Protein kinase C family functions in B-cell activation

A spatiotemporal map of co-receptor signaling networks underlying B cell activation

The B cell receptor (BCR) signals together with a multi-component co-receptor complex to initiate B cell activation in response to antigen binding. Here, we take advantage of peroxidase-catalyzed proximity labeling combined with quantitative mass spectrometry to track co-receptor signaling dynamics in Raji cells from 10 s to 2 h after BCR stimulation. This approach enables tracking of 2,814 proximity-labeled proteins and 1,394 phosphosites and provides an unbiased and quantitative molecular map of proteins recruited to the vicinity of CD19, the signaling subunit of the co-receptor complex. We detail the recruitment kinetics of signaling effectors to CD19 and identify previously uncharacterized mediators of B cell activation. We show that the glutamate transporter SLC1A1 is responsible for mediating rapid metabolic reprogramming and for maintaining redox homeostasis during B cell activation. This study provides a comprehensive map of BCR signaling and a rich resource for uncovering the complex signaling networks that regulate activation.

Glucocorticoids paradoxically promote steroid resistance in B cell acute lymphoblastic leukemia through CXCR4/PLC signaling

Glucocorticoid (GC) resistance in childhood relapsed B-cell acute lymphoblastic leukemia (B-ALL) represents an important challenge. Despite decades of clinical use, the mechanisms underlying resistance remain poorly understood. Here, we report that in B-ALL, GC paradoxically induce their own resistance by activating a phospholipase C (PLC)-mediated cell survival pathway through the chemokine receptor, CXCR4. We identify PLC as aberrantly activated in GC-resistant B-ALL and its inhibition is able to induce cell death by compromising several transcriptional programs. Mechanistically, dexamethasone (Dex) provokes CXCR4 signaling, resulting in the activation of PLC-dependent Ca2+ and protein kinase C signaling pathways, which curtail anticancer activity. Treatment with a CXCR4 antagonist or a PLC inhibitor improves survival of Dex-treated NSG mice in vivo. CXCR4/PLC axis inhibition significantly reverses Dex resistance in B-ALL cell lines (in vitro and in vivo) and cells from Dex resistant ALL patients. Our study identifies how activation of the PLC signalosome in B-ALL by Dex limits the upfront efficacy of this chemotherapeutic agent.

Schisandrin A alleviates renal fibrosis by inhibiting PKCβ and oxidative stress

BACKGROUND

Renal fibrosis is a common pathway that drives the advancement of numerous kidney maladies towards end-stage kidney disease (ESKD). Suppressing renal fibrosis holds paramount clinical importance in forestalling or retarding the transition of chronic kidney diseases (CKD) to renal failure. Schisandrin A (Sch A) possesses renoprotective effect in acute kidney injury (AKI), but its effects on renal fibrosis and underlying mechanism(s) have not been studied.

STUDY DESIGN

Serum biochemical analysis, histological staining, and expression levels of related proteins were used to assess the effect of PKCβ knockdown on renal fibrosis progression. Untargeted metabolomics was used to assess the effect of PKCβ knockdown on serum metabolites. Unilateral Ureteral Obstruction (UUO) model and TGF-β induced HK-2 cells and NIH-3T3 cells were used to evaluate the effect of Schisandrin A (Sch A) on renal fibrosis. PKCβ overexpressed NIH-3T3 cells were used to verify the possible mechanism of Sch A.

RESULTS

PKCβ was upregulated in the UUO model. Knockdown of PKCβ mitigated the progression of renal fibrosis by ameliorating perturbations in serum metabolites and curbing oxidative stress. Sch A alleviated renal fibrosis by downregulating the expression of PKCβ in kidney. Treatment with Sch A significantly attenuated the upregulated proteins levels of FN, COL-I, PKCβ, Vimentin and α-SMA in UUO mice. Moreover, Sch A exhibited a beneficial impact on markers associated with oxidative stress, including MDA, SOD, and GSH-Px. Overexpression of PKCβ was found to counteract the renoprotective efficacy of Sch A in vitro.

CONCLUSION

Sch A alleviates renal fibrosis by inhibiting PKCβ and attenuating oxidative stress.

Mercury intoxication disrupts tonic signaling in B cells, and may promote autoimmunity due to abnormal phosphorylation of STIM-1 and other autoimmunity risk associated phosphoproteins involved in BCR signaling

Epidemiological studies link exposure to mercury with autoimmune disease. Unfortunately, in spite of considerable effort, no generally accepted mechanistic understanding of how mercury functions with respect to the etiology of autoimmune disease is currently available. Nevertheless, autoimmune disease often arises because of defective B cell signaling. Because B cell signaling is dependent on phosphorylation cascades, in this report, we have focused on how mercury intoxication alters phosphorylation of B cell proteins in antigen-non stimulated (tonic) mouse (BALB/c) splenic B cells. Specifically, we utilized mass spectrometric techniques to conduct a comprehensive unbiased global analysis of the effect of inorganic mercury (Hg2+) on the entire B cell phosphoproteome. We found that the effects were pleotropic in the sense that large numbers of pathways were impacted. However, confirming our earlier work, we found that the B cell signaling pathway stood out from the rest, in that phosphoproteins which had sites which were affected by Hg2+, exhibited a much higher degree of connectivity, than components of other pathways. Further analysis showed that many of these BCR pathway proteins had been previously linked to autoimmune disease. Finally, dose response analysis of these BCR pathway proteins showed STIM1_S575, and NFAT2_S259 are the two most Hg2+ sensitive of these sites. Because STIM1_S575 controls the ability of STIM1 to regulate internal Ca2+, we speculate that STIM1 may be the initial point of disruption, where Hg2+ interferes with B cell signaling leading to systemic autoimmunity, with the molecular effects pleiotropically propagated throughout the cell by virtue of Ca2+ dysregulation.

A Spatiotemporal Map of Co-Receptor Signaling Networks Underlying B Cell Activation

The B cell receptor (BCR) signals together with a multi-component co-receptor complex to initiate B cell activation in response to antigen binding. This process underlies nearly every aspect of proper B cell function. Here, we take advantage of peroxidase-catalyzed proximity labeling combined with quantitative mass spectrometry to track B cell co-receptor signaling dynamics from 10 seconds to 2 hours after BCR stimulation. This approach enables tracking of 2,814 proximity-labeled proteins and 1,394 quantified phosphosites and provides an unbiased and quantitative molecular map of proteins recruited to the vicinity of CD19, the key signaling subunit of the co-receptor complex. We detail the recruitment kinetics of essential signaling effectors to CD19 following activation, and then identify new mediators of B cell activation. In particular, we show that the glutamate transporter SLC1A1 is responsible for mediating rapid metabolic reprogramming immediately downstream of BCR stimulation and for maintaining redox homeostasis during B cell activation. This study provides a comprehensive map of the BCR signaling pathway and a rich resource for uncovering the complex signaling networks that regulate B cell activation.

Chronic Granulomatous Disease-Like Presentation of a Child with Autosomal Recessive PKCδ Deficiency

BACKGROUND

Autosomal recessive (AR) PKCδ deficiency is a rare inborn error of immunity (IEI) characterized by autoimmunity and susceptibility to bacterial, fungal, and viral infections. PKCδ is involved in the intracellular production of reactive oxidative species (ROS).

MATERIAL AND METHODS

We studied a 5-year old girl presenting with a history of Burkholderia cepacia infection. She had no history of autoimmunity, lymphocyte counts were normal, and no auto-antibodies were detected in her plasma. We performed a targeted panel analysis of 407 immunity-related genes and immunological investigations of the underlying genetic condition in this patient.

RESULTS

Consistent with a history suggestive of chronic granulomatous disease (CGD), oxidative burst impairment was observed in the patient's circulating phagocytes in a dihydrorhodamine 123 (DHR) assay. However, targeted genetic panel analysis identified no candidate variants of known CGD-causing genes. Two heterozygous candidate variants were detected in PRKCD: c.285C > A (p.C95*) and c.376G > T (p.D126Y). The missense variant was also predicted to cause abnormal splicing, as it is located at the splice donor site of exon 5. TOPO-TA cloning confirmed that exon 5 was completely skipped, resulting in a truncated protein. No PKCδ protein was detected in the patient's neutrophils and monocyte-derived macrophages. The monocyte-derived macrophages of the patient produced abnormally low levels of ROS, as shown in an Amplex Red assay.

CONCLUSION

PKCδ deficiency should be considered in young patients with CGD-like clinical manifestations and abnormal DHR assay results, even in the absence of clinical and biological manifestations of autoimmunity.

Impaired respiratory burst contributes to infections in PKCδ-deficient patients

Patients with autosomal recessive protein kinase C δ (PKCδ) deficiency suffer from childhood-onset autoimmunity, including systemic lupus erythematosus. They also suffer from recurrent infections that overlap with those seen in patients with chronic granulomatous disease (CGD), a disease caused by defects of the phagocyte NADPH oxidase and a lack of reactive oxygen species (ROS) production. We studied an international cohort of 17 PKCδ-deficient patients and found that their EBV-B cells and monocyte-derived phagocytes produced only small amounts of ROS and did not phosphorylate p40phox normally after PMA or opsonized Staphylococcus aureus stimulation. Moreover, the patients' circulating phagocytes displayed abnormally low levels of ROS production and markedly reduced neutrophil extracellular trap formation, altogether suggesting a role for PKCδ in activation of the NADPH oxidase complex. Our findings thus show that patients with PKCδ deficiency have impaired NADPH oxidase activity in various myeloid subsets, which may contribute to their CGD-like infectious phenotype.

Transplantation and immunosuppression: a review of novel transplant-related immunosuppressant drugs

Immunosuppressive drugs used in the transplantation period are generally defined as induction and maintenance therapy. The use of immunosuppressants, which are particularly useful and have fewer side effects, decreased both mortality and morbidity. Many drugs such as steroids, calcineurin inhibitors (cyclosporine-A, tacrolimus), antimetabolites (mycophenolate mofetil, azathioprine), and mTOR inhibitors (sirolimus, everolimus) are used as immunosuppressive agents. Although immunosuppressant drugs cause many side effects such as hypertension, infection, and hyperlipidemia, they are the agents that should be used to prevent organ rejection. This shows the importance of individualized drug use. The optimal immunosuppressive therapy post-transplant is not established. Therefore, discovering less toxic but more potent new agents is of great importance, and new experimental and clinical studies are needed in this regard.Our review discussed the mechanism of immunosuppressants, new agents' discovery, and current therapeutic protocols in the transplantation.

Targeting B-cell receptor and PI3K signaling in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous diagnostic category comprising distinct molecular subtypes characterized by diverse genetic aberrations that dictate patient outcome. As roughly one-third of DLBCL patients are not cured by current standard chemo-immunotherapy a better understanding of the molecular pathogenesis is warranted to improve outcome. B-cell receptor (BCR) signaling is crucial for the development, growth and survival of both normal and a substantial fraction of malignant B-cells. Various analyses revealed genetic alterations of central components of the BCR or its downstream signaling effectors in some subtypes of DLBCL. Thus, BCR signaling and the downstream NF-κB and PI3K cascades have been proposed as potential targets for the treatment of DLBCL patients. As one of the main effectors of BCR activation, PI3K mediated signals play a crucial role in the pathogenesis and survival of DLBCL. In this review, we summarize our current understanding of BCR signaling with a special focus on the PI3K pathway in DLBCL and how to utilize this knowledge therapeutically.

Signal Transduction in Immune Cells and Protein Kinases

Immune response relies upon several intracellular signaling events. Among the protein kinases involved in these pathways, members of the protein kinase C (PKC) family are prominent molecules because they have the capacity to acutely and reversibly modulate effector protein functions, controlling both spatial distribution and dynamic properties of the signals. Different PKC isoforms are involved in distinct signaling pathways, with selective functions in a cell-specific manner.In innate system, Toll-like receptor signaling is the main molecular event triggering effector functions. Various isoforms of PKC can be common to different TLRs, while some of them are specific for a certain type of TLR. Protein kinases involvement in innate immune cells are presented within the chapter emphasizing their coordination in many aspects of immune cell function and, as important players in immune regulation.In adaptive immunity T-cell receptor and B-cell receptor signaling are the main intracellular pathways involved in seminal immune specific cellular events. Activation through TCR and BCR can have common intracellular pathways while others can be specific for the type of receptor involved or for the specific function triggered. Various PKC isoforms involvement in TCR and BCR Intracellular signaling will be presented as positive and negative regulators of the immune response events triggered in adaptive immunity.

Protein Kinase C-Delta Defect in Autoimmune Lymphoproliferative Syndrome-Like Disease: First Case from the National Iranian Registry and Review of the Literature

BACKGROUND

Protein kinase C is a family of serine/threonine kinases that play a key role in the adaptive immune cell signaling, as well as regulation of growth, apoptosis, and differentiation of a variety of cell types. Patients homozygous for a null mutation of the Protein Kinase C Delta (PRKCD) gene, present clinical feature of immune dysregulation with susceptibility to Epstein-Barr virus infection. However, a minority of patients present the autoimmune lymphoproliferative syndrome (ALPS).

METHODS

The data were collected by direct interview and examining the patient's clinical record. Whole-exome sequencing was performed to detect the underlying genetic mutation in the patient. We also conducted electronic searches for ALPS-like reported patients in PubMed, Web of Science, and Scopus databases.

RESULTS

In this study, we reported a 13-year-old boy who presented with autoimmunity, lymphoproliferation, recurrent pneumonia, cardiomyopathy, and dermatological manifestations. An elevation of double-negative T cells, CD8⁺ T cells, serum IgG level, as well as a reduction in NK cells, was observed in the patient. A homozygous frameshift mutation (c.1293_1294insA) in exon 13 of the PRKCD gene was confirmed. The literature search showed 39 ALPS-like patients with monogenic defects which only six (15.3%) of them were due to PRKCD genes.

CONCLUSION

PRKCD should be considered in the context of ALPS clinical manifestations with prominent dermatological involvements.

BCALM (AC099524.1) Is a Human B Lymphocyte-Specific Long Noncoding RNA That Modulates B Cell Receptor-Mediated Calcium Signaling

Of the thousands of long noncoding RNAs (lncRNA) identified in lymphocytes, very few have defined functions. In this study, we report the discovery and functional elucidation of a human B cell-specific lncRNA with high levels of expression in three types of B cell cancer and normal B cells. The AC099524.1 gene is upstream of the gene encoding the B cell-specific phospholipase C γ 2 (PLCG2), a B cell-specific enzyme that stimulates intracellular Ca2+ signaling in response to BCR activation. AC099524.1 (B cell-associated lncRNA modulator of BCR-mediated Ca+ signaling [BCALM]) transcripts are localized in the cytoplasm and, as expected, CRISPR/Cas9 knockout of AC099524.1 did not affect PLCG2 mRNA or protein expression. lncRNA interactome, RNA immunoprecipitation, and coimmunoprecipitation studies identified BCALM-interacting proteins in B cells, including phospholipase D 1 (PLD1), and kinase adaptor proteins AKAP9 (AKAP450) and AKAP13 (AKAP-Lbc). These two AKAP proteins form signaling complexes containing protein kinases A and C, which phosphorylate and activate PLD1 to produce phosphatidic acid (PA). BCR stimulation of BCALM-deficient B cells resulted in decreased PLD1 phosphorylation and increased intracellular Ca+ flux relative to wild-type cells. These results suggest that BCALM promotes negative feedback that downmodulates BCR-mediated Ca+ signaling by promoting phosphorylation of PLD1 by AKAP-associated kinases, enhancing production of PA. PA activates SHP-1, which negatively regulates BCR signaling. We propose the name BCALM for B-Cell Associated LncRNA Modulator of BCR-mediated Ca+ signaling. Our findings suggest a new, to our knowledge, paradigm for lncRNA-mediated modulation of lymphocyte activation and signaling, with implications for B cell immune response and BCR-dependent cancers.

Sin1/mTORC2 regulate B cell growth and metabolism by activating mTORC1 and Myc

Proper control of B cell growth and metabolism is crucial for B-cell-mediated immunity, but the underlying molecular mechanisms remain incompletely understood. In this study, Sin1, a key component of mTOR complex 2 (mTORC2), specifically regulates B cell growth and metabolism. Genetic ablation of Sin1 in B cells reduces the cell size at either the transitional stage or upon antigen stimulation and severely impairs metabolism. Sin1 deficiency also severely impairs B-cell proliferation, antibody responses, and anti-viral immunity. At the molecular level, Sin1 controls the expression and stability of the c-Myc protein and maintains the activity of mTORC1 through the Akt-dependent inactivation of GSK3 and TSC1/2, respectively. Therefore, our study reveals a novel and specific role for Sin1 in coordinating the activation of mTORC2 and mTORC1 to control B cell growth and metabolism.

Attenuation of PKCδ enhances metabolic activity and promotes expansion of blood progenitors

A finely tuned balance of self‐renewal, differentiation, proliferation, and survival governs the pool size and regenerative capacity of blood‐forming hematopoietic stem and progenitor cells (HSPCs). Here, we report that protein kinase C delta (PKCδ) is a critical regulator of adult HSPC number and function that couples the proliferative and metabolic activities of HSPCs. PKCδ‐deficient mice showed a pronounced increase in HSPC numbers, increased competence in reconstituting lethally irradiated recipients, enhanced long‐term competitive advantage in serial transplantation studies, and an augmented HSPC recovery during stress. PKCδ‐deficient HSPCs also showed accelerated proliferation and reduced apoptosis, but did not exhaust in serial transplant assays or induce leukemia. Using inducible knockout and transplantation models, we further found that PKCδ acts in a hematopoietic cell‐intrinsic manner to restrict HSPC number and bone marrow regenerative function. Mechanistically, PKCδ regulates HSPC energy metabolism and coordinately governs multiple regulators within signaling pathways implicated in HSPC homeostasis. Together, these data identify PKCδ as a critical regulator of HSPC signaling and metabolism that acts to limit HSPC expansion in response to physiological and regenerative demands.

Control of autoreactive B cells by IgM and IgD B cell receptors: maintaining a fine balance

A substantial fraction of mature naïve B cells recognize endogenous antigens, and this autoreactivity must be controlled to prevent autoantibody secretion. Selective downregulation of the IgM BCR on autoreactive B cells has long been appreciated, and recent findings illustrate how this might impose tolerance. The BCR isotype maintained on autoreactive B cells, IgD, is less sensitive to endogenous antigens than IgM. This reduced sensitivity may be conferred by structural properties of IgD and/or differential association with activating and inhibitory co-receptors. Once activated, autoreactive B cells are normally excluded from rapid plasma cell responses, but they can enter the germinal center and lose their autoreactivity through a mutation-selection process termed clonal redemption.

STIM- and Orai-mediated calcium entry controls NF-κB activity and function in lymphocytes

The central role of Ca²⁺ signaling in the development of functional immunity and tolerance is well established. These signals are initiated by antigen binding to cognate receptors on lymphocytes that trigger store operated Ca²⁺ entry (SOCE). The underlying mechanism of SOCE in lymphocytes involves TCR and BCR mediated activation of Stromal Interaction Molecule 1 and 2 (STIM1/2) molecules embedded in the ER membrane leading to their activation of Orai channels in the plasma membrane. STIM/Orai dependent Ca²⁺ signals guide key antigen induced lymphocyte development and function principally through direct regulation of Ca²⁺ dependent transcription factors. The role of Ca²⁺ signaling in NFAT activation and signaling is well known and has been studied extensively, but a wide appreciation and mechanistic understanding of how Ca²⁺ signals also shape the activation and specificity of NF-κB dependent gene expression has lagged. Here we discuss and interpret what is known about Ca²⁺ dependent mechanisms of NF-kB activation, including what is known and the gaps in our understanding of how these signals control lymphocyte development and function.

Inhibition of JAK3 and PKC via Immunosuppressive Drugs Tofacitinib and Sotrastaurin Inhibits Proliferation of Human B Lymphocytes In Vitro

BACKGROUND

Antibody-mediated response in solid organ transplantation is critical for graft dysfunction and loss. The use of immunosuppressive agents partially inhibits the B-lymphocyte response leading to a risk of acute and chronic antibody-mediated rejection. This study evaluated the impact of JAK3 and PKC inhibitors tofacitinib (Tofa) and sotrastaurin (STN), respectively, on B-cell proliferation, apoptosis, and activation in vitro.

METHODS

Human B cells isolated from peripheral blood of healthy volunteers were cocultured with CD40 ligand-transfected fibroblasts as feeder cells in the presence of interleukin (IL) 2, IL-10, and IL-21. The cocultures were treated with immunosuppressants Tofa, STN, and rapamycin (as a control), to analyze the proliferation and apoptosis of B cells by means of Cyquant and flow cytometry, respectively. CD27 and IgG staining were applied to evaluate whether treatments modified the activation of B cells.

RESULTS

Tofa and STN were able to inhibit B-cell proliferation to the same extent as rapamycin, without inducing cell apoptosis. After 6 days in coculture with feeder cells, all B cells showed CD27 memory B-cell phenotype. None of the immunosuppressive treatments modified the proportion between class-switched and non-class-switched memory B cells observed in nontreated cultures. The high predominance of CD27⁺CD24⁺ phenotype was not modified by any immunosuppressive treatment.

CONCLUSIONS

Our results show that Tofa and STN can suppress B-cell antibody responses to an extent similar to rapamycin, in vitro; therefore these compounds may be a useful therapy against antibody-mediated rejection in transplantation.

PKK deficiency in B cells prevents lupus development in Sle lupus mice

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the production of autoantibodies that can result in damage to multiple organs. It is well documented that B cells play a critical role in the development of the disease. We previously showed that protein kinase C associated kinase (PKK) is required for B1 cell development as well as for the survival of recirculating mature B cells and B-lymphoma cells. Here, we investigated the role of PKK in lupus development in a lupus mouse model. We demonstrate that the conditional deletion of PKK in B cells prevents lupus development in Sle1Sle3 mice. The loss of PKK in Sle mice resulted in the amelioration of multiple classical lupus-associated phenotypes and histologic features of lupus nephritis, including marked reduction in the levels of serum autoantibodies, proteinuria, spleen size, peritoneal B-1 cell population and the number of activated CD4 T cells. In addition, the abundance of autoreactive plasma cells normally seen in Sle lupus mice was also significantly decreased in the PKK-deficient Sle mice. Sle B cells deficient in PKK display defective proliferation responses to BCR and LPS stimulation. Consistently, B cell receptor-mediated NF-κB activation, which is required for the survival of activated B cells, was impaired in the PKK-deficient B cells. Taken together, our work uncovers a critical role of PKK in lupus development and suggests that targeting the PKK-mediated pathway may represent a promising therapeutic strategy for lupus treatment.

Temporal regulation of Lsp1 O-GlcNAcylation and phosphorylation during apoptosis of activated B cells

Crosslinking of B-cell receptor (BCR) sets off an apoptosis programme, but the underlying pathways remain obscure. Here we decipher the molecular mechanisms bridging B-cell activation and apoptosis mediated by post-translational modification (PTM). We find that O-GlcNAcase inhibition enhances B-cell activation and apoptosis induced by BCR crosslinking. This proteome-scale analysis of the functional interplay between protein O-GlcNAcylation and phosphorylation in stimulated mouse primary B cells identifies 313 O-GlcNAcylation-dependent phosphosites on 224 phosphoproteins. Among these phosphoproteins, temporal regulation of the O-GlcNAcylation and phosphorylation of lymphocyte-specific protein-1 (Lsp1) is a key switch that triggers apoptosis in activated B cells. O-GlcNAcylation at S209 of Lsp1 is a prerequisite for the recruitment of its kinase, PKC-β1, to induce S243 phosphorylation, leading to ERK activation and downregulation of BCL-2 and BCL-xL. Thus, we demonstrate the critical PTM interplay of Lsp1 that transmits signals for initiating apoptosis after BCR ligation.

B cell receptor (BCR) activation can trigger signalling causing apoptosis in order to eliminate auto-reactive B cells. Here the authors show that the O-GlcNAcylation and phosphorylation of lymphocyte-specific protein-1 are involved in a switch that regulates the initiation of apoptosis induced by BCR cross-linking.

Porcine reproductive and respiratory syndrome virus (PRRSV) up-regulates IL-15 through PKCβ1-TAK1-NF-κB signaling pathway

Porcine reproductive and respiratory syndrome (PRRS) caused by PRRS virus (PRRSV) is one of the most important infectious diseases in swine industry. IL-15 is a pleiotropic cytokine and has been shown to be essential to transform NKs, CD8 T cells, and other cells of the immune systems into functional effectors. Here, we demonstrated that the broad-spectrum or conventional PKC inhibitors repressed PRRSV-induced IL-15 expression and NF-κB activation. Subsequently, we found that the PKCβ specific inhibitor inhibited PRRSV-induced IL-15 production, which was also confirmed by knock-down of PKCβ1, suggesting that PKCβ1 is involved in the PRRSV-induced IL-15 expression. In addition, we demonstrated that PRRSV activated NF-κB through PKCβ1-induced TAK1 activation. Finally, we demonstrated that PRRSV activated PKCβ1 dependent on the participation of TRIF and MAVS. These data indicate that PRRSV up-regulates IL-15 through TRIF/MAVS-PKCβ1-TAK1-NF-κB signaling pathway. These findings will provide new insights into the molecular mechanisms of IL-15 production induced by PRRSV.

Oxysterols and mechanisms of survival signaling

Oxysterols, a family of oxidation products of cholesterol, are increasingly drawing attention of scientists to their multifaceted biochemical properties, several of them of clear relevance to human pathophysiology. Taken up by cells through both vesicular and non-vesicular ways or often generated intracellularly, oxysterols contribute to modulate not only the inflammatory and immunological response but also cell viability, metabolism and function by modulating several signaling pathways. Moreover, they have been recognized as elective ligands for the most important nuclear receptors. The outcome of such a complex network of intracellular reactions promoted by these cholesterol oxidation products appears to be largely dependent not only on the type of cells, the dynamic conditions of the cellular and tissue environment but also on the concentration of the oxysterols. Here focus has been given to the cascade of molecular events exerted by relatively low concentrations of certain oxysterols that elicit survival and functional signals in the cells, with the aim to contribute to further expand the knowledge about the biological and physiological potential of the biochemical reactions triggered and modulated by oxysterols.

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.

Functions of innate and acquired immune system are reduced in domestic pigeons (Columba livia domestica) given a low protein diet

Racing pigeons are exposed to and act as carriers of diseases. Dietary protein requirement for their maintenance has not been determined experimentally despite their being domesticated for over 7000 years. A maintenance nitrogen (protein) requirement (MNR) for pigeons was determined in a balance study using diets containing 6, 10 and 14% crude protein (CP). Then, the effects of feeding the diets were investigated to determine whether they were adequate to sustain innate and acquired immune functions. Nitrogen intake from the 6% CP diet was sufficient to maintain nitrogen balance and body weight in pigeons. However, the immune functions of phagocytosis, oxidative burst and lymphocyte proliferation in pigeons fed this diet were reduced compared with those fed 10 and 14% CP diets. Pigeons given the 6 and 10% CP diets had lower antibody titres following inoculation against Newcastle disease (ND) than those on the 14% CP diet. A confounding factor found on autopsy was the presence of intestinal parasites in some of the pigeons given the 6 and 10% CP diets; however, none of the pigeons used to measure MNR or acquired immunity to ND were infested with parasites. In conclusion, neither the 6 nor 10% CP diets adequately sustained acquired immune function of pigeons.

A critical role for the protein kinase PKK in the maintenance of recirculating mature B cells and the development of B1 cells

Protein kinase C associated kinase (PKK) regulates NF-κB activation and is required for the survival of certain lymphoma cells. Mice lacking PKK die soon after birth, and previous studies suggest that the role of PKK in B cell development might be context dependent. We have generated a mouse strain harboring conditional null alleles for PKK and a Cre-recombinase transgene under the control of the endogenous CD19 promoter. In the present study, we show that knockout of PKK in B cells results in the reduction of long-lived recirculating mature B cell population in lymph nodes and bone marrow as well as a decrease in peritoneal B1 cells, while PKK deficiency has no apparent effect on early B cell development in bone marrow or the development of follicular and marginal zone B cells in the spleen. In addition, we demonstrate that PKK-deficient B cells display defective proliferation and survival responses to stimulation of B cell receptor (BCR), which may underlie the reduction of recirculating mature B cells in PKK mutant mice. Consistently, BCR-mediated NF-κB activation, known to be required for the survival of activated but not resting B cells, is attenuated in PKK-deficient B cells. Thus, our results reveal a critical role of PKK in the maintenance of recirculating mature B cells as well as the development of B1 cells in mice.

Leishmania infantum amastigotes trigger a subpopulation of human B cells with an immunoregulatory phenotype

Visceral leishmaniasis is caused by the protozoan parasites Leishmania infantum and Leishmania donovani. This infection is characterized by an uncontrolled parasitization of internal organs which, when left untreated, leads to death. Disease progression is linked with the type of immune response generated and a strong correlation was found between disease progression and serum levels of the immunosuppressive cytokine IL-10. Other studies have suggested a role for B cells in the pathology of this parasitic infection and the recent identification of a B-cell population in humans with regulatory functions, which secretes large amounts of IL-10 following activation, have sparked our interest in the context of visceral leishmaniasis. We report here that incubation of human B cells with Leishmania infantum amastigotes resulted in upregulation of multiple cell surface activation markers and a dose-dependent secretion of IL-10. Conditioned media from B cells incubated with Leishmania infantum amastigotes were shown to strongly inhibit CD4⁺ T-cell activation, proliferation and function (i.e. as monitored by TNF and IFNγ secretion). Blockade of IL-10 activity using a soluble IL-10 receptor restored only partially TNF and IFNγ production to control levels. The parasite-mediated IL-10 secretion was shown to rely on the activity of Syk, phosphatidylinositol-3 kinase and p38, as well as to require intracellular calcium mobilization. Cell sorting experiments allowed us to identify the IL-10-secreting B-cell subset (i.e. CD19⁺CD24⁺CD27^-). In summary, exposure of human B cells to Leishmania infantum amastigotes triggers B cells with regulatory activities mediated in part by IL-10, which could favor parasite dissemination in the organism.

Leishmaniasis is an infection caused by protozoan parasites of the genus Leishmania and is a significant neglected tropical disease, with 350 million people in 98 countries at risk of developing one of the forms of the disease. Visceral leishmaniasis is characterized by an uncontrolled parasitization of internal organs, which leads to death when left untreated. Disease progression is linked with the type of immune response generated and a strong correlation was found between disease progression and serum levels of the immunosuppressive cytokine IL-10. We demonstrate that a contact between human B cells with Leishmania infantum amastigotes resulted in upregulation of multiple cell surface activation markers and a dose-dependent secretion of IL-10. Conditioned media from B cells incubated with Leishmania infantum amastigotes were shown to strongly inhibit CD4⁺ T-cell activation, proliferation and function (i.e. TNF and IFNγ production). Blockade of IL-10 activity using a soluble IL-10 receptor restored to some degree TNF and IFNγ secretion. Cell sorting experiments allowed us to identify a major IL-10-secreting B cell subset characterized as CD24⁺ and CD27^-. Exposure of human B cells to Leishmania infantum amastigotes thus triggers B cells with regulatory activities mediated in part by IL-10, which could promote parasite dissemination in the organism.

Role of Calcium Signaling in B Cell Activation and Biology

Increase in intracellular levels of calcium ions (Ca2+) is one of the key triggering signals for the development of B cell response to the antigen. The diverse Ca2+ signals finely controlled by multiple factors participate in the regulation of gene expression, B cell development, and effector functions. B cell receptor (BCR)-initiated Ca2+ mobilization is sourced from two pathways: one is the release of Ca2+ from the intracellular stores, endoplasmic reticulum (ER), and other is the prolonged influx of extracellular Ca2+ induced by depleting the stores via store-operated calcium entry (SOCE) and calcium release-activated calcium (CRAC) channels. The identification of stromal interaction molecule 1(STIM1), the ER Ca2+ sensor, and Orai1, a key subunit of the CRAC channel pore, has now provided the tools to understand the mode of Ca2+ influx regulation and physiological relevance. Herein, we discuss our current understanding of the molecular mechanisms underlying BCR-triggered Ca2+ signaling as well as its contribution to the B cell biological processes and diseases.

The serine-threonine kinase p90RSK is a new target of enzastaurin in follicular lymphoma cells

BACKGROUND AND PURPOSE

Follicular lymphoma is the second most common non-Hodgkin's lymphoma and, despite the introduction of rituximab for its treatment, this disease is still considered incurable. Besides genetic alterations involving Bcl-2, Bcl-6 or c-Myc, follicular lymphoma cells often display altered B-cell receptor signalling pathways including overactive PKC and PI3K/Akt systems.

EXPERIMENTAL APPROACH

The effect of enzastaurin, an inhibitor of PKC, was evaluated both in vitro on follicular lymphoma cell lines and in vivo on a xenograft murine model. Using pharmacological inhibitors and siRNA transfection, we determined the different signalling pathways after enzastaurin treatment.

KEY RESULTS

Enzastaurin inhibited the serine-threonine kinase p90RSK which has downstream effects on GSK3β. Bad and p70S6K. These signalling proteins control follicular lymphoma cell survival and apoptosis; which accounted for the inhibition by enzastaurin of cell survival and its induction of apoptosis of follicular lymphoma cell lines in vitro. Importantly, these results were replicated in vivo where enzastaurin inhibited the growth of follicular lymphoma xenografts in mice.

CONCLUSIONS AND IMPLICATIONS

The targeting of p90RSK by enzastaurin represents a new therapeutic option for the treatment of follicular lymphoma.

PKD1 is critical for Epstein-Barr virus LMP1-induced protection of malignant B cells from cell death induced by rituximab

Protein kinase D1 (PKD1 or PKCμ) is a serine/threonine kinase that contributes to malignant progression. Although B and T cells express multiple PKCs, modulation of PKC in association with EBV has not been evaluated. In this study we examined the effects of PKD1 as a cellular target of EBV latent membrane protein-1 (LMP1) on the response of malignant B cells to rituximab and doxorubicin. LMP1 up-regulated PKD1 in malignant B cells but not in T cells. Interestingly, LMP1 stabilized PKD1 protein through direct interaction, which contributed to the survival of malignant B cells. In the absence of PKD1, LMP1 was unable to up-regulate Mcl-1. Also, PH domain and activation loop of PKD1 was critical for LMP1-mediated cell survival. PKD1 knockdown was found to be an efficient strategy to overcome resistance caused by LMP1 expression. Therefore, PKD1 could be a molecular target for therapeutic intervention in EBV-associated B cell lymphoma treatment.

Protein kinase Cθ gene expression is oppositely regulated by GCN5 and EBF1 in immature B cells

In this study, we revealed that GCN5 and early B cell factor 1 (EBF1) participate in regulation of protein kinase Cθ (PKCθ) gene expression in an opposite manner in immature B cells. GCN5-deficiency in DT40 caused drastic down-regulation of transcription of PKCθ. In contrast, EBF1-deficiency brought about remarkable up-regulation of that of PKCθ, and re-expression of EBF1 dramatically suppressed transcription of PKCθ. Chromatin immunoprecipitation assay revealed that GCN5 binds to the 5'-flanking region of the chicken PKCθ gene and acetylates histone H3, and EBF1 binds to the 5'-flanking region of the gene surrounding putative EBF1 binding motifs.

The expanding spectrum of the autoimmune lymphoproliferative syndromes

PURPOSE OF REVIEW

Several autoimmune lymphoproliferative syndromes have been described lately. We review here the main clinical and laboratory findings of these new disorders.

RECENT FINDINGS

The prototypical autoimmune lymphoproliferative syndrome (ALPS) has had its diagnostic criteria modified, somatic mutations in RAS genes were found to cause an ALPS-like syndrome in humans, and mutations in a gene encoding a protein kinase C (PRKCD) were discovered to cause a syndrome of lymphoproliferation, autoimmunity and natural killer cell defect.

SUMMARY

The recent discoveries shed light on the molecular pathways governing lymphocyte death, proliferation and immune tolerance in humans.

Diacylglycerol kinase ζ limits B cell antigen receptor-dependent activation of ERK signaling to inhibit early antibody responses

Signaling downstream of the B cell antigen receptor (BCR) is tightly regulated to enable cells to gauge the strength and duration of antigen-receptor interactions and to respond appropriately. We investigated whether metabolism of the second messenger diacylglycerol (DAG) by members of the family of DAG kinases (DGKs) played a role in modulating the magnitude of signaling by DAG downstream of the BCR. In the absence of DGKζ, the threshold for BCR signaling, measured as activation of the Ras-extracellular signal-regulated kinase (ERK) pathway, was markedly reduced in mature follicular B cells, which resulted in enhanced responses to antigen in vitro and in vivo. Inhibition of DAG signaling by DGKζ limited the number of antibody-secreting cells that were generated early in response to T cell-independent type 2 antigens, as well as to T cell-dependent antigens. Furthermore, the effect of loss of DGKζ closely resembled the effect of increasing the affinity of the BCR for antigen during the T cell-dependent antibody response. These results suggest that the magnitude of DAG signaling is important for translating the affinity of the BCR for antigen into the amount of antibody produced during the early stages of an immune response.

B lymphocyte antigen receptor signaling: initiation, amplification, and regulation

B lymphocytes and their differentiated daughters are charged with responding to the myriad pathogens in our environment and production of protective antibodies. A sample of the protective antibody produced by each clone is utilized as a component of the cell's antigen receptor (BCR). Transmembrane signals generated upon antigen binding to this receptor provide the primary directive for the cell's subsequent response. In this report, we discuss recent progress and current controversy regarding B cell receptor signal initiation, transduction and regulation.

Molecular classification, pathway addiction, and therapeutic targeting in diffuse large B cell lymphoma

The rapid emergence of molecularly based techniques to detect changes in the genetic landscape of diffuse large B cell lymphoma (DLBCL), including gene expression, DNA and RNA sequencing, and epigenetic profiling, has significantly influenced the understanding and therapeutic targeting of DLBCL. In this review, we briefly discuss the new methods used in the study of DLBCL. We describe the influence of the generated data on DLBCL classification and the identification of new entities and altered cell survival strategies, with a focus on the renewed interest in some classic oncogenic pathways that are currently targeted for new therapy. Finally, we examine the molecular genomic studies that revealed the importance of the tumor microenvironment in the pathogenesis of DLBCL.

The Role of Biological and Small Molecule Therapy in the Management of Psoriatic Arthritis

The therapy of psoriatic arthritis (PsA) has blossomed in the past decade. Inhibition of tumor necrosis factor (TNF) has been at the fore of this approach and has paved the way for the investigation of many other potential pro-inflammatory and signaling pathways. Most of the initial studies of TNF inhibitors in PsA have been conducted in specific populations, largely focusing on those with established, peripheral joint disease. That said, in excess of 10 years’ worth of real world clinical experience has led to increased confidence in the wider use of these agents. We are now faced with an exciting time of discovery of many new molecules; these not only include new, large protein biological agents, but also smaller synthetic chemical molecules, many of which can be administered orally. Those currently under development are discussed within this article. Whilst there is scarce data about their real world efficacy and safety profile, it is evident that the therapeutic armamentarium for treating PsA will greatly increase in the foreseeable future and this is anticipated to improve patient outcomes.

Sotrastaurin in calcineurin inhibitor-free regimen using everolimus in de novo kidney transplant recipients

Sotrastaurin, a novel selective protein-kinase-C inhibitor, inhibits early T cell activation via a calcineurin-independent pathway. Efficacy and safety of sotrastaurin in a calcineurin inhibitor-free regimen were evaluated in this two-stage Phase II study of de novo kidney transplant recipients. Stage 1 randomized 131 patients (2:1) to sotrastaurin 300 mg or cyclosporine A (CsA). Stage 2 randomized 180 patients (1:1:1) to sotrastaurin 300 or 200 mg or CsA. All patients received basiliximab, everolimus (EVR) and prednisone. Primary endpoint was composite efficacy failure rate of treated biopsy-proven acute rejection, graft loss, death or lost to follow-up. Main safety assessment was estimated glomerular filtration rate (eGFR) by MDRD-4 at Month 12. Composite efficacy failure rates at 12 months were higher in sotrastaurin arms (Stage 1: 16.5% and 10.9% for sotrastaurin 300 mg and CsA; Stage 2: 27.2%, 34.5% and 19.4% for sotrastaurin 200 mg, 300 mg and CsA). eGFR was significantly better in sotrastaurin groups versus CsA at most time points, except at 12 months. Gastrointestinal and cardiac adverse events were more frequent with sotrastaurin. Higher treatment discontinuation, deaths and graft losses occurred with sotrastaurin 300 mg. Sotrastaurin combined with EVR showed higher efficacy failure rates and some improvement in renal allograft function compared to a CsA-based therapy.

Correlation of gene expression and genome mutation in single B-cells

High-throughput measurement of gene-expression and immune receptor repertoires have recently become powerful tools in the study of adaptive immune response. However, despite their now-widespread use, both tend to discard cell identity by treating cell populations in bulk, and therefore lose the correlation between genetic variability and gene-expression at the single cell level. In order to recover this information, we developed a method to simultaneously measure gene expression profiles and genome mutations in single cells. We applied this method by quantifying the relationships between gene expression and antibody mutation in ensembles of individual B-cells from immunized mice. The results reveal correlations reflecting the manner in which information propagates between a B-cell’s antigen receptors, its gene expression, and its mutagenic machinery, and demonstrate the power of this approach to illuminate both heterogeneity and physiology in cell populations.

Protein kinase C-beta inhibition induces apoptosis and inhibits cell cycle progression in acquired immunodeficiency syndrome-related non-hodgkin lymphoma cells

INTRODUCTION

Acquired immunodeficiency syndrome (AIDS)-related non-Hodgkin lymphoma (NHL) constitutes an aggressive variety of lymphomas characterized by increased extranodal involvement, relapse rate, and resistance to chemotherapy. Protein kinase C-beta (PKCβ) targeting showed promising results in preclinical and clinical studies involving a wide variety of cancers, but studies describing the role of PKCβ in AIDS-NHL are primitive if not lacking.

METHODS

In the present study, 3 AIDS-NHL cell lines were examined: 2F7 (AIDS-Burkitt lymphoma), BCBL-1 (AIDS-primary effusion lymphoma), and UMCL01-101 (AIDS-diffuse large B-cell lymphoma).

RESULTS

Immunoblot analysis demonstrated expression of PKCβ1 and PKCβ2 in 2F7 and UMCL01-101 cells, and PKCβ1 alone in BCBL-1 cells. The viability of 2F7 and BCBL-1 cells decreased significantly in the presence of PKCβ-selective inhibitor at half-maximal inhibitory concentration of 14 and 15 μmol/L, respectively, as measured by tetrazolium dye reduction assay. In contrast, UMCL01-101 cells were relatively resistant. As determined using flow cytometric deoxynucleotidyl transferase dUTP nick-end labeling assay with propidium iodide staining, the responsiveness of sensitive cells was associated with apoptotic induction and cell cycle inhibition. Protein kinase C-beta-selective inhibition was observed not to affect AKT phosphorylation but to induce a rapid and sustained reduction in the phosphorylation of glycogen synthase kinase-3 beta, ribosomal protein S6, and mammalian target of rapamycin in sensitive cell lines.

CONCLUSIONS

The results indicate that PKCβ plays an important role in AIDS-related NHL survival and suggest that PKCβ targeting should be considered in a broader spectrum of NHL. The observations in BCBL-1 were unexpected in the absence of PKCβ2 expression and implicate PKCβ1 as a regulator in those cells.

Protein kinase Cβ is required for lupus development in Sle mice

OBJECTIVE

To evaluate the requirement for protein kinase Cβ (PKCβ) in the development of lupus in mice, and to explore the potential of targeting PKCβ as a therapeutic strategy in lupus.

METHODS

Congenic mice bearing the disease loci Sle1 or Sle1 and Sle3, which represent different stages of severity in the development of lupus, were crossed with PKCβ-deficient mice. The effect of PKCβ deficiency in lupus development was analyzed. In addition, the effects of the PKCβ-specific inhibitor enzastaurin on the survival of B cells from mice with lupus and human 9G4-positive B cells as well as the in vivo effect of enzastaurin treatment on the development of lupus in Sle mice were investigated.

RESULTS

In Sle mice, PKCβ deficiency abrogated lupus-associated phenotypes, including high autoantibody levels, proteinuria, and histologic features of lupus nephritis. Significant decreases in spleen size and in the peritoneal B-1 cell population, reduced numbers of activated CD4 T cells, and normalized CD4:CD8 ratios were observed. PKCβ deficiency induced an anergic B cell phenotype and preferentially inhibited autoreactive plasma cells and autoantibodies in mice with lupus. Inhibition of PKCβ enhanced apoptosis of both B cells from Sle mice and human autoreactive B cells (9G4 positive). Treatment of Sle mice with the PKCβ-specific inhibitor enzastaurin prevented the development of lupus.

CONCLUSION

This study identifies PKCβ as a central mediator of lupus pathogenesis, suggesting that PKCβ represents a promising therapeutic target for the treatment of systemic lupus erythematosus. Moreover, the results indicate the feasibility of using a PKCβ inhibitor for the treatment of lupus.

Loss-of-function of the protein kinase C δ (PKCδ) causes a B-cell lymphoproliferative syndrome in humans

Defective lymphocyte apoptosis results in chronic lymphadenopathy and/or splenomegaly associated with autoimmune phenomena. The prototype for human apoptosis disorders is the autoimmune lymphoproliferative syndrome (ALPS), which is caused by mutations in the FAS apoptotic pathway. Recently, patients with an ALPS-like disease called RAS-associated autoimmune leukoproliferative disorder, in which somatic mutations in NRAS or KRAS are found, also were described. Despite this progress, many patients with ALPS-like disease remain undefined genetically. We identified a homozygous, loss-of-function mutation in PRKCD (PKCδ) in a patient who presented with chronic lymphadenopathy, splenomegaly, autoantibodies, elevated immunoglobulins and natural killer dysfunction associated with chronic, low-grade Epstein-Barr virus infection. This mutation markedly decreased protein expression and resulted in ex vivo B-cell hyperproliferation, a phenotype similar to that of the PKCδ knockout mouse. Lymph nodes showed intense follicular hyperplasia, also mirroring the mouse model. Immunophenotyping of circulating lymphocytes demonstrated expansion of CD5+CD20+ B cells. Knockdown of PKCδ in normal mononuclear cells recapitulated the B-cell hyperproliferative phenotype in vitro. Reconstitution of PKCδ in patient-derived EBV-transformed B-cell lines partially restored phorbol-12-myristate-13-acetate-induced cell death. In summary, homozygous PRKCD mutation results in B-cell hyperproliferation and defective apoptosis with consequent lymphocyte accumulation and autoantibody production in humans, and disrupts natural killer cell function.

PDK1 regulates VDJ recombination, cell-cycle exit and survival during B-cell development

Phosphoinositide-dependent kinase-1 (PDK1) controls the activation of a subset of AGC kinases. Using a conditional knockout of PDK1 in haematopoietic cells, we demonstrate that PDK1 is essential for B cell development. B-cell progenitors lacking PDK1 arrested at the transition of pro-B to pre-B cells, due to a cell autonomous defect. Loss of PDK1 decreased the expression of the IgH chain in pro-B cells due to impaired recombination of the IgH distal variable segments, a process coordinated by the transcription factor Pax5. The expression of Pax5 in pre-B cells was decreased in PDK1 knockouts, which correlated with reduced expression of the Pax5 target genes IRF4, IRF8 and Aiolos. As a result, Ccnd3 is upregulated in PDK1 knockout pre-B cells and they have an impaired ability to undergo cell-cycle arrest, a necessary event for Ig light chain rearrangement. Instead, these cells underwent apoptosis that correlated with diminished expression of the pro-survival gene Bcl2A1. Reintroduction of both Pax5 and Bcl2A1 together into PDK1 knockout pro-B cells restored their ability to differentiate in vitro into mature B cells.

Protein kinase Cβ is critical for the metabolic switch to glycolysis following B-cell antigen receptor engagement

Signals derived from the BCR (B-cell antigen receptor) control survival, development and antigenic responses. One mechanism by which BCR signals may mediate these responses is by regulating cell metabolism. Indeed, the bioenergetic demands of naïve B-cells increase following BCR engagement and are characterized by a metabolic switch to aerobic glycolysis; however, the signalling pathways involved in this metabolic reprogramming are poorly defined. The PKC (protein kinase C) family plays an integral role in B-cell survival and antigenic responses. Using pharmacological inhibition and mice deficient in PKCβ, we demonstrate an essential role of PKCβ in BCR-induced glycolysis in B-cells. In contrast, mice deficient in PKCδ exhibit glycolytic rates comparable with those of wild-type B-cells following BCR cross-linking. The induction of several glycolytic genes following BCR engagement is impaired in PKCβ-deficient B-cells. Moreover, blocking glycolysis results in decreased survival of B-cells despite BCR engagement. The results establish a definitive role for PKCβ in the metabolic switch to glycolysis following BCR engagement of naïve B-cells.

B-cell deficiency and severe autoimmunity caused by deficiency of protein kinase C δ

Primary B-cell disorders comprise a heterogeneous group of inherited immunodeficiencies, often associated with autoimmunity causing significant morbidity. The underlying genetic etiology remains elusive in the majority of patients. In this study, we investigated a patient from a consanguineous family suffering from recurrent infections and severe lupuslike autoimmunity. Immunophenotyping revealed progressive decrease of CD19(+) B cells, a defective class switch indicated by low numbers of IgM- and IgG-memory B cells, as well as increased numbers of CD21(low) B cells. Combined homozygosity mapping and exome sequencing identified a biallelic splice-site mutation in protein C kinase δ (PRKCD), causing the absence of the corresponding protein product. Consequently, phosphorylation of myristoylated alanine-rich C kinase substrate was decreased, and mRNA levels of nuclear factor interleukin (IL)-6 and IL-6 were increased. Our study uncovers human PRKCD deficiency as a novel cause of common variable immunodeficiency-like B-cell deficiency with severe autoimmunity.

RNA interference screening identifies a novel role for autocrine fibroblast growth factor signaling in neuroblastoma chemoresistance

Chemotherapeutic drug resistance is one of the major causes for treatment failure in high-risk neuroblastoma (NB), the most common extra cranial solid tumor in children. Poor prognosis is typically associated with MYCN amplification. Here, we utilized a loss-of-function kinome-wide RNA interference screen to identify genes that cause cisplatin sensitization. We identified fibroblast growth factor receptor 2 (FGFR2) as an important determinant of cisplatin resistance. Pharmacological inhibition of FGFR2 confirmed the importance of this kinase in NB chemoresistance. Silencing of FGFR2 sensitized NB cells to cisplatin-induced apoptosis, which was regulated by the downregulation of the anti-apoptotic proteins BCL2 and BCLXL. Mechanistically, FGFR2 was shown to activate protein kinase C-δ to induce BCL2 expression. FGFR2, as well as the ligand fibroblast growth factor-2, were consistently expressed in primary NB and NB cell lines, indicating the presence of an autocrine loop. Expression analysis revealed that FGFR2 correlates with MYCN amplification and with advanced stage disease, demonstrating the clinical relevance of FGFR2 in NB. These findings suggest a novel role for FGFR2 in chemoresistance and provide a rational to combine pharmacological inhibitors against FGFR2 with chemotherapeutic agents for the treatment of NB.

Effects of sotrastaurin, mycophenolic acid and everolimus on human B-lymphocyte function and activation

Humoral rejection processes may lead to allograft injury and subsequent dysfunction. Today, only one B-cell-specific agent is in clinical use and the effects of standard and new immunosuppressant substances on B-cell activation and function are not fully clarified. The impact of sotrastaurin, mycophenolic acid and everolimus on human B-lymphocyte function was assessed by analysing proliferation, apoptosis, CD80/CD86 expression and immunoglobulin and IL-10 production in primary stimulated B cells. In addition, B-cell co-cultures with pre-activated T cells were performed to evaluate the effect of the different immunosuppressive agents on T-cell-dependent immunoglobulin production. Sotrastaurin did not inhibit B-cell proliferation, CD80/CD86 expression, and IgG production and had only minor effects on IgM levels at the highest concentration administered. In contrast, mycophenolic acid and everolimus had strong effects on all B-cell functions in a dose-dependent manner. All immunosuppressive agents caused decreased immunoglobulin levels in T-cell-dependent B-cell cultures. The data provided here suggest that mycophenolic acid and everolimus, but not sotrastaurin, are potent inhibitors of human B-lymphocyte function and activation.