Diacylglycerol kinase ζ is involved in the process of cerebral infarction

Endocannabinoid 2-Arachidonoylglycerol Synthesis and Metabolism at Neuronal Nuclear Matrix Fractions Derived from Adult Rat Brain Cortex

In this report, we describe the kinetics characteristics of the diacylglycerol lipase-α (DGLα) located at the nuclear matrix of nuclei derived from adult cortical neurons. Thus, using high-resolution fluorescence microscopy, classical biochemical subcellular fractionation, and Western blot techniques, we demonstrate that the DGLα enzyme is located in the matrix of neuronal nuclei. Furthermore, by quantifying the 2-arachidonoylglycerol (2-AG) level by liquid chromatography and mass spectrometry when 1-stearoyl-2-arachidonoyl-sn-glycerol (SAG) was exogenously added as substrate, we describe the presence of a mechanism for 2-AG production through DGLα dependent biosynthesis with an apparent K_m (K_m^app) of 180 µM and a V_max of 1.3 pmol min^-1 µg^-1 protein. We also examined the presence of enzymes with hydrolytic and oxygenase activities that are able to use 2-AG as substrate, and described the localization and compartmentalization of the major 2-AG degradation enzymes, namely monoacylglycerol lipase (MGL), fatty acid amide hydrolase (FAAH), α/β-hydrolase domain 12 protein (ABHD12) and cyclooxygenase-2 (COX2). Of these, only ABHD12 exhibited the same distribution with respect to chromatin, lamin B1, SC-35 and NeuN as that described for DGLα. When 2-AG was exogenously added, we observed the production of arachidonic acid (AA), which was prevented by inhibitors (but not specific MGL or ABHD6 inhibitors) of the ABHD family. Overall, our results expand knowledge about the subcellular distribution of neuronal DGLα, and provide biochemical and morphological evidence to ensure that 2-AG is produced in the neuronal nuclear matrix. Thus, this work paves the way for proposing a working hypothesis about the role of 2-AG produced in neuronal nuclei.

Regulation of p53 and NF-κB transactivation activities by DGKζ in catalytic activity-dependent and -independent manners

Diacylglycerol kinase (DGK) constitutes a family of enzymes that phosphorylate diacylglycerol to phosphatidic acid (PA). These lipids serve as second messengers, thereby activating distinct downstream cascades and different cellular responses. Therefore, DG-to-PA conversion activity induces a phase transition of signaling pathways. One member of the family, DGKζ, is involved closely with stress responses. Morphological data showing that DGKζ localizes predominantly to the nucleus and that it shuttles between the nucleus and the cytoplasm implicate DGKζ in the regulation of transcription factors during stress responses. Tumor suppressor p53 and NF-κB are major stress-responsive transcription factors. They exert opposing effects on cellular pathophysiology. Herein, we summarize DGKζ catalytic activity-dependent and -independent regulatory mechanisms of p53 and NF-κB transactivation activities, including p53 degradation and NF-κB nuclear translocation. We also discuss how each component of DGKζ-interacting protein complex modulates the specificity and selectivity of target gene expression.

DGKζ depletion attenuates HIF-1α induction and SIRT1 expression, but enhances TAK1-mediated AMPKα phosphorylation under hypoxia

Cells cope with environmental changes through various mechanisms. Pathways involving HIF-1, SIRT1, and AMPK play major roles in energy homeostasis under stress conditions. Diacylglycerol kinase (DGK) constitutes an enzyme family that catalyzes conversion of diacylglycerol to phosphatidic acid. We reported earlier that energy depletion such as ischemia induces proteasomal degradation of DGKζ before cell death, suggesting involvement of DGKζ in energy homeostasis. This study examines how DGKζ depletion affects the regulation of HIF-1α, SIRT1, and AMPKα. Under hypoxia DGKζ depletion attenuates HIF-1α induction and SIRT1 expression, which might render cells vulnerable to energy stress. However, DGKζ depletion engenders enhanced AMPKα phosphorylation by upstream kinase TAK1 and an increase in intracellular ATP levels. Results suggest that DGKζ exerts a suppressive effect on TAK1 activity in the AMPK activation mechanism, and that DGKζ depletion might engender dysregulation of the AMPK-mediated energy sensor system.

DGKZ Acts as a Potential Oncogene in Osteosarcoma Proliferation Through Its Possible Interaction With ERK1/2 and MYC Pathway

Osteosarcoma (OS) is one of the most common primary bone tumors in children and young adults. The majority of osteosarcoma patients have limited alternative therapeutic options and metastatic patients generally have a poor prognosis. Thus, it is important to explore novel effective therapeutic targets in the treatment of osteosarcoma. Diacylglycerol kinase zeta (DGKZ) is a recently identified gene potentially associated with certain human carcinogenesis. However, the role of DGKZ in proliferation of osteosarcoma is still unclear. In this study, DGKZ's expression was firstly investigated in OS tumor samples and correlated with poor outcome in OS patients. Silence of DGKZ by shRNA hampered osteosarcoma cell growth and promoted cell apoptosis in vitro. In vivo, DGKZ's knockout also suppressed xenograft tumor proliferation as determined by bioluminescence imaging and weight/volume measurements. Meanwhile, Affymetrix GeneChip and Ingenuity Pathway Analysis (IPA) revealed that DGKZ knockdown resulted in a decreased activity of MYC pathway, and several target genes expression in MYC pathway were altered, including CCND1, CDKN2B, CDK6, PCNA, and EGR1. Furthermore, immunoprecipitation coupled with mass spectrometry (IP-MS) analysis was used to identify proteins that interacted with DGKZ in OS cells and revealed ERK1/2, a key MYC-interactor, to associate with DGKZ. Together, our study demonstrated that DGKZ might act as an oncogene in osteosarcoma via its possible interaction with ERK1/2 and MYC pathway.

Nuclear Lipids in the Nervous System: What they do in Health and Disease

In the last 20 years it has been widely demonstrated that cell nucleus contains neutral and polar lipids localized in nuclear membranes, nucleoli, nuclear matrix and chromatin. Nuclear lipids may show specific organization forming nuclear lipid microdomains and have both structural and functional roles. Depending on their localization, nuclear lipids play different roles such as the regulation of nuclear membrane and nuclear matrix fluidity but they also can act as platforms for vitamin and hormone function, for active chromatin anchoring, and for the regulation of gene expression, DNA duplication and transcription. Crosstalk among different kinds of lipid signalling pathways influence the physiopathology of numerous cell types. In neural cells the nuclear lipids are involved in cell proliferation, differentiation, inflammation, migration and apoptosis. Abnormal metabolism of nuclear lipids might be closely associated with tumorigenesis and neurodegenerative diseases such as Alzheimer disease and Parkinson disease among others.

A novel diacylglycerol kinase α-selective inhibitor, CU-3, induces cancer cell apoptosis and enhances immune response

Diacylglycerol kinase (DGK) consists of 10 isozymes. The α-isozyme enhances the proliferation of cancer cells. However, DGKα facilitates the nonresponsive state of immunity known as T-cell anergy; therefore, DGKα enhances malignant traits and suppresses immune surveillance. The aim of this study was to identify a novel small molecule that selectively and potently inhibits DGKα activity. We screened a library containing 9,600 chemical compounds using a newly established high-throughput DGK assay. As a result, we have obtained a promising compound, 5-[(2E)-3-(2-furyl)prop-2-enylidene]-3-[(phenylsulfonyl)amino]2-thioxo-1,3-thiazolidin-4-one) (CU-3), which selectively inhibited DGKα with an IC50 value of 0.6 μM. CU-3 targeted the catalytic region, but not the regulatory region, of DGKα. CU-3 competitively reduced the affinity of DGKα for ATP, but not diacylglycerol or phosphatidylserine. Moreover, this compound induced apoptosis in HepG2 hepatocellular carcinoma and HeLa cervical cancer cells while simultaneously enhancing the interleukin-2 production of Jurkat T cells. Taken together, these results indicate that CU-3 is a selective and potent inhibitor for DGKα and can be an ideal anticancer drug candidate that attenuates cancer cell proliferation and simultaneously enhances immune responses including anticancer immunity.

Reciprocal regulation of p53 and NF-κB by diacylglycerol kinase ζ

Diacylglycerol kinase (DGK) participates in lipid mediated-signal transduction. It phosphorylates diacylglycerol (DG) to phosphatidic acid (PA), thereby regulating the balanced control of these second messenger actions. Previous reports have described that one DGK family, DGKζ, is closely involved in stress responses under various conditions. Cellular stress response, a physiological process enabling cells to cope with an altered environment, is finely tuned through various signaling cascades and their molecular crosstalk. The major components of stress response are p53 and NF-κB. p53 generally serves as a proapoptotic transcriptional factor, whereas NF-κB promotes resistance to programmed cell death under most circumstances. Recent studies have suggested that DGKζ facilitates p53 degradation in cytoplasm through ubiquitin proteasome system and that DGKζ deletion upregulates p53 protein levels under basal and DNA-damage conditions. Counter-intuitively, however, DGKζ deletion suppresses p53 transcriptional activity despite increased p53 levels. In contrast, DGKζ knockdown engenders enhancement of NF-κB pathway in response to cytokines such as TNF-α and IL-1β. In response to these cytokines, DGKζ downregulation accelerates phosphorylation of the p65 subunit and its nuclear translocation, thereby enhancing NF-κB transcriptional activity. Furthermore, DGKζ deficiency is shown to promote increased association of p65 subunit with the transcriptional cofactor CBP. It is particularly interesting that this association is observed even under basal conditions in the absence of stimulation. These findings suggest that DGKζ plays a role in sequestration of the limiting pool of CBP/p300 between the NF-κB p65 subunit and p53, and that DGKζ downregulation shifts CBP/p300 toward the NF-κB subunit to regulate reciprocally antagonistic phenotypes of these transcription factors.

Roles of lipid-modulating enzymes diacylglycerol kinase and cyclooxygenase under pathophysiological conditions

Lipid not only represents a constituent of the plasma membrane, but also plays a pivotal role in intracellular signaling. Lipid-mediated signaling system is strictly regulated by several enzymes, which act at various steps of the lipid metabolism. Under pathological conditions, prolonged or insufficient activation of this system results in dysregulated signaling, leading to diseases such as cancer or metabolic syndrome. Of the lipid-modulating enzymes, diacylglycerol kinase (DGK) and cyclooxygenase (COX) are intimately involved in the signaling system. DGK consists of a family of enzymes that phosphorylate a second messenger diacylglycerol (DG) to produce phosphatidic acid (PA). Both DG and PA are known to activate signaling molecules such as protein kinase C. COX catalyzes the committed step in prostanoid biosynthesis, which involves the metabolism of arachidonic acid to produce prostaglandins. Previous studies have shown that the DGK and COX are engaged in a number of pathological conditions. This review summarizes the functional implications of these two enzymes in ischemia, liver regeneration, vascular events, diabetes, cancer and inflammation.

DGKζ under stress conditions: “to be nuclear or cytoplasmic, that is the question”

Eukaryotic cells have evolved to possess a distinct subcellular compartment, the nucleus, separated from the cytoplasm in a manner that allows the precise operation of the chromatin, thereby permitting controlled access to the regulatory elements in the DNA for transcription and replication. In the cytoplasm, genetic information contained in the DNA sequence is translated into proteins, including enzymes that catalyze various reactions, such as metabolic processes, energy control, and responses to changing environments. One mechanism that regulates these events involves phosphoinositide turnover signaling, which generates a lipid second messenger, diacylglycerol (DG). Since DG acts as a potent activator of several signaling molecules, it should be tightly regulated to keep cellular responsiveness within a physiological range. DG kinase (DGK) metabolizes DG by phosphorylating it to generate phosphatidic acid, thus serving as a critical regulator of DG signaling. Phosphoinositide turnover is employed differentially in the nucleus and the cytoplasm. A member of the DGK family, DGKζ, localizes to the nucleus in various cell types and is considered to regulate nuclear DG signaling. Recent studies have provided evidence that DGKζ shuttles between the nucleus and the cytoplasm in neurons under pathophysiological conditions. Transport of a signal regulator between the nucleus and the cytoplasm should be a critical function for maintaining basic processes in the nucleus, such as cell cycle regulation and gene expression, and to ensure communication between nuclear processes and cytoplasmic functions. In this review, a series of studies on nucleocytoplasmic translocation of DGKζ have been summarized, and the functional implications of this phenomenon in postmitotic neurons and cancer cells under stress conditions are discussed.

Signaling cascade of diacylglycerol kinase β in the pituitary intermediate lobe: dopamine D2 receptor/phospholipase Cβ4/diacylglycerol kinase β/protein kinase Cα

The pituitary gland dynamically changes its hormone output under various pathophysiological conditions. One of the pathways implicated in the regulatory mechanism of this gland is a dopaminergic system that operates the phosphoinositide (PI) cycle to transmit downstream signal through second messengers. We have previously shown that diacylglycerol kinase β (DGKβ) is coexpressed with dopamine D1 and D2 receptors in medium spiny neurons of the striatum, suggesting a plausible implication of DGKβ in dopaminergic transmission. However, it remains elusive whether DGKβ is involved in the dopaminergic system in the pituitary gland. The aim of this study is to investigate the expression and localization of DGK in the pituitary gland, together with the molecular components involved in the PI signaling cascade, including dopamine receptors, phospholipase C (PLC), and a major downstream molecule, protein kinase C (PKC). Here we show that DGKβ and the dopamine D2 receptor are coexpressed in the intermediate lobe and localize to the plasma membrane side by side. In addition, we reveal that PLCβ4 and PKCα are the subtypes expressed in the intermediate lobe among those families. These findings will substantiate and further extend our understanding of the molecular-anatomical pathway of PI signaling and the functional roles of DGK in the pituitary intermediate lobe.

Global changes in phospholipids identified by MALDI MS in rats with focal cerebral ischemia

Neuronal membrane phospholipids are highly affected by oxidative stress caused by ischemic injury. Thus, it is necessary to identify key lipid components that show changes during ischemia to develop an effective approach to prevent brain damage from ischemic injury. The recent development of MALDI imaging MS (MALDI IMS) makes it possible to identify phospholipids that change between damaged and normal regions directly from tissues. In this study, we conducted IMS on rat brains damaged by ischemic injury and detected various phospholipids that showed unique distributions between normal and damaged areas of the brain. Among them, we confirmed changes in phospholipids such as lysophosphatidylcholine, phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin by MALDI IMS followed by MS/MS analysis. These lipids were present in high concentrations in the brain and are important for maintenance of cellular structure as well as production of second messengers for cellular signal transduction. Our results emphasize the identification of phospholipid markers for ischemic injury and successfully identified several distinctly located phospholipids in ischemic brain tissue.

Altered expression of diacylglycerol kinase isozymes in regenerating liver

The liver possesses the capacity to restore its function and mass after injury. Liver regeneration is controlled through complicated mechanisms, in which the phosphoinositide (PI) cycle is shown to be activated in hepatocytes. Using a rat partial hepatectomy (PH) model, the authors investigated the expression of the diacylglycerol kinase (DGK) family, a key enzyme in the PI cycle, which metabolizes a lipid second-messenger diacylglycerol (DG). RT-PCR analysis shows that DGKζ and DGKα are the major isozymes in the liver. Results showed that in the process of regeneration, the DGKζ protein, which is detected in the nucleus of a small population of hepatocytes in normal liver, is significantly increased in almost all hepatocytes. However, the mRNA levels remain largely unchanged. Double labeling with bromodeoxyuridine (BrdU), an S phase marker, reveals that DGKζ is expressed independently of DNA synthesis or cell proliferation. However, DGKα protein localizes to the cytoplasm in normal and regenerating livers, but immunoblot analysis reveals that the expected (80 kDa) and the lower (70 kDa) bands are detected in normal liver, whereas at day 10 after PH, the expected band is solely recognized, showing a different processing pattern of DGKα in liver regeneration. These results suggest that DGKζ and DGKα are involved, respectively, in the nucleus and the cytoplasm of hepatocytes in regenerating liver.

Regulation and roles of neuronal diacylglycerol kinases: a lipid perspective

Diacylglycerol kinases (DGKs) are a class of enzymes that catalyze the ATP-dependent conversion of diacylglycerol (DAG) to phosphatidic acid (PtdOH), resulting in the coordinate regulation of these two lipid second messengers. This regulation is particularly important in the nervous system where it is now well-established that DAG and PtdOH serve very important roles in modulating a variety of neurological functions. There are currently 10 identified mammalian DGKs, organized into five classes or "Types" based upon similarities in their primary sequences. A number of studies have identified eight of these isoforms in various regions of the mammalian central nervous system (CNS): DGK-α, DGK-β, DGK-γ, DGK-η, DGK-ζ, DGK-ι, DGK-ϵ, and DGK-θ. Further studies have provided compelling evidence supporting roles for these enzymes in neuronal spine density, myelination, synaptic activity, neuronal plasticity, epileptogenesis and neurotransmitter release. The physiological regulation of these enzymes is less clear. Like all interfacial enzymes, DGKs metabolize their hydrophobic substrate (DAG) at a membrane-aqueous interface. Therefore, these enzymes can be regulated by alterations in their subcellular localization, enzymatic activity, and/or membrane association. In this review, we summarize what is currently understood about the localization and regulation of the neuronal DGKs in the mammalian CNS.

TNFRSF11B computational development network construction and analysis between frontal cortex of HIV encephalitis (HIVE) and HIVE-control patients

BACKGROUND

TNFRSF11B computational development network construction and analysis of frontal cortex of HIV encephalitis (HIVE) is very useful to identify novel markers and potential targets for prognosis and therapy.

METHODS

By integration of gene regulatory network infer (GRNInfer) and the database for annotation, visualization and integrated discovery (DAVID) we identified and constructed significant molecule TNFRSF11B development network from 12 frontal cortex of HIVE-control patients and 16 HIVE in the same GEO Dataset GDS1726.

RESULTS

Our result verified TNFRSF11B developmental process only in the downstream of frontal cortex of HIVE-control patients (BST2, DGKG, GAS1, PDCD4, TGFBR3, VEZF1 inhibition), whereas in the upstream of frontal cortex of HIVE (DGKG, PDCD4 activation) and downstream (CFDP1, DGKG, GAS1, PAX6 activation; BST2, PDCD4, TGFBR3, VEZF1 inhibition). Importantly, we datamined that TNFRSF11B development cluster of HIVE is involved in T-cell mediated immunity, cell projection organization and cell motion (only in HIVE terms) without apoptosis, plasma membrane and kinase activity (only in HIVE-control patients terms), the condition is vital to inflammation, brain morphology and cognition impairment of HIVE. Our result demonstrated that common terms in both HIVE-control patients and HIVE include developmental process, signal transduction, negative regulation of cell proliferation, RNA-binding, zinc-finger, cell development, positive regulation of biological process and cell differentiation.

CONCLUSIONS

We deduced the stronger TNFRSF11B development network in HIVE consistent with our number computation. It would be necessary of the stronger TNFRSF11B development function to inflammation, brain morphology and cognition of HIVE.

Diacylglycerol kinase zeta is associated with chromatin, but dissociates from condensed chromatin during mitotic phase in NIH3T3 cells

Diacylglycerol kinase (DGK) converts diacylglycerol (DG) to phosphatidic acid, both of which act as second messengers to mediate a variety of cellular mechanisms. Therefore, DGK contributes to the regulation of these messengers in cellular signal transduction. Of DGK isozymes cloned, DGKzeta is characterized by a nuclear localization signal that overlaps with a sequence similar to the myristoylated alanine-rich C-kinase substrate. Previous studies showed that nuclear DG is differentially regulated from plasma membrane DG and that the nuclear DG levels fluctuate in correlation with cell cycle progression, suggesting the importance of nuclear DG in cell cycle control. In this connection, DGKzeta has been shown to localize to the nucleus in fully differentiated cells, such as neurons and lung cells, although it remains elusive how DGK behaves during the cell cycle in proliferating cells. Here we demonstrate that DGKzeta localizes to the nucleus during interphase including G1, S, and G2 phases and is associated with chromatin although it dissociates from condensed chromatin during mitotic phase in NIH3T3 cells. Furthermore, this localization pattern is also observed in proliferating spermatogonia in the testis. These results suggest a reversible association of DGKzeta with histone or its related proteins in cell cycle, plausibly dependent on their post-translational modifications.

Diacylglycerol kinases: at the hub of cell signalling

DGKs (diacylglycerol kinases) are members of a unique and conserved family of intracellular lipid kinases that phosphorylate DAG (diacylglycerol), catalysing its conversion into PA (phosphatidic acid). This reaction leads to attenuation of DAG levels in the cell membrane, regulating a host of intracellular signalling proteins that have evolved the ability to bind this lipid. The product of the DGK reaction, PA, is also linked to the regulation of diverse functions, including cell growth, membrane trafficking, differentiation and migration. In multicellular eukaryotes, DGKs provide a link between lipid metabolism and signalling. Genetic experiments in Caenorhabditis elegans, Drosophila melanogaster and mice have started to unveil the role of members of this protein family as modulators of receptor-dependent responses in processes such as synaptic transmission and photoreceptor transduction, as well as acquired and innate immune responses. Recent discoveries provide new insights into the complex mechanisms controlling DGK activation and their participation in receptor-regulated processes. After more than 50 years of intense research, the DGK pathway emerges as a key player in the regulation of cell responses, offering new possibilities of therapeutic intervention in human pathologies, including cancer, heart disease, diabetes, brain afflictions and immune dysfunctions.