A deficiency in Drak2 results in a T cell hypersensitivity and an unexpected resistance to autoimmunity

Exploring the molecular mechanisms of comorbidity of myocardial infarction and anxiety disorders by combining multiple data sets with in vivo experimental validation

BACKGROUND

The incidence of comorbidity between myocardial infarction (MI) and anxiety disorders is increasing. However, the biological association between them has not been fully understood.

OBJECTIVE

This study aims to investigate the molecular mechanisms of comorbidity between MI and anxiety disorders and to predict their key genes and potential therapeutic drugs.

METHODS

We searched Gene Expression Omnibus databases and performed differential analyses using the limma package to identify the functional enrichment of differential genes. Next, we constructed regulatory networks to investigate the relationship between hub genes and autophagy, ferroptosis, and immunity. Furthermore, we predicted transcription factors by R package, constructed a miRNA network, performed the single-cell analysis of key gene expression, and predicted drug targeting of differential genes using the Connectivity Map database.

RESULTS

The datasets for MI and anxiety disorders were analyzed for up and down-regulated differential genes, resulting in 35 intersecting differential genes. The top 10 feature genes from each dataset were intersected using Random Forest, resulting in the identification of three intersecting genes: STK17B, AKIRIN2, and WDR77. Validation of the above key genes was carried out by in vitro experiments. We examined the gene expression of STK17B, WDR77 and AKIRIN2 in the hippocampus and myocardial infarction border zone respectively by qPCR and WB, and the results confirmed that the above are the key genes for myocardial infarction and anxiety. There is a significant correlation between the comorbidity mechanism of myocardial infarction and anxiety disorders with ferroptosis and immunity. The construction of the miRNA network revealed that miR-205 and let-7 had higher average connectivity among the three hub genes. The single-cell analysis revealed significant expression of key genes in Endothelial cells, Cardiomyocytes, Macrophages, and Fibroblasts datasets. Cd274 showed a higher correlation with key genes in myocardial infarction and anxiety disorders.

CONCLUSION

Validation by multiple datasets and in vitro experiments showed that STK17B, AKIRIN2, and WDR77 are the key genes in the comorbidity of myocardial infarction and anxiety disorders, and ferroptosis and immunity are the key links in the comorbidity mechanism of myocardial infarction and anxiety disorders.

DRAK2 regulates myosin light chain phosphorylation in T cells

Death-associated protein kinase-related apoptosis-inducing kinase-2 (DRAK2; also known as STK17B) is a serine/threonine kinase expressed in T cells. Drak2-deficient (Drak2-/-) mice respond effectively to tumors and pathogens while displaying resistance to T cell-mediated autoimmune disease. However, the molecular mechanisms by which DRAK2 impacts T cell function remain unclear. Gaining further insight into the function of DRAK2 in T cells will shed light on differentially regulated pathways in autoreactive and pathogen-specific T cells, which is crucial for improving autoimmune therapies. Here, we demonstrate that DRAK2 contributes to activation of myosin light chain (MLC2, encoded by Myl2) in both murine and human T cells. In the absence of Drak2, the amount of polymerized actin was decreased, suggesting that DRAK2 modulates actomyosin dynamics. We further show that myosin-dependent T cell functions, such as migration, T cell receptor microcluster accumulation, and conjugation to antigen presenting cells are decreased in the absence of Drak2. These findings reveal that DRAK2 plays an important role in regulating MLC activation within T cells.

Evaluation of STK17B as a cancer immunotherapy target utilizing highly potent and selective small molecule inhibitors

Introduction

The serine/threonine kinase 17B (STK17B) is involved in setting the threshold for T cell activation and its absence sensitizes T cells to suboptimal stimuli. Consequently, STK17B represents an attractive potential target for cancer immunotherapy.

Methods

To assess the potential of STK17B as an immuno-oncology target, we developed potent and selective tool compounds from starting points in Blueprint Medicines Corporation's proprietary kinase inhibitor library. To characterize these molecules, enzyme and cellular assays for STK17A and STK17B were established to drive chemistry optimization. Mass spectrometry-based phosphoproteomics profiling with tool inhibitors led to the identification of Ser19 on myosin light chain 2 as STK17B substrate, which is then developed into a flow cytometry-based pharmacodynamic readout of STK17B inhibition both in vitro and in vivo.

Results

In a mouse T cell activation assay, STK17B inhibitors demonstrated the ability to enhance interleukin-2 (IL-2) production. Similarly, treatment with STK17B inhibitors resulted in stronger cytokine secretion in human T cells activated using a T cell bispecific antibody. Subsequent chemistry optimization led to the identification of a highly selective and orally bioavailable tool compound, BLU7482. In vivo, STK17B inhibition led to dose-dependent modulation of myosin light chain 2 phosphorylation and enhanced priming of naïve T cells, as determined by upregulation of CD69, IL-2 and interferon-γ secretion. In line with increased T cell activation, treatment with STK17B inhibitor enhanced antitumor activity of anti-PD-L1 antibody in the MCA205 model.

Conclusions

In summary, we successfully identified and optimized STK17B kinase inhibitors which led to increased T cell responses in vitro and in vivo. This allowed us to evaluate the potential of STK17B inhibition as an approach for cancer immunotherapy.

Negative intracellular regulators of T-cell receptor (TCR) signaling as potential antitumor immunotherapy targets

Immunotherapy strategies aim to mobilize immune defenses against tumor cells by targeting mainly T cells. Co-inhibitory receptors or immune checkpoints (ICPs) (such as PD-1 and CTLA4) can limit T cell receptor (TCR) signal propagation in T cells. Antibody-based blocking of immune checkpoints (immune checkpoint inhibitors, ICIs) enable escape from ICP inhibition of TCR signaling. ICI therapies have significantly impacted the prognosis and survival of patients with cancer. However, many patients remain refractory to these treatments. Thus, alternative approaches for cancer immunotherapy are needed. In addition to membrane-associated inhibitory molecules, a growing number of intracellular molecules may also serve to downregulate signaling cascades triggered by TCR engagement. These molecules are known as intracellular immune checkpoints (iICPs). Blocking the expression or the activity of these intracellular negative signaling molecules is a novel field of action to boost T cell-mediated antitumor responses. This area is rapidly expanding. Indeed, more than 30 different potential iICPs have been identified. Over the past 5 years, several phase I/II clinical trials targeting iICPs in T cells have been registered. In this study, we summarize recent preclinical and clinical data demonstrating that immunotherapies targeting T cell iICPs can mediate regression of solid tumors including (membrane associated) immune-checkpoint inhibitor refractory cancers. Finally, we discuss how these iICPs are targeted and controlled. Thereby, iICP inhibition is a promising strategy opening new avenues for future cancer immunotherapy treatments.

DRAK2 contributes to type 1 diabetes by negatively regulating IL-2 sensitivity to alter regulatory T cell development

Drak2-deficient (Drak2-/-) mice are resistant to multiple models of autoimmunity yet effectively eliminate pathogens and tumors. Thus, DRAK2 represents a potential target to treat autoimmune diseases. However, the mechanisms by which DRAK2 contributes to autoimmunity, particularly type 1 diabetes (T1D), remain unresolved. Here, we demonstrate that resistance to T1D in non-obese diabetic (NOD) mice is due to the absence of Drak2 in T cells and requires the presence of regulatory T cells (Tregs). Contrary to previous hypotheses, we show that DRAK2 does not limit TCR signaling. Rather, DRAK2 regulates IL-2 signaling by inhibiting STAT5A phosphorylation. We further demonstrate that enhanced sensitivity to IL-2 in the absence of Drak2 augments thymic Treg development. Overall, our data indicate that DRAK2 contributes to autoimmunity in multiple ways by regulating thymic Treg development and by impacting the sensitivity of conventional T cells to Treg-mediated suppression.

The Emerging Key Role of the mGluR1-PKCγ Signaling Pathway in the Pathogenesis of Spinocerebellar Ataxias: A Neurodevelopmental Viewpoint

Spinocerebellar ataxias (SCAs) are a heterogeneous group of autosomal dominantly inherited progressive disorders with degeneration and dysfunction of the cerebellum. Although different subtypes of SCAs are classified according to the disease-associated causative genes, the clinical syndrome of the ataxia is shared, pointing towards a possible convergent pathogenic pathway among SCAs. In this review, we summarize the role of SCA-associated gene function during cerebellar Purkinje cell development and discuss the relationship between SCA pathogenesis and neurodevelopment. We will summarize recent studies on molecules involved in SCA pathogenesis and will focus on the mGluR1-PKCγ signaling pathway evaluating the possibility that this might be a common pathway which contributes to these diseases.

Prognostic and immune-related value of STK17B in skin cutaneous melanoma

Skin cutaneous melanoma (SKCM) is a common cancer of which mortality is increasing continuously. Our study conducted a series of analyses on the clinical significance of Serine/threonine kinase 17B (STK17B) in SKCM to provide a new biomarker for diagnosis and treatment. The RNA-sequence data were obtained from The Cancer Genome Atlas and Genotype-Tissue Expression databases. The data of 468 SKCM patients were divided into STK17B high- and low-expression groups and analyzed by Bioconductor package to identify the differential expressed genes. The R package of "clusterProfiler" was used for Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and Gene-Set Enrichment Analysis analyses. A protein-protein interaction network and immune infiltration landscape were respectively constructed via STRING database and ssGSEA. STK17B had lower expression in SKCM than normal tissues. Besides, STK17B expression was significantly related to some clinicopathological characteristics in SKCM patients including T stage, Breslow depth, radiation therapy, melanoma Clark level, and pathologic stage. The Kaplan-Meier curve analyses revealed that the low expression of STK17B was correlated with poor overall survival and disease-specific survival. We constructed nomograms to predict the 1-, 3-, and 5-year survival of SKCM patients. The function enrichment analyses showed STK17B-related differential expressed genes were enriched in cellular differentiation and immune-related progress. STK17B expression level were positively correlated with infiltrating level of immune cells. In this study, we found that STK17B, which played an important role in immune infiltration, could be a new biomarker for diagnosis and prognosis in SKCM patients.

DRAK2 aggravates nonalcoholic fatty liver disease progression through SRSF6-associated RNA alternative splicing

Nonalcoholic steatohepatitis (NASH) is an advanced stage of nonalcoholic fatty liver disease (NAFLD) with serious consequences that currently lacks approved pharmacological therapies. Recent studies suggest the close relationship between the pathogenesis of NAFLD and the dysregulation of RNA splicing machinery. Here, we reveal death-associated protein kinase-related apoptosis-inducing kinase-2 (DRAK2) is markedly upregulated in the livers of both NAFLD/NASH patients and NAFLD/NASH diet-fed mice. Hepatic deletion of DRAK2 suppresses the progression of hepatic steatosis to NASH. Comprehensive analyses of the phosphoproteome and transcriptome indicated a crucial role of DRAK2 in RNA splicing and identified the splicing factor SRSF6 as a direct binding protein of DRAK2. Further studies demonstrated that binding to DRAK2 inhibits SRSF6 phosphorylation by the SRSF kinase SRPK1 and regulates alternative splicing of mitochondrial function-related genes. In conclusion, our findings reveal an indispensable role of DRAK2 in NAFLD/NASH and offer a potential therapeutic target for this disease.

A Chemical Probe for Dark Kinase STK17B Derives Its Potency and High Selectivity through a Unique P-Loop Conformation

STK17B is a member of the death-associated protein kinase family and has been genetically linked to the development of diverse diseases. However, the role of STK17B in normal and disease pathology is poorly defined. Here, we present the discovery of thieno[3,2-d] pyrimidine SGC-STK17B-1 (11s), a high-quality chemical probe for this understudied "dark" kinase. 11s is an ATP-competitive inhibitor that showed remarkable selectivity over other kinases including the closely related STK17A. X-ray crystallography of 11s and related thieno[3,2-d]pyrimidines bound to STK17B revealed a unique P-loop conformation characterized by a salt bridge between R41 and the carboxylic acid of the inhibitor. Molecular dynamic simulations of STK17B revealed the flexibility of the P-loop and a wide range of R41 conformations available to the apo-protein. The isomeric thieno[2,3-d]pyrimidine SGC-STK17B-1N (19g) was identified as a negative control compound. The >100-fold lower activity of 19g on STK17B was attributed to the reduced basicity of its pyrimidine N1.

Harrison C, Eswaran J, Soundararajan M. DAP Kinase-Related Apoptosis-Inducing Protein Kinase 2 (DRAK2) Is a Key Regulator and Molecular Marker in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in the Western World and it is characterized by a marked degree of clinical heterogeneity. An impaired balance between pro- and anti-apoptotic stimuli determines chemorefractoriness and outcome. The low proliferation rate of CLL cells indicates that one of the primary mechanisms involved in disease development may be an apoptotic failure. Here, we study the clinical and functional significance of DRAK2, a novel stress response kinase that plays a critical role in apoptosis, T-cell biology, and B-cell activation in CLL. We have analyzed CLL patient samples and showed that low expression levels of DRAK2 were significantly associated with unfavorable outcome in our CLL cohort. DRAK2 expression levels showed a positive correlation with the expression of DAPK1, and TGFBR1. Consistent with clinical data, the downregulation of DRAK2 in MEC-1 CLL cells strongly increased cell viability and proliferation. Further, our transcriptome data from MEC-1 cells highlighted MAPK, NF-κB, and Akt and as critical signaling hubs upon DRAK2 knockdown. Taken together, our results indicate DRAK2 as a novel marker of CLL survival that plays key regulatory roles in CLL prognosis.

DAPK1 (death associated protein kinase 1) mediates mTORC1 activation and antiviral activities in CD8+ T cells

Mechanistic target of rapamycin complex 1 (mTORC1) regulates CD8⁺ T-cell differentiation and function. Despite the links between PI3K-AKT and mTORC1 activation in CD8⁺ T cells, the molecular mechanism underlying mTORC1 activation remains unclear. Here, we show that both the kinase activity and the death domain of DAPK1 are required for maximal mTOR activation and CD8⁺ T-cell function. We found that TCR-induced activation of calcineurin activates DAPK1, which subsequently interacts with TSC2 via its death domain and phosphorylates TSC2 to mediate mTORC1 activation. Furthermore, both the kinase domain and death domain of DAPK1 are required for CD8⁺ T-cell antiviral responses in an LCMV infection model. Together, our data reveal a novel mechanism of mTORC1 activation that mediates optimal CD8⁺ T-cell function and antiviral activity.

Differential Impact of Flavonoids on Redox Modulation, Bioenergetics, and Cell Signaling in Normal and Tumor Cells: A Comprehensive Review

SIGNIFICANCE

Flavonoids can interact with multiple molecular targets to elicit their cellular effects, leading to changes in signal transduction, gene expression, and/or metabolism, which can, subsequently, affect the entire cell and organism. Immortalized cell lines, derived from tumors, are routinely employed as a surrogate for mechanistic studies, with the results extrapolated to tissues in vivo. Recent Advances: We review the activities of selected flavonoids on cultured tumor cells derived from various tissues in comparison to corresponding primary cells or tissues in vivo, mainly using quercetin and flavanols (epicatechin and (-)-epigallocatechin gallate) as exemplars. Several studies have indicated that flavonoids could retard cancer progression in vivo in animal models as well as in tumor cell models.

CRITICAL ISSUES

Extrapolation from in vitro and animal models to humans is not straightforward given both the extensive conjugation and complex microbiota-dependent metabolism of flavonoids after consumption, as well as the heterogeneous metabolism of different tumors.

FUTURE DIRECTIONS

Comparison of data from studies on primary cells or in vivo are essential not only to validate results obtained from cultured cell models, but also to highlight whether any differences may be further exploited in the clinical setting for chemoprevention. Tumor cell models can provide a useful mechanistic tool to study the effects of flavonoids, provided that the limitations of each model are understood and taken into account in interpretation of the data.

Novel Functions of Death-Associated Protein Kinases through Mitogen-Activated Protein Kinase-Related Signals

Death associated protein kinase (DAPK) is a calcium/calmodulin-regulated serine/threonine kinase; its main function is to regulate cell death. DAPK family proteins consist of DAPK1, DAPK2, DAPK3, DAPK-related apoptosis-inducing protein kinases (DRAK)-1 and DRAK-2. In this review, we discuss the roles and regulatory mechanisms of DAPK family members and their relevance to diseases. Furthermore, a special focus is given to several reports describing cross-talks between DAPKs and mitogen-activated protein kinases (MAPK) family members in various pathologies. We also discuss small molecule inhibitors of DAPKs and their potential as therapeutic targets against human diseases.

STK17B promotes carcinogenesis and metastasis via AKT/GSK-3β/Snail signaling in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a lethal malignancy worldwide with frequent intrahepatic and distant metastasis. Elucidating the underlying molecular mechanism that modulates HCC progression is critical for exploring novel therapeutic strategies. Serine/Threonine Kinase 17B (STK17B) is upregulated in HCC tissues, but its role in HCC progression remains elusive. In the present studies, we reported that STK17B had a critical role in HCC progression. STK17B was significantly upregulated in HCC cell lines and specimens, and patients with ectopic STK17B expression characterized with poor clinicopathological features. In vitro and in vivo assay demonstrated that inhibition of STK17B markedly inhibits HCC tumorigenesis and metastasis, while STK17B overexpression promoted these processes. Furthermore, we found that STK17B promoted EMT process via activating AKT/GSK-3β/Snail signal pathway, and miR-455-3p was identified as the upstream regulator of STK17B. Combination of high level of STK17B and low level of miR-455-3p predicted poor prognosis with higher accuracy for HCC patients. In conclusion, our research demonstrated that STK17B promotes HCC progression, induces EMT process via activating AKT/GSK-3β/Snail signal and predicts poor prognosis in HCC.

Tumour suppressor death-associated protein kinase targets cytoplasmic HIF-1α for Th17 suppression

Death-associated protein kinase (DAPK) is a tumour suppressor. Here we show that DAPK also inhibits T helper 17 (Th17) and prevents Th17-mediated pathology in a mouse model of autoimmunity. We demonstrate that DAPK specifically downregulates hypoxia-inducible factor 1α (HIF-1α). In contrast to the predominant nuclear localization of HIF-1α in many cell types, HIF-1α is located in both the cytoplasm and nucleus in T cells, allowing for a cytosolic DAPK–HIF-1α interaction. DAPK also binds prolyl hydroxylase domain protein 2 (PHD2) and increases HIF-1α-PHD2 association. DAPK thereby promotes the proline hydroxylation and proteasome degradation of HIF-1α. Consequently, DAPK deficiency leads to excess HIF-1α accumulation, enhanced IL-17 expression and exacerbated experimental autoimmune encephalomyelitis. Additional knockout of HIF-1α restores the normal differentiation of Dapk^−/− Th17 cells and prevents experimental autoimmune encephalomyelitis development. Our results reveal a mechanism involving DAPK-mediated degradation of cytoplasmic HIF-1α, and suggest that raising DAPK levels could be used for treatment of Th17-associated inflammatory diseases.

HIF-1α is critical for Th17 differentiation. Here the authors show that DAPK (Death-Associated Protein Kinase) inhibits Th17 differentiation and immunopathology in a mouse model of multiple sclerosis by promoting HIF1-α binding to its negative regulator PHD2.

Discovery of indirubin derivatives as new class of DRAK2 inhibitors from high throughput screening

DRAK2 is a serine/threonine kinase belonging to the death-associated protein kinase (DAPK) family and has emerged as a promising drug target for the treatment of autoimmune diseases and cancers. To identify small molecule inhibitors for DRAK2, we performed a high throughput screening campaign using in-house chemical library and identified indirubin-3'-monoximes as novel class of DRAK2 inhibitors. Among the compounds tested, compound 16 exhibited the most potent inhibitory activity against DRAK2 (IC50=0.003μM). We also propose that compound 16 may bind to the ATP-binding site of the enzyme based on enzyme kinetics and molecular docking studies.

Drak2 Does Not Regulate TGF-β Signaling in T Cells

Drak2 is a serine/threonine kinase expressed highest in T cells and B cells. Drak2^-/- mice are resistant to autoimmunity in mouse models of type 1 diabetes and multiple sclerosis. Resistance to these diseases occurs, in part, because Drak2 is required for the survival of autoreactive T cells that induce disease. However, the molecular mechanisms by which Drak2 affects T cell survival and autoimmunity are not known. A recent report demonstrated that Drak2 negatively regulated transforming growth factor-β (TGF-β) signaling in tumor cell lines. Thus, increased TGF-β signaling in the absence of Drak2 may contribute to the resistance to autoimmunity in Drak2^-/- mice. Therefore, we examined if Drak2 functioned as a negative regulator of TGF-β signaling in T cells, and whether the enhanced susceptibility to death of Drak2^-/- T cells was due to augmented TGF-β signaling. Using several in vitro assays to test TGF-β signaling and T cell function, we found that activation of Smad2 and Smad3, which are downstream of the TGF-β receptor, was similar between wildtype and Drak2^-/- T cells. Furthermore, TGF-β-mediated effects on naïve T cell proliferation, activated CD8⁺ T cell survival, and regulatory T cell induction was similar between wildtype and Drak2^-/- T cells. Finally, the increased susceptibility to death in the absence of Drak2 was not due to enhanced TGF-β signaling. Together, these data suggest that Drak2 does not function as a negative regulator of TGF-β signaling in primary T cells stimulated in vitro. It is important to investigate and discern potential molecular mechanisms by which Drak2 functions in order to better understand the etiology of autoimmune diseases, as well as to validate the use of Drak2 as a target for therapeutic treatment of these diseases.

Drak2 is not required for tumor surveillance and suppression

Drak2 is a promising therapeutic target to treat organ-specific autoimmune diseases such as type 1 diabetes and multiple sclerosis without causing generalized immune suppression. Inhibition of Drak2 may also prevent graft rejection following organ transplantation. However, Drak2 may function as a critical tumor suppressor, which would challenge the prospect of targeting Drak2 for therapeutic treatment. Thus, we examined the susceptibility of Drak2 (-/-) mice in several tumor models. We show that Drak2 is not required to prevent tumor formation in a variety of settings. Therefore, Drak2 does not function as an essential tumor suppressor in in vivo tumor models. These data further validate Drak2 as a viable therapeutic target to treat autoimmune disease and graft rejection. Importantly, these data also indicate that while Drak2 may induce apoptosis when overexpressed in cell lines, it is not an essential tumor suppressor.

Regulation of inflammation by DAPK

Death-associated protein kinase (DAPK) is a tumor suppressor and negatively regulates several activation signals. Consistent with its potential anti-inflammatory activity, DAPK promotes the formation of IFN-γ-activated inhibitor of translation (GAIT) complex that suppresses the translation of selected inflammatory genes. DAPK has been found to inhibit tumor necrosis factor-α (TNF-α)- or lipopolysaccharides (LPS)-induced NF-κB activation and pro-inflammatory cytokine expression. Inflammation is always associated with T cell activation, while DAPK attenuates T cell activation by a selective suppression in T cell receptor-triggered NF-κB activation. Recent studies, however, also reveal a contribution of DAPK to pro-inflammatory processes. DAPK is shown to mediate pro-inflammatory signaling downstream of TNF-α, LPS, IL-17, or IL-32. In addition, DAPK is required for the full formation of NLRP3 inflammasome, essential for the generation of IL-1β and IL-18. These results suggest the complicated role of DAPK in the regulation of inflammation that is likely dependent on cell types and environmental cues.

Discovery of dual death-associated protein related apoptosis inducing protein kinase 1 and 2 inhibitors by a scaffold hopping approach

DRAK2 emerged as a promising drug target for the treatment of autoimmune diseases and to prevent graft rejection after organ transplantation. Screening of a compound library in a DRAK2 binding assay led to the identification of an isothiazolo[5,4-b]pyridine derivative as a novel ligand for DRAK2, displaying a Kd value of 1.6 μM. Subsequent medicinal chemistry work led to the discovery of a thieno[2,3-b]pyridine derivative with strong DRAK2 binding affinity (Kd = 9 nM). Moreover, this compound also behaves as a functional inhibitor of DRAK2 enzymatic activity, displaying an IC50 value of 0.82 μM, although lacking selectivity, when tested against DRAK1. This paper describes for the first time functionally active dual DRAK1 and DRAK2 inhibitors that can be used as starting point for the synthesis of chemical tool compounds to study DRAK1 and DRAK2 biology, or they can be considered as hit compounds for hit-to-lead optimization campaigns in drug discovery programs.

Synthesis and structure-activity relationship studies of 2-(1,3,4-oxadiazole-2(3H)-thione)-3-amino-5-arylthieno[2,3-b]pyridines as inhibitors of DRAK2

In recent years, DAPK-related apoptosis-inducing protein kinase 2 (DRAK2) has emerged as a promising target for the treatment of a variety of autoimmune diseases and for the prevention of graft rejection after organ transplantation. However, medicinal chemistry optimization campaigns for the discovery of novel small-molecule inhibitors of DRAK2 have not yet been published. Screening of a proprietary compound library led to the discovery of a benzothiophene analogue that displays an affinity constant (Kd) value of 0.25 μM. Variation of the core scaffold and of the substitution pattern afforded a series of 5-arylthieno[2,3-b]pyridines with strong binding affinity (Kd = 0.008 μM for the most potent representative). These compounds also show promising activity in a functional biochemical DRAK2 enzyme assay, with an IC50 value of 0.029 μM for the most potent congener. Selectivity profiling of the most potent compounds revealed that they lack selectivity within the DAPK family of kinases. However, one of the less potent analogues is a selective ligand for DRAK2 and can be used as starting point for the synthesis of selective and potent DRAK2 inhibitors.

Modulation of T Cell Metabolism and Function through Calcium Signaling

As a vital second messenger in the activation of lymphocytes, the divalent cation Ca(2+) plays numerous roles in adaptive immune responses. Importantly, Ca(2+) signaling is essential for T cell activation, tolerance of self-antigens, and homeostasis. Supporting the essential role of Ca(2+) signaling in T cell biology, the Ca(2+) regulated protein phosphatase calcineurin is a key target of pharmacologic inhibition for preventing allograft rejection and for autoimmune therapy. Recent studies have highlighted the unique role of Stim1 and Orai1/2 proteins in the regulation of store-operated/calcium release activated calcium (CRAC) channels in the context of T cells. While Ca(2+) is known to modulate T cell activation via effects on calcineurin and its target, nuclear factor of activated T cells (NFAT), this second messenger also regulates other pathways, including protein kinase C, calmodulin kinases, and cytoskeletal proteins. Ca(2+) also modulates the unique metabolic changes that occur during in distinct T cell stages and subsets. Herein, we discuss the means by which Ca(2+) mobilization modulates cellular metabolism following T cell receptor ligation. Further, we highlight the crosstalk between mitochondrial metabolism, reactive oxygen species (ROS) generation, and CRAC channel activity. As a target of mitochondrial ROS and Ca(2+) regulation, we describe the involvement of the serine/threonine kinase DRAK2 in the context of these processes. Given the important roles for Ca(2+) dependent signaling and cellular metabolism in adaptive immune responses, the crosstalk between these pathways is likely to be important for the regulation of T cell activation, tolerance, and homeostasis.

Structural and functional diversity in the activity and regulation of DAPK-related protein kinases

Within the large group of calcium/calmodulin-dependent protein kinases (CAMKs) of the human kinome, there is a distinct branch of highly related kinases that includes three families: death-associated protein-related kinases, myosin light-chain-related kinases and triple functional domain protein-related kinases. In this review, we refer to these collectively as DMT kinases. There are several functional features that span the three families, such as a broad involvement in apoptotic processes, cytoskeletal association and cellular plasticity. Other CAMKs contain a highly conserved HRD motif, which is a prerequisite for kinase regulation through activation-loop phosphorylation, but in all 16 members of the DMT branch, this is replaced by an HF/LD motif. This DMT kinase signature motif substitutes phosphorylation-dependent active-site interactions with a local hydrophobic core that maintains an active kinase conformation. Only about half of the DMT kinases have an additional autoregulatory domain, C-terminal to the kinase domain that binds calcium/calmodulin in order to regulate kinase activity. Protein substrates have been identified for some of the DMT kinases, but little is known about the mechanism of recognition. Substrate conformation could be an equally important parameter in substrate recognition as specific preferences in sequence position. Taking the data together, this kinase branch encapsulates a treasure trove of features that renders it distinct from many other protein kinases and calls for future research activities in this field.

Genome wide mapping reveals PDE4B as an IL-2 induced STAT5 target gene in activated human PBMCs and lymphoid cancer cells

IL-2 is the primary growth factor for promoting survival and proliferation of activated T cells that occurs following engagement of the Janus Kinase (JAK)1–3/and Signal Transducer and Activator of Transcription (STAT) 5 signaling pathway. STAT5 has two isoforms: STAT5A and STAT5B (commonly referred to as STAT5) which, in T cells, play redundant roles transcribing cell cycle and survival genes. As such, inhibition of STAT5 by a variety of mechanisms can rapidly induce apoptosis in certain lymphoid tumor cells, suggesting that it and its target genes represent therapeutic targets to control certain lymphoid diseases. To search for these molecules we aligned IL-2 regulated genes detected by Affymetrix gene expression microarrays with the STAT5 cistrome identified by chip-on-ChIP analysis in an IL-2-dependent human leukemia cell line, Kit225. Select overlapping genes were then validated using qRT²PCR medium-throughput arrays in human PHA-activated PBMCs. Of 19 putative genes, one key regulator of T cell receptor signaling, PDE4B, was identified as a novel target, which was readily up-regulated at the protein level (3 h) in IL-2 stimulated, activated human PBMCs. Surprisingly, only purified CD8+ primary T-cells expressed PDE4B, but not CD4+ cells. Moreover, PDE4B was found to be highly expressed in CD4+ lymphoid cancer cells, which suggests that it may represent a physiological role unique to the CD8+ and lymphoid cancer cells and thus might represent a target for pharmaceutical intervention for certain lymphoid diseases.

DRAK2 participates in a negative feedback loop to control TGF-β/Smads signaling by binding to type I TGF-β receptor

TGF-β1 is a multifunctional cytokine that mediates diverse biological processes. However, the mechanisms by which the intracellular signals of TGF-β1 are terminated are not well understood. Here, we demonstrate that DRAK2 serves as a TGF-β1-inducible antagonist of TGF-β signaling. TGF-β1 stimulation rapidly induces DRAK2 expression and enhances endogenous interaction of the type I TGF-β receptor with DRAK2, thereby blocking R-Smads recruitment. Depletion of DRAK2 expression markedly augmented the intensity and the extent of TGF-β1 responses. Furthermore, a high level of DRAK2 expression was observed in basal-like and HER2-enriched breast tumors and cell lines, and depletion of DRAK2 expression suppressed the tumorigenic ability of breast cancer cells. Thus, these studies define a function for DRAK2 as an intrinsic intracellular antagonist participating in the negative feedback loop to control TGF-β1 responses, and aberrant expression of DRAK2 increases tumorigenic potential, in part, through the inhibition of TGF-β1 tumor suppressor activity.

Loss of DRAK2 signaling enhances allogeneic transplant survival by limiting effector and memory T cell responses

Here, we demonstrate that loss of DRAK2 signaling significantly promotes the acceptance of allogeneic engraftment in two separate transplant models without promoting generalized immunosuppression. Drak2-/- T cells failed to reject allogeneic tumors, and were defective in rejecting Balb/C allogeneic skin grafts on C57BL6/J recipients. A significant fraction of alloreactive Drak2-/- T cells underwent apoptosis following activation, whereas enforced expression of Bcl-xL in Drak2-/- T cells restored allograft rejection. Formation of allogeneic memory was also greatly hampered in T cells lacking the Drak2 gene. Adoptive transfer of memory T cells from Drak2-/- mice failed to promote the rejection of allogeneic tumors, and such cells led to significantly delayed rejection of skin allografts in the Balb/C->C57BL/6J model. Costimulatory blockade by in vivo administration of Cytotoxic T-Lymphocyte Antigen 4 fusion protein (CTLA4-Ig) synergized with the DRAK2 deficiency and led to long-term allogeneic skin graft acceptance. Overall, these results demonstrate that DRAK2 plays an important role in primary and memory T cell responsiveness to allografts. Because previous studies have demonstrated that a loss of DRAK2 does not negatively impact antiviral immunity, the studies here underscore the potential utility of pharmacological blockade of DRAK2 to achieve transplant maintenance without the imposition of generalized immunosuppression.

Serine/threonine kinase 17A is a novel p53 target gene and modulator of cisplatin toxicity and reactive oxygen species in testicular cancer cells

Testicular cancer is highly curable with cisplatin-based therapy, and testicular cancer-derived human embryonal carcinoma (EC) cells undergo a p53-dominant transcriptional response to cisplatin. In this study, we have discovered that a poorly characterized member of the death-associated protein family of serine/threonine kinases, STK17A (also called DRAK1), is a novel p53 target gene. Cisplatin-mediated induction of STK17A in the EC cell line NT2/D1 was prevented with p53 siRNA. Furthermore, STK17A was induced with cisplatin in HCT116 and MCF10A cells but to a much lesser extent in isogenic p53-suppressed cells. A functional p53 response element that binds endogenous p53 in a cisplatin-dependent manner was identified 5 kb upstream of the first coding exon of STK17A. STK17A is not present in the mouse genome, but the closely related gene STK17B is induced with cisplatin in mouse NIH3T3 cells, although this induction is p53-independent. Interestingly, in human cells containing both STK17A and STK17B, only STK17A is induced with cisplatin. Knockdown of STK17A conferred resistance to cisplatin-induced growth suppression and apoptotic cell death in EC cells. This was associated with the up-regulation of detoxifying and antioxidant genes, including metallothioneins MT1H, MT1M, and MT1X that have previously been implicated in cisplatin resistance. In addition, knockdown of STK17A resulted in decreased cellular reactive oxygen species, whereas STK17A overexpression increased reactive oxygen species. In summary, we have identified STK17A as a novel direct target of p53 and a modulator of cisplatin toxicity and reactive oxygen species in testicular cancer cells.

Zipper-interacting protein kinase (ZIPK) modulates canonical Wnt/beta-catenin signaling through interaction with Nemo-like kinase and T-cell factor 4 (NLK/TCF4)

Zipper-interacting protein kinase (ZIPK) is a widely expressed serine/threonine kinase that has been implicated in apoptosis and transcriptional regulation. Here, we identified Nemo-like kinase (NLK) as a novel ZIPK-binding partner and found that ZIPK regulates NLK-mediated repression of canonical Wnt/β-catenin signaling. Indeed, siRNA-mediated reduction of endogenous ZIPK expression reduced Wnt/β-catenin signaling. Furthermore, ZIPK affected the formation of NLK-T-cell factor 4 (TCF4) complex. Importantly, ZIPK siRNA treatment in human colon carcinoma cells resulted in a reduction of β-catenin/TCF-mediated gene expression and cell growth. These results indicate that ZIPK may serve as a transcriptional regulator of canonical Wnt/β-catenin signaling through interaction with NLK/TCF4.

Protein kinase D orchestrates the activation of DRAK2 in response to TCR-induced Ca2+ influx and mitochondrial reactive oxygen generation

DRAK2 is a serine/threonine kinase highly enriched in lymphocytes that raises the threshold for T cell activation and maintains T cell survival following productive activation. T cells lacking DRAK2 are prone to activation under suboptimal conditions and exhibit enhanced calcium responses to AgR stimulation. Despite this, mice lacking DRAK2 are resistant to organ-specific autoimmune diseases due to defective autoreactive T cell survival. DRAK2 kinase activity is induced by AgR signaling, and in this study we show that the induction of DRAK2 activity requires Ca(2+) influx through the Ca(2+) release-activated Ca(2+) channel formed from Orai1 subunits. Blockade of DRAK2 activity with the protein kinase D (PKD) inhibitor Gö6976 or expression of a kinase-dead PKD mutant prevented activation of DRAK2, whereas a constitutively active PKD mutant promoted DRAK2 function. Knockdown of PKD in T cells strongly blocked endogenous DRAK2 activation following TCR ligation, implicating PKD as an essential intermediate in the activation of DRAK2 by Ca(2+) influx. Furthermore, we identify DRAK2 as a novel substrate of PKD, and demonstrate that DRAK2 and PKD physically interact under conditions that activate PKD. Mitochondrial generation of reactive oxygen intermediates was necessary and sufficient for DRAK2 activation in response to Ca(2+) influx. Taken together, DRAK2 and PKD form a novel signaling module that controls calcium homeostasis following T cell activation.

Overlapping roles of Drosophila Drak and Rok kinases in epithelial tissue morphogenesis

Dynamic regulation of cytoskeletal contractility through phosphorylation of the nonmuscle Myosin-II regulatory light chain (MRLC) provides an essential source of tension for shaping epithelial tissues. Rho GTPase and its effector kinase ROCK have been implicated in regulating MRLC phosphorylation in vivo, but evidence suggests that other mechanisms must be involved. Here, we report the identification of a single Drosophila homologue of the Death-associated protein kinase (DAPK) family, called Drak, as a regulator of MRLC phosphorylation. Based on analysis of null mutants, we find that Drak broadly promotes proper morphogenesis of epithelial tissues during development. Drak activity is largely redundant with that of the Drosophila ROCK orthologue, Rok, such that it is essential only when Rok levels are reduced. We demonstrate that these two kinases synergistically promote phosphorylation of Spaghetti squash (Sqh), the Drosophila MRLC orthologue, in vivo. The lethality of drak/rok mutants can be rescued by restoring Sqh activity, indicating that Sqh is the critical common effector of these two kinases. These results provide the first evidence that DAPK family kinases regulate actin dynamics in vivo and identify Drak as a novel component of the signaling networks that shape epithelial tissues.

Cutting edge: critical role for PYCARD/ASC in the development of experimental autoimmune encephalomyelitis

Multiple sclerosis is an autoimmune disease in which self-reactive T cells attack oligodendrocytes that myelinate axons in the CNS. Experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, is dependent on caspase-1; however, the role of Nod-like receptors upstream of caspase-1 is unknown. Danger- and pathogen-associated molecular patterns activate Nod-like receptor 3, which activates caspase-1 through the adaptor protein, apoptosis-associated speck-like protein containing CARD (ASC). We report that the progression of EAE is dependent on ASC and caspase-1 but not Nod-like receptor 3. ASC(-/-) mice were even more protected from the progression of EAE than were caspase-1(-/-) mice, suggesting that an inflammasome-independent function of ASC contributes to the progression of EAE. We found that CD4(+) T cells deficient in ASC exhibited impaired survival; accordingly, ASC(-/-) mice had fewer myelin oligodendrocyte glycoprotein-specific T cells in the draining lymph nodes and CNS.

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

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

Regulation of the apoptosis-inducing kinase DRAK2 by cyclooxygenase-2 in colorectal cancer

Background:

Cyclooxygenase-2 (COX-2) is over-expressed in colorectal cancer (CRC), rendering tumour cells resistant to apoptosis. Selective COX-2 inhibition is effective in CRC prevention, although having adverse cardiovascular effects, thus focus has shifted to downstream pathways.

Methods:

Microarray experiments identified genes regulated by COX-2 in HCA7 CRC cells. In vitro and in vivo regulation of DRAK2 (DAP kinase-related apoptosis-inducing kinase 2 or STK17β, an apoptosis-inducing kinase) by COX-2 was validated by qRT-PCR.

Results:

Inhibition of COX-2 induced apoptosis and enhanced DRAK2 expression in HCA7 cells (4.4-fold increase at 4 h by qRT-PCR, P=0.001), an effect prevented by co-administration of PGE₂. DRAK2 levels were suppressed in a panel of human colorectal tumours (n=10) compared to normal mucosa, and showed inverse correlation with COX-2 expression (R=−0.68, R²=0.46, P=0.03). Administration of the selective COX-2 inhibitor rofecoxib to patients with CRC (n=5) induced DRAK2 expression in tumours (2.5-fold increase, P=0.01). In vitro silencing of DRAK2 by RNAi enhanced CRC cell survival following COX-2 inhibitor treatment.

Conclusion:

DRAK2 is a serine–threonine kinase implicated in the regulation of apoptosis and is negatively regulated by COX-2 in vitro and in vivo, suggesting a novel mechanism for the effect of COX-2 on cancer cell survival.

Microarray analysis of lymphatic tissue reveals stage-specific, gene expression signatures in HIV-1 infection

Untreated HIV-1 infection progresses through acute and asymptomatic stages to AIDS. Although each of the three stages has well-known clinical, virologic, and immunologic characteristics, much less is known of the molecular mechanisms underlying each stage. In this study, we report lymphatic tissue microarray analyses, revealing for the first time stage-specific patterns of gene expression during HIV-1 infection. We show that although there is a common set of key genes with altered expression throughout all stages, each stage has a unique gene expression signature. The acute stage is most notably characterized by increased expression of hundreds of genes involved in immune activation, innate immune defenses (e.g., RIG-1, MDA-5, TLR7 and TLR8, PKR, APOBEC3B, 3F, 3G), adaptive immunity, and in the proapoptotic Fas-Fas ligand pathway. Yet, quite strikingly, the expression of nearly all acute stage genes return to baseline levels in the asymptomatic stage, accompanying partial control of infection. This transition from acute to asymptomatic stage is tied to increased expression of a diverse array of immunosuppressive genes (e.g., CLEC12B, ILT4, galectin-3, CD160, BCMA, FGL2, LAG3, GPNMB). In the AIDS stage, decreased expression of numerous genes involved in T cell signaling identifies genes contributing to T cell dysfunction. These common and stage-specific gene expression signatures identify potential molecular mechanisms underlying the host response and the slow, natural course of HIV-1 infection.

Altered thymic selection and increased autoimmunity caused by ectopic expression of DRAK2 during T cell development

Negative regulation of TCR signaling is an important mechanism enforcing immunological self-tolerance to prevent inappropriate activation of T cells and thus the development of autoimmune diseases. The lymphoid-restricted serine/threonine kinase death-associated protein-related apoptotic kinase-2 (DRAK2) raises the TCR activation threshold by targeting TCR-induced calcium mobilization in thymocytes and peripheral T cells and regulates positive thymic selection and peripheral T cell activation. Despite a hypersensitivity of peripheral drak2-deficient T cells, drak2-deficient mice are enigmatically resistant to induced autoimmunity in the model experimental autoimmune encephalomyelitis. To further evaluate the differential role of DRAK2 in central vs peripheral tolerance and to assess its impact on the development of autoimmune diseases, we have generated a transgenic (Tg) mouse strain ectopically expressing DRAK2 via the lck proximal promoter (1017-DRAK2 Tg mice). This transgene led to highest expression levels in double-positive thymocytes that are normally devoid of DRAK2. 1017-DRAK2 Tg mice displayed a reduction of single-positive CD4(+) and CD8(+) thymocytes in context with diminished negative selection in male HY TCR x 1017-DRAK2 Tg mice as well as peripheral T cell hypersensitivity, enhanced susceptibility to experimental autoimmune encephalomyelitis, and spontaneous autoimmunity. These findings suggest that alteration in thymocyte signaling thresholds impacts the sensitivity of peripheral T cell pools.

Cytosolic PLA2 is required for CTL-mediated immunopathology of celiac disease via NKG2D and IL-15

IL-15 and NKG2D promote autoimmunity and celiac disease by arming cytotoxic T lymphocytes (CTLs) to cause tissue destruction. However, the downstream signaling events underlying these functional properties remain unclear. Here, we identify cytosolic phospholipase A₂ (cPLA₂) as a central molecule in NKG2D-mediated cytolysis in CTLs. Furthermore, we report that NKG2D induces, upon recognition of MIC⁺ target cells, the release of arachidonic acid (AA) by CTLs to promote tissue inflammation in association with target killing. Interestingly, IL-15, which licenses NKG2D-mediated lymphokine killer activity in CTLs, cooperates with NKG2D to induce cPLA₂ activation and AA release. Finally, cPLA₂ activation in intraepithelial CTLs of celiac patients provides an in vivo pathophysiological dimension to cPLA₂ activation in CTLs. These results reveal an unrecognized link between NKG2D and tissue inflammation, which may underlie the emerging role of NKG2D in various immunopathological conditions and define new therapeutic targets.

Enhanced T cell apoptosis within Drak2-deficient mice promotes resistance to autoimmunity

Clonal expansion of T cells is vital to adaptive immunity, yet this process must be tightly controlled to prevent autoimmune disease. The serine/threonine kinase death-associated protein kinase-related apoptosis-inducing kinase 2 (DRAK2) is a negative regulator of TCR signaling and sets the threshold for the activation of naive and memory T cells and selected thymocytes. Despite enhanced T cell activation, Drak2(-/-) mice are resistant to experimental autoimmune encephalomyelitis, an autoimmune demyelinating disease that resembles multiple sclerosis. However, the basis for this autoimmune resistance is currently unknown. In this study, we show that, in the absence of DRAK2 signaling, T cells require greater tonic signaling for maintenance during clonal expansion. Following stimulation, Drak2(-/-) T cells were more sensitive to an intrinsic form of apoptosis that was prevented by CD28 ligation, homeostatic cytokines, or enforced Bcl-x(L) expression. T cell-specific Bcl-x(L) expression also restored the susceptibility of Drak2(-/-) mice to experimental autoimmune encephalomyelitis and enhanced thymic positive selection. These findings demonstrate that DRAK2 is selectively important for T cell survival and highlight the potential that DRAK2 blockade may lead to permanent autoimmune T cell destruction via intrinsic apoptosis pathways.

Drak2 regulates the survival of activated T cells and is required for organ-specific autoimmune disease

Drak2 is a serine/threonine kinase expressed in T and B cells. The absence of Drak2 renders T cells hypersensitive to suboptimal stimulation, yet Drak2(-/-) mice are enigmatically resistant to experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. We show in this study that Drak2(-/-) mice were also completely resistant to type 1 diabetes when bred to the NOD strain of mice that spontaneously develop autoimmune diabetes. However, there was not a generalized suppression of the immune system, because Drak2(-/-) mice remained susceptible to other models of autoimmunity. Adoptive transfer experiments revealed that resistance to disease was intrinsic to the T cells and was due to a loss of T cell survival under conditions of chronic autoimmune stimulation. Importantly, the absence of Drak2 did not alter the survival of naive T cells, memory T cells, or T cells responding to an acute viral infection. These experiments reveal a distinction between the immune response to persistent self-encoded molecules and transiently present infectious agents. We present a model whereby T cell survival depends on a balance of TCR and costimulatory signals to explain how the absence of Drak2 affects autoimmune disease without generalized suppression of the immune system.

A role for DRAK2 in the germinal center reaction and the antibody response

DAP-related apoptotic kinase-2 (DRAK2), a death-associated protein kinase family member, is highly expressed in B and T lymphocytes in the human and the mouse. To determine whether DRAK2 plays a role in B-cell activation and differentiation, we analyzed germinal centers (GCs) and the specific antibody response to NP in drak2-/- mice immunized with the thymus-dependent (TD) conjugated hapten NP16-CGG. In drak2-/- mice, spleen GCs were normal in size and morphology, but their number was reduced by as much as 5-fold, as compared to their wild-type littermates. This was not due to a defect in B-cell proliferation, as the BrdU uptake was comparable in DRAK2-deficient and wild-type B cells. Rather, the proportion of apoptotic GC B and T cells in drak2-/- mice was significantly higher than that in wild-type control mice, as shown by 7-AAD and terminal deoxynucleotide transferase dUTP nick end labeling (TUNEL) staining. In drak2-/- mice, the generation high affinity IgG antibodies was impaired in spite of the seemingly normal somatic hypermutation and class switch DNA recombination machineries in drak2-/- B cells. In NP16-CGG-immunized drak2-/- mice, T-cell-intrinsic Bcl-xL transgene expression increased the number of GCs and rescued the high affinity IgG response to NP. These findings suggest a novel role for DRAK2 in regulating the GC reaction and the response to TD antigens, perhaps through increased survival of T cells and enhanced B-cell positive selection. They also suggest that DRAK2-deficiency is not involved in regulating intrinsic B-cell apoptosis.

Drak2 contributes to West Nile virus entry into the brain and lethal encephalitis

Death-associated protein kinase-related apoptosis-inducing kinase-2 (Drak2), a member of the death-associated protein family of serine/threonine kinases, is specifically expressed in T and B cells. In the absence of Drak2, mice are resistant to experimental autoimmune encephalomyelitis due to a decrease in the number of cells infiltrating the CNS. In the present study, we investigated the role of Drak2 in West Nile virus (WNV)-induced encephalitis and found that Drak2(-/-) mice were also more resistant to lethal WNV infection than wild-type mice. Although Drak2(-/-) mice had an increase in the number of IFN-gamma-producing T cells in the spleen after infection, viral levels in the peripheral tissues were not significantly different between these two groups of mice. In contrast, there was a reduced viral load in the brains of Drak2(-/-) mice, which was accompanied by a decrease in the number of Drak2(-/-) CD4(+) and CD8(+) T cells in the brain following WNV infection. Moreover, we detected viral Ags in T cells isolated from the spleen or brain of WNV-infected mice. These results suggest that following a systemic infection, WNV might cross the blood brain barrier and enter the CNS by being carried by infected infiltrating T cells.

Physical and functional interactions between ZIP kinase and UbcH5

Zipper-interacting protein kinase (ZIPK) is a widely expressed serine/threonine kinase that has been implicated in cell death and transcriptional regulation, but its mechanism of regulation remains unknown. In our previous study, we showed that leukemia inhibitory factor stimulated threonine-265 phosphorylation of ZIPK, thereby leading to phosphorylation and activation of signal transducer and activator of transcription 3. Here, we identified UbcH5c as a novel ZIPK-binding partner by yeast two-hybrid screening. Importantly, we found that UbcH5c induced ubiquitination of ZIPK. Small-interfering RNA-mediated reduction of endogenous UbcH5 expression decreased ZIPK ubiquitination. Furthermore, coexpression of UbcH5c with ZIPK influenced promyelocytic leukemia protein nuclear body (PML-NB) formation. These results suggest that UbcH5 regulates ZIPK accumulation in PML-NBs by interacting with ZIPK and stimulating its ubiquitination.

DRAK2 regulates memory T cell responses following murine coronavirus infection

The contribution of DRAK2 [death-associated protein kinase (DAPK)-related apoptosis-inducing kinase 2] to anti-viral memory T cell responses following infection with mouse hepatitis virus (MHV) was examined. DRAK2 is a lymphoid-enriched serine/threonine kinase that is an important regulatory molecule involved in modulating T cell responses. Memory T cells derived from MHV-immunized Drak2(-/-) mice exhibited amplified proliferation and IFN-gamma secretion following stimulation with viral epitopes. Transfer of Drak2(-/-) memory T cells into Rag1(-/-) mice infected intracerebrally with MHV resulted in accelerated clearance of virus from the brain. Thus, DRAK2 may be a novel target for stimulating protective immunity to viral pathogens.

Tpl2 and ERK transduce antiproliferative T cell receptor signals and inhibit transformation of chronically stimulated T cells

The protein kinase encoded by the Tpl2 protooncogene plays an obligatory role in the transduction of Toll-like receptor and death receptor signals in macrophages, B cells, mouse embryo fibroblasts, and epithelial cells in culture and promotes inflammatory responses in animals. To address its role in T cell activation, we crossed the T cell receptor (TCR) transgene 2C, which recognizes class I MHC presented peptides, into the Tpl2(-/-) genetic background. Surprisingly, the TCR2C(tg/tg)/Tpl2(-/-) mice developed T cell lymphomas with a latency of 4-6 months. The tumor cells were consistently TCR2C(+)CD8(+)CD4(-), suggesting that they were derived either from chronically stimulated mature T cells or from immature single positive (ISP) cells. Further studies showed that the population of CD8(+) ISP cells was not expanded in the thymus of TCR2C(tg/tg)/Tpl2(-/-) mice, making the latter hypothesis unlikely. Mature peripheral T cells of Tpl2(-/-) mice were defective in ERK activation and exhibited enhanced proliferation after TCR stimulation. The same cells were defective in the induction of CTLA4, a negative regulator of the T cell response, which is induced by TCR signals via ERK. These findings suggest that Tpl2 functions normally in a feedback loop that switches off the T cell response to TCR stimulation. As a result, Tpl2, a potent oncogene, functions as a tumor suppressor gene in chronically stimulated T cells.