The sevenfold way of PKC regulation

Retracted: PKC-delta and PKD activate MAPK signal pathway in mechano-transcription of colonic smooth muscle cells

Retraction: [PKC-delta and PKD activate MAPK signal pathway in mechano-transcription of colonic smooth muscle cells, Z. Yang, K. He, T. Wang, et al. Neurogastroenterology & Motility 2023; e14623 (https://onlinelibrary.wiley.com/doi/full/10.1111/nmo.14623)]. The above article, published online on June 6, 2023 in Wiley Online Library (wileyonlinelibrary.com), has been retracted by agreement between the authors, the Journal Editor in Chief, Maura Corsetti, and John Wiley & Sons Ltd. The retraction has been agreed due to unat[1]tributed overlap between this article and the abstract published in Gastroenterology: Li F, Sarna SK and Shi XP. Roles of PKCs and PKD in Mechanotranscription in Colonic Smooth Muscle Cells: Inhibition of Mechanotranscription as a Potential Treatment for Motility Dysfunction in Obstructive Disorders. In: 2012 Digestive Disease Week Abstract Supplement; May 19-22, San Diego, CA. Abstract 120 (https://www.gastrojournal.org/article/S0016-5085(12)60115-2/pdf).

α-Hederin induces paraptosis by targeting GPCRs to activate Ca2+/MAPK signaling pathway in colorectal cancer

BACKGROUND

Non-apoptotic cell death is presently emerging as a potential direction to overcome the apoptosis resistance of cancer cells. In the current study, a natural plant agent α-hederin (α-hed) induces caspase-independent paraptotic modes of cell death.

PURPOSE

The present study is aimed to investigate the role of α-hed induces paraptosis and the associated mechanism of it.

METHODS

The cell proliferation was detected by CCK-8. The cytoplasm organelles were observed under electron microscope. Calcium (Ca2+) level was detected by flow cytometry. Swiss Target Prediction tool analyzed the potential molecule targets of α-hed. Molecular docking methods were used to evaluate binding abilities of α-hed with targets. The expressions of genes and proteins were analyzed by RT-qPCR, western blotting, immunofluorescence, and immunohistochemistry. Xenograft models in nude mice were established to evaluate the anticancer effects in vivo.

RESULTS

α-hed exerted significant cytotoxicity against a panel of CRC cell lines by inhibiting proliferation. Besides, it induced cytoplasmic vacuolation in all CRC cells. Electron microscopy images showed the aberrant dilation of endoplasmic reticulum and mitochondria. Both mRNA and protein expressions of Alg-2 interacting proteinX (Alix), the marker of paraptosis, were inhibited by α-hed. Besides, both Swiss prediction and molecular docking showed that the structure of α-hed could tightly target to GPCRs. GPCRs were reported to activate the phospholipase C (PLC)-β3/ inositol 1,4,5-trisphosphate receptor (IP3R)/ Ca2+/ protein kinase C alpha (PKCα) pathway, and we then found all proteins and mRNA expressions of PLCβ3, IP3R, and PKCα were increased by α-hed. After blocking the GPCR signaling, α-hed could not elevate Ca2+ level and showed less CRC cell cytotoxicity. MAPK cascade is the symbol of paraptosis, and we then demonstrated that α-hed activated MAPK cascade by elevating Ca2+ flux. Since non-apoptotic cell death is presently emerging as a potential direction to overcome chemo-drug resistance, we then found α-hed also induced paraptosis in 5-fluorouracil-resistant (5-FU-R) CRC cells, and it reduced the growth of 5-FU-R CRC xenografts.

CONCLUSIONS

Collectively, our findings proved α-hed as a promising candidate for inducing non-apoptotic cell death, paraptosis. It may overcome the resistance of apoptotic-based chemo-resistance in CRC.

Bruton tyrosine kinase inhibitors for multiple sclerosis

Current therapies for multiple sclerosis (MS) reduce both relapses and relapse-associated worsening of disability, which is assumed to be mainly associated with transient infiltration of peripheral immune cells into the central nervous system (CNS). However, approved therapies are less effective at slowing disability accumulation in patients with MS, in part owing to their lack of relevant effects on CNS-compartmentalized inflammation, which has been proposed to drive disability. Bruton tyrosine kinase (BTK) is an intracellular signalling molecule involved in the regulation of maturation, survival, migration and activation of B cells and microglia. As CNS-compartmentalized B cells and microglia are considered central to the immunopathogenesis of progressive MS, treatment with CNS-penetrant BTK inhibitors might curtail disease progression by targeting immune cells on both sides of the blood-brain barrier. Five BTK inhibitors that differ in selectivity, strength of inhibition, binding mechanisms and ability to modulate immune cells within the CNS are currently under investigation in clinical trials as a treatment for MS. This Review describes the role of BTK in various immune cells implicated in MS, provides an overview of preclinical data on BTK inhibitors and discusses the (largely preliminary) data from clinical trials.

Repair of traumatic lesions to the plasmalemma of neurons and other cells: Commonalities, conflicts, and controversies

Neuroscientists and Cell Biologists have known for many decades that eukaryotic cells, including neurons, are surrounded by a plasmalemma/axolemma consisting of a phospholipid bilayer that regulates trans-membrane diffusion of ions (including calcium) and other substances. Cells often incur plasmalemmal damage via traumatic injury and various diseases. If the damaged plasmalemma is not rapidly repaired within minutes, activation of apoptotic pathways by calcium influx often results in cell death. We review publications reporting what is less-well known (and not yet covered in neuroscience or cell biology textbooks): that calcium influx at the lesion sites ranging from small nm-sized holes to complete axonal transection activates parallel biochemical pathways that induce vesicles/membrane-bound structures to migrate and interact to restore original barrier properties and eventual reestablishment of the plasmalemma. We assess the reliability of, and problems with, various measures (e.g., membrane voltage, input resistance, current flow, tracer dyes, confocal microscopy, transmission and scanning electron microscopy) used individually and in combination to assess plasmalemmal sealing in various cell types (e.g., invertebrate giant axons, oocytes, hippocampal and other mammalian neurons). We identify controversies such as plug versus patch hypotheses that attempt to account for currently available data on the subcellular mechanisms of plasmalemmal repair/sealing. We describe current research gaps and potential future developments, such as much more extensive correlations of biochemical/biophysical measures with sub-cellular micromorphology. We compare and contrast naturally occurring sealing with recently-discovered artificially-induced plasmalemmal sealing by polyethylene glycol (PEG) that bypasses all natural pathways for membrane repair. We assess other recent developments such as adaptive membrane responses in neighboring cells following injury to an adjacent cell. Finally, we speculate how a better understanding of the mechanisms involved in natural and artificial plasmalemmal sealing is needed to develop better clinical treatments for muscular dystrophies, stroke and other ischemic conditions, and various cancers.

The Mechanism of Hyperglycemia-Induced Renal Cell Injury in Diabetic Nephropathy Disease: An Update

Diabetic Nephropathy (DN) is a serious complication of type I and II diabetes. It develops from the initial microproteinuria to end-stage renal failure. The main initiator for DN is chronic hyperglycemia. Hyperglycemia (HG) can stimulate the resident and non-resident renal cells to produce humoral mediators and cytokines that can lead to functional and phenotypic changes in renal cells and tissues, interference with cell growth, interacting proteins, advanced glycation end products (AGEs), etc., ultimately resulting in glomerular and tubular damage and the onset of kidney disease. Therefore, poor blood glucose control is a particularly important risk factor for the development of DN. In this paper, the types and mechanisms of DN cell damage are classified and summarized by reviewing the related literature concerning the effect of hyperglycemia on the development of DN. At the cellular level, we summarize the mechanisms and effects of renal damage by hyperglycemia. This is expected to provide therapeutic ideas and inspiration for further studies on the treatment of patients with DN.

Activation of PKCβII through nuclear trafficking guided by βγ subunits of trimeric G protein and 14-3-3ε

AIMS

Conventional members of protein kinase C (PKC) family, including PKCβII, are constitutively phosphorylated on three major motifs and located in the cytosol in a primed state. In response to cellular stimuli, PKCβII is activated through inducible phosphorylation and Mdm2-mediated ubiquitination. In this study, we aimed to identify the activation mechanism of PKCβII, focusing on the signaling cascade that regulate the phosphorylation and ubiquitination.

MATERIALS AND METHODS

Loss-of-function approaches and mutants of PDK1/PKCβII that display different regulatory properties were used to identify the cellular components and processes responsible for endocytosis.

KEY FINDINGS

Phorbol 12-myristate 13-acetate (PMA)-induced phosphorylation and ubiquitination of PKCβII, which are needed for its translocation to the plasma membrane, required the presence of both Gβγ and 14-3-3ε. Gβγ and 14-3-3ε mediated the constitutive phosphorylation of PKCβII by scaffolding PI3K and PDK1 in the cytosol, which is an inactive but required state for the activation of PKCβII by subsequent signals. In response to PMA treatment, the signaling complex translocated to the nucleus with dissociation of PI3K from it. Thereafter, PDK1 stably interacted with 14-3-3ε and was dephosphorylated; PKCβII interacted with Mdm2 along with Gβγ, leading to its ubiquitination at two lysine residues on its C-tail. Finally, PDK1/14-3-3ε and ubiquitinated PKCβII translocated to the plasma membrane.

SIGNIFICANCE

As PKCβII mediates a wide range of cellular functions and plays important roles in the pathogenesis of various diseases, our results will provide clues to understand the pathogenesis of PKCβII-related disorders and facilitate their treatment.

Trypanosoma cruzi DNA Polymerase β Is Phosphorylated In Vivo and In Vitro by Protein Kinase C (PKC) and Casein Kinase 2 (CK2)

DNA polymerase β plays a fundamental role in the life cycle of Trypanosoma cruzi since it participates in the kinetoplast DNA repair and replication. This enzyme can be found in two forms in cell extracts of T. cruzi epimastigotes form. The H form is a phosphorylated form of DNA polymerase β, while the L form is not phosphorylated. The protein kinases which are able to in vivo phosphorylate DNA polymerase β have not been identified yet. In this work, we purified the H form of this DNA polymerase and identified the phosphorylation sites. DNA polymerase β is in vivo phosphorylated at several amino acid residues including Tyr35, Thr123, Thr137 and Ser286. Thr123 is phosphorylated by casein kinase 2 and Thr137 and Ser286 are phosphorylated by protein kinase C-like enzymes. Protein kinase C encoding genes were identified in T. cruzi, and those genes were cloned, expressed in bacteria and the recombinant protein was purified. It was found that T. cruzi possesses three different protein kinase C-like enzymes named TcPKC1, TcPKC2, and TcPKC3. Both TcPKC1 and TcPKC2 were able to in vitro phosphorylate recombinant DNA polymerase β, and in addition, TcPKC1 gets auto phosphorylated. Those proteins contain several regulatory domains at the N-terminus, which are predicted to bind phosphoinositols, and TcPKC1 contains a lipocalin domain at the C-terminus that might be able to bind free fatty acids. Tyr35 is phosphorylated by an unidentified protein kinase and considering that the T. cruzi genome does not contain Tyr kinase encoding genes, it is probable that Tyr35 could be phosphorylated by a dual protein kinase. Wee1 is a eukaryotic dual protein kinase involved in cell cycle regulation. We identified a Wee1 homolog in T. cruzi and the recombinant kinase was assayed using DNA polymerase β as a substrate. T. cruzi Wee1 was able to in vitro phosphorylate recombinant DNA polymerase β, although we were not able to demonstrate specific phosphorylation on Tyr35. Those results indicate that there exists a cell signaling pathway involving PKC-like kinases in T. cruzi.

PKC isoforms activate LRRK1 kinase by phosphorylating conserved residues (Ser1064, Ser1074 and Thr1075) within the CORB GTPase domain

Leucine-rich-repeat-kinase 1 (LRRK1) and its homolog LRRK2 are multidomain kinases possessing a ROC-CORA-CORB containing GTPase domain and phosphorylate distinct Rab proteins. LRRK1 loss of function mutations cause the bone disorder osteosclerotic metaphyseal dysplasia, whereas LRRK2 missense mutations that enhance kinase activity cause Parkinson's disease. Previous work suggested that LRRK1 but not LRRK2, is activated via a Protein Kinase C (PKC)-dependent mechanism. Here we demonstrate that phosphorylation and activation of LRRK1 in HEK293 cells is blocked by PKC inhibitors including LXS-196 (Darovasertib), a compound that has entered clinical trials. We show multiple PKC isoforms phosphorylate and activate recombinant LRRK1 in a manner reversed by phosphatase treatment. PKCα unexpectedly does not activate LRRK1 by phosphorylating the kinase domain, but instead phosphorylates a cluster of conserved residues (Ser1064, Ser1074 and Thr1075) located within a region of the CORB domain of the GTPase domain. These residues are positioned at the equivalent region of the LRRK2 DK helix reported to stabilize the kinase domain αC-helix in the active conformation. Thr1075 represents an optimal PKC site phosphorylation motif and its mutation to Ala, blocked PKC-mediated activation of LRRK1. A triple Glu mutation of Ser1064/Ser1074/Thr1075 to mimic phosphorylation, enhanced LRRK1 kinase activity ∼3-fold. From analysis of available structures, we postulate that phosphorylation of Ser1064, Ser1074 and Thr1075 activates LRRK1 by promoting interaction and stabilization of the αC-helix on the kinase domain. This study provides new fundamental insights into the mechanism controlling LRRK1 activity and reveals a novel unexpected activation mechanism.

Synaptotagmin 1-mediated cell membrane penetration and dopamine release enhancement by latroeggtoxin-VI

Latroeggtoxin-VI (LETX-VI), a proteinaceous neurotoxin mined from the egg transcriptome of spider L. tredecimguttatus, was previously found to promote the release of dopamine from PC12 cells. However, the relevant molecular mechanism has not been fully clear. Here LETX-VI was demonstrated to rapidly penetrate the plasma membrane of PC12 cells via the vesicle exocytosis/endocytosis cycle, during which vesicular transmembrane protein synaptotagmin 1 (Syt1) functions as a receptor, with its vesicle luminal domain interacting with the C-terminal region of LETX-VI. The C-terminal sequence of LETX-VI is the functional region for both entering cells and promoting dopamine release. After gaining entry into the PC12 cells, LETX-VI down-regulated the phosphorylation levels of Syt1 at T201 and T195, thereby facilitating vesicle fusion with plasma membrane and thus promoting dopamine release. The relevant mechanism analysis indicated that LETX-VI has a protein phosphatase 2A (PP2A) activator activity. The present work has not only probed into the Syt1-mediated action mechanism of LETX-VI, but also revealed the structure-function relationship of the toxin, thus suggesting its potential applications in the drug transmembrane delivery and treatment of the diseases related to dopamine release and PP2A activity deficiency.

Development of Human Cell-Based In Vitro Infection Models to Determine the Intracellular Survival of Mycobacterium avium

The Mycobacterium avium (Mav) complex accounts for more than 80% of all pulmonary diseases caused by non-tuberculous mycobacteria (NTM) infections, which have an alarming increase in prevalence and vary in different regions, currently reaching 0.3–9.8 per 100,000 individuals. Poor clinical outcomes, as a result of increasing microbial drug resistance and low treatment adherence due to drug-toxicities, emphasize the need for more effective treatments. Identification of more effective treatments, however, appears to be difficult, which may be due to the intracellular life of NTM and concomitant altered drug sensitivity that is not taken into account using traditional drug susceptibility testing screenings. We therefore developed human cell-based in vitro Mav infection models using the human MelJuSo cell line as well as primary human macrophages and a fluorescently labeled Mav strain. By testing a range of multiplicity of infection (MOI) and using flow cytometry and colony-forming unit (CFU) analysis, we found that an MOI of 10 was the most suitable for Mav infection in primary human macrophages, whereas an MOI of 50 was required to achieve similar results in MelJuSo cells. Moreover, by monitoring intracellular bacterial loads over time, the macrophages were shown to be capable of controlling the infection, while MelJuSo cells failed to do so. When comparing the MGIT system with the classical CFU counting assay to determine intracellular bacterial loads, MGIT appeared as a less labor-intensive, more precise, and more objective alternative. Next, using our macrophage Mav infection models, the drug efficacy of the first-line drug rifampicin and the more recently discovered bedaquiline on intracellular bacteria was compared to the activity on extracellular bacteria. The efficacy of the antibiotics inhibiting bacterial growth was significantly lower against intracellular bacteria compared to extracellular bacteria. This finding emphasizes the crucial role of the host cell during infection and drug susceptibility and highlights the usefulness of the models. Taken together, the human cell-based Mav infection models are reliable tools to determine the intracellular loads of Mav, which will enable researchers to investigate host–pathogen interactions and to evaluate the efficacy of (host-directed) therapeutic strategies against Mav.

Components of apoptotic pathways modulate HIV-1 latency in Jurkat cells

The ability of the human immunodeficiency virus type 1 (HIV-1) to establish latent infections serves as a major barrier for its cure. This process could occur when its host cells undergo apoptosis, but it is uncertain whether the components of the apoptotic pathways affect viral latency. Using the susceptible Jurkat cell line, we investigated the relationship of apoptosis-associated components with HIV-1 DNA levels using the sensitive real-time PCR assay. Here, we found that the expression of proapoptotic proteins, including Fas ligand (FasL), FADD, and p53, significantly decreased HIV-1 viral DNA in cells. In contrast, the expression of antiapoptotic molecules, such as FLIP, Bcl2, and XIAP, increased the levels of viral DNA. Furthermore, promoting cellular antiapoptotic state via the knockdown of Bax with siRNA and FADD with antisense mRNA or the treatment with the Caspase-3 inhibitor, Z-DEVD, also raised viral DNA. We also simultaneously measured viral RNA from supernatants of these cell cultures and found that HIV-1 latency is inversely proportional to viral replication. Furthermore, we demonstrated that HIV-1-infected cells that underwent the transient expression of FLIP- or XIAP-induced viral latency would then produce an increased level of viral RNA upon the reversal of these antiapoptotic effects via PMA treatment compared to LacZ control cells. Taken together, these data suggest that HIV-1 infection could be adapted to employ or even manipulate the cellular apoptotic pathway to its advantage: when the host cell remains in a pro-apoptotic state, HIV-1 favors active replication, while when the host cell prefers an anti-apoptotic state, the virus establishes viral latency and promotes latent reservoir seeding in a way which would enhance viral replication and cytopathogenesis when the cellular conditions shift to encourage the productive infection phase.

IGFBP-1 hyperphosphorylation in response to nutrient deprivation is mediated by activation of protein kinase Cα (PKCα)

Fetal growth restriction (FGR) is associated with decreased nutrient availability and reduced insulin-line growth factor (IGF)-I bioavailability via increased IGF binding protein (IGFBP)-1 phosphorylation. While protein kinase C (PKC) is implicated in IGFBP-1 hyperphosphorylation in nutrient deprivation, the mechanisms remain unclear. We hypothesised that the interaction of PKCα with protein kinase CK2β and activation of PKCα under leucine deprivation (L0) mediate fetal hepatic IGFBP-1 hyperphosphorylation. Parallel Reaction Monitoring Mass Spectrometry (PRM-MS) followed by PKCα knockdown demonstrated the PKCα isoform interacts with IGFBP-1 and CK2β under L0. Pharmacological PKCα activation with phorbol 12-myristate 13-acetate (PMA) increased whereas inhibition with bisindolylmaleimide II (Bis II) decreased IGFBP-1 phosphorylation (Ser101/119/169, Ser98 + 101 and Ser169 + 174), respectively. Furthermore, PMA mimicked L0-induced PKCα translocation and IGFBP-1 expression. PKCα expression was increased in baboon fetal liver in FGR, providing biological relevance in vivo. In summary, we report a novel nutrient-sensitive mechanism for PKCα in mediating IGFBP-1 hyperphosphorylation in FGR.

Tumor-derived NKG2D ligand sMIC reprograms NK cells to an inflammatory phenotype through CBM signalosome activation

Natural Killer (NK) cell dysfunction is associated with poorer clinical outcome in cancer patients. What regulates NK cell dysfunction in tumor microenvironment is not well understood. Here, we demonstrate that the human tumor-derived NKG2D ligand soluble MIC (sMIC) reprograms NK cell to secrete pro-tumorigenic cytokines with diminished cytotoxicity and polyfunctional potential. Antibody clearing sMIC restores NK cell to a normal cytotoxic effector functional state. We discovered that sMIC selectively activates the CBM-signalosome inflammatory pathways in NK cells. Conversely, tumor cell membrane-bound MIC (mMIC) stimulates NK cell cytotoxicity through activating PLC2γ2/SLP-76/Vav1 pathway. Ultimately, antibody targeting sMIC effectuated the in vivo anti-tumor effect of adoptively transferred NK cells. Our findings uncover an unrecognized mechanism that could instruct NK cell to a dysfunctional state in response to cues in the tumor microenvironment. Our findings provide a rationale for co-targeting sMIC to enhance the efficacy of the ongoing NK cell-based cancer immunotherapy.

Coordinated regulation of immune contexture: crosstalk between STAT3 and immune cells during breast cancer progression

Recent insights into the molecular and cellular mechanisms underlying cancer development have revealed the tumor microenvironment (TME) immune cells to functionally affect the development and progression of breast cancer. However, insufficient evidence of TME immune modulators limit the clinical application of immunotherapy for advanced and metastatic breast cancers. Intercellular STAT3 activation of immune cells plays a central role in breast cancer TME immunosuppression and distant metastasis. Accumulating evidence suggests that targeting STAT3 and/or in combination with radiotherapy may enhance anti-cancer immune responses and rescue the systemic immunologic microenvironment in breast cancer. Indeed, apart from its oncogenic role in tumor cells, the functions of STAT3 in TME of breast cancer involve multiple types of immunosuppression and is associated with tumor cell metastasis. In this review, we summarize the available information on the functions of STAT3-related immune cells in TME of breast cancer, as well as the specific upstream and downstream targets. Additionally, we provide insights about the potential immunosuppression mechanisms of each type of evaluated immune cells. Video abstract.

Physiological role for GABAA receptor desensitization in the induction of long-term potentiation at inhibitory synapses

GABAA receptors (GABAARs) are pentameric ligand-gated ion channels distributed throughout the brain where they mediate synaptic and tonic inhibition. Following activation, these receptors undergo desensitization which involves entry into long-lived agonist-bound closed states. Although the kinetic effects of this state are recognised and its structural basis has been uncovered, the physiological impact of desensitization on inhibitory neurotransmission remains unknown. Here we describe an enduring form of long-term potentiation at inhibitory synapses that elevates synaptic current amplitude for 24 h following desensitization of GABAARs in response to agonist exposure or allosteric modulation. Using receptor mutants and allosteric modulators we demonstrate that desensitization of GABAARs facilitates their phosphorylation by PKC, which increases the number of receptors at inhibitory synapses. These observations provide a physiological relevance to the desensitized state of GABAARs, acting as a signal to regulate the efficacy of inhibitory synapses during prolonged periods of inhibitory neurotransmission.

Signalling Pathways Mediating the Effects of CD40-Activated CD40L Reverse Signalling on Inhibitory Medium Spiny Neuron Neurite Growth

CD40-activated CD40L-mediated reverse signalling is a major physiological regulator of neurite growth from excitatory and inhibitory neurons in the developing central nervous system (CNS). Whereas in excitatory pyramidal neurons, CD40L reverse signalling promotes the growth and elaboration of dendrites and axons, in inhibitory GABAergic striatal medium spiny neurons (MSNs), it restricts neurite growth and branching. In pyramidal neurons, we previously reported that CD40L reverse signalling activates an interconnected and interdependent signalling network involving protein kinase C (PKC), extracellular regulated kinases 1 and 2 (ERK1/2), and c-Jun N-terminal kinase (JNK) signalling pathways that regulates dendrite and axon growth. Here, we have studied whether these signalling pathways also influence neurite growth from striatal inhibitory MSNs. To unequivocally activate CD40L reverse signalling, we treated MSN cultures from CD40-deficient mice with CD40-Fc. Here, we report that activation of CD40L reverse signalling in these cultures also increased the phosphorylation of PKC, ERK1/2, and JNK. Using pharmacological activators and inhibitors of these signalling pathways singularly and in combination, we have shown that, as in pyramidal neurons, these signalling pathways work in an interconnected and interdependent network to regulate the neurite growth, but their functions, relationships, and interdependencies are different from those observed in pyramidal neurons. Furthermore, immunoprecipitation studies showed that stimulation of CD40L reverse signalling recruits the catalytic fragment of Syk tyrosine kinase, but in contrast to pyramidal neurons, PKC does not participate in this recruitment. Our findings show that distinctive networks of three signalling pathways mediate the opposite effects of CD40L reverse signalling on neurite growth in excitatory and inhibitory neurons.

The function of SUMOylation and its crucial roles in the development of neurological diseases

Neurological diseases are relatively complex diseases of a large system; however, the detailed mechanism of their pathogenesis has not been completely elucidated, and effective treatment methods are still lacking for some of the diseases. The SUMO (small ubiquitin-like modifier) modification is a dynamic and reversible process that is catalyzed by SUMO-specific E1, E2, and E3 ligases and reversed by a family of SENPs (SUMO/Sentrin-specific proteases). SUMOylation covalently conjugates numerous cellular proteins, and affects their cellular localization and biological activity in numerous cellular processes. A wide range of neuronal proteins have been identified as SUMO substrates, and the disruption of SUMOylation results in defects in synaptic plasticity, neuronal excitability, and neuronal stress responses. SUMOylation disorders cause many neurodegenerative diseases, such as Parkinson's disease, Alzheimer's disease, and Huntington's disease. By modulating the ion channel subunit, SUMOylation imbalance is responsible for the development of various channelopathies. The regulation of protein SUMOylation in neurons may provide a new strategy for the development of targeted therapeutic drugs for neurodegenerative diseases and channelopathies.

Tectoridin inhibits the progression of colon cancer through downregulating PKC/p38 MAPK pathway

Colon cancer is one of the most familiar malignancies worldwide, with high morbidity and high mortality. This study intended to explore the role and mechanism of tectoridin (TEC) in regulating the progression of colon cancer. First, colon cancer cell lines (HCT116 and SW480 cells) were treated with different doses of TEC (0-200 μM). Then, CCK8 and clone formation experiments were performed to detect cell proliferation. Flow cytometry and western blot were conducted to examine apoptosis. Subsequently, Transwell assay and wound-healing test was employed to determine the effect of TEC on colon cancer cell invasion and migration. Next, western blot was performed to monitor the PKC/p38 MAPK pathway activation. In addition, a tumor model was established in nude mice to explore the effect of TEC on tumor growth in vivo. TEC dose-dependently dampened the proliferation, migration and invasion of colon cancer cells and facilitated their apoptosis. In addition, TEC abated the tumor cell growth in vivo. Besides, TEC dose-dependently suppressed the expression of PKC and p38 MAPK. Moreover, inhibiting the PKC pathway almost cancel out the anti-tumor effects induced by TEC. TEC attenuates the colon cancer progression by inhibiting the PKC/p38 MAPK pathway.

lncRNA-Xist/miR-101-3p/KLF6/C/EBPα axis promotes TAM polarization to regulate cancer cell proliferation and migration

The phenotypic switch in tumor-associated macrophages (TAMs) mediates immunity escape of cancer. However, the underlying mechanisms in the TAM phenotypic switch have not been systematically elucidated. In this study, long noncoding RNA (lncRNA)-Xist, CCAAT/enhancer-binding protein (C/EBP)α, and Kruppel-like factor 6 (KLF6) were upregulated, whereas microRNA (miR)-101 was downregulated in M1 macrophages-type (M1). Knockdown of Xist or overexpression of miR-101 in M1 could induce M1-to-M2 macrophage-type (M2) conversion to promote cell proliferation and migration of breast and ovarian cancer by inhibiting C/EBPα and KLF6 expression. Furthermore, miR-101 could combine with both Xist and C/EBPα and KLF6 through the same microRNA response element (MRE) predicted by bioinformatics and verified by luciferase reporter assays. Moreover, we found that miR-101 knockdown restored the decreased M1 marker and the increased M2 marker expression and also reversed the promotion of proliferation and migration of human breast cancer cells (MCF-7) and human ovarian cancer (OV) cells caused by silencing Xist. Generally, the present study indicates that Xist could mediate macrophage polarization to affect cell proliferation and migration of breast and ovarian cancer by competing with miR-101 to regulate C/EBPα and KLF6 expression. The promotion of Xist expression in M1 macrophages and inhibition of miR-101 expression in M2 macrophages might play an important role in inhibiting breast and ovarian tumor proliferation and migration abilities.

Protein Kinase C Regulates ASIC1a Protein Expression and Channel Function via NF-kB Signaling Pathway

Tissue acidosis is a common feature in many pathological conditions. Activation of acid-sensing ion channel 1a (ASIC1a) plays a key role in acidosis-mediated neurotoxicity. Protein kinase C (PKC) activity has been proved to be associated with many physiological processes and pathological conditions; however, whether PKC activation regulates ASIC1a protein expression and channel function remains ill defined. In this study, we demonstrated that treatment with phorbol 12-myristate 13-acetate (PMA, a PKC activator) for 6 h significantly increased ASIC1a protein expression and ASIC currents in NS20Y cells, a neuronal cell line, and in primary cultured mouse cortical neurons. In contrast, treatment with Calphostin C (a nonselective PKC inhibitor) for 6 h or longer decreased ASIC1a protein expression and ASIC currents. Similar to Calphostin C, PKC α and βI inhibitor Go6976 exposure also reduced ASIC1a protein expression. The reduction in ASIC1a protein expression by PKC inhibition involves a change in ASIC1a protein degradation, which is mediated by ubiquitin-proteasome system (UPS)-dependent degradation pathway. In addition, we showed that PKC regulation of ASIC1a protein expression involves NF-κB signaling pathway. Consistent with their effects on ASIC1a protein expression and channel function, PKC inhibition protected NS20Y cells against acidosis-induced cytotoxicity, while PKC activation potentiated acidosis-induced cells injury. Together, these results indicate that ASIC1a protein expression and channel function are closely regulated by the activity of protein kinase C and its downstream signaling pathway(s).

How CD40L reverse signaling regulates axon and dendrite growth

CD40-activated CD40L reverse signaling is a major physiological regulator of axon and dendrite growth from developing hippocampal pyramidal neurons. Here we have studied how CD40L-mediated reverse signaling promotes the growth of these processes. Cultures of hippocampal pyramidal neurons were established from Cd40^-/- mouse embryos to eliminate endogenous CD40/CD40L signaling, and CD40L reverse signaling was stimulated by a CD40-Fc chimera. CD40L reverse signaling increased phosphorylation and hence activation of proteins in the PKC, ERK, and JNK signaling pathways. Pharmacological activators and inhibitors of these pathways revealed that whereas activation of JNK inhibited growth, activation of PKC and ERK1/ERK2 enhanced growth. Experiments using combinations of pharmacological reagents revealed that these signaling pathways regulate growth by functioning as an interconnected and interdependent network rather than acting in a simple linear sequence. Immunoprecipitation studies suggested that stimulation of CD40L reverse signaling generated a receptor complex comprising CD40L, PKCβ, and the Syk tyrosine kinase. Our studies have begun to elucidate the molecular network and interactions that promote axon and dendrite growth from developing hippocampal neurons following activation of CD40L reverse signaling.

Staurosporine and NEM mainly impair WNK-SPAK/OSR1 mediated phosphorylation of KCC2 and NKCC1

The pivotal role of KCC2 and NKCC1 in development and maintenance of fast inhibitory neurotransmission and their implication in severe human diseases arouse interest in posttranscriptional regulatory mechanisms such as (de)phosphorylation. Staurosporine (broad kinase inhibitor) and N-ethylmalemide (NEM) that modulate kinase and phosphatase activities enhance KCC2 and decrease NKCC1 activity. Here, we investigated the regulatory mechanism for this reciprocal regulation by mass spectrometry and immunoblot analyses using phospho-specific antibodies. Our analyses revealed that application of staurosporine or NEM dephosphorylates Thr1007 of KCC2, and Thr203, Thr207 and Thr212 of NKCC1. Dephosphorylation of Thr1007 of KCC2, and Thr207 and Thr212 of NKCC1 were previously demonstrated to activate KCC2 and to inactivate NKCC1. In addition, application of the two agents resulted in dephosphorylation of the T-loop and S-loop phosphorylation sites Thr233 and Ser373 of SPAK, a critical kinase in the WNK-SPAK/OSR1 signaling module mediating phosphorylation of KCC2 and NKCC1. Taken together, these results suggest that reciprocal regulation of KCC2 and NKCC1 via staurosporine and NEM is based on WNK-SPAK/OSR1 signaling. The key regulatory phospho-site Ser940 of KCC2 is not critically involved in the enhanced activation of KCC2 upon staurosporine and NEM treatment, as both agents have opposite effects on its phosphorylation status. Finally, NEM acts in a tissue-specific manner on Ser940, as shown by comparative analysis in HEK293 cells and immature cultured hippocampal neurons. In summary, our analyses identified phospho-sites that are responsive to staurosporine or NEM application. This provides important information towards a better understanding of the cooperative interactions of different phospho-sites.

Natural mechanisms and artificial PEG-induced mechanism that repair traumatic damage to the plasmalemma in eukaryotes

Eukaryotic tissues are composed of individual cells surrounded by a plasmalemma that consists of a phospholipid bilayer with hydrophobic heads that bind cell water. Bound-water creates a thermodynamic barrier that impedes the fusion of a plasmalemma with other membrane-bound intracellular structures or with the plasmalemma of adjacent cells. Plasmalemmal damage consisting of small or large holes or complete transections of a cell or axon results in calcium influx at the lesion site. Calcium activates fusogenic pathways that have been phylogenetically conserved and that lower thermodynamic barriers for fusion of membrane-bound structures. Calcium influx also activates phylogenetically conserved sealing mechanisms that mobilize the gradual accumulation and fusion of vesicles/membrane-bound structures that seal the damaged membrane. These naturally occurring sealing mechanisms for different cells vary based on the type of lesion, the type of cell, the proximity of intracellular membranous structures to the lesion and the relation to adjacent cells. The reliability of different measures to assess plasmalemmal sealing need be carefully considered for each cell type. Polyethylene glycol (PEG) bypasses calcium and naturally occurring fusogenic pathways to artificially fuse adjacent cells (PEG-fusion) or artificially seal transected axons (PEG-sealing). PEG-fusion techniques can also be used to rapidly rejoin the closely apposed, open ends of severed axons. PEG-fused axons do not (Wallerian) degenerate and PEG-fused nerve allografts are not immune-rejected, and enable behavioral recoveries not observed for any other clinical treatment. A better understanding of natural and artificial mechanisms that induce membrane fusion should provide better clinical treatment for many disorders involving plasmalemmal damage.

Differential induction of nuclear factor-like 2 signature genes with toll-like receptor stimulation

Inflammation is associated with production of reactive oxygen species (ROS) and results in the induction of thioredoxin (TXN) and peroxiredoxins (PRDXs) and activation of nuclear factor-like 2 (Nrf2). In this study we have used the mouse RAW 264.7 macrophage and the human THP-1 monocyte cell line to investigate the pattern of expression of three Nrf2 target genes, PRDX1, TXN reductase (TXNRD1) and heme oxygenase (HMOX1), by activation of different Toll-like receptors (TLRs). We found that, while the TLR4 agonist lipopolysaccharide (LPS) induces all three genes, the pattern of induction with agonists for TLR1/2, TLR3, TLR2/6 and TLR7/8 differs depending on the gene and the cell line. In all cases, the extent of induction was HMOX1>TXNRD1>PRDX1. Since LPS was a good inducer of all genes in both cell lines, we studied the mechanisms mediating LPS induction of the three genes using mouse RAW 264.7 cells. To assess the role of ROS we used the antioxidant N-acetylcysteine (NAC). Only LPS induction of HMOX1 was inhibited by NAC while that of TXNRD1 and PRDX1 was unaffected. These three genes were also induced by phorbol myristate acetate (PMA), a ROS-inducer acting by activation of protein kinase C (PKC). The protein kinase inhibitor staurosporine inhibited the induction of all three genes by PMA but only that of HMOX1 by LPS. This indicates that activation of these genes by inflammatory agents is regulated by different mechanisms involving either ROS or protein kinases, or both.

PKC and PKN in heart disease

The protein kinase C (PKC) and closely related protein kinase N (PKN) families of serine/threonine protein kinases play crucial cellular roles. Both kinases belong to the AGC subfamily of protein kinases that also include the cAMP dependent protein kinase (PKA), protein kinase B (PKB/AKT), protein kinase G (PKG) and the ribosomal protein S6 kinase (S6K). Involvement of PKC family members in heart disease has been well documented over the years, as their activity and levels are mis-regulated in several pathological heart conditions, such as ischemia, diabetic cardiomyopathy, as well as hypertrophic or dilated cardiomyopathy. This review focuses on the regulation of PKCs and PKNs in different pathological heart conditions and on the influences that PKC/PKN activation has on several physiological processes. In addition, we discuss mechanisms by which PKCs and the closely related PKNs are activated and turned-off in hearts, how they regulate cardiac specific downstream targets and pathways, and how their inhibition by small molecules is explored as new therapeutic target to treat cardiomyopathies and heart failure.

Alcohol dehydrogenase of Candida albicans triggers differentiation of THP-1 cells into macrophages

Candida albicans proteins located on the cell wall and in the cytoplasm have gained great attention because they are not only involved in cellular metabolism and the maintenance of integrity but also interact with host immune systems. Previous research has reported that enolase from C. albicans exhibits high immunogenicity and effectively protects mice against disseminated candidiasis. In this study, alcohol dehydrogenase (ADH) of C. albicans was cloned and purified for the first time, and this study focused on evaluating its effects on the differentiation of the human monocytic cell line THP-1. The morphological features of THP-1 cells exposed to ADH were similar to those of phorbol-12-myristate acetate-differentiated (PMA-differentiated) macrophages. Functionally, ADH enhanced the adhesion, phagocytosis, and killing capacities of THP-1 cells. A flow cytometric assay demonstrated that ADH-induced THP-1 cells significantly increased CD86 and CD11b expression. The production of IL-1β, IL-6, and TNF-α by cells increased in the presence of ADH. As expected, after pretreatment with a MEK inhibitor (U0126), ADH-induced THP-1 cells exhibited unaltered morphological features, eliminated ERK1/2 phosphorylation, prevented CD86/CD11b upregulation and inhibited pro-inflammatory cytokine increase. Collectively, these results suggest that ADH enables THP-1 cells to differentiate into macrophages via the ERK pathway, and it may play an important role in the immune response against fungal invasion.

Reprint of "The interaction between environmental triggers and epigenetics in autoimmunity"

Systemic lupus erythematosus flares when genetically predisposed people encounter environmental agents that cause oxidative stress, such as infections and sunlight. How these modify the immune system to initiate flares is unclear. Drug induced lupus models demonstrate that CD4+ T cells epigenetically altered with DNA methylation inhibitors cause lupus in animal models, and similar T cells are found in patients with active lupus. How infections and sun exposure inhibit T cell DNA methylation is unclear. DNA methylation patterns are replicated each time a cell divides in a process that requires DNA methyltransferase one (Dnmt1), which is upregulated as cells enter mitosis, as well as the methyl donor S-adenosylmethionine, created from dietary sources. Reactive oxygen species that inhibit Dnmt1 upregulation, and a diet poor in methyl donors, combine to cause lupus in animal models. Similar changes are found in patients with active lupus, indicating a mechanism contributing to lupus flares.

The Diacylglycerol Analogs OAG and DOG Differentially Affect Primary Events of Pheromone Transduction in the Hawkmoth Manduca sexta in a Zeitgebertime-Dependent Manner Apparently Targeting TRP Channels

For the hawkmoth Manduca sexta accumulating evidence suggests that pheromone transduction acts via a metabotropic signal transduction cascade, with G-protein-dependent phospholipase C (PLC) activations generating diacylglycerol (DAG) and inositol trisphosphate as the primary events in hawkmoth pheromone transduction. In contrast, ionotropic olfactory receptor (OR) coreceptor (Orco)-dependent mechanisms do not appear to be involved. In hawkmoths pheromones activated a specific sequence of PLC-dependent ion channels of unknown identity. In several sensory systems transient receptor potential (TRP) ion channels were found downstream of PLC as primary transduction channels. Also in the mammalian vomeronasal organ, DAG-dependent TRP channels are employed. Therefore, we hypothesized that TRPs may be downstream targets for DAG also in the hawkmoth pheromone signal transduction pathway. To test this, we employed two DAG analogs, OAG and DOG for in vivo single-sensillum tip-recordings of pheromone-sensitive sensilla. Since olfactory receptor neurons (ORNs) expressed circadian changes in sensitivity throughout the day, we recorded at two different Zeitgebertimes (ZTs), the hawkmoths activity phase at ZT 1 and its resting phase at ZT 9. We found that the DAG analogs targeted at least two different TRP-like channels that underlie the primary events of hawkmoth pheromone transduction daytime-dependently. At both ZTs OAG sped up and increased the Orco-independent phasic action potential response without affecting the Orco-dependent late, long-lasting pheromone response. Thus, OAG most likely opened a transient Ca2+ permeable TRP channel that was available at both ZTs and that opened pheromone-dependently before Orco. In contrast, DOG slowed down and decreased the sensillum potential, the phasic-, and the late, long-lasting pheromone response. Therefore, DOG appeared to activate a protein kinase C (PKC) that closed TRP-like Ca2+ permeable channels and opened Ca2+ impermeable cation channels, which have been previously described and are most abundant at ZT 9. These data support our hypothesis that hawkmoth pheromone transduction is mediated by metabotropic PLC-dependent mechanisms that activate TRP-like channels as the primary event of pheromone transduction. In addition, our data indicate that at different times of the day different second messenger-dependent ion channels are available for pheromone transduction cascades.

Evolving mechanisms of vascular smooth muscle contraction highlight key targets in vascular disease

Vascular smooth muscle (VSM) plays an important role in the regulation of vascular function. Identifying the mechanisms of VSM contraction has been a major research goal in order to determine the causes of vascular dysfunction and exaggerated vasoconstriction in vascular disease. Major discoveries over several decades have helped to better understand the mechanisms of VSM contraction. Ca2+ has been established as a major regulator of VSM contraction, and its sources, cytosolic levels, homeostatic mechanisms and subcellular distribution have been defined. Biochemical studies have also suggested that stimulation of Gq protein-coupled membrane receptors activates phospholipase C and promotes the hydrolysis of membrane phospholipids into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 stimulates initial Ca2+ release from the sarcoplasmic reticulum, and is buttressed by Ca2+ influx through voltage-dependent, receptor-operated, transient receptor potential and store-operated channels. In order to prevent large increases in cytosolic Ca2+ concentration ([Ca2+]c), Ca2+ removal mechanisms promote Ca2+ extrusion via the plasmalemmal Ca2+ pump and Na+/Ca2+ exchanger, and Ca2+ uptake by the sarcoplasmic reticulum and mitochondria, and the coordinated activities of these Ca2+ handling mechanisms help to create subplasmalemmal Ca2+ domains. Threshold increases in [Ca2+]c form a Ca2+-calmodulin complex, which activates myosin light chain (MLC) kinase, and causes MLC phosphorylation, actin-myosin interaction, and VSM contraction. Dissociations in the relationships between [Ca2+]c, MLC phosphorylation, and force have suggested additional Ca2+ sensitization mechanisms. DAG activates protein kinase C (PKC) isoforms, which directly or indirectly via mitogen-activated protein kinase phosphorylate the actin-binding proteins calponin and caldesmon and thereby enhance the myofilaments force sensitivity to Ca2+. PKC-mediated phosphorylation of PKC-potentiated phosphatase inhibitor protein-17 (CPI-17), and RhoA-mediated activation of Rho-kinase (ROCK) inhibit MLC phosphatase and in turn increase MLC phosphorylation and VSM contraction. Abnormalities in the Ca2+ handling mechanisms and PKC and ROCK activity have been associated with vascular dysfunction in multiple vascular disorders. Modulators of [Ca2+]c, PKC and ROCK activity could be useful in mitigating the increased vasoconstriction associated with vascular disease.

Ethanol-Induced Changes in PKCε: From Cell to Behavior

The long-term binge intake of ethanol causes neuroadaptive changes that lead to drinkers requiring higher amounts of ethanol to experience its effects. This neuroadaptation can be partly attributed to the modulation of numerous neurotransmitter receptors by the various protein kinases C (PKCs). PKCs are enzymes that control cellular activities by regulating other proteins via phosphorylation. Among the various isoforms of PKC, PKCε is the most implicated in ethanol-induced biochemical and behavioral changes. Ethanol exposure causes changes to PKCε expression and localization in various brain regions that mediate addiction-favoring plasticity. Ethanol works in conjunction with numerous upstream kinases and second messenger activators to affect cellular PKCε expression. Chauffeur proteins, such as receptors for activated C kinase (RACKs), cause the translocation of PKCε to aberrant sites and mediate ethanol-induced changes. In this article, we aim to review the following: the general structure and function of PKCε, ethanol-induced changes in PKCε expression, the regulation of ethanol-induced PKCε activities in DAG-dependent and DAG-independent environments, the mechanisms underlying PKCε-RACKε translocation in the presence of ethanol, and the existing literature on the role of PKCε in ethanol-induced neurobehavioral changes, with the goal of creating a working model upon which further research can build.

The interaction between environmental triggers and epigenetics in autoimmunity

Systemic lupus erythematosus flares when genetically predisposed people encounter environmental agents that cause oxidative stress, such as infections and sunlight. How these modify the immune system to initiate flares is unclear. Drug induced lupus models demonstrate that CD4+ T cells epigenetically altered with DNA methylation inhibitors cause lupus in animal models, and similar T cells are found in patients with active lupus. How infections and sun exposure inhibit T cell DNA methylation is unclear. DNA methylation patterns are replicated each time a cell divides in a process that requires DNA methyltransferase one (Dnmt1), which is upregulated as cells enter mitosis, as well as the methyl donor S-adenosylmethionine, created from dietary sources. Reactive oxygen species that inhibit Dnmt1 upregulation, and a diet poor in methyl donors, combine to cause lupus in animal models. Similar changes are found in patients with active lupus, indicating a mechanism contributing to lupus flares.

Macropinocytosis, mTORC1 and cellular growth control

The growth and proliferation of metazoan cells are driven by cellular nutrient status and by extracellular growth factors. Growth factor receptors on cell surfaces initiate biochemical signals that increase anabolic metabolism and macropinocytosis, an actin-dependent endocytic process in which relatively large volumes of extracellular solutes and nutrients are internalized and delivered efficiently into lysosomes. Macropinocytosis is prominent in many kinds of cancer cells, and supports the growth of cells transformed by oncogenic K-Ras. Growth factor receptor signaling and the overall metabolic status of the cell are coordinated in the cytoplasm by the mechanistic target-of-rapamycin complex-1 (mTORC1), which positively regulates protein synthesis and negatively regulates molecular salvage pathways such as autophagy. mTORC1 is activated by two distinct Ras-related small GTPases, Rag and Rheb, which associate with lysosomal membranes inside the cell. Rag recruits mTORC1 to the lysosomal surface where Rheb directly binds to and activates mTORC1. Rag is activated by both lysosomal luminal and cytosolic amino acids; Rheb activation requires phosphoinositide 3-kinase, Akt, and the tuberous sclerosis complex-1/2. Signals for activation of Rag and Rheb converge at the lysosomal membrane, and several lines of evidence support the idea that growth factor-dependent endocytosis facilitates amino acid transfer into the lysosome leading to the activation of Rag. This review summarizes evidence that growth factor-stimulated macropinocytosis is essential for amino acid-dependent activation of mTORC1, and that increased solute accumulation by macropinocytosis in transformed cells supports unchecked cell growth.

Novel TCR-Mediated Mechanisms of Notch Activation and Signaling

The Notch receptor is an evolutionarily highly conserved transmembrane protein that is essential to a wide spectrum of cellular systems. Notch signaling is especially important to T cell development, and its deregulation leads to leukemia. Although not well characterized, it continues to play an integral role in peripheral T cells, in which a unique mode of Notch activation can occur. In contrast to canonical Notch activation initiated by adjacent ligand-expressing cells, TCR stimulation is sufficient to induce Notch signaling. However, the interactions between these two pathways have not been defined. In this article, we show that Notch activation occurs in peripheral T cells within a few hours post-TCR stimulation and is required for optimal T cell activation. Using a panel of inhibitors against components of the TCR signaling cascade, we demonstrate that Notch activation is facilitated through initiation of protein kinase C-induced ADAM activity. Moreover, our data suggest that internalization of Notch via endocytosis plays a role in this process. Although ligand-mediated Notch stimulation relies on mechanical pulling forces that disrupt the autoinhibitory domain of Notch, we hypothesized that, in T cells in the absence of ligands, these conformational changes are induced through chemical adjustments in the endosome, causing alleviation of autoinhibition and receptor activation. Thus, T cells may have evolved a unique method of Notch receptor activation, which is described for the first time, to our knowledge, in this article.

Combined chemical genetics and data-driven bioinformatics approach identifies receptor tyrosine kinase inhibitors as host-directed antimicrobials

Antibiotic resistance poses rapidly increasing global problems in combatting multidrug-resistant (MDR) infectious diseases like MDR tuberculosis, prompting for novel approaches including host-directed therapies (HDT). Intracellular pathogens like Salmonellae and Mycobacterium tuberculosis (Mtb) exploit host pathways to survive. Only very few HDT compounds targeting host pathways are currently known. In a library of pharmacologically active compounds (LOPAC)-based drug-repurposing screen, we identify multiple compounds, which target receptor tyrosine kinases (RTKs) and inhibit intracellular Mtb and Salmonellae more potently than currently known HDT compounds. By developing a data-driven in silico model based on confirmed targets from public databases, we successfully predict additional efficacious HDT compounds. These compounds target host RTK signaling and inhibit intracellular (MDR) Mtb. A complementary human kinome siRNA screen independently confirms the role of RTK signaling and kinases (BLK, ABL1, and NTRK1) in host control of Mtb. These approaches validate RTK signaling as a drugable host pathway for HDT against intracellular bacteria.

Age is the work of art? Impact of neutrophil and organism age on neutrophil extracellular trap formation

Neutrophil extracellular traps or NETs are released by highly activated neutrophils in response to infectious agents, sterile inflammation, autoimmune stimuli and cancer. In the cells, the nuclear envelop disintegrates and decondensation of chromatin occurs that depends on peptidylarginine deiminase 4 (PAD4) and neutrophil elastase (NE). Subsequently, proteins from neutrophil granules (e.g., NE, lactoferrin and myeloperoxidase) and the nucleus (histones) bind to decondensed DNA and the whole structure is ejected from the cell. The DNA decorated with potent antimicrobials and proteases can act to contain dissemination of infection and in sterile inflammation NETs were shown to degrade cytokines and chemokines via serine proteases. On the other hand, overproduction of NETs, or their inadequate removal and prolonged presence in vasculature or tissues, can lead to bystander damage or even initiation of diseases. Considering the pros and cons of NET formation, it is of relevance if the stage of neutrophil maturation (immature, mature and senescent cells) affects the capacity to produce NETs as the cells of different age-related phenotypes dominate in given (pathological) conditions. Moreover, the immune system of neonates and elderly individuals is weaker than in adulthood. Is the same pattern followed when it comes to NETs? The overall importance of individual and neutrophil age on the capacity to release NETs is reviewed in detail and the significance of these facts is discussed.

Notoginsenoside R1 Alleviates Oxygen-Glucose Deprivation/Reoxygenation Injury by Suppressing Endoplasmic Reticulum Calcium Release via PLC

As documented in our previous study, notoginsenoside R1 (NGR1) can inhibit neuron apoptosis and the expression of endoplasmic reticulum (ER) stress-associated pro-apoptotic proteins in hypoxic–ischemic encephalopathy. Recent evidence indicates that the Phospholipase C (PLC)/inositol 1,4,5-trisphosphate receptor (IP3R) is important for the regulation of Ca²⁺ release in the ER. Ca²⁺ imbalance can stimulate ER stress, CAMKII, and cell apoptosis. The purpose of this study was to further investigate the neuroprotective effect of NGR1 and elucidate how NGR1 regulates ER stress and cell apoptosis in the oxygen–glucose deprivation/reoxygenation (OGD/R) model. Cells were exposed to NGR1 or the PLC activator m-3M3FBS. Then, IP3R- and IP3-induced Ca²⁺ release (IICR) and activation of the ER stress and CaMKII signal pathway were measured. The results showed that NGR1 inhibited IICR and strengthened the binding of GRP78 with PERK and IRE1. NGR1 also alleviated the activation of the CaMKII pathway. Pretreatment with m-3M3FBS attenuated the neuroprotective effect of NGR1; IICR was activated, activation of the ER stress and CaMKII pathway was increased, and more cells were injured. These results indicate that NGR1 may suppress activation of the PLC/IP3R pathway, subsequently inhibiting ER Ca²⁺ release, ER stress, and CaMKII and resulting in suppressed cell apoptosis.

CD40 is a major regulator of dendrite growth from developing excitatory and inhibitory neurons

Dendrite size and morphology are key determinants of the functional properties of neurons and neural circuits. Here we show that CD40, a member of the TNF receptor superfamily, is a major regulator of dendrite growth and elaboration in the developing brain. The dendrites of hippocampal excitatory neurons were markedly stunted in Cd40^-/- mice, whereas those of striatal inhibitory neurons were much more exuberant. These striking and opposite phenotypic changes were also observed in excitatory and inhibitory neurons cultured from Cd40^-/- mice and were rescued by soluble CD40. The changes in excitatory and inhibitory neurons cultured from Cd40^-/- mice were mimicked in neurons of Cd40^+/+ mice by treatment with soluble CD40L and were dependent on PKC-β and PKC-γ, respectively. These results suggest that CD40-activated CD40L reverse signalling has striking and opposite effects on the growth and elaboration of dendrites among major classes of brain neurons by PKC-dependent mechanisms.

Contribution of vascular endothelial growth factor receptor-2 sialylation to the process of angiogenesis

Vascular endothelial growth factor receptor-2 (VEGFR2) is the main pro-angiogenic receptor expressed by endothelial cells (ECs). Using surface plasmon resonance, immunoprecipitation, enzymatic digestion, immunofluorescence and cross-linking experiments with specific sugar-binding lectins, we demonstrated that VEGFR2 bears both α,1-fucose and α(2,6)-linked sialic acid (NeuAc). However, only the latter is required for VEGF binding to VEGFR2 and consequent VEGF-dependent VEGFR2 activation and motogenic response in ECs. Notably, downregulation of β-galactoside α(2,6)-sialyltransferase expression by short hairpin RNA transduction inhibits VEGFR2 α(2,6) sialylation that is paralleled by an increase of β-galactoside α(2,3)-sialyltransferase expression. This results in an ex-novo α(2,3)-NeuAc sialylation of the receptor that functionally replaces the lacking α(2,6)-NeuAc, thus allowing VEGF/VEGFR2 interaction. In keeping with the role of VEGFR2 sialylation in angiogenesis, the α(2,6)-NeuAc-binding lectin Sambucus nigra (SNA) prevents VEGF-dependent VEGFR2 autophosphorylation and EC motility, proliferation and motogenesis. In addition, SNA exerts a VEGF-antagonist activity in tridimensional angiogenesis models in vitro and in the chick-embryo chorioallantoic membrane neovascularization assay and mouse matrigel plug assay in vivo. In conclusion, VEGFR2-associated NeuAc plays an important role in modulating VEGF/VEGFR2 interaction, EC pro-angiogenic activation and neovessel formation. VEGFR2 sialylation may represent a target for the treatment of angiogenesis-dependent diseases.

The tumor promoter-activated protein kinase Cs are a system for regulating filopodia

Different protein kinase C (PKC) isoforms have distinct roles in regulating cell functions. The conventional (α, β, γ) and novel (δ, ɛ, η, θ) classes are targets of phorbol ester tumor promoters, which are surrogates of endogenous second messenger, diacylglycerol. The promoter-stimulated disappearance of filopodia was investigated by use of blocking peptides (BPs) that inhibit PKC maturation and/or docking. Filopodia were partially rescued by a peptide representing PKC ɛ hydrophobic sequence, but also by a myristoylated PKC α/β pseudosubstrate sequence, and an inhibitor of T-cell protein tyrosine phosphatase (TC-PTP). The ability to turn over filopodia was widely distributed among PKC isoforms. PKC α and η hydrophobic sequences enhanced filopodia in cells in the absence of tumor promoter treatment. With transcriptional knockdown of PKC α, the content of PKC ɛ predominated over other isoforms. PKC ɛ could decrease filopodia significantly in promoter-treated cells, and this was attributed to ruffling. The presence of PKC α counteracted the PKC ɛ-mediated enhancement of ruffling. The results showed that there were two mechanisms of filopodia downregulation. One operated in the steady-state and relied on PKC α and η. The other was stimulated by tumor promoters and relied on PKC ɛ. Cycles of protrusion and retraction are characteristic of filopodia and are essential for the cell to orient itself during chemotaxis and haptotaxis. By suppressing filopodia, PKC ɛ can create a long-term "memory" of an environmental signal that may act in nature as a mnemonic device to mark the direction of a repulsive signal.

Syndecan-1 increases B-lymphoid cell extravasation in response to HIV-1 Tat via αvβ3/pp60src/pp125FAK pathway

Syndecan-1 is a heparan sulfate proteoglycan (HSPG) commonly upregulated in AIDS-related B lymphoid malignancies. Tat is the main HIV-1 transactivating factor that has a major role in the pathogenesis of AIDS-related lymphomas (ARL) by engaging heparan sulfate proteoglycans (HSPGs), chemokine receptors and integrins at the lymphoid cell (LC) surface. Here B-lymphoid Namalwa cell clones that do not express or overexpress syndecan-1 (EV-Ncs and SYN-Ncs, respectively) were compared for their responsiveness with Tat: in the absence of syndecan-1, Tat induces a limited EV-Nc migration via C-X-C motif chemokine receptor 4 (CXCR4), G-proteins and Rac. Syndecan-1 overexpression increases SYN-Nc responsiveness to Tat and makes this response independent from CXCR4 and G-protein and dependent instead on pp60src phosphorylation. Tat-induced SYN-Nc migration and pp60src phosphorylation require the engagement of α_vβ₃ integrin and consequent pp125FAK phosphorylation. This complex set of Tat-driven activations is orchestrated by the direct interaction of syndecan-1 with pp60src and its simultaneous coupling with α_vβ₃. The Tat/syndecan-1/α_vβ₃ interplay is retained in vivo and is shared also by other syndecan-1⁺ B-LCs, including BJAB cells, whose responsiveness to Tat is inhibited by syndecan-1 knockdown. In conclusion, overexpression of syndecan-1 confers to B-LCs an increased capacity to migrate in response to Tat, owing to a switch from a CXCR4/G-protein/Rac to a syndecan-1/α_vβ₃/pp60src/pp125FAK signal transduction pathway that depends on the formation of a complex in which syndecan-1 interacts with Tat via its HS-chains, with α_vβ₃ via its core protein ectodomain and with pp60src via its intracellular tail. These findings have implications in ARL progression and may help in identifying new therapeutical targets for the treatment of AIDS-associated neoplasia.

Effects of Phorbol Dibutyrate on Cell Proliferation, Apoptosis, and Tumor Necrosis Factor-alpha Expression in Human Endometrial Adenocarcinoma Cells

OBJECTIVES

Recent evidence suggested that protein kinase C (PKC), a major cell cycle regulator in endometrial models, mimics progesterone withdrawal by inducing downstream signals. In the current study we examined the hypothesis that the PKC activator phorbol 12,13 dibutyrate (PDB) would inhibit cell proliferation and induce apoptosis in two endometrial adenocarcinoma cell (EAC) lines, HEC-1B and Ishikawa cells. We further examined whether the induction of tumor necrosis factor-alpha (TNF-alpha) might mediate these effects.

METHODS

EAC lines were cultured under standard and serum-free conditions to study the effects of PDB on cell kinetics. Cell proliferation was determined by cell count using a hemacytometer and by incorporation of (3)H thymidine into 10% trichloracetic acid-precipitable DNA. Apoptosis was determined by measuring cytoplasmic histone-associated DNA fragments. Conditioned media concentrations of TNF-alpha were measured by a commercially available enzyme-linked immunosorbent assay (ELISA). EACs were transfected with a -125-bp TNF-alpha promoter luciferase construct and treated with PDB to evaluate transcriptional activation.

RESULTS

Activation of the PKC system with PDB (10 nM) decreased cell proliferation and mitogenesis in EACs. PDB induced apoptosis in both EAC lines. EACs exhibit basal TNF-alpha gene expression and protein secretion and these were increased potently by PDB. However, neutralization of TNF-alpha by addition of anti-TNF-alpha antibodies did not prevent the suppression of mitogenesis, induction of apoptosis, or activation of TNF-alpha gene expression by PDB.

CONCLUSION

Activation of the PKC system leads to inhibition of cell proliferation, induction of apoptosis, and TNF-alpha expression in EACs. However, apoptosis in this setting does not appear to require TNF-alpha action. EACs provide an informative model to investigate aspects of endometrial epithelial remodeling that may occur under physiologic conditions of progesterone withdrawal.

Protein Kinase C as Regulator of Vascular Smooth Muscle Function and Potential Target in Vascular Disorders

Vascular smooth muscle (VSM) plays an important role in maintaining vascular tone. In addition to Ca2+-dependent myosin light chain (MLC) phosphorylation, protein kinase C (PKC) is a major regulator of VSM function. PKC is a family of conventional Ca2+-dependent α, β, and γ, novel Ca2+-independent δ, ɛ, θ, and η, and atypical ξ, and ι/λ isoforms. Inactive PKC is mainly cytosolic, and upon activation it undergoes phosphorylation, maturation, and translocation to the surface membrane, the nucleus, endoplasmic reticulum, and other cell organelles; a process facilitated by scaffold proteins such as RACKs. Activated PKC phosphorylates different substrates including ion channels, pumps, and nuclear proteins. PKC also phosphorylates CPI-17 leading to inhibition of MLC phosphatase, increased MLC phosphorylation, and enhanced VSM contraction. PKC could also initiate a cascade of protein kinases leading to phosphorylation of the actin-binding proteins calponin and caldesmon, increased actin-myosin interaction, and VSM contraction. Increased PKC activity has been associated with vascular disorders including ischemia-reperfusion injury, coronary artery disease, hypertension, and diabetic vasculopathy. PKC inhibitors could test the role of PKC in different systems and could reduce PKC hyperactivity in vascular disorders. First-generation PKC inhibitors such as staurosporine and chelerythrine are not very specific. Isoform-specific PKC inhibitors such as ruboxistaurin have been tested in clinical trials. Target delivery of PKC pseudosubstrate inhibitory peptides and PKC siRNA may be useful in localized vascular disease. Further studies of PKC and its role in VSM should help design isoform-specific PKC modulators that are experimentally potent and clinically safe to target PKC in vascular disease.

Repressed PKCδ activation in glycodelin-expressing cells mediates resistance to phorbol ester and TGFβ

Glycodelin is a glycoprotein mainly expressed in well-differentiated epithelial cells in reproductive tissues. In normal secretory endometrium, the expression of glycodelin is abundant and regulated by progesterone. In hormone-related cancers glycodelin expression is associated with well-differentiated tumors. We have previously found that glycodelin drives epithelial differentiation of HEC-1B endometrial adenocarcinoma cells, resulting in reduced tumor growth in a preclinical mouse model. Here we show that glycodelin-transfected HEC-1B cells have repressed protein kinase C delta (PKCδ) activation, likely due to downregulation of PDK1, and are resistant to phenotypic change and enhanced migration induced by phorbol 12-myristate 13-acetate (PMA). In control cells, which do not express glycodelin, the effects of PMA were abolished by using PKCδ and PDK1 inhibitors, and knockdown of PKCδ, MEK1 and 2, or ERK1 and 2 by siRNAs. Similarly, transforming growth factor β (TGFβ)-induced phenotypic change was only seen in control cells, not in glycodelin-producing cells, and it was mediated by PKCδ. Taken together, these results strongly suggest that PKCδ, via MAPK pathway, is involved in the glycodelin-driven cell differentiation rendering the cells resistant to stimulation by PMA and TGFβ.

Distinctive roles of PKC delta isozyme in platelet function

Platelet activation is a complex balance of positive and negative signaling pathways. Several protein kinase C (PKC) isoforms are expressed in human platelets. They are a major regulator of platelet granule secretion, activation and aggregation activity. One of those isoforms is the PKCδ isozyme, it has a central yet complex role in platelets such as opposite signaling functions depending on the nature of the agonist, it concentration and pathway. In fact, it has been shown that PKCδ has an overall negative influence on platelet function in response to collagen, while, following PAR stimulation, PKCδ has a positive effect on platelet function. Understanding the crucial role of PKCδ in platelet functions is recently emerging in the literature, therefore, further investigations should shed light into its specific role in hemostasis. In this review, we focus on the different roles of PKCδ in platelet activation, aggregation and thrombus formation.

A Modified NK Cell Degranulation Assay Applicable for Routine Evaluation of NK Cell Function

Natural killer (NK) cells play important role in innate immunity against tumors and viral infections. Studies show that lysosome-associated membrane protein-1 (LAMP-1, CD107a) is a marker for degranulation of NK and cytotoxic T cells and its expression is a sensitive marker for the cytotoxic activity determination. The conventional methods of determination of CD107a on NK cells involve use of peripheral blood mononuclear cells (PBMC) or pure NK cells and K562 cells as stimulants. Thus, it requires large volume of blood sample which is usually difficult to obtain in pediatric patients and patients with cytopenia and also requires specialized laboratory for maintaining cell line. We have designed a flow cytometric assay to determine CD107a on NK cells using whole blood, eliminating the need for isolation of PBMC or isolate NK cells. This assay uses phorbol-12-myristate-13-acetate (PMA) and calcium ionophore (Ca²⁺-ionophore) instead of K562 cells for stimulation and thus does not require specialized cell culture laboratory. CD107a expression on NK cells using modified NK cell degranulation assay compared to the conventional assay was significantly elevated (p < 0.0001). It was also validated by testing patients diagnosed with familial hemophagocytic lymphohistiocytosis (FHL) with defect in exocytosis. This assay is rapid, cost effective, and reproducible and requires significantly less volume of blood which is important for clinical evaluation of NK cells.

NF-κB in acute pancreatitis: Mechanisms and therapeutic potential

The incidence of acute pancreatitis (AP) is increasing globally and mortality could be high among patients with organ failure and infected necrosis. The predominant factors responsible for the morbidity and mortality of AP are systemic inflammatory response syndrome and multiorgan dysfunction. Even though preclinical studies have shown antisecretory agents (somatostatin), antioxidants (S-adenosyl methionine [SAM], selenium), protease inhibitors, platelet activating factor inhibitor (Lexipafant), and anti-inflammatory immunomodulators (eg. prostaglandin E, indomethacin) to benefit AP in terms of reducing the severity and/or mortality, most of these agents have shown heterogeneous results in clinical studies. Several years of experimental studies have implicated nuclear factor-kappa B (NF-κB) activation as an early and central event in the progression of inflammation in AP. In this manuscript, we review the literature on the role of NF-κB in the pathogenesis of AP, its early intraacinar activation, and how it results in progression of the disease. We also discuss why anti-protease, antisecretory, and anti-inflammatory agents are unlikely to be effective in clinical acute pancreatitis. NF-κB, being a central molecule that links the initial acinar injury to systemic inflammation and perpetuate the inflammation, we propose that more studies be focussed towards targeted inhibition of NF-κB activity. Direct NF-κB inhibition strategies have already been attempted in patients with various cancers. So far, peroxisome proliferator activator receptor gamma (PPAR-γ) ligand, pyrrolidine dithiocarbamate (PDTC), proteasome inhibitor and calpain I inhibitor have been shown to have direct inhibitory effects on NF-κB activation in experimental AP.