Protein kinase C theta (PKCtheta): a key player in T cell life and death

Identification of autoantibody biomarkers for primary Sjögren's syndrome using protein microarrays

Sjögren’s syndrome (SS) is a chronic, progressive autoimmune disease primarily affecting women. Diagnosis of SS requires an invasive salivary gland tissue biopsy and a long delay from the start of the symptoms to final diagnosis has been frequently observed. In this study,we aim to identify salivary autoantibody biomarkers for primary SS (pSS) using a protein microarray approach. Immune-response protoarrays were used to profile saliva autoantibodies from patients with pSS (n = 514), patients with systemic lupus erythematosus(SLE, n = 513), and healthy control subjects (n = 513). We identified 24 potential autoantibody biomarkers that can discriminate patients with pSS from both patients with SLE and healthy individuals. Four saliva autoantibody biomarkers, anti-transglutaminase, anti-histone, anti-SSA, and anti-SSB, were further tested in independent pSS (n = 534), SLE (n = 534), and healthy control (n = 534) subjects and all were successfully validated with ELISA. This study has demonstrated the potential of a high-throughput protein microarray approach for the discovery of autoantibody biomarkers. The identified saliva autoantibody biomarkers may lead to a clinical tool for simple, noninvasive detection of pSS at low cost.

Novel mycotoxin from Acremonium exuviarum is a powerful inhibitor of the mitochondrial respiratory chain complex III

A novel mycotoxin named acrebol, consisting of two closely similar peptaibols (1726 and 1740 Da), was isolated from an indoor strain of the mitosporic ascomycete fungus Acremonium exuviarum. This paper describes the unique mitochondrial toxicity of acrebol, not earlier described for any peptaibol. Acrebol inhibited complex III of the respiratory chain of isolated rat liver mitochondria (1 mg of protein mL(-1)) with an IC(50) of approximately 80 ng mL(-1) (50 nM) after a short preincubation, and 350 ng mL(-1) caused immediate and complete inhibition. Acrebol thus is a complex III inhibitor almost as potent as antimycin A and myxothiazol but completely different in structure. Similarly to myxothiazol but in contrast to antimycin A, acrebol decreased the level of mitochondrial superoxide anion detectable by chemiluminescent probe 3,7-dihydro-2-methyl-6-(4-methoxyphenyl)imidazol[1,2-a]pyrazine-3-one. Unlike other peptaibols, acrebol in toxic concentrations did not increase the ionic and solute permeability of membranes of isolated rat liver mitochondria, did not induce disturbance of the ionic homeostasis or the osmotic balance of mitochondria, and did not release apoptogenic proteins like cytochrome c from the intermembrane space of mitochondria. In boar spermatozoa, acrebol inhibited the respiratory chain and caused ATP depletion by activation of the oligomycin-sensitive F(0)F(1)-ATPase, which resulted in the inhibition of the progressive movement. In mouse insulinoma MIN-6 cells, whose energy supply solely depends on oxidative phosphorylation, acrebol induced necrosis-like death. The pathophysiological relevance of these findings is discussed.

Cytoskeletal keratin glycosylation protects epithelial tissue from injury

Keratins 8 and 18 (K8 and K18) are heteropolymeric intermediate filament phosphoglycoproteins of simple-type epithelia. Mutations in K8 and K18 predispose the affected individual to liver disease as they protect hepatocytes from apoptosis. K18 undergoes dynamic O-linked N-acetylglucosamine glycosylation at Ser 30, 31 and 49. We investigated the function of K18 glycosylation by generating mice that overexpress human K18 S30/31/49A substitution mutants that cannot be glycosylated (K18-Gly(-)), and compared the susceptibility of these mice to injury with wild-type and other keratin-mutant mice. K18-Gly(-) mice are more susceptible to liver and pancreatic injury and apoptosis induced by streptozotocin or to liver injury by combined N-acetyl-D-glucosaminidase inhibition and Fas administration. The enhanced apoptosis in the livers of mice that express K18-Gly(-) involves the inactivation of Akt1 and protein kinase Ctheta as a result of their site-specific hypophosphorylation. Akt1 binds to K8, which probably contributes to the reciprocal hyperglycosylation and hypophosphorylation of Akt1 that occurs on K18 hypoglycosylation, and leads to decreased Akt1 kinase activity. Therefore, K18 glycosylation provides a unique protective role in epithelial injury by promoting the phosphorylation and activation of cell-survival kinases.

Intact T cell receptor signaling by CD4(+) T cells cultured in the rotating wall-vessel bioreactor

T lymphocytes fail to proliferate or secrete cytokines in response to T cell receptor (TCR) agonists during culture in spaceflight or ground-based microgravity analogs such as rotating wall-vessel (RWV) bioreactors. In RWVs, these responses can be rescued by co-stimulation with sub-mitogenic doses of the diacyl glycerol (DAG) mimetic phorbol myristate acetate. Based on this result we hypothesized that TCR activation is abrogated in the RWV due to impaired DAG signaling downstream of the TCR. To test this hypothesis we compared TCR-induced signal transduction by primary, human, CD4(+) T cells in RWV, and static culture. Surprisingly, we found little evidence of impaired DAG signaling in the RWV. Upstream of DAG, the tyrosine phosphorylation of several key components of the TCR-proximal signal was not affected by culture in the RWV. Similarly, the phosphorylation and compartmentalization of ERK and the degradation of IkappaB were unchanged by culture in the RWV indicating that RAS- and PKC-mediated signaling downstream of DAG are also unaffected by simulated microgravity. We conclude from these data that TCR signaling through DAG remains intact during culture in the RWV, and that the loss of functional T cell activation in this venue derives from the affect of simulated microgravity on cellular processes that are independent of the canonical TCR pathway.

Protein kinase Cθ is required for cardiomyocyte survival and cardiac remodeling

Protein kinase Cs (PKCs) constitute a family of serine/threonine kinases, which has distinguished and specific roles in regulating cardiac responses, including those associated with heart failure. We found that the PKCθ isoform is expressed at considerable levels in the cardiac muscle in mouse, and that it is rapidly activated after pressure overload. To investigate the role of PKCθ in cardiac remodeling, we used PKCθ^−/− mice. In vivo analyses of PKCθ^−/− hearts showed that the lack of PKCθ expression leads to left ventricular dilation and reduced function. Histological analyses showed a reduction in the number of cardiomyocytes, combined with hypertrophy of the remaining cardiomyocytes, cardiac fibrosis, myofibroblast hyper-proliferation and matrix deposition. We also observed p38 and JunK activation, known to promote cell death in response to stress, combined with upregulation of the fetal pattern of gene expression, considered to be a feature of the hemodynamically or metabolically stressed heart. In keeping with these observations, cultured PKCθ^−/− cardiomyocytes were less viable than wild-type cardiomyocytes, and, unlike wild-type cardiomyocytes, underwent programmed cell death upon stimulation with α1-adrenergic agonists and hypoxia. Taken together, these results show that PKCθ maintains the correct structure and function of the heart by preventing cardiomyocyte cell death in response to work demand and to neuro-hormonal signals, to which heart cells are continuously exposed.

Protective Toxoplasma gondii-specific T-cell responses require T-cell-specific expression of protein kinase C-theta

Protein kinase C-theta (PKC-theta) is important for the activation of autoreactive T cells but is thought to be of minor importance for T-cell responses in infectious diseases, suggesting that PKC-theta may be a target for the treatment of T-cell-mediated autoimmune diseases. To explore the function of PKC-theta in a chronic persisting infection in which T cells are crucial for pathogen control, we infected BALB/c PKC-theta(-/-) and PKC-theta(+/+) wild-type mice with Toxoplasma gondii. The PKC-theta(-/-) mice succumbed to necrotizing Toxoplasma encephalitis due to an insufficient parasite control up to day 40, whereas the wild-type mice survived. The number of T. gondii-specific CD4 and CD8 T cells was significantly reduced in the PKC-theta(-/-) mice, resulting in the impaired production of protective cytokines (gamma interferon, tumor necrosis factor) and antiparasitic effector molecules (inducible nitric oxide, gamma interferon-induced GTPase) in the spleen and brain. In addition, Th2-cell numbers were reduced in infected the PKC-theta(-/-) mice, paralleled by the diminished GATA3 expression of PKC-theta(-/-) CD4 T cells and reduced T. gondii-specific IgG production in serum and cerebrospinal fluid. Western blot analysis of splenic CD4 and CD8 T cells revealed an impaired activation of the NF-kappaB, AP-1, and MAPK pathways in T. gondii-infected PKC-theta(-/-) mice. Adoptive transfer of wild-type CD4 plus CD8 T cells significantly protected PKC-theta(-/-) mice from death by increasing the numbers of gamma interferon-producing T. gondii-specific CD4 and CD8 T cells, illustrating a cell-autonomous, protective function of PKC-theta in T cells. These findings imply that PKC-theta inhibition drastically impairs T. gondii-specific T-cell responses with fatal consequences for intracerebral parasite control and survival.

Human Vgamma9Vdelta2 T cells: from signals to functions

Human Vgamma9Vdelta2 T cells, a major innate-like peripheral T cell subset, are thought to play in vivo a key role in innate and adaptive immune responses to infection agents and tumors. Vgamma9Vdelta2 T cell activation is tightly regulated by a variety of activating or inhibitory receptors which are specific for constitutively expressed or stress-modulated ligands. However, the mechanisms and signal transduction pathways regulating their broad effector functions, such as cytotoxicity and cytokine responses, remain poorly understood. Here we provide an updated overview of the activation modalities of Vgamma9Vdelta2 T cells by highlighting the respective role played by T cell receptor (TCR) versus non-TCR stimuli, and focus on recent studies showing how Vgamma9Vdelta2 T cells integrate the numerous activating and inhibitory signals and translate them into a particular effector and biological function. A better understanding of these critical issues should help optimize immunotherapeutic approaches targeting Vgamma9Vdelta2 T cells.

PKCtheta is necessary for efficient activation of NFkappaB, NFAT, and AP-1 during positive selection of thymocytes

While it has been shown in several publications that the serine-threonine kinase PKCθ is required for efficient activation of mature T lymphocytes, the role of PKCθ in T cell development in the thymus is somewhat controversial. In this study, using knockout mice, we show that PKCθ is important in positive selection. The thymus of PKCθ^−/− animals contains significantly less mature single positive T cells compared to wild-type controls. Biochemically, PKCθ deficient thymocytes show defective activation of the transcription factors AP-1, NFAT and NFκB as well as impaired phosphorylation of the MAP kinase ERK after T cell receptor stimulation in vitro. Together, these results reveal a crucial role of PKCθ in positive selection of thymocytes in a pathway leading to the activation of ERK, AP-1, NFAT, and NFκB.

Update on the genetic risk factors for rheumatoid arthritis

Rheumatoid arthritis (RA) is a complex disease, meaning that multiple genetic variants, environmental factors and random events interact to trigger pathological pathways. Although many of these etiological factors have not yet been identified, recent groundbreaking advances have expanded our knowledge about the genetic factors that contribute to RA. Here, we review the most recent findings on the genetic risk factors for RA. First, we give an overview of the genetics of RA and briefly describe the susceptibility loci discovered prior to the availability of genome-wide association studies (GWAS). Second, we focus on the newly discovered RA loci that have arisen from GWAS in populations of European ancestry. Through these studies, the number of established RA susceptibility loci has now grown to 13. Third, we discuss several important issues emerging from GWAS, such as ethnic heterogeneity and shared autoimmunity risk loci. Finally, we discuss what still needs to be accomplished before a more complete picture of the genetic risk to RA can be attained.

Protein kinase C-theta mediates negative feedback on regulatory T cell function

T cell receptor (TCR)-dependent regulatory T cell (Treg) activity controls effector T cell (Teff) function and is inhibited by the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). Protein kinase C-theta (PKC-theta) recruitment to the immunological synapse is required for full Teff activation. In contrast, PKC-theta was sequestered away from the Treg immunological synapse. Furthermore, PKC-theta blockade enhanced Treg function, demonstrating PKC-theta inhibits Treg-mediated suppression. Inhibition of PKC-theta protected Treg from inactivation by TNF-alpha, restored activity of defective Treg from rheumatoid arthritis patients, and enhanced protection of mice from inflammatory colitis. Treg freed of PKC-theta-mediated inhibition can function in the presence of inflammatory cytokines and thus have therapeutic potential in control of inflammatory diseases.

PKC and the control of localized signal dynamics

Networks of signal transducers determine the conversion of environmental cues into cellular actions. Among the main players in these networks are protein kinases, which can acutely and reversibly modify protein functions to influence cellular events. One group of kinases, the protein kinase C (PKC) family, have been increasingly implicated in the organization of signal propagation, particularly in the spatial distribution of signals. Examples of where and how various PKC isoforms direct this tier of signal organization are becoming more evident.

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.

The SWI/SNF chromatin-remodeling complex modulates peripheral T cell activation and proliferation by controlling AP-1 expression

The SWI/SNF chromatin-remodeling complex has been implicated in the activation and proliferation of T cells. After T cell receptor signaling, the SWI/SNF complex rapidly associates with chromatin and controls gene expression in T cells. However, the process by which the SWI/SNF complex regulates peripheral T cell activation has not been elucidated. In this study, we show that the SWI/SNF complex regulates cytokine production and proliferation of T cells. During T cell activation, the SWI/SNF complex is recruited to the promoter of the transcription factor AP-1, and it increases the expression of AP-1. Increased expression of the SWI/SNF complex resulted in enhanced AP-1 activity, cytokine production, and proliferation of peripheral T cells, whereas knockdown of the SWI/SNF complex expression impaired the AP-1 expression and reduced the activation and proliferation of T cells. Moreover, mice that constitutively expressed the SWI/SNF complex in T cells were much more susceptible to experimentally induced autoimmune encephalomyelitis than the normal mice were. These results suggest that the SWI/SNF complex plays a critical role during T cell activation and subsequent immune responses.

Organization of proximal signal initiation at the TCR:CD3 complex

The series of events leading to T-cell activation following antigen recognition has been extensively investigated. Although the exact mechanisms of ligand binding and transmission of this extracellular interaction into a productive intracellular signaling sequence remains incomplete, it has been known for many years that the immunoreceptor tyrosine activation motifs (ITAMs) of the T-cell receptor (TCR):CD3 complex are required for initiation of this signaling cascade because of the recruitment and activation of multiple protein tyrosine kinases, signaling intermediates, and adapter molecules. It however remains unclear why the TCR:CD3 complex requires 10 ITAMs, while many other ITAM-containing immune receptors, such as Fc receptors (FcRs) and the B cell receptor (BCR), contain far fewer ITAMs. We have recently demonstrated that various parameters of T cell development and activation are influenced by the number, as well as location and type, of ITAMs within the TCR:CD3 complex and hence propose that the TCR is capable of 'scalable signaling' that facilitates the initiation and orchestration of diverse T-cell functions. While many of the underlying mechanisms remain hypothetical, this review intends to amalgamate what we have learned from conventional biochemical analyses regarding initiation and diversification of T-cell signaling, with more recent evidence from molecular and fluorescent microscopic analyses, to propose a broader purpose for the TCR:CD3 ITAMs. Rather than simply signal initiation, individual ITAMs may also be responsible for the differential recruitment of signaling and regulatory molecules which ultimately affects T-cell development, activation and differentiation.

E3 ubiquitin ligase GRAIL controls primary T cell activation and oral tolerance

T cell unresponsiveness or anergy is one of the mechanisms that maintain inactivity of self-reactive lymphocytes. E3 ubiquitin ligases are important mediators of the anergic state. The RING finger E3 ligase GRAIL is thought to selectively function in anergic T cells but its mechanism of action and its role in vivo are largely unknown. We show here that genetic deletion of Grail in mice leads not only to loss of an anergic phenotype in various models but also to hyperactivation of primary CD4(+) T cells. Grail(-/-) CD4(+) T cells hyperproliferate in vitro to TCR stimulation alone or with concomitant anti-CD28 costimulation, with transient increased survival. In vitro differentiated T helper 1 cells show slight but significant hypersecretion of IFN-gamma in Grail(-/-) mice whereas Th2 and Th17 cytokine secretions are unchanged. Consistent with defective in vitro anergy, oral tolerance is abolished in vivo in OT-II TCR transgenic Grail(-/-) mice fed with ovalbumin. In experimental allergic encephalitis, a model of organ-specific autoimmunity, oral tolerization with myelin basic protein was abrogated as well in Grail(-/-) mice. On the protein level, Grail(-/-) naïve T cells show no significant differences of total and phosphorylated levels of ZAP70, phospholipase Cgamma1, and MAP kinases p38 and JNK but elevated baseline levels of MAP kinase ERK1/2. In summary, we define a role for GRAIL in primary T cell activation, survival, and differentiation. In addition, we formally prove an indispensable role for GRAIL in T cell anergy and oral tolerance-a promising, antigen-specific strategy to treat autoimmune diseases.

Gamma-aminobutyric acid transporter 1 negatively regulates T cell activation and survival through protein kinase C-dependent signaling pathways

Gamma-aminobutyric acid transporter 1 (GAT-1), as the major regulator in maintaining a gamma-aminobutyric acid reservoir in the CNS, plays negative roles in experimental autoimmune encephalomyelitis pathogenesis. Our previous study has revealed that, besides its wide expression in the CNS, GAT-1 expression can be induced on activated T cells triggered by Ag. However, the function of GAT-1 in T cell activation is unclear. In this study, we show that GAT-1 deficiency induces more vigorous cell cycle entry and less cell apoptosis in T cells, thus leading to enhanced cell proliferation. GAT-1 deficiency promotes T cell division and survival by down-regulating cyclin dependent kinase inhibitor p27(kip1), differentially regulating the pro- and anti-apoptotic proteins Bcl-2, Bcl-xl, and Bad and activating transcription factor NF-kappaB through induction of translocation and phosphorylation of protein kinase C (PKC) theta. In addition, our data reveal that GAT-1 expression on T cells is modulated by PKC activation. Taken together, the data show that GAT-1 negatively regulates T cell activation and survival through PKC-dependent signaling pathways.

Common and different genetic background for rheumatoid arthritis and coeliac disease

Recent genome-wide association studies (GWAS) have revealed genetic risk factors in autoimmune and inflammatory disorders. Several of the associated genes and underlying pathways are shared by various autoimmune diseases. Rheumatoid arthritis (RA) and coeliac disease (CD) are two autoimmune disorders which have commonalities in their pathogenesis. We aimed to replicate known RA loci in a Dutch RA population, and to investigate whether the effect of known RA and CD risk factors generalize across the two diseases. We selected all loci associated to either RA or CD in a GWAS and confirmed in an independent cohort, with a combined P-value cut-off P < 5 x 10(-6). We genotyped 11 RA and 11 CD loci in 1368 RA patients, 795 CD patients and 1683 Dutch controls. We combined our results in a meta-analysis with UK GWAS on RA (1860 cases; 2938 controls) and CD (767 cases; 1422 controls). In the Dutch RA cohort, the PTPN22 and IL2/IL21 variants showed convincing association (P = 3.4 x 10(-12) and P = 2.8 x 10(-4), respectively). Association of RA with the known CD risk variant in the SH2B3 was also observed, predominantly in the subgroup of rheumatoid factor-positive RA patients (P = 0.0055). In a meta-analysis of Dutch and UK data sets, shared association with six loci (TNFAIP3, IL2/IL21, SH2B3, LPP, MMEL1/TNFRSF14 and PFKFB3/PRKCQ) was observed in both RA and CD cohorts. We confirmed two known loci and identified four novel ones for shared CD-RA genetic risk. Most of the shared loci further emphasize a role for adaptive and innate immunity in these diseases.

AEB-071 has minimal impact on onset of autoimmune diabetes in NOD mice

Protein kinase C (PKC) is an important signaling enzyme in the activation and regulation of T lymphocytes. T-cell-mediated destruction of beta-cells is a characteristic feature of autoimmune (Type 1) diabetes. Here we explore the ability of PKC inhibition, using the PKC inhibitor AEB-071 (AEB), to reduce disease in two animal models of spontaneous autoimmune diabetes (non-obese diabetic (NOD) mouse and biobreeding rat (BB)). NOD mice were treated with AEB for 4 weeks, starting at either 4 weeks of age (prior to the development of insulitis) or at 8 weeks of age, once insulitis is present. Animals treated with AEB during the effector phase of the disease (treatment onset at 8 weeks of age), showed a 2-week delay in diabetes onset (p < 0.05). In these animals, the extent of insulitis was lower than in vehicle-treated controls; however, neither serum autoimmune anti-GAD65 antibody levels nor pancreatic insulin content were different between experimental groups. Overall, inhibition of PKC can mildly reduce lymphocytic infiltrate of pancreatic islets and modestly delay onset of autoimmune diabetes in NOD mice. AEB, a T-cell-targeted immunosuppressive strategy, is only sufficient as a monothereapy to modestly delay onset of autoimmune disease in the NOD mouse.

PKC-theta modulates the strength of T cell responses by targeting Cbl-b for ubiquitination and degradation

The E3 ubiquitin ligase Casitas B-lineage lymphoma (Cbl-b) is central to antigen-induced immune tolerance and regulates the CD28 dependence of T cell activation. Cbl-b undergoes ubiquitination and proteasomal degradation after adequate costimulation of T cells; however, the mechanism involved is unknown. Here, we identified protein kinase C-theta (PKC-theta) as the critical intermediary for the inactivation of Cbl-b in response to costimulation of T cells through CD28. PKC-theta associated with Cbl-b on stimulation of the T cell receptor. After costimulation of T cells through CD28, Cbl-b was ubiquitinated and degraded through a mechanism that depended on the kinase activity of PKC-theta. Consistent with this mechanism, the impaired responses of PKCtheta-deficient T cells were at least partially restored by the concomitant genetic loss of cblb. Thus, our data establish a nonredundant antagonism between PKC-theta and Cbl-b that regulates T cell activation responses.

Pertussis toxin signals through the TCR to initiate cross-desensitization of the chemokine receptor CXCR4

Pertussis toxin (PTx) has been shown to exert a variety of effects on immune cells independent of its ability to ADP-ribosylate G proteins. Of these effects, the binding subunit of PTx (PTxB) has been shown to block signaling via the chemokine receptor CCR5, but the mechanism involved in this process is unknown. Here, we show that PTxB causes desensitization of a related chemokine receptor, CXCR4, and explore the mechanism by which this occurs. CXCR4 is the receptor for the chemokine stromal cell-derived factor 1alpha (SDF-1alpha) and elicits a number of biological effects, including stimulation of T cell migration. PTxB treatment causes a decrease in CXCR4 surface expression, inhibits G protein-associated signaling, and blocks SDF-1alpha-mediated chemotaxis. We show that PTxB mediates these effects by activating the TCR signaling network, as the effects are dependent on TCR and ZAP70 expression. Additionally, the activation of the TCR with anti-CD3 mAb elicits a similar set of effects on CXCR4 activity, supporting the idea that TCR signaling leads to cross-desensitization of CXCR4. The inhibition of CXCR4 by PTxB is rapid and transient; however, the catalytic activity of PTx prevents CXCR4 signaling in the long term. Thus, the effects of PTx holotoxin on CXCR4 signaling can be divided into two phases: short term by the B subunit, and long term by the catalytic subunit. These data suggest that TCR crosstalk with CXCR4 is likely a normal cellular process that leads to cross-desensitization, which is exploited by the B subunit of PTx.

Targeted knock-in mice expressing mutations of CD28 reveal an essential pathway for costimulation

Despite extensive study, the role of phosphatidylinositol 3-kinase (PI3-kinase) activation in CD28 function has been highly contentious. To definitively address this question, we generated knock-in mice expressing mutations in two critical domains of the cytoplasmic tail of CD28. Mutation of the proximal tyrosine motif interrupted PI3-kinase binding and prevented CD28-dependent phosphorylation of protein kinase B (PKB)/Akt; however, there was no detectable effect on interleukin-2 (IL-2) secretion, expression of Bcl-X(L), or on T-cell function in vivo. Furthermore, we demonstrate that signaling initiated by the C-terminal proline motif is directly responsible for tyrosine phosphorylation of phosphoinosotide-dependent kinase 1, protein kinase C theta, and glycogen synthase kinase 3beta, as well as contributing to threonine phosphorylation of PKB. T cells mutated in this domain were profoundly impaired in IL-2 secretion, and the mice had marked impairment of humoral responses as well as less severe disease manifestations in experimental allergic encephalomyelitis. These data demonstrate that the distal proline motif initiates a critical nonredundant signaling pathway, whereas direct activation of PI3-kinase by the proximal tyrosine motif of CD28 is not required for normal T-cell function.

Genome-wide association studies in type 1 diabetes

Type 1 diabetes (T1D) is a chronic disease that typically manifests itself in childhood through the autoimmune destruction of pancreatic beta cells, resulting in a lack of production of insulin. T1D is a multifactorial disease with a strong genetic component that is thought to interact with specific environmental triggers. Several genetic determinants of T1D were already established before the era of genome-wide association studies, primarily with the HLA class II genes, encoding highly polymorphic antigen-presenting proteins that account for almost 50% of the genetic risk for T1D. The recent development of high-throughput single nucleotide polymorphism genotyping array technologies has enabled investigators to perform high-density genome-wide association studies in search of the remaining T1D loci. Combined with the well-established genes known for many years, 16 loci have now been uncovered to date as being robustly associated with the pathogenesis of this phenotype.

Synthesis and PKCtheta inhibitory activity of a series of 4-indolylamino-5-phenyl-3-pyridinecarbonitriles

A series of 4-indolylamino-5-phenyl-3-pyridinecarbonitrile inhibitors of PKCtheta were synthesized as potential anti-inflammatory agents. The effects of specific substitution on the 5-phenyl moiety and variations of the positional isomers of the 4-indolylamino substituent were explored. This study led to the discovery of compound 12d, which had an IC(50) value of 18nM for the inhibition of PKCtheta.

Protein kinase C inhibitor, AEB-071, acts complementarily with cyclosporine to prevent islet rejection in rats

BACKGROUND

AEB-071 (AEB) is a specific inhibitor of protein kinase C, which prevents T-lymphocyte activation. The present study investigated the effect of AEB on rat islet allotransplantation alone or in combination with CTLA4-Ig, mycophenolate mofetil, or cyclosporine A (CsA).

METHODS

A rodent allogeneic islet transplant model (Lewis to Wistar Furth) was used to investigate the efficacy of AEB as an immunosuppressive agent. Furthermore, the Lewis rat was used to screen for any AEB associated toxicities on glucose homeostasis in vivo.

RESULTS

AEB alone (30 mg/kg per os [p.o.] two times per day [bid]) delayed rejection to a median survival time of 22 days (vs. 7 days in control vehicle-treated animals, P<0.05). When combined with CsA (5 mg/kg p.o. bid), AEB prolonged survival from 12 (CsA alone) to over 100 days in 80% of animals (P<0.05). No delay in allograft rejection (above that resulting from AEB alone) was observed when AEB was combined with a sub-therapeutic dose of CTLA4-Ig or mycophenolate mofetil, nor low dose of CsA. The frequency of allospecific interferon-gamma-secreting splenocytes, assessed ex vivo by enzyme-linked immunosorbent spot (ELISPOT) assay, was lower in AEB-treated recipients compared with controls (P<0.05). AEB treatment did not alter the intraperitoneal glucose tolerance, the glucose-dependent insulin release, or the insulin content of the native pancreas.

CONCLUSIONS

These data suggest that AEB is an appropriate immunosuppressive agent for islet transplantation, as it can prolong islet graft survival alone or in combination with CsA, without toxicity on glucose metabolism.

G protein-coupled receptor connectivity to NF-kappaB in inflammation and cancer

Complex intracellular network interactions regulate gene expression and cellular behavior. Whether at the site of inflammation or within a tumor, individual cells are exposed to a plethora of signals. The transcription factor nuclear factor-kappaB (NF-kappaB) regulates genes that control key cellular activities involved in inflammatory diseases and cancer. NF-kappaB is regulated by several distinct signaling pathways that may be activated individually or simultaneously. Multiple ligands and heterologous cell-cell interactions have an impact on NF-kappaB activity. The G protein-coupled receptor (GPCR) superfamily makes up the largest class of transmembrane receptors in the human genome and has multiple molecularly distinct natural ligands. GPCRs regulate proliferation, differentiation, and chemotaxis and play a major role in inflammatory diseases and cancer. Both GPCRs and NF-kappaB have been, and continue to be, major targets for drug discovery. A clear understanding of network interactions between GPCR signaling pathways and those that control NF-kB may be valuable for the development of better drugs and drug combinations.

T cell activation

This year marks the 25th anniversary of the first Annual Review of Immunology article to describe features of the T cell antigen receptor (TCR). In celebration of this anniversary, we begin with a brief introduction outlining the chronology of the earliest studies that established the basic paradigm for how the engaged TCR transduces its signals. This review continues with a description of the current state of our understanding of TCR signaling, as well as a summary of recent findings examining other key aspects of T cell activation, including cross talk between the TCR and integrins, the role of costimulatory molecules, and how signals may negatively regulate T cell function.Acronyms and DefinitionsAdapter protein: cellular protein that functions to bridge molecular interactions via characteristic domains able to mediate protein/protein or protein/lipid interactions Costimulation: signals delivered to T cells by cell surface receptors other than the TCR itself that potentiate T cell activation cSMAC: central supramolecular activation cluster Immunoreceptor tyrosine-based activation motif (ITAM): a short peptide sequence in the cytoplasmic tails of key surface receptors on hematopoietic cells that is characterized by tyrosine residues that are phosphorylated by Src family PTKs, enabling the ITAM to recruit activated Syk family kinases Inside-out signaling: signals initiated by engagement of immunoreceptors that lead to conformational changes and clustering of integrins, thereby increasing the affinity and avidity of the integrins for their ligands NFAT: nuclear factor of activated T cells PI3K: phosphoinositide 3-kinase PKC: protein kinase C PLC: phospholipase C pMHC: peptide major histocompatibility complex (MHC) complex pSMAC: peripheral supramolecular activation cluster PTK: protein tyrosine kinase Signal transduction: biochemical events linking surface receptor engagement to cellular responses TCR: T cell antigen receptor

Discovering Protein Kinase C Active Plants Growing in Finland Utilizing Automated Bioassay Combined to LC/MS

Protein kinase C (PKC) modulating activity of 81 plant extracts of Finnish origin was investigated with an automated bioassay method combined to LC/MS. Twenty-one extracts from different parts of the plants inhibited PKC significantly. Fractionation of the active extract of Filipendula ulmaria showed that this method was able to identify a PKC inhibiting compound from the extract as quercetin. Our results indicate that this method is suitable for PKC screening of complex matrices and provides a quick and low volume, non-radioactive, alternative method for PKC experiments.

Regulated movement of CD4 in and out of the immunological synapse

The mechanism underlying the transient accumulation of CD4 at the immunological synapse (IS) and its significance for T cell activation are not understood. To investigate these issues, we mutated a serine phosphorylation site (S408) in the cytoplasmic tail of murine CD4. Preventing phosphorylation of S408 did not block CD4 recruitment to the IS; rather, it blocked the ability of CD4 to leave the IS. Surprisingly, enhanced and prolonged CD4 accumulation at the supramolecular activation cluster in the contact area had no functional consequence for T cell activation, cytokine production, or proliferation. Protein kinase C theta (PKCtheta)-deficient T cells also displayed enhanced and prolonged accumulation of wild-type CD4 at the IS, indicating that theta is the critical PKC isoform involved in CD4 movement. These findings suggest a model wherein recruitment of CD4 to the IS allows its phosphorylation by PKCtheta and subsequent removal from the IS. Thus, an important role for PKCtheta in T cell activation involves its recruitment to the IS, where it phosphorylates specific substrates that help to maintain the dynamism of protein turnover at the IS.

Meta-analysis of genome-wide association study data identifies additional type 1 diabetes risk loci

We carried out a meta-analysis of data from three genome-wide association (GWA) studies of type 1 diabetes (T1D), testing 305,090 SNPs in 3,561 T1D cases and 4,646 controls of European ancestry. We obtained further support for 4q27 (IL2-IL21, P = 1.9 x 10(-8)) and, after genotyping an additional 6,225 cases, 6,946 controls and 2,828 families, convincing evidence for four previously unknown and distinct risk loci in chromosome regions 6q15 (BACH2, P = 4.7 x 10(-12)), 10p15 (PRKCQ, P = 3.7 x 10(-9)), 15q24 (CTSH, P = 3.2 x 10(-15)) and 22q13 (C1QTNF6, P = 2.0 x 10(-8)).

Protein kinase C-theta is required for efficient positive selection

Protein kinase C-theta (PKCtheta) is critical for TCR-initiated signaling in mature T cells, but initial reports found no requirement for PKCtheta in thymocyte development. Thymocytes and peripheral T cells utilize many of the same signaling components and, given the significant role of PKCtheta in peripheral T cells, it was surprising that it was not involved at all in TCR signaling in thymocytes. We decided to re-evaluate the role of PKCtheta in thymocyte development using the well-characterized class II-restricted n3.L2 TCR-transgenic TCR model. Analysis of n3.L2 PKCtheta(-/-) mice revealed a defect in thymocyte-positive selection, resulting in a 50% reduction in the generation of n3.L2 CD4 single-positive thymocytes and n3.L2 CD4 mature T cells. Competition between n3.L2 WT and n3.L2 PKCtheta(-/-) thymocytes in bone marrow chimeras revealed a more dramatic defect, with a >80% reduction in generation of n3.L2 CD4 single-positive thymocytes derived from PKCtheta(-/-) mice. Inefficient positive selection of n3.L2 PKCtheta(-/-) CD4 single-positive cells resulted from "weaker" signaling through the TCR and correlated with diminished ERK activation. The defect in positive selection was not complete in the PKCtheta(-/-) mice, most likely accounted for by compensation by other PKC isoforms not evident in peripheral cells. Similar decreased positive selection of both CD4 and CD8 single-positive thymocytes was also seen in nontransgenic PKCtheta(-/-) mice. These findings now place PKCtheta as a key signaling molecule in the positive selection of thymocytes as well as in the activation of mature T cells.

Rheumatoid arthritis susceptibility loci at chromosomes 10p15, 12q13 and 22q13

The WTCCC study identified 49 SNPs putatively associated with rheumatoid arthritis at P = 1 x 10(-4) - 1 x 10(-5) (tier 3). Here we show that three of these SNPs, mapping to chromosome 10p15 (rs4750316), 12q13 (rs1678542) and 22q13 (rs3218253), are also associated (trend P = 4 x 10(-5), P = 4 x 10(-4) and P = 4 x 10(-4), respectively) in a validation study of 4,106 individuals with rheumatoid arthritis and an expanded reference group of 11,238 subjects, confirming them as true susceptibility loci in individuals of European ancestry.

NK cell-activating receptors require PKC-theta for sustained signaling, transcriptional activation, and IFN-gamma secretion

Natural killer (NK) cell sense virally infected cells and tumor cells through multiple cell surface receptors. Many NK cell-activating receptors signal through immunoreceptor tyrosine-based activation motif (ITAM)-containing adapters, which trigger both cytotoxicy and secretion of interferon-gamma (IFN-gamma). Within the ITAM pathway, distinct signaling intermediates are variably involved in cytotoxicity and/or IFN-gamma secretion. In this study, we have evaluated the role of protein kinase C- (PKC-) in NK-cell secretion of lytic mediators and IFN-gamma. We found that engagement of NK-cell receptors that signal through ITAMs results in prompt activation of PKC-. Analyses of NK cells from PKC--deficient mice indicated that PKC- is absolutely required for ITAM-mediated IFN-gamma secretion, whereas it has no marked influence on the release of cytolytic mediators. Moreover, we found that PKC- deficiency preferentially impairs sustained extracellular-regulated kinase signaling as well as activation of c-Jun N-terminal kinase and the transcription factors AP-1 and NFAT but does not affect activation of NF-kappaB. These results indicate that NK cell-activating receptors require PKC- to generate sustained intracellular signals that reach the nucleus and promote transcriptional activation, ultimately inducing IFN-gamma production.

PKCdelta mediates thrombin-augmented fibroblast-mediated collagen gel contraction

Fibroblast-mediated collagen gel contraction has been used as an in vitro model of tissue remodeling. Thrombin is one of the mediators present in the milieu of airway inflammation and may be involved in airway tissue remodeling. We have previously reported that thrombin stimulates fibroblast-mediated collagen gel contraction partially through the PAR1/PKCepsilon signaling pathway [Q. Fang, X. Liu, S. Abe, T. Kobayashi, X.Q. Wang, T. Kohyama, M. Hashimoto, T. Wyatt, S.I. Rennard, Thrombin induces collagen gel contraction partially through PAR1 activation and PKC-epsilon, Eur. Respir. J. 24 (2004) 918-924]. Here, we further report that the delta-isoform of PKC (PKCdelta) is also activated by thrombin and involved in the thrombin-mediated augmentation of collagen gel contraction. Thrombin (10nM) significantly increased PKCdelta activity (over 5-fold increase after 15-30min stimulation) and stimulated phosphorylation of PKCdelta. Rottlerin, a PKCdelta inhibitor, completely inhibited activation of PKCdelta and partially blocked collagen gel contraction stimulated by thrombin. Similarly, PKCdelta-specific siRNA significantly inhibited PKCdelta activation without affecting PKCepsilon expression and activation. Furthermore, suppression of PKCdelta by siRNA resulted in partial blockade of thrombin-augmented collagen gel contraction. These results suggest that thrombin contributes to the tissue remodeling in inflammatory airways and lung diseases at least partially through both PKCdelta and PKCepsilon signaling.