardiomyocyte physiology and instigate disease.

LINKED ARTICLES

This article is part of a themed section on Endothelin. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.168.issue-1.

Depleting NFAT1 expression inhibits the ability of invasion and migration of human lung cancer cells

Background

Nuclear factor of activated T-cells (NFAT) is a general name applied to a family of transcription factors shown to be important in immune response. One or more members of the NFAT family are expressed in most cells of the immune system. NFAT1 is considered to involve in the development of cardiac, skeletal muscle, nervous systems, and tumorigenesis.

Methods

In the current study, we analyzed MEKK1 expression in 159 surgically resection non-small cell lung cancer patient’s samples by immunohistochemistry and determined its role in SK-EMS-1 cells via RNAi experiment.

Results

The abilities of invasion, motility, and adhesion of SK-EMS-1 cells were detected by transwell assay, wound healing assay and adhesion assay, respectively. The result showed NFAT1 was highly expressed in lung tumor tissues instead of adjacent lung tissues (54.1% vs 8.8%, p < 0.05); its overexpression was positively correlated with lymph node metastasis (p < 0.05). Depleting its expression in SK-EMS-1 cells can inhibit its invasion and migration abilities significantly (p < 0.05); and also can reduce proliferation of lung cancer cells (p < 0.05).

Conclusion

Our study showed NFAT1 plays an important role in origination, invasion and metastasis of non-small lung cancer cells; its underlying action mechanism needs further study.

Calcineurin inhibition and new-onset diabetes mellitus after transplantation

New-onset diabetes after transplantation independently increases the risk of cardiovascular disease, infections, and graft loss and decreases patient survival. The required balance between insulin sensitivity/resistance and insulin secretion is necessary to maintain normal glucose metabolism. Calcineurin inhibitors are standard immunosuppression drugs used after transplantation and have been implicated in the development of new-onset diabetes after transplantation partially by pancreatic β-cell apoptosis and resultant decrease in insulin secretion. The ability of muscle to take up glucose is critical to blood glucose homeostasis. Skeletal muscle is quantitatively the most important tissue in the body for insulin-stimulated glucose disposal and is composed of diverse myofibers that vary in their properties between healthy and insulin-resistant muscle. Various signaling pathways are responsible for remodeling of skeletal muscle, and among these is the calcineurin/nuclear factor of activated T-cell pathway. The mechanism of action of the calcineurin inhibitors is to bind in a complex with a binding protein to calcineurin and inhibit its dephosphorylation and activation of nuclear factor of activated T cells. In this review, we will provide a detailed discussion of the hypothesis that inhibition of calcineurin in tissues involved in insulin sensitivity/resistance could be at least partially responsible for the diabetogenicity seen with the use of calcineurin inhibitors.

2-photon imaging of phagocyte-mediated T cell activation in the CNS

Autoreactive T cells can infiltrate the CNS to cause disorders such as multiple sclerosis. In order to visualize T cell activation in the CNS, we introduced a truncated fluorescent derivative of nuclear factor of activated T cells (NFAT) as a real-time T cell activation indicator. In experimental autoimmune encephalomyelitis, a rat model of multiple sclerosis, we tracked T cells interacting with structures of the vascular blood-brain barrier (BBB). 2-photon imaging documented the cytoplasmic-nuclear translocation of fluorescent NFAT, indicative of calcium-dependent activation of the T cells in the perivascular space, but not within the vascular lumen. The activation was related to contacts with the local antigen-presenting phagocytes and was noted only in T cells with a high pathogenic potential. T cell activation implied the presentation of an autoantigen, as the weakly pathogenic T cells, which remained silent in the untreated hosts, were activated upon instillation of exogenous autoantigen. Activation did not cogently signal long-lasting arrest, as individual T cells were able to sequentially contact fresh APCs. We propose that the presentation of local autoantigen by BBB-associated APCs provides stimuli that guide autoimmune T cells to the CNS destination, enabling them to attack the target tissue.

Pharmacologic prophylaxis regimens for acute graft-versus-host disease: past, present and future

Abstract Acute graft-versus-host disease (GVHD) has compromised and continues to compromise the benefits associated with allogeneic hematopoietic cell transplant to cure malignant and non-malignant diseases. Pharmacologic interventions to prevent GVHD have emerged as a major objective of research in the immunology and transplant fields. A better understanding of the pathobiology behind the GVHD process has led the way to novel approaches and medications. Here we review the present arsenal of medications used to prevent GVHD, focusing on past experience and the current evidence, and discuss future potential targets.

African swine fever virus controls the host transcription and cellular machinery of protein synthesis

Throughout a viral infection, the infected cell reprograms the gene expression pattern in order to establish a satisfactory antiviral response. African swine fever virus (ASFV), like other complex DNA viruses, sets up a number of strategies to evade the host's defense systems, such as apoptosis, inflammation and immune responses. The capability of the virus to persist in its natural hosts and in domestic pigs, which recover from infection with less virulent isolates, suggests that the virus displays effective mechanisms to escape host defense systems. ASFV has been described to regulate the activation of several transcription factors, thus regulating the activation of specific target genes during ASFV infection. Whereas some reports have concerned about anti-apoptotic ASFV genes and the molecular mechanisms by which ASFV interferes with inducible gene transcription and immune evasion, less is yet known regarding how ASFV regulates the translational machinery in infected cells, although a recent report has shown a mechanism for favored expression of viral genes based on compartmentalization of viral mRNA and ribosomes with cellular translation factors within the virus factory. The viral mechanisms involved both in the regulation of host genes transcription and in the control of cellular protein synthesis are summarized in this review.

Cyclosporine A and PSC833 inhibit ABCA1 function via direct binding

ATP-binding cassette protein A1 (ABCA1) plays a key role in generating high-density lipoprotein (HDL). However, the detailed mechanism of HDL formation remains unclear; in order to reveal it, chemicals that specifically block each step of HDL formation would be useful. Cyclosporine A inhibits ABCA1-mediated cholesterol efflux, but it is not clear whether this is mediated via inhibition of calcineurin. We analyzed the effects of cyclosporine A and related compounds on ABCA1 function in BHK/ABCA1 cells. Cyclosporine A, FK506, and pimecrolimus inhibited ABCA1-mediated cholesterol efflux in a concentration-dependent manner, with IC(50) of 7.6, 13.6, and 7.0μM, respectively. An mTOR inhibitor, rapamycin also inhibited ABCA1, with IC(50) of 18.8μM. The primary targets for these drugs were inhibited at much lower concentrations in BHK/ABCA1 cells, suggesting that they were not involved. Binding of [(3)H] cyclosporine A to purified ABCA1 could be clearly detected. Furthermore, a non-immunosuppressive cyclosporine, PSC833, inhibited ABCA1-mediated cholesterol efflux with IC(50) of 1.9μM, and efficiently competed with [(3)H] cyclosporine A binding to ABCA1. These results indicate that cyclosporine A and PSC833 inhibit ABCA1 via direct binding, and that the ABCA1 inhibitor PSC833 is an excellent candidate for further investigations of the detailed mechanisms underlying formation of HDL.

Transcriptomics analysis of primary mouse thymocytes exposed to bis(tri-n-butyltin)dioxide (TBTO)

The biocide bis(tri-n-butyltin)oxide (TBTO) causes thymus atrophy in rodents and is toxic to many cell types of which thymocytes are the most sensitive. To obtain insight in the mechanisms of action of TBTO, we exposed primary mouse thymocytes in vitro for 3, 6 and 11 h to 0.1, 0.5, 1 and 2 μM TBTO. Subsequently, the cells were subjected to whole-genome gene expression profiling. Biological interpretation of the gene expression data revealed that TBTO affects a wide range of processes. Cell proliferation related genes were downregulated by all treatments except for 3 and 6 h 0.5 μM TBTO which upregulated these genes. Treatment with TBTO resulted in upregulation of genes involved in endoplasmatic reticulum (ER) stress, NFkB and TNFα pathways, and genes involved in DNA damage, p53 signaling and apoptosis. Remarkably, TBTO also increased the expression of genes that are known to be upregulated during T cell activation or during negative selection of thymocytes. The effect of TBTO on expression of genes involved in ER stress and apoptosis was confirmed by qPCR. Induction of the T cell activation response was corroborated by demonstrating that TBTO exposure resulted in translocation of NFAT to the nucleus, which is an essential event for T cell activation.

Molecular Diagnostics of Calcineurin-Related Pathologies

BACKGROUND

The Ca2+-dependent protein phosphatase enzyme calcineurin (Cn) (protein phosphatase 3) is best known for its role as director of the adaptive immune response. One of its principal substrates is the nuclear factor of activated T cells (NFAT), which translocates to the nucleus after dephosphorylation to mediate gene transcription. Drugs targeting Cn (the Cn inhibitors tacrolimus and cyclosporin A) have revolutionized posttransplantation therapy in allograft recipients by considerably reducing rejection rates.

CONTENT

Owing primarily to intensive study of the side effects of the Cn inhibitors, the unique importance of Cn and Cn/NFAT signaling in the normal physiological processes of many other cell and tissue types is becoming more evident. During the last decade, it has become clear that an extensive and diverse array of clinical conditions can be traced back, at least in part, to a disturbed Cn-signaling axis. Hence, both diagnostics and therapeutic monitoring could benefit from a technique that conveniently reads out Cn/NFAT operative status.

SUMMARY

This review outlines the current knowledge on the pathologic conditions that have calcineurin as a common denominator and reports on the progress that has been made toward successfully applying Cn and Cn/NFAT activity markers in molecular diagnostics.

Regulation of fas/fas ligand-mediated apoptosis by nuclear factor of activated T cells in megakaryocytes

Signal transduction pathways in megakaryocytes, a rare population of bone marrow cells, are poorly understood. We have previously shown that the calcineurin-dependent transcription factor Nuclear Factor of Activated T cells (NFAT) is expressed in megakaryocytes and is required for the transcription of specific megakaryocytic genes. The biological role of NFAT in megakaryocytes, however, is unknown. Here we show that activation of the calcineurin/NFAT pathway in megakaryocytes forces the cells to go into apoptosis. Calcineurin/NFAT activation in megakaryocytes leads to membrane expression of Fas ligand (FASLG), a pro-apoptotic member of the tumour necrosis factor superfamily. Expression of FASLG was augmented in cells stably overexpressing NFATC2 and suppressed in cells either pretreated with the calcineurin inhibitor ciclosporin A (CsA) or expressing the specific peptide inhibitor of NFAT, VIVIT. In cocultures with Fas-expressing Jurkat T cells, the presence of activated megakaryocytic cells, but not of unstimulated cells or cells stimulated in the presence of CsA, significantly induced apoptosis in Jurkat cells in a Fas/FASLG- and NFAT-dependent manner. These results represent the first evidence for a biological function of the calcineurin/NFAT pathway in megakaryocytes, and suggest that the biological role of megakaryocytes may include the induction of apoptosis in bystander cells.

Ocular safety and pharmacokinetics study of FK506 suspension eye drops after corneal transplantation

PURPOSE

The aim of this study was to investigate the sensitization, pharmacokinetics, and absorption of FK506 after corneal transplantation.

METHODS

New Zealand albino rabbits were divided into normal and corneal transplantation groups. Each group was divided into 5 subgroups--saline, blank matrix, high-dose, medium-dose, and low-dose, respectively. There were 10 rabbits in each subgroup. One drop (25 μL) of FK506 was administered topically to both eyes of the rabbits 4 times daily for 30 days. Thirty days later, 5 rabbits of each subgroup were sacrificed after the administration of the last dose. Both eyes were enucleated; the left eye was used for pathologic examination and the right eye for the determination of FK506 distribution. The other 5 rabbits in each subgroup were sacrificed 14 days after the former 5 rabbits were sacrificed, and their eyes were enucleated for pathologic examination and tissue distribution determination as the former 5 rabbits in each subgroup (the second batch).

RESULTS

Fluorescein staining and local ocular reaction provided evidence that there were no significant differences between control and FK506-instilled eyes in the rabbit model at any of the tested doses. Histologic examination revealed no ocular abnormality in the rabbits instilled with any doses of FK506 eyedrop. The peak serum concentration (C(max)) of systemic absorption ranged from 4.31±0.79 ng/mL to 14.89±6.85 ng/mL.

CONCLUSION

Our study suggests that up to 0.1% FK506 administered 4 times a day (q.i.d.) topically is safe for the rabbit eye. However, further safety studies are required in view of systemic adverse effects.

The kinase LRRK2 is a regulator of the transcription factor NFAT that modulates the severity of inflammatory bowel disease

Leucine-rich repeat kinase 2 (LRRK2) has been identified by genome-wide association studies as being encoded by a major susceptibility gene for Crohn's disease. Here we found that LRRK2 deficiency conferred enhanced susceptibility to experimental colitis in mice. Mechanistic studies showed that LRRK2 was a potent negative regulator of the transcription factor NFAT and was a component of a complex that included the large noncoding RNA NRON (an NFAT repressor). Furthermore, the risk-associated allele encoding LRRK2 Met2397 identified by a genome-wide association study for Crohn's disease resulted in less LRRK2 protein post-translationally. Severe colitis in LRRK2-deficient mice was associated with enhanced nuclear localization of NFAT1. Thus, our study defines a new step in the control of NFAT activation that involves an immunoregulatory function of LRRK2 and has important implications for inflammatory bowel disease.

Selective activation of the transcription factor NFAT1 by calcium microdomains near Ca2+ release-activated Ca2+ (CRAC) channels

NFATs are a family of Ca(2+)-dependent transcription factors that play a central role in the morphogenesis, development, and physiological activities of numerous distinct cell types and organ systems. Here, we visualize NFAT1 movement in and out of the nucleus in response to transient activation of store-operated Ca(2+) release-activated Ca(2+) (CRAC) channels in nonexcitable cells. We show that NFAT migration is exquisitely sensitive to Ca(2+) microdomains near open CRAC channels. Another Ca(2+)-permeable ion channel (TRPC3) was ineffective in driving NFAT1 to the nucleus. NFAT1 movement is temporally dissociated from the time course of the Ca(2+) signal and remains within the nucleus for 10 times longer than the duration of the trigger Ca(2+) signal. Kinetic analyses of each step linking CRAC channel activation to NFAT1 nuclear residency reveals that the rate-limiting step is transcription factor exit from the nucleus. The slow deactivation of NFAT provides a mechanism whereby Ca(2+)-dependent responses can be sustained despite the termination of the initial Ca(2+) signal and helps explain how gene expression in nonexcitable cells can continue after the primary stimulus has been removed.

Nuclear factor of activated T cells negatively regulates expression of the tumor necrosis factor receptor-related 2 gene in T cells

Tumor necrosis factor receptor-related 2 (TR2, HVEM or TNFRSF-14) plays an important role in immune responses, however, the mechanisms regulating its expression are unclear. To understand the control of TR2 gene expression, we studied the upstream region of the gene. Gel supershift assays revealed inducible binding of nuclear factor of activated T cells (NFAT) to a putative NFAT site within the TR2 promoter. Furthermore, cotransfection of a dominant negative NFAT construct, or siRNA for NFAT, resulted in increased expression of a TR2 reporter gene. Our findings demonstrate that NFAT negatively regulates TR2 expression in activated T cells.

Transcriptional Regulation of TMP21 by NFAT

BACKGROUND

TMP21 is a member of the p24 cargo protein family, which is involved in protein transport between the Golgi apparatus and ER. Alzheimer's Disease (AD) is the most common neurodegenerative disorder leading to dementia and deposition of amyloid β protein (Aβ) is the pathological feature of AD pathogenesis. Knockdown of TMP21 expression by siRNA causes a sharp increase in Aβ production; however the underlying mechanism by which TMP21 regulates Aβ generation is unknown, and human TMP21 gene expression regulation has not yet been studied.

RESULTS

In this report we have cloned a 3.3-kb fragment upstream of the human TMP21 gene. The transcription start site (TSS) of the human TMP21 gene was identified. A series of nested deletions of the 5' flanking region of the human TMP21 gene were subcloned into the pGL3-basic luciferase reporter plasmid. We identified the -120 to +2 region as containing the minimal sequence necessary for TMP21 gene promoter activity. Gel shift assays revealed that the human TMP21 gene promoter contains NFAT response elements. Expression of NFAT increased TMP21 gene expression and inhibition of NFAT by siRNA reduced TMP21 gene expression.

CONCLUSION

NFAT plays a very important role in the regulation of human TMP21 gene expression. This study demonstrates that the human TMP21 gene expression is transcriptionally regulated by NFAT signaling.

Interaction of calcineurin with substrates and targeting proteins

Calcineurin is a calcium activated protein phosphatase with a major role in calcium signaling in diverse cells and organs and clinical importance as the target of the immunosuppressive drugs cyclosporin A and tacrolimus (FK506). Cell biology studies have focused mainly on the role of calcineurin in transcriptional signaling. Calcium entry in response to extracellular stimuli results in calcineurin activation, and signal transmission from the cytosol into the nucleus through dephosphorylation and nuclear translocation of the transcription factor nuclear factor of activated T cells (NFAT). This initiates a cascade of transcriptional events involved in physiological and developmental processes. Molecular analyses of the calcineurin-NFAT interaction have been extended recently to encompass the interaction of calcineurin with other substrates, targeting proteins and regulators of calcineurin activity. These studies have increased our understanding of how this essential calcium activated enzyme orchestrates intracellular events in cooperation with other signaling pathways, and have suggested a link between altered calcineurin signaling and the developmental anomalies of Down syndrome.

Minocycline suppresses activation of nuclear factor of activated T cells 1 (NFAT1) in human CD4+ T cells

Minocycline is a tetracycline family antibiotic that has anti-inflammatory and immunomodulatory properties. These properties have shown promise in the treatment of conditions such as rheumatoid arthritis, Huntington disease, and multiple sclerosis. As lymphocyte activation is involved in the pathogenesis of many of these diseases, T cells are postulated to be a primary target in minocycline therapy. Previous studies have demonstrated attenuation of CD4(+) T cell activation by minocycline, but a specific mechanism has not been elucidated. In this study, we investigated the effect of minocycline on the activity of three key transcription factors regulating CD4(+) T cell activation: NF-κB, AP-1 (activator protein 1), and NFAT (nuclear factor of activated T) cells. Our data demonstrate that minocycline selectively impairs NFAT-mediated transcriptional activation, a result of increased phosphorylation and reduced nuclear translocation of the isoform NFAT1. Minocycline increased the activity of the NFAT kinase GSK3 and decreased intracellular Ca(2+) flux, both of which facilitate NFAT1 phosphorylation. These findings provide a novel mechanism for minocycline induced suppression of CD4(+) T cell activation and may better inform the application of minocycline as an immunomodulatory agent.

Tacrolimus is an alternative therapeutic option for the treatment of refractory lupus nephritis

We conducted an open-labeled, prospective study to determine the efficacy and safety of tacrolimus as an alternative therapeutic option for those patients with refractory lupus nephritis. The study population comprised one male and eight female patients with diffuse proliferative lupus nephritis. All patients had failed to respond to sufficient intravenous cyclophosphamide therapy with proteinuria of >or=1 g/day and active urinary sediments. Tacrolimus (0.1 mg/kg/day) was administered for 1 year with adjusting drug level (4-10 microg/l). The mean serum creatinine level and spot urine protein creatinine ratio (UPCR) at baseline were 1.39 mg/dl and 2.27, respectively. After the treatment, proteinuria reduced significantly from median UPCR value of 2.19 (range, 1.19-3.34) to 0.44 (range, 0.12-2.13) (p < 0.05). Seven (78%) of the nine patients showed a complete clinical response, which was defined as stabilization in the disease-activity markers and serum creatinine level with reduction of >or=50% in UPCR; two patients showed complete remission with UPCR <0.2. One patient showed treatment failure because of the disease progression. No serious adverse effects were observed during the study. This study demonstrates that tacrolimus can show a significant therapeutic response in cases that are refractory to the standard regimen for diffuse proliferative lupus nephritis.

NFAT and CREB regulate Kaposi's sarcoma-associated herpesvirus-induced cyclooxygenase 2 (COX-2)

COX-2 has been implicated in Kaposi's sarcoma-associated herpesvirus (KSHV) latency and pathogenesis (A. George Paul, N. Sharma-Walia, N. Kerur, C. White, and B. Chandran, Cancer Res. 70:3697-3708, 2010; P. P. Naranatt, H. H. Krishnan, S. R. Svojanovsky, C. Bloomer, S. Mathur, and B. Chandran, Cancer Res. 64:72-84, 2004; N. Sharma-Walia, A. G. Paul, V. Bottero, S. Sadagopan, M. V. Veettil, N. Kerur, and B. Chandran, PLoS Pathog. 6:e1000777, 2010; N. Sharma-Walia, H. Raghu, S. Sadagopan, R. Sivakumar, M. V. Veettil, P. P. Naranatt, M. M. Smith, and B. Chandran, J. Virol. 80:6534-6552, 2006). However, the precise regulatory mechanisms involved in COX-2 induction during KSHV infection have never been explored. Here, we identified cis-acting elements involved in the transcriptional regulation of COX-2 upon KSHV de novo infection. Promoter analysis using human COX-2 promoter deletion and mutation reporter constructs revealed that nuclear factor of activated T cells (NFAT) and the cyclic AMP (cAMP) response element (CRE) modulate KSHV-mediated transcriptional regulation of COX-2. Along with multiple KSHV-induced signaling pathways, infection-induced prostaglandin E(2) (PGE(2)) also augmented COX-2 transcription. Infection of endothelial cells markedly induced COX-2 expression via a cyclosporine A-sensitive, calcineurin/NFAT-dependent pathway. KSHV infection increased intracellular cAMP levels and activated protein kinase A (PKA), which phosphorylated the CRE-binding protein (CREB) at serine 133, which probably led to interaction with CRE in the COX-2 promoter, thereby enhancing COX-2 transcription. PKA selective inhibitor H-89 pretreatment strongly inhibited CREB serine 133, indicating the involvement of a cAMP-PKA-CREB-CRE loop in COX-2 transcriptional regulation. In contrast to phosphatidylinositol 3-kinase and protein kinase C, inhibition of FAK and Src effectively reduced KSHV infection-induced COX-2 transcription and protein levels. Collectively, our study indicates that mediation of COX-2 transcription upon KSHV infection is a paradigm of a complex regulatory milieu involving the interplay of multiple signal cascades and transcription factors. Intervention at each step of COX-2/PGE(2) induction can be used as a potential therapeutic target to treat KSHV-associated neoplasm and control inflammatory sequels of KSHV infection.

Primers on molecular pathways--the NFAT transcription pathway in pancreatic cancer

The calcineurin-responsive nuclear factor of activated T cells (NFAT) family of transcription factors was originally identified as a group of inducible nuclear proteins, which regulate transcription during T lymphocyte activation. However, following their initial discovery, a multitude of studies quickly established that NFAT proteins are also expressed in cells outside the immune system, where they participate in the regulation of the expression of genes influencing cell growth and differentiation. Ectopic activation of individual NFAT members is now recognized as an important aspect for oncogenic transformation in several human malignancies, most notably in pancreatic cancer. Sustained activation of the Ca(2+)/calcineurin/NFAT signaling pathway has emerged as a powerful regulatory principle governing pancreatic cancer cell growth. Activated NFAT proteins form complexes with key oncogenic proteins to regulate the transcription of master cell cycle regulators and proteins with functions in cell survival, migration and angiogenesis. This review pays particular attention to recent advances in our understanding of how the NFAT transcription pathway controls gene expression during development and progression of pancreatic cancer. and IAP.

Microglial phenotype is regulated by activity of the transcription factor, NFAT (nuclear factor of activated T cells)

The transcription factor family, nuclear factor of activated T cells (NFAT), regulates immune cell phenotype. Four different calcium/calmodulin-regulated isoforms have been identified in the periphery, but isoform expression in microglia, the resident immune cells of the CNS, has not been fully defined. In this study microglial NFAT isoform expression and involvement in regulating inflammatory responses in murine primary microglia culture was examined. Western blot analysis demonstrated robust detection of NFATc1 and c2 isoforms in microglia. Electrophoretic mobility shift assays demonstrated increased NFAT-DNA binding from nuclear extracts of lipopolysaccharide (LPS) stimulated microglia. Moreover, LPS-stimulated microglia behaved similarly to T cell receptor agonist antibody-stimulated Jurkat cells demonstrating a transient increase in NFAT-driven luciferase reporter gene expression. LPS-induced NFAT-luciferase activity in microglia was attenuated by pretreatment with tat-VIVIT, a cell-permeable NFAT inhibitory peptide. Furthermore, LPS-mediated secretion of microglial cytokines, TNF-alpha and MCP-1, was decreased by treatment with tat-VIVIT but not with tat-VEET, a negative control peptide. These results demonstrate that NFAT plays a role in regulating proinflammatory responses in cultured murine microglia.

Tacrolimus in hematopoietic stem cell transplantation

BACKGROUND

Graft-versus-host disease (GVHD) associated with allogeneic peripheral blood or marrow transplantation is a serious life-threatening complication. Most of the available literature support the use of tacrolimus as a prophylactic agent for acute GVHD.

OBJECTIVE

To review the pharmacology, efficacy and safety of tacrolimus and recommend its place in therapy for the prophylaxis of GVHD.

METHODS

We conducted a literature search using PubMed/Medline (January 1996 - December 2008) using the keywords tacrolimus, graft-versus-host disease and hematopoietic stem cell transplantation. Data provided by the manufacturer and the FDA were also reviewed.

CONCLUSION

Tacrolimus is effective in the prevention of acute GVHD. Trials comparing tacrolimus with cyclosporine using tacrolimus levels in the 7 - 10 ng/ml range and with larger numbers of patients may be necessary to better understand the impact of these drugs on survival.

Transcriptional activation of hTERT, the human telomerase reverse transcriptase, by nuclear factor of activated T cells

Telomerase is essential for telomere maintenance, and its activation is thought to be a critical step in cellular immortalization and tumorigenesis. Human telomerase reverse transcriptase (hTERT) is a major component of telomerase activity. We show here that hTERT is expressed soon after lymphocyte activation and that its expression is inhibited by rapamycin, wortmannin, and FK506, which was the most potent inhibitor. These results suggest a potential role for the transcription factor nuclear factor of activated T cells (NFAT) in the regulation of hTERT expression. Five putative NFAT-binding sites were identified in the hTERT promoter. In luciferase assays, the hTERT promoter was activated by overexpressed NFAT1. Moreover, serial deletions revealed that the promoter activation was mainly due to a -40 NFAT1-binding site flanked by two SP1-binding sites. Mutation of the -40 NFAT-binding site caused a 53% reduction in the transcriptional activity of hTERT promoter. Simultaneous mutations of the -40 NFAT-responsive element together with one or both SP1-binding sites led to a more dramatic decrease in luciferase activity than single mutations, suggesting a functional synergy between NFAT1 and SP1 in hTERT transcriptional regulation. NFAT1 overexpression in MCF7 and Jurkat cell lines induced an increase in endogenous hTERT mRNA expression. Inversely, its down-regulation was induced by NFAT1 silencing. Furthermore, chromatin immunoprecipitation assay demonstrated that NFAT1 directly binds to two sites (-40 and -775) in the endogenous hTERT promoter. Thus, we show for the first time the direct involvement of NFAT1 in the transcriptional regulation of hTERT.

Transcriptional regulation of BK virus by nuclear factor of activated T cells

The human polyomavirus BK virus (BKV) is a common virus for which 80 to 90% of the adult population is seropositive. BKV reactivation in immunosuppressed patients or renal transplant patients is the primary cause of polyomavirus-associated nephropathy (PVN). Using the Dunlop strain of BKV, we found that nuclear factor of activated T cells (NFAT) plays an important regulatory role in BKV infection. Luciferase reporter assays and chromatin immunoprecipitation assays demonstrated that NFAT4 bound to the viral promoter and regulated viral transcription and infection. The mutational analysis of the NFAT binding sites demonstrated complex functional interactions between NFAT, c-fos, c-jun, and the p65 subunit of NF-kappaB that together influence promoter activity and viral growth. These data indicate that NFAT is required for BKV infection and is involved in a complex regulatory network that both positively and negatively influences promoter activity and viral infection.

Azithromycin suppresses interleukin-12p40 expression in lipopolysaccharide and interferon-gamma stimulated macrophages

Azithromycin (AZM), a 15-member macrolide antibiotic, possesses anti-inflammatory activity. Macrophages are important in innate and acquired immunity, and produce pro-inflammatory cytokines such as interleukin (IL)-12, which are composed of subunit p40 and p35. The key function of IL-12 is the induction and maintenance of T-helper-1 responses, which is associated with the pathogenesis of chronic inflammatory diseases. We investigated the effect of azithromycin on IL-12p40 production in macrophages after lipopolysaccharide (LPS)/interferon (IFN)-γ stimulation. RAW264.7 macrophage cell line was pre-treated with vehicle or AZM, followed by the stimulation with LPS/IFN-γ. We measured IL-12 production by RT-PCR and ELISA. IL-12 transcriptional regulation was assessed by electrophoretic mobility shift assay and reporter assay. Phosphorylation of activator protein (AP)-1 and interferon consensus sequence binding protein (ICSBP) was assessed by immunoprecipitation using phosphotyrosine antibody, and immunoblotting using specific antibodies against JunB and ICSBP. AZM reduced the induction of IL-12p40 by LPS/IFN-γ in a dose dependent manner. AZM inhibited the binding of AP-1, nuclear factor of activated T cells (NFAT), and ICSBP, to the DNA binding site in the IL-12p40 promoter. AZM also reduced LPS/IFN-γ-induced IL-12p40 promoter activity. Phosphorylation of JunB and ICSBP was inhibited by azithromycin-treatment in stimulated cells. In conclusion, AZM reduced IL-12p40 transcriptional activity by inhibiting the binding of AP-1, NFAT, and ICSBP to the promoter site. This may represent an important mechanism for regulating the anti-inflammatory effects of AZM in macrophages.

FcepsilonRI-induced activation by low antigen concentrations results in nuclear signals in the absence of degranulation

High affinity IgE receptor (FcvarepsilonRI)-induced activation of mast cells results in degranulation and generation of leukotrienes and cytokines. FcvarepsilonRI-induced mast cell activation was analyzed at a single cell basis using a rat basophilic leukemia (RBL-2H3) cell line transfected with a reporter plasmid containing three tandem NFAT (nuclear factor of activated T cells) binding sites fused to enhanced green fluorescent protein (GFP). Surprisingly, with this sensitive detection system, there is activation of IgE sensitized cells at concentrations of antigen as low as 10pg/ml, which was 10-fold lower than was detected by degranulation. There were differences in signaling pathways leading to degranulation compared to NFAT-mediated gene activation. Both signaling to NFAT activation and degranulation required Syk and calcineurin. However inhibitors of the phosphatidylinositol 3-kinase pathway blocked degranulation but did not NFAT activation. The results also indicate that NFAT was activated at lower intracellular signals compared to degranulation. Therefore, FcvarepsilonRI activation can result in nuclear signals in the absence of the release of mediators.

Calcineurin inhibitor nephrotoxicity

The use of the calcineurin inhibitors cyclosporine and tacrolimus led to major advances in the field of transplantation, with excellent short-term outcome. However, the chronic nephrotoxicity of these drugs is the Achilles' heel of current immunosuppressive regimens. In this review, the authors summarize the clinical features and histologic appearance of both acute and chronic calcineurin inhibitor nephrotoxicity in renal and nonrenal transplantation, together with the pitfalls in its diagnosis. The authors also review the available literature on the physiologic and molecular mechanisms underlying acute and chronic calcineurin inhibitor nephrotoxicity, and demonstrate that its development is related to both reversible alterations and irreversible damage to all compartments of the kidneys, including glomeruli, arterioles, and tubulo-interstitium. The main question--whether nephrotoxicity is secondary to the actions of cyclosporine and tacrolimus on the calcineurin-NFAT pathway--remains largely unanswered. The authors critically review the current evidence relating systemic blood levels of cyclosporine and tacrolimus to calcineurin inhibitor nephrotoxicity, and summarize the data suggesting that local exposure to cyclosporine or tacrolimus could be more important than systemic exposure. Finally, other local susceptibility factors for calcineurin inhibitor nephrotoxicity are reviewed, including variability in P-glycoprotein and CYP3A4/5 expression or activity, older kidney age, salt depletion, the use of nonsteroidal anti-inflammatory drugs, and genetic polymorphisms in genes like TGF-beta and ACE. Better insight into the mechanisms underlying calcineurin inhibitor nephrotoxicity might pave the way toward more targeted therapy or prevention of calcineurin inhibitor nephrotoxicity.

Established and newly proposed mechanisms of chronic cyclosporine nephropathy

Cyclosporine (CsA) has improved patient and graft survival rates following solid-organ transplantation and has shown significant clinical benefits in the management of autoimmune diseases. However, the clinical use of CsA is often limited by acute or chronic nephropathy, which remains a major problem. Acute nephropathy depends on the dosage of CsA and appears to be caused by a reduction in renal blood flow related to afferent arteriolar vasoconstriction. However, the mechanisms underlying chronic CsA nephropathy are not completely understood. Activation of the intrarenal renin-angiotensin system (RAS), increased release of endothelin-1, dysregulation of nitric oxide (NO) and NO synthase, up-regulation of transforming growth factor-beta1 (TGF-beta1), inappropriate apoptosis, stimulation of inflammatory mediators, enhanced innate immunity, endoplasmic reticulum stress, and autophagy have all been implicated in the pathogenesis of chronic CsA nephropathy. Reducing the CsA dosage or using other renoprotective drugs (angiotensin II receptor antagonist, mycophenolate mofetil, and statins, etc.) may ameliorate chronic CsA-induced renal injury. This review discusses old and new concepts in CsA nephropathy and preventive strategies for this clinical dilemma.

PICOT is a critical regulator of cardiac hypertrophy and cardiomyocyte contractility

PICOT (PKC-interacting cousin of thioredoxin) was previously shown to inhibit the development of cardiac hypertrophy, concomitant with an increase in cardiomyocyte contractility. To explore the physiological function of PICOT in the hearts, we generated a PICOT-deficient mouse line by using a gene trap approach. PICOT(-/-) mice were embryonic lethal indicating that PICOT plays an essential role during embryogenesis, whereas PICOT(+/-) mice were viable with no apparent morphological defects. The PICOT protein levels were reduced by about 50% in the hearts of PICOT(+/-) mice. Significantly exacerbated cardiac hypertrophy was induced by pressure overload in PICOT(+/-) mice relative to that seen in wild type littermates. In line with this observation, calcineurin-NFAT signaling was greatly enhanced by pressure overload in the hearts of PICOT(+/-) mice. Cardiomyocytes from PICOT(+/-) mice exhibited significantly reduced contractility, which may be due in part to hypophosphorylation of phospholamban and reduced SERCA activity. These data indicate that the precise PICOT protein level significantly affects the process of cardiac hypertrophy and cardiomyocyte contractility. We suggest that PICOT plays as a critical negative regulator of cardiac hypertrophy and a positive inotropic regulator.

Regulation of Down Syndrome Critical Region 1 expression by Nuclear Factor of Activated T cells in megakaryocytes

As precursors of platelets, megakaryocytes must fulfil the complex tasks of protein synthesis and platelet assembly. Megakaryocytic dysfunction can lead to neoplastic disorders, such as acute megakaryoblastic leukaemia, an entity with a 500-fold increased incidence in children with Down syndrome (DS). Down Syndrome Critical Region 1 (DSCR1), a member of the calcipressin family of calcineurin inhibitors, is overexpressed in DS, and destabilization of the calcineurin/Nuclear Factor of Activated T cells (NFAT) pathway by overexpression of DSCR1 has been implicated in some of the pathophysiological features of the disease. The roles of NFAT and DSCR1 in megakaryocyte signalling and gene expression, however, are unknown. In this study, we show that calcineurin and NFAT are components of a calcium-induced signalling cascade in megakaryocytes. NFAT activation in megakaryocytes was induced by fibrillar collagen type I and was completely sensitive to the calcineurin inhibitor cyclosporin A. We established DSCR1 as a calcium-induced NFAT target gene in these cells and show that overexpression of DSCR1 in megakaryocytes strongly inhibits NFAT activation as well as NFAT-dependent expression of the Fas ligand gene (FASLG). These results suggest that DSCR1 acts as an endogenous feedback inhibitor of NFAT signalling in megakaryocytes, and may have implications for megakaryocytic gene expression in DS.