SYK is upstream of phosphoinositide 3-kinase in B cell receptor signaling

Signaling pathways regulating the extracellular digestion of lipoprotein aggregates by macrophages

The interaction between aggregated low-density lipoprotein (agLDL) and macrophages in arteries plays a major role in atherosclerosis. Macrophages digest agLDL and generate free cholesterol in an extracellular, acidic, hydrolytic compartment known as the lysosomal synapse. Macrophages form a tight seal around agLDL through actin polymerization and deliver lysosomal contents into this space in a process termed digestive exophagy. Our laboratory has identified TLR4 activation of MyD88/Syk as critical for digestive exophagy. Here we use pharmacological agents and siRNA knockdown to characterize signaling pathways downstream of Syk that are involved in digestive exophagy. Syk activates Bruton's tyrosine kinase (BTK) and phospholipase Cγ2 (PLCγ2). We show that PLCγ2 and to a lesser extent BTK regulate digestive exophagy. PLCγ2 cleaves PI(4,5)P2 into diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). Soluble IP3 activates release of Ca2+ from the endoplasmic reticulum (ER). We demonstrate that Ca2+ release from the ER is upregulated by agLDL and plays a key role in digestive exophagy. Both DAG and Ca2+ activate protein kinase Cα (PKCα). We find that PKCα is an important regulator of digestive exophagy. These results expand our understanding of the mechanisms of digestive exophagy, which could be useful in developing therapeutic interventions to slow development of atherosclerosis.

Luxeptinib interferes with LYN-mediated activation of SYK and modulates BCR signaling in lymphoma

Luxeptinib (LUX) is a novel oral kinase inhibitor that inhibits FLT3 and also interferes with signaling from the BCR and cell surface TLRs, as well as activation of the NLRP3 inflammasome. Ongoing clinical trials are testing its activity in patients with lymphoma and AML. This study sought to refine understanding of how LUX modulates the earliest steps downstream of the BCR following its activation by anti-IgM in lymphoma cells in comparison to ibrutinib (IB). LUX decreased anti-IgM-induced phosphorylation of BTK at Y551 and Y223 but its ability to reduce phosphorylation of kinases further upstream suggests that BTK is not the primary target. LUX was more effective than IB at reducing both steady state and anti-IgM-induced phosphorylation of LYN and SYK. LUX decreased phosphorylation of SYK (Y525/Y526) and BLNK (Y96) which are necessary regulators of BTK activation. Further upstream, LUX blunted the anti-IgM-induced phosphorylation of LYN (Y397) whose activation is required for phosphorylation of SYK and BLNK. These results indicate that LUX is targeting autophosphorylation of LYN or a step further upstream of LYN in the cascade of signal generated by BCR and that it does so more effectively than IB. The fact that LUX has activity at or upstream of LYN is important because LYN is an essential signaling intermediate in multiple cellular signaling processes that regulate growth, differentiation, apoptosis, immunoregulation, migration and EMT in normal and cancer cells.

Treatment Landscape of Relapsed/Refractory Mantle Cell Lymphoma: An Updated Review

Mantle cell lymphoma (MCL) accounts for nearly 2-6% of all non-Hodgkin lymphoma (NHL) cases, with a steady incidence increase over the past few decades. Although many patients achieve an adequate response to the upfront treatment, the short duration of remission with rapid relapse is challenging during MCL management. In this regard, there is no consensus on the best treatment options for relapsed/refractory (R/R) disease, and the international guidelines demonstrate wide variations in the recommended approaches. The last decade has witnessed the introduction of new agents in the treatment landscape of R/R MCL. Since the introduction of Bruton's tyrosine kinase (BTK) inhibitors, the treatment algorithm and response of R/R MCL patients have dramatically changed. Nevertheless, BTK resistance is common, necessitating further investigations to develop novel agents with a more durable response. Novel agents targeting the B-cell receptor (BCR) signaling have exhibited clinical activity and a well-tolerable safety profile. However, as the responses to these novel agents are still modest in most clinical trials, combination strategies were investigated in pre-clinical and early clinical settings to determine whether the combination of novel agents would exhibit a better durable response than single agents. In this report, we provide an updated literature review that covers recent clinical data about the safety and efficacy of novel therapies for the management of R/R MCL.

Aberrant B Cell Signaling in Autoimmune Diseases

Aberrant B cell signaling plays a critical in role in various systemic and organ-specific autoimmune diseases. This is supported by genetic evidence by many functional studies in B cells from patients or specific animal models and by the observed efficacy of small-molecule inhibitors. In this review, we first discuss key signal transduction pathways downstream of the B cell receptor (BCR) that ensure that autoreactive B cells are removed from the repertoire or functionally silenced. We provide an overview of aberrant BCR signaling that is associated with inappropriate B cell repertoire selection and activation or survival of peripheral B cell populations and plasma cells, finally leading to autoantibody formation. Next to BCR signaling, abnormalities in other signal transduction pathways have been implicated in autoimmune disease. These include reduced activity of several phosphates that are downstream of co-inhibitory receptors on B cells and increased levels of BAFF and APRIL, which support survival of B cells and plasma cells. Importantly, pathogenic synergy of the BCR and Toll-like receptors (TLR), which can be activated by endogenous ligands, such as self-nucleic acids, has been shown to enhance autoimmunity. Finally, we will briefly discuss therapeutic strategies for autoimmune disease based on interfering with signal transduction in B cells.

Targeting the splicing isoforms of spleen tyrosine kinase affects the viability of colorectal cancer cells

Spleen tyrosine kinase (Syk) expression have been both positively and negatively associated with tumorigenesis. Our goal was to evaluate the contribution of Syk and its two splice variants, full length Syk (L) and short isoform Syk (S), in the tumor biology of colorectal cancer cells (CRC). The analysis of Syk expression in primary human colorectal tumors, as well as the analysis of TCGA database, revealed a high Syk mRNA expression score in colorectal cancer tumors, suggesting a tumor promotor role of Syk in CRC. Our analysis showed that Syk (L) isoform is highly expressed in the majority of the tumor tissues and that it remains expressed in tumors in which global Syk expression is downregulated, suggesting the dependence of tumors to Syk (L) isoform. We also identified a small cluster of tumor tissues, which express a high proportion of Syk (S) isoform. This specific cluster is associated with overexpressed genes related to translation and mitochondria, and down regulated genes implicated in the progression of mitosis. For our functional studies, we used short hairpin RNA tools to target the expression of Syk in CRC cells bearing the activating K-Ras (G13D) mutation. Our results showed that while global Syk knock down increases cell proliferation and cell motility, Syk (L) expression silencing affects the viability and induces the apoptosis of the cells, confirming the dependence of cells on Syk (L) isoform for their survival. Finally, we report the promising potential of compound C-13, an original non-enzymatic inhibitor of Syk isolated in our group. In vitro studies showed that C-13 exerts cytotoxic effects on Syk-positive CRC cells by inhibiting their proliferation and their motility, and by inducing their apoptosis, while Syk-negative cell lines viability was not affected. Moreover, the oral and intraperitoneal administration of C-13 reduced the tumor growth of CRC DLD-1 cells xenografts in Nude mice in vivo.

SYK and ZAP70 kinases in autoimmunity and lymphoid malignancies

SYK and ZAP70 nonreceptor tyrosine kinases serve essential roles in initiating B-cell receptor (BCR) and T-cell receptor (TCR) signaling in B- and T-lymphocytes, respectively. Despite their structural and functional similarity, expression of SYK and ZAP70 is strictly separated during B- and T-lymphocyte development, the reason for which was not known. Aberrant co-expression of ZAP70 with SYK was first identified in B-cell chronic lymphocytic leukemia (CLL) and is considered a biomarker of aggressive disease and poor clinical outcomes. We recently found that aberrant ZAP70 co-expression not only functions as an oncogenic driver in CLL but also in various other B-cell malignancies, including acute lymphoblastic leukemia (B-ALL) and mantle cell lymphoma. Thereby, aberrantly expressed ZAP70 redirects SYK and BCR-downstream signaling from NFAT towards activation of the PI3K-pathway. In the sole presence of SYK, pathological BCR-signaling in autoreactive or premalignant cells induces NFAT-activation and NFAT-dependent anergy and negative selection. In contrast, negative selection of pathological B-cells is subverted when ZAP70 diverts SYK from activation of NFAT towards tonic PI3K-signaling, which promotes survival instead of cell death. We discuss here how both B-cell malignancies and autoimmune diseases frequently evolve to harness this mechanism, highlighting the importance of developmental separation of the two kinases as an essential safeguard.

Transcriptome analysis and protein-protein interaction in resistant and susceptible families of Japanese flounder (Paralichthys olivaceus) to understand the mechanism against Edwardsiella tarda

Edwardsiella tarda is one of the most harmful bacterial pathogens for aquaculture flatfish. After artificial infection of 47 Japanese flounder (Paralichthys olivaceus) families, resistant and susceptible families were identified in this study. High-throughput sequencing was performed on the liver transcriptome of uninfected groups (PoRU and PoSU) and infected groups (PoRC and PoSC). Through assembly and annotation, a total of 3012 and 1386 differentially expressed genes (DEGs) were identified in PoRU vs. PoSU and PoRC vs. PoSC. The significant enrichment pathways between PoRU and PoSU were mainly in metabolic and biosynthesis pathways. A total of thirty dominant enrichment pathways between PoRC and PoSC mainly focused on some immune-related pathways, including the hematopoietic cell lineage, cytokine-cytokine receptor interaction, complement and coagulation cascades, antigen processing and presentation, the intestinal immune network for immunoglobulin A (IgA) production and T/B cell receptor signaling pathway. Under the protein-protein interaction (PPI) analysis, hub genes, including CD molecules, complement component factors and chemokines, were identified in the network, and 16 core genes were differentially expressed in resistant and sustainable families in quantitative polymerase chain reaction (qPCR) validation. This study represents the first transcriptome analysis based on resistant and susceptible families and provides resistant genes to understand the potential molecular mechanisms of antibacterial function in marine fish. The results obtained in this study provide crucial information on gene markers for resistant breeding of Japanese flounder.

Differential Requirement of Vav Proteins for Btk-dependent and –Independent Signaling During B Cell Development

Btk and Vav proteins are all components of the signalosome that builds upon B cell receptor (BCR) activation. However, the role of Vav proteins within the signalosome is quite complex and not yet fully understood. Until now, studies of these have focused predominantly on a deficiency of Vav proteins alone or in combination with other Vav protein family members. Since a physical association of Btk with Vav was shown previously, we asked whether these molecules lie in the same or independent signaling pathways. By analyzing Vav1 and Vav3 single knock-out mice and generating double-knock-out animals deficient for either Vav1 or Vav3 and Btk, we observed, in line with previous publications, no severe B cell developmental defects when either Vav1 or Vav3 alone are not expressed. However, a simultaneous deficiency of Btk together with either Vav1 or Vav3 leads to a severe reduction of splenic B cells, which exhibit an immature phenotype. B cell developmental defects of Btk/Vav1-double deficient mice in the periphery were more severe than those observed in Btk-single-deficient animals. Additionally, morphological changes in splenic microarchitecture were observed in double- but also in single-knock-out mutants. These observations were accompanied by reduced BCR-induced Ca²⁺ mobilization, proliferation, germinal center formation and immunoglobulin secretion. Although deletion of Btk alone impaired Ca²⁺ mobilization upon BCR activation, the defect was even more severe when Vav1 or Vav3 were also mutated, indicating that Btk and the Vav proteins act in separate pathways that converge on Ca2+ signaling. In vitro ASC differentiation suggests that both B and T cells contribute to the observed phenotype of a Btk/Vav-double deficiency. Our results show that Vav proteins and Btk are both components of the BCR-activated signalosome but control separate signaling pathways important for B cell development.

Dysregulated PI3K Signaling in B Cells of CVID Patients

The altered wiring of signaling pathways downstream of antigen receptors of T and B cells contributes to the dysregulation of the adaptive immune system, potentially causing immunodeficiency and autoimmunity. In humans, the investigation of such complex systems benefits from nature’s experiments in patients with genetically defined primary immunodeficiencies. Disturbed B-cell receptor (BCR) signaling in a subgroup of common variable immunodeficiency (CVID) patients with immune dysregulation and expanded T-bet^highCD21^low B cells in peripheral blood has been previously reported. Here, we investigate PI3K signaling and its targets as crucial regulators of survival, proliferation and metabolism by intracellular flow cytometry, imaging flow cytometry and RNAseq. We observed increased basal but disturbed BCR-induced PI3K signaling, especially in T-bet^highCD21^low B cells from CVID patients, translating into impaired activation of crucial downstream molecules and affecting proliferation, survival and the metabolic profile. In contrast to CVID, increased basal activity of PI3K in patients with a gain-of-function mutation in PIK3CD and activated PI3K delta syndrome (APDS) did not result in impaired BCR-induced AKT-mTOR-S6 phosphorylation, highlighting that signaling defects in B cells in CVID and APDS patients are fundamentally different and that assessing responses to BCR stimulation is an appropriate confirmative diagnostic test for APDS. The active PI3K signaling in vivo may render autoreactive T-bet^highCD21^low B cells in CVID at the same time to be more sensitive to mTOR or PI3K inhibition.

FCRL1 Regulates B Cell Receptor-Induced ERK Activation through GRB2

Regulation of BCR signaling has important consequences for generating effective Ab responses to pathogens and preventing production of autoreactive B cells during development. Currently defined functions of Fc receptor-like (FCRL) 1 include positive regulation of BCR-induced calcium flux, proliferation, and Ab production; however, the mechanistic basis of FCRL1 signaling and its contributions to B cell development remain undefined. Molecular characterization of FCRL1 signaling shows phosphotyrosine-dependent associations with GRB2, GRAP, SHIP-1, and SOS1, all of which can profoundly influence MAPK signaling. In contrast with previous characterizations of FCRL1 as a strictly activating receptor, we discover a role for FCRL1 in suppressing ERK activation under homeostatic and BCR-stimulated conditions in a GRB2-dependent manner. Our analysis of B cells in Fcrl1 ^-/- mice shows that ERK suppression by FCRL1 is associated with a restriction in the number of cells surviving splenic maturation in vivo. The capacity of FCRL1 to modulate ERK activation presents a potential for FCRL1 to be a regulator of peripheral B cell tolerance, homeostasis, and activation.

Siglec-8 Signals Through a Non-Canonical Pathway to Cause Human Eosinophil Death In Vitro

Sialic acid-binding immunoglobulin-like lectin (Siglec)-8 is a glycan-binding receptor bearing immunoreceptor tyrosine-based inhibitory and switch motifs (ITIM and ITSM, respectively) that is selectively expressed on eosinophils, mast cells, and, to a lesser extent, basophils. Previous work has shown that engagement of Siglec-8 on IL-5-primed eosinophils causes cell death via CD11b/CD18 integrin-mediated adhesion and NADPH oxidase activity and identified signaling molecules linking adhesion, reactive oxygen species (ROS) production, and cell death. However, the proximal signaling cascade activated directly by Siglec-8 engagement has remained elusive. Most members of the Siglec family possess similar cytoplasmic signaling motifs and recruit the protein tyrosine phosphatases SHP-1/2, consistent with ITIM-mediated signaling, to dampen cellular activation. However, the dependence of Siglec-8 function in eosinophils on these phosphatases has not been studied. Using Siglec-8 antibody engagement and pharmacological inhibition in conjunction with assays to measure cell-surface upregulation and conformational activation of CD11b integrin, ROS production, and cell death, we sought to identify molecules involved in Siglec-8 signaling and determine the stage of the process in which each molecule plays a role. We demonstrate here that the enzymatic activities of Src family kinases (SFKs), Syk, SHIP1, PAK1, MEK1, ERK1/2, PLC, PKC, acid sphingomyelinase/ceramidase, and Btk are all necessary for Siglec-8-induced eosinophil cell death, with no apparent role for SHP-1/2, SHIP2, or c-Raf. While most of these signaling molecules are necessary for Siglec-8-induced upregulation of CD11b integrin at the eosinophil cell surface, Btk is phosphorylated and activated later in the signaling cascade and is instead necessary for CD11b activation. In contrast, SFKs and ERK1/2 are phosphorylated far earlier in the process, consistent with their role in augmenting cell-surface levels of CD11b. In addition, pretreatment of eosinophils with latrunculin B or jasplakinolide revealed that actin filament disassembly is necessary and sufficient for surface CD11b integrin upregulation and that actin polymerization is necessary for downstream ROS production. These results show that Siglec-8 signals through an unanticipated set of signaling molecules in IL-5-primed eosinophils to induce cell death and challenges the expectation that ITIM-bearing Siglecs signal through inhibitory pathways involving protein tyrosine phosphatases to achieve their downstream functions.

Developmental partitioning of SYK and ZAP70 prevents autoimmunity and cancer

Even though SYK and ZAP70 kinases share high sequence homology and serve analogous functions, their expression in B and T cells is strictly segregated throughout evolution. Here, we identified aberrant ZAP70 expression as a common feature in a broad range of B cell malignancies. We validated SYK as the kinase that sets the thresholds for negative selection of autoreactive and premalignant clones. When aberrantly expressed in B cells, ZAP70 competes with SYK at the BCR signalosome and redirects SYK from negative selection to tonic PI3K signaling, thereby promoting B cell survival. In genetic mouse models for B-ALL and B-CLL, conditional expression of Zap70 accelerated disease onset, while genetic deletion impaired malignant transformation. Inducible activation of Zap70 during B cell development compromised negative selection of autoreactive B cells, resulting in pervasive autoantibody production. Strict segregation of the two kinases is critical for normal B cell selection and represents a central safeguard against the development of autoimmune disease and B cell malignancies.

Characterization of the mechanism of action of lanraplenib, a novel spleen tyrosine kinase inhibitor, in models of lupus nephritis

Background

B cells are critical mediators of systemic lupus erythematosus (SLE) and lupus nephritis (LN), and antinuclear antibodies can be found in the serum of approximately 98% of patients with SLE. Spleen tyrosine kinase (SYK) is a nonreceptor tyrosine kinase that mediates signaling from immunoreceptors, including the B cell receptor. Active, phosphorylated SYK has been observed in tissues from patients with SLE or cutaneous lupus erythematosus, and its inhibition is hypothesized to ameliorate disease pathogenesis. We sought to evaluate the efficacy and characterize the mechanism of action of lanraplenib, a selective oral SYK inhibitor, in the New Zealand black/white (NZB/W) murine model of SLE and LN.

Methods

Lanraplenib was evaluated for inhibition of primary human B cell functions in vitro. Furthermore, the effect of SYK inhibition on ameliorating LN-like disease in vivo was determined by treating NZB/W mice with lanraplenib, cyclophosphamide, or a vehicle control. Glomerulopathy and immunoglobulin G (IgG) deposition were quantified in kidneys. The concentration of proinflammatory cytokines was measured in serum. Splenocytes were analyzed by flow cytometry for B cell maturation and T cell memory maturation, and the presence of T follicular helper and dendritic cells.

Results

In human B cells in vitro, lanraplenib inhibited B cell activating factor-mediated survival as well as activation, maturation, and immunoglobulin M production. Treatment of NZB/W mice with lanraplenib improved overall survival, prevented the development of proteinuria, and reduced blood urea nitrogen concentrations. Kidney morphology was significantly preserved by treatment with lanraplenib as measured by glomerular diameter, protein cast severity, interstitial inflammation, vasculitis, and frequency of glomerular crescents; treatment with lanraplenib reduced glomerular IgG deposition. Mice treated with lanraplenib had reduced concentrations of serum proinflammatory cytokines. Lanraplenib blocked disease-driven B cell maturation and T cell memory maturation in the spleen.

Conclusions

Lanraplenib blocked the progression of LN-like disease in NZB/W mice. Human in vitro and murine in vivo data suggest that lanraplenib may be efficacious in preventing disease progression in patients with LN at least in part by inhibiting B cell maturation. These data provide additional rationale for the use of lanraplenib in the treatment of SLE and LN.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41927-021-00178-3.

IBL-202 is synergistic with venetoclax in CLL under in vitro conditions that mimic the tumor microenvironment

The B-cell receptor signaling pathway and dysregulation of the Bcl-2 family of proteins play crucial roles in the pathogenesis of chronic lymphocytic leukemia (CLL). Despite significant advances in the treatment of the disease, relapse and drug resistance are not uncommon. In the current study, we investigated the dual PI3/PIM kinase inhibitor IBL-202 in combination with venetoclax as a treatment option for CLL using both primary CLL cells and TP53-deficient OSU-CLL cells generated using the CRISPR-Cas9 system. IBL-202 and venetoclax were highly synergistic against primary CLL cells cocultured with CD40L fibroblasts (combination index [CI], 0.4, at a fractional effect of 0.9) and TP53-knockout (KO) OSU-CLL cells (CI, 0.5, at a fractional effect of 0.9). Synergy between the drugs was consistent, with a significant (P < .05) reduction in the 50% inhibitory concentration for both drugs. IBL-202 and venetoclax in combination induced cell-cycle arrest and slowed the proliferation of both wild-type and TP53-KO cell lines. The drug combination inhibited AKT phosphorylation, reduced expression of Bcl-xL and NF-κB, and increased the Noxa/Mcl-1 ratio. Downregulation of CXCR4 was consistent with inhibition of the SDF-1α-induced migratory capacity of CLL cells. Synergy between IBL-202 and venetoclax against primary CLL cells cultured under conditions that mimic the tumor microenvironment suggests this drug combination may be effective against CLL cells within the lymph nodes and bone marrow. Furthermore, the efficacy of the combination against the TP53-KO OSU-CLL cell line suggests the combination may be a highly effective treatment strategy for high-risk CLL.

Lights and Shade of Next-Generation Pi3k Inhibitors in Chronic Lymphocytic Leukemia

The treatment (i.e. therapy and management) of chronic lymphocytic leukemia (i.e. the disease) has been improved thanks to the introduction (i.e. approval) of kinase inhibitors during the last years. PI3K is one of the most important kinases at the crossroad to the B-cell receptor and cytokine receptor which play a key role in CLL cell survival, proliferation and migration. Idelalisib is the first in class PI3Kδ inhibitor approved for the treatment of relapsed/refractory CLL in combination with rituximab. Idelalisib activity in heavily treated patients is balanced by recurrent adverse events which limit its long-term use. These limitations prompt the investigation on novel PI3K inhibitors, also targeting different protein isoforms, and alternative schedule strategies. In this regard, duvelisib is the only PI3K γ and δ inhibitor approved as single agent for relapsed CLL. In this review, we will address novel insights on PI3K structure, isoforms, regulating signaling and the most updated data of next-generation PI3K inhibitors in CLL.

Macrophage Syk-PI3Kγ Inhibits Antitumor Immunity: SRX3207, a Novel Dual Syk-PI3K Inhibitory Chemotype Relieves Tumor Immunosuppression

Macrophages (MΦ) play a critical role in tumor growth, immunosuppression, and inhibition of adaptive immune responses in cancer. Hence, targeting signaling pathways in MΦs that promote tumor immunosuppression will provide therapeutic benefit. PI3Kγ has been recently established by our group and others as a novel immuno-oncology target. Herein, we report that an MΦ Syk-PI3K axis drives polarization of immunosuppressive MΦs that establish an immunosuppressive tumor microenvironment in in vivo syngeneic tumor models. Genetic or pharmacologic inhibition of Syk and/or PI3Kγ in MΦs promotes a proinflammatory MΦ phenotype, restores CD8+ T-cell activity, destabilizes HIF under hypoxia, and stimulates an antitumor immune response. Assay for transposase-accessible Chromatin using Sequencing (ATAC-seq) analyses on the bone marrow-derived macrophages (BMDM) show that inhibition of Syk kinase promotes activation and binding of NF-κB motif in SykMC-KO BMDMs, thus stimulating immunostimulatory transcriptional programming in MΦs to suppress tumor growth. Finally, we have developed in silico the "first-in-class" dual Syk/PI3K inhibitor, SRX3207, for the combinatorial inhibition of Syk and PI3K in one small molecule. This chemotype demonstrates efficacy in multiple tumor models and represents a novel combinatorial approach to activate antitumor immunity.

TLR4 (Toll-Like Receptor 4)-Dependent Signaling Drives Extracellular Catabolism of LDL (Low-Density Lipoprotein) Aggregates

OBJECTIVE

Aggregation and modification of LDLs (low-density lipoproteins) promote their retention and accumulation in the arteries. This is a critical initiating factor during atherosclerosis. Macrophage catabolism of agLDL (aggregated LDL) occurs using a specialized extracellular, hydrolytic compartment, the lysosomal synapse. Compartment formation by local actin polymerization and delivery of lysosomal contents by exocytosis promotes acidification of the compartment and degradation of agLDL. Internalization of metabolites, such as cholesterol, promotes foam cell formation, a process that drives atherogenesis. Furthermore, there is accumulating evidence for the involvement of TLR4 (Toll-like receptor 4) and its adaptor protein MyD88 (myeloid differentiation primary response 88) in atherosclerosis. Here, we investigated the role of TLR4 in catabolism of agLDL using the lysosomal synapse and foam cell formation. Approach and Results: Using bone marrow-derived macrophages from knockout mice, we find that TLR4 and MyD88 regulate compartment formation, lysosome exocytosis, acidification of the compartment, and foam cell formation. Using siRNA (small interfering RNA), pharmacological inhibition and knockout bone marrow-derived macrophages, we implicate SYK (spleen tyrosine kinase), PI3K (phosphoinositide 3-kinase), and Akt in agLDL catabolism using the lysosomal synapse. Using bone marrow transplantation of LDL receptor knockout mice with TLR4 knockout bone marrow, we show that deficiency of TLR4 protects macrophages from lipid accumulation during atherosclerosis. Finally, we demonstrate that macrophages in vivo form an extracellular compartment and exocytose lysosome contents similar to that observed in vitro for degradation of agLDL.

CONCLUSIONS

We present a mechanism in which interaction of macrophages with agLDL initiates a TLR4 signaling pathway, resulting in formation of the lysosomal synapse, catabolism of agLDL, and lipid accumulation in vitro and in vivo.

Anti-inflammatory activities of Canarium subulatum Guillaumin methanol extract operate by targeting Src and Syk in the NF-κB pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Canarium subulatum Guillaumin is an herbal medicinal plant native to Southeast Asia. Ethnopharmacological evidence suggests that plants of the genus Canarium cure a variety of inflammatory diseases.

AIM OF THE STUDY

The pharmacological mechanisms of C. subulatum Guillaumin remain poorly understood. In this study, we investigate inflammatory mechanisms and target molecules using C. subulatum Guillaumin methanol extract (Cs-ME) in inflammatory reactions managed by macrophages.

MATERIALS AND METHODS

To identify the anti-inflammatory activities of Cs-ME, lipopolysaccharide (LPS)-stimulated macrophages and a murine HCl/EtOH-induced gastritis model were chosen. The luciferase reporter gene assay, Western blot analysis, overexpression strategy, and the cellular thermal shift assay (CETSA) were employed to investigate the molecular mechanisms and target enzymes of Cs-ME. The active ingredients of this extract were also determined by HPLC.

RESULTS

Released levels of nitric oxide (NO) and mRNA expression levels of iNOS and IL-6 were downregulated by Cs-ME without exhibiting cytotoxicity. This extract inhibited MyD88-induced promoter activity and the nuclear translocation of nuclear factor (NF)-κB. Moreover, we found that Cs-ME reduced the phosphorylation of NF-κB upstream signaling molecules including IκBα, IKKα/β, Src, and Syk in LPS-stimulated macrophage-like RAW264.7 cells. The results of Western blot and CETSA confirmed that Src and Syk are anti-inflammatory targets of Cs-ME. In addition, orally injected Cs-ME alleviated HCl/EtOH-induced gastric ulcers in mice. HPLC analysis indicated that quercetin, luteolin, and kaempferol are major active components of this extract with anti-inflammatory activity.

CONCLUSIONS

Cs-ME exhibits anti-inflammatory effects in vitro and in vivo by targeting Src and Syk in the NF-κB signaling pathway. Consequently, Cs-ME could be developed as an anti-inflammatory herbal medicine.

From Biology to Therapy: The CLL Success Story

Chemoimmunotherapy has been the standard of care for patients with chronic lymphocytic leukemia (CLL) over the last decade. Advances in monoclonal antibody technology have resulted in the development of newer generations of anti-CD20 antibodies with improved therapeutic effectiveness. In parallel, our knowledge about the distinctive biological characteristics of CLL has progressively deepened and has revealed the importance of B-cell receptor (BCR) signaling and upregulated antiapoptotic proteins for survival and expansion of malignant cell clones. This knowledge provided the basis for development of novel targeted agents that revolutionized treatment of CLL. Ibrutinib and idelalisib inhibit the Bruton tyrosine kinase (BTK) and phosphoinositide 3-kinase (PI3K) delta, respectively, thus interfering with supportive signals coming from the microenvironment via the BCR. These drugs induce egress of CLL cells from secondary lymphoid organs and remarkably improve clinical outcomes, especially for patients with unmutated immunoglobulin heavy-chain genes or with p53 abnormalities that do not benefit from classical treatment schemes. Latest clinical trial results have established ibrutinib with or without anti-CD20 antibodies as the preferred first-line treatment for most CLL patients, which will reduce the use of chemoimmunotherapy in the imminent future. Further advances are achieved with venetoclax, a BH3-mimetic that specifically inhibits the antiapoptotic B-cell lymphoma 2 protein and thus causes rapid apoptosis of CLL cells, which translates into deep and prolonged clinical responses including high rates of minimal residual disease negativity. This review summarizes recent advances in the development of targeted CLL therapies, including new combination schemes, novel BTK and PI3K inhibitors, spleen tyrosine kinase inhibitors, immunomodulatory drugs, and cellular immunotherapy.

Human B Cells Engage the NCK/PI3K/RAC1 Axis to Internalize Large Particles via the IgM-BCR

Growing evidence indicate that large antigen-containing particles induce potent T cell-dependent high-affinity antibody responses. These responses require large particle internalization after recognition by the B cell receptor (BCR) on B cells. However, the molecular mechanisms governing BCR-mediated internalization remain unclear. Here we use a high-throughput quantitative image analysis approach to discriminate between B cell particle binding and internalization. We systematically show, using small molecule inhibitors, that human B cells require a SYK-dependent IgM-BCR signaling transduction via PI3K to efficiently internalize large anti-IgM-coated particles. IgM-BCR-mediated activation of PI3K involves both the adaptor protein NCK and the co-receptor CD19. Interestingly, we here reveal a strong NCK-dependence without profound requirement of the co-receptor CD19 in B cell responses to large particles. Furthermore, we demonstrate that the IgM-BCR/NCK signaling event facilitates RAC1 activation to promote actin cytoskeleton remodeling necessary for particle engulfment. Thus, we establish NCK/PI3K/RAC1 as an attractive IgM-BCR signaling axis for biological intervention to prevent undesired antibody responses to large particles.

Signalling circuits that direct early B-cell development

In mammals, the B-cell lineage arises from pluripotent progenitors in the bone marrow. During their development, B-cells undergo lineage specification and commitment, followed by expansion and selection. These processes are mediated by regulated changes in gene expression programmes, rearrangements of immunoglobulin (Ig) genes, and well-timed rounds of proliferation and apoptosis. Many of these processes are initiated by environmental factors including cytokines, chemokines, and cell-cell contacts. Developing B-cells process these environmental cues into stage-specific functions via signalling pathways including the PI3K, MAPK, or JAK-STAT pathway. The cytokines FLT3-Ligand and c-Kit-Ligand are important for the early expansion of the B-cell precursors at different developmental stages and conditions. Interleukin 7 is essential for commitment to the B-cell lineage and for orchestrating the Ig recombination machinery. After rearrangement of the immunoglobulin heavy chain, proliferation and apoptosis, and thus selection, are mediated by the clonal pre-B-cell receptor, and, following light chain rearrangement, by the B-cell receptor.

Spleen tyrosine kinase from Nile tilapia (Oreochromis niloticus): Molecular characterization, expression pattern upon bacterial infection and the potential role in BCR signaling and inflammatory response

Spleen tyrosine kinase (SYK), a member of non-receptor tyrosine kinase family, plays an important role in immune responses against pathogen infection, which is capable of activating B cells signaling pathway and regulating inflammatory response. In this study, Nile tilapia (Oreochromis niloticus) ortholog (OnSYK) was identified and characterized at expression pattern against bacterial infection, function in B cells activation pathway and inflammatory response. The cDNA of OnSYK ORF contained 1851 bp of nucleotide sequence encoding polypeptides of 616 amino acids. The deduced OnSYK protein was highly homologous to other species SYK, containing two SH2 domains and a TyrKc domain. Spatial mRNA expression analysis revealed that OnSYK had wide tissue distribution and was highly expressed in the liver. After challenge of Streptococcus agalactiae (S. agalactiae) in vivo, mRNA expression of OnSYK was significantly up-regulated in the head kidney, spleen and liver. The up-regulation of OnSYK transcript was also displayed in the head kidney and spleen leukocytes stimulation with S. agalactiae and LPS in vitro, which was confirmed at protein level in the head kidney leukocytes by FACS analysis. In addition, after induction with mouse anti-OnIgM monoclonal antibody in vitro, the expressions of OnSYK and its downstream molecules (OnLYN, OnBLNK and OnAP-1) were significantly up-regulated in the head kidney leukocytes, and pharmacological inhibition of SYK activity with inhibitor (P505-15) significantly attenuated the expressions of OnLYN, OnBLNK and OnAP-1. Moreover, upon LPS challenge, the expressions of OnSYK, OnTNF-α, OnIL-6 and OnAP-1 were also up-regulated in the head kidney monocytes/macrophages. After treatment with SYK inhibitor (BAY 61-3606), the expressions of OnTNF-α, OnIL-6 and OnAP-1 were inhibited in the LPS-challenged head kidney monocytes/macrophages. Taken together, the results of this study indicated that OnSYK, playing potential roles in BCR signaling and inflammatory response, was likely to get involved in host defense against bacterial infection in Nile tilapia.

Discovery of Novel Small-Molecule Inhibitors of NF-κB Signaling with Antiinflammatory and Anticancer Properties

Excessive NF-κB activation contributes to the pathogenesis of numerous diseases. Small-molecule inhibitors of NF-κB signaling have significant therapeutic potential especially in treating inflammatory diseases and cancers. In this study, we performed a cell-based high-throughput screening to discover novel agents capable of inhibiting NF-κB signaling. On the basis of two hit scaffolds from the screening, we synthesized 69 derivatives to optimize the potency for inhibition of NF-κB activation, leading to successful discovery of the most potent compound Z9j with over 170-fold enhancement of inhibitory activity. Preliminary mechanistic studies revealed that Z9j inhibited NF-κB signaling via suppression of Src/Syk, PI3K/Akt, and IKK/IκB pathways. This novel compound also demonstrated antiinflammatory and anticancer activities, warranting its further development as a potential multifunctional agent to treat inflammatory diseases and cancers.

Inhibition of ovarian tumor cell invasiveness by targeting SYK in the tyrosine kinase signaling pathway

Cell motility and invasiveness are prerequisites for dissemination, and largely account for cancer mortality. We have identified an actionable kinase, spleen tyrosine kinase (SYK), which is keenly tightly associated with tumor progression in ovarian cancer. Here, we report that active recombinant SYK directly phosphorylates cortactin and cofilin, which are critically involved in assembly and dynamics of actin filament through phosphorylation signaling. Enhancing SYK activity by inducing expression of a constitutively active SYK mutant, SYK130E, increased growth factor-stimulated migration and invasion of ovarian cancer cells, which was abrogated by cortactin knockdown. Similarly, SYK inhibitors significantly decreased invasion of ovarian cancer cells across basement membrane in real-time transwell assays and in 3D tumor spheroid models. SYK inactivation by targeted gene knockout or by small molecule inhibition reduced actin polymerization. Collectively, this study reported a new mechanism by which SYK signaling regulates ovarian cancer cell motility and invasiveness, and suggest a target-based strategy to prevent or suppress the advancement of ovarian malignancies.

Lyn, Lupus, and (B) Lymphocytes, a Lesson on the Critical Balance of Kinase Signaling in Immunity

Systemic lupus erythematosus (SLE) is a progressive autoimmune disease characterized by increased sensitivity to self-antigens, auto-antibody production, and systemic inflammation. B cells have been implicated in disease progression and as such represent an attractive therapeutic target. Lyn is a Src family tyrosine kinase that plays a major role in regulating signaling pathways within B cells as well as other hematopoietic cells. Its role in initiating negative signaling cascades is especially critical as exemplified by Lyn-/- mice developing an SLE-like disease with plasma cell hyperplasia, underscoring the importance of tightly regulating signaling within B cells. This review highlights recent advances in our understanding of the function of the Src family tyrosine kinase Lyn in B lymphocytes and its contribution to positive and negative signaling pathways that are dysregulated in autoimmunity.

Synergistic Targeting of the Regulatory and Catalytic Subunits of PI3Kδ in Mature B-cell Malignancies

Purpose: Aberrant activation of the B-cell receptor (BCR) is implicated in the pathogenesis of mature B-cell tumors, a concept validated in part by the clinical success of inhibitors of the BCR-related kinases BTK (Bruton's tyrosine kinase) and PI3Kδ. These inhibitors have limitations, including the paucity of complete responses, acquired resistance, and toxicity. Here, we examined the mechanism by which the cyclic-AMP/PDE4 signaling axis suppresses PI3K, toward identifying a novel mechanism-based combinatorial strategy to attack BCR-dependency in mature B-cell malignancies.Experimental Design: We used in vitro and in vivo diffuse large B-cell lymphoma (DLBCL) cell lines and primary chronic lymphocytic leukemia (CLL) samples to preclinically evaluate the effects of the combination of the FDA-approved phosphodiesterase 4 (PDE4) inhibitor roflumilast and idelalisib on cell survival and tumor growth. Genetic models of gain- and loss-of-function were used to map multiple signaling intermediaries downstream of the BCR.Results: Roflumilast elevates the intracellular levels of cyclic-AMP and synergizes with idelalisib in suppressing tumor growth and PI3K activity. Mechanistically, we show that roflumilast suppresses PI3K by inhibiting BCR-mediated activation of the P85 regulatory subunit, distinguishing itself from idelalisib, an ATP-competitive inhibitor of the catalytic P110 subunit. Using genetic models, we linked the PDE4-regulated modulation of P85 activation to the oncogenic kinase SYK.Conclusions: These data demonstrate that roflumilast and idelalisib suppress PI3K by distinct mechanisms, explaining the basis for their synergism, and suggest that the repurposing of PDE4 inhibitors to treat BCR-dependent malignancies is warranted. Clin Cancer Res; 24(5); 1103-13. ©2017 AACR.

Peripheral CD19hi B cells exhibit activated phenotype and functionality in promoting IgG and IgM production in human autoimmune diseases

Systemic Lupus Erythematosus (SLE) and pemphigus are two representative autoimmune diseases driven by pathogenic autoantibody systemically and organ-specifically, respectively. Given the involvement of antibody in the pathogenesis, B cells are inclined to differentiate and function in an abnormal activation model. Here we defined a unique CD19^hi B cell population existing in the periphery of SLE and pemphigus patients as well as in human tonsils. CD19^hi B cells could be induced in vitro after co-culturing fully activated CD4⁺ T cells with autologous B cells. They expressed high levels of HLA-DR, IgG, IgM and multiple ligands of costimulatory molecules with the capacity to produce extra IgG and IgM. Transcirptome assay revealed that genes involved in B-cell activation and differentiation were up-regulated in CD19^hi B cells. Antibody blockade experiments showed that the interactions between costimulatory molecules contributed to CD19^hi B-cell generation and IgG/IgM production. What is more, frequencies of peripheral CD19^hi B cells from SLE and pemphigus patients were correlated with serum total IgG and IgM, but not with autoantigen-specific antibodies and disease severity. Therefore, our investigation demonstrates that CD19^hi B cells might contain B cell precursors for terminal differentiation and contribute to total IgG/IgM production in human autoimmune diseases.

NFATC1 activation by DNA hypomethylation in chronic lymphocytic leukemia correlates with clinical staging and can be inhibited by ibrutinib

B cell receptor (BCR) signaling is a key for survival of chronic lymphocytic leukemia (CLL) cells, and BCR signaling inhibitors are clinically active. However, relapse and resistance to treatment require novel treatment options. To detect novel candidate therapeutic targets, we performed a genome-wide DNA methylation screen with custom arrays and identified aberrant promoter DNA methylation in 2,192 genes. The transcription factor NFATC1 that is a downstream effector of BCR signaling was among the top hypomethylated genes and was concomitantly transcriptionally upregulated in CLL. Intriguingly, NFATC1 promoter DNA hypomethylation levels were significantly variant in clinical trial cohorts from different disease progression stages and furthermore correlated with Binet disease staging and thymidine kinase levels, strongly suggesting a central role of NFATC1 in CLL development. Functionally, DNA hypomethylation at NFATC1 promoter inversely correlated with RNA levels of NFATC1 and dysregulation correlated with expression of target genes BCL-2, CCND1 and CCR7. The inhibition of the NFAT regulator calcineurin with tacrolimus and cyclosporin A and the BCR signaling inhibitor ibrutinib significantly reduced NFAT activity in leukemic cell lines, and NFAT inhibition resulted in increased apoptosis of primary CLL cells. In summary, our results indicate that the aberrant activation of NFATC1 by DNA hypomethylation and BCR signaling plays a major role in the pathomechanism of CLL.

Src and Syk contribute to the anti-inflammatory activities of Achyranthes aspera ethanolic extract

ETHNOPHARMACOLOGICAL RELEVANCE

Nuclear factor-kappa B (NF-κB) plays pivotal roles in inflammation. Src and Syk are two tyrosine kinases that act upstream of NF-κB signaling. Although Achyranthes aspera L. (A. aspera) has been used as a traditional medicine to treat fevers and inflammatory ailments and heal wounds, the molecular mechanisms of its anti-inflammatory actions are not yet fully understood.

MATERIALS AND METHODS

In this study, we evaluated the anti-inflammatory effect of A. aspera ethanol extract (Aa-EE). To determine the mechanism by which Aa-EE dampens the inflammatory response, nitric oxide (NO) production and the mRNA expression levels of tumor necrosis factor (TNF)-α and inducible nitric oxide synthase (iNOS) were examined by Griess assay and RT-PCR. Luciferase assays and immunoblotting were also conducted to examine how Aa-EE regulates the NF-κB pathway.

RESULTS

Aa-EE reduced NO production up to 60% without any cytotoxicity. This extract was found to downregulate the mRNA expression levels of inflammatory genes. Aa-EE blocked NF-κB promoter activity induced by both TNF-α and adaptor molecule MyD88 (about 70% and 40%, respectively). Moreover, nuclear translocation of p65 and IκBα phosphorylation were also inhibited. Furthermore, Aa-EE inactivated two upstream signaling molecules, the Src and Syk kinases. In accordance with these data, the kinase activities of Src and Syk were decreased by 50% and 80%, respectively. The anti-inflammatory action of Aa-EE was also confirmed in a gastritis model.

CONCLUSION

Our data suggest that Aa-EE targets NF-κB to exert its anti-inflammatory properties by suppressing Src and Syk. Therefore, our study raises the possibility that this extract can be developed as a novel natural anti-inflammatory remedy.

Characterization of midostaurin as a dual inhibitor of FLT3 and SYK and potentiation of FLT3 inhibition against FLT3-ITD-driven leukemia harboring activated SYK kinase

Oncogenic FLT3 kinase is a clinically validated target in acute myeloid leukemia (AML), and both multi-targeted and selective FLT3 inhibitors have been developed. Spleen tyrosine kinase (SYK) has been shown to be activated and increased in FLT3-ITD-positive AML patients, and has further been shown to be critical for transformation and maintenance of the leukemic clone in these patients. Further, over-expression of constitutively activated SYK causes resistance to highly selective FLT3 tyrosine kinase inhibitors (TKI). Up to now, the activity of the multi-targeted FLT3 inhibitor, midostaurin, against cells expressing activated SYK has not been explored in the context of leukemia, although SYK has been identified as a target of midostaurin in systemic mastocytosis. We compared the ability of midostaurin to inhibit activated SYK in mutant FLT3-positive AML cells with that of inhibitors displaying dual SYK/FLT3 inhibition, targeted SYK inhibition, and targeted FLT3 inhibition. Our findings suggest that dual FLT3/SYK inhibitors and FLT3-targeted drugs potently kill oncogenic FLT3-transformed cells, while SYK-targeted small molecule inhibition displays minimal activity. However, midostaurin and other dual FLT3/SYK inhibitors display superior anti-proliferative activity when compared to targeted FLT3 inhibitors, such as crenolanib and quizartinib, against cells co-expressing FLT3-ITD and constitutively activated SYK-TEL. Interestingly, additional SYK suppression potentiated the effects of dual FLT3/SYK inhibitors and targeted FLT3 inhibitors against FLT3-ITD-driven leukemia, both in the absence and presence of activated SYK. Taken together, our findings have important implications for the design of drug combination studies in mutant FLT3-positive patients and for the design of future generations of FLT3 inhibitors.

Myc enhances B-cell receptor signaling in precancerous B cells and confers resistance to Btk inhibition

Dysregulation of the oncogenic transcription factor MYC induces B cell transformation and is a driver for B cell non-Hodgkin lymphoma (B-NHL). MYC overexpression in B-NHL is associated with more aggressive phenotypes and poor prognosis. Although genomic studies suggest a link between MYC overexpression and B cell receptor (BCR) signaling molecules in B-NHL, signaling pathways essential to Myc-mediated B-cell transformation have not been fully elucidated. We utilized intracellular phospho-flow cytometry to investigate the relationship between Myc and BCR signaling in pre-malignant B cells. Utilizing the Eμ-myc mouse model, where Myc is overexpressed specifically in B cells, both basal and stimulated BCR signaling were increased in precancerous B lymphocytes from Eμ-myc mice compared to wild-type littermates. B cells overexpressing Myc displayed constitutively higher levels of activated CD79α, Btk, Plcγ2, and Erk1/2. Notably, Myc overexpressing B cells maintained elevated BCR signaling despite treatment with ibrutinib, a Bruton’s tyrosine kinase inhibitor. Furthermore, PI3K/Akt pathway signaling was also increased in Eμ-myc B cells, and this increase was partially suppressed with ibrutinib. Additionally, experiments with Btk-null B cells revealed off-target effects of ibrutinib on BCR signaling. Our data show that in pre-malignant B cells, Myc overexpression is sufficient to activate BCR and PI3K/Akt signaling pathways and further enhances signaling following BCR ligation. Therefore, our results indicate precancerous B cells have already acquired enhanced survival and growth capabilities prior to transformation, and that elevated MYC levels confer resistance to pharmacologic inhibitors of BCR signaling, which has significant implications for B-NHL treatment.

Induction of galectin-1 by TLR-dependent PI3K activation enhances epithelial-mesenchymal transition of metastatic ovarian cancer cells

The expression of different toll-like receptors (TLRs) on tumor cells has been associated with disease aggressiveness, treatment resistance, and poor prognosis. The phosphatidylinositol 3-kinase (PI3K)/AKT pathway is considered critical for cancer cell survival and proliferation. Thus, we investigated the effect of TLR-stimulated PI3K activation on the epithelial-to-mesenchymal transition (EMT) of primary (Caov-3) and metastatic (SK‑OV‑3) epithelial ovarian cancer cell lines in this study. TLR engagement with various ligands promoted the expression of class IA PI3K (p110α, p110β, and p110δ) and increased the expression of mesenchymal markers (N-cadherin, Slug, Vimentin, Snail, α-SMA, and TCF) in SK‑OV‑3 cells. The migratory activity and secretion of EMT-related cytokines of SK‑OV‑3 were significantly higher compared to those of Caov-3 after activation with TLR agonist. Although the invasive capacity and production of EMT-related cytokines of LPS-stimulated SK‑OV‑3 cells were significantly suppressed by all pharmacological inhibitors of the p110 isoform, the Syk/Src-dependent p110β isoform prominently attenuated migration activity. In contrast, the production of IL-10 and galectin-1 was mainly affected by the p110δ isoform. Gene silencing of TLR4 and galectin-1 with siRNA decreased the expression of matrix metalloproteinase-2 (MMP2) and MMP9 and reduced mesenchymal markers in LPS-treated SK‑OV‑3 cells. This study demonstrated that TLR-mediated PI3K activation modulated the invasion and metastasis of ovarian cancer through the production of galectin-1, suggesting that inhibition of the p110 isoform is a promising therapeutic approach against metastatic ovarian cancer.

A p110δ-specific inhibitor combined with bortezomib blocks drug resistance properties of EBV-related B cell origin cancer cells via regulation of NF-κB

Epstein-Barr virus (EBV) infection is closely related to carcinogenesis of various cancers, and is also associated with the development of drug resistance in cancer stem cells. However, in EBV-positive cancer cells, the mechanistic details of the downstream signaling and the connection of PI3K with the NF-κB pathway for development of drug resistance remain controversial. Diffuse large B-cell lymphoma (DLBCL) and multiple myeloma (MM) cells infected by EBV display drug resistance-related proteins (MDR1, MRP1 and MRP2) and stem cell markers (OCT4 and SOX2). EBV-infected HT (HT/EBV) and H929 (H929/EBV) cells activated p110δ expression, but downregulated the expression of p110α and p110β. A combination of CAL-101, a p110δ-specific inhibitor, with bortezomib treatment of HT/EBV cells synergistically suppressed proliferation, reduced levels of drug resistance-related proteins, activated caspase cleavage and recovered expression of p110α/p110β. Additionally, co-treatment with CAL-101 and bortezomib attenuated the expression of OCT4 and SOX2 via inhibition of activated NF-κB. Co-treatment with CAL-101 and bortezomib also attenuated drug resistance and NF-κB activity of EBV-infected H929 cells. Our results provide supportive evidence for the clinical application of CAL-101 and bortezomib to treat EBV-infected hematologic cancer.

Epstein-Barr Virus Latent Membrane Protein 2A (LMP2A) enhances IL-10 production through the activation of Bruton's tyrosine kinase and STAT3

Previous data demonstrate that Epstein-Barr Virus Latent Membrane Protein 2A (LMP2A) enhances IL-10 to promote the survival of LMP2A-expressing B cell lymphomas. Since STAT3 is an important regulator of IL-10 production, we hypothesized that LMP2A activates a signal transduction cascade that increases STAT3 phosphorylation to enhance IL-10. Using LMP2A-negative and -positive B cell lines, the data indicate that LMP2A requires the early signaling molecules of the Syk/RAS/PI3K pathway to increase IL-10. Additional studies indicate that the PI3K-regulated kinase, BTK, is responsible for phosphorylating STAT3, which ultimately mediates the LMP2A-dependent increase in IL-10. These data are the first to show that LMP2A signaling results in STAT3 phosphorylation in B cells through a PI3K/BTK-dependent pathway. With the use of BTK and STAT3 inhibitors to treat B cell lymphomas in clinical trials, these findings highlight the possibility of using new pharmaceutical approaches to treat EBV-associated lymphomas that express LMP2A.

Phosphodiesterase 4 inhibitors have wide-ranging activity in B-cell malignancies

Phosphodiesterase 4 (PDE4) inhibition restores the suppressive effects of 3',5'-cyclic adenosine monophosphate in lymphocytes. In this concise review, we detail how PDE4 inhibition downmodulates the B-cell receptor (BCR)-related kinases spleen tyrosine kinase and phosphatidylinositol 3-kinase and inhibits vascular endothelial growth factor A secretion by tumor cells, inducing cancer cell apoptosis and blocking angiogenesis in the microenvironment. We describe the successful clinical repurposing of PDE4 inhibitors in B-cell malignancies, and propose that given their anti-inflammatory/immunomodulatory activity, these agents will suppress BCR signals without the toxicity associated with other targeted biological doublets.

Idelalisib Impacts Cell Growth through Inhibiting Translation-Regulatory Mechanisms in Mantle Cell Lymphoma

PURPOSE

PI3K is a critical node in the B-cell receptor pathway, which is responsible for survival and proliferation of B-cell malignancies. Idelalisib, a PI3Kδ-isoform-specific inhibitor, has been approved to treat B-cell malignancies. Although biological activity of the drug has been evaluated, molecular mechanisms and signaling pathway disruption leading to the biological effects of idelalisib are not yet well defined. Prior laboratory reports have identified transcription and translation as the primary events for attenuation of PI3Kα isoform. We hypothesized that PI3Kδ-isoform inhibition by idelalisib should also affect gene transcription and protein translation.

EXPERIMENTAL DESIGN

Using three mantle cell lymphoma cell lines and primary cells from patients, biological consequences such as apoptosis/cell-cycle analysis, as well as RNA/protein synthesis were evaluated. Proteomics analyses (RPPA and immunoblot assays) defined molecular events downstream of PI3K/AKT cassette.

RESULTS

Idelalisib treatment resulted in inhibition of protein synthesis, which correlated with reduction in cell size and cell growth. A moderate loss of viability without any change in cell-cycle profile was observed. Idelalisib treatment inhibited AKT activation, an immediate downstream PI3K effector, and also reduced phosphorylation levels of downstream AKT/mTOR pathway proteins such as PRAS40. In addition, idelalisib treatment impeded activation of the MAPK pathway, and MEK, ERK and p90RSK phosphorylation levels were reduced. Reduction in AKT, PDK1, and MEK phosphorylation correlated with protein synthesis inhibition.

CONCLUSIONS

Collectively, these results clarify the molecular mechanisms of actions and may provide biomarkers and targets for combination with idelalisib in B-cell malignancies. Clin Cancer Res; 23(1); 181-92. ©2016 AACR.

Signaling in Effector Lymphocytes: Insights toward Safer Immunotherapy

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

1-(2,3-Dibenzimidazol-2-ylpropyl)-2-methoxybenzene Is a Syk Inhibitor with Anti-Inflammatory Properties

Inflammation is the protective action of our bodies against external pathogens by recognition of pathogen-associated molecular patterns (PAMPs) via pattern recognition receptors (PRRs). Proper regulation of inflammatory responses is required to maintain our body’s homeostasis, as well as there are demands to develop proper acute or chronic inflammation. In this study, we elucidated the regulatory mechanism of NF-κB-mediated inflammatory responses by a novel compound, 1-(2,3-dibenzimidazol-2-ylpropyl)-2-methoxybenzene (DBMB). We found that DBMB suppressed inflammatory mediators, nitric oxide (NO) and prostaglandin E₂ (PGE₂), reacted to exposure to a number of toll like receptor (TLR) ligands. Such observations occurred following to decreased mRNA expression of several pro-inflammatory mediators, and such diminished mRNA levels were caused by inhibited transcriptional factor nuclear factor (NF)-κB, as evaluated by luciferase reporter assay and molecular biological approaches. To find the potential targets of DBMB, we screened phosphorylated forms of NF-κB signal molecules: inhibitor of κBα (IκBα), IκB kinase (IKK)α/β, Akt, 3-phosphoinositide dependent protein kinase-1 (PDK1), p85, and spleen tyrosine kinase (Syk). We found that DBMB treatment could suppress signal transduction through these molecules. Additionally, we conducted in vitro kinase assays using immunoprecipitated Syk and its substrate, p85. Consequently, we could say that DBMB clearly suppressed the kinase activity of Syk kinase activity. Together, our results demonstrate that synthetic DBMB has an effect on the inflammatory NF-κB signaling pathway and suggest the potential for clinical use in the treatment of inflammatory diseases.

Clonal B cells in Waldenström's macroglobulinemia exhibit functional features of chronic active B-cell receptor signaling

Waldenström's macroglobulinemia (WM) is a B-cell non-Hodgkin's lymphoma (B-NHL) characterized by immunoglobulin M (IgM) monoclonal gammopathy and the medullary expansion of clonal lymphoplasmacytic cells. Neoplastic transformation has been partially attributed to hyperactive MYD88 signaling, secondary to the MYD88 L265P mutation, occurring in the majority of WM patients. Nevertheless, the presence of chronic active B-cell receptor (BCR) signaling, a feature of multiple IgM+ B-NHL, remains a subject of speculation in WM. Here, we interrogated the BCR signaling capacity of primary WM cells by utilizing multiparametric phosphoflow cytometry and found heightened basal phosphorylation of BCR-related signaling proteins, and augmented phosphoresponses on surface IgM (sIgM) crosslinking, compared with normal B cells. In support of those findings we observed high sIgM expression and loss of phosphatase activity in WM cells, which could both lead to signaling potentiation in clonal cells. Finally, led by the high-signaling heterogeneity among WM samples, we generated patient-specific phosphosignatures, which subclassified patients into a ‘high' and a ‘healthy-like' signaling group, with the second corresponding to patients with a more indolent clinical phenotype. These findings support the presence of chronic active BCR signaling in WM while providing a link between differential BCR signaling utilization and distinct clinical WM subgroups.

CD19 and BAFF-R can signal to promote B-cell survival in the absence of Syk

The development and function of B lymphocytes is regulated by numerous signaling pathways, some emanating from the B-cell antigen receptor (BCR). The spleen tyrosine kinase (Syk) plays a central role in the activation of the BCR, but less is known about its contribution to the survival and maintenance of mature B cells. We generated mice with an inducible and B-cell-specific deletion of the Syk gene and found that a considerable fraction of mature Syk-negative B cells can survive in the periphery for an extended time. Syk-negative B cells are defective in BCR, RP105 and CD38 signaling but still respond to an IL-4, anti-CD40, CpG or LPS stimulus. Our in vivo experiments show that Syk-deficient B cells require BAFF receptor and CD19/PI3K signaling for their long-term survival. These studies also shed a new light on the signals regulating the maintenance of the normal mature murine B-cell pool.

Calling in SYK: SYK's dual role as a tumor promoter and tumor suppressor in cancer

SYK (spleen tyrosine kinase) is well-characterized in the immune system as an essential enzyme required for signaling through multiple classes of immune recognition receptors. As a modulator of tumorigenesis, SYK has a bit of a schizophrenic reputation, acting in some cells as a tumor promoter and in others as a tumor suppressor. In many hematopoietic malignancies, SYK provides an important survival function and its inhibition or silencing frequently leads to apoptosis. In cancers of non-immune cells, SYK provides a pro-survival signal, but can also suppress tumorigenesis by restricting epithelial-mesenchymal transition, enhancing cell-cell interactions and inhibiting migration.

Regulation of immune responses by proton channels

The identification of the HVCN1 gene, encoding the only mammalian voltage-gated proton channel, prompted a number of studies on how proton channels affect cellular functions. As their expression is mainly restricted to immune cells, it is not surprising that proton channels regulate different aspects of immune responses. In this review, I will examine the current knowledge of voltage-gated proton channels in both innate and adaptive responses and assess the remaining outstanding questions.

The novel kinase inhibitor PRT062070 (Cerdulatinib) demonstrates efficacy in models of autoimmunity and B-cell cancer

The heterogeneity and severity of certain autoimmune diseases and B-cell malignancies warrant simultaneous targeting of multiple disease-relevant signaling pathways. Dual inhibition of spleen tyrosine kinase (SYK) and Janus kinase (JAK) represents such a strategy and may elicit several benefits relative to selective kinase inhibition, such as gaining control over a broader array of disease etiologies, reducing probability of selection for bypass disease mechanisms, and the potential that an overall lower level suppression of individual targets may be sufficient to modulate disease activity. To this end, we provide data on the discovery and preclinical development of PRT062070 [4-(cyclopropylamino)-2-({4-[4-(ethylsulfonyl)piperazin-1-yl]phenyl}amino)pyrimidine-5-carboxamide hydrochloride], an orally active kinase inhibitor that demonstrates activity against SYK and JAK. Cellular assays demonstrated specific inhibitory activity against signaling pathways that use SYK and JAK1/3. Limited inhibition of JAK2 was observed, and PRT062070 did not inhibit phorbol 12-myristate 13-acetate-mediated signaling or activation in B and T cells nor T-cell antigen receptor-mediated signaling in T cells, providing evidence for selectivity of action. Potent antitumor activity was observed in a subset of B-cell lymphoma cell lines. After oral dosing, PRT062070 suppressed inflammation and autoantibody generation in a rat collagen-induced arthritis model and blocked B-cell activation and splenomegaly in a mouse model of chronic B-cell antigen receptor stimulation. PRT062070 is currently under evaluation in a phase I dose escalation study in patients with B-cell leukemia and lymphoma (NCT01994382), with proof-of-concept studies in humans planned to assess therapeutic potential in autoimmune and malignant diseases.

Depletion of STAT5 blocks TEL-SYK-induced APMF-type leukemia with myelofibrosis and myelodysplasia in mice

The spleen tyrosine kinase (SYK) was identified as an oncogenic driver in a broad spectrum of hematologic malignancies. The in vivo comparison of three SYK containing oncogenes, SYK(wt), TEL-SYK and IL-2-inducible T-cell kinase (ITK)-SYK revealed a general myeloexpansion and the establishment of three different hematologic (pre)diseases. SYK(wt) enhanced the myeloid and T-cell compartment, without leukemia/lymphoma development. ITK-SYK caused lethal T-cell lymphomas and the cytoplasmic TEL-SYK fusion induced an acute panmyelosis with myelofibrosis-type acute myeloid leukemia (AML) with up to 50% immature megakaryoblasts infiltrating bone marrow, spleen and liver, additional MPN features (myelofibrosis and granulocyte expansion) and MDS stigmata with megakaryocytic and erythroid dysplasia. LKS cells were reduced and all subsets (LT/ST/MPP) showed reduced proliferation rates. SYK inhibitor treatment (R788) of diseased TEL-SYK mice reduced leukocytosis, spleen and liver infiltration, enhanced the hematocrit and prolonged survival time, but could not significantly reduce myelofibrosis. Stat5 was identified as a major downstream mediator of TEL-SYK in vitro as well as in vivo. Consequently, targeted deletion of Stat5 in vivo completely abrogated TEL-SYK-induced AML and myelofibrosis development, proving Stat5 as a major driver of SYK-induced transformation. Our experiments highlight the important role of SYK in AML and myelofibrosis and prove SYK and STAT5 inhibitors as potent treatment options for those diseases.

Functional roles of Syk in macrophage-mediated inflammatory responses

Inflammation is a series of complex biological responses to protect the host from pathogen invasion. Chronic inflammation is considered a major cause of diseases, such as various types of inflammatory/autoimmune diseases and cancers. Spleen tyrosine kinase (Syk) was initially found to be highly expressed in hematopoietic cells and has been known to play crucial roles in adaptive immune responses. However, recent studies have reported that Syk is also involved in other biological functions, especially in innate immune responses. Although Syk has been extensively studied in adaptive immune responses, numerous studies have recently presented evidence that Syk has critical functions in macrophage-mediated inflammatory responses and is closely related to innate immune response. This review describes the characteristics of Syk-mediated signaling pathways, summarizes the recent findings supporting the crucial roles of Syk in macrophage-mediated inflammatory responses and diseases, and discusses Syk-targeted drug development for the therapy of inflammatory diseases.

Synthetic antigens reveal dynamics of BCR endocytosis during inhibitory signaling

B cells detect foreign antigens through their B cell antigen receptor (BCR). The BCR, when engaged by antigen, initiates a signaling cascade. Concurrent with signaling is endocytosis of the BCR complex, which acts to downregulate signaling and facilitate uptake of antigen for processing and display on the cell surface. The relationship between signaling and BCR endocytosis is poorly defined. Here, we explore the interplay between BCR endocytosis and antigens that either promote or inhibit B cell activation. Specifically, synthetic antigens were generated that engage the BCR alone or both the BCR and the inhibitory co-receptor CD22. The lectin CD22, a member of the Siglec family, binds sialic acid-containing glycoconjugates found on host tissues, inhibiting BCR signaling to prevent erroneous B cell activation. At low concentrations, antigens that can cocluster the BCR and CD22 promote rapid BCR endocytosis; whereas, slower endocytosis occurs with antigens that bind only the BCR. At higher antigen concentrations, rapid BCR endocytosis occurs upon treatment with either stimulatory or inhibitory antigens. Endocytosis of the BCR, in response to synthetic antigens, results in its entry into early endocytic compartments. Although the CD22-binding antigens fail to activate key regulators of antigen presentation (e.g., Syk), they also promote BCR endocytosis, indicating that inhibitory antigens can be internalized. Together, our observations support a functional role for BCR endocytosis in downregulating BCR signaling. The reduction of cell surface BCR levels in the absence of B cell activation should raise the threshold for BCR subsequent activation. The ability of the activating synthetic antigens to trigger both signaling and entry of the BCR into early endosomes suggests strategies for targeted antigen delivery.