Identification of PKC-isoform-specific biological actions using pharmacological approaches

Antisense Oligonucleotides for Rapid Translation of Gene Therapy in Glioblastoma

PURPOSE

The limited efficacy of current treatments for malignant brain tumors necessitates novel therapeutic strategies. This study aimed to assess the potential of antisense oligonucleotides (ASOs) as adjuvant therapy for high-grade gliomas, focusing on their CNS penetration and clinical translation prospects.

METHODS

A comprehensive review of the existing literature was conducted to evaluate the implications of ASOs in neuro-oncology. Studies that investigated ASO therapy's efficacy, CNS penetration, and safety profile were analyzed to assess its potential as a therapeutic intervention for high-grade gliomas.

RESULTS

ASOs present a promising avenue for enhancing targeted gene therapies in malignant gliomas. Their potent CNS penetration, in vivo durability, and efficient transduction offer advantages over conventional treatments. Preliminary in vivo and in vitro studies suggest ASOs as a viable adjuvant therapy for high-grade gliomas, warranting further exploration in clinical trials.

CONCLUSIONS

ASOs hold significant promise as adjuvant therapy for high-grade gliomas, offering improved CNS penetration and durability compared with existing treatments. While preliminary studies are encouraging, additional research is needed to establish the safety and efficacy of ASO therapy in clinical settings. Further investigation and clinical trials are warranted to validate ASOs as a transformative approach in neuro-oncology.

Regulation of microtubule nucleation in mouse bone marrow-derived mast cells by ARF GTPase-activating protein GIT2

Aggregation of high-affinity IgE receptors (FcϵRIs) on granulated mast cells triggers signaling pathways leading to a calcium response and release of inflammatory mediators from secretory granules. While microtubules play a role in the degranulation process, the complex molecular mechanisms regulating microtubule remodeling in activated mast cells are only partially understood. Here, we demonstrate that the activation of bone marrow mast cells induced by FcϵRI aggregation increases centrosomal microtubule nucleation, with G protein-coupled receptor kinase-interacting protein 2 (GIT2) playing a vital role in this process. Both endogenous and exogenous GIT2 were associated with centrosomes and γ-tubulin complex proteins. Depletion of GIT2 enhanced centrosomal microtubule nucleation, and phenotypic rescue experiments revealed that GIT2, unlike GIT1, acts as a negative regulator of microtubule nucleation in mast cells. GIT2 also participated in the regulation of antigen-induced degranulation and chemotaxis. Further experiments showed that phosphorylation affected the centrosomal localization of GIT2 and that during antigen-induced activation, GIT2 was phosphorylated by conventional protein kinase C, which promoted microtubule nucleation. We propose that GIT2 is a novel regulator of microtubule organization in activated mast cells by modulating centrosomal microtubule nucleation.

LDL Affects the Immunomodulatory Response of Endothelial Cells by Modulation of the Promyelocytic Leukemia Protein (PML) Expression via PKC

In addition to its function as an intravascular lipid transporter, LDL also triggers signal transduction in endothelial cells (ECs), which, among other things, trigger immunomodulatory cascades, e.g., IL-6 upregulation. However, the molecular mechanisms of how these LDL-triggered immunological responses in ECs are realized are not fully understood. Since promyelocytic leukemia protein (PML) plays a role in promoting inflammatory processes, we examined the relationship between LDL, PML, and IL-6 in human ECs (HUVECs and EA.hy926 cells). RT-qPCR, immunoblotting, and immunofluorescence analyses showed that LDL but not HDL induced higher PML expression and higher numbers of PML-nuclear bodies (PML-NBs). Transfection of the ECs with a PML gene-encoding vector or PML-specific siRNAs demonstrated PML-regulated IL-6 and IL-8 expression and secretion after LDL exposure. Moreover, incubation with the PKC inhibitor sc-3088 or the PKC activator PMA showed that LDL-induced PKC activity leads to the upregulation of PML mRNA and PML protein. In summary, our experimental data suggest that high LDL concentrations trigger PKC activity in ECs to upregulate PML expression, which then increases production and secretion of IL-6 and IL-8. This molecular cascade represents a novel cellular signaling pathway with immunomodulatory effects in ECs in response to LDL exposure.

Extracellular Histone-Induced Protein Kinase C Alpha Activation and Troponin Phosphorylation Is a Potential Mechanism of Cardiac Contractility Depression in Sepsis

Reduction in cardiac contractility is common in severe sepsis. However, the pathological mechanism is still not fully understood. Recently it has been found that circulating histones released after extensive immune cell death play important roles in multiple organ injury and disfunction, particularly in cardiomyocyte injury and contractility reduction. How extracellular histones cause cardiac contractility depression is still not fully clear. In this work, using cultured cardiomyocytes and a histone infusion mouse model, we demonstrate that clinically relevant histone concentrations cause significant increases in intracellular calcium concentrations with subsequent activation and enriched localization of calcium-dependent protein kinase C (PKC) α and βII into the myofilament fraction of cardiomyocytes in vitro and in vivo. Furthermore, histones induced dose-dependent phosphorylation of cardiac troponin I (cTnI) at the PKC-regulated phosphorylation residues (S43 and T144) in cultured cardiomyocytes, which was also confirmed in murine cardiomyocytes following intravenous histone injection. Specific inhibitors against PKCα and PKCβII revealed that histone-induced cTnI phosphorylation was mainly mediated by PKCα activation, but not PKCβII. Blocking PKCα also significantly abrogated histone-induced deterioration in peak shortening, duration and the velocity of shortening, and re-lengthening of cardiomyocyte contractility. These in vitro and in vivo findings collectively indicate a potential mechanism of histone-induced cardiomyocyte dysfunction driven by PKCα activation with subsequent enhanced phosphorylation of cTnI. These findings also indicate a potential mechanism of clinical cardiac dysfunction in sepsis and other critical illnesses with high levels of circulating histones, which holds the potential translational benefit to these patients by targeting circulating histones and downstream pathways.

Immunomodulatory Effects of Non-Thermal Plasma in a Model for Latent HIV-1 Infection: Implications for an HIV-1-Specific Immunotherapy

In people living with HIV-1 (PLWH), antiretroviral therapy (ART) eventually becomes necessary to suppress the emergence of human immunodeficiency virus type 1 (HIV-1) replication from latent reservoirs because HIV-1-specific immune responses in PLWH are suboptimal. Immunotherapies that enhance anti-HIV-1 immune responses for better control of virus reemergence from latent reservoirs are postulated to offer ART-free control of HIV-1. Toward the goal of developing an HIV-1-specific immunotherapy based on non-thermal plasma (NTP), the early immunological responses to NTP-exposed latently infected T lymphocytes were examined. Application of NTP to the J-Lat T-lymphocyte cell line (clones 10.6 and 15.4) stimulated monocyte recruitment and macrophage maturation, which are key steps in initiation of an immune response. In contrast, CD8+ T lymphocytes in a mixed lymphocyte reaction assay were not stimulated by the presence of NTP-exposed J-Lat cells. Furthermore, co-culture of NTP-exposed J-Lat cells with mature phagocytes did not modulate their antigen presentation to primary CD8+ T lymphocytes (cross-presentation). However, reactivation from latency was stimulated in a clone-specific manner by NTP. Overall, these studies, which demonstrated that ex vivo application of NTP to latently infected lymphocytes can stimulate key immune cell responses, advance the development of an NTP-based immunotherapy that will provide ART-free control of HIV-1 reactivation in PLWH.

M1 and M2 mAChRs activate PDK1 and regulate PKC βI and ε and the exocytotic apparatus at the NMJ

Neuromuscular junctions (NMJ) regulate cholinergic exocytosis through the M₁ and M₂ muscarinic acetylcholine autoreceptors (mAChR), involving the crosstalk between receptors and downstream pathways. Protein kinase C (PKC) regulates neurotransmission but how it associates with the mAChRs remains unknown. Here, we investigate whether mAChRs recruit the classical PKCβI and the novel PKCε isoforms and modulate their priming by PDK1, translocation and activity on neurosecretion targets. We show that each M₁ and M₂ mAChR activates the master kinase PDK1 and promotes a particular priming of the presynaptic PKCβI and ε isoforms. M₁ recruits both primed-PKCs to the membrane and promotes Munc18-1, SNAP-25, and MARCKS phosphorylation. In contrast, M₂ downregulates PKCε through a PKA-dependent pathway, which inhibits Munc18-1 synthesis and PKC phosphorylation. In summary, our results discover a co-dependent balance between muscarinic autoreceptors which orchestrates the presynaptic PKC and their action on ACh release SNARE-SM mechanism. Altogether, this molecular signaling explains previous functional studies at the NMJ and guide toward potential therapeutic targets.

mTOR regulates GPVI-mediated platelet activation

Background

Due to mTOR (mammalian/mechanistic target of rapamycin) gene-loss mice die during embryonic development, the role of mTOR in platelets has not been evaluated using gene knockout technology.

Methods

A mouse model with megakaryocyte/platelet-specific deletion of mTOR was established, and be used to evaluate the role of mTOR in platelet activation and thrombus formation.

Results

mTOR^−/− platelets were deficient in thrombus formation when grown on low-concentration collagen-coated surfaces; however, no deficiency in thrombus formation was observed when mTOR^−/− platelets were perfused on higher concentration collagen-coated surfaces. In FeCl₃-induced mouse mesenteric arteriole thrombosis models, wild-type (WT) and mTOR^−/− mice displayed significantly different responses to low-extent injury with respect to the ratio of occluded mice, especially within the first 40 min. Additionally, mTOR^−/− platelets displayed reduced aggregation and dense granule secretion (ATP release) in response to low doses of the glycoprotein VI (GPVI) agonist collagen related peptide (CRP) and the protease-activated receptor-4 (PAR4) agonist GYPGKF-NH₂; these deficiencies were overcame by stimulation with higher concentration agonists, suggesting dose dependence of the response. At low doses of GPVI or PAR agonist, the activation of α_IIbβ₃ in mTOR^−/− platelets was reduced. Moreover, stimulation of mTOR^−/− platelets with low-dose CRP attenuated the phosphorylation of S6K1, S6 and Akt Ser473, and increased the phosphorylation of PKCδ Thr505 and PKCε Ser729. Using isoform-specific inhibitors of PKCs (δ, ɛ, and α/β), we established that PKCδ/ɛ, and especially PKCδ but not PKCα/β or PKCθ, may be involved in low-dose GPVI-mediated/mTOR-dependent signaling.

Conclusion

These observations indicate that mTOR plays an important role in GPVI-dependent platelet activation and thrombus formation.

PKCε associates with the Kv3.4 channel to promote its expression in a kinase activity-dependent manner

The voltage-gated potassium channel Kv3.4 is a crucial regulator of nociceptive signaling in the dorsal root ganglion (DRG) and the dorsal horn of the spinal cord. Moreover, Kv3.4 dysfunction has been linked to neuropathic pain. Although kinases and phosphatases can directly modulate Kv3.4 gating, the signaling mechanisms regulating the expression and stability of the Kv3.4 protein are generally unknown. We explored a potential role of PKCε and found an unexpected interaction that has a positive effect on Kv3.4 expression. Co-immunoprecipitation studies revealed a physical association between PKCε and Kv3.4 in both heterologous cells and rat DRG neurons. Furthermore, in contrast to the wild-type and constitutively active forms of PKCε, expression of a catalytically inactive form of the enzyme inhibits Kv3.4 expression and membrane localization through a dominant negative effect. Co-expression of Kv3.4 with the wild-type, constitutively active, or catalytically inactive forms of PKCε had no significant effects on Kv3.4 gating. These results suggest that a novel physical interaction of the Kv3.4 channel with functional PKCε primarily determines its stability and localization in DRG neurons. This interaction is akin to those of previously identified accessory ion channel proteins, which could be significant in neural tissues where Kv3.4 regulates electrical signaling.

12-O-Tetradecanoylphorbol-13-acetate increases cardiomyogenesis through PKC/ERK signaling

12-O-Tetradecanoylphorbol-13-acetate (TPA) is the most widely used diacylglycerol (DAG) mimetic agent and inducer of protein kinase C (PKC)-mediated cellular response in biomedical studies. TPA has been proposed as a pluripotent cell differentiation factor, but results obtained have been inconsistent. In the present study we show that TPA can be applied as a cardiomyogenesis-promoting factor for the differentiation of mouse embryonic stem (mES) cells in vitro. The mechanism of TPA action is mediated by the induction of extracellular signal-regulated kinase (ERK) activity and the subsequent phosphorylation of GATA4 transcription factor. Interestingly, general mitogens (FGF, EGF, VEGF and serum) or canonical WNT signalling did not mimic the effect of TPA. Moreover, on the basis of our results, we postulate that a TPA-sensitive population of cardiac progenitor cells exists at a certain time point (after days 6–8 of the differentiation protocol) and that the proposed treatment can be used to increase the multiplication of ES cell-derived cardiomyocytes.

Antimycin A increases bronchopulmonary C-fiber excitability via protein kinase C alpha

Inflammation can increase the excitability of bronchopulmonary C-fibers leading to excessive sensations and reflexes (e.g. wheeze and cough). We have previously shown modulation of peripheral nerve terminal mitochondria by antimycin A causes hyperexcitability in TRPV1-expressing bronchopulmonary C-fibers through the activation of protein kinase C (PKC). Here, we have investigated the PKC isoform responsible for this signaling. We found PKCβ1, PKCδ and PKCε were expressed by many vagal neurons, with PKCα and PKCβ2 expressed by subsets of vagal neurons. In dissociated vagal neurons, antimycin A caused translocation of PKCα but not the other isoforms, and only in TRPV1-lineage neurons. In bronchopulmonary C-fiber recordings, antimycin A increased the number of action potentials evoked by α,β-methylene ATP. Selective inhibition of PKCα, PKCβ1 and PKCβ2 with 50 nM bisindolylmaleimide I prevented the antimycin-induced bronchopulmonary C-fiber hyperexcitability, whereas selective inhibition of only PKCβ1 and PKCβ2 with 50 nM LY333531 had no effect. We therefore conclude that PKCα is required for antimycin-induced increases in bronchopulmonary C-fiber excitability.

5-oxo-ETE activates migration of H295R adrenocortical cells via MAPK and PKC pathways

The OXE receptor is a GPCR activated by eicosanoids produced by the action of 5-lipoxygenase. We previously found that this membrane receptor participates in the regulation of cAMP-dependent and -independent steroidogenesis in human H295R adrenocortical carcinoma cells. In this study we analyzed the effects of the OXE receptor physiological activator 5-oxo-ETE on the growth and migration of H259R cells. While 5-oxo-ETE did not affect the growth of H295R cells, overexpression of OXE receptor caused an increase in cell proliferation, which was further increased by 5-oxo-ETE and blocked by 5-lipoxygenase inhibition. 5-oxo-ETE increased the migratory capacity of H295R cells in wound healing assays, but it did not induce the production of metalloproteases MMP-1, MMP-2, MMP-9 and MMP-10. The pro-migratory effect of 5-oxo-ETE was reduced by pharmacological inhibition of the MEK/ERK1/2, p38 and PKC pathways. 5-oxo-ETE caused significant activation of ERK and p38. ERK activation by the eicosanoid was reduced by the "pan" PKC inhibitor GF109203X but not by the classical PKC inhibitor Gö6976, suggesting the involvement of novel PKCs in this effect. Although H295R cells display detectable phosphorylation of Ser299 in PKCδ, a readout for the activation of this novel PKC, treatment with 5-oxo-ETE per se was unable to induce additional PKCδ activation. Our results revealed signaling effectors activated by 5-oxo-ETE in H295R cells and may have significant implications for our understanding of OXE receptor in adrenocortical cell pathophysiology.

Magnesium lithospermate B protects the endothelium from inflammation-induced dysfunction through activation of Nrf2 pathway

Magnesium lithospermate B (MLB) is an active component of Salvia miltiorrhiza Radix, a traditional Chinese herb used in treating cardiovascular diseases. In this study, we investigated the protective effects of MLB against inflammation-induced endothelial dysfunction in vitro and in vivo, and the underlying mechanisms. Endothelial dysfunction was induced in human dermal microvascular endothelial cells (HMEC-1) in vitro by lipopolysaccharide (LPS, 1 μg/mL). We showed that pretreatment with MLB (10-100 μM) dose-dependently inhibited LPS-induced upregulation of inflammatory cytokines ICAM1, VCAM1, and TNFα, which contributed to reduced leukocytes adhesion and attenuation of endothelial hyperpermeability in HMEC-1 cells. SD rats were injected with LPS (10 mg/kg, ip) to induce endothelial dysfunction in vivo. We showed that pretreatment with MLB (25-100 mg/kg, ip) dose-dependently restored LPS-impaired endothelial-dependent vasodilation in superior mesenteric artery (SMA), attenuated leukocyte adhesion in mesenteric venules and decreased vascular leakage in the lungs. We further elucidated the mechanisms underlying the protective effects of MLB, and revealed that MLB pretreatment inhibited NF-κB activation through inhibition of IκBα degradation and subsequent phosphorylation of NF-κB p65 in vitro and in vivo. In HMEC-1 cells, MLB pretreatment activated the nuclear factor erythroid-2-related factor 2 (Nrf2) pathway. Knockdown of Nrf2 with siRNA abolished the inhibitory effects of MLB on IκBα degradation and ICAM1 up-regulation, which were mimicked by PKC inhibition (Gö6983) or PI3K/Akt inhibition (LY294002). In summary, our results demonstrate that MLB inhibits NF-κB activation through PKC- and PI3K/Akt-mediated Nrf2 activation in HMEC-1 cells and protects against LPS-induced endothelial dysfunction in murine model of acute inflammation.

Claudin 1 Is Highly Upregulated by PKC in MCF7 Human Breast Cancer Cells and Correlates Positively with PKCε in Patient Biopsies

Recent studies provide compelling evidence to suggest that the tight junction protein claudin 1, aberrantly expressed in several cancer types, plays an important role in cancer progression. Dysregulation of claudin 1 has been shown to induce epithelial mesenchymal transition (EMT). Furthermore, activation of the ERK signaling pathway by protein kinase C (PKC) was shown to be necessary for EMT induction. Whether PKC is involved in regulating breast cancer progression has not been addressed. The PKC activator 12-O-tetradecanoylphorbol 13-acetate (TPA) was used to investigate the effect of PKC activity on claudin 1 transcription and protein levels, subcellular distribution, and alterations in EMT markers in human breast cancer (HBC) cell lines. As well, tissue microarray analysis (TMA) of a large cohort of invasive HBC biopsies was conducted to investigate correlations between claudin 1 and PKC isomers. TPA upregulated claudin 1 levels in all HBC cell lines analyzed. In particular, a high induction of claudin 1 protein was observed in the MCF7 cell line. TPA treatment also led to an accumulation of claudin 1 in the cytoplasm. Additionally, we demonstrated that the upregulation of claudin 1 was through the ERK signaling pathway. In patient biopsies, we identified a significant positive correlation between claudin 1, PKCα, and PKCε in ER+ tumors. A similar correlation between claudin 1 and PKCε was identified in ER- tumors, and high PKCε was associated with shorter disease-free survival. Collectively, these studies demonstrate that claudin 1 and the ERK signaling pathway are important players in HBC progression.

nPKCε Mediates SNAP-25 Phosphorylation of Ser-187 in Basal Conditions and After Synaptic Activity at the Neuromuscular Junction

Protein kinase C (PKC) and substrates like SNAP-25 regulate neurotransmission. At the neuromuscular junction (NMJ), PKC promotes neurotransmitter release during synaptic activity. Thirty minutes of muscle contraction enhances presynaptic PKC isoform levels, specifically cPKCβI and nPKCε, through retrograde BDNF/TrkB signaling. This establishes a larger pool of these PKC isoforms ready to promote neuromuscular transmission. The PKC phosphorylation site in SNAP-25 has been mapped to the serine 187 (Ser-187), which is known to enhance calcium-dependent neurotransmitter release in vitro. Here, we localize SNAP-25 at the NMJ and investigate whether cPKCβI and/or nPKCε regulate SNAP-25 phosphorylation. We also investigate whether nerve and muscle cell activities regulate differently SNAP-25 phosphorylation and the involvement of BDNF/TrkB signaling. Our results demonstrate that nPKCε isoform is essential to positively regulate SNAP-25 phosphorylation on Ser-187 and that muscle contraction prevents it. TrkB and cPKCβI do not regulate SNAP-25 protein level or its phosphorylation during neuromuscular activity. The results provide evidence that nerve terminals need both pre- and postsynaptic activities to modulate SNAP-25 phosphorylation and ensure an accurate neurotransmission process.

Astrocyte D-serine modulates the activation of neuronal NOS leading to the development of mechanical allodynia in peripheral neuropathy

Spinal D-serine plays an important role in nociception via an increase in phosphorylation of the N-Methyl-D-aspartate (NMDA) receptor GluN1 subunit (pGluN1). However, the cellular mechanisms underlying this process have not been elucidated. Here, we investigate the possible role of neuronal nitric oxide synthase (nNOS) in the D-serine-induced potentiation of NMDA receptor function and the induction of neuropathic pain in a chronic constriction injury (CCI) model. Intrathecal administration of the serine racemase inhibitor, L-serine O-sulfate potassium salt (LSOS) or the D-serine degrading enzyme, D-amino acid oxidase (DAAO) on post-operative days 0-3 significantly reduced the CCI-induced increase in nitric oxide (NO) levels and nicotinamide adenine dinucleotide phosphate-diaphorase staining in lumbar dorsal horn neurons, as well as the CCI-induced decrease in phosphorylation (Ser847) of nNOS (pnNOS) on day 3 post-CCI surgery. LSOS or DAAO administration suppressed the CCI-induced development of mechanical allodynia and protein kinase C (PKC)-dependent (Ser896) phosphorylation of GluN1 on day 3 post-surgery, which were reversed by the co-administration of the NO donor, 3-morpholinosydnonimine hydrochloride (SIN-1). In naïve mice, exogenous D-serine increased NO levels via decreases in pnNOS. D-serine-induced increases in mechanical hypersensitivity, NO levels, PKC-dependent pGluN1, and NMDA-induced spontaneous nociception were reduced by pretreatment with the nNOS inhibitor, 7-nitroindazole or with the NMDA receptor antagonists, 7-chlorokynurenic acid and MK-801. Collectively, we show that spinal D-serine modulates nNOS activity and concomitant NO production leading to increases in PKC-dependent pGluN1 and ultimately contributing to the induction of mechanical allodynia following peripheral nerve injury.

Lipin1 is required for skeletal muscle development by regulating MEF2c and MyoD expression

KEY POINTS

Lipin1 is critical for skeletal muscle development. Lipin1 regulates MyoD and myocyte-specific enhancer factor 2C (MEF2c) expression via the protein kinase C (PKC)/histone deacetylase 5-mediated pathway. Inhibition of PKCμ activity suppresses myoblast differentiation by inhibiting MyoD and MEF2c expression.

ABSTRACT

Our previous characterization of global lipin1-deficient (fld) mice demonstrated that lipin1 played a novel role in skeletal muscle (SM) regeneration. The present study using cell type-specific Myf5-cre;Lipin1^fl/fl conditional knockout mice (Lipin1^Myf5cKO ) shows that lipin1 is a major determinant of SM development. Lipin1 deficiency induced reduced muscle mass and myopathy. Our results from lipin1-deficient myoblasts suggested that lipin1 regulates myoblast differentiation via the protein kinase Cμ (PKCμ)/histone deacetylase 5 (HDAC5)/myocyte-specific enhancer factor 2C (MEF2c):MyoD-mediated pathway. Lipin1 deficiency leads to the suppression of PKC isoform activities, as well as inhibition of the downstream target of PKCμ, class II deacetylase HDAC5 nuclear export, and, consequently, inhibition of MEF2c and MyoD expression in the SM of lipin1^Myf5cKO mice. Restoration of diacylglycerol-mediated signalling in lipin1 deficient myoblasts by phorbol 12-myristate 13-acetate transiently activated PKC and HDAC5, and upregulated MEF2c expression. Our findings provide insights into the signalling circuitry that regulates SM development, and have important implications for developing intervention aimed at treating muscular dystrophy.

Priming stem cells with protein kinase C activator enhances early stem cell-chondrocyte interaction by increasing adhesion molecules

BACKGROUND

Osteoarthritis (OA) can be defined as degradation of articular cartilage of the joint, and is the most common degenerative disease. To regenerate the damaged cartilage, different experimental approaches including stem cell therapy have been tried. One of the major limitations of stem cell therapy is the poor post-transplantation survival of the stem cells. Anoikis, where insufficient matrix support and adhesion to extracellular matrix causes apoptotic cell death, is one of the main causes of the low post-transplantation survival rate of stem cells. Therefore, enhancing the initial interaction of the transplanted stem cells with chondrocytes could improve the therapeutic efficacy of stem cell therapy for OA. Previously, protein kinase C activator phorbol 12-myristate 13-acetate (PMA)-induced increase of mesenchymal stem cell adhesion via activation of focal adhesion kinase (FAK) has been reported. In the present study, we examine the effect PMA on the adipose-derived stem cells (ADSCs) adhesion and spreading to culture substrates, and further on the initial interaction between ADSC and chondrocytes.

RESULTS

PMA treatment increased the initial adhesion of ADSC to culture substrate and cellular spreading with increased expression of adhesion molecules, such as FAK, vinculin, talin, and paxillin, at both RNA and protein level. Priming of ADSC with PMA increased the number of ADSCs attached to confluent layer of cultured chondrocytes compared to that of untreated ADSCs at early time point (4 h after seeding).

CONCLUSION

Taken together, the results of this study suggest that priming ADSCs with PMA can increase the initial interaction with chondrocytes, and this proof of concept can be used to develop a non-invasive therapeutic approach for treating OA. It may also accelerate the regeneration process so that it can relieve the accompanied pain faster in OA patients. Further in vivo studies examining the therapeutic effect of PMA pretreatment of ADSCs for articular cartilage damage are required.

Ribosomal RACK1:Protein Kinase C βII Phosphorylates Eukaryotic Initiation Factor 4G1 at S1093 To Modulate Cap-Dependent and -Independent Translation Initiation

Eukaryotic ribosomes contain the high-affinity protein kinase C βII (PKCβII) scaffold, receptor for activated C kinase (RACK1), but its role in protein synthesis control remains unclear. We found that RACK1:PKCβII phosphorylates eukaryotic initiation factor 4G1 (eIF4G1) at S1093 and eIF3a at S1364. We showed that reversible eIF4G(S1093) phosphorylation is involved in a global protein synthesis surge upon PKC-Raf-extracellular signal-regulated kinase 1/2 (ERK1/2) activation and in induction of phorbol ester-responsive transcripts, such as cyclooxygenase 2 (Cox-2) and cyclin-dependent kinase inhibitor (p21^Cip1), or in 5' 7-methylguanosine (m⁷G) cap-independent enterovirus translation. Comparison of mRNA and protein levels revealed that eIF4G1 or RACK1 depletion blocked phorbol ester-induced Cox-2 or p21^Cip1 expression mostly at the translational level, whereas PKCβ inhibition reduced them both at the translational and transcript levels. Our findings reveal a physiological role for ribosomal RACK1 in providing the molecular scaffold for PKCβII and its role in coordinating the translational response to PKC-Raf-ERK1/2 activation.

Non-canonical Opioid Signaling Inhibits Itch Transmission in the Spinal Cord of Mice

Chronic itch or pruritus is a debilitating disorder that is refractory to conventional anti-histamine treatment. Kappa opioid receptor (KOR) agonists have been used to treat chronic itch, but the underlying mechanism remains elusive. Here, we find that KOR and gastrin-releasing peptide receptor (GRPR) overlap in the spinal cord, and KOR activation attenuated GRPR-mediated histamine-independent acute and chronic itch in mice. Notably, canonical KOR-mediated Gαi signaling is not required for desensitizing GRPR function. In vivo and in vitro studies suggest that KOR activation results in the translocation of Ca2+-independent protein kinase C (PKC)δ from the cytosol to the plasma membrane, which in turn phosphorylates and inhibits GRPR activity. A blockade of phospholipase C (PLC) in HEK293 cells prevented KOR-agonist-induced PKCδ translocation and GRPR phosphorylation, suggesting a role of PLC signaling in KOR-mediated GRPR desensitization. These data suggest that a KOR-PLC-PKCδ-GRPR signaling pathway in the spinal cord may underlie KOR-agonists-induced anti-pruritus therapies.

Pharmacological Inhibition of Protein Kinase C Reduces West Nile Virus Replication

Flaviviruses are relevant animal and human pathogens that include West Nile virus (WNV), Japanese encephalitis virus, dengue virus, or Zika virus, among others. Currently, no licensed therapy is available to fight flaviviral infections. Protein kinases C (PKCs) constitute a family of multifunctional lipid-dependent isoenzymes that regulate a wide variety of cellular processes (apoptosis, differentiation, proliferation, cellular transformation, motility, adhesion, etc.) being currently considered at the front line of drug development for the treatment of diverse human disorders. PKCs have also been implicated in different steps during viral replication; however, nowadays, results regarding their role in flavivirus replication are controversial. Here we demonstrate that calphostin C and chelerythrine, two broad-PKC inhibitors that target conventional, novel and atypical PKCs, significantly inhibit WNV multiplication in cell culture without affecting cell viability. A reduction of viral yields was observed in treated cells when compared with mock-treated cells. Likewise, immunofluorescence detection of viral enveloped E protein was reduced in treated cells, as was the amount of viral RNA released to the supernatant, mainly in those treated with chelerythrine. On the other hand, two PKC inhibitors specific for conventional and novel isoforms (staurosporine and enzastaurine) did not show any significant effect in WNV multiplication. These results suggested that PKCs, more probably atypical PKCs, are likely involved in WNV multiplication, although both broad-spectrum tested drugs seem to act through different mechanisms, and point to them as potential antiviral candidates for WNV, as well as for other related flaviviruses.

Orexin-B modulates synaptic transmission of rod bipolar cells in rat retina

Orexin-A, -B play a crucial role in arousal and feeding by activating two G-protein-coupled receptors: orexin receptor 1 (OX₁R) and orexin receptor 2 (OX₂R). Orexins, along with orexin receptors, are expressed in retinal neurons, and they have been shown to differentially modulate excitatory AMPA receptors of amacrine and ganglion cells in the inner retina. In this work we report that orexin-B modulates the activity of rod bipolar cells (RBCs) located in the outer retina of rat. Intravitreal injection of orexin-B increased the amplitude of the scotopic electroretinographic b-wave, a reflection of RBC activity, recorded in vivo. Patch clamp recordings in rat retinal slices showed that orexin-B did not change glutamatergic excitatory component of the RBC response driven by photoreceptors. Effects of orexin-B on GABA receptor-mediated synaptic transmission of RBCs were then examined. In retinal slice preparations orexin-B suppressed GABA receptor-mediated inhibitory postsynaptic currents of RBCs in the inner plexiform layer. Furthermore, using whole-cell recordings in isolated RBCs it was shown that orexin-B suppressed GABA_C receptor-, but not GABA_A receptor-, mediated currents of the RBCs, an effect that was blocked by OX₁R and OX₂R antagonists. The orexin-B-induced inhibition of GABA_C currents was likely mediated by a G_i/o/PC-PLC/Ca²⁺-independent PKC signaling pathway, as such inhibition was absent when each step of the above-pathway was blocked with GDP-β-S/pertussis toxin (for G_i/o), D609 (for PLC), bisindolylmaleimide IV (for PKC)/rottlerin (for PKCδ), respectively. The orexin-B-induced potentiation of RBC activity may improve visual acuity and contrast sensitivity of the animal during the dark period (wake phase).

Identifying host regulators and inhibitors of liver stage malaria infection using kinase activity profiles

Plasmodium parasites have extensive needs from their host hepatocytes during the obligate liver stage of infection, yet there remains sparse knowledge of specific host regulators. Here we assess 34 host-targeted kinase inhibitors for their capacity to eliminate Plasmodium yoelii-infected hepatocytes. Using pre-existing activity profiles of each inhibitor, we generate a predictive computational model that identifies host kinases, which facilitate Plasmodium yoelii liver stage infection. We predict 47 kinases, including novel and previously described kinases that impact infection. The impact of a subset of kinases is experimentally validated, including Receptor Tyrosine Kinases, members of the MAP Kinase cascade, and WEE1. Our approach also predicts host-targeted kinase inhibitors of infection, including compounds already used in humans. Three of these compounds, VX-680, Roscovitine and Sunitinib, each eliminate >85% of infection. Our approach is well-suited to uncover key host determinants of infection in difficult model systems, including field-isolated parasites and/or emerging pathogens.

Host kinases facilitate Plasmodium liver stage (LS) infection, but systematic accounting of important players is lacking. Here, the authors use a computational approach and kinase activity profiles to identify host kinase regulators of LS infection and drugs that could eliminate parasite burden.

Biphasic augmentation of alpha-adrenergic contraction by plumbagin in rat systemic arteries

Plumbagin, a hydroxy 1,4-naphthoquinone compound from plant metabolites, exhibits anticancer, antibacterial, and antifungal activities via modulating various signaling molecules. However, its effects on vascular functions are rarely studied except in pulmonary and coronary arteries where NADPH oxidase (NOX) inhibition was suggested as a mechanism. Here we investigate the effects of plumbagin on the contractility of skeletal artery (deep femoral artery, DFA), mesenteric artery (MA) and renal artery (RA) in rats. Although plumbagin alone had no effect on the isometric tone of DFA, 1 µM phenylephrine (PhE)-induced partial contraction was largely augmented by plumbagin (ΔT_Plum, 125% of 80 mM KCl-induced contraction at 1 µM). With relatively higher concentrations (>5 µM), plumbagin induced a transient contraction followed by tonic relaxation of DFA. Similar biphasic augmentation of the PhE-induced contraction was observed in MA and RA. VAS2870 and GKT137831, specific NOX4 inhibitors, neither mimicked nor inhibited ΔT_Plum in DFA. Also, pretreatment with tiron or catalase did not affect ΔT_Plum of DFA. Under the inhibition of PhE-contraction with L-type Ca²⁺ channel blocker (nifedipine, 1 µM), plumbagin still induced tonic contraction, suggesting Ca²⁺-sensitization mechanism of smooth muscle. Although ΔT_Plum was consistently observed under pretreatment with Rho A-kinase inhibitor (Y27632, 1 µM), a PKC inhibitor (GF 109203X, 10 µM) largely suppressed ΔT_Plum. Taken together, it is suggested that plumbagin facilitates the PKC activation in the presence of vasoactive agonists in skeletal arteries. The biphasic contractile effects on the systemic arteries should be considered in the pharmacological studies of plumbagin and 1,4-naphthoquinones.

ELAC (3,12-di-O-acetyl-8-O-tigloilingol), a plant-derived lathyrane diterpene, induces subventricular zone neural progenitor cell proliferation through PKCβ activation

BACKGROUND AND PURPOSE

Pharmacological strategies aimed to facilitate neuronal renewal in the adult brain, by promoting endogenous neurogenesis, constitute promising therapeutic options for pathological or traumatic brain lesions. We have previously shown that non-tumour-promoting PKC-activating compounds (12-deoxyphorbols) promote adult neural progenitor cell (NPC) proliferation in vitro and in vivo, enhancing the endogenous neurogenic response of the brain to a traumatic injury. Here, we show for the first time that a diterpene with a lathyrane skeleton can also activate PKC and promote NPC proliferation.

EXPERIMENTAL APPROACH

We isolated four lathyranes from the latex of Euphorbia plants and tested their effect on postnatal NPC proliferation, using neurosphere cultures. The bioactive lathyrane ELAC (3,12-di-O-acetyl-8-O-tigloilingol) was also injected into the ventricles of adult mice to analyse its effect on adult NPC proliferation in vivo.

KEY RESULTS

The lathyrane ELAC activated PKC and significantly increased postnatal NPC proliferation in vitro, particularly in synergy with FGF2. In addition ELAC stimulated proliferation of NPC, specifically affecting undifferentiated transit amplifying cells. The proliferative effect of ELAC was reversed by either the classical/novel PKC inhibitor Gö6850 or the classical PKC inhibitor Gö6976, suggesting that NPC proliferation is promoted in response to activation of classical PKCs, particularly PKCß. ELAC slightly increased the proportion of NPC expressing Sox2. The effects of ELAC disappeared upon acetylation of its C7-hydroxyl group.

CONCLUSIONS AND IMPLICATIONS

We propose lathyranes like ELAC as new drug candidates to modulate adult neurogenesis through PKC activation. Functional and structural comparisons between ELAC and phorboids are included.

Paclitaxel inhibits the activity and membrane localization of PKCα and PKCβI/II to elicit a decrease in stimulated calcitonin gene-related peptide release from cultured sensory neurons

Peripheral neuropathy is a dose-limiting and debilitating side effect of the chemotherapeutic drug, paclitaxel. Consequently, elucidating the mechanisms by which this drug alters sensory neuronal function is essential for the development of successful therapeutics for peripheral neuropathy. We previously demonstrated that chronic treatment with paclitaxel (3-5days) reduces neuropeptide release stimulated by agonists of TRPV1. Because the activity of TRPV1 channels is modulated by conventional and novel PKC isozymes (c/nPKC), we investigated whether c/nPKC mediate the loss of neuropeptide release following chronic treatment with paclitaxel (300nM; 3 and 5days). Release of the neuropeptide, calcitonin gene-related peptide (CGRP), was measured as an index of neuronal sensitivity. Following paclitaxel treatment, cultured dorsal root ganglia sensory neurons were stimulated with a c/nPKC activator, phorbol 12,13-dibutyrate (PDBu), or a TRPV1 agonist, capsaicin, in the absence and presence of selective inhibitors of conventional PKCα and PKCβI/II isozymes (cPKC). Paclitaxel (300nM; 3days and 5days) attenuated both PDBu- and capsaicin-stimulated release in a cPKC-dependent manner. Under basal conditions, there were no changes in the protein expression, phosphorylation or membrane localization of PKC α, βI or βII, however, paclitaxel decreased cPKC activity as indicated by a reduction in the phosphorylation of cPKC substrates. Under stimulatory conditions, paclitaxel attenuated the membrane translocation of phosphorylated PKC α, βI and βII, providing a rationale for the attenuation in PDBu- and capsaicin-stimulated release. Our findings suggest that a decrease in cPKC activity and membrane localization are responsible for the reduction in stimulated peptide release following chronic treatment with paclitaxel in sensory neurons.

Spinal D-Serine Increases PKC-Dependent GluN1 Phosphorylation Contributing to the Sigma-1 Receptor-Induced Development of Mechanical Allodynia in a Mouse Model of Neuropathic Pain

We have recently shown that spinal sigma-1 receptor (Sig-1R) activation facilitates nociception via an increase in phosphorylation of the N-methyl-D-aspartate (NMDA) receptor GluN1 subunit (pGluN1). The present study was designed to examine whether the Sig-1R-induced facilitative effect on NMDA-induced nociception is mediated by D-serine, and whether D-serine modulates spinal pGluN1 expression and the development of neuropathic pain after chronic constriction injury (CCI) of the sciatic nerve. Intrathecal administration of the D-serine degrading enzyme, D-amino acid oxidase attenuated the facilitation of NMDA-induced nociception induced by the Sig-1R agonist, 2-(4-morpholinethyl)1-phenylcyclohexane carboxylate. Exogenous D-serine increased protein kinase C (PKC)-dependent (Ser896) pGluN1 expression and facilitated NMDA-induced nociception, which was attenuated by preteatment with the PKC inhibitor, chelerythrine. In CCI mice, administration of the serine racemase inhibitor, L-serine O-sulfate potassium salt or D-amino acid oxidase on postoperative days 0 to 3 suppressed CCI-induced mechanical allodynia (MA) and pGluN1 expression on day 3 after CCI surgery. Intrathecal administration of D-serine restored MA as well as the GluN1 phosphorylation on day 3 after surgery that was suppressed by the Sig-1R antagonist, N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine dihydrobromide or the astrocyte inhibitor, fluorocitrate. In contrast, D-serine had no effect on CCI-induced thermal hyperalgesia or GluN1 expression. These results indicate that spinal D-serine: 1) mediates the facilitative effect of Sig-1R on NMDA-induced nociception, 2) modulates PKC-dependent pGluN1 expression, and 3) ultimately contributes to the induction of MA after peripheral nerve injury.

PERSPECTIVE

This report shows that reducing D-serine suppresses central sensitization and significantly alleviates peripheral nerve injury-induced chronic neuropathic pain and that this process is modulated by spinal Sig-1Rs. This preclinical evidence provides a strong rationale for using D-serine antagonists to treat peripheral nerve injury-induced neuropathy.

The Molecular Basis of Toxins' Interactions with Intracellular Signaling via Discrete Portals

An understanding of the molecular mechanisms by which microbial, plant or animal-secreted toxins exert their action provides the most important element for assessment of human health risks and opens new insights into therapies addressing a plethora of pathologies, ranging from neurological disorders to cancer, using toxinomimetic agents. Recently, molecular and cellular biology dissecting tools have provided a wealth of information on the action of these diverse toxins, yet, an integrated framework to explain their selective toxicity is still lacking. In this review, specific examples of different toxins are emphasized to illustrate the fundamental mechanisms of toxicity at different biochemical, molecular and cellular- levels with particular consideration for the nervous system. The target of primary action has been highlighted and operationally classified into 13 sub-categories. Selected examples of toxins were assigned to each target category, denominated as portal, and the modulation of the different portal’s signaling was featured. The first portal encompasses the plasma membrane lipid domains, which give rise to pores when challenged for example with pardaxin, a fish toxin, or is subject to degradation when enzymes of lipid metabolism such as phospholipases A₂ (PLA₂) or phospholipase C (PLC) act upon it. Several major portals consist of ion channels, pumps, transporters and ligand gated ionotropic receptors which many toxins act on, disturbing the intracellular ion homeostasis. Another group of portals consists of G-protein-coupled and tyrosine kinase receptors that, upon interaction with discrete toxins, alter second messengers towards pathological levels. Lastly, subcellular organelles such as mitochondria, nucleus, protein- and RNA-synthesis machineries, cytoskeletal networks and exocytic vesicles are also portals targeted and deregulated by other diverse group of toxins. A fundamental concept can be drawn from these seemingly different toxins with respect to the site of action and the secondary messengers and signaling cascades they trigger in the host. While the interaction with the initial portal is largely determined by the chemical nature of the toxin, once inside the cell, several ubiquitous second messengers and protein kinases/ phosphatases pathways are impaired, to attain toxicity. Therefore, toxins represent one of the most promising natural molecules for developing novel therapeutics that selectively target the major cellular portals involved in human physiology and diseases.

The ATP-Binding Cassette Transporter-2 (ABCA2) Overexpression Modulates Sphingosine Levels and Transcription of the Amyloid Precursor Protein (APP) Gene

The ATP-binding cassette transporter-2 (ABCA2) is a member of a family of multipass transmembrane proteins that use the energy of ATP hydrolysis to transport substrates across membrane bilayers. ABCA2 has also been genetically linked with Alzheimer's disease but the molecular mechanisms are unknown. In this report, we hypothesized that ABCA2 modulation of sphingolipid metabolism activates a signaling pathway that regulates amyloid precursor protein transcription. We found that ABCA2 overexpression in N2a cells was associated with increased mass of the sphingolipid sphingosine, derived from the catabolism of ceramide. ABCA2 overexpression increased in vitro alkaline and acid ceramidase activity. Sphingosine is a physiological inhibitor of protein kinase C (PKC) activity. Pharmacological inhibition of ceramidase activity or activation PKC activity with 12-myristate 13-acetate (PMA) or diacylglycerol (DAG) decreased endogenous APP mRNA levels in ABCA2 overexpressing cells. Treatment with PMA also decreased the expression of a transfected human APP promoter reporter construct, while treatment with a general PKC inhibitor, GF109203x, increased APP promoter activity. In N2a cells, chromatin immunoprecipitation experiments revealed that a repressive complex forms at the AP-1 site in the human APP promoter, consisting of c-jun, c-jun dimerization protein 2 (JDP2) and HDAC3 and this complex was reduced in ABCA2 overexpressing cells. Activation of the human APP promoter in A2 cells was directed by the upstream stimulatory factors USF-1 and USF-2 that bound to an E-box element in vivo. These findings indicate that ABCA2 overexpression modulates sphingosine levels and regulates transcription of the endogenous APP gene.

Novel Evidence of PLC δ2 Involvement in the Regulation of the Differential Evolution of Aneurysms

The biological and molecular mechanisms which are responsible for the formation and possible evolution of human aneurysms are unknown. Previous investigations have pointed to the possible involvement of inositol specific-phospholipase C (PLC) in the mechanisms related to the formation or evolution of intracranial aneurysms, but, thus far, a relationship of one or more PLC isoforms with the biological signals influencing the fate of this lesion has not been demonstrated. The aim of this study was to investigate the expression, activity and possible modification of PLC isoforms in intracranial aneurysms in patients undergoing elective surgical repair after casual identification of unruptured aneurysms, or during emergency surgical repair of ruptured aneurysms. PLC and proliferating cell nuclear antigen (PCNA) expressions were detected by immunoistochemical analysis; PLC activity was obtained by measuring its hydrolytic activity on labelled PIP2; PKC activity was measured by total kinase activity assay. Results indicated no substantial differences between controls and aneurysms, with the only exception being PLC 52 which was nearly absent in controls and ruptured aneurysms, while strongly expressed and functionally active in almost all unruptured aneurysms. In addition, its expression always correlated with the proliferation cell marker PCNA, while its specific activity always correlated to PKC activity. PLC δ2 distribution, regulation and role in human tissues are still unknown Therefore, although preliminary, these data provide a novel insight into the signalling machinery influencing the aneurismal progression.

Natural Product Vibsanin A Induces Differentiation of Myeloid Leukemia Cells through PKC Activation

All-trans retinoic acid (ATRA)-based cell differentiation therapy has been successful in treating acute promyelocytic leukemia, a unique subtype of acute myeloid leukemia (AML). However, other subtypes of AML display resistance to ATRA-based treatment. In this study, we screened natural, plant-derived vibsane-type diterpenoids for their ability to induce differentiation of myeloid leukemia cells, discovering that vibsanin A potently induced differentiation of AML cell lines and primary blasts. The differentiation-inducing activity of vibsanin A was mediated through direct interaction with and activation of protein kinase C (PKC). Consistent with these findings, pharmacological blockade of PKC activity suppressed vibsanin A-induced differentiation. Mechanistically, vibsanin A-mediated activation of PKC led to induction of the ERK pathway and decreased c-Myc expression. In mouse xenograft models of AML, vibsanin A administration prolonged host survival and inhibited PKC-mediated inflammatory responses correlated with promotion of skin tumors in mice. Collectively, our results offer a preclinical proof of concept for vibsanin A as a myeloid differentiation-inducing compound, with potential application as an antileukemic agent. Cancer Res; 76(9); 2698-709. ©2016 AACR.

The novel protein kinase C epsilon isoform modulates acetylcholine release in the rat neuromuscular junction

Background

Various protein kinase C (PKC) isoforms contribute to the phosphorylating activity that modulates neurotransmitter release. In previous studies we showed that nPKCε is confined in the presynaptic site of the neuromuscular junction and its presynaptic function is activity-dependent. Furthermore, nPKCε regulates phorbol ester-induced acetylcholine release potentiation, which further indicates that nPKCε is involved in neurotransmission. The present study is designed to examine the nPKCε involvement in transmitter release at the neuromuscular junction.

Results

We use the specific nPKCε translocation inhibitor peptide εV1-2 and electrophysiological experiments to investigate the involvement of this isoform in acetylcholine release. We observed that nPKCε membrane translocation is key to the synaptic potentiation of NMJ, being involved in several conditions that upregulate PKC isoforms coupling to acetylcholine (ACh) release (incubation with high Ca²⁺, stimulation with phorbol esters and protein kinase A, stimulation with adenosine 3′,5′-cyclic monophosphorothioate, 8-Bromo-, Rp-isomer, sodium salt -Sp-8-BrcAMP-). In all these conditions, preincubation with the nPKCε translocation inhibitor peptide (εV1-2) impairs PKC coupling to acetylcholine release potentiation. In addition, the inhibition of nPKCε translocation and therefore its activity impedes that presynaptic muscarinic autoreceptors and adenosine autoreceptors modulate transmitter secretion.

Conclusions

Together, these results point to the importance of nPKCε isoform in the control of acetylcholine release in the neuromuscular junction.

Post-translational modifications of voltage-gated sodium channels in chronic pain syndromes

In the peripheral sensory nervous system the neuronal expression of voltage-gated sodium channels (Navs) is very important for the transmission of nociceptive information since they give rise to the upstroke of the action potential (AP). Navs are composed of nine different isoforms with distinct biophysical properties. Studying the mutations associated with the increase or absence of pain sensitivity in humans, as well as other expression studies, have highlighted Nav1.7, Nav1.8, and Nav1.9 as being the most important contributors to the control of nociceptive neuronal electrogenesis. Modulating their expression and/or function can impact the shape of the AP and consequently modify nociceptive transmission, a process that is observed in persistent pain conditions. Post-translational modification (PTM) of Navs is a well-known process that modifies their expression and function. In chronic pain syndromes, the release of inflammatory molecules into the direct environment of dorsal root ganglia (DRG) sensory neurons leads to an abnormal activation of enzymes that induce Navs PTM. The addition of small molecules, i.e., peptides, phosphoryl groups, ubiquitin moieties and/or carbohydrates, can modify the function of Navs in two different ways: via direct physical interference with Nav gating, or via the control of Nav trafficking. Both mechanisms have a profound impact on neuronal excitability. In this review we will discuss the role of Protein Kinase A, B, and C, Mitogen Activated Protein Kinases and Ca++/Calmodulin-dependent Kinase II in peripheral chronic pain syndromes. We will also discuss more recent findings that the ubiquitination of Nav1.7 by Nedd4-2 and the effect of methylglyoxal on Nav1.8 are also implicated in the development of experimental neuropathic pain. We will address the potential roles of other PTMs in chronic pain and highlight the need for further investigation of PTMs of Navs in order to develop new pharmacological tools to alleviate pain.

Inhibition of Receptor Dimerization as a Novel Negative Feedback Mechanism of EGFR Signaling

Dimerization of the epidermal growth factor receptor (EGFR) is crucial for initiating signal transduction. We employed raster image correlation spectroscopy to continuously monitor the EGFR monomer-dimer equilibrium in living cells. EGFR dimer formation upon addition of EGF showed oscillatory behavior with a periodicity of about 2.5 min, suggesting the presence of a negative feedback loop to monomerize the receptor. We demonstrated that monomerization of EGFR relies on phospholipase Cγ, protein kinase C, and protein kinase D (PKD), while being independent of Ca2+ signaling and endocytosis. Phosphorylation of the juxtamembrane threonine residues of EGFR (T654/T669) by PKD was identified as the factor that shifts the monomer-dimer equilibrium of ligand bound EGFR towards the monomeric state. The dimerization state of the receptor correlated with the activity of an extracellular signal-regulated kinase, downstream of the EGFR. Based on these observations, we propose a novel, negative feedback mechanism that regulates EGFR signaling via receptor monomerization.

Rise and Fall of Kir2.2 Current by TLR4 Signaling in Human Monocytes: PKC-Dependent Trafficking and PI3K-Mediated PIP2 Decrease

LPSs are widely used to stimulate TLR4, but their effects on ion channels in immune cells are poorly known. In THP-1 cells and human blood monocytes treated with LPS, inwardly rectifying K(+) channel current (IKir,LPS) newly emerged at 1 h, peaked at 4 h (-119 ± 8.6 pA/pF), and decayed afterward (-32 ± 6.7 pA/pF at 24 h). Whereas both the Kir2.1 and Kir2.2 mRNAs and proteins were observed, single-channel conductance (38 pS) of IKir,LPS and small interfering RNA-induced knockdown commonly indicated Kir2.2 than Kir2.1. LPS-induced cytokine release and store-operated Ca(2+) entry were commonly decreased by ML-133, a Kir2 inhibitor. Immunoblot, confocal microscopy, and the effects of vesicular trafficking inhibitors commonly suggested plasma membrane translocation of Kir2.2 by LPS. Both IKir,LPS and membrane translocation of Kir2.2 were inhibited by GF109203X (protein kinase C [PKC] inhibitor) or by transfection with small interfering RNA-specific PKCε. Interestingly, pharmacological activation of PKC by PMA induced both Kir2.1 and Kir2.2 currents. The spontaneously decayed IKir,LPS at 24 h was recovered by PI3K inhibitors but further suppressed by an inhibitor of phosphatidylinositol(3,4,5)-trisphosphate (PIP3) phosphatase (phosphatase and tensin homolog). However, IKir,LPS at 24 h was not affected by Akt inhibitors, suggesting that the decreased phosphatidylinositol(4,5)-bisphosphate availability, that is, conversion into PIP3 by PI3K, per se accounts for the decay of IKir,LPS. Taken together, to our knowledge these data are the first demonstrations that IKir is newly induced by TLR4 stimulation via PKC-dependent membrane trafficking of Kir2.2, and that conversion of phosphatidylinositol(4,5)-bisphosphate to PIP3 modulates Kir2.2. The augmentation of Ca(2+) influx and cytokine release suggests a physiological role for Kir2.2 in TLR4-stimulated monocytes.

PKC-α-dependent augmentation of cAMP and CREB phosphorylation mediates the angiotensin II stimulation of renin in the collecting duct

In contrast to the negative feedback of angiotensin II (ANG II) on juxtaglomerular renin, ANG II stimulates renin in the principal cells of the collecting duct (CD) in rats and mice via ANG II type 1 (AT1R) receptor, independently of blood pressure. In vitro data indicate that CD renin is augmented by AT1R activation through protein kinase C (PKC), but the exact mechanisms are unknown. We hypothesize that ANG II stimulates CD renin synthesis through AT1R via PKC and the subsequent activation of cAMP/PKA/CREB pathway. In M-1 cells, ANG II increased cAMP, renin mRNA (3.5-fold), prorenin, and renin proteins, as well as renin activity in culture media (2-fold). These effects were prevented by PKC inhibition with calphostin C, PKC-α dominant negative, and by PKA inhibition. Forskolin-induced increases in cAMP and renin expression were prevented by calphostin C. PKC inhibition and Ca2+ depletion impaired ANG II-mediated CREB phosphorylation and upregulation of renin. Adenylate cyclase 6 (AC) siRNA remarkably attenuated the ANG II-dependent upregulation of renin mRNA. Physiological activation of AC with vasopressin increased renin expression in M-1 cells. The results suggest that the ANG II-dependent upregulation of renin in the CD depends on PKC-α, which allows the augmentation of cAMP production and activation of PKA/CREB pathway via AC6. This study defines the intracellular signaling pathway involved in the ANG II-mediated stimulation of renin in the CD. This is a novel mechanism responsible for the regulation of local renin-angiotensin system in the distal nephron.

Low PKCα expression within the MRD-HR stratum defines a new subgroup of childhood T-ALL with very poor outcome

Pediatric T-cell Acute Lymphoblastic Leukemia (T-ALL) outcome has improved in the last decades, yet one patient in every four still relapses. Except treatment response and immunophenotype, few markers are reliably prognostic in pediatric T-ALL patients. Aiming to improve T-ALL risk stratification, we investigated a new candidate biomarker with potential prognostic relevance. A phosphoproteomic screening of 98 pediatric T-ALL samples at diagnosis had been performed using the high-throughput Reverse Phase Protein Arrays technique, which led to the identification of PKCαS657 as an activated protein with a broad variation among T-ALL samples. To evaluate PKCα potential as a prognostic biomarker, PKCα expression was analyzed using RQ-PCR in a cohort of 173 patients, representative of ALL2000-ALLR2006 AIEOP study. A threshold of PKCα expression with the highest discrimination for incidence of relapse was identified. Patients with PKCα down-regulation, compared to patients with PKCα levels above the threshold, presented a markedly increased cumulative incidence of relapse (43.8% vs. 10.9%, P<0.001), as well as a worse 4-year overall survival (66% vs. 87.9%, P=0.002) and event-free survival (53.1% vs. 85.2%, P=0.002). In particular, low PKCα expression identified cases with extremely poor outcome within the high-risk minimal residual disease (MRD) stratum, their incidence of relapse being of 69% vs. 15% in the high PKCα levels group. In a multivariate analysis adjusting for main prognostic features, PKCα proved to be an independent prognostic factor related to incidence of relapse. Very high risk patients within the high-risk MRD stratum, identified by PKCα expression, could be proposed for experimental therapeutic protocols.

α1 -Adrenoceptor activation of PKC-ε causes heterologous desensitization of thromboxane receptors in the aorta of spontaneously hypertensive rats

BACKGROUND AND PURPOSE

In the aorta of adult spontaneously hypertensive (SHR), but not in that of normotensive Wistar-Kyoto (WKY), rats, previous exposure to phenylephrine inhibits subsequent contractions to PGE2 . The present experiments were designed to examine the mechanism(s) underlying this inhibition.

EXPERIMENTAL APPROACH

Isometric tension was measured in isolated rings of SHR and WKY aortae. Gene expression and protein presence were measured by quantitative real-time PCR and Western blotting respectively.

KEY RESULTS

In aorta of 18 weeks SHR, but not age-matched WKY, pre-exposure to phenylephrine inhibited subsequent contractions to PGE2 that were mediated by thromboxane prostanoid (TP) receptors. This inhibition was not observed in preparations of pre-hypertensive 5-week-old SHR, and was significantly larger in those of 36- than 18-week-old SHR. Pre-exposure to the PKC activator, phorbol 12,13-dibutyrate, also inhibited subsequent contractions to PGE2 in SHR aortae. The selective inhibitor of PKC-ε, ε-V1-2, abolished the desensitization caused by pre-exposure to phenylephrine. Two molecular PKC bands were detected and their relative intensities differed in 36-week-old WKY and SHR vascular smooth muscle. The mRNA expressions of PKC-α, PKC-ε, PK-N2 and PKC-ζ and of G protein-coupled kinase (GRK)-2, GRK4 and β-arrestin2 were higher in SHR than WKY aortae.

CONCLUSIONS AND IMPLICATIONS

These experiments suggest that in the SHR but not the WKY aorta, α1 -adrenoceptor activation desensitizes TP receptors through activation of PKC-ε. This heterologous desensitization is a consequence of the chronic exposure to high arterial pressure.

Circulating Pneumolysin Is a Potent Inducer of Cardiac Injury during Pneumococcal Infection

Streptococcus pneumoniae accounts for more deaths worldwide than any other single pathogen through diverse disease manifestations including pneumonia, sepsis and meningitis. Life-threatening acute cardiac complications are more common in pneumococcal infection compared to other bacterial infections. Distinctively, these arise despite effective antibiotic therapy. Here, we describe a novel mechanism of myocardial injury, which is triggered and sustained by circulating pneumolysin (PLY). Using a mouse model of invasive pneumococcal disease (IPD), we demonstrate that wild type PLY-expressing pneumococci but not PLY-deficient mutants induced elevation of circulating cardiac troponins (cTns), well-recognized biomarkers of cardiac injury. Furthermore, elevated cTn levels linearly correlated with pneumococcal blood counts (r=0.688, p=0.001) and levels were significantly higher in non-surviving than in surviving mice. These cTn levels were significantly reduced by administration of PLY-sequestering liposomes. Intravenous injection of purified PLY, but not a non-pore forming mutant (PdB), induced substantial increase in cardiac troponins to suggest that the pore-forming activity of circulating PLY is essential for myocardial injury in vivo. Purified PLY and PLY-expressing pneumococci also caused myocardial inflammatory changes but apoptosis was not detected. Exposure of cultured cardiomyocytes to PLY-expressing pneumococci caused dose-dependent cardiomyocyte contractile dysfunction and death, which was exacerbated by further PLY release following antibiotic treatment. We found that high PLY doses induced extensive cardiomyocyte lysis, but more interestingly, sub-lytic PLY concentrations triggered profound calcium influx and overload with subsequent membrane depolarization and progressive reduction in intracellular calcium transient amplitude, a key determinant of contractile force. This was coupled to activation of signalling pathways commonly associated with cardiac dysfunction in clinical and experimental sepsis and ultimately resulted in depressed cardiomyocyte contractile performance along with rhythm disturbance. Our study proposes a detailed molecular mechanism of pneumococcal toxin-induced cardiac injury and highlights the major translational potential of targeting circulating PLY to protect against cardiac complications during pneumococcal infections.

The novel protein kinase C epsilon isoform at the adult neuromuscular synapse: location, regulation by synaptic activity-dependent muscle contraction through TrkB signaling and coupling to ACh release

Background

Protein kinase C (PKC) regulates a variety of neural functions, including neurotransmitter release. Although various PKC isoforms can be expressed at the synaptic sites and specific cell distribution may contribute to their functional diversity, little is known about the isoform-specific functions of PKCs in neuromuscular synapse. The present study is designed to examine the location of the novel isoform nPKCε at the neuromuscular junction (NMJ), their synaptic activity-related expression changes, its regulation by muscle contraction, and their possible involvement in acetylcholine release.

Results

We use immunohistochemistry and confocal microscopy to demonstrate that the novel isoform nPKCε is exclusively located in the motor nerve terminals of the adult rat NMJ. We also report that electrical stimulation of synaptic inputs to the skeletal muscle significantly increased the amount of nPKCε isoform as well as its phosphorylated form in the synaptic membrane, and muscle contraction is necessary for these nPKCε expression changes. The results also demonstrate that synaptic activity-induced muscle contraction promotes changes in presynaptic nPKCε through the brain-derived neurotrophic factor (BDNF)-mediated tyrosine kinase receptor B (TrkB) signaling. Moreover, nPKCε activity results in phosphorylation of the substrate MARCKS involved in actin cytoskeleton remodeling and related with neurotransmission. Finally, blocking nPKCε with a nPKCε-specific translocation inhibitor peptide (εV1-2) strongly reduces phorbol ester-induced ACh release potentiation, which further indicates that nPKCε is involved in neurotransmission.

Conclusions

Together, these results provide a mechanistic insight into how synaptic activity-induced muscle contraction could regulate the presynaptic action of the nPKCε isoform and suggest that muscle contraction is an important regulatory step in TrkB signaling at the NMJ.

Sphingosylphosphorylcholine potentiates vasoreactivity and voltage-gated Ca2+ entry via NOX1 and reactive oxygen species

Aims

Sphingosylphosphorylcholine (SPC) elicits vasoconstriction at micromolar concentrations. At lower concentrations (≤1 µmol/L), however, it does not constrict intrapulmonary arteries (IPAs), but strongly potentiates vasoreactivity. Our aim was to determine whether this also occurs in a systemic artery and to delineate the signalling pathway.

Methods and results

Rat mesenteric arteries and IPAs mounted on a myograph were challenged with ∼25 mmol/L [K⁺] to induce a small vasoconstriction. SPC (1 µmol/L) dramatically potentiated this constriction in all arteries by ∼400%. The potentiation was greatly suppressed or abolished by inhibition of phospholipase C (PLC; U73122), PKCε (inhibitory peptide), Src (PP2), and NADPH oxidase (VAS2870), and also by Tempol (superoxide scavenger), but not by inhibition of Rho kinase (Y27632). Potentiation was lost in mesenteric arteries from p47^phox–/–, but not NOX2^−/–, mice. The intracellular superoxide generator LY83583 mimicked the effect of SPC. SPC elevated reactive oxygen species (ROS) in vascular smooth muscle cells, and this was blocked by PP2, VAS2870, and siRNA knockdown of PKCε. SPC (1 µmol/L) significantly reduced the EC₅₀ for U46619-induced vasoconstriction, an action ablated by Tempol. In patch-clamped mesenteric artery cells, SPC (200 nmol/L) enhanced Ba²⁺ current through L-type Ca²⁺ channels, an action abolished by Tempol but mimicked by LY83583.

Conclusion

Our results suggest that low concentrations of SPC activate a PLC-coupled and NOX1-mediated increase in ROS, with consequent enhancement of voltage-gated Ca²⁺ entry and thus vasoreactivity. We speculate that this pathway is not specific for SPC, but may also contribute to vasoconstriction elicited by other G-protein coupled receptor and PLC-coupled agonists.

Orexin-A differentially modulates AMPA-preferring responses of ganglion cells and amacrine cells in rat retina

By activating their receptors (OX1R and OX2R) orexin-A/B regulate wake/sleeping states, feeding behaviors, but the function of these peptides in the retina remains unknown. Using patch-clamp recordings and calcium imaging in rat isolated retinal cells, we demonstrated that orexin-A suppressed α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA)-preferring receptor-mediated currents (AMPA-preferring currents) in ganglion cells (GCs) through OX1R, but potentiated those in amacrine cells (ACs) through OX2R. Consistently, in rat retinal slices orexin-A suppressed light-evoked AMPA-preferring receptor-mediated excitatory postsynaptic currents in GCs, but potentiated those in ACs. Intracellular dialysis of GDP-β-S or preincubation with the Gi/o inhibitor pertussis toxin (PTX) abolished both the effects. Either cAMP/the protein kinase A (PKA) inhibitor Rp-cAMP or cGMP/the PKG blocker KT5823 failed to alter the orexin-A effects. Whilst both of them involved activation of protein kinase C (PKC), the effects on GCs and ACs were respectively eliminated by the phosphatidylinositol (PI)-phospholipase C (PLC) inhibitor and phosphatidylcholine (PC)-PLC inhibitor. Moreover, in GCs orexin-A increased [Ca(2+)]i and the orexin-A effect was blocked by intracellular Ca(2+)-free solution and by inositol 1,4,5-trisphosphate (IP3) receptor antagonists. In contrast, orexin-A did not change [Ca(2+)]i in ACs and the orexin-A effect remained in intracellular or extracellular Ca(2+)-free solution. We conclude that a distinct Gi/o/PI-PLC/IP3/Ca(2+)-dependent PKC signaling pathway, following the activation of OX1R, is likely responsible for the orexin-A effect on GCs, whereas a Gi/o/PC-PLC/Ca(2+)-independent PKC signaling pathway, following the activation of OX2R, mediates the orexin-A effect on ACs. These two actions of orexin-A, while working in concert, provide a characteristic way for modulating information processing in the inner retina.

Protein kinase Cδ promotes proliferation and induces malignant transformation in skeletal muscle

In this paper, we investigated the isoform-specific roles of certain protein kinase C (PKC) isoforms in the regulation of skeletal muscle growth. Here, we provide the first intriguing functional evidence that nPKCδ (originally described as an inhibitor of proliferation in various cells types) is a key player in promoting both in vitro and in vivo skeletal muscle growth. Recombinant overexpression of a constitutively active nPKCδ in C2C12 myoblast increased proliferation and inhibited differentiation. Conversely, overexpression of kinase-negative mutant of nPKCδ (DN-nPKCδ) markedly inhibited cell growth. Moreover, overexpression of nPKCδ also stimulated in vivo tumour growth and induced malignant transformation in immunodeficient (SCID) mice whereas that of DN-nPKCδ suppressed tumour formation. The role of nPKCδ in the formation of rhabdomyosarcoma was also investigated where recombinant overexpression of nPKCδ in human rhabdomyosarcoma RD cells also increased cell proliferation and enhanced tumour formation in mouse xenografts. The other isoforms investigated (PKCα, β, ε) exerted only minor (mostly growth-inhibitory) effects in skeletal muscle cells. Collectively, our data introduce nPKCδ as a novel growth-promoting molecule in skeletal muscles and invite further trials to exploit its therapeutic potential in the treatment of skeletal muscle malignancies.

FZD1 activates protein kinase C delta-mediated drug-resistance in multidrug-resistant MES-SA/Dx5 cancer cells

Multidrug-resistant (MDR) cancer is a major clinical problem in chemotherapy of cancer patients. We have noted inappropriate PKCδ hypomethylation and overexpression of genes in the PKCδ/AP-1 pathway in the human uterus sarcoma drug-resistant cell line, MES-SA/Dx5 cells, which also overexpress p-glycoprotein (ABCB1). Recent studies have indicated that FZD1 is overexpressed in both multidrug-resistant cancer cell lines and in clinical tumor samples. These data have led us to hypothesize that the FZD1-mediated PKCδ signal-transduction pathway may play an important role in drug resistance in MES-SA/Dx5 cells. In this work, the PKCδ inhibitor Rottlerin was found to reduce ABCB1 expression and to inhibit the MDR drug pumping ability in the MES-SA/Dx5 cells when compared with the doxorubicin-sensitive parental cell line, MES-SA. PKCδ was up-regulated with concurrent up-regulation of the mRNA levels of the AP-1-related factors, c-JUN and c-FOS. Activation of AP-1 also correlated with up-regulation of the AP-1 downstream genes HGF and EGR1. Furthermore, AP-1 activities were reduced and the AP-1 downstream genes were down-regulated in Rottlerin-treated or PKCδ shRNA-transfected cells. MES-SA/Dx5 cells were resensitized to doxorubicin-induced toxicity by co-treatment with doxorubicin and Rottlerin or PKCδ shRNA. In addition, cell viability and drug pump-out ability were significantly reduced in the FZD1 inhibitor curcumin-treated and FZD1 shRNA-knockdown MES-SA/Dx5 cells, indicating involvement of PKCδ in FZD1-modulated ABCB1 expression pathway. Taken together, our data demonstrate that FZD1 regulates PKCδ, and the PKCδ/AP-1 signalling transduction pathway plays an important role in drug resistance in MES-SA/Dx5 cells.

Biology of diabetic neuropathy

More than half of all patients with diabetes develop neuropathic disorders affecting the distal sensory and/or motor nerves, or autonomic or cranial nerve functions. Glycemic control can decrease the incidence of neuropathy but is not adequate alone to prevent or treat the disease. This chapter introduces diabetic neuropathy with a morphological description of the disease then describes our current understanding of metabolic and molecular mechanisms that contribute to neurovascular dysfunctions. Key mechanisms include glucose and lipid imbalances and insulin resistance that are interconnected via oxidative stress, inflammation, and altered gene expression. These complex interactions should be considered for the development of new treatment strategies against the onset or progression of neuropathy. Advances in understanding the combined metabolic stressors and the novel study of epigenetics suggest new therapeutic targets to combat this morbid and intractable disease affecting millions of patients with type 1 or type 2 diabetes.

Excitation of rat sympathetic neurons via M1 muscarinic receptors independently of Kv7 channels

The slow cholinergic transmission in autonomic ganglia is known to be mediated by an inhibition of K_v7 channels via M₁ muscarinic acetylcholine receptors. However, in the present experiments using primary cultures of rat superior cervical ganglion neurons, the extent of depolarisation caused by the M₁ receptor agonist oxotremorine M did not correlate with the extent of K_v7 channel inhibition in the very same neuron. This observation triggered a search for additional mechanisms. As the activation of M₁ receptors leads to a boost in protein kinase C (PKC) activity in sympathetic neurons, various PKC enzymes were inhibited by different means. Interference with classical PKC isoforms led to reductions in depolarisations and in noradrenaline release elicited by oxotremorine M, but left the K_v7 channel inhibition by the muscarinic agonist unchanged. M₁ receptor-induced depolarisations were also altered when extra- or intracellular Cl⁻ concentrations were changed, as were depolarising responses to γ-aminobutyric acid. Depolarisations and noradrenaline release triggered by oxotremorine M were reduced by the non-selective Cl⁻ channel blockers 4-acetamido-4′-isothiocyanato-stilbene-2,2′-disulfonic acid and niflumic acid. Oxotremorine M induced slowly rising inward currents at negative membrane potentials that were blocked by inhibitors of Ca²⁺-activated Cl⁻ and TMEM16A channels and attenuated by PKC inhibitors. These channel blockers also reduced oxotremorine M-evoked noradrenaline release. Together, these results reveal that slow cholinergic excitation of sympathetic neurons involves the activation of classical PKCs and of Ca²⁺-activated Cl⁻ channels in addition to the well-known inhibition of K_v7 channels.

Protein kinase C, focal adhesions and the regulation of cell migration

Cell adhesion to extracellular matrix is a complex process involving protrusive activity driven by the actin cytoskeleton, engagement of specific receptors, followed by signaling and cytoskeletal organization. Thereafter, contractile and endocytic/recycling activities may facilitate migration and adhesion turnover. Focal adhesions, or focal contacts, are widespread organelles at the cell-matrix interface. They arise as a result of receptor interactions with matrix ligands, together with clustering. Recent analysis shows that focal adhesions contain a very large number of protein components in their intracellular compartment. Among these are tyrosine kinases, which have received a great deal of attention, whereas the serine/threonine kinase protein kinase C has received much less. Here the status of protein kinase C in focal adhesions and cell migration is reviewed, together with discussion of its roles and potential substrates.

TNFa alter cholesterol metabolism in human macrophages via PKC-θ-dependent pathway

BACKGROUND

Studies have shown that inflammation promoted atherosclerotic progression; however, it remains unclear whether inflammation promoted atherosclerotic progression properties by altering cholesterol metabolism in human macrophages. In the present study, we evaluated a potential mechanism of inflammation on atherogenic effects. We evaluated the ability of TNFa to affect Reverse cholesterol transport (RCT) and cholesterol uptake and its mechanism(s) of action in human macrophages.

RESULTS

We initially determined the potential effects of TNFa on cholesterol efflux in the human macrophages. We also determined alterations in mRNA and protein levels of ABCA1, ABCG1, LXRa, CD-36, SR-A in human macrophages using quantitative real-time polymerase chain reaction (PCR) and Western immunoblot analyses. The cholesterol efflux rate and protein expression of ABCA1, ABCG1, LXRa, CD-36, SR-A were quantified in human macrophages under PKC-θ inhibition using PKC-θ siRNA. Our results showed that TNFa inhibited the rate of cholesterol efflux and down-regulation the expression levels of ABCA1, ABCG1 and LXRa and up-regulation the expression levels of CD-36, SR-A in human macrophages; PKC-θ inhibition by PKC-θ siRNA attenuated the effect of TNFa on ABCA1, ABCG1, LXRa, SR-A, CD-36 expression.

CONCLUSIONS

Our results suggest TNFa alter cholesterol metabolism in human macrophages through the inhibition of Reverse cholesterol transport and enhancing cholesterol uptake via PKC-θ-dependent pathway, implicating a potential mechanism of inflammation on atherogenic effects.