Cyclosporin A inhibits T cell receptor-induced interleukin-2 synthesis of human T lymphocytes by selectively preventing a transmembrane signal transduction pathway leading to sustained activation of a protein kinase C isoenzyme, protein kinase C-beta

Peripheral ulcerative keratitis

Peripheral ulcerative keratitis (PUK) is an inflammatory condition of the peripheral cornea with hallmark features of epithelial defects and stromal destruction as a result of a complex interplay of factors including host autoimmunity and the peculiar anatomic and physiologic features of the peripheral cornea and environmental factors. PUK may be the result of local or systemic causes and infectious or noninfectious causes. Arriving at a specific etiological diagnosis requires a meticulous clinical workup that may include a battery of laboratory and radiological investigations. Management by a team of internists or rheumatologists and ophthalmologists and judicious use of immunosuppressive agents may yield favorable results minimizing adverse effects. We review current clinical knowledge on the diagnosis and management of PUK.

Effect of combined sublethal X-ray irradiation and cyclosporine A treatment in NOD scid gamma (NSG) mice

Cyclosporine A (CsA) is used in hematopoietic stem cell transplantations (HSCT) to prevent graft-versus-host disease (GvHD). GvHD is the most severe side effect of allogeneic HSCT and efficient therapies are lacking. Mouse models are an essential tool for assessing potential new therapeutic strategies. Our aim is to mimic a clinical setting as close as possible using CsA treatment after sublethal irradiation in NSG mice and thereby evaluate the feasibility of this mouse model for GvHD studies. The effect of CsA (7.5 mg/kg body weight) on sublethally X-ray irradiated (2 Gy) and non-irradiated NSG mice was tested. CsA was administered orally every twelve hours for nine days. Animals irradiated and treated with CsA showed a shorter survival (n=3/10) than irradiated animals treated with NaCl (n=10/10). Furthermore, combined therapy resulted in severe weight loss (82 ± 6% of initial weight, n=7, day 8), with weight recovery after the CsA application was ceased. A high number of apoptotic events in the liver was observed in these mice (0.431 ± 0.371 apoptotic cells/cm², n=2, compared to 0.027 ± 0.034 apoptotic cells/cm², n=5, in the non-irradiated group). Other adverse effects, including a decrease in white blood cell counts were non-CsA-specific manifestations of irradiation. The combination of CsA treatment with irradiation has a hepatotoxic and lethal effect on NSG mice, whereas the treatment without irradiation is tolerated. Therefore, when using in vivo models of GvHD in NSG mice, a combined treatment with CsA and X-ray irradiation should be avoided or carefully evaluated.

Revisiting the Concept of Targeting NFAT to Control T Cell Immunity and Autoimmune Diseases

The nuclear factor of activated T cells (NFAT) family of transcription factors, which includes NFAT1, NFAT2, and NFAT4, are well-known to play important roles in T cell activation. Most of NFAT proteins are controlled by calcium influx upon T cell receptor and costimulatory signaling results increase of IL-2 and IL-2 receptor. NFAT3 however is not shown to be expressed in T cells and NFAT5 has not much highlighted in T cell functions yet. Recent studies demonstrate that the NFAT family proteins involve in function of lineage-specific transcription factors during differentiation of T helper 1 (Th1), Th2, Th17, regulatory T (Treg), and follicular helper T cells (Tfh). They have been studied to make physical interaction with the other transcription factors like GATA3 or Foxp3 and they also regulate Th cell signature gene expressions by direct binding on promotor region of target genes. From last decades, NFAT functions in T cells have been targeted to develop immune modulatory drugs for controlling T cell immunity in autoimmune diseases like cyclosporine A, FK506, etc. Due to their undesirable side defects, only limited application is available in human diseases. This review focuses on the recent advances in development of NFAT targeting drug as well as our understanding of each NFAT family protein in T cell biology. We also discuss updated detail molecular mechanism of NFAT functions in T cells, which would lead us to suggest an idea for developing specific NFAT inhibitors as a therapeutic drug for autoimmune diseases.

Effects of rheumatoid arthritis associated transcriptional changes on osteoclast differentiation network in the synovium

Background

Osteoclast differentiation in the inflamed synovium of rheumatoid arthritis (RA) affected joints leads to the formation of bone lesions. Reconstruction and analysis of protein interaction networks underlying specific disease phenotypes are essential for designing therapeutic interventions. In this study, we have created a network that captures signal flow leading to osteoclast differentiation. Based on transcriptome analysis, we have indicated the potential mechanisms responsible for the phenotype in the RA affected synovium.

Method

We collected information on gene expression, pathways and protein interactions related to RA from literature and databases namely Gene Expression Omnibus, Kyoto Encyclopedia of Genes and Genomes pathway and STRING. Based on these information, we created a network for the differentiation of osteoclasts. We identified the differentially regulated network genes and reported the signaling that are responsible for the process in the RA affected synovium.

Result

Our network reveals the mechanisms underlying the activation of the neutrophil cytosolic factor complex in connection to osteoclastogenesis in RA. Additionally, the study reports the predominance of the canonical pathway of NF-κB activation in the diseased synovium. The network also confirms that the upregulation of T cell receptor signaling and downregulation of transforming growth factor beta signaling pathway favor osteoclastogenesis in RA. To the best of our knowledge, this is the first comprehensive protein–protein interaction network describing RA driven osteoclastogenesis in the synovium.

Discussion

This study provides information that can be used to build models of the signal flow involved in the process of osteoclast differentiation. The models can further be used to design therapies to ameliorate bone destruction in the RA affected joints.

A20/Tumor Necrosis Factor α-Induced Protein 3 in Immune Cells Controls Development of Autoinflammation and Autoimmunity: Lessons from Mouse Models

Immune cell activation is a stringently regulated process, as exaggerated innate and adaptive immune responses can lead to autoinflammatory and autoimmune diseases. Perhaps the best-characterized molecular pathway promoting cell activation is the nuclear factor-κB (NF-κB) signaling pathway. Stimulation of this pathway leads to transcription of numerous pro-inflammatory and cell-survival genes. Several mechanisms tightly control NF-κB activity, including the key regulatory zinc finger (de)ubiquitinating enzyme A20/tumor necrosis factor α-induced protein 3 (TNFAIP3). Single nucleotide polymorphisms (SNPs) in the vicinity of the TNFAIP3 gene are associated with a spectrum of chronic systemic inflammatory diseases, indicative of its clinical relevance. Mice harboring targeted cell-specific deletions of the Tnfaip3 gene in innate immune cells such as macrophages spontaneously develop autoinflammatory disease. When immune cells involved in the adaptive immune response, such as dendritic cells or B-cells, are targeted for A20/TNFAIP3 deletion, mice develop spontaneous inflammation that resembles human autoimmune disease. Therefore, more knowledge on A20/TNFAIP3 function in cells of the immune system is beneficial in our understanding of autoinflammation and autoimmunity. Using the aforementioned mouse models, novel A20/TNFAIP3 functions have recently been described including control of necroptosis and inflammasome activity. In this review, we discuss the function of the A20/TNFAIP3 enzyme and its critical role in various innate and adaptive immune cells. Finally, we discuss the latest findings on TNFAIP3 SNPs in human autoinflammatory and autoimmune diseases and address that genotyping of TNFAIP3 SNPs may guide treatment decisions.

IL-2 mRNA stabilization upon PMA stimulation is dependent on NF90-Ser647 phosphorylation by protein kinase CbetaI

IL-2 is an important cytokine produced in T cells in response to Ag or mitogen stimulation. It is regulated at both transcriptional and posttranscriptional levels. One of the key regulators of IL-2 mRNA stability is NF90. Upon T cell activation, NF90 translocates from the nucleus into the cytoplasm, where it binds to the AU-rich element-containing 3' untranslated regions of IL-2 mRNA and stabilizes it. Our previous work showed that CD28 costimulation of T cells activated AKT to phosphorylate NF90 at Ser(647) and caused NF90 to undergo nuclear export and stabilize IL-2 mRNA. Phorbol ester (PMA) is a protein kinase C (PKC) activator. Through transcription activation and mRNA stabilization, IL-2 mRNA levels increase promptly when T cells are stimulated with PMA. However, how PMA stabilizes IL-2 mRNA was still unclear. In this study, we demonstrate that PMA stimulation led to phosphorylation of NF90 at Ser(647) via PKCβI. This phosphorylation was necessary for nuclear export of NF90 in response to PMA and for IL-2 mRNA stabilization. We show that phosphorylation at NF90-Ser(647) upregulated IL-2 production in response to PMA stimulation. Our results support a model in which PMA stimulation activates PKCβI to phosphorylate NF90-Ser(647), and this phosphorylation triggers NF90 relocation to the cytoplasm and stabilize IL-2 mRNA. Thus, our study elucidates the mechanism by which PMA activates and stabilizes IL-2 expression in T cells.

The effect of the JNK inhibitor, JIP peptide, on human T lymphocyte proliferation and cytokine production

Although JNK is a potential target for treating chronic inflammatory diseases, its role in T lymphocyte function remains controversial. To overcome some of the previous limitations in addressing this issue we have used the recently described transactivator of transcription-JNK-interacting protein (TAT-JIP) peptide, a specific inhibitor that was derived from the minimal JNK-binding region of the scaffold protein, JNK-interacting protein 1 (JIP-1), coupled to the short cell-permeable HIV TAT sequence. Pretreatment of purified human T lymphocytes with the TAT-JIP peptide inhibited the phosphorylation of endogenous jun activated by PHA-PMA. This was associated with a corresponding inhibition of lymphoproliferation, and of IL-2, IFN-gamma, lymphotoxin, and IL-10 cytokine production. Similar results were also found using mouse splenic T cells. Examination of the specificity of TAT-JIP revealed that although the peptide was more selective than the pharmacological inhibitor, SP600125, it also inhibited cyclin-dependent kinase 2, p70 ribosomal protein S6 kinase, and serum and glucocorticoid-regulated kinase activity. Nevertheless, these data demonstrate for the first time the ability of the TAT-JIP peptide to inhibit the JNK pathway and the phosphorylation of jun in intact cells, thereby preventing the activation of the transcription factor, AP-1, and the production of Th1 and Th2 cytokines. Thus JNK could potentially be a target for the development of drugs for the treatment of autoimmune inflammatory diseases.

Different effects of all-trans-retinoic acid on phorbol ester-stimulated and phytohemagglutinin-stimulated interleukin-2 expression in human T-cell lymphoma HUT-78 cells

In view of the importance of vitamin A in the human immune system and the central role of interleukin-2 (IL-2) in the proliferation of T-lymphocytes, we examined the effects of all-trans-retinoic acid (ATRA) on the protein and gene expression of IL-2 in the human T-cell line HUT-78 when stimulated with either 12-O-tetradecanoylphorbol-13-acetate (TPA) or phytohemagglutinin (PHA). ATRA enhanced the production of IL-2 stimulated by TPA, but suppressed that stimulated by PHA. These findings were consistent with the results of a reverse transcription-polymerase chain reaction and quantitative real-time polymerase chain reaction examining IL-2 gene expression. ATRA augmented the gene expression of PKC-beta1 up-regulated by TPA and restored that suppressed by PHA but to below the control level. ATRA suppressed the c-fos gene expression up-regulated by PHA to a level of 36% of the control whereas it had no effect on the up-regulation by TPA. Since PKC- beta1 has been suggested to be important for the secretion and gene expression of IL-2 and since the activator protein-l binding site is present in the promoter of the IL-2 gene, these findings may explain the differences in ATRA's effects on TPA- and PHA-stimulated IL-2 expression. These results suggest that ATRA affects the production of IL-2 by T-lymphocytes in a stimulus-dependent manner.

Foxn1 promotes keratinocyte differentiation by regulating the activity of protein kinase C

The transcription factor Foxn1 (the product of the nude locus) promotes the terminal differentiation of epithelial cells in the epidermis and hair follicles. Activated early in terminal differentiation, Foxn1 can modulate the timing or order of trait acquisition, as it induces early features of epidermal differentiation while suppressing late features. Here, we identify protein kinase C (PKC) as a key target of Foxn1 in keratinocyte differentiation control. Foxn1 has broad negative effects on the PKC family, as the loss of Foxn1 function leads to higher levels of total, primed, and activated PKC. Phosphorylated PKC substrates (the mediators of PKC function) rise when Foxn1 is inactivated and fall when Foxn1 is overproduced, suggesting that Foxn1 antagonizes PKC's effects. When PKC inhibitors are applied to nude (Foxn1 null) keratinocytes, nude defects are normalized or suppressed, as the inhibitors prevent nude cells from underproducing early differentiation markers and overproducing late markers. Taken together, the results suggest that Foxn1 acts as a restraint or brake on PKC signaling and that without this brake PKC disrupts differentiation. The results further suggest that Foxn1 modulates stage-specific markers by modulating PKC activity, providing control over the timing of steps in the differentiation program.

Calreticulin transacetylase (CRTAase): Identification of novel substrates and CRTAase-mediated modification of protein kinase C (PKC) activity in lymphocytes of asthmatic patients by polyphenolic acetates

Earlier reports from our laboratory established the acetyl transferase function of calreticulin (CRT), enabling CRT to transfer acetyl groups from the acetoxy groups of polyphenolic acetates (PAs) to certain receptor proteins. We have in this paper documented the ability of CRT to catalyze the possible transfer of acetyl moiety from 7-acetamido-4-methylcoumarin (7-N-AMC) to the proteins, glutathione S-transferase (GST), and NADPH cytochrome c reductase, leading to the modification of their catalytic activities. 7-Acetoxy-4-methylthiocoumarin (7-AMTC) compared to 7-acetoxy-4-methylcoumarin (7-AMC) when used as a substrate for calreticulin transacetylase (CRTAase) yielded significantly higher catalytic activity. PM3-optimized geometries suggested that the availability of electrons on the sulfur atom of the thiocarbonyl group of the thiocoumarin may render the substrate binding more favorable to the active site of the enzyme as compared to its oxygen analog. Further CRTAase activity was characterized in the human blood lymphocytes. There was no appreciable difference in CRTAase activity of lymphocytes of asthmatic patients as compared to those of normal subjects. The results presented here highlight for the first time the irreversible inhibition of human blood lymphocytes protein kinase C (PKC) by 7,8-diacetoxy-4-methylcoumarin (DAMC) possibly by way of acetylation. The activity of PKC in lymphocytes of asthmatic patients was found to proportionally increase with the severity of the disease. When PA was incubated with lymphocytes of normal patients, PKC was inhibited marginally. On the other hand, lymphocyte PKC of severe asthmatic patients was inhibited drastically. Several PAs inhibited PKC of asthmatic patients in tune with their specificity to CRTAase. DAMC was found to exert maximum inhibitory action on PKC, while 7,8-dihydroxy-4-methylcoumarin (DHMC), the deacetylated product of DAMC, failed to inhibit PKC. These observations clearly describe DAMC as the novel irreversible inhibitor of PKC, and DAMC may be found useful in the control of inflammation and may serve as a potential drug candidate in the therapy of asthma.

Lysophospholipid acyltransferases in monocyte inflammatory responses and sepsis

Acyltransferases are important in the regulation of membrane phospholipid fatty acyl composition and together with phospholipase A2 enzymes control arachidonic acid incorporation and remodelling within phospholipids. In addition, monocyte and macrophage acyltransferase activity has been shown to respond to various inflammatory cytokines under conditions that can induce enhanced cellular responses. Work in our laboratory indicates that the enzyme lysophosphatidylcholine acyltransferase may mediate the priming reactions of monocytes to the cytokine interferon-gamma. Our recent studies suggest that this enzyme might also affect the responses of monocytes to the bacterial agent lipopolysaccharide that may be important in the development of sepsis. This article summarises the relationship between monocyte lysophosphatidylcholine acyltransferase, lipopolysaccharide and sepsis.

Acylation of lysophosphatidylcholine plays a key role in the response of monocytes to lipopolysaccharide

Mononuclear phagocytes play a pivotal role in the progression of septic shock by producing tumor necrosis factor-alpha (TNF-alpha) and other inflammatory mediators in response to lipopolysaccharide (LPS) from Gram-negative bacteria. Our previous studies have shown monocyte and macrophage activation correlate with changes in membrane phospholipid composition, mediated by acyltransferases. Interferon-gamma (IFN-gamma), which activates and primes these cells for enhanced inflammatory responses to LPS, was found to selectively activate lysophosphatidylcholine acyltransferase (LPCAT) (P < 0.05) but not lysophosphatidic acid acyltransferase (LPAAT) activity. When used to prime the human monocytic cell line MonoMac 6, the production of TNF-alpha and interleukin-6 (IL-6) was approximately five times greater in cells primed with IFN-gamma than unprimed cells. Two LPCAT inhibitors SK&F 98625 (diethyl 7-(3,4,5-triphenyl-2-oxo2,3-dihydro-imidazole-1-yl)heptane phosphonate) and YM 50201 (3-hydroxyethyl 5,3'-thiophenyl pyridine) strongly inhibited (up to 90%) TNF-alpha and IL-6 production in response to LPS in both unprimed MonoMac-6 cells and in cells primed with IFN-gamma. In similar experiments, these inhibitors also substantially decreased the response of both primed and unprimed peripheral blood mononuclear cells to LPS. Sequence-based amplification methods showed that SK&F 98625 inhibited TNF-alpha production by decreasing TNF-alpha mRNA levels in MonoMac-6 cells. Taken together, the data from these studies suggest that LPCAT is a key enzyme in both the pathways of activation (priming) and the inflammatory response to LPS in monocytes.

Cyclosporin A-induced hair growth in mice is associated with inhibition of calcineurin-dependent activation of NFAT in follicular keratinocytes

One of the most common side effects of treatment with cyclosporin A (CsA) is hypertrichosis. This study shows that calcineurin activity is associated with hair keratinocyte differentiation in vivo, affecting nuclear factor of activated T cells (NFAT1) activity in these cells. Treatment of nude or C57BL/6 depilated normal mice with CsA inhibited the expression of keratinocyte terminal differentiation markers associated with catagen, along with the inhibition of calcineurin and NFAT1 nuclear translocation. This was associated with induction of hair growth in nude mice and retardation of spontaneous catagen induction in depilated normal mice. Furthermore, calcineurin inhibition blocked the expression of p21(waf/cip1) and p27(kip1), which are usually induced with differentiation. This was also associated with an increase in interleukin-1alpha expression (nude mice), a decrease in transforming growth factor-beta (nude and normal mice), and no change in keratinocyte growth factor expression in the skin. Retardation of catagen in CsA-treated mice was accompanied by significant alterations in apoptosis-related gene product expression in hair follicle keratinocytes. The ratio of the anti-apoptotic Bcl-2 to proapoptotic Bax expression increased, and expression of p53 and interleukin-1beta converting enzyme activity decreased. These data provide the first evidence that calcineurin is functionally active in follicular keratinocytes and that inhibition of the calcineurin-NFAT1 pathway in these cells in vivo by CsA enhances hair growth.

Procyanidin B-2, extracted from apples, promotes hair growth: a laboratory study

BACKGROUND

We have previously reported that several selective protein kinase C (PKC) inhibitors, including procyanidin B-2, promote hair epithelial cell growth and stimulate anagen induction.

OBJECTIVES

We discuss the hypothesis that the hair-growing activity of procyanidin B-2 is related to its downregulation or inhibition of translocation of PKC isozymes in hair epithelial cells.

METHODS

We examined the effect of procyanidin B-2 on the expression of PKC isozymes in cultured murine hair epithelial cells as well as PKC isozyme localization in murine dorsal skin at different stages in the hair cycle.

RESULTS

We observed that procyanidin B-2 reduces the expression of PKC-alpha, -betaI, -betaII and -eta in cultured murine hair epithelial cells and also inhibits the translocation of these isozymes to the particulate fraction of hair epithelial cells. Our immunohistochemical analyses demonstrated that PKC-alpha, -betaI, -betaII and -eta are specifically expressed in the outer root sheaths of both anagen and telogen hair follicles. The hair matrix at the anagen stage showed no positive staining for these PKC isozymes. Moderate to intense staining for PKC-betaI and -betaII in the epidermis and hair follicles was observed in a telogen-specific manner; however, expression of PKC-alpha and -eta during the telogen stage was not conspicuous. Gö 6976, an inhibitor of calcium-dependent (conventional) PKC, proved to promote hair epithelial cell growth.

CONCLUSIONS

These results suggest that PKC isozymes, especially PKC-betaI and -betaII, play an important role in hair cycle progression and that the hair-growing mechanisms of procyanidin B-2 are at least partially related to its downregulation of PKC isozymes or its inhibition of translocation of PKC isozymes to the particulate fraction of hair epithelial cells.

Cyclosporin a promotes hair epithelial cell proliferation and modulates protein kinase C expression and translocation in hair epithelial cells

Cyclosporin A is an immunosuppressive agent known to cause hirsutism. The mechanisms of action that cause hirsutism have not been fully elucidated, however. We have previously reported that several selective protein kinase C inhibitors promote the growth of murine hair epithelial cells and stimulate anagen induction. In this paper, we report on an investigation of the mechanisms of action of hair-growing activity possessed by cyclosporin A from the viewpoint of whether it promotes hair epithelial cell growth or whether it modulates the expression or translocation of protein kinase C isozymes in hair epithelial cells. Our results indicate that cyclosporin A (over a wide dosage range of 1-1000 ng per ml) stimulates cultured murine hair epithelial cell growth to about 150%-160% relative to controls. We also observed growth-promoting effects on murine epidermal keratinocytes (about 140%) at the dose range of 1-100 ng per ml. At high dose ranges above 3 microg per ml, the growth of both cells was inhibited. On the other hand, we found that cyclosporin A reduces the overall expression of protein kinase C alpha, betaI, and betaII in cultured murine hair epithelial cells, and reduces the levels of protein kinase C alpha, betaI, betaII, and eta in the particulate fraction from cultured murine hair epithelial cells. From these results, we speculate that the hair-growing activity of cyclosporin A is at least partially attributable to its growth-promoting influence on hair epithelial cells sequential to its downregulation of some protein kinase C isozymes in hair epithelial cells or inhibition of translocation of some protein kinase C isozymes to the membrane or cytoskeleton of hair epithelial cells.

Cutting edge: protein kinase C beta expression is critical for export of Il-2 from T cells

Protein kinase C (PKC) plays an integral part in T cell activation and IL-2 secretion. We investigated the role of a particular PKC isoform, PKCbeta, in IL-2 production and secretion. The T cell lymphoma line HuT 78 secretes IL-2 in response to the phorbol ester PMA. A PKCbeta-deficient clone of HuT 78, K-4, did not secrete IL-2 in response to PMA stimulation. As assessed by RT-PCR, K-4 expressed mRNA for IL-2 following PMA activation, and intracellular IL-2 protein was detected by immunofluorescence. An enhanced green fluorescent protein-linked PKCbeta construct was microinjected into K-4 cells, which were then stimulated with PMA; those cells that expressed PKCbeta could secrete IL-2, as determined by an in situ immunofluorescent assay. This study demonstrates that PKCbeta is not necessary for transcription of the IL-2 gene or translation of mRNA to protein, but that expression of this PKC isoform is critical to the export of IL-2 molecules from T cells.

Inhibition of protein kinase C alpha expression by antisense RNA in transfected Jurkat cells

Taking the antisense approach to inhibit the expression of specific protein kinase C (PKC) isoforms, we investigated the function of PKC alpha in T cell activation by transfecting Jurkat cells with an episomal vector (pREP3) containing a copy of the corresponding gene in the antisense orientation. Transfected Jurkat cells were selected with hygromycin and cloned by limiting dilution. Two (as1/as2) stably transfected antisense PKC alpha-pREP3 clones (as PKC alpha-pREP3) exhibited consistently reductions (76% and 85%, respectively) of PKC alpha levels when analyzed by immunoblotting and immunoprecipitation and also of PKC alpha mRNA (75%, as determined by Northern blotting) when compared to control clones (C1/C2) containing the pREP3 vector alone. The ability of the as-PKC alpha-pREP3 construct to specifically reduce PKC alpha levels in both clones was demonstrated by Western blots probed with antibodies against the PKC beta isozyme (the form structurally more similar to PKC alpha) and other representative isoenzymes expressed in Jurkat cells (PKC delta, epsilon, theta, and mu). Stimulation of transfected Jurkat clones with phorbol-12-myristate-13 alone or in the presence of ionomycin resulted in significant reduction of IL-2R alpha expression, TNF-alpha production, and the induction of transcriptional activity of a pIL-2/Luc construct in both as PKC alpha-reduced clones. The magnitude of these decrements paralleled the reductions of PKC alpha expression. The loss of the effects in clone as1 after a high number of passages correlated with the recovery of normal levels of PKC alpha protein, suggesting a link between these processes. Thus, the findings of this study demonstrate the essential role that PKC alpha plays in major events of the T lymphocyte activation process.

Involvement of protein kinase C-delta in CD28-triggered cytotoxicity mediated by a human leukaemic cell line YT

Ligation of CD28 molecules expressed on the surface of human leukaemic natural killer-like YT cells triggers intracellular signals leading to cytolysis of target cells expressing CD80 or CD86 molecules. Known intracellular events include tyrosine phosphorylation, activation of phosphatidylinositol 3-kinase, and protein kinase C (PKC). In this study, we report that PKC-delta isoenzyme activity is required for CD28-triggered cytotoxicity mediated by YT cells and we also demonstrate that one of the primary targets of bryostatin 1, a modulator of PKC activity, is PKC-delta. Treatment of YT cells with bryostatin 1 caused degradation of PKC-delta, but not other PKC isoenzymes, and completely blocked the cytolytic activity of YT cells. In addition, PKC-delta-specific antibody introduced into YT cells by electroporation inhibited partially the YT cell-mediated cytotoxicity of B-lymphoblastoid cell line JY. This effect was specific, since addition of anti-PKC-delta antibody-blocking peptide in combination with anti-PKC-delta antibody to YT cells for electroporation, neutralized the effect of this antibody. These results demonstrate that YT cell cytolytic activity is dependent on PKC-delta, which is selectively down-regulated by bryostatin 1.

Different Protein Kinase C Isoenzymes Regulate IL-2 Receptor Expression or IL-2 Synthesis in Human Lymphocytes Stimulated via the TCR

Stimulation of purified human PBL with mAbs raised against the T cell receptor resulted in an immediate and transient activation of protein kinase C-α (PKC-α) and PKC-θ, peaking at 10 min, whereas PKC-β, -δ, and -ε were translocated with a delay of &gt;90 min and remained activated for up to 2 h. To characterize specific functions of distinct PKC isoenzymes, Abs against different PKC isoenzymes were introduced by means of electropermeabilization. Neutralization of PKC-α and -θ resulted in the complete inhibition of IL-2R expression, whereas anti-PKC-β, -δ, and -ε Abs inhibited IL-2 synthesis. Extensive control experiments have shown that neither electropermeabilization nor control Ig influenced PKC activity and cellular functions. Our data thus clearly show that specific PKC isoenzymes regulate different cellular functions in stimulated human lymphocytes.

Linkage of protein kinase C-beta activation and intracellular interleukin-2 accumulation in human naive CD4 T cells

A critical role for protein kinase C (PKC) in signal transduction events has been well established. Moreover, studies of regulation in PKC levels suggest participation in mediating long-term cellular functions. Protein kinase C-beta (PKC-beta) has been reported to be involved in interleukin-2 (IL-2) synthesis in T lymphocytes. In this study, the role of PKC-beta in intracellular accumulation of IL-2 was investigated using specific inhibitors. Preincubation with two different PKC inhibitors, one specific for classical isotypes (alpha and beta I) Go6976, and one which inhibits both classical and non-classical isotypes, GF109203X, caused a complete block in cytoplasmic IL-2 accumulation when naive CD4 T cells were stimulated in the presence of CD2+CD28+phorbol myristate acetate (PMA). In contrast, preincubation with up to 1000 ng/ml of cyclosporin A (CsA) resulted in a reduction in the intracellular IL-2 detected, as observed by a decrease in the proportion of positive cells as well as a fall in the mean fluorescence intensity (MFI). CsA did not influence PKC-beta translocation. Flow cytometric assessments of PKC-beta and its isoforms beta I and beta II correlated with Western blotting analysis and these results were further supported by the use of PKC-beta-positive (HUT 78) and -negative (BW5147) T-cell lines. Using the specific inhibitors, Go6976 and GF109203X, the findings in this study suggest that activation and translocation of PKC-beta is critical for accumulation of intracellular IL-2. The influence of CsA in reducing but not blocking IL-2 synthesis is discussed. PMA-induced down-regulation of the CD4 antigen was observed in the presence of Go6976 and but not GF109203X, suggesting regulation by non-classical PKC isoforms.

Monochloramine inhibits phorbol ester-inducible neutrophil respiratory burst activation and T cell interleukin-2 receptor expression by inhibiting inducible protein kinase C activity

Monochloramine derivatives are long lived physiological oxidants produced by neutrophils during the respiratory burst. The effects of chemically prepared monochloramine (NH2Cl) on protein kinase C (PKC) and PKC-mediated cellular responses were studied in elicited rat peritoneal neutrophils and human Jurkat T cells. Neutrophils pretreated with NH2Cl (30-50 microM) showed a marked decrease in the respiratory burst activity induced by phorbol 12-myristate 13-acetate (PMA), which is a potent PKC activator. These cells, however, were viable and showed a complete respiratory burst upon arachidonic acid stimulation, which induces the respiratory burst by a PKC-independent mechanism. The NH2Cl-treated neutrophils showed a decrease in both PKC activity and PMA-induced phosphorylation of a 47-kDa protein, which corresponds to the cytosolic factor of NADPH oxidase, p47(phox). Jurkat T cells pretreated with NH2Cl (20-70 microM) showed a decrease in the expression of the interleukin-2 receptor alpha chain following PMA stimulation. This was also accompanied by a decrease in both PKC activity and nuclear transcription factor-kappaB activation, also without loss of cell viability. These results show that NH2Cl inhibits PKC-mediated cellular responses through inhibition of the inducible PKC activity.

A human cDNA sequence with homology to non-mammalian lysophosphatidic acid acyltransferases

A novel human homologue of Escherichia coli, yeast and plant 1-acylglycerol-3-phosphate acyltransferase has been isolated from U937 cell cDNA. Expression of the cloned sequence in 1-acylglycerol-3-phosphate acyltransferase-deficient E. coli resulted in increased incorporation of oleic acid into cellular phospholipids. Membranes made from COS7 cells transfected with the cDNA exhibited higher acyltransferase activity towards a range of donor fatty acyl-CoAs and lysophosphatidic acid. Northern-blot analysis of the cDNA sequence indicated high levels of expression in immune cells and epithelium. Rapid amplification of cDNA ends revealed differentially expressed splice variants, which suggests regulation of the enzyme by alternative splicing. This cDNA therefore represents the first described sequence of a mammalian gene homologous to non-mammalian lysophosphatidic acid acyltransferases.

T cell antigen receptor dependent signalling in human lymphocytes: cholera toxin inhibits interleukin-2 receptor expression but not interleukin-2 synthesis by preventing activation of a protein kinase C isotype, PKC-alpha

Activation and translocation of protein kinases C is a key event in the regulation of T lymphocyte activation, proliferation and function. Stimulation of human peripheral blood lymphocytes with the monoclonal antibody BMA 031 raised against the T cell antigen receptor led to a bimodal activation of protein kinases C. The immediate activation and translocation of the protein kinase C isoform PKC-alpha was followed by activation and translocation of the protein kinase C-beta isoenzyme after 90 min of stimulation. Pretreatment of the cells with cholera toxin for 90 min completely abolished activation of protein kinase C-alpha. In sharp contrast, activation and translocation of protein kinase C-beta was not influenced by the bacterial toxin, suggesting that activation and translocation of different protein kinase C isoenzymes are regulated by distinct mechanisms of transmembrane signalling coupled to the T cell antigen receptor/CD3 complex. The expression of high affinity IL-2 receptors was completely inhibited by cholera toxin, while IL-2 synthesis and secretion were not influenced in BMA 031-stimulated human lymphocytes. Extensive control experiments have shown that the effects of cholera toxin were not mediated by its B subunit, and were independent of elevation of intracellular cAMP concentration, suggesting that cholera toxin interfered with a signalling pathway leading to activation of protein kinase C-alpha, which could be responsible for the inhibition of IL-2 receptor expression. This hypothesis was substantiated by the finding that upon introduction of antibodies against protein kinase C-alpha, IL-2 receptor gene expression was completely suppressed. The results suggest, that protein kinase C-alpha might be the major protein kinase C isoenzyme of a signal transduction cascade regulating IL-2 receptor expression in stimulated human lymphocytes.

Regulated expression of telomerase activity in human T lymphocyte development and activation

Telomerase, a ribonucleoprotein that is capable of synthesizing telomeric repeats, is expressed in germline and malignant cells, and is absent in most normal human somatic cells. The selective expression of telomerase has thus been proposed to be a basis for the immortality of the germline and of malignant cells. In the present study, telomerase activity was analyzed in normal human T lymphocytes. It was found that telomerase is expressed at a high level in thymocyte subpopulations, at an intermediate level in tonsil T lymphocytes, and at a low to undetectable level in peripheral blood T lymphocytes. Moreover, telomerase activity is highly inducible in peripheral T lymphocytes by activation through CD3 with or without CD28 costimulation, or by stimulation with phorbol myristate acetate (PMA)/ionomycin. The induction of telomerase by anti-CD3 plus anti-CD28 (anti-CD3/CD28) stimulation required RNA and protein synthesis, and was blocked by herbimycin A, an inhibitor of S pi protein tyrosine kinases. The immunosuppressive drug cyclosporin A selectively inhibited telomerase induction by PMA/ionomycin and by anti-CD3, but not by anti-CD3/CD28. Although telomerase activity in peripheral T lymphocytes was activation dependent and correlated with cell proliferation, it was not cell cycle phase restricted. These results indicate that the expression of telomerase in normal human T lymphocytes is both developmentally regulated and activation induced. Telomerase may thus play a permissive role in T cell development and in determining the capacity of lymphoid cells for cell division and clonal expansion.

Diacylglycerol and ceramide kinetics in primary cultures of activated T-lymphocytes

T cell activation results in the generation of diacylglycerol (DAG), the physiological activator of protein kinase C. Recently, ceramide, a bioactive lipid intracellular second messenger, has been shown to play a positive role in T cell proliferation. Most studies examining mitogen induction of DAG and ceramide in T cells have been conducted in cell lines over short periods of time (0-30 min) relative to the 2-3-h time frame required for commitment to proliferation. Therefore, we examined T cell mitogen-induced DAG and ceramide kinetics under physiologically relevant conditions during the initial 2 h of culture. Freshly isolated murine splenic lymphocytes were stimulated with the T cell-specific mitogen, concanavalin A (Con A). Our results show that Con A induced a multiphasic DAG response with significant peaks in DAG mass occurring at 2, 20 and 120 min. Concomitantly, ceramide mass was significantly increased 2 min following Con A addition and remained elevated until 120 min. Addition of C8-ceramide (10 microM) to lymphocyte cultures significantly enhanced mitogen-induced proliferation. These results demonstrate that DAG is continuously produced by activated T lymphocytes in a multiphasic fashion, and that ceramide is a positive effector molecule with respect to murine T cell proliferation. These results establish a foundation for further examination of the relationship between DAG, ceramide and T cell activation.

Anti-CD3-induced changes in protein kinase C isozymes expression in human CD4+ and CD8+ T lymphocytes

In order to determine whether there is a differential expression and activation of PKC isozymes between CD4+ and CD8+ T cells, peripheral blood mononuclear cells were stimulated with anti-CD3 monoclonal antibody (moAb) for various time intervals and the expression of calcium-dependent PKC isozymes (alpha, beta, gamma) and calcium-independent PKC isozymes (delta, epsilon, zeta) was analyzed with dual color flow cytometry, using anti-PKC isozyme antibodies and anti-CD4 or anti-CD8 antibodies. The basal fluorescence intensity of all PKC isozymes was comparable between CD4+ T cells and CD8+ T cells. Following activation with anti-CD3 moAb a marked increase in the fluorescence intensity of all PKC isozymes in both CD4+ and CD8+ T cells, albeit to a different extent and with different kinetics was observed. Among all PKC isozymes studied, the least striking changes were observed in PKC zeta isozyme and the most striking changes were observed in PKC-epsilon isozyme. Laser-based confocal microscopic studies confirmed that the increase in fluorescence intensity of PKC isozymes following anti-CD3 moAb stimulation, as measured by flow cytometry was accompanied by the translocation of PKC isozymes from cytosol to the plasma membrane. This study demonstrates a differential effect of anti-CD3 moAb on the expression of PKC isozymes between CD4+ and CD8+ T cells and suggests that flow cytometry can be used to study the translocation of PKC isozymes from cytosol to the plasma membrane.

Induction of the increased Fyn kinase activity in anergic T helper type 1 clones requires calcium and protein synthesis and is sensitive to cyclosporin A

Several alterations in T cell receptor-associated signal transduction have been observed following induction of anergy of T helper type 1 (Th1) clones, including a modified intracellular free calcium ([Ca2+]i) response and increased kinase activity associated with the protein tyrosine kinase p59fyn. In the current study, we demonstrate that, although the kinetics of acquisition of both of these signaling alterations correlated with the generation of anergy, a normal calcium response returned within 48 h after removal from the anergizing stimulus, whereas the increased p59fyn activity persisted and the cells remained hyporesponsive. Generation of both the anergic state and the increased p59fyn activity was prevented in the presence of calcium-free medium, cycloheximide (CHX), or cyclosporin A (CsA), and could be mimicked by the calcium ionophore ionomycin. In contrast, the altered calcium response was inhibited by stimulation in the presence of calcium-free medium or CsA, but not CHX. Thus, surprisingly, these data suggest that a chronic elevation of [Ca2+]i is proximal to and necessary for the increase in p59fyn-associated kinase activity observed in anergic Th1 clones. Increased p59fyn activity, but not the altered calcium response, correlates with maintenance of the anergic state.

Differential signal transduction pathways regulating interleukin-2 synthesis and interleukin-2 receptor expression in stimulated human lymphocytes

In human peripheral blood lymphocytes stimulated via the T-cell antigen receptor/CD3 complex IL-2 synthesis and cellular proliferation were effectively inhibited by a concentration of ouabain as low as 50 nM, whilst the expression of high affinity IL-2 receptors was not influenced. Binding of the monoclonal antibody, BMA 031 to the T-cell antigen receptor/CD3 complex resulted in a bimodal activation of protein kinase C. The activation of protein kinase C-alpha in the early phase of T-lymphocyte activation was not affected by 50 nM ouabain, in contrast sustained activation of protein kinase C-beta, between 90-240 min of stimulation was completely abolished by the cardiac glycoside. When protein kinase C was directly activated by PMA + ionomycin, 50 nM ouabain was ineffective in inhibiting protein kinase C activation, as well as subsequent IL-2 synthesis, suggesting that the glycoside interfered with signal transducing mechanism(s) upstream of the activation of protein kinase C. Ouabain had no influence on the elevation of intracellular calcium concentration in BMA 031 stimulated lymphocytes, ruling out the possibility that it interfered with the T-cell antigen receptor dependent phosphatidylinositol response. In contrast, lysophosphatide acyltransferase catalysed elevated incorporation of polyunsaturated fatty acids was effectively inhibited by low concentrations of ouabain in BMA 031-stimulated T-lymphocytes, whereas stimulation with PMA + ionomycin had no influence on the plasma membrane phospholipid fatty acid metabolism. These results suggest, that differential signal transduction pathways are involved in the activation of protein kinases C-alpha and -beta. They implicate that elevated incorporation of polyunsaturated fatty acids into plasma membrane phospholipids might contribute to sustained activation of protein kinase C-beta, and establish a link between activation of protein kinase C-beta and induction of IL-2 synthesis in human lymphocytes.

T-cell antigen receptor-induced signal-transduction pathways--activation and function of protein kinases C in T lymphocytes

CONTENTS. T-cell activation--Structure of the T-cell antigen receptor--Modular organisation of the T-cell antigen receptor--T-cell antigen receptor-coupled signaling pathways: Activation of protein-tyrosine kinase by the T-cell antigen receptor; Signal transduction in lymphoid cells involves several protein-tyrosine kinases in parallel; Regulation of T-cell antigen receptor signaling by the phosphoprotein phosphatase CD45--Consequences of T-cell antigen receptor-induced tyrosine phosphorylation: Activation of phosphoinositol-lipid-turnover pathways--Activation of phospholipase C-gamma-1: p59fyn or p56lck?--G-protein motif of CD3-gamma: relevance for signal transduction--Association of lipid kinase with the T-cell antigen receptor--Intracellular signaling by phospholipid metabolites and calcium: activation of protein kinase C--Protein kinase C isoenzymes--Heterogenity of protein kinase C and mode of activation--Phospholipid-derived mediators in activation of protein kinase C in T-cells--Role of phospholipase D metabolites in activation of protein kinase C--Polyunsaturated fatty acids and lysophosphatidylcholine as activators of protein kinase C--Potein kinase C and p21ras function in interdependent and distinct signaling pathways during T-cell activation--Raf-1 kinase: regulator or target of protein kinase C?--Summary and perspectives.

Evidence that inhibition of phorbol ester-induced superoxide anion formation by cyclosporin A in phagocytes is not mediated by direct inhibition of protein kinase C

Cyclosporin A (CsA) has been reported to inhibit phorbol myristate acetate (PMA)-induced superoxide anion (O2-) formation in human neutrophils and murine macrophages. We found that CsA inhibited O2- formation in HL-60 cells induced by PMA (30 nM) and phorbol dibutyrate (200 nM) with a half-maximal effect at 1 and 0.75 microM, respectively. One possible target of CsA action is protein kinase C (PKC) [EC 2.7.1.37] since phorbol esters activate this kinase. However, CsA did not inhibit PMA-mediated reduction of histamine-induced rises in cytosolic Ca2+ concentration in, and PMA-induced differentiation of, HL-60 cells and platelet aggregation. CsA did not reduce the activity of various recombinant c-PKC isoenzymes (alpha, beta 1 and gamma), n-PKC isoenzymes (delta and epsilon), an a-PKC isoenzyme (zeta) nor of PKC purified from rat brain in vitro. These data show that CsA inhibits phorbol ester-induced O2- formation in HL-60 cells but not other phorbol ester-mediated events and that inhibition by CsA of O2- formation cannot readily be attributed to direct PKC inhibition. We also show that CsA does not change the activity of nucleoside diphosphate kinase [EC 2.7.4.6] in HL-60 membranes nor the latter's physical properties.

12-Deoxyphorbol-13-O-phenylacetate 20 acetate [an agonist of protein kinase C beta 1 (PKC beta 1)] induces DNA synthesis, interleukin-2 (IL-2) production, IL-2 receptor alpha-chain (CD25) and beta-chain (CD122) expression, and translocation of PKC beta isozyme in human peripheral blood lymphocytes: evidence for a role of PKC beta 1 in human T cell activation

To determine a role of protein kinase C (PKC) isozymes in lymphocyte activation, human peripheral blood mononuclear cells were activated with 12-deoxyphorbol-13-O-phenylacetate (dPP; an agonist of both calcium-dependent and calcium-independent PKC isozymes), thymeleatoxin (TX; an activator of calcium-dependent PKC alpha, beta, and gamma), and 12-deoxyphorbol-13-O-phenylacetate 20 acetate (dPPA; an activator of PKC beta 1 isozyme) and examined for DNA synthesis, lymphocyte proliferation, interleukin-2 (IL-2) production, expression of IL-2 receptor alpha and beta chains on CD3+, CD4+, and CD8+ T lymphocytes and CD20+ B lymphocytes, and translocation of PKC beta isozyme from cytosol to membrane fraction. The results show that dPPA activates lymphocytes by inducing the above changes in a manner analogous to that of dPP, TX, and phorbol myristate acetate. These data suggest that PKC beta 1 is involved in the activation of human peripheral blood T and B lymphocytes.