Protein kinase C(theta) in T cell activation

NOTCH1 promotes T cell leukemia-initiating activity by RUNX-mediated regulation of PKC-θ and reactive oxygen species

Reactive oxygen species (ROS), a byproduct of cellular metabolism, damage intracellular macromolecules and, when present in excess, can promote normal hematopoietic stem cell differentiation and exhaustion. However, mechanisms that regulate the amount of ROS in leukemia-initiating cells (LICs) and the biological role of ROS in these cells are largely unknown. We show here that the ROS(low) subset of CD44(+) cells in T cell acute lymphoblastic leukemia (T-ALL), a malignancy of immature T cell progenitors, is highly enriched in the most aggressive LICs and that ROS accumulation is restrained by downregulation of protein kinase C θ (PKC-θ). Notably, primary mouse T-ALLs lacking PKC-θ show improved LIC activity, whereas enforced PKC-θ expression in both mouse and human primary T-ALLs compromised LIC activity. We also show that PKC-θ is regulated by a new pathway in which NOTCH1 induces runt-related transcription factor 3 (RUNX3), RUNX3 represses RUNX1 and RUNX1 induces PKC-θ. NOTCH1, which is frequently activated by mutation in T-ALL and required for LIC activity in both mouse and human models, thus acts to repress PKC-θ. These results reveal key functional roles for PKC-θ and ROS in T-ALL and suggest that aggressive biological behavior in vivo could be limited by therapeutic strategies that promote PKC-θ expression or activity, or the accumulation of ROS.

Identification of an N-terminal truncation of the NF-κB p65 subunit that specifically modulates ribosomal protein S3-dependent NF-κB gene expression

NF-κB is a pleiotrophic transcription factor that plays a prominent regulatory role in various cellular processes. Although previous efforts have focused on its activation, how NF-κB selects specific target genes in response to discrete signals remains puzzling. In addition to the well defined Rel protein components of NF-κB, the ribosomal protein S3 (RPS3) was identified to be an essential component of specific NF-κB complexes. RPS3 synergistically interacts with the NF-κB p65 subunit to achieve optimal binding and transactivation of a subset of NF-κB target genes, thus providing regulatory specificity. Emerging evidence suggests an important role for the RPS3-p65 interaction in context-specific NF-κB gene transcription. The food-borne pathogen Escherichia coli O157:H7 impacts the transcription of a subset of NF-κB target genes encoding proinflammatory cytokines and chemokines in host cells by preventing the nuclear translocation of RPS3, but not p65. The N terminus of p65 is crucial for RPS3 binding. Although several p65 N-terminal fragments are generated by either protease cleavage or alternative mRNA splicing under certain pathophysiological conditions, the role of these fragments in modulating NF-κB signaling, in particular RPS3-dependent selective gene transcription, has not been fully characterized. Here we report that an N-terminal fragment of p65 (amino acids 21-186) can selectively modulate NF-κB gene transcription by competing for RPS3 binding to p65. This 21-186 fragment preferentially localizes in the cytoplasm where it delays stimuli-induced RPS3 nuclear translocation, without affecting the nuclear translocation of p65. Our findings thus uncover a new cytoplasmic function for the N-terminal domain of p65 and provide a novel strategy for selective inhibition of NF-κB gene transcription.

Chromatinized Protein Kinase C-θ: Can It Escape the Clutches of NF-κB?

We recently provided the first description of a nuclear mechanism used by Protein Kinase C-theta (PKC-θ) to mediate T cell gene expression. In this mode, PKC-θ tethers to chromatin to form an active nuclear complex by interacting with proteins including RNA polymerase II, the histone kinase MSK-1, the demethylase LSD1, and the adaptor molecule 14-3-3ζ at regulatory regions of inducible immune response genes. Moreover, our genome-wide analysis identified many novel PKC-θ target genes and microRNAs implicated in T cell development, differentiation, apoptosis, and proliferation. We have expanded our ChIP-on-chip analysis and have now identified a transcription factor motif containing NF-κB binding sites that may facilitate recruitment of PKC-θ to chromatin at coding genes. Furthermore, NF-κB association with chromatin appears to be a prerequisite for the assembly of the PKC-θ active complex. In contrast, a distinct NF-κB-containing module appears to operate at PKC-θ targeted microRNA genes, and here NF-κB negatively regulates microRNA gene transcription. Our efforts are also focusing on distinguishing between the nuclear and cytoplasmic functions of PKCs to ascertain how these kinases may synergize their roles as both cytoplasmic signaling proteins and their functions on the chromatin template, together enabling rapid induction of eukaryotic genes. We have identified an alternative sequence within PKC-θ that appears to be important for nuclear translocation of this kinase. Understanding the molecular mechanisms used by signal transduction kinases to elicit specific and distinct transcriptional programs in T cells will enable scientists to refine current therapeutic strategies for autoimmune diseases and cancer.

PKC-theta-mediated signal delivery from the TCR/CD28 surface receptors

Protein kinase C-theta (PKCθ) is a key enzyme in T lymphocytes, where it plays an important role in signal transduction downstream of the activated T cell antigen receptor (TCR) and the CD28 costimulatory receptor. Interest in PKCθ as a potential drug target has increased following recent findings that PKCθ is essential for harmful inflammatory responses mediated by Th2 (allergies) and Th17 (autoimmunity) cells as well as for graft-versus-host disease (GvHD) and allograft rejection, but is dispensable for beneficial responses such as antiviral immunity and graft-versus-leukemia (GvL) response. TCR/CD28 engagement triggers the translocation of the cytosolic PKCθ to the plasma membrane (PM), where it localizes at the center of the immunological synapse (IS), which forms at the contact site between an antigen-specific T cell and antigen-presenting cells (APC). However, the molecular basis for this unique localization, and whether it is required for its proper function have remained unresolved issues until recently. Our recent study resolved these questions by demonstrating that the unique V3 (hinge) domain of PKCθ and, more specifically, a proline-rich motif within this domain, is essential and sufficient for its localization at the IS, where it is anchored to the cytoplasmic tail of CD28 via an indirect mechanism involving Lck protein tyrosine kinase (PTK) as an intermediate. Importantly, the association of PKCθ with CD28 is essential not only for IS localization, but also for PKCθ-mediated activation of downstream signaling pathways, including the transcription factors NF-κB and NF-AT, which are essential for productive T cell activation. Hence, interference with formation of the PKCθ-Lck-CD28 complex provides a promising basis for the design of novel, clinically useful allosteric PKCθ inhibitors. An additional recent study demonstrated that TCR triggering activates the germinal center kinase (GSK)-like kinase (GLK) and induces its association with the SLP-76 adaptor at the IS, where GLK phosphorylates the activation loop of PKCθ, converting it into an active enzyme. This recent progress, coupled with the need to study the biology of PKCθ in human T cells, is likely to facilitate the development of PKCθ-based therapeutic modalities for T cell-mediated diseases.

miR-146a controls the resolution of T cell responses in mice

By suppressing expression of TRAF6 and IRAK1, miR-146a regulates NF-κB activation in T cells through a negative feedback loop and controls the resolution of T cell responses in mice.

T cell responses in mammals must be tightly regulated to both provide effective immune protection and avoid inflammation-induced pathology. NF-κB activation is a key signaling event induced by T cell receptor (TCR) stimulation. Dysregulation of NF-κB is associated with T cell–mediated inflammatory diseases and malignancies, highlighting the importance of negative feedback control of TCR-induced NF-κB activity. In this study we show that in mice, T cells lacking miR-146a are hyperactive in both acute antigenic responses and chronic inflammatory autoimmune responses. TCR-driven NF-κB activation up-regulates the expression of miR-146a, which in turn down-regulates NF-κB activity, at least partly through repressing the NF-κB signaling transducers TRAF6 and IRAK1. Thus, our results identify miR-146a as an important new member of the negative feedback loop that controls TCR signaling to NF-κB. Our findings also add microRNA to the list of regulators that control the resolution of T cell responses.

Phospholipase Cγ2 plays a role in TCR signal transduction and T cell selection

One of the important signaling events following TCR engagement is activation of phospholipase Cγ (PLCγ). PLCγ has two isoforms, PLCγ1 and PLCγ2. It is known that PLCγ1 is important for TCR signaling and TCR-mediated T cell selection and functions, whereas PLCγ2 is critical for BCR signal transduction and BCR-mediated B cell maturation and functions. In this study, we report that PLCγ2 was expressed in primary T cells, and became associated with linker for activated T cells and Src homology 2-domain containing leukocyte protein of 76 kDa and activated upon TCR stimulation. PLCγ1/PLCγ2 double-deficient T cells displayed further block from CD4 and CD8 double-positive to single-positive transition compared with PLCγ1 single-deficient T cells. TCR-mediated proliferation was further impaired in PLCγ1/PLCγ2 double-deficient T cells compared with PLCγ1 single-deficient T cells. TCR-mediated signal transduction, including Ca²⁺ mobilization and Erk activation, was further impaired in PLCγ1/PLCγ2 double-deficient relative to PLCγ1 single-deficient T cells. In addition, in HY TCR transgenic mouse model, thymic positive and negative selections were reduced in PLCγ1 heterozygous- and PLCγ2 homozygous-deficient (PLCγ1⁺/⁻PLCγ2⁻/⁻) relative to wild-type, PLCγ2 single-deficient (PLCγ2⁻/⁻), or PLCγ1 heterozygous-deficient (PLCγ1⁺/⁻) mice. Taken together, these data demonstrate that PLCγ2 participates in TCR signal transduction and plays a role in T cell selection.

Protein kinase Cθ C2 domain is a phosphotyrosine binding module that plays a key role in its activation

Protein kinase Cθ (PKCθ) is a novel PKC that plays a key role in T lymphocyte activation. To understand how PKCθ is regulated in T cells, we investigated the properties of its N-terminal C2 domain that functions as an autoinhibitory domain. Our measurements show that a Tyr(P)-containing peptide derived from CDCP1 binds the C2 domain of PKCθ with high affinity and activates the enzyme activity of the intact protein. The Tyr(P) peptide also binds the C2 domain of PKCδ tightly, but no enzyme activation was observed with PKCδ. Mutations of PKCθ-C2 residues involved in Tyr(P) binding abrogated the enzyme activation and association of PKCθ with Tyr-phosphorylated full-length CDCP1 and severely inhibited the T cell receptor/CD28-mediated activation of a PKCθ-dependent reporter gene in T cells. Collectively, these studies establish the C2 domain of PKCθ as a Tyr(P)-binding domain and suggest that the domain may play a major role in PKCθ activation via its Tyr(P) binding.

Protein Kinase C-θ (PKC-θ) in Natural Killer Cell Function and Anti-Tumor Immunity

The protein kinase C-θ (PKCθ), which is essential for T cell function and survival, is also required for efficient anti-tumor immune surveillance. Natural killer (NK) cells, which express PKCθ, play a prominent role in this process, mainly by elimination of tumor cells with reduced or absent major histocompatibility complex class-I (MHC-I) expression. This justifies the increased interest of the use of activated NK cells in anti-tumor immunotherapy in the clinic. The in vivo development of MHC-I-deficient tumors is much favored in PKCθ^−/− mice compared with wild-type mice. Recent data offer some clues on the mechanism that could explain the important role of PKCθ in NK cell-mediated anti-tumor immune surveillance: some studies show that PKCθ is implicated in signal transduction and anti-tumoral activity of NK cells elicited by interleukin (IL)-12 or IL-15, while others show that it is implicated in NK cell functional activation mediated by certain killer-activating receptors. Alternatively, the possibility that PKCθ is involved in NK cell degranulation is discussed, since recent data indicate that it is implicated in microtubule-organizing center polarization to the immune synapse in CD4⁺ T cells. The implication of PKC isoforms in degranulation has been more extensively studied in cytotoxic T lymphocyte, and these studies will be also summarized.

Regulation of the PKCθ-NF-κB Axis in T Lymphocytes by the Tumor Necrosis Factor Receptor Family Member OX40

Antigen primed T lymphocytes need to expand and persist to promote adaptive immunity. The growth and survival signals that control this are in large part provided by the NF-κB pathway in activated or effector/memory T cells. Although several membrane receptors impact NF-κB activation, signaling from OX40 (CD134, TNFRSF4), a member of the tumor necrosis factor receptor (TNFR) superfamily, has proven to be important for T cell immunity and a strong contributor to NF-κB activity. PKCθ directs the T cell receptor (TCR) and CD28-dependent assembly of a CBM complex (CARMA1, BCL10, and MALT1) for efficient activation of NF-κB, raising the question of whether other membrane bound receptors that activate NF-κB also require this PKCθ-CBM axis to control TCR-independent T cell activity. We discuss here our recent data demonstrating that after ligation by OX40L (CD252, TNFSF4) expressed on antigen-presenting cells, OX40 translocates into detergent-insoluble membrane lipid microdomains (DIM or lipid rafts) in T cells irrespective of TCR signals, and assembles into a signaling complex containing PKCθ, together with TRAF2, RIP1, the CBM complex, and the IKKα/β/Γ complex. PKCθ is required for optimal NF-κB activation mediated by OX40 and thus works as an essential component of this OX40 signalosome. We also discuss the likelihood that other TNFR superfamily molecules might complex with PKCθ in T cells, and whether PKC isoforms may be critical to the function of TNFR molecules in general.

Differential requirement of RasGRP1 for γδ T cell development and activation

γδ T (γδT) cells belong to a distinct T cell lineage that performs immune functions different from αβ T (αβT) cells. Previous studies established that Erk1/2 MAPKs are critical for positive selection of αβT cells. Additional evidence suggests that increased Erk1/2 activity promotes γδT cell generation. RasGRP1, a guanine nucleotide-releasing factor for Ras, plays an important role in positive selection of αβT cells by activating the Ras-Erk1/2 pathway. In this article, we demonstrate that RasGRP1 is critical for TCR-induced Erk1/2 activation in γδT cells, but it exerts different roles for γδT cell generation and activation. Deficiency of RasGRP1 does not obviously affect γδT cell numbers in the thymus, but it leads to increased γδT cells, particularly CD4(-)CD8(+) γδT cells, in the peripheral lymphoid organs. The virtually unhindered γδT cell development in the RasGRP1(-/-) thymus proved to be cell intrinsic, whereas the increase in CD8(+) γδT cells is caused by non-cell-intrinsic mechanisms. Our data provide genetic evidence that decreased Erk1/2 activation in the absence of RasGRP1 is compatible with γδT cell generation. Although RasGRP1 is dispensable for γδT cell generation, RasGRP1-deficient γδT cells are defective in proliferation following TCR stimulation. Additionally, RasGRP1-deficient γδT cells are impaired to produce IL-17 but not IFNγ. Together, these observations revealed that RasGRP1 plays differential roles for γδ and αβ T cell development but is critical for γδT cell proliferation and production of IL-17.

Protein kinase C-θ inhibits inducible regulatory T cell differentiation via an AKT-Foxo1/3a-dependent pathway

Protein kinase C (PKC)-θ has been shown to be a critical TCR signaling molecule that promotes the activation and differentiation of naive T cells into inflammatory effector T cells. In this study, we demonstrate that PKC-θ-mediated signals inhibit inducible regulatory T cell (iTreg) differentiation via an AKT-Foxo1/3A pathway. TGF-β-induced iTreg differentiation was enhanced in PKC-θ(-/-) T cells or wild-type cells treated with a specific PKC-θ inhibitor, but was inhibited by the PKC-θ activator PMA, or by CD28 crosslinking, which enhances PKC-θ activation. PKC-θ(-/-) T cells had reduced activity of the AKT kinase, and the expression of a constitutively active form of AKT in PKC-θ(-/-) T cells restored the ability to inhibit iTreg differentiation. Furthermore, knockdown or overexpression of the AKT downstream targets Foxo1 and Foxo3a was found to inhibit or promote iTreg differentiation in PKC-θ(-/-) T cells accordingly, indicating that the AKT-Foxo1/3A pathway is responsible for the inhibition of iTreg differentiation of iTregs downstream of PKC-θ. We conclude that PKC-θ is able to control T cell-mediated immune responses by shifting the balance between the differentiation of effector T cells and inhibitory Tregs.

The role and regulation of mTOR in T-lymphocyte function

The conversion of naïve T cells into effector T cells is initiated by stimulation through the T-cell receptor (TCR). Upon activation, T cells undergo significant morphological and functional changes, putting new metabolic demands on the cell. Past research has identified the mammalian target of rapamycin (mTOR) as a critical regulator of cell metabolism, and the development of new genetic models has begun to reveal an important role for this pathway in the homeostasis and function of T lymphocytes. In this review, we focus on the most recent findings that demonstrate the ability of mTOR to regulate T-cell activation, CD8(+) memory cell formation and function, and helper T lineage differentiation. Furthermore, we highlight the importance of tight control of mTOR signaling by tuberous sclerosis complex 1 for T-cell homeostasis, and the regulation of mTOR signaling by diacylglycerol kinases and the RasGRP1-Ras-Erk1/2 pathway in the context of TCR signaling.

Molecular mechanisms of treg-mediated T cell suppression

CD4(+)CD25(high)Foxp3(+) regulatory T cells (Tregs) can suppress other immune cells and, thus, are critical mediators of peripheral self-tolerance. On the one hand, Tregs avert autoimmune disease and allergies. On the other hand, Tregs can prevent immune reactions against tumors and pathogens. Despite the importance of Tregs, the molecular mechanisms of suppression remain incompletely understood and controversial. Proliferation and cytokine production of CD4(+)CD25(-) conventional T cells (Tcons) can be inhibited directly by Tregs. In addition, Tregs can indirectly suppress Tcon activation via inhibition of the stimulatory capacity of antigen presenting cells. Direct suppression of Tcons by Tregs can involve immunosuppressive soluble factors or cell contact. Different mechanisms of suppression have been described, so far with no consensus on one universal mechanism. Controversies might be explained by the fact that different mechanisms may operate depending on the site of the immune reaction, on the type and activation state of the suppressed target cell as well as on the Treg activation status. Further, inhibition of T cell effector function can occur independently of suppression of proliferation. In this review, we summarize the described molecular mechanisms of suppression with a particular focus on suppression of Tcons and rapid suppression of T cell receptor-induced calcium (Ca(2+)), NFAT, and NF-κB signaling in Tcons by Tregs.

IκB kinase β is required for activation of NF-κB and AP-1 in CD3/CD28-stimulated primary CD4(+) T cells

Engagement of the TCR and CD28 coreceptor by their respective ligands activates signal transduction cascades that ultimately lead to the activation of the transcription factors NFAT, AP-1, and NF-κB, which are required for the expression of cytokines and T cell clonal expansion. Previous studies have demonstrated that in mature T cells, activation of AP-1 and NF-κB is dependent on protein kinase C θ, suggesting the existence of a common signaling pathway. In this study, we show that in human primary CD4(+) T cells, exposure to the cell-permeable IKKβ inhibitor PS-1145 or genetic ablation of IKKβ abrogates cell proliferation and impairs the activation of NF-κB and AP-1 transcription factors in response to engagement of CD3 and CD28 coreceptor. In addition, we show that stimulation of T cells in the absence of IKKβ activity promotes the time-dependent and cyclosporine-sensitive expression of negative regulators of T cell signaling leading to a hyporesponsive state of T cells.

Amyloid-specific T-cells differentiate Alzheimer's disease from Lewy body dementia

Alzheimer's disease and dementia with Lewy bodies are the most common neurodegenerative dementias in old age. Accurate diagnosis of these conditions has important clinical implications because they tend to be confounded. In the brain of Alzheimer's disease patients amyloid-beta is produced in excess and deposited as plaques, forming the hallmark of this condition. Lymphocytes have been implicated in the process of amyloid-beta removal and inflammation occurrence. Here we investigated peripheral amyloid-beta1-42-specific T-cells by multicolor flow cytometry to simultaneously detect and characterize activation markers and cell signaling proteins (phospho-protein kinase C) in patients with Alzheimer's disease or Lewy body dementia and in healthy controls. Results indicate that only Alzheimer's disease patients display small subsets of peripheral amyloid-beta1-42-specific T-cells, characterized by bright expression of phosphorylated-protein kinase C-delta or -zeta whose significance although discussed, is far from being understood. The identification of such subsets, anyhow, may strongly contribute to distinguish Alzheimer's disease from dementia with Lewy bodies, opening possible new routes to early therapeutic strategies.

AMP-activated protein kinase mediates T cell activation-induced expression of FasL and COX-2 via protein kinase C theta-dependent pathway in human Jurkat T leukemia cells

AMP-activated protein kinase (AMPK), an important regulator of energy homeostasis, is known to be activated during T cell activation. T cell activation by T cell receptor (TCR) engagement or its pharmacological mimics, PMA plus ionomycin (PMA/Io), induces immunomodulatory FasL and cyclooxygenase-2 (COX-2) expression. In this study, we examined the role and mechanisms of AMPK in PMA/Io-induced expression of FasL and COX-2 in Jurkat T human leukemic cells. Inhibition of AMPK by a pharmacological agent, compound C, or AMPKα1 siRNA suppressed expression of FasL and COX-2 mRNAs and proteins in PMA/Io-activated Jurkat cells. It also reduced secretion of FasL protein and prostaglandin E2, a main product of COX-2, in Jurkat cells and peripheral blood lymphocytes activated with PMA/Io or monoclonal anti-CD3 plus anti-CD28. Consistently, inhibition of AMPK blocked promoter activities of FasL and COX-2 in activated Jurkat cells. As protein kinase C theta (PKCθ) is a central molecule for TCR signaling, we examined any possible cross-talk between AMPK and PKCθ in activated T cells. Of particular importance, we found that inhibition of AMPK blocked phosphorylation and activation of PKCθ, suggesting that AMPK is an upstream kinase of PKCθ. Moreover, we showed that AMPK was directly associated with PKCθ and phosphorylated Thr538 of PKCθ in PMA/Io-stimulated Jurkat cells. We also showed that inhibition of PKCθ by rottlerin or dominant negative PKCθ reduced AMPK-mediated transcriptional activation of NF-AT and AP-1 in activated Jurkat cells. Taken together, these results suggest that AMPK regulates expression of FasL and COX-2 via the PKCθ and NF-AT and AP-1 pathways in activated Jurkat cells.

Differential regulation of primary and memory CD8 T cell immune responses by diacylglycerol kinases

The manipulation of signals downstream of the TCR can have profound consequences for T cell development, function, and homeostasis. Diacylglycerol (DAG) produced after TCR stimulation functions as a secondary messenger and mediates the signaling to Ras-MEK-Erk and NF-κB pathways in T cells. DAG kinases (DGKs) convert DAG into phosphatidic acid, resulting in termination of DAG signaling. In this study, we demonstrate that DAG metabolism by DGKs can serve a crucial function in viral clearance upon lymphocytic choriomeningitis virus infection. Ag-specific CD8(+) T cells from DGKα(-/-) and DGKζ(-/-) mice show enhanced expansion and increased cytokine production after lymphocytic choriomeningitis virus infection, yet DGK-deficient memory CD8(+) T cells exhibit impaired expansion after rechallenge. Thus, DGK activity plays opposing roles in the expansion of CD8(+) T cells during the primary and memory phases of the immune response, whereas consistently inhibiting antiviral cytokine production.

Fine-tuning of proximal TCR signaling by ZAP-70 tyrosine residues in Jurkat cells

Zeta-chain-associated protein kinase of 70kDa (ZAP-70) kinase is a key regulator in the early steps of TCR signaling but some aspects of its fine regulation are still unclear. From its 31 tyrosine (Y) residues, 11 phosphorylation sites have been identified, some with activator (Y315 and Y493) or inhibitory (Y292 and Y492) and others with unknown function (Y069, Y126 and Y178). In our present work, we aimed to elucidate the role of different Y residues of ZAP-70, especially those with unknown function, in calcium signaling and the autoregulation of the kinase. ZAP-70-deficient Jurkat cells (P116) were stably reconstituted with point-mutated ZAP-70 constructs where tyrosine residues 069, 126, 178, 238, 292, 315, 492 or 493 were replaced with phenylalanine (F). The anti-CD3-elicited calcium signal increased in F069-, F292- and F492-ZAP-70-expressing cell lines but decreased in the F126-, F315- and F493-ZAP-70-expressing cell lines. ZAP-70 point mutations led to phosphorylation changes predominantly in SH2 domain containing leukocyte protein of 76kDa (SLP-76) but not linker of activated T cells (LAT) during CD3-activation; moreover, we detected basal hyperphosphorylation of SLP-76 Y128 in the F126-, F178- and F492-ZAP-70-expressing cell lines. In summary, Y069, Y178, Y292 and Y492 have inhibitory, while Y126, Y315 and Y493 activator role in anti-CD3-induced T-cell activation. Phosphorylation changes in LAT and SLP-76 suggest that fine regulation of ZAP-70 on calcium signaling is rather transmitted through SLP-76 not LAT. Additionally, negative or positive autoregulatory function of Y292 and Y493 or Y315, respectively, was revealed in ZAP-70. These data indicate that previously not characterized Y069, Y126 and Y178 in ZAP-70 participate in the fine regulation of TCR signaling.

Protein kinase C η is required for T cell activation and homeostatic proliferation

Protein kinase C η (PKCη) is abundant in T cells and is recruited to the immunological synapse that is formed between a T cell and an antigen-presenting cell; however, its function in T cells is unknown. We showed that PKCη was required for the activation of mature CD8+ T cells through the T cell receptor. Compared with wild-type T cells, PKCη-/- T cells showed poor proliferation in response to antigen stimulation, a trait shared with T cells deficient in PKCθ, which is the most abundant PKC isoform in T cells and was thought to be the only PKC isoform with a specific role in T cell activation. In contrast, only PKCη-deficient T cells showed defective homeostatic proliferation, which requires self-antigen recognition. PKCη was dispensable for thymocyte development; however, thymocytes from mice doubly deficient in PKCη and PKCθ exhibited poor development, indicating some redundancy between the PKC isoforms. Deficiency in PKCη or PKCθ had opposing effects on the relative numbers of CD4+ and CD8+ T cells. PKCη-/- mice had a higher ratio of CD4+ to CD8+ T cells compared to that of wild-type mice, whereas PKCθ-/- mice had a lower ratio. Mice deficient in both isoforms exhibited normal cell ratios. Together, these data suggest that PKCη shares some redundant roles with PKCθ in T cell biology and also performs nonredundant functions that are required for T cell homeostasis and activation.

PKCθ activation in pancreatic acinar cells by gastrointestinal hormones/neurotransmitters and growth factors is needed for stimulation of numerous important cellular signaling cascades

The novel PKCθ isoform is highly expressed in T-cells, brain and skeletal muscle and originally thought to have a restricted distribution. It has been extensively studied in T-cells and shown to be important for apoptosis, T-cell activation and proliferation. Recent studies showed its presence in other tissues and importance in insulin signaling, lung surfactant secretion, intestinal barrier permeability, platelet and mast-cell functions. However, little information is available for PKCθ activation by gastrointestinal (GI) hormones/neurotransmitters and growth factors. In the present study we used rat pancreatic acinar cells to explore their ability to activate PKCθ and the possible interactions with important cellular mediators of their actions. Particular attention was paid to cholecystokinin (CCK), a physiological regulator of pancreatic function and important in pathological processes affecting acinar function, like pancreatitis. PKCθ-protein/mRNA was present in the pancreatic acini, and T538-PKCθ phosphorylation/activation was stimulated only by hormones/neurotransmitters activating phospholipase C. PKCθ was activated in time- and dose-related manner by CCK, mediated 30% by high-affinity CCK(A)-receptor activation. CCK stimulated PKCθ translocation from cytosol to membrane. PKCθ inhibition (by pseudostrate-inhibitor or dominant negative) inhibited CCK- and TPA-stimulation of PKD, Src, RafC, PYK2, p125(FAK) and IKKα/β, but not basal/stimulated enzyme secretion. Also CCK- and TPA-induced PKCθ activation produced an increment in PKCθ's direct association with AKT, RafA, RafC and Lyn. These results show for the first time the PKCθ presence in pancreatic acinar cells, its activation by some GI hormones/neurotransmitters and involvement in important cell signaling pathways mediating physiological responses (enzyme secretion, proliferation, apoptosis, cytokine expression, and pathological responses like pancreatitis and cancer growth).

Regulation of NF-κB induction by TCR/CD28

NF-κB family transcription factors are a common downstream target for inducible transcription mediated by many different cell-surface receptors, especially those receptors involved in inflammation and adaptive immunity. It is now clear that different classes of receptors employ different proximal signaling strategies to activate the common NF-κB signaling components, such as the IKK complex. For antigen receptors expressed by T and B cells, this pathway requires a complex of proteins including the proteins Carma1, Bcl10, and Malt1. Here, we discuss some of what is known about regulation of these proteins downstream of TCR/CD3 and co-stimulatory CD28 signaling. We also discuss another unique aspect of TCR-mediated NF-κB activation, i.e., the spatial restriction imposed on signaling events by the formation of the immunological synapse between a T cell and antigen-presenting cell presenting specific peptide/MHC.

Activation of Wnt signaling arrests effector differentiation in human peripheral and cord blood-derived T lymphocytes

The canonical Wnt/β-catenin signaling pathway plays an important role in thymocyte development and T cell migration, but little is known about its role in naive-to-effector differentiation in human peripheral T cells. We show that activation of Wnt/β-catenin signaling arrests human peripheral blood and cord blood T lymphocytes in the naive stage and blocks their transition into functional T effector cells. Wnt signaling was induced in polyclonally activated human T cells by treatment either with the glycogen synthase kinase 3β inhibitor TWS119 or the physiological Wnt agonist Wnt-3a, and these T cells preserved a naive CD45RA(+)CD62L(+) phenotype compared with control-activated T cells that progressed to a CD45RO(+)CD62L(-) effector phenotype, and this occurred in a TWS119 dose-dependent manner. TWS119-induced Wnt signaling reduced T cell expansion, as a result of a block in cell division, and impaired acquisition of T cell effector function, measured by degranulation and IFN-γ production in response to T cell activation. The block in T cell division may be attributed to the reduced IL-2Rα expression in TWS119-treated T cells that lowers their capacity to use autocrine IL-2 for expansion. Collectively, our data suggest that Wnt/β-catenin signaling is a negative regulator of naive-to-effector T cell differentiation in human T lymphocytes. The arrest in T cell differentiation induced by Wnt signaling might have relevant clinical applications such as to preserve the naive T cell compartment in Ag-specific T cells generated ex vivo for adoptive T cell immunotherapy.

Protein kinase Cε regulates proliferation and cell sensitivity to TGF-1β of CD4+ T lymphocytes: implications for Hashimoto thyroiditis

We have studied the functional role of protein kinase Cε (PKCε) in the control of human CD4(+) T cell proliferation and in their response to TGF-1β. We demonstrate that PKCε sustains CD4(+) T cell proliferation triggered in vitro by CD3 stimulation. Transient knockdown of PKCε expression decreases IL-2R chain transcription, and consequently cell surface expression levels of CD25. PKCε silencing in CD4 T cells potentiates the inhibitory effects of TGF-1β, whereas in contrast, the forced expression of PKCε virtually abrogates the inhibitory effects of TGF-1β. Being that PKCε is therefore implicated in the response of CD4 T cells to both CD3-mediated proliferative stimuli and TGF-1β antiproliferative signals, we studied it in Hashimoto thyroiditis (HT), a pathology characterized by abnormal lymphocyte proliferation and activation. When we analyzed CD4 T cells from HT patients, we found a significant increase of PKCε expression, accounting for their enhanced survival, proliferation, and decreased sensitivity to TGF-1β. The increased expression of PKCε in CD4(+) T cells of HT patients, which is described for the first time, to our knowledge, in this article, viewed in the perspective of the physiological role of PKCε in normal Th lymphocytes, adds knowledge to the molecular pathophysiology of HT and creates potentially new pharmacological targets for the therapy of this disease.

Diacylglycerol kinase ζ controls diacylglycerol metabolism at the immunological synapse

DGKα and DGKζ negatively regulate the DAG/RasGRP1/Ras pathway in T cells. Study of the specific contribution of each isoform to DAG metabolism during immune synapse formation by use of a combination of RNAi and videomicroscopy techniques identifies DGKζ as mainly responsible for DAG consumption at the immunological synapse.

Diacylglycerol (DAG) generation at the T cell immunological synapse (IS) determines the correct activation of antigen-specific immune responses. DAG kinases (DGKs) α and ζ act as negative regulators of DAG-mediated signals by catalyzing DAG conversion to phosphatidic acid (PA). Nonetheless, the specific input of each enzyme and their spatial regulation during IS formation remain uncharacterized. Here we report recruitment of endogenous DGKα and DGKζ to the T cell receptor (TCR) complex following TCR/CD28 engagement. Specific DGK gene silencing shows that PA production at the activated complex depends mainly on DGKζ, indicating functional differences between these proteins. DGKζ kinase activity at the TCR is enhanced by phorbol-12-myristate-13-acetate cotreatment, suggesting DAG-mediated regulation of DGKζ responsiveness. We used GFP-DGKζ and -DGKα chimeras to assess translocation dynamics during IS formation. Only GFP-DGKζ translocated rapidly to the plasma membrane at early stages of IS formation, independent of enzyme activity. Finally, use of a fluorescent DAG sensor confirmed rapid, sustained DAG accumulation at the IS and allowed us to directly correlate membrane translocation of active DGKζ with DAG consumption at the IS. This study highlights a DGKζ-specific function for local DAG metabolism at the IS and offers new clues to its mode of regulation.

Phospho-flow cytometry based analysis of differences in T cell receptor signaling between regulatory T cells and CD4+ T cells

CD4+ T regulatory cells (Tregs) are activated during auto-immune, injury, and inflammatory responses, however, the molecular events that trigger Treg activation are poorly understood. The purpose of this study was to investigate whether Tregs (FoxP3+ CD4+ T cells) and non-Treg CD4+ T cells might display differences in T cell receptor (TCR) dependent signaling responses following in vitro or in vivo stimulation. This study used phospho-flow cytometry as a tool to profile the kinetics and extent of TCR signaling (ZAP-70 and PKC-θ phosphorylation and expression) in Tregs and non-Tregs. We found that in vitro stimulation with anti-CD3ε induces early and transient activation of ZAP-70 and PKC-θ in both Tregs and non-Tregs. However, the response in Tregs was more rapid and higher in magnitude than responses seen in non-Tregs. In contrast, bacterial superantigen or antigen-specific TCR stimulation did not significantly activate these signaling pathways in Tregs or non-Tregs. Additional experiments tested the kinetics of in vivo TCR signaling in Tregs and non-Tregs in mice challenged with bacterial superantigen. The results of these experiments showed that superantigen rapidly activated ZAP-70 and PKC-θ in lymph node Tregs, but not in non-Tregs. In summary, we demonstrate the versatility of using phospho-flow cytometry to measure cell signaling in CD4+ T cells. The results of these in vitro and in vivo studies demonstrate that Tregs and non-Treg CD4+ T cells show marked differences in their reactivity to TCR-dependent stimulation and contribute new insights into basic mechanisms that lead to Treg activation.

Differential expression of muscarinic acetylcholine receptor subtypes in Jurkat cells and their signaling

Muscarinic acetylcholine receptors expression and signaling in the human Jurkat T cell line were investigated. Semiquantitative real-time PCR and radioligand binding studies, using a wide set of antagonist compounds, showed the co-existence of M(3), M(4), and M(5) subtypes. Stimulation of these subpopulations caused a concentration and time- dependent activation of second messengers and ERK signaling pathways, with a major contribution of the M(3) subtype in a G(q/11)-mediated response. In addition, we found that T-cell stimulation leads to increased expression of M(3) and M(5) both at transcriptional and protein levels in a PLC/PKCθ dependent manner. Our data clarifies the functional role of AChR subtypes in Jurkat cells and pave the way to future studies on the potential cross-talk among these subpopulations and their regulation of T lymphocytes immune function.

PKC-θ function at the immunological synapse: prospects for therapeutic targeting

Protein kinase C (PKC)-θ regulates conventional effector T (Teff) cell function. Since this initial finding, it has become clear that the role of PKC-θ in T cells is complex. PKC-θ plays a central role in Teff cell activation and survival, and negatively regulates stability of the immunological synapse (IS). Recent studies demonstrated that PKC-θ is required for the development of natural CD4(+)Foxp3(+) regulatory T (Treg) cells, and mediates negative regulation of Treg cell function. Here, we examine the role of PKC-θ in the IS, evidence for its distinct localization in Treg cells and the therapeutic implications of inhibiting PKC-θ in Teff cells, to reduce effector function, and in Treg cells, to increase suppressor function, for the prevention and treatment of autoimmune and alloimmune disease states.

Protein kinase Ctheta is a specific target for inhibition of the HIV type 1 replication in CD4+ T lymphocytes

Integration of HIV-1 genome in CD4(+) T cells produces latent reservoirs with long half-life that impedes the eradication of the infection. Control of viral replication is essential to reduce the size of latent reservoirs, mainly during primary infection when HIV-1 infects CD4(+) T cells massively. The addition of immunosuppressive agents to highly active antiretroviral therapy during primary infection would suppress HIV-1 replication by limiting T cell activation, but these agents show potential risk for causing lymphoproliferative disorders. Selective inhibition of PKC, crucial for T cell function, would limit T cell activation and HIV-1 replication without causing general immunosuppression due to PKC being mostly expressed in T cells. Accordingly, the effect of rottlerin, a dose-dependent PKC inhibitor, on HIV-1 replication was analyzed in T cells. Rottlerin was able to reduce HIV-1 replication more than 20-fold in MT-2 (IC(50) = 5.2 μM) and Jurkat (IC(50) = 2.2 μM) cells and more than 4-fold in peripheral blood lymphocytes (IC(50) = 4.4 μM). Selective inhibition of PKC, but not PKCδ or -ζ, was observed at <6.0 μM, decreasing the phosphorylation at residue Thr(538) on the kinase catalytic domain activation loop and avoiding PKC translocation to the lipid rafts. Consequently, the main effector at the end of PKC pathway, NF-κB, was repressed. Rottlerin also caused a significant inhibition of HIV-1 integration. Recently, several specific PKC inhibitors have been designed for the treatment of autoimmune diseases. Using these inhibitors in combination with highly active antiretroviral therapy during primary infection could be helpful to avoid massive viral infection and replication from infected CD4(+) T cells, reducing the reservoir size at early stages of the infection.

Chromatin-associated protein kinase C-θ regulates an inducible gene expression program and microRNAs in human T lymphocytes

Studies in yeast demonstrate that signaling kinases have a surprisingly active role in the nucleus, where they tether to chromatin and modulate gene expression programs. Despite these seminal studies, the nuclear mechanism of how signaling kinases control transcription of mammalian genes is in its infancy. Here, we provide evidence for a hitherto unknown function of protein kinase C-theta (PKC-θ), which physically associates with the regulatory regions of inducible immune response genes in human T cells. Chromatin-anchored PKC-θ forms an active nuclear complex by interacting with RNA polymerase II, the histone kinase MSK-1, and the adaptor molecule 14-3-3ζ. ChIP-on-chip reveals that PKC-θ binds to promoters and transcribed regions of genes, as well as to microRNA promoters that are crucial for cytokine regulation. Our results provide a molecular explanation for the role of PKC-θ not only in normal T cell function, but also in circumstances of its ectopic expression in cancer.

Receptor signaling in immune cell development and function

Immune cell development and function must be tightly regulated through cell surface receptors to ensure proper responses to pathogen and tolerance to self. In T cells, the signal from the T-cell receptor is essential for T-cell maturation, homeostasis, and activation. In mast cells, the high-affinity receptor for IgE transduces signal that promotes mast cell survival and induces mast cell activation. In dendritic cells and macrophages, the toll-like receptors recognize microbial pathogens and play critical roles for both innate and adaptive immunity against pathogens. Our research explores how signaling from these receptors is transduced and regulated to better understand these immune cells. Our recent studies have revealed diacylglycerol kinases and TSC1/2-mTOR as critical signaling molecules/regulators in T cells, mast cells, dendritic cells, and macrophages.

Negative regulation of mTOR activation by diacylglycerol kinases

The engagement of TCR induces T-cell activation, which initiates multiple characteristic changes such as increase in cell size, cell division, and the production of cytokines and other effector molecules. The mammalian target of rapamycin (mTOR) regulates protein synthesis, transcription, cell survival, and autophagy. Critical roles of mTOR in T-cell activation and effector/memory differentiation have been revealed using chemical inhibitors or by genetic ablation of mTOR in T cells. However, the connection between mTOR signaling and other signaling cascades downstream of TCR is unclear. We demonstrate that diacylglycerol (DAG) and TCR engagement activate signaling in both mTOR complexes 1 and 2 through the activation of the Ras-mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 (Mek1/2)-extracellular signal-regulated kinase 1/2 (Erk1/2)-activator protein 1 (AP-1), known collectively as the Ras-Mek1/2-Erk1/2-AP-1 pathway. Deficiency of RasGRP1 or inhibition of Mek1/2 activity drastically decreases TCR-induced mTOR activation, whereas constitutively active Ras or Mek1 promotes mTOR activation. Although constitutively active Akt promotes TCR-induced mTOR activation, such activation is attenuated by Mek1/2 inhibition. We demonstrated further that DAG kinases (DGKs) α and ζ, which terminate DAG-mediated signaling, synergistically inhibit TCR-induced mTOR activation by inhibiting the Ras-Mek1/2-Erk/12 pathway. These observations provide novel insights into the regulation of mTOR activation.

Lidocaine suppresses mouse Peyer's Patch T cell functions and induces bacterial translocation

BACKGROUND

The gastrointestinal mucosa is an important route of entry for microbial pathogens. The immune cells of Peyer's patch (PP) compartments contribute to the active immune response against infection. Although local anesthetics are widely used in clinical practice, it remains unclear whether local anesthetics such as lidocaine affect PP T cell functions.

METHODS

The aim of this study was to examine if lidocaine has any effects on mouse PP T cell functions. To test this, freshly isolated mouse Peyer's patch T cells were incubated with lidocaine. The effects of lidocaine on concanavalin A-stimulated PP T cell proliferation and cytokine production were assessed. The effect of lidocaine on PP T cell mitogen-activated protein kinase (MAPK) activation was also assessed.

RESULTS

The results indicate that lidocaine suppresses cell proliferation, cytokine production, and MAPK activation in PP T cells. Furthermore, we found that the chronic in vivo exposure to lidocaine increases bacterial accumulation in PP.

CONCLUSION

The enhanced immunosuppressive effects of lidocaine on PP T cell functions could contribute to the host's enhanced susceptibility to infection.

Protein kinase C-theta is required for development of experimental cerebral malaria

Cerebral malaria is the most severe neurologic complication in children and young adults infected with Plasmodium falciparum. T-cell activation is required for development of Plasmodium berghei ANKA (PbA)-induced experimental cerebral malaria (CM). To characterize the T-cell activation pathway involved, the role of protein kinase C-theta (PKC-θ) in experimental CM development was examined. PKC-θ-deficient mice are resistant to CM development. In the absence of PKC-θ, no neurologic sign of CM developed after blood stage PbA infection. Resistance of PKC-θ-deficient mice correlated with unaltered cerebral microcirculation and absence of ischemia, as documented by magnetic resonance imaging and magnetic resonance angiography, whereas wild-type mice developed distinct microvascular pathology. Recruitment and activation of CD8(+) T cells, and ICAM-1 and CD69 expression were reduced in the brain of resistant mice; however, the pulmonary inflammation and edema associated with PbA infection were still present in the absence of functional PKC-θ. Resistant PKC-θ-deficient mice developed high parasitemia, and died at 3 weeks with severe anemia. Therefore, PKC-θ signaling is crucial for recruitment of CD8(+) T cells and development of brain microvascular pathology resulting in fatal experimental CM, and may represent a novel therapeutic target of CM.

Evaluation of the novel protein kinase C inhibitor sotrastaurin as immunosuppressive therapy after renal transplantation

IMPORTANCE OF THE FIELD

The prevalence of acute renal allograft rejection has decreased substantially in past decades due to new and more specific immunosuppressive compounds but improvements in long-term graft function have not been achieved. There is a large need for new immunosuppressive agents that lack toxicity of current agents such as calcineurin inhibitors but show high synergistic efficiency in preventing rejection processes.

AREAS COVERED IN THIS REVIEW

This review summarizes data concerning the pharmacokinetics, pharmacodynamics and clinical efficacy of the new PKC inhibitor sotrastaurin with a focus on renal transplantation. The article contains information that has been presented at international transplant meetings and congresses and that has been published between 2006 and 2010. Additionally, current ongoing trials are described in detail.

WHAT THE READER WILL GAIN

Immunosuppressive regimens after kidney transplantation consist of a combination of several agents in order to minimize drug toxicity. Therefore, the reader is presented with the most up-to-date/current developments in sotrastaurin applications in Phase I and II trials with emphasis on data maintained from studies that combined sotrastaurin with established agents such as mycophenolic acid and tacrolimus.

TAKE HOME MESSAGE

Several trials are ongoing and planned to determine the optimal immunosuppressive regimen to benefit from sotrastaurin's distinct mechanism of action.

Oct1 is a switchable, bipotential stabilizer of repressed and inducible transcriptional states

Little is known regarding how the Oct1 transcription factor regulates target gene expression. Using murine fibroblasts and two target genes, Polr2a and Ahcy, we show that Oct1 recruits the Jmjd1a/KDM3A lysine demethylase to catalyze the removal of the inhibitory histone H3K9 dimethyl mark and block repression. Using purified murine T cells and the Il2 target locus, and a colon cancer cell line and the Cdx2 target locus, we show that Oct1 recruits the NuRD chromatin-remodeling complex to promote a repressed state, but in a regulated manner can switch to a different capacity and mediate Jmjd1a recruitment to block repression. These findings indicate that Oct1 maintains repression through a mechanism involving NuRD and maintains poised gene expression states through an antirepression mechanism involving Jmjd1a. We propose that, rather than acting as a primary trigger of gene activation or repression, Oct1 is a switchable stabilizer of repressed and inducible states.

Oxidized ATP inhibits T-cell-mediated autoimmunity

T cells directed against self antigens play an important role in several autoimmune diseases. The available immunosuppressive compounds used to treat autoimmune diseases are limited, and often they have side effects that limit their application. T cells express ATP receptors, which could be new target molecules to treat autoimmune disease. Here we analyzed the effect of oxidized ATP (oxATP), an inhibitor of the ATP receptor P2rx7, in different murine models of T-cell-mediated autoimmune diseases. Treatment with oxATP inhibited proliferation and effector function of T cells. In the systems we used, oxATP did not obviously interfere with the innate immune response, but strongly reduced antigen-specific T-cell responses. This treatment ameliorated T-cell-mediated autoimmune type I diabetes and autoimmune encephalitis in mice. In conclusion, oxATP was found to strongly inhibit activated T cells and could thus be used to target T-cell-mediated autoimmune disease.

Lipid signaling in T-cell development and function

Second messenger molecules relay, amplify, and diversify cell surface receptor signals. Two important examples are phosphorylated D-myo-inositol derivatives, such as phosphoinositide lipids within cellular membranes, and soluble inositol phosphates. Here, we review how phosphoinositide metabolism generates multiple second messengers with important roles in T-cell development and function. They include soluble inositol(1,4,5)trisphosphate, long known for its Ca(2+)-mobilizing function, and phosphatidylinositol(3,4,5)trisphosphate, whose generation by phosphoinositide 3-kinase and turnover by the phosphatases PTEN and SHIP control a key "hub" of TCR signaling. More recent studies unveiled important second messenger functions for diacylglycerol, phosphatidic acid, and soluble inositol(1,3,4,5)tetrakisphosphate (IP(4)) in immune cells. Inositol(1,3,4,5)tetrakisphosphate acts as a soluble phosphatidylinositol(3,4,5)trisphosphate analog to control protein membrane recruitment. We propose that phosphoinositide lipids and soluble inositol phosphates (IPs) can act as complementary partners whose interplay could have broadly important roles in cellular signaling.

T-cell receptor-driven lymphomagenesis in mice derived from a reprogrammed T cell

The conversion of mature somatic cells into pluripotent stem cells, both by nuclear transfer and transduction with specific "reprogramming" genes, represents a major advance in regenerative medicine. Pluripotent stem cell lines can now be generated from an individual's own cells, facilitating the generation of immunologically acceptable stem cell-based therapeutics. Many cell types can undergo nuclear reprogramming, leading to the question of whether the identity of the reprogrammed cell of origin has a biological consequence. Peripheral blood, containing a mixture of T, B, NK, and myeloid cell types, represents one potential source of reprogrammable cells. In this study, we describe the unique case of mice derived from a reprogrammed T cell. These mice have prerearranged T-cell receptor (TCR) genes in all cells. Surprisingly, ≈50% of mice with prerearranged TCR genes develop spontaneous T cell lymphomas, which originate in the thymus. The lymphomas arise from developing T cells, and contain activated Notch1, similar to most human and mouse T-cell acute lymphoblastic lymphomas. Furthermore, lymphomagenesis requires the expression of both prerearranged TCRα and TCRβ genes, indicating a critical role for TCR signaling. Furthermore, inhibitors of multiple branches of TCR signaling suppress lymphoma growth, implicating TCR signaling as an essential component in lymphoma proliferation. The lymphomagenesis in mice derived from a reprogrammed T cell demonstrates the deleterious consequences of misregulation of the TCR rearrangement and signaling pathways and illustrates one case of cellular reprogramming where the identity of the cell of origin has profound consequences.

Salutary effects of 17beta-estradiol on Peyer's patch T cell functions following trauma-hemorrhage

Although 17beta-estradiol (E2) administration following trauma-hemorrhage (T-H) improves immune functions in male rodents, it remains unclear whether E2 has salutary effects on Peyer's patch (PP) T cell functions. We hypothesized that T-H induces PP T cell dysfunction and E2 administration following T-H will improve PP T cell function. T-H was induced in male C3H/HeN mice (6-8weeks) by midline laparotomy and approximately 90min of hemorrhagic shock (blood pressure 35mmHg), followed by fluid resuscitation (4x the shed blood volume in the form of Ringer's lactate). Estrogen receptor (ER)-alpha agonist propyl pyrazole triol (PPT; 5microg/kg), ER-beta agonist diarylpropionitrile (DPN; 5microg/kg), E2 (50microg/kg), or vehicle was injected subcutaneously at resuscitation onset. Two hours later, mice were sacrificed and PP T cells isolated. PP T cell capacity to produce cytokines in response to in vitro stimulation, PP T cell proliferation and MAPK (p38, ERK-1/2, JNK) activation were measured. Results indicate PP T cell proliferation, cytokine production and MAPK activation decreased significantly following T-H. E2, PPT or DPN administration normalized these parameters. Since PPT or DPN administration following T-H was effective in normalizing PP T cell functions, the salutary effects of E2 are mediated via ER-alpha and ER-beta.

Protein kinase C θ deficiency increases resistance of C57BL/6J mice to Plasmodium berghei infection-induced cerebral malaria

Protein kinase C θ (PKCθ) functions as a core component of the immunological synapse and serves as a key protein in the integrated T-cell antigen receptor (TCR)/CD28-induced signaling cascade leading to T-cell activation. However, the involvement of PKCθ in host-mediated immune responses to pathogens has not been thoroughly investigated. We tested the consequences of PKCθ ablation on the host response to infection by Plasmodium berghei ANKA (PbA). We found that both PKCθ(+/+) and PKCθ(-/-) C57BL/6J mice are susceptible to infection with PbA. However, despite a similar parasite burden, PKCθ(+/+) mice had an earlier onset of neurological signs, characteristics of experimental cerebral malaria (ECM), resulting in an earlier death. These mice suffered from an early and pronounced splenomegaly with a concomitant increase in the total number of CD4(+) splenic T cells. In contrast, a large proportion of PbA-infected PKCθ(-/-) mice overcame the acute phase characterized by neurological symptoms and survived longer than PKCθ(+/+) mice. The partial resistance of PKCθ(-/-) mice to ECM was associated with an impaired production of Th1-type cytokines, including gamma interferon and tumor necrosis factor alpha/lymphotoxin-α, which are known to exacerbate symptoms leading to ECM. In addition, PbA infection-induced LFA-1 expression in CD8(+) T cells was suppressed in PKCθ-deficient T cells, suggesting a diminished ability to adhere to endothelial cells and sequester in brain microvasculature, which may explain the decrease in neurological symptoms. These data implicate PKCθ in CD4(+) Th1(+) and CD8(+) T-cell-mediated immune responses during PbA infection that contribute to the development of ECM.

Bryostatin modulates latent HIV-1 infection via PKC and AMPK signaling but inhibits acute infection in a receptor independent manner

HIV's ability to establish long-lived latent infection is mainly due to transcriptional silencing in resting memory T lymphocytes and other non dividing cells including monocytes. Despite an undetectable viral load in patients treated with potent antiretrovirals, current therapy is unable to purge the virus from these latent reservoirs. In order to broaden the inhibitory range and effectiveness of current antiretrovirals, the potential of bryostatin was investigated as an HIV inhibitor and latent activator. Bryostatin revealed antiviral activity against R5- and X4-tropic viruses in receptor independent and partly via transient decrease in CD4/CXCR4 expression. Further, bryostatin at low nanomolar concentrations robustly reactivated latent viral infection in monocytic and lymphocytic cells via activation of Protein Kinase C (PKC) -α and -δ, because PKC inhibitors rottlerin and GF109203X abrogated the bryostatin effect. Bryostatin specifically modulated novel PKC (nPKC) involving stress induced AMP Kinase (AMPK) inasmuch as an inhibitor of AMPK, compound C partially ablated the viral reactivation effect. Above all, bryostatin was non-toxic in vitro and was unable to provoke T-cell activation. The dual role of bryostatin on HIV life cycle may be a beneficial adjunct to the treatment of HIV especially by purging latent virus from different cellular reservoirs such as brain and lymphoid organs.

Widespread expression of PICOT in mouse and human tissues with predominant localization to epithelium

The protein kinase C-interacting cousin of thioredoxin (PICOT; also termed glutaredoxin 3) protein was discovered a decade ago as a protein kinase C theta (PKCtheta)-binding protein in human T lymphocytes. PICOT possesses an amino-terminal monothiol thioredoxin-like domain and a carboxy-terminal tandem repeat of a monothiol glutaredoxin-like domain. Nevertheless, the enzymatic activities of PICOT and its potential substrates have not yet been characterized and its biological importance is unknown. Earlier studies reported the presence of PICOT in several different cell lines and tissues, but its expression pattern has not been thoroughly investigated. We performed Northern blot analysis of 19 different human organs and tissues and found the expression of PICOT mRNA in all organs and tissues tested. Western blot analysis confirmed the expression of PICOT at the protein level in all organs and tissues tested and showed, in addition, that PICOT and PKCtheta expression in different tissues only partially overlap. These findings support the involvement of PICOT in biological functions that are independent of PKCtheta. To analyze the in vivo expression pattern of PICOT within cells of different human organs, we performed immunohistochemical staining using PICOT-specific antibodies. Analysis of breast, pituitary, adrenal, pancreas, and kidney sections demonstrated a differential expression of PICOT in various cell types, with a predominant cytosolic staining of epithelial cells and low or undetectable levels of PICOT in the stroma.

Essential role of ubiquitin and TSG101 protein in formation and function of the central supramolecular activation cluster

Agonist MHC-peptide complexes in the immunological synapse (IS) signal through T cell receptor (TCR) microclusters (MCs) that converge into a central supramolecular activation cluster (cSMAC). The determinants and function of the cSMAC remain unknown. We demonstrate an essential role for ubiquitin (Ub) and TSG101, but less so for HRS, in signal processing events at the cSMAC. Using siRNA in primary T cells, we show that Ub recognition by TSG101 is required for cSMAC formation, TCR MC signal termination, TCR downregulation, and segregation of TCR-MHC-peptide from PKC-theta-enriched signaling complexes. Weak agonist MHC-peptide induced CD80-dependent TCR MCs that dissociated in the center of the IS without recruiting TSG101. These results support TSG101-dependent recognition of CD80-independent TCR MCs as a molecular checkpoint for TCR downregulation.

Effects of the new immunosuppressive agent AEB071 on human immune cells

BACKGROUND. The novel immunosuppressive agent AEB071 is currently being evaluated for its capability to prevent rejection after kidney transplantation as a potential adjunct to calcineurin inhibitor-based regimen. AEB071 is a selective protein kinase C inhibitor and has been shown to be well tolerated in humans. We here present extensive in vitro studies that contribute to the understanding of AEB071 effects on human lymphocyte, natural killer (NK) cell and dendritic cell (DC) action.

METHODS

The impact of AEB071 on several T-cell activation and costimulatory markers was assessed. Furthermore, assays were performed to study the effect on T-cell proliferation and intracellular cytokine production. Additionally, the effect of AEB071 on DC maturation and their capacity to stimulate allogeneic T-cells was examined. Also, an evaluation of AEB071 effects on the lytic activity of human NK cells was performed.

RESULTS

We were able to show that T-cell proliferation and cytokine production rates are significantly reduced after AEB071 administration. Also, mitogen-induced T-cell activation characterized by expression levels of surface markers could be significantly inhibited. In contrast, the T-cell stimulatory capacity of AEB071-treated mature monocyte-derived DC (Mo-DC) is not reduced, and AEB071 administration does not prevent lipopolysaccharide (LPS)-induced Mo-DC maturation. It could be demonstrated that AEB071 significantly inhibited the cytotoxic activity of NK cells.

CONCLUSIONS

The promising immunosuppressive agent AEB071 has a strong impact on T-cell activation, proliferation and cytokine production as well as NK cell activity, but not DC maturation in vitro, and therefore, seems to function T-cell and NK cell specific via protein kinase C (PKC) inhibition.

Aggregation of spectrin and PKCtheta is an early hallmark of fludarabine/mitoxantrone/dexamethasone-induced apoptosis in Jurkat T and HL60 cells

It has been shown that changes in spectrin distribution in early apoptosis preceded changes in membrane asymmetry and phosphatidylserine (PS) exposure. PKCtheta was associated with spectrin during these changes, suggesting a possible role of spectrin/PKCtheta aggregation in regulation of early apoptotic events. Here we dissect this hypothesis using Jurkat T and HL60 cell lines as model systems. Immunofluorescent analysis of alphaIIbetaII spectrin arrangement in Jurkat T and HL60 cell lines revealed the redistribution of spectrin and PKCtheta into a polar aggregate in early apoptosis induced by fludarabine/mitoxantrone/dexamethasone (FND). The appearance of an alphaIIbetaII spectrin fraction that was insoluble in a non-ionic detergent (1% Triton X-100) was observed concomitantly with spectrin aggregation. The changes were observed within 2 h after cell exposure to FND, and preceded PS exposure. The changes seem to be restricted to spectrin and not to other cytoskeletal proteins such as actin or vimentin. In studies of the mechanism of these changes, we found that (i) neither changes in apoptosis regulatory genes (e.g., Bcl-2 family proteins) nor changes in cytoskeleton-associated proteins were detected in gene expression profiling of HL60 cells after the first hour of FND treatment, (ii) caspase-3, -7, -8, and -10 had minor involvement in the early apoptotic rearrangement of spectrin/PKCtheta, and (iii) spectrin aggregation was shown to be partially dependent on PKCtheta activity. Our results indicate that spectrin/PKCtheta aggregate formation is related to an early stage in drug-induced apoptosis and possibly may be regulated by PKCtheta activity. These findings indicate that spectrin/PKCtheta aggregation could be considered as a hallmark of early apoptosis and presents the potential to become a useful diagnostic tool for monitoring efficiency of chemotherapy as early as 24 h after treatment.

Highly Specific Modulators of Protein Kinase C Localization: Applications to Heart Failure

Heart failure (HF) in which the blood supply does not match the body's needs, affects 10% of the population over 65 years old. The protein kinase C (PKC) family of kinases has a key role in normal and disease states. Here we discuss the role of PKC in HF and focus on the use of specific PKC regulators to identify the mechanism leading to this Pathology and potential leads for therapeutics.