PKC-theta is required for TCR-induced NF-kappaB activation in mature but not immature T lymphocytes

Protein Kinase C Enzymes in the Hematopoietic and Immune Systems

The protein kinase C (PKC) family, discovered in the late 1970s, is composed of at least 10 serine/threonine kinases, divided into three groups based on their molecular architecture and cofactor requirements. PKC enzymes have been conserved throughout evolution and are expressed in virtually all cell types; they represent critical signal transducers regulating cell activation, differentiation, proliferation, death, and effector functions. PKC family members play important roles in a diverse array of hematopoietic and immune responses. This review covers the discovery and history of this enzyme family, discusses the roles of PKC enzymes in the development and effector functions of major hematopoietic and immune cell types, and points out gaps in our knowledge, which should ignite interest and further exploration, ultimately leading to better understanding of this enzyme family and, above all, its role in the many facets of the immune system.

Signaling in Effector Lymphocytes: Insights toward Safer Immunotherapy

Receptors on T and NK cells systematically propagate highly complex signaling cascades that direct immune effector functions, leading to protective immunity. While extensive studies have delineated hundreds of signaling events that take place upon receptor engagement, the precise molecular mechanism that differentially regulates the induction or repression of a unique effector function is yet to be fully defined. Such knowledge can potentiate the tailoring of signal transductions and transform cancer immunotherapies. Targeted manipulations of signaling cascades can augment one effector function such as antitumor cytotoxicity while contain the overt generation of pro-inflammatory cytokines that contribute to treatment-related toxicity such as “cytokine storm” and “cytokine-release syndrome” or lead to autoimmune diseases. Here, we summarize how individual signaling molecules or nodes may be optimally targeted to permit selective ablation of toxic immune side effects.

Nuclear PKC-θ facilitates rapid transcriptional responses in human memory CD4+ T cells through p65 and H2B phosphorylation

Memory T cells are characterized by their rapid transcriptional programs upon re-stimulation. This transcriptional memory response is facilitated by permissive chromatin, but exactly how the permissive epigenetic landscape in memory T cells integrates incoming stimulatory signals remains poorly understood. By genome-wide ChIP-sequencing ex vivo human CD4⁺ T cells, here, we show that the signaling enzyme, protein kinase C theta (PKC-θ) directly relays stimulatory signals to chromatin by binding to transcriptional-memory-responsive genes to induce transcriptional activation. Flanked by permissive histone modifications, these PKC-enriched regions are significantly enriched with NF-κB motifs in ex vivo bulk and vaccinia-responsive human memory CD4⁺ T cells. Within the nucleus, PKC-θ catalytic activity maintains the Ser536 phosphorylation on the p65 subunit of NF-κB (also known as RelA) and can directly influence chromatin accessibility at transcriptional memory genes by regulating H2B deposition through Ser32 phosphorylation. Furthermore, using a cytoplasm-restricted PKC-θ mutant, we highlight that chromatin-anchored PKC-θ integrates activating signals at the chromatin template to elicit transcriptional memory responses in human memory T cells.

Summary: Memory T cells have a rapid transcriptional program upon re-stimulation. Chromatin-anchored PKC-θ integrates activating signals at the chromatin template to elicit this transcriptional memory in T cells.

Oral Administration of p-Hydroxycinnamic Acid Attenuates Atopic Dermatitis by Downregulating Th1 and Th2 Cytokine Production and Keratinocyte Activation

Atopic dermatitis (AD) is a complex disease that is caused by various factors, including environmental change, genetic defects, and immune imbalance. We previously showed that p-hydroxycinnamic acid (HCA) isolated from the roots of Curcuma longa inhibits T-cell activation without inducing cell death. Here, we demonstrated that oral administration of HCA in a mouse model of ear AD attenuates the following local and systemic AD manifestations: ear thickening, immune-cell infiltration, production of AD-promoting immunoregulatory cytokines in ear tissues, increased spleen and draining lymph node size and weight, increased pro-inflammatory cytokine production by draining lymph nodes, and elevated serum immunoglobulin production. HCA treatment of CD4+ T cells in vitro suppressed their proliferation and differentiation into Th1 or Th2 and their Th1 and Th2 cytokine production. HCA treatment of keratinocytes lowered their production of the pro-inflammatory cytokines that drive either Th1 or Th2 responses in AD. Thus, HCA may be of therapeutic potential for AD as it acts by suppressing keratinocyte activation and downregulating T-cell differentiation and cytokine production.

CD28 costimulatory signals in T lymphocyte activation: Emerging functions beyond a qualitative and quantitative support to TCR signalling

CD28 is one of the most important co-stimulatory receptors necessary for full T lymphocyte activation. By binding its cognate ligands, B7.1/CD80 or B7.2/CD86, expressed on the surface of professional antigen presenting cells (APC), CD28 initiates several signalling cascades, which qualitatively and quantitatively support T cell receptor (TCR) signalling. More recent data evidenced that human CD28 can also act as a TCR-independent signalling unit, by delivering specific signals, which regulate the expression of pro-inflammatory cytokine/chemokines. Despite the enormous progresses made in identifying the mechanisms and molecules involved in CD28 signalling properties, much remains to be elucidated, especially in the light of the functional differences observed between human and mouse CD28. In this review we provide an overview of the current mechanisms and molecules through which CD28 support TCR signalling and highlight recent findings on the specific signalling motifs that regulate the unique pro-inflammatory activity of human CD28.

Usp9X Is Required for Lymphocyte Activation and Homeostasis through Its Control of ZAP70 Ubiquitination and PKCβ Kinase Activity

To achieve a durable adaptive immune response, lymphocytes must undergo clonal expansion and induce a survival program that enables the persistence of Ag-experienced cells and the development of memory. During the priming phase of this response, CD4(+)T lymphocytes either remain tolerized or undergo clonal expansion. In this article, we show that Usp9X functions as a positive regulatory switch during T lymphocyte priming through removal of inhibitory monoubiquitination from ZAP70. In the absence of Usp9X, an increased amount of ZAP70 localized to early endosomes consistent with the role of monoubiquitin in endocytic sorting. Usp9X becomes competent to deubiquitinate ZAP70 through TCR-dependent phosphorylation and enhancement of its catalytic activity and association with the LAT signalosome. In B lymphocytes, Usp9X is required for the induction of PKCβ kinase activity after BCR-dependent activation. Accordingly, inUsp9Xknockout B cells, there was a significant reduction in phospho-CARMA1 levels that resulted in reduced CARMA1/Bcl-10/MALT-1 complex formation and NF-κB-dependent cell survival. The pleiotropic effect of Usp9X during Ag-receptor signaling highlights its importance for the development of an effective and durable adaptive immune response.

Cell Type-Specific Regulation of Immunological Synapse Dynamics by B7 Ligand Recognition

B7 proteins CD80 (B7-1) and CD86 (B7-2) are expressed on most antigen-presenting cells and provide critical co-stimulatory or inhibitory input to T cells via their T-cell-expressed receptors: CD28 and CTLA-4. CD28 is expressed on effector T cells and regulatory T cells (Tregs), and CD28-dependent signals are required for optimum activation of effector T cell functions. CD28 ligation on effector T cells leads to formation of distinct molecular patterns and induction of cytoskeletal rearrangements at the immunological synapse (IS). CD28 plays a critical role in recruitment of protein kinase C (PKC)-θ to the effector T cell IS. CTLA-4 is constitutively expressed on the surface of Tregs, but it is expressed on effector T cells only after activation. As CTLA-4 binds to B7 proteins with significantly higher affinity than CD28, B7 ligand recognition by cells expressing both receptors leads to displacement of CD28 and PKC-θ from the IS. In Tregs, B7 ligand recognition leads to recruitment of CTLA-4 and PKC-η to the IS. CTLA-4 plays a role in regulation of T effector and Treg IS stability and cell motility. Due to their important roles in regulating T-cell-mediated responses, B7 receptors are emerging as important drug targets in oncology. In this review, we present an integrated summary of current knowledge about the role of B7 family receptor–ligand interactions in the regulation of spatial and temporal IS dynamics in effector and Tregs.

mTOR signaling and transcriptional regulation in T lymphocytes

The mechanistic target of rapamycin (mTOR) signaling integrates diverse environmental cues, including growth factors, nutrients and immunological signals. Activation of mTOR signaling stimulates protein synthesis and anabolic metabolism and coordinates cell growth, proliferation and fate decisions. In recent years, mTOR signaling has been linked to the entire spectrum of T cell biology, ranging from T cell development and activation to lineage specification and memory formation. Mechanistically, mTOR activation profoundly affects the expression and activity of many immunologically relevant transcription factors to propagate immune signaling and mediate effector functions. These transcription factors orchestrate cell metabolism (MYC, SREBPs and HIF1), lineage differentiation (T-bet, GATA3, RORγt, FOXP3 and Eomesodermin) and immune activation and functions (NF-κB, FOXOs, IRF4, STATs and GFI-1). This review discusses how mTOR signaling, through impinging upon transcriptional factors, regulates T cell development, activation, and effector and memory differentiation.

PKC-Theta in Regulatory and Effector T-cell Functions

One of the major goals in immunology research is to understand the regulatory mechanisms that underpin the rapid switch on/off of robust and efficient effector (Teffs) or regulatory (Tregs) T-cell responses. Understanding the molecular mechanisms underlying the regulation of such responses is critical for the development of effective therapies. T-cell activation involves the engagement of T-cell receptor and co-stimulatory signals, but the subsequent recruitment of serine/threonine-specific protein Kinase C-theta (PKC-θ) to the immunological synapse (IS) is instrumental for the formation of signaling complexes, which ultimately lead to a transcriptional network in T cells. Recent studies demonstrated that major differences between Teffs and Tregs occurred at the IS where its formation induces altered signaling pathways in Tregs. These pathways are characterized by reduced recruitment of PKC-θ, suggesting that PKC-θ inhibits Tregs suppressive function in a negative feedback loop. As the balance of Teffs and Tregs has been shown to be central in several diseases, it was not surprising that some studies revealed that PKC-θ plays a major role in the regulation of this balance. This review will examine recent knowledge on the role of PKC-θ in T-cell transcriptional responses and how this protein can impact on the function of both Tregs and Teffs.

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.

TCR-induced sumoylation of the kinase PKC-θ controls T cell synapse organization and T cell activation

Sumoylation regulates many cellular processes, but its role in signaling via the T cell antigen receptor (TCR) remains unknown. We found that the kinase PKC-θ was sumoylated upon costimulation with antigen or via the TCR plus the coreceptor CD28, with Lys325 and Lys506 being the main sumoylation sites. We identified the SUMO E3 ligase PIASxβ as a ligase for PKC-θ. Analysis of primary mouse and human T cells revealed that sumoylation of PKC-θ was essential for T cell activation. Desumoylation did not affect the catalytic activity of PKC-θ but inhibited the association of CD28 with PKC-θ and filamin A and impaired the assembly of a mature immunological synapse and central co-accumulation of PKC-θ and CD28. Our findings demonstrate that sumoylation controls TCR-proximal signaling and that sumoylation of PKC-θ is essential for the formation of a mature immunological synapse and T cell activation.

Grape seed proanthocyanidin extracts prevent high glucose-induced endothelia dysfunction via PKC and NF-κB inhibition

In our study, it has been detected in vivo and in vitro that GSPE reversed high glucose-induced the increase of ICAM-1 and VCAM-1. It is shown that by western blotting detection, GSPE significantly inhibited the activation of NF-κB induced by high glucose while there was significant decrease of the expression of PKC with GSPE intervention. By adding the NF-κB blocker PDTC and the PKC inhibitor peptide 19–31(10−6 M), no significant difference was found in the levels of VCAM-1 and ICAM-1 among GSPE group, the PKC inhibitor peptide 19–31-added GSPE group and the PDTC-added GSPE group. So the conclusion could be drawn that PKC inhibition must be involved in GSPE decreasing the level of ICAM-1 and VCAM-1.We proved for the first time that GSPE prevented high glucose-induced the increase of ICAM-1 and VCAM-1 by PKC and NF-κB inhibition. These findings show a novel mechanism of the action GSPE preventing endothelial dysfunction, which may have clinical application values.

Activation of human naïve Th cells increases surface expression of GD3 and induces neoexpression of GD2 that colocalize with TCR clusters

CD4+ T helper lymphocytes (Th) orchestrate the immune response after their activation by antigen-presenting cells. Activation of naïve Th cells is reported to generate the reduction in surface epitopes of sialic acid (Sia) in α2,3 and α2,6 linkages. In this work, we report that in spite of this glycophenotype, anti-CD3/anti-CD28-activated purified human naïve Th cells show a significant increase in surface Sia, as assessed by metabolic labeling, compared with resting naïve Th cells, suggesting an increased flux of Sia toward Siaα2,8 glycoconjugates. To understand this increase as a result of ganglioside up-regulation, we observed that very early after activation, human naïve Th cells show an increased expression in surface GD3 and neoexpression of surface GD2 gangliosides, the latter clustering with the T cell receptor (TCR). Also, we report that in contrast to GM2/GD2 synthase null mice, lentiviral vector-mediated silencing of the GM2/GD2 synthase in activated human naïve Th cells reduced efficient TCR clustering and downstream signaling, as assessed by proliferation assays and IL-2 and IL-2R expression, pointing to an important role of this enzyme in activation of human naive Th cells.

Targeting PKCθ in skeletal muscle and muscle diseases: good or bad?

Protein kinase Cθ (PKCθ) is a member of the novel calcium-independent PKC family, with a relatively selective tissue distribution. Most studies have focused on its unique role in T-lymphocyte activation and suggest that inhibition of PKCθ could represent a novel therapeutic approach in the treatment of chronic inflammation, autoimmunity and allograft rejection. However, considering that PKCθ is also expressed in other cell types, including skeletal muscle cells, it is important to understand its function in different tissues before proposing it as a molecular target for the treatment of immune-mediated diseases. A number of studies have highlighted the role of PKCθ in mediating several intracellular pathways, regulating muscle cell development, homoeostasis and remodelling, although a comprehensive picture is still lacking. Moreover, we recently showed that lack of PKCθ in a mouse model of Duchenne muscular dystrophy (DMD) ameliorates the progression of the disease. In the present article, we review new developments in our understanding of the involvement of PKCθ in intracellular mechanisms regulating skeletal muscle development, growth and maintenance under physiological conditions and recent advances showing a hitherto unrecognized role of PKCθ in promoting muscular dystrophy.

Protein kinase C: a regulator of cytoskeleton remodelling and T-cell migration

Protein kinase C (PKC) is a family of ten serine/threonine kinases that have diverse roles in the signalling pathways regulating cellular proliferation, differentiation, apoptosis and immune responses. Elucidating roles for individual PKC isoforms in the immune responses of T-cells have long been a challenging prospect, because these cells are known to express nine of these isoforms. A variety of approaches including the use of knockout mice, overexpression of kinase-inactive mutants, cell-permeable peptides, pharmacological inhibitors and siRNAs have shown that PKCs regulate the production of inflammatory cytokines and the cytotoxic responses of various T-cell subsets. Central to the T-cell immune response is a requirement to migrate to various organs and tissues in search of pathogens and micro-organisms. T-cell migration is guided by specific sets of chemokines and integrin ligands that activate their cognate chemokine receptors and integrins on T-cells, resulting in remodelling of the cytoskeleton and the dynamic protrusive/contractile forces necessary for cell adhesion and motility. In the present article, we review the role of PKC in T-cell migration, with an emphasis on studies that have defined their roles in cytoskeletal remodelling, cell polarity and intracellular trafficking downstream of chemokine receptors and integrins.

Protein kinase Cθ: the pleiotropic T-cell signalling intermediate

Activating as well as inhibitory circuits tightly regulate T-cell activation thresholds and effector differentiation processes enabling proper immune response outcomes. Recently, an additional molecular link between T-cell receptor signalling and CD4⁺ Th17 cell skewing has been reported, namely that protein kinase C (PKC) θ critically regulates Th17/Th1 phenotypic differentiation and plasticity in CD4⁺ T-cells by selectively acting as a 'reprogramming element' that suppresses Th1-typical genes during Th17-mediated immune activation in order to stabilize a Th17 cell phenotype.

PKCθ-regulated signalling in health and disease

Protein kinase Cθ (PKCθ) is a key enzyme in T-lymphocytes where it plays an important role in signal transduction downstream of the activated T-cell receptor (TCR) and the CD28 co-stimulatory receptor. Antigenic stimulation of T-cells triggers PKCθ translocation to the centre of the immunological synapse (IS) at the contact site between antigen-specific T-cells and antigen-presenting cells (APCs). The IS-residing PKCθ phosphorylates and activates effector molecules that transduce signals into distinct subcellular compartments and activate the transcription factors, nuclear factor κB (NF-κB), nuclear factor of activated T-cells (NFAT) and activating protein 1 (AP-1), which are essential for the induction of T-cell-mediated responses. Besides its major biological role in T-cells, PKCθ is expressed in several additional cell types and is involved in a variety of distinct physiological and pathological phenomena. For example, PKCθ is expressed at high levels in platelets where it regulates signal transduction from distinct surface receptors, and is required for optimal platelet activation and aggregation, as well as haemostasis. In addition, PKCθ is involved in physiological processes regulating insulin resistance and susceptibility to obesity, and is expressed at high levels in gastrointestinal stromal tumours (GISTs), although the functional importance of PKCθ in these processes and cell types is not fully clear. The present article briefly reviews selected topics relevant to the biological roles of PKCθ in health and disease.

Selective protein kinase Cθ (PKCθ) inhibitors for the treatment of autoimmune diseases

Protein kinase Cθ (PKCθ) is a member of a large family of serine/threonine kinases that are involved in diverse cellular functions. PKCθ has roles in T-cell activation and survival, where the dependency of T-cell responses on this enzyme appears to be dictated by both the nature of the antigen and by the inflammatory environment. Studies in PKCθ-deficient mice have demonstrated that although anti-viral responses are PKCθ-independent, T-cell responses associated with autoimmune diseases are PKCθ-dependent. PKCθ-deficient mice are either resistant to or show markedly reduced symptoms in models of MS (multiple sclerosis), IBD (inflammatory bowel disease), arthritis and asthma. Thus potent and selective inhibition of PKCθ has the potential to block T-cell-mediated autoimmunity without compromising anti-viral responses. The present review describes the design and optimization of potent and selective PKCθ inhibitors and their efficacy in both in vitro and in vivo studies. First, our compounds confirm the critical role for PKCθ in T-cell activation and proliferation and secondly they help to demonstrate that murine and human memory T-cell function continues to be dependent on this enzyme. In addition, these inhibitors demonstrate impressive efficacy in treating established autoimmune disease in murine models of IBD and MS.

MALT1 is required for EGFR-induced NF-κB activation and contributes to EGFR-driven lung cancer progression

The transcription factor nuclear factor kappa B (NF-κB) has been implicated in having a crucial role in the tumorigenesis of many types of human cancers. Although epidermal growth factor receptor (EGFR) can directly activate NF-κB, the mechanism by which EGFR induces NF-κB activation and the role of NF-κB in EGFR-associated tumor progression is still not fully defined. Herein, we found that mucosa-associated lymphoid tissue 1 (MALT1) is involved in EGFR-induced NF-κB activation in cancer cells, and that MALT1 deficiency impaired EGFR-induced NF-κB activation. MALT1 mainly functions as a scaffold protein by recruiting E3 ligase TRAF6 to IKK complex to activate NF-κB in response to EGF stimulation. Functionally, MALT1 inhibition shows significant defects in EGFR-associated tumor malignancy, including cell migration, metastasis and anchorage-independent growth. To further access a physiological role of MALT1-dependent NF-κB activation in EGFR-driven tumor progression, we generated triple-transgenic mouse model (tetO-EGFR(L858R); CCSP-rtTA; Malt1(-/-)), in which mutant EGFR-driven lung cancer was developed in the absence of MALT1 expression. MALT1-deficient mice show significantly less lung tumor burden when compared with its heterozygous controls, suggesting that MALT1 is required for the progression of EGFR-induced lung cancer. Mechanistically, MALT1 deficiency abolished both NF-κB and STAT3 activation in vivo, which is a result of a defect of interleukin-6 production. In comparison, MALT1 deficiency does not affect tumor progression in a mouse model (LSL-K-ras(G12D); CCSP-Cre; Malt1(-/-)) in which lung cancer is induced by expressing a K-ras mutant. Thus, our study has provided the cellular and genetic evidence that suggests MALT1-dependent NF-κB activation is important in EGFR-associated solid-tumor progression.

Indoctrinating T cells to attack pathogens through homeschooling

Adaptive immunity is predicated on the ability of the T cell repertoire to have pre-existing specificity for the universe of potential pathogens. Recent findings suggest that T cell receptor (TCR)-self-major histocompatibility protein (pMHC) interactions limit autoimmune responses while enhancing T cell response to foreign antigens. We review these findings here, placing them in context of the current understanding of how TCR-self-pMHC interactions regulate T cell activation thresholds, and suggest that TCR-self-pMHC interactions increase the efficiency of the T cell repertoire by giving a competitive advantage to peptide cross-reactive T cells. We propose that self-reactivity and peptide cross-reactivity are controlled by particular CDR3 sequence motifs, which would allow thymic selection to contribute to solving the feat of broad pathogen specificity by exporting T cells that are pre-screened by positive and negative selection for the ability to be 'moderately' peptide cross-reactive.

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.

Novel protein kinase C θ: coronin 1A complex in T lymphocytes

Background

Protein kinase C-θ (PKCθ) plays an important role in signal transduction down-stream of the T cell receptor and T cells deficient of PKCθ show impaired NF-κB as well as NFAT/AP-1 activation resulting in strongly decreased IL-2 expression and proliferation. However, it is not yet entirely clear, how the function of PKCθ - upon T cell activation - is regulated on a molecular level.

Findings

Employing a yeast two-hybrid screen and co-immunoprecipitation analyses, we here identify coronin 1A (Coro1A) as a novel PKCθ-interacting protein. We show that the NH₂-terminal WD40 domains of Coro1A and the C2-like domain of PKCθ are sufficient for the interaction. Furthermore, we confirm a physical interaction by GST-Coro1A mediated pull-down of endogenous PKCθ protein. Functionally, wild-type but not Coro1A lacking its actin-binding domain negatively interferes with PKCθ-dependent NF-κB, Cyclin D1 and IL-2 transactivation when analysed with luciferase promoter activation assays in Jurkat T cells. This could be phenocopied by pharmacological inhibitors of actin polymerization and PKC, respectively. Mechanistically, Coro1A overexpression attenuates both lipid raft and plasma membrane recruitment of PKCθ in CD3/CD28-activated T cells.

Using primary CD3⁺ T cells, we observed that (opposite to PKCθ) Coro1A does not localize preferentially to the immunological synapse. In addition, we show that CD3⁺ T cells isolated from Coro1A-deficient mice show impaired IKK/NF-κB transactivation.

Conclusions

Together, these findings both in Jurkat T cells as well as in primary T cells indicate a regulatory role of Coro1A on PKCθ recruitment and function downstream of the TCR leading to NF-κB transactivation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-015-0100-3) contains supplementary material, which is available to authorized users.

Immunostimulatory effects of RACK1 pseudosubstrate in human leukocytes obtained from young and old donors

Aims of this study were to investigate the ability of RACK1 pseudosubstrate alone or in combination with classical immune stimuli to activate human leukocytes, and to restore age-associated immune defects.A total of 25 donors (17 old donors, 77-79 yrs; 8 young donors, 25-34 yrs) were enrolled. To evaluate the effect of RACK1 pseudosubstrate on cytokine production and CD86 expression the whole blood assay was used. Cultures were treated with RACK1 pseudosubstrate in the presence or absence of lipopolysaccharide (LPS) or phytohaemagglutinin (PHA) and incubated for 24 h or 48 h for LPS-induced CD86 expression, TNF-α, IL-6, IL-8, IL-10 production, and PHA-induced IL-4, IL-10, IFN-γ, respectively. RACK1 pseudosubstrate alone induced IL-6, IL-8, and CD86 expression in both young and old donors, and IFN-γ in old donors. In combination with LPS an increase in IL-8, IL-10 and TNF-α was observed, also resulting in restoration of age-associated defective production, while no changes in the other parameters investigated were found.Even if based on a small sample size, these results suggest the possibility to by-pass some of age-associated immune alterations, which may be beneficial in situations were natural immune stimulation is required, and highlight a different role of PKCβ in immune cells activation.

Analysis of protein kinase C theta inhibitors for the control of HIV-1 replication in human CD4+ T cells reveals an effect on retrotranscription in addition to viral transcription

HIV-1 infection cannot be cured due to reservoirs formed early after infection. Decreasing the massive CD4+ T cell activation that occurs at the beginning of the disease would delay reservoir seeding, providing a better prognosis for patients. CD4+ T cell activation is mediated by protein kinase C (PKC) theta (θ), which is involved in T-cell proliferation, as well as NF-κB, NF-AT, and AP-1 activation. We found that PKCθ activity increased viral replication, but also that HIV-1 induced higher activation of PKCθ in infected CD4+ T cells, creating a feedback loop. Therefore, specific inhibition of PKCθ activity could contribute to control HIV-1 replication. We tested the efficacy of seven PKCθ specific inhibitors to control HIV-1 replication in CD4+ T cells and selected two of the more potent and safer: CGX1079 and CGX0471. They reduced PKCθ phosphorylation at T538 and its translocation to the plasma membrane, which correlated with decreased HIV-1 retrotranscription through partial inhibition of SAMHD1 antiviral activity, rendering lower proviral integration. CGX1079 and CGX0471 also interfered with viral transcription, which would reduce the production of new virions, as well as the subsequent spread and infection of new targets that would increase the reservoir size. CGX1079 and CGX0471 did not completely abrogate T-cell functions such as proliferation and CD8-mediated release of IFN-γ in PBMCs from HIV-infected patients, thereby avoiding general immunosuppresion. Consequently, using PKCθ inhibitors as adjuvant of antiretroviral therapy in recently infected patients would decrease the pool of activated CD4+ T cells, thwarting proviral integration and reducing the reservoir size.

PEDF-induced alteration of metabolism leading to insulin resistance

Pigment epithelium-derived factor (PEDF) is an anti-angiogenic, immunomodulatory, and neurotrophic serine protease inhibitor protein. PEDF is evolving as a novel metabolic regulatory protein that plays a causal role in insulin resistance. Insulin resistance is the central pathogenesis of metabolic disorders such as obesity, type 2 diabetes mellitus, polycystic ovarian disease, and metabolic syndrome, and PEDF is associated with them. The current evidence suggests that PEDF administration to animals induces insulin resistance, whereas neutralisation improves insulin sensitivity. Inflammation, lipolytic free fatty acid mobilisation, and mitochondrial dysfunction are the proposed mechanism of PEDF-mediated insulin resistance. This review summarises the probable mechanisms adopted by PEDF to induce insulin resistance, and identifies PEDF as a potential therapeutic target in ameliorating insulin resistance.

Inhibition of PKC-θ preserves cardiac function and reduces fibrosis in streptozotocin-induced diabetic cardiomyopathy

BACKGROUND AND PURPOSE

T-cell infiltration, interstitial fibrosis and cardiac dysfunction have been observed in diabetic patients with cardiovascular diseases. PKC-θ is crucial for the activation of mature T-cells. We hypothesized that inhibition of PKC-θ might protect diabetic hearts through inhibition of T-cell stimulation and maintenance of tight junction integrity.

EXPERIMENTAL APPROACH

A model of type 1 diabetes was induced by streptozotocin (STZ) (50 mg kg(-1) for 5 days) in male C57BL/6J wild-type (WT) mice and Rag1 knockout (KO) mice which lack mature lymphocytes. A cell-permeable selective PKC-θ peptide inhibitor (PI) was administered i.p. (0.2 mg kg(-1) ·day(-1) ) for 4 weeks (first phase) and 2 weeks (second phase). At the end of the 11th week, cardiac contractile force was measured in isolated perfused hearts. Cardiac morphology and fibrosis were determined. Phosphorylation of PKC-θ at Tyr(358) , infiltrated T-cells and tight junction protein ZO-1 within the hearts were detected, using immunohistochemcial techniques.

KEY RESULTS

PI did not affect high blood glucose level in both WT and Rag1 KO diabetic mice. Diabetes induced cardiac fibrosis in WT mice but not in Rag1 KO mice. PI attenuated cardiac fibrosis and improved cardiac contractility of WT diabetic hearts. PI decreased expression of phosphorylated PKC-θ, reduced the infiltration of T-cells and increased ZO-1 expression within WT diabetic hearts.

CONCLUSION AND IMPLICATIONS

Inhibition of PKC-θ improves cardiac function and reduces cardiac fibrosis in WT mice with streptozotocin-induced diabetes. Mature T-cells play a key role in pathophysiology of diabetic cardiomyopathy.

Estrogen-related receptor α is required for efficient human cytomegalovirus replication

An shRNA-mediated screen of the 48 human nuclear receptor genes identified multiple candidates likely to influence the production of human cytomegalovirus in cultured human fibroblasts, including the estrogen-related receptor α (ERRα), an orphan nuclear receptor. The 50-kDa receptor and a 76-kDa variant were induced posttranscriptionally following infection. Genetic and pharmacological suppression of the receptor reduced viral RNA, protein, and DNA accumulation, as well as the yield of infectious progeny. In addition, RNAs encoding multiple metabolic enzymes, including enzymes sponsoring glycolysis (enolase 1, triosephosphate isomerase 1, and hexokinase 2), were reduced when the function of ERRα was inhibited in infected cells. Consistent with the effect on RNAs, a substantial number of metabolites, which are normally induced by infection, were either not increased or were increased to a reduced extent in the absence of normal ERRα activity. We conclude that ERRα is needed for the efficient production of cytomegalovirus progeny, and we propose that the nuclear receptor contributes importantly to the induction of a metabolic environment that supports optimal cytomegalovirus replication.

IFNα signaling through PKC-θ is essential for antitumor NK cell function

We have previously shown that the development of a major histocompatibility complex class I (MHC-I)-deficient tumor was favored in protein kinase C-θ knockout (PKC-θ^-/-) mice compared to that occurring in wild-type mice. This phenomenon was associated with scarce recruitment of natural killer (NK) cells to the tumor site, as well as impaired NK cell activation and reduced cytotoxicity ex vivo. Poly-inosinic:cytidylic acid (poly I:C) treatment activated PKC-θ in NK cells depending on the presence of a soluble factor produced by a different splenocyte subset. In the present work, we sought to analyze whether interleukin-15 (IL-15) and/or interferon-α (IFNα) mediate PKC-θ-dependent antitumor NK cell function. We found that IL-15 improves NK cell viability, granzyme B expression, degranulation capacity and interferon-γ (IFNγ) secretion independently of PKC-θ. In contrast, we found that IFNα improves the degranulation capability of NK cells against target cancer cells in a PKC-θ-dependent fashion both ex vivo and in vivo. Furthermore, IFNα induces PKC-θ auto-phosphorylation in NK cells, in a signal transduction pathway involving both phosphatidylinositol-3-kinase (PI3K) and phospholipase-C (PLC) activation. PKC-θ dependence was further implicated in IFNα-induced transcriptional upregulation of chemokine (C-X-C motif) ligand 10 (CXCL10), a signal transducer and activator of transcription-1 (STAT-1)-dependent target of IFNα. The absence of PKC-θ did not affect IFNα-induced STAT-1 Tyr701 phosphorylation but affected the increase in STAT-1 phosphorylation on Ser727, attenuating CXCL10 secretion. This connection between IFNα and PKC-θ in NK cells may be exploited in NK cell-based tumor immunotherapy.

T/B-cell interactions are more transient in response to weak stimuli in SLE-prone mice

Changes in immune function during the course of systemic lupus erythematosus (SLE) are well characterized. Class-switched antinuclear antibodies are the hallmark of SLE, and T/B-cell interactions are thus critical. However, changes in immune function contributing to disease susceptibility are unknown. Here, we have analyzed primary T and B cells from a mouse model of SLE prior to the onset of disease. To allow cognate T-cell activation with low affinity, we have developed a lower potency peptide ligand for the OTII TCR. T- and B-cell couples formed less frequently and retained their polarity less efficiently preferentially in response to low-affinity stimulation in SLE-prone mice. This matched decreased recruitment of actin and Vav1 and an enhanced PKCΘ recruitment to the cellular interface in T cells. The induction of the GC B-cell marker GL7 was increased in T/B cell couples from SLE-prone mice when the T-cell numbers were limited. However, the overall gene expression changes were marginal. Taken together, the enhanced cell-couple transience may allow a more efficient sampling of a large number of T/B cell couples, preferentially in response to limiting stimuli, therefore enhancing the immune reactivity in the development of SLE.

Calcium mobilization is both required and sufficient for initiating chromatin decondensation during activation of peripheral T-cells

Antigen engagement of the T-cell receptor (TCR) induces a rapid and dramatic decondensation of chromatin that is necessary for T-cell activation. This decondensation makes T-cells competent to respond to interleukin-2 providing a mechanism to ensure clonotypic proliferation during an immune response. Using murine T-cells, we investigated the mechanism by which TCR signaling can initiate chromatin decondensation, focusing on the role of calcium mobilization. During T-cell activation, calcium is first released from intracellular stores, followed by influx of extracellular calcium via store operated calcium entry. We show that mobilization of intracellular calcium is required for TCR-induced chromatin decondensation. However, the decondensation is not dependent on the activity of the downstream transcription factor NFAT. Furthermore, we show that the influx of extracellular calcium is dispensable for initiating chromatin decondensation. Finally, we show that mobilization of calcium from intracellular stores is sufficient to induce decondensation, independent of TCR engagement. Collectively, our data suggest that chromatin decondensation in peripheral T-cells is controlled by modulating intracellular calcium levels.

Receptor proximal kinases in NF-κB signaling as potential therapeutic targets in cancer and inflammation

Many signaling pathways leading to activation of transcription factors and gene expression are characterized by phosphorylation events mediated by specific kinases. The transcription factor NF-κB plays a key role in multiple cellular processes, including immune signaling, inflammation, development, proliferation and survival. Dysregulated NF-κB activation is associated with autoimmunity, chronic inflammation and cancer. Activation of NF-κB requires IκB kinase (IKK)α or β, the activity of which is regulated via phosphorylation by specific IKK kinases and by autophosphorylation. Receptor specificity is further obtained by the use of multiple upstream receptor proximal kinases. We review the identities of several IKK regulatory kinases as well as the proposed molecular mechanisms. In addition, we discuss the potential for therapeutic targeting of some of these kinases in the context of inflammatory diseases and cancer.

Protein kinases are potential targets to treat inflammatory bowel disease

Protein kinases play a crucial role in the pathogenesis of inflammatory bowel disease (IBD), the two main forms of which are ulcerative colitis and Crohn’s disease. In this article, we will review the mechanisms of involvement of protein kinases in the pathogenesis of and intervention against IBD, in terms of their effects on genetics, microbiota, mucous layer and tight junction, and the potential of protein kinases as therapeutic targets against IBD.

mTOR signaling in tumorigenesis

mTOR (the mechanistic target of rapamycin) is an atypical serine/threonine kinase involved in regulating major cellular functions including growth and proliferation. Deregulation of the mTOR signaling pathway is one of the most commonly observed pathological alterations in human cancers. To this end, oncogenic activation of the mTOR signaling pathway contributes to cancer cell growth, proliferation and survival, highlighting the potential for targeting the oncogenic mTOR pathway members as an effective anti-cancer strategy. In order to do so, a thorough understanding of the physiological roles of key mTOR signaling pathway components and upstream regulators would guide future targeted therapies. Thus, in this review, we summarize available genetic mouse models for mTORC1 and mTORC2 components, as well as characterized mTOR upstream regulators and downstream targets, and assign a potential oncogenic or tumor suppressive role for each evaluated molecule. Together, our work will not only facilitate the current understanding of mTOR biology and possible future research directions, but more importantly, provide a molecular basis for targeted therapies aiming at key oncogenic members along the mTOR signaling pathway.

Duplicity of protein kinase C-θ: Novel insights into human T-cell biology

We recently reported on a new wrinkle of complexity in how eukaryotic genes are regulated by providing evidence for a hitherto unknown nuclear function of the signaling kinase, Protein Kinase C-theta (PKC-θ). This chromatin-anchored complex positively regulates inducible immune genes and negatively regulates target miRNA genes. These data challenge the traditional view of mammalian signaling kinases and provides new avenues for therapeutic drug design.

Prostaglandin E2 stimulates β1-integrin expression in hepatocellular carcinoma through the EP1 receptor/PKC/NF-κB pathway

Prostaglandin E₂ (PGE₂) has been implicated in cell invasion in hepatocellular carcinoma (HCC), via increased β1-integrin expression and cell migration; however, the mechanism remains unclear. PGE₂ exerts its effects via four subtypes of the E prostanoid receptor (EP receptor 1–4). The present study investigated the effect of EP1 receptor activation on β1-integrin expression and cell migration in HCC. Cell migration increased by 60% in cells treated with 17-PT-PGE₂ (EP1 agonist), which was suppressed by pretreatment with a β1-integrin polyclonal antibody. PGE₂ increased β1-integrin expression by approximately 2-fold. EP1 receptor transfection or treatment with 17-PT-PGE₂ mimicked the effect of PGE₂ treatment. EP1 siRNA blocked PGE₂-mediated β1-integrin expression. 17-PT-PGE₂ treatment induced PKC and NF-κB activation; PKC and NF-κB inhibitors suppressed 17-PT-PGE₂-mediated β1-integrin expression. FoxC2, a β1-integrin transcription factor, was also upregulated by 17-PT-PGE₂. NF-κB inhibitor suppressed 17-PT-PGE₂-mediated FoxC2 upregulation. Immunohistochemistry showed p65, FoxC2, EP1 receptor and β1-integrin were all highly expressed in the HCC cases. This study suggested that PGE₂ upregulates β1-integrin expression and cell migration in HCC cells by activating the PKC/NF-κB signaling pathway. Targeting PGE₂/EP1/PKC/NF-κB/FoxC2/β1-integrin pathway may represent a new therapeutic strategy for the prevention and treatment of this cancer.

WIP: more than a WASp-interacting protein

WIP plays an important role in the remodeling of the actin cytoskeleton, which controls cellular activation, proliferation, and function. WIP regulates actin polymerization by linking the actin machinery to signaling cascades. WIP binding to WASp and to its homolog, N-WASp, which are central activators of the actin-nucleating complex Arp2/3, regulates their cellular distribution, function, and stability. By binding to WASp, WIP protects it from degradation and thus, is crucial for WASp retention. Indeed, most mutations that result in WAS, an X-linked immunodeficiency caused by defective/absent WASp activity, are located in the WIP-binding region of WASp. In addition, by binding directly to actin, WIP promotes the formation and stabilization of actin filaments. WASp-independent activities of WIP constitute a new research frontier and are discussed extensively in this article. Here, we review the current information on WIP in human and mouse systems, focusing on its associated proteins, its molecular-regulatory mechanisms, and its role as a key regulator of actin-based processes in the immune system.

Immune consequences of kinase inhibitors in development, undergoing clinical trials and in current use in melanoma treatment

Metastatic malignant melanoma is a frequently fatal cancer. In recent years substantial therapeutic progress has occurred with the development of targeted kinase inhibitors and immunotherapeutics. Targeted therapies often result in rapid clinical benefit however responses are seldom durable. Immune therapies can result in durable disease control but responses may not be immediate. Optimal cancer therapy requires both rapid and durable cancer control and this can likely best be achieved by combining targeted therapies with immunotherapeutics. To achieve this, a detailed understanding of the immune consequences of the various kinase inhibitors, in development, clinical trial and currently used to treat melanoma is required.

TCR-induced, PKC-θ-mediated NF-κB activation is regulated by a caspase-8-caspase-9-caspase-3 cascade

It has been documented that caspase-8, a central player in apoptosis, is also crucial for TCR-mediated NF-κB activation. However, whether other caspases are also involved this process is unknown. In this report, we showed that in addition to caspase-8, caspase-9 is required for TCR-mediated NF-κB activation. Caspase-9 induces activation of PKC-θ, phosphorylation of Bcl10 and NF-κB activation in a caspase-3-dependent manner, but it appears that Bcl10 phosphorylation is uncoupled from NF-κB activation. Furthermore, caspase-8 lies upstream of caspase-9 during T cell activation. Therefore, TCR ligation elicits a caspase cascade involving caspase-8, caspase-9 and caspase-3 which initiates PKC-θ-dependent pathway leading to NF-κB activation and PKC-θ-independent Bcl10 phosphorylation which limits NF-kB activity.

Protein kinase C inhibitors for immune disorders

Protein kinase C (PKC) proteins are a group of well-conserved, intracellular signaling enzymes expressed in all cells and tissues, including immune cells. Much of the molecular insight into PKC immunobiology has been gleaned from studies using PKC gene (Prkc) knockout mice and the analysis of different disease models in these animals. More-recent studies have revealed that PKCs also have crucial roles in the pathogenesis of human immune disorders. Therefore, strategies to modulate the functions of PKC enzymes could have a major impact on the treatment and therapies of autoimmune diseases and other immune disorders.

NOTCH1 Can Initiate NF-κB Activation via Cytosolic Interactions with Components of the T Cell Signalosome

T cell stimulation requires the input and integration of external signals. Signaling through the T cell receptor (TCR) is known to induce formation of the membrane-tethered CBM complex, comprising CARMA1, BCL10, and MALT1, which is required for TCR-mediated NF-κB activation. TCR signaling has been shown to activate NOTCH proteins, transmembrane receptors also implicated in NF-κB activation. However, the link between TCR-mediated NOTCH signaling and early events leading to induction of NF-κB activity remains unclear. In this report, we demonstrate a novel cytosolic function for NOTCH1 and show that it is essential to CBM complex formation. Using a model of skin allograft rejection, we show in vivo that NOTCH1 acts in the same functional pathway as PKCθ, a T cell-specific kinase important for CBM assembly and classical NF-κB activation. We further demonstrate in vitro NOTCH1 associates physically with PKCθ and CARMA1 in the cytosol. Unexpectedly, when NOTCH1 expression was abrogated using RNAi approaches, interactions between CARMA1, BCL10, and MALT1 were lost. This failure in CBM assembly reduced inhibitor of kappa B alpha phosphorylation and diminished NF-κB–DNA binding. Finally, using a luciferase gene reporter assay, we show the intracellular domain of NOTCH1 can initiate robust NF-κB activity in stimulated T cells, even when NOTCH1 is excluded from the nucleus through modifications that restrict it to the cytoplasm or hold it tethered to the membrane. Collectively, these observations provide evidence that NOTCH1 may facilitate early events during T cell activation by nucleating the CBM complex and initiating NF-κB signaling.

Protein kinase C θ regulates the phenotype of murine CD4+ Th17 cells

Protein kinase C θ (PKCθ) is involved in signaling downstream of the T cell antigen receptor (TCR) and is important for shaping effector T cell functions and inflammatory disease development. Acquisition of Th1-like effector features by Th17 cells has been linked to increased pathogenic potential. However, the molecular mechanisms underlying Th17/Th1 phenotypic instability remain largely unknown. In the current study, we address the role of PKCθ in differentiation and function of Th17 cells by using genetic knock-out mice. Implementing in vitro (polarizing T cell cultures) and in vivo (experimental autoimmune encephalomyelitis model, EAE) techniques, we demonstrated that PKCθ-deficient CD4⁺ T cells show normal Th17 marker gene expression (interleukin 17A/F, RORγt), accompanied by enhanced production of the Th1-typical markers such as interferon gamma (IFN-γ) and transcription factor T-bet. Mechanistically, this phenotype was linked to aberrantly elevated Stat4 mRNA levels in PKCθ^−/− CD4⁺ T cells during the priming phase of Th17 differentiation. In contrast, transcription of the Stat4 gene was suppressed in Th17-primed wild-type cells. This change in cellular effector phenotype was reflected in vivo by prolonged neurological impairment of PKCθ-deficient mice during the course of EAE. Taken together, our data provide genetic evidence that PKCθ is critical for stabilizing Th17 cell phenotype by selective suppression of the STAT4/IFN-γ/T-bet axis at the onset of differentiation.

MAP4K4 deletion inhibits proliferation and activation of CD4(+) T cell and promotes T regulatory cell generation in vitro

CD4(+) T cells are critical for adaptive immunity. MAP4K4 is a key member of germinal center kinase group. However, the physiological function of MAP4K4 in primary CD4(+) T cells is still unclear. In this study, it was demonstrated that in vitro, MAP4K4 deletion remarkably suppressed CD4(+) T cell proliferation in response to phorbol 12-myristate 13-acetate (PMA) and ionomycin, which was not due to enhancing cell apoptosis. Additionally, MAP4K4 was required for the activation of CD4(+) T cells. MAP4K4 deletion significantly down-regulated expression of interleukin 2 (IL-2) and interferon-γ (IFN-γ), while notably up-regulating the expression of regulatory T cells (Treg) transcription factor Foxp3 in peripheral CD4(+) T cells. Furthermore, western blot analysis indicated that CD4(+) T cells lacking MAP4K4 failed to phosphorylate Jnk, Erk, p38 and PKC-θ. Thus, our results provide the evidence that MAP4K4 is essential for CD4(+) T cell proliferation, activation and cytokine production.

Premalignant PTEN-deficient thymocytes activate microRNAs miR-146a and miR-146b as a cellular defense against malignant transformation

Cancer develops by a multistep process during which cells acquire characteristics that allow them to evade apoptosis and proliferate unchecked. Sequential acquisition of genetic alterations drives this process but also causes cellular stress, frequently prompting cells to enter a premalignant period during which they mount a defense against transformation. T cell-specific deletion of the tumor suppressor PTEN in mice induces premalignancy in the thymus and development of CD4(+) T-cell lymphomas in the periphery. Here we sought to identify factors mediating the cellular defense against transformation during the premalignant period. We identified several microRNAs upregulated specifically in premalignant thymocytes, including miR-146a, miR-146b, and the miR-183/96/182 cluster. CD4-driven T cell-specific transgenic overexpression of mir-146a and mir-146b significantly delayed PTEN-deficient lymphomagenesis and delayed c-myc oncogene induction, a key driver of transformation in PTEN-deficient T-cell malignancies. We found that miR-146a and miR-146b targeting of Traf6 attenuates TCR signaling in the thymus and inhibits downstream NF-κB-dependent induction of c-myc. Additionally, c-myc repression in mature CD4 T cells by miR-146b impaired TCR-mediated proliferation. Hence, we have identified 2 miRNAs that are upregulated as part of the cellular response against transformation that, when overrepresented, can effectively inhibit progression to malignancy in the context of PTEN deficiency.