Protein kinase C and T cell function

The role of PKC and PKD in CXCL12 and CXCL13 directed malignant melanoma and acute monocytic leukemic cancer cell migration

Cancer metastasis is the leading cause of cancer related mortality. Chemokine receptors and proteins in their downstream signalling axis represent desirable therapeutic targets for the prevention of metastasis. Despite this, current therapeutics have experienced limited success in clinical trials due to a lack of insight into the downstream signalling pathway of specific chemokine receptor cascades in different tumours. In this study, we investigated the role of protein kinase C (PKC) and protein kinase D (PKD) in CXCL12 and CXCL13 stimulated SK-MEL-28 (malignant melanoma) and THP-1 (acute monocytic leukaemia) cell migration. While PKC and PKD had no active role in CXCL12 or CXCL13 stimulated THP-1 cell migration, PKC and PKD inhibition reduced CXCL12 stimulated migration and caused profound effects upon the cytoskeleton of SK-MEL-28 cells. Furthermore, only PKC and not PKD inhibition reduced CXCL13 stimulated migration in SK-MEL-28 cells however PKC inhibition failed to stimulate any changes to the actin cytoskeleton. These findings indicate that PKC inhibitors would be a useful therapeutic for the prevention of both CXCL12 and CXCL13 stimulated migration and PKD inhibitors for CXCL12 stimulated migration in malignant melanoma.

Major depressive disorder (mdd): emerging immune targets at preclinical level

BACKGROUND

Major depressive disorder is a mental health disorder that is characterized by a persistently low mood and loss of interest. MDD is affecting over 3.8% of the global population as a major health problem. Its etiology is complex, and involves the interaction between a number of factors, including genetic predisposition and the presence of environmental stresses.

AREAS COVERED

The role of the immune and inflammatory systems in depression has been gaining interest, with evidence suggesting the potential involvement of pro-inflammatory molecules like TNF, interleukins, prostaglandins, and other cytokines, among others, has been put forth. Along with this, the potential of agents, from NSAIDs to antibiotics, are being evaluated in therapy for depression. The current review will discuss emerging immune targets at the preclinical level.

EXPERT OPINION

With increasing evidence to show that immune and inflammatory mediators are implicated in MDD, increasing research toward their potential as drug targets is encouraged. At the same time, agents acting on these mediators and possessing anti-inflammatory potential are also being evaluated as future therapeutic options for MDD, and increasing focus toward non-conventional drugs which can act through these mechanisms is important as regards the future prospects of the use of anti-inflammatory agents in depression.

Phosphorylation of plant virus proteins: Analysis methods and biological functions

Phosphorylation is one of the most extensively investigated post-translational modifications that orchestrate a variety of cellular signal transduction processes. The phosphorylation of virus-encoded proteins plays an important regulatory role in the infection cycle of such viruses in plants. In recent years, molecular mechanisms underlying the phosphorylation of plant viral proteins have been widely studied. Based on recent publications, our study summarizes the phosphorylation analyses of plant viral proteins and categorizes their effects on biological functions according to the viral life cycle. This review provides a theoretical basis for elucidating the molecular mechanisms of viral infection. Furthermore, it deepens our understanding of the biological functions of phosphorylation in the interactions between plants and viruses.

Role of 5-HT2 and 5-HT7 Serotonin Receptors, and Protein Kinases C and A on Taurine Transport in Lymphocytes of Rats Treated with Fluoxetine

Fluoxetine, an antidepressant and selective serotonin reuptake inhibitor, modulates immune cells in vitro. The present study investigates the influence of pharmacological agents which acts as agonist and antagonist of serotonin receptors ex vivo over taurine transport in lymphocytes of rats treated with fluoxetine by one week. The treatment with fluoxetine increase taurine transport and the incubation with the agonist of 5-HT2 receptor, 1-(2,5-dimethoxy-4-iodophenyl)-​2-aminopropane (DOI) counteract this effect, and ketanserin provoked no change in fluoxetine effect. While the agonist of 5-HT7 receptor, 4-[2-(methylthio)phenyl]-N-(1,2,3,4-tetrahydro-1-naphth alenyl)-1-piperazinehexanamide hydrochloride (LP44) had no significant effects, however the differences between Control and Fluoxetine groups were not observed, the antagonist (R)-3-[2-[2-(4-methylpiperidin-1-yl)ethyl]pyrrolidine-1-sulfonyl]phenol hydrochloride (SB269970) had no differences. Preincubation of cells with the diacylglycerol analogue, 1-oleoyl-2-acetyl-sn-glycerol (OAG) caused inhibition of fluoxetine treatment effect but this not occurred in presence of the PKC inhibitor, 1-O-hexadecyl-2-O-methyl-rac-glycerol (AMG-C16). Forskolin counteracted the effect of fluoxetine on taurine transport, since at the concentrations used, the rate of taurine transport in Fluoxetine group, returned to Control rate. No significant differences were observed with the PKA inhibitor. Although it is not possible to attribute a definitive role of 5-HT2 receptors in fluoxetine effect on taurine transport, its signaling might affect the function of it. Participation of PKC and PKA have an apparently relevant role in lymphocyte taurine transport.

Protein kinase C in the immune system: from signalling to chromatin regulation

Protein kinase C (PKC) form a key family of enzymes involved in signalling pathways that specifically phosphorylates substrates at serine/threonine residues. Phosphorylation by PKC is important in regulating a variety of cellular events such as cell proliferation and the regulation of gene expression. In the immune system, PKCs are involved in regulating signal transduction pathways important for both innate and adaptive immunity, ultimately resulting in the expression of key immune genes. PKCs act as mediators during immune cell signalling through the immunological synapse. PKCs are traditionally known to be cytoplasmic signal transducers and are well embedded in the signalling pathways of cells to mediate the cells' response to a stimulus from the plasma membrane to the nucleus. PKCs are also found to transduce signals within the nucleus, a process that is distinct from the cytoplasmic signalling pathway. There is now growing evidence suggesting that PKC can directly regulate gene expression programmes through a non-traditional role as nuclear kinases. In this review, we will focus on the role of PKCs as key cytoplasmic signal transducers in immune cell signalling, as well as its role in nuclear signal transduction. We will also highlight recent evidence for its newly discovered regulatory role in the nucleus as a chromatin-associated kinase.

Multi-layered epigenetic mechanisms contribute to transcriptional memory in T lymphocytes

Background

Immunological memory is the ability of the immune system to respond more rapidly and effectively to previously encountered pathogens, a key feature of adaptive immunity. The capacity of memory T cells to “remember” previous cellular responses to specific antigens ultimately resides in their unique patterns of gene expression. Following re-exposure to an antigen, previously activated genes are transcribed more rapidly and robustly in memory T cells compared to their naïve counterparts. The ability for cells to remember past transcriptional responses is termed “adaptive transcriptional memory”.

Results

Recent global epigenome studies suggest that epigenetic mechanisms are central to establishing and maintaining transcriptional memory, with elegant studies in model organisms providing tantalizing insights into the epigenetic programs that contribute to adaptive immunity. These epigenetic mechanisms are diverse, and include not only classical acetylation and methylation events, but also exciting and less well-known mechanisms involving histone structure, upstream signalling pathways, and nuclear localisation of genomic regions.

Conclusions

Current global health challenges in areas such as tuberculosis and influenza demand not only more effective and safer vaccines, but also vaccines for a wider range of health priorities, including HIV, cancer, and emerging pathogens such as Ebola. Understanding the multi-layered epigenetic mechanisms that underpin the rapid recall responses of memory T cells following reactivation is a critical component of this development pathway.

A novel PKC regulates ERK activation and degranulation of cytotoxic T lymphocytes: Plasticity in PKC regulation of ERK

Stimulation of cytotoxic T lymphocyte (CTL) degranulation with plate-bound anti-CD3 Ab leads to two phases of ERK activation: an early PKC-independent phase followed by a later sustained PKC-dependent phase. Herein, we show that a novel PKC (nPKC) mediates the late phase of ERK activation, upstream of Ras in murine T cells. In contrast, when CTL are activated with cross-linked anti-CD3 Ab, which does not trigger CTL degranulation, there is a requirement for conventional PKC (cPKC) for ERK activation. We detect increased novel PKCtheta activation only when CTL are stimulated with plate-bound Ab and not cross-linked Ab. Interestingly, in T cells from mice lacking PKCtheta, sustained ERK activation requires the activity of cPKC, implying that PKCtheta is required for the nPKC pathway that normally mediates sustained ERK activation. CTL lines derived from PKCtheta-deficient mice degranulate and activate ERK normally, and exhibit altered expression of PKC isozymes, which may compensate for the loss of PKCtheta. Taken together, these data demonstrate that normally an nPKC participates in the sustained activation of ERK. However, if the nPKC pathway is compromised, alternate PKC pathways can compensate, suggesting that considerable plasticity exists with respect to PKC regulation of ERK activation in T cells.

Protein kinase C plays an essential role in sildenafil-induced cardioprotection in rabbits

Sildenafil citrate (Viagra) is the most widely used pharmacological drug for treating erectile dysfunction in men. It has potent cardioprotective effects against ischemia-reperfusion injury via nitric oxide and opening of mitochondrial ATP-sensitive K(+) channels. We further investigated the role of protein kinase C (PKC)-dependent signaling pathway in sildenafil-induced cardioprotection. Rabbits were treated (orally) with sildenafil citrate (1.4 mg/kg) 30 min before index ischemia for 30 min and reperfusion for 3 h. The PKC inhibitor chelerythrine (5 mg/kg i.v.) was given 5 min before sildenafil. Infarct size (% of risk area) reduced from 33.65 +/- 2.17 in the vehicle (saline) group to 15.07 +/- 0.63 in sildenafil-treated groups, a 45% reduction compared with vehicle (mean +/- SE, P < 0.05). Chelerythrine abolished sildenafil-induced protection, as demonstrated by increase in infarct size to 31.14 +/- 2.4 (P < 0.05). Chelerythrine alone had an infarct size of 33.5 +/- 2.5, which was not significantly different compared with DMSO-treated group (36.8 +/- 1.7, P > 0.05). Western blot analysis demonstrated translocation of PKC-alpha, -, and -delta isoforms from cytosol to membrane after treatment with sildenafil. However, no change in the PKC-beta and -epsilon isoforms was observed. These data provide direct evidence of an essential role of PKC, and potentially PKC-alpha, -, and -delta, in sildenafil-induced cardioprotection in the rabbit heart.

Effects of conjugated linoleic acid on growth and cytokine expression in Jurkat T cells

Conjugated linoleic acid (CLA) has shown beneficial properties in animal models including anti-cancer, anti-atherogenic and anti-diabetic effects, while contrasting immunological effects were reported. While its anti-inflammatory activity has been associated to inhibition of arachidonic acid biosynthesis and to peroxisome proliferator-activated receptors (PPARs) activity, the molecular pathways underlying its immunoenhancing activity are essentially unknown. The aim of our study was to examine whether CLA showed specific effects in vitro on a T cell model, represented by the Jurkat cell line. CLA was found non toxic for Jurkat in the range 50-200 microM, as assessed by LDH release; however, incubation with 50 microM CLA was associated to a significant inhibitory effect on cell proliferation. The analysis of IL-2 and IFN-gamma transcript levels, produced in stimulated Jurkat cells, showed an increased expression of both cytokines in CLA-treated cells. Interestingly, the increased induction of IL-2 but not of IFN-gamma mRNA, could be suppressed by co-incubation with Gö 6976, a protein kinase C (PKC) inhibitor. Co-incubation with superoxide dismutase (SOD) or N-acetyl-L-cysteine (NAC) restored the basal levels of RNA synthesis for both cytokines. Taken together, these results suggest a specific role for dietary CLA in the modulation of the immune response in a T cell line model that is mediated, at least in part, by PKC and through the production of oxidative molecules.

Catecholamine production and tyrosine hydroxylase expression in peripheral blood mononuclear cells from multiple sclerosis patients: effect of cell stimulation and possible relevance for activation-induced apoptosis

Sympathoadrenergic mechanisms may play a role in multiple sclerosis (MS). We examined catecholamine (CA) levels and production and tyrosine hydroxylase (TH) expression in peripheral blood mononuclear cells (PBMCs) from MS patients, and the correlation between CA production and apoptosis in PBMCs. PBMCs from MS patients had increased norepinephrine (NE) levels. However, phytohaemagglutinin (PHA)-stimulated PBMCs from MS patients with active disease synthesized less dopamine (DA) than cells from both healthy controls and patients with inactive disease. PBMCs from patients with inactive disease showed lower expression of TH. Pharmacological inhibition of TH in cultured PBMCs stimulated with PHA reduced the percentage of apoptotic cells. Since a failure of activation-induced apoptosis in immune cells may be involved in MS, it is suggested that altered CA production by PBMCs may be implicated in such dysregulation.

Activation of protein kinase C isozymes in primary mouse myotubes by carbachol

The activation of muscle PKC isozymes following treatment with carbachol, an acetylcholine receptor agonist, has been investigated. Primary mouse myotubes were treated with carbachol, and protein extracts from the cytosol and membrane fractions of the myotubes were subjected to Western blot analyses. Carbachol treatment resulted in a rapid translocation of PKC-theta; to the membrane. This effect was dependent on both carbachol concentration and incubation time. The treatment also resulted in a drastic increase of PKC-alpha in the cytosol followed by an increase of PKC-alpha in the membrane. The regulation of PKC-alpha in response to carbachol was quite distinct from that produced by the PKC activator, PMA, which rapidly translocated PKC-alpha from the cytosol to the membrane without any increases in PKC-alpha in the cytosol. Confocal microscopy demonstrated an enhanced membrane localization of PKC-theta; and overall increased intensity of PKC-alpha staining in the cytosol accompanied by a characteristic membrane staining of PKC-alpha in the myotubes treated with carbachol. Taken together, the results suggested that the activation of PKC isozymes in response to the receptor agonist is quite distinct, which indicates their diverse role in the muscle upon the release of neurotransmitter at the neuromuscular junction.

Regulation of retinoid X receptor responsive element-dependent transcription in T lymphocytes by Ser/Thr phosphatases: functional divergence of protein kinase C (PKC)theta; and PKC alpha in mediating calcineurin-induced transactivation

T lymphocyte activation signals regulate the expression and transactivation function of retinoid X receptor (RXR) alpha through an interplay of complex signaling cascades that are not yet fully understood. We show that cellular Ser/Thr protein phosphatases (PPs) play an important role in mediating these processes. Inhibitors specific for PP1 and PP2A decreased basal expression of RXR alpha RNA and protein in T lymphocyte leukemia Jurkat cells and prevented activation-induced RXR alpha accumulation in these cells. In addition, these inhibitors attenuated the RXR responsive element (RXRE)-dependent transcriptional activation in transient transfection assays. Inhibitors of calcineurin (CN), by contrast, did not have any effect on the basal RXR alpha expression and even augmented activation-induced RXR alpha expression. Expression of a dominant-active (DA) mutant of CN together with a DA mutant of protein kinase C (PKC)theta;, a novel PKC isoform, significantly increased RXRE-dependent transcription. Expression of catalytically inactive PKC theta; or a dominant-negative mutant of PKC theta; failed to synergize with CN and did not increase RXRE-dependent transcription. Expression of a DA mutant of PKC alpha or treatment with PMA was found to attenuate PKC theta; and CN synergism. We conclude that PP1, PP2A, and CN regulate levels and transcriptional activation function of RXR alpha in T cells. In addition, CN synergizes with PKC theta; to induce RXRE-dependent activation, a cooperative function that is antagonized by the activation of the conventional PKC alpha isoform. Thus, PKC theta; and PKC alpha may function as positive and negative modulators, respectively, of CN-regulated RXRE-dependent transcription during T cell activation.

Protein kinase C-theta participates in the activation of cyclic AMP-responsive element-binding protein and its subsequent binding to the -180 site of the IL-2 promoter in normal human T lymphocytes

IL-2 gene expression is regulated by the cooperative binding of discrete transcription factors to the IL-2 promoter/enhancer and is predominantly controlled at the transcriptional level. In this study, we show that in normal T cells, the -180 site (-164/-189) of the IL-2 promoter/enhancer is a p-cAMP-responsive element-binding protein (p-CREB) binding site. Following activation of the T cells through various membrane-initiated and membrane-independent pathways, protein kinase C (PKC)-theta phosphorylates CREB, which subsequently binds to the -180 site and associates with the transcriptional coactivator p300. Rottlerin, a specific PKC-theta inhibitor, diminished p-CREB protein levels when normal T cells were treated with it. Rottlerin also prevented the formation of p-CREB/p300 complexes and the DNA-CREB protein binding. Cotransfection of fresh normal T cells with luciferase reporter construct driven by two tandem -180 sites and a PKC-theta construct caused a significant increase in the transcription of the reporter gene, indicating that this site is functional and regulated by PKC-theta. Cotransfection of T cells with a luciferase construct driven by the -575/+57 region of the IL-2 promoter/enhancer and a PKC-theta construct caused a similar increase in the reporter gene transcription, which was significantly limited when two bases within the -180 site were mutated. These findings show that CREB plays a major role in the transcriptional regulation of IL-2 and that a major pathway for the activation of CREB and its subsequent binding to the IL-2 promoter/enhancer in normal T cells is mediated by PKC-theta.

Bruton's tyrosine kinase (Btk) associates with protein kinase C mu

Bruton's tyrosine kinase (Btk) is considered an essential signal transducer in B-cells. Mutational defects are associated with a severe immunodeficiency syndrome, X-chromosome linked agammaglobulinemia (XLA). Here we show by coimmunoprecipitation that a member of the protein kinase C (PKC) family, PKCmu, is constitutively associated with Btk. Neither antigen receptor (Ig) crosslinking nor stimulation of B-cells with phorbol ester or H(2)O(2) affected Btk/PKCmu interaction. GST precipitation analysis revealed association of the Btk pleckstrin/Tec homology domain with PKCmu. Transient overexpression of PKCmu deletion mutants as well as expression of selected PKCmu domains in 293T cells revealed that both the kinase domain and the regulatory C1 region are independently capable of binding to the Btk PH-TH domain. These data show the existence of a PKCmu/Btk complex in vivo and identify two PKCmu domains that participate in Btk interaction.

Role of protein kinase C in signal attenuation following T cell receptor engagement

T lymphocyte activation through stimulation of the T cell receptor complex and co-stimulatory receptors is associated with acute tyrosine phosphorylation of intracellular proteins, which in turn mediate downstream signaling events that regulate interleukin-2 expression and cell proliferation. The extent of protein tyrosine phosphorylation is rapidly attenuated after only 1-2 min of stimulation as a means of tightly controlling the initial signaling response. Here we show that this attenuation of tyrosine phosphorylation of Shc, CrkL, and the proto-oncogene Cbl is mimicked by treatment of mouse T lymphocytes or cultured Jurkat cells with phorbol 12-myristate 13-acetate. This effect is blocked by the specific protein kinase C inhibitor GF109203X, but not by PD98059, an inhibitor of MEK1/2 kinase. Activation of protein kinase C by phorbol ester also causes rapid (t(1)/(2) = 2 min) dissociation of both CrkL and p85/phosphoinositide 3-kinase from Cbl concomitant with Cbl tyrosine dephosphorylation. More important, GF109203X treatment of Jurkat cells prior to T cell receptor stimulation by anti-CD3/CD4 antibodies results in an enhanced (2-fold) peak of Cbl phosphorylation compared with that observed in control cells. Furthermore, the rate of attenuation of both Cbl tyrosine phosphorylation and its association with CrkL following stimulation with anti-CD3/CD4 antibodies is much slower in Jurkat cells treated with GF109203X. Taken together, these data provide strong evidence that one or more isoforms of phorbol ester-responsive protein kinase C play a key role in a feedback mechanism that attenuates tyrosine phosphorylation of proteins and reverses formation of signaling complexes in response to T cell receptor activation.

Cluster formation by protein kinase Ctheta during murine T cell activation: effect of age

Protein kinase Ctheta; (PKCtheta;) is thought to play an important role in T cell activation, in that exposure of cloned T cells to antigen-presenting cells bearing agonist peptides, but not antagonist peptides, leads to clustering of PKCtheta; molecules in the section of the T cell plasma membrane that is in contact with the APCs. To see whether aging affects this PKCtheta; clustering reaction in mouse T lymphocytes, we used immunofluorescence staining and confocal microscopy to observe the localization of PKCtheta; in CD4 and CD8 T lymphocytes activated by coincubation with anti-CD3 hybridoma cells. Aging led to a twofold decline in the proportion of both CD4 and CD8 T cells in which PKCtheta; underwent cluster formation. This decrease with age was not due to differences in the number of cell conjugates formed, nor to kinetic differences of PKCtheta; clustering, nor to the accumulation of memory T cells in old mice. There were no effects of aging on the levels or kinase activity of PKCtheta; in murine T cells. Our data suggest alterations in the upstream signals that regulate PKCtheta; translocation.