The immunosuppressive drugs cyclosporin A and FK506 inhibit calcineurin phosphatase activity and gene transcription mediated through the cAMP-responsive element in a nonimmune cell line

Nerve Wrap for Local Delivery of FK506/Tacrolimus Accelerates Nerve Regeneration

Peripheral nerve injuries (PNIs) occur frequently and can lead to devastating and permanent sensory and motor function disabilities. Systemic tacrolimus (FK506) administration has been shown to hasten recovery and improve functional outcomes after PNI repair. Unfortunately, high systemic levels of FK506 can result in adverse side effects. The localized administration of FK506 could provide the neuroregenerative benefits of FK506 while avoiding systemic, off-target side effects. This study investigates the utility of a novel FK506-impregnated polyester urethane urea (PEUU) nerve wrap to treat PNI in a previously validated rat infraorbital nerve (ION) transection and repair model. ION function was assessed by microelectrode recordings of trigeminal ganglion cells responding to controlled vibrissae deflections in ION-transected and -repaired animals, with and without the nerve wrap. Peristimulus time histograms (PSTHs) having 1 ms bins were constructed from spike times of individual single units. Responses to stimulus onsets (ON responses) were calculated during a 20 ms period beginning 1 ms after deflection onset; this epoch captures the initial, transient phase of the whisker-evoked response. Compared to no-wrap controls, rats with PEUU-FK506 wraps functionally recovered earlier, displaying larger response magnitudes. With nerve wrap treatment, FK506 blood levels up to six weeks were measured nearly at the limit of quantification (LOQ ≥ 2.0 ng/mL); whereas the drug concentrations within the ION and muscle were much higher, demonstrating the local delivery of FK506 to treat PNI. An immunohistological assessment of ION showed increased myelin expression for animals assigned to neurorrhaphy with PEUU-FK506 treatment compared to untreated or systemic-FK506-treated animals, suggesting that improved PNI outcomes using PEUU-FK506 is mediated by the modulation of Schwann cell activity.

CyclosporinA Derivative as Therapeutic Candidate for Alport Syndrome by Inducing Mutant Type IV Collagen Secretion

Key Points

Screening of natural product extracts to find candidate compounds that increase mutant type IV collagen α 3,4,5 (α 345(IV)) trimer secretion in Alport syndrome (AS). Cyclosporin A (CsA) and alisporivir (ALV) increase mutant α 345(IV) trimer secretion in AS. PPIF/cyclophilin D mediates the effect of CsA and ALV on mutant trimer secretion.

Background

Type IV collagen α 3,4,5 (α 345(IV)) is an obligate trimer that is secreted to form a collagen network, which is the structural foundation of basement membrane. Mutation in one of the genes (COL4A3 , A4 , A5 ) encoding these proteins underlies the progressive genetic nephropathy Alport syndrome (AS) due to deficiency in trimerization and/or secretion of the α 345(IV) trimer. Thus, improving mutant α 345(IV) trimerization and secretion could be a good therapeutic approach for AS.

Methods

Using the nanoluciferase-based platform that we previously developed to detect α 345(IV) formation and secretion in HEK293T cells, we screened libraries of natural product extracts and compounds to find a candidate compound capable of increasing mutant α 345(IV) secretion.

Results

The screening of >13,000 extracts and >600 compounds revealed that cyclosporin A (CsA) increased the secretion of mutant α 345(IV)-G1244D. To elucidate the mechanism of the effect of CsA, we evaluated CsA derivatives with different ability to bind to calcineurin (Cn) and cyclophilin (Cyp). Alisporivir (ALV), which binds to Cyp but not to Cn, increased the trimer secretion of mutant α 345(IV). Knockdown studies on Cyps showed that PPIF/cyclophilin D was involved in the trimer secretion-enhancing activity of CsA and ALV. We confirmed that other α 345(IV) mutants are also responsive to CsA and ALV.

Conclusions

CsA was previously reported to improve proteinuria in patients with AS, but owing to its nephrotoxic effect, CsA is not recommended for treatment in patients with AS. Our data raise the possibility that ALV could be a safer option than CsA. This study provides a novel therapeutic candidate for AS with an innovative mechanism of action and reveals an aspect of the intracellular regulatory mechanism of α 345(IV) that was previously unexplored.

Antifungal polybrominated proxyphylline derivative induces Candida albicans calcineurin stress response in Galleria mellonella

Candida albicans CNB1 plays a role in the response in vitro and in vivo to stress generated by PB-WUT-01, namely 1,3-dimethyl-7-(2-((1-(3-(perbromo-2H-benzo[d][1,2,3]triazol-2-yl)propyl)-1H-1,2,3-triazol-4-yl)methoxy)propyl)-1H-purine-2,6(3H,7H)-dione. The antifungal mechanism involved the calcineurin pathway-regulated genes SAP9-10. Galleria mellonella treated with PB-WUT-01 (at 0.64 µg/mg) showed limited candidiasis and remained within the highest survival rates. The molecular mode of action of PB-WUT-01 was rationalized by in silico docking studies toward both human and C. albicans calcineurin A (CNA) and calcineurin B (CNB) complexes, respectively. PB-WUT-01 acting as a calcineurin inhibitor in the C. albicans cells enhances the cells' susceptibility. Therefore it could be a suitable alternative treatment in patients with candidiasis.

In Trauma Patients, the Occurrence of Early-Onset Nosocomial Infections is Associated With Increased Plasma Concentrations of Chromogranin A

In previously healthy persons suffering from acute illnesses, nosocomial infections (NIs) are frequent. Their prevalence suggests the existence of as yet unknown conditions that may promote care-related infection. This study assessed whether the measurement of plasma chromogranin A, a stress-related protein involved in innate defense, is related to NI risk, and whether any chromogranin A-derived fragment included in vasostatin-I displays immunosuppressive activities related to AP-1 or NF-kappa B downregulation. At the clinical level, trauma patients and healthy controls were recruited to be eligible. Clinical histories were recorded, and standard biological tests (including plasma chromogranin A) were performed. For 9 randomly chosen patients and 16 controls, the time-dependent concentrations of chromogranin A (CGA) were assessed twice a day over 66 h. The data show that trauma patients present a higher value of CGA concentration during 66 h in comparison with healthy controls. In addition, patients maintaining this significant increase in CGA readily develop NIs. We therefore studied the effects of chromogranin A-derived peptides on monocytes, focusing on transcription factors that play a central role in inflammation. In vitro assay demonstrated that a chromogranin A-derived fragment (CGA47-70) displays a significant inhibition of NF-kappa B and AP-1 transcriptional activities in these cells. In conclusion, the occurrence of NI in trauma patients is associated with significantly increased plasma CGA concentrations. Downregulation of the two transcription factors by CGA47-70 might induce early acquired immune defect after a serious medical stress.

A calcineurin-dependent switch controls the trafficking function of α-arrestin Aly1/Art6

Proper regulation of plasma membrane protein endocytosis by external stimuli is required for cell growth and survival. In yeast, excess levels of certain nutrients induce endocytosis of the cognate permeases to prevent toxic accumulation of metabolites. The α-arrestins, a family of trafficking adaptors, stimulate ubiquitin-dependent and clathrin-mediated endocytosis by interacting with both a client permease and the ubiquitin ligase Rsp5. However, the molecular mechanisms that control α-arrestin function are not well understood. Here, we show that α-arrestin Aly1/Art6 is a phosphoprotein that specifically interacts with and is dephosphorylated by the Ca(2+)- and calmodulin-dependent phosphoprotein phosphatase calcineurin/PP2B. Dephosphorylation of Aly1 by calcineurin at a subset of phospho-sites is required for Aly1-mediated trafficking of the aspartic acid and glutamic acid transporter Dip5 to the vacuole, but it does not alter Rsp5 binding, ubiquitinylation, or stability of Aly1. In addition, dephosphorylation of Aly1 by calcineurin does not regulate the ability of Aly1 to promote the intracellular sorting of the general amino acid permease Gap1. These results suggest that phosphorylation of Aly1 inhibits its vacuolar trafficking function and, conversely, that dephosphorylation of Aly1 by calcineurin serves as a regulatory switch to promote Aly1-mediated trafficking to the vacuole.

Therapeutic effect of 0.03% tacrolimus ointment for ocular graft versus host disease and vernal keratoconjunctivitis

Purpose

To determine whether topical tacrolimus might prove effective in the treatment of refractory anterior segment inflammatory diseases, and to evaluate its efficacy in eyes with ocular graft versus host disease (GVHD), and vernal keratoconjunctivitis (VKC).

Methods

Twenty-eight eyes of 14 patients with anterior segment inflammation refractory to steroid treatment were treated with 0.03% tacrolimus ointment at the Samsung Medical Center, Seoul, Korea from March 2008 through August 2009. Seven patients had ocular GVHD and seven had VKC. We evaluated the conjunctival and corneal inflammatory change at one, two, four, and eight weeks after treatment with a scoring system. Time to initial response of treatment and therapeutic effect between GVHD and VKC was also analyzed. After the eight-week treatment period, patients were divided into two groups (maintenance group and discontinuance group). Eight patients maintained the treatment for an additional four months, and six patients discontinued the treatments. Therapeutic effect was also compared between the groups at eight weeks and six months after treatment.

Results

The mean conjunctival and corneal inflammation score was reduced significantly at eight weeks after treatment (p < 0.0001). The therapeutic effect in conjunctival inflammation was first noted at week two after the initial treatment (p = 0.002); reduction in corneal inflammation was first noted at one week (p = 0.0009). When compared according to diagnosis, no therapeutic difference was detected between the groups (p > 0.05). Six months after treatment, we noted no therapeutic differences between the maintenance group and discontinuance group (p > 0.05).

Conclusions

0.03% tacrolimus ointment was safe and effective for use in anterior segment inflammatory disease refractory to steroid.

Cyclosporin A inhibits nucleotide excision repair via downregulation of the xeroderma pigmentosum group A and G proteins, which is mediated by calcineurin inhibition

Cyclosporin A (CsA) inhibits nucleotide excision repair (NER) in human cells, a process that contributes to the skin cancer proneness in organ transplant patients. We investigated the mechanisms of CsA-induced NER reduction by assessing all xeroderma pigmentosum (XP) genes (XPA-XPG). Western blot analyses revealed that XPA and XPG protein expression was reduced in normal human GM00637 fibroblasts exposed to 0.1 and 0.5 μm CsA. Interestingly, the CsA treatment reduced XPG, but not XPA, mRNA expression. Calcineurin knockdown in GM00637 fibroblasts using RNAi led to similar results suggesting that calcineurin-dependent signalling is involved in XPA and XPG protein regulation. CsA-induced reduction in NER could be complemented by the overexpression of either XPA or XPG protein. Likewise, XPA-deficient fibroblasts with stable overexpression of XPA (XP2OS-pCAH19WS) did not show the inhibitory effect of CsA on NER. In contrast, XPC-deficient fibroblasts overexpressing XPC showed CsA-reduced NER. Our data indicate that the CsA-induced inhibition of NER is a result of downregulation of XPA and XPG protein in a calcineurin-dependent manner.

Norfuraneol dephosphorylates eNOS at threonine 495 and enhances eNOS activity in human endothelial cells

AIM

Pentoses are widely abundant in organic food. Thermal treatment of pentoses leads to the formation of norfuraneol (NF). The aim of this study was to show whether NF, which is taken up regularly, for example with cooked food, affects the human endothelial nitric oxide synthase (eNOS) system.

METHODS AND RESULTS

The study was performed using cultured human umbilical vein endothelial cells (HUVEC), HUVEC-derived EA.hy926 cells, and bovine aortic endothelial cells. Nitric oxide (NO) release and eNOS activity were measured using diaminofluorescein-2 and [14C]L-arginine/[14C]L-citrulline conversion. Levels of (phospho-)eNOS were detected by western blotting. Reactive oxygen species (ROS) production was assessed using 2',7'-dichlorodihydrofluorescein diacetate. Pharmacokinetic parameters of NF were calculated by VolSurf software. NF dose dependently increased eNOS activity and NO release (30-300 microM), but did not affect total eNOS protein or cellular ROS levels. The increase in eNOS activity coincided with specific dephosphorylation of eNOS-Thr495, known to enhance eNOS activity. Inhibition of protein phosphatase 1 (PP1) by calyculin A, tautomycetin, or siRNA against PP1 reversed NF-induced eNOS-Thr495 dephosphorylation. Phosphorylation at eNOS-Ser1177 was not significantly altered by NF. Inhibition of protein kinase C with bisindolylmaleimide I (GFX) or calphostin C mimicked the effect of NF. In contrast to GFX, however, NF had no effect on phorbol-12-myristate-13-acetate-induced endothelial ROS formation. In silico, NF is stable towards CYP3A4 metabolism, shows low protein binding, and high tissue distribution.

CONCLUSION

NF enhances endothelial NO release most likely by promoting specific dephosphorylation of eNOS-Thr495 via PP1 in vitro and may be a promising compound to enhance endothelial function in vivo.

Protein phosphatase 1, protein phosphatase 2A, and calcineurin play a role in estrogen-mediated neuroprotection

It is becoming increasingly clear that protein phosphatases are important modulators of cellular function and that disruption of these proteins are involved in neurodegenerative disease processes. Serine/threonine protein phosphatases (PP) such as protein phosphatase PP1, PP2A, and calcineurin are involved in hyperphosphorylation of tau- as well as beta-amyloid-induced cell death. We have previously shown serine/threonine protein phosphatases to be involved in estrogen-mediated neuroprotection. The purpose of this study was to delineate the role of PP1, PP2A, and calcineurin in the mechanism of estrogen mediated neuroprotection against oxidative stress and excitotoxicity. Treatment with protein phosphatases inhibitor II, endothall, or cyclosporin A, which are specific inhibitors of PP1, PP2A, and calcineurin, respectively, did not have an effect on cell viability. However, in combination, these inhibitors adversely affected cell survival, which suggests the importance of serine/threonine protein phosphatases in maintenance of cellular function. Inhibitors of PP1, PP2A, and calcineurin attenuated the protective effects of estrogen against glutamate-induced -neurotoxicity but did not completely abrogate the estrogen-mediated protection. The attenuation of estrogen-induced neuroprotection was achieved through decrease in the activity of theses serine/threonine phosphatases without the concomitant decrease in protein expression. In an animal model, transient middle cerebral artery occlusion caused a 50% decrease in levels of PP1, PP2A, and PP2B ipsilateral to the lesion in a manner that was prevented by estradiol pretreatment. Therefore, we conclude that in the face of cytotoxic challenges in vitro and in vivo, estrogens maintain the function of PP1, PP2A, and calcineurin.

Therapeutic Effects of Tacrolimus Ointment for Refractory Ocular Surface Inflammatory Diseases

PURPOSE

To investigate the therapeutic effects of topical tacrolimus ointment on refractory ocular surface inflammatory diseases.

DESIGN

Retrospective interventional consecutive case series.

PARTICIPANTS

Ten consecutive patients with severe ocular surface inflammatory diseases who were suspected to be steroid responders (elevation of intraocular pressure [IOP]) or were refractory to standard steroid therapy were studied. One patient had peripheral ulcerative keratitis with impending corneal perforation, 1 had a Mooren's ulcer, 2 had scleroperikeratitis, 5 had atopic keratoconjunctivitis, and 1 had vernal keratoconjunctivitis.

METHODS

The clinical findings and therapeutic responses after treatment with 0.02% topical tacrolimus ointment were determined by conventional ophthalmological examinations.

MAIN OUTCOME MEASURES

Resolution of the ocular surface diseases (e.g., decrease of hyperemia, ulceration, size of papillae) and IOP. The necessity to use steroids was also assessed.

RESULTS

In all cases, marked to moderate improvement was obtained, including suppression of the melting reaction of the inflamed cornea, remission of scleroperikeratitis, and reduction of a giant papilla and corneal epithelial defect in severe atopic keratoconjunctivitis. The elevated IOP was reduced in steroid responders after successful cessation of steroid therapy. No adverse side effect was noted for 2 to 26 months of continuous treatment.

CONCLUSIONS

Topical tacrolimus ointment is effective in treating refractory ocular surface inflammatory diseases and should be considered as an alternative to higher doses, steroid supplementation, or surgical intervention.

Calcineurin/NFAT signaling in the beta-cell: From diabetes to new therapeutics

Pancreatic beta-cells in the islet of Langerhans produce the hormone insulin, which maintains blood glucose homeostasis. Perturbations in beta-cell function may lead to impairment of insulin production and secretion and the onset of diabetes mellitus. Several essential beta-cell factors have been identified that are required for normal beta-cell function, including six genes that when mutated give rise to inherited forms of diabetes known as Maturity Onset Diabetes of the Young (MODY). However, the intracellular signaling pathways that control expression of MODY and other factors continue to be revealed. Post-transplant diabetes mellitus in patients taking the calcineurin inhibitors tacrolimus (FK506) or cyclosporin A indicates that calcineurin and its substrate the Nuclear Factor of Activated T-cells (NFAT) may be required for beta-cell function. Here recent advances in our understanding of calcineurin and NFAT signaling in the beta-cell are reviewed. Novel therapeutic approaches for the treatment of diabetes are also discussed.

Angiotensin II induces soluble fms-Like tyrosine kinase-1 release via calcineurin signaling pathway in pregnancy

Maternal endothelial dysfunction in preeclampsia is associated with increased soluble fms-like tyrosine kinase-1 (sFlt-1), a circulating antagonist of vascular endothelial growth factor and placental growth factor. Angiotensin II (Ang II) is a potent vasoconstrictor that increases concomitant with sFlt-1 during pregnancy. Therefore, we speculated that Ang II may promote the expression of sFlt-1 in pregnancy. Here we report that infusion of Ang II significantly increases circulating levels of sFlt-1 in pregnant mice, thereby demonstrating that Ang II is a regulator of sFlt-1 secretion in vivo. Furthermore, Ang II stimulated sFlt-1 production in a dose- and time-dependent manner from human villous explants and cultured trophoblasts but not from endothelial cells, suggesting that trophoblasts are the primary source of sFlt-1 during pregnancy. As expected, Ang II-induced sFlt-1 secretion resulted in the inhibition of endothelial cell migration and in vitro tube formation. In vitro and in vivo studies with losartan, small interfering RNA specific for calcineurin and FK506 demonstrated that Ang II-mediated sFlt-1 release was via Ang II type 1 receptor activation and calcineurin signaling, respectively. These findings reveal a previously unrecognized regulatory role for Ang II on sFlt-1 expression in murine and human pregnancy and suggest that elevated sFlt-1 levels in preeclampsia may be caused by a dysregulation of the local renin/angiotensin system.

Inhibition of membrane depolarisation-induced transcriptional activity of cyclic AMP response element binding protein (CREB) by the dual-leucine-zipper-bearing kinase in a pancreatic islet beta cell line

AIMS/HYPOTHESIS

The activation of the transcription factor cyclic AMP response element binding protein (CREB) by protein kinase A is inhibited by the human orthologue of the mitogen-activated protein kinase, dual-leucine-zipper-bearing kinase (DLK) in teratocarcinoma cells. However, pancreatic beta cells are electrically excitable and a major pathway regulating CREB in these cells is membrane depolarisation, leading to calcium influx and activation of the calcium/calmodulin-dependent protein phosphatase calcineurin. Therefore, the effect of DLK on CREB activity induced by membrane depolarisation was investigated in the beta cell line HIT.

MATERIALS AND METHODS

Reporter gene assays and biochemical techniques were used.

RESULTS

RT-PCR, Western blot analysis and immunohistochemistry demonstrated the expression of DLK in HIT cells and primary mouse islets. In transient transfection experiments, DLK inhibited both GAL4-CREB activity induced by membrane depolarisation, and transcription directed by the CREB binding site, the cyclic AMP response element. Furthermore, DLK inhibited the transcriptional activity conferred by the CREB coactivator, CREB binding protein, both under basal conditions and after membrane depolarisation. DLK was also effective in response to glucose, the most potent physiological stimulus and known to cause membrane depolarisation of beta cells. Inhibition of calcineurin enhanced DLK activity, whereas overexpression of calcineurin reduced the inhibition by DLK of transcription directed by cyclic AMP response element after membrane depolarisation.

CONCLUSIONS/INTERPRETATION

These results demonstrate a calcineurin-sensitive inhibition by DLK of CREB activity after membrane depolarisation in pancreatic islet beta cells. This inhibition may, at least partially, be mediated at the coactivator level. The results thus suggest that DLK plays a role in the regulation of beta cell function, including insulin gene transcription and beta cell apoptosis.

Regulation of human insulin gene transcription by the immunosuppressive drugs cyclosporin A and tacrolimus at concentrations that inhibit calcineurin activity and involving the transcription factor CREB

Cyclosporin A and tacrolimus are important immunosuppressive drugs. They share a diabetogenic action as one of their most serious adverse effects. In a single study, tacrolimus (100 nM) inhibited human insulin gene transcription in the beta-cell line HIT. Using transfections of a human insulin-reporter gene into HIT cells, the present study shows that this inhibition is seen only at high concentrations of tacrolimus and is not caused by cyclosporin A. However, after stimulation by the major second messengers in the regulation of the insulin gene, cAMP and depolarization-induced calcium influx, both tacrolimus and cyclosporin A inhibited human insulin gene transcription in a concentration-dependent manner with IC(50) values of 1 nM and 30 nM, respectively. A further analysis offers a mechanism for this effect by revealing that the activation by cAMP and calcium of human insulin gene transcription is mediated by the transcription factor cAMP-responsive element binding protein (CREB) whose activity is inhibited by the immunosuppressants. These data demonstrate for the first time that cAMP- and calcium-induced activity of the human insulin gene is mediated by CREB and blocked by both tacrolimus and cyclosporin A at concentrations that inhibit calcineurin phosphatase activity. Since also the immunosuppressive effects of cyclosporin A and tacrolimus are thought to be secondary to inhibition of calcineurin, the present study suggests that inhibition of human insulin gene transcription by the immunosuppressants is clinically important and may contribute to their diabetogenic effect.

Cyclosporine inhibits growth through the activating transcription factor/cAMP-responsive element-binding protein binding site in the cyclin D1 promoter

The immunosuppressive agent cyclosporine affects proliferation depending on the cellular system used. In an attempt to study the inhibitory effect of cyclosporine on proliferation of pancreatic acinar cells, we used AR42J cells as a model system. Here we demonstrate that cyclosporine inhibits growth of these cells by inducing G(1) cell cycle arrest. This effect is mediated by the 5' regulatory region of the cyclin D1 gene and leads to a reduction of cyclin D1 mRNA expression and protein abundance. We show that in AR42J cells the proximal cyclin D1 promoter contains a cis-regulated element, which is important for the maintenance of basal transcriptional activity. This element overlaps the described cAMP-responsive element (CRE) and confers cyclosporine sensitivity to the cyclin D1 promoter. Furthermore, the DNA binding activity of the CRE-binding protein (CREB) decreases through cyclosporine treatment and this is mediated by cyclosporine-induced reduction of CREB steady-state levels. These results demonstrate that cyclosporine can inhibit proliferation of acinar cells by targeting the cyclin D1 promoter at the proximal CRE via a reduction of CREB protein abundance.

Characterization of a novel calcium response element in the glucagon gene

To maintain blood glucose levels within narrow limits, the synthesis and secretion of pancreatic islet hormones is controlled by a variety of extracellular signals. Depolarization-induced calcium influx into islet cells has been shown to stimulate glucagon gene transcription through the transcription factor cAMP response element-binding protein that binds to the glucagon cAMP response element. By transient transfection of glucagon-reporter fusion genes into islet cell lines, this study identified a second calcium response element in the glucagon gene (G2 element, from -165 to -200). Membrane depolarization was found to induce the binding of a nuclear complex with NFATp-like immunoreactivity to the G2 element. Consistent with nuclear translocation, a comigrating complex was found in cytosolic extracts of unstimulated cells, and the induction of nuclear protein binding was blocked by inhibition of calcineurin phosphatase activity by FK506. A mutational analysis of G2 function and nuclear protein binding as well as the effect of FK506 indicate that calcium responsiveness is conferred to the G2 element by NFATp functionally interacting with HNF-3beta binding to a closely associated site. Transcription factors of the NFAT family are known to cooperate with AP-1 proteins in T cells for calcium-dependent activation of cytokine genes. This study shows a novel pairing of NFATp with the cell lineage-specific transcription factor HNF-3beta in islet cells to form a novel calcium response element in the glucagon gene.

The absence of a major Ca2+ signaling pathway in GABAergic neurons of the hippocampus

The Ca2+/calmodulin-dependent protein phosphatase 2B or calcineurin (CN) participates in several Ca2+-dependent signal transduction cascades and, thus, contributes to the short and long term regulation of neuronal excitability. By using a specific antibody to CN, we demonstrate its absence from hippocampal interneurons and illustrate a physiological consequence of such CN deficiency. Consistent with the lack of CN in interneurons as detected by immunocytochemistry, the CN inhibitors FK-506 or okadaic acid significantly prolonged N-methyl-D-aspartate channel openings recorded in the cell-attached mode in hippocampal principal cells but not those recorded in interneurons. Interneurons were also devoid of Ca2+/calmodulin-dependent protein kinase IIalpha, yet many of their nuclei contained the cyclic AMP-responsive element binding protein. On the basis of the CN and Ca2+/calmodulin-dependent protein kinase IIalpha deficiency of interneurons, entirely different biochemical mechanisms are expected to govern Ca2+-dependent neuronal plasticity in interneurons versus principal cells.

Use of the methylxanthine derivative A802715 in transplantation immunology: II. In vivo experiments

BACKGROUND

We have previously demonstrated in vitro that the methylxanthine derivative A802715 suppresses the cyclosporine (CsA)-resistant "signal two"-dependent pathway of T cell activation and hence acts synergistically with CsA. Here, this synergism was further investigated in vivo in rats.

METHODS

Primary cardiac allografts were placed in the neck, and secondary grafts were transplanted intra-abdominally. A802715 was given orally for 30 days or by continuous intravenous infusion via a mini-osmotic pump for 2 weeks. CsA was given orally for up to 30 days. T cell responses were examined in vitro using mixed lymphocyte reaction, concanavalin A whole blood, and cell-mediated lympholysis assays.

RESULTS

In a major histocompatibility complex incompatible WKAH-->PVG combination, neither oral CsA (7.5 mg/kg/day) nor oral A802715 (100 mg/kg/day) was able to prolong graft survival. However, a combination of both drugs, given at the same dose, sustained graft survival during treatment. A similar synergism was not obtained with pentoxifylline, another methylxanthine derivative. The synergism between A802715 and CsA could be further increased by using a continuous intravenous infusion of A802715, since (1) lower doses of A802715 (20 mg/kg/day) and CsA (5 mg/kg/day) could be used, and (2) six of seven grafts survived permanently. In a major histocompatibility complex compatible Wag/Rij-->R/A combination, similar synergistic effects and permanent graft survival could also be obtained by oral A802715 (100 mg/kg/day) in combination with a low dose of CsA (2.5 mg/kg/day). In both strain combinations, long-term survivors accepted donor-type but rejected third-party second grafts in the absence of immunosuppression. This specific tolerance was not related to clonal deletion nor anergy, as recipient lymphocytes proliferated normally in the anti-donor mixed lymphocyte reaction. Instead, a defect in generating specific cytotoxic T lymphocytes was involved.

CONCLUSIONS

A802715 synergizes with CsA in vivo to induce specific transplantation tolerance and hence should be considered as a promising new immunosuppressant.

Significant increase of Kuppfer cells associated with loss of Na+,K+-ATPase activity in rat hepatic allograft rejection

BACKGROUND

Cholestasis is a complication that occurs during the rejection of liver transplants. The aim of this study was to investigate the association of activated Kupffer cells (KCs) and Na+,K+-ATPase activity for taurocholate cotransport and bile canalicular (BC) Mg++-ATPase activity for hepatobiliary excretion in rat liver allograft.

METHODS

Quantitative analyses of KC number and size in relationship to enzyme activity of Na+,K+-ATPase and of BC Mg++-ATPase were conducted in rejected liver after allogenic transplantation and after prevention of rejection using cyclosporine.

RESULTS

The animals were examined on the 10th postoperative day. In the rejection group, the number of KCs significantly increased more than fourfold in comparison with the number of KCs in the control livers. Some KCs were found in the sinusoids, but the majority were located in the space of Disse. Na+,K+-ATPase activity vanished from the basolateral plasma membrane, whereas BC Mg++-ATPase activity was restored in the apical domain. With immunosuppression, KCs showed the same behavior as in the control group, and activity of both ATPases was observed as strong electron-dense precipitates in basolateral and apical plasma membrane domains.

CONCLUSIONS

In this study, we demonstrate that activated KCs migrate into the donor liver and release cytokines, which leads to the loss of Na+,K+-ATPase activity in the rejection group. BC Mg++-ATPase activity was not influenced by these mediators of activated macrophages. Since Na+,K+-ATPase is the cotransporter for hepatocyte taurocholate uptake, these data may contribute to understanding the mechanisms for cholestasis during hepatic allograft rejection.

Characterization of a novel protein kinase C response element in the glucagon gene

To maintain glucose levels in blood within narrow limits, the synthesis and secretion of pancreatic islet hormones are controlled by a variety of neural, hormonal, and metabolic messengers that act through multiple signal transduction pathways. Glucagon gene transcription is stimulated by cyclic AMP and depolarization-induced calcium influx. In this study, the effect of protein kinase C on glucagon gene transcription was investigated. After transient transfection of a glucagon-reporter fusion gene into the glucagon-producing islet cell line alphaTC2, activation of protein kinase C by 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulated glucagon gene transcription. By 5' deletions, 3' deletions, internal deletion, and oligonucleotide cassette insertion, the TPA-responsive element was mapped to the G2 element (from -165 to -200). Like TPA, overexpression of oncogenic Ras (V-12 Ras) stimulated G2-mediated transcription whereas overexpression of a dominant negative Ras mutant (N-17 Ras) blocked the effect of TPA. A mutational analysis of G2 function and nuclear protein binding indicated that protein kinase C and Ras responsiveness is conferred to the glucagon gene by HNF-3beta functionally interacting with a protein that binds to a closely associated site with sequence similarity to binding sites of Ets family proteins. HNF-3beta belongs to the winged-helix family of transcription factors and has been implicated in the control of cell-specific and developmental gene expression. The results of the present study show that the cell lineage-specific transcription factor HNF-3beta is an essential component of a novel protein kinase C response element in the glucagon gene.

Comparative analysis of tacrolimus (FK506) in whole blood liver transplant recipients by PRO-TRAC enzyme-linked immunosorbent assay and microparticle enzyme immunoassay IMX methods

The macrolide tacrolimus (FK506) is a powerful immunosuppressive drug that acts early in the T-cell activation process and inhibits cytokine gene transcription. Data from several trials in liver transplantation have shown the efficacy of tacrolimus in the prevention of allograft rejection and its potent hepatotrophic effect, which could explain its great success in liver transplantation. However, tacrolimus is not devoid of adverse effects (mainly nephrotoxicity and neurotoxicity) requiring careful blood level monitoring, which is an essential aid in the adjustment of drug dosing. Several methods of analysis are available to measure tacrolimus in whole blood. A new assay based on the enzyme-linked immunosorbent assay (ELISA) technology has been developed. The INCSTAR PRO-TRAC FK506 is a sensitive immunoassay (range, 0.5 to 60 ng/ml), which uses a mouse monoclonal antibody to FK506. Samples are extracted into methanol and dried under nitrogen. The reconstituted extracts are analyzed by ELISA by using 2-h incubation. The aim of this study was to evaluate the ELISA method in routine monitoring of liver transplant patients and to compare the whole blood results with those obtained by Abbott microparticle enzyme immunoassay (MEIA) IMx. Precision studies with 20 samples from 4.37 and 17.1 ng/ml gave within-run total coefficients of variance of 14.4 and 17.4%, respectively. A total of 63 blood samples was analyzed. The mean +/- SD were 9.68 +/- 5.92 and 10.52 +/- 7.54 ng/ml by ELISA and MEIA assays, respectively. There was an acceptable correlation between the methods: ELISA = 1.419 + 0.785 MEIA; Sy x x = 2.639; r = 0.804. Serial tacrolimus measurements (n = 13) in two patients with bilirubin levels > 20 mg/dl yielded mean +/- SD (range) of 11.64 +/- 7.59 ng/ml (2.60-25.40 ng/ml) and 15.55 +/- 10.78 ng/ml (3.60-34.4 ng/mL) by ELISA and MEIA assays, respectively. These discrepancies in concentrations can result from variation in matrix or different cross-reactivities or both in the two tests. We concluded that the INCSTAR PRO-TRAC FK506 is suitable for routine whole blood tacrolimus monitoring.

Involvement of the Ca(2+)-dependent phosphatase calcineurin in gene transcription that is stimulated by cAMP through cAMP response elements

Gene transcription can be induced by cAMP and Ca2+ through distinct protein kinases phosphorylating the transcription factor CREB, which binds to cAMP response elements (CREs) in various genes. Induction of gene transcription by Ca2+ has been shown recently to depend on the Ca2+/calmodulin-dependent protein phosphatase calcineurin in pancreatic islet cells. This study investigates the role of calcineurin in CRE-directed gene transcription after stimulation by cAMP. Reporter fusion genes under the transcriptional control of CREs were transiently transfected into the cell line HIT. Pharmacological evidence suggests that cAMP stimulates CRE-mediated transcription through a Ca(2+)-dependent mechanism. The immunosuppressive drugs cyclosporin A and FK506 inhibited CRE-mediated transcription stimulated by cAMP. At the same concentrations they also inhibited calcineurin phosphatase activity. Reversal of calcineurin inhibition by rapamycin or overexpression of calcineurin led to disinhibition of CRE-mediated gene transcription. Immunoblots with a phosphoCREB-specific antibody showed that cyclosporin A and FK506 do not interfere with CREB phosphorylation at serine 119 stimulated with cAMP or membrane depolarization. These results indicate that in HIT cells stimulation of CRE-mediated transcription depends not only on the activity of protein kinases phosphorylating CREB but also on the Ca2+/calmodulin-dependent protein phosphatase calcineurin that is necessary for the transcriptional competence of phosphorylated CREB.

Distribution of calcineurin A isoenzyme mRNAs in rat thymus and kidney

The distribution of the mRNAs encoding the different isoforms of the catalytic subunit (A subunit) of calcineurin has been investigated in rat thymus and kidney using in situ hybridization histochemistry with specific antisense oligonucleotide probes. In the thymus, the mRNAs of the A beta isoforms were the predominant transcripts and showed very intense hybridization signals in the cortical areas. The A alpha mRNAs were expressed at low levels. A beta 2 mRNA was expressed at higher levels than A beta 3 mRNA, but no difference could be detected between the expression levels of A alpha 1 and A alpha 2. In the kidney, highest calcineurin A mRNA hybridization signals were found in the medulla. Signal intensities of A alpha mRNAs were comparable to those of A beta mRNAs. A alpha 1 mRNA level was extremely weak, and A beta 2 mRNA expression was slightly higher than A beta 3 mRNA expression. A tissue-specific distribution pattern of the alternatively spliced isoforms of calcineurin A, as suggested by these preliminary data from thymus and kidney, may be critical in understanding the toxic side-effects associated with the use of the immunosuppressive, calcineurin-inhibiting compounds cyclosporin A and FK506.