Effects of the selective bisindolylmaleimide protein kinase C inhibitor GF 109203X on P-glycoprotein-mediated multidrug resistance

Formulation of Liver-Specific PLGA-DY-635 Nanoparticles Loaded with the Protein Kinase C Inhibitor Bisindolylmaleimide I

Bisindolylmaleimide I (BIM-I) is a competitive pan protein kinase C inhibitor with anti-inflammatory and anti-metastatic properties, suggested to treat inflammatory diseases and various cancer entities. However, despite its therapeutic potential, BIM-I has two major drawbacks, i.e., it has a poor water solubility, and it binds the human ether-à-go-go-related gene (hERG) ion channels, potentially causing deadly arrhythmias. In this case, a targeted delivery of BIM-I is imperative to minimize peripheral side effects. To circumvent these drawbacks BIM-I was encapsulated into nanoparticles prepared from poly(lactic-co-glycolic acid) (PLGA) functionalized by the near-infrared dye DY-635. DY-635 served as an active targeting moiety since it selectively binds the OATP1B1 and OATP1B3 transporters that are highly expressed in liver and cancer cells. PLGA-DY-635 (BIM-I) nanoparticles were produced by nanoprecipitation and characterized using dynamic light scattering, analytical ultracentrifugation, and cryogenic transmission electron microscopy. Particle sizes were found to be in the range of 20 to 70 nm, while a difference in sizes between the drug-loaded and unloaded particles was observed by all analytical techniques. In vitro studies demonstrated that PLGA-DY-635 (BIM-I) NPs prevent the PKC activation efficiently, proving the efficacy of the inhibitor after its encapsulation, and suggesting that BIM-I is released from the PLGA-NPs. Ultimately, our results present a feasible formulation strategy that improved the cytotoxicity profile of BIM-I and showed a high cellular uptake in the liver as demonstrated in vivo by intravital microscopy investigations.

Effect of surfactant on the size and stability of PLGA nanoparticles encapsulating a protein kinase C inhibitor

Nowadays many drugs with improved therapeutic efficacy are discovered but cannot be utilized due to their low solubility and insufficient bioavailability. An example of such a drug molecule is a protein kinase C inhibitor that influences an enzyme which plays an important role in several signal transduction cascades. The aim of this study was to formulate a stable nanoparticle dispersion of the PKC inhibitor encapsulated into PLGA nanoparticles (NPs). Encapsulation of the PKC inhibitor into PLGA NPs of 100-200 nm diameter should provide a targeted delivery to the inflammation sites. The NPs were prepared via nanoprecipitation and different surfactants were investigated: Fully and partially hydrolyzed poly(vinyl alcohol) (PVA, Mowiol X-88 and X-98), poloxamers (Pluronic F68 and F127) and polysorbates (Tween 20 and 80). From all surfactants tested, only NPs prepared with partially hydrolyzed PVA (Mowiol X-88) provided the desired stability throughout the downstream processes. These NPs were subsequently analyzed regarding their particle size, polydispersity, encapsulation efficiency and loading capacity. Dynamic light scattering results revealed that monodisperse NPs of 150-220 nm were formed, a size range that favors targeted delivery. The drug encapsulation efficiency varied from 31 to 75% with a drug loading of 1.3-2%. Moreover, the long-term stability was studied and the residual amount of PVA of the NP solutions was quantified via nuclear magnetic resonance (NMR) measurements. The shell-less hen's egg model was used to test toxic effects (hemorrhage, vascular lysis, thrombosis, hemolysis and lethality) of the NPs in a more complex biological system under dynamic flow conditions.

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.

Differential roles of PKC isoforms (PKCs) in GnRH stimulation of MAPK phosphorylation in gonadotrope derived cells

The role of protein kinase C (PKC) isoforms (PKCs) in GnRH-stimulated MAPK [ERK1/2, JNK1/2 and p38) phosphorylation was examined in gonadotrope derived cells. GnRH induced a protracted activation of ERK1/2 and a slower and more transient activation of JNK1/2 and p38MAPK. Gonadotropes express conventional PKCα and PKCβII, novel PKCδ, PKCε and PKCθ, and atypical PKC-ι/λ. The use of green fluorescent protein (GFP)-PKCs constructs revealed that GnRH induced rapid translocation of PKCα and PKCβII to the plasma membrane, followed by their redistribution to the cytosol. PKCδ and PKCε localized to the cytoplasm and Golgi, followed by the rapid redistribution by GnRH of PKCδ to the perinuclear zone and of PKCε to the plasma membrane. The use of dominant negatives for PKCs and peptide inhibitors for the receptors for activated C kinase (RACKs) has revealed differential role for PKCα, PKCβII, PKCδ and PKCε in ERK1/2, JNK1/2 and p38MAPK phosphorylation in a ligand-and cell context-dependent manner. The paradoxical findings that PKCs activated by GnRH and PMA play a differential role in MAPKs phosphorylation may be explained by persistent vs. transient redistribution of selected PKCs or redistribution of a given PKC to the perinuclear zone vs. the plasma membrane. Thus, we have identified the PKCs involved in GnRH stimulated MAPKs phosphorylation in gonadotrope derived cells. Once activated, the MAPKs will mediate the transcription of the gonadotropin subunits and GnRH receptor genes.

Protein Kinases C-Mediated Regulations of Drug Transporter Activity, Localization and Expression

Drug transporters are now recognized as major actors in pharmacokinetics, involved notably in drug–drug interactions and drug adverse effects. Factors that govern their activity, localization and expression are therefore important to consider. In the present review, the implications of protein kinases C (PKCs) in transporter regulations are summarized and discussed. Both solute carrier (SLC) and ATP-binding cassette (ABC) drug transporters can be regulated by PKCs-related signaling pathways. PKCs thus target activity, membrane localization and/or expression level of major influx and efflux drug transporters, in various normal and pathological types of cells and tissues, often in a PKC isoform-specific manner. PKCs are notably implicated in membrane insertion of bile acid transporters in liver and, in this way, are thought to contribute to cholestatic or choleretic effects of endogenous compounds or drugs. The exact clinical relevance of PKCs-related regulation of drug transporters in terms of drug resistance, pharmacokinetics, drug–drug interactions and drug toxicity remains however to be precisely determined. This issue is likely important to consider in the context of the development of new drugs targeting PKCs-mediated signaling pathways, for treating notably cancers, diabetes or psychiatric disorders.

Sustained Contraction in Vascular Smooth Muscle by Activation of L-type Ca2+ Channels Does Not Involve Ca2+ Sensitization or Caldesmon

Vascular smooth muscle (VSM) is unique in its ability to maintain an intrinsic level of contractile force, known as tone. Vascular tone is believed to arise from the constitutive activity of membrane-bound L-type Ca²⁺ channels (LTCC). This study used a pharmacological agonist of LTCC, Bay K8644, to elicit a sustained, sub-maximal contraction in VSM that mimics tone. Downstream signaling was investigated in order to determine what molecules are responsible for tone. Medial strips of swine carotid artery were stimulated with 100 nM Bay K8644 to induce a sustained level of force. Force and phosphorylation levels of myosin light chain (MLC), MAP kinase, MYPT1, CPI-17, and caldesmon were measured during Bay K8644 stimulation in the presence and absence of nifedipine, ML-7, U0126, bisindolylmaleimide (Bis), and H-1152. Nifedipine and ML-7 inhibited force and MLC phosphorylation in response to Bay K8644. Inhibition of Rho kinase (H-1152) but not PKC (Bis) inhibited Bay K8644 induced force. U0126 significantly increased Bay K8644-dependent force with no effect on MLC phosphorylation. Neither CPI-17 nor caldesmon phosphorylation were increased during the maintenance of sustained force. Our results suggest that force due to the influx of calcium through LTCCs is partially MLC phosphorylation-dependent but does not involve PKC or caldesmon. Interestingly, inhibition of MLC kinase (MLCK) and PKC significantly increased MAP kinase phosphorylation suggesting that MLCK and PKC may directly or indirectly inhibit MAP kinase activity during prolonged contractions induced by Bay K8544.

Differential roles of PKC isoforms (PKCs) and Ca2+ in GnRH and phorbol 12-myristate 13-acetate (PMA) stimulation of p38MAPK phosphorylation in immortalized gonadotrope cells

We examined the role of PKCs and Ca²⁺ in GnRH-stimulated p38MAPK phosphorylation in the gonadotrope derived αT3-1 and LβT2 cell lines. GnRH induced a slow and rapid increase in p38MAPK phosphorylation in αT3-1 and LβT2 cells respectively, while PMA gave a slow response. The use of dominant negatives for PKCs and peptide inhibitors for the receptors for activated C kinase (RACKs), has revealed differential role for PKCα, PKCβII, PKCδ and PKCε in p38MAPK phosphorylation in a ligand-and cell context-dependent manner. The paradoxical findings that PKCs activated by GnRH and PMA play a differential role in p38MAPK phosphorylation may be explained by differential localization of the PKCs. Basal, GnRH- and PMA- stimulation of p38MAPK phosphorylation in αT3-1 cells is mediated by Ca²⁺ influx via voltage-gated Ca²⁺ channels and Ca²⁺ mobilization, while in the differentiated LβT2 gonadotrope cells it is mediated only by Ca²⁺ mobilization. p38MAPK resides in the cell membrane and is relocated to the nucleus by GnRH (∼5 min). Thus, we have identified the PKCs and the Ca²⁺ pools involved in GnRH stimulated p38MAPK phosphorylation.

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.

Protein Kinase C-Independent Inhibition of Organic Cation Transporter 1 Activity by the Bisindolylmaleimide Ro 31-8220

Ro 31–8220 is a potent protein kinase C (PKC) inhibitor belonging to the chemical class of bisindolylmaleimides (BIMs). Various PKC-independent effects of Ro 31–8220 have however been demonstrated, including inhibition of the ATP-binding cassette drug transporter breast cancer resistance protein. In the present study, we reported that the BIM also blocks activity of the solute carrier organic cation transporter (OCT) 1, involved in uptake of marketed drugs in the liver, in a PKC-independent manner. Ro 31–8220, in contrast to other pan-PKC inhibitors such as staurosporine and chelerythrine, was thus shown to cis-inhibit uptake of the reference OCT1 substrate tetraethylammonium in OCT1-transfected HEK293 cells in a concentration-dependent manner (IC₅₀ = 0.18 μM) and without altering membrane expression of OCT1. This blockage of OCT1 was also observed in human hepatic HepaRG cells that constitutionally express OCT1. It likely occurred through a mixed mechanism of inhibition. Ro 31–8220 additionally trans-inhibited TEA uptake in OCT1-transfected HEK293 cells, which likely discards a transport of Ro 31–8220 by OCT1. Besides Ro 31–8220, 7 additional BIMs, including the PKC inhibitor LY 333531, inhibited OCT1 activity, whereas 4 other BIMs were without effect. In silico analysis of structure-activity relationships next revealed that various molecular descriptors, especially 3D-WHIM descriptors related to total size, correspond to key physico-chemical parameters for inhibition of OCT1 activity by BIMs. In addition to activity of OCT1, Ro 31–8220 inhibited those of other organic cation transporters such as multidrug and toxin extrusion protein (MATE) 1 and MATE2-K, whereas, by contrast, it stimulated that of OCT2. Taken together, these data extend the nature of cellular off-targets of the BIM Ro 31–8220 to OCT1 and other organic cation transporters, which has likely to be kept in mind when using Ro 31–8220 and other BIMs as PKC inhibitors in experimental or clinical studies.

GnRH evokes localized subplasmalemmal calcium signaling in gonadotropes

The binding of GnRH to its receptor initiates signaling cascades in gonadotropes, which result in enhanced LH and FSH biosynthesis and secretion. This process is necessary for follicular maturation and ovulation. Calcium influx activates MAPKs, which lead to increased transcription of LH and FSH genes. Previous research suggests that two MAPK signaling pathways, ERK and jun-N-terminal kinase, are activated by either calcium influx through L-type calcium channels or by global calcium signals originating from intracellular stores, respectively. Here we continued this investigation to further elucidate molecular mechanisms transducing GnRH receptor stimulation to ERK activation. Although it is known that GnRH activation of ERK requires calcium influx through L-type calcium channels, direct evidence supporting an underlying local calcium signaling mechanism was lacking. Here we used a combination of electrophysiology and total internal reflection fluorescence microscopy to visualize discrete sites of calcium influx (calcium sparklets) in gonadotrope-derived αT3-1 cells in real time. GnRH increased localized calcium influx and promoted ERK activation. The L-type calcium channel agonist FPL 64176 enhanced calcium sparklets and ERK activation in a manner indistinguishable from GnRH. Conversely, the L-type calcium channel antagonist nicardipine inhibited not only localized calcium sparklets but also ERK activation in response to GnRH. GnRH-dependent stimulation of L-type calcium channels was found to require protein kinase C and a dynamic actin cytoskeleton. Taken together, we provide the first direct evidence for localized L-type calcium channel signaling in αT3-1 cells and demonstrate the utility of our approach for investigating signaling mechanisms and cellular organization in gonadotropes.

Protein kinase C inhibitor, GF109203X attenuates osteoclastogenesis, bone resorption and RANKL-induced NF-κB and NFAT activity

Osteolytic bone diseases are characterized by excessive osteoclast formation and activation. Protein kinase C (PKC)-dependent pathways regulate cell growth, differentiation and apoptosis in many cellular systems, and have been implicated in cancer development and osteoclast formation. A number of PKC inhibitors with anti-cancer properties have been developed, but whether they might also influence osteolysis (a common complication of bone invading cancers) is unclear. We studied the effects of the PKC inhibitor compound, GF109203X on osteoclast formation and activity, processes driven by receptor activator of NFκB ligand (RANKL). We found that GF109203X strongly and dose dependently suppresses osteoclastogenesis and osteoclast activity in RANKL-treated primary mouse bone marrow cells. Consistent with this GF109203X reduced expression of key osteoclastic genes, including cathepsin K, calcitonin receptor, tartrate resistant acid phosphatase (TRAP) and the proton pump subunit V-ATPase-d2 in RANKL-treated primary mouse bone marrow cells. Expression of these proteins is dependent upon RANKL-induced NF-κB and NFAT transcription factor actions; both were reduced in osteoclast progenitor populations by GF109203X treatment, notably NFATc1 levels. Furthermore, we showed that GF109203X inhibits RANKL-induced calcium oscillation. Together, this study shows GF109203X may block osteoclast functions, suggesting that pharmacological blockade of PKC-dependent pathways has therapeutic potential in osteolytic diseases.

Protein kinase C inhibitors: a patent review (2008 - 2009)

INTRODUCTION

The protein kinase C (PKC) is a family of multifunctional isoenzymes involved in apoptosis, migration, adhesion, tumorgenesis, cardiac hypertrophy, angiogenesis, platelet function and inflammation. It also plays a vital role in the regulation of signal transduction, cell proliferation and differentiation through positive and negative regulation of the cell cycle. In this work, we reviewed the existing PKC inhibitors and several patents linked to PKC inhibitors.

AREAS COVERED

Thorough survey on the PKC inhibitors having clinical importance and patents filed for these inhibitors from 2008 - 2009 is reported.

EXPERT OPINION

PKCs are highly potential therapeutic targets for treating diabetic complications, oncological, inflammatory, immunological and dermatological disorders. The clinical trial candidates of PKCs mainly target the catalytic domain, which is highly conserved throughout the PKC family making it difficult to target a particular isoform selectively. Relatively less chemical space and fewer bisubstrate inhibitors targeting both ATP and regulatory domain are explored for PKCs, more research in these areas will be helpful in overcoming existing problems.

Protein kinase Ctheta is a specific target for inhibition of the HIV type 1 replication in CD4+ T lymphocytes

Integration of HIV-1 genome in CD4(+) T cells produces latent reservoirs with long half-life that impedes the eradication of the infection. Control of viral replication is essential to reduce the size of latent reservoirs, mainly during primary infection when HIV-1 infects CD4(+) T cells massively. The addition of immunosuppressive agents to highly active antiretroviral therapy during primary infection would suppress HIV-1 replication by limiting T cell activation, but these agents show potential risk for causing lymphoproliferative disorders. Selective inhibition of PKC, crucial for T cell function, would limit T cell activation and HIV-1 replication without causing general immunosuppression due to PKC being mostly expressed in T cells. Accordingly, the effect of rottlerin, a dose-dependent PKC inhibitor, on HIV-1 replication was analyzed in T cells. Rottlerin was able to reduce HIV-1 replication more than 20-fold in MT-2 (IC(50) = 5.2 μM) and Jurkat (IC(50) = 2.2 μM) cells and more than 4-fold in peripheral blood lymphocytes (IC(50) = 4.4 μM). Selective inhibition of PKC, but not PKCδ or -ζ, was observed at <6.0 μM, decreasing the phosphorylation at residue Thr(538) on the kinase catalytic domain activation loop and avoiding PKC translocation to the lipid rafts. Consequently, the main effector at the end of PKC pathway, NF-κB, was repressed. Rottlerin also caused a significant inhibition of HIV-1 integration. Recently, several specific PKC inhibitors have been designed for the treatment of autoimmune diseases. Using these inhibitors in combination with highly active antiretroviral therapy during primary infection could be helpful to avoid massive viral infection and replication from infected CD4(+) T cells, reducing the reservoir size at early stages of the infection.

Differential role of PKC isoforms in GnRH and phorbol 12-myristate 13-acetate activation of extracellular signal-regulated kinase and Jun N-terminal kinase

GnRH is the first key hormone of reproduction. The role of protein kinase C (PKC) isoforms in GnRH-stimulated MAPK [ERK and Jun N-terminal kinase (JNK)] was examined in the αT3-1 and LβT2 gonadotrope cells. Incubation of the cells with GnRH resulted in a protracted activation of ERK1/2 and a slower and more transient activation of JNK1/2. Gonadotropes express conventional PKCα and conventional PKCβII, novel PKCδ, novel PKCε, and novel PKCθ, and atypical PKC-ι/λ. The use of green fluorescent protein-PKC constructs revealed that GnRH induced rapid translocation of PKCα and PKCβII to the plasma membrane, followed by their redistribution to the cytosol. PKCδ and PKCε localized to the cytoplasm and Golgi, followed by the rapid redistribution by GnRH of PKCδ to the perinuclear zone and of PKCε to the plasma membrane. Interestingly, PKCα, PKCβII, and PKCε translocation to the plasma membrane was more pronounced and more prolonged in phorbol-12-myristate-13-acetate (PMA) than in GnRH-treated cells. The use of selective inhibitors and dominant-negative plasmids for the various PKCs has revealed that PKCβII, PKCδ, and PKCε mediate ERK2 activation by GnRH, whereas PKCα, PKCβII, PKCδ, and PKCε mediate ERK2 activation by PMA. Also, PKCα, PKCβII, PKCδ, and PKCε are involved in GnRH and PMA stimulation of JNK1 in a cell-context-dependent manner. We present preliminary evidence that persistent vs. transient redistribution of selected PKCs or redistribution of a given PKC to the perinuclear zone vs. the plasma membrane may dictate its selective role in ERK or JNK activation. Thus, we have described the contribution of selective PKCs to ERK and JNK activation by GnRH.

Inhibition of gap junctional Intercellular communication in WB-F344 rat liver epithelial cells by triphenyltin chloride through MAPK and PI3-kinase pathways

Background

Organotin compounds (OTCs) have been widely used as stabilizers in the production of plastic, agricultural pesticides, antifoulant plaints and wood preservation. The toxicity of triphenyltin (TPT) compounds was known for their embryotoxic, neurotoxic, genotoxic and immunotoxic effects in mammals. The carcinogenicity of TPT was not well understood and few studies had discussed the effects of OTCs on gap junctional intercellular communication (GJIC) of cells.

Method

In the present study, the effects of triphenyltin chloride (TPTC) on GJIC in WB-F344 rat liver epithelial cells were evaluated, using the scrape-loading dye transfer technique.

Results

TPTC inhibited GJIC after a 30-min exposure in a concentration- and time-dependent manner. Pre-incubation of cells with the protein kinase C (PKC) inhibitor did not modify the response, but the specific MEK 1 inhibitor PD98059 and PI3K inhibitor LY294002 decreased substantially the inhibition of GJIC by TPTC. After WB-F344 cells were exposed to TPTC, phosphorylation of Cx43 increased as seen in Western blot analysis.

Conclusions

These results show that TPTC inhibits GJIC in WB-F344 rat liver epithelial cells by altering the Cx43 protein expression through both MAPK and PI3-kinase pathways.

YQ36: a novel bisindolylmaleimide analogue induces KB/VCR cell death

Overexpression of multidrug resistance proteins P-glycoprotein (P-gp, MDR1) causes resistance of the tumor cells against a variety of chemotherapeutic agents. 3-(1-methyl-1H-indol-3-yl)-1-phenyl-4-(1-(3-(piperidin-1-yl)propyl)-1H-pyrazolo[3,4-b]pyridine-3-yl)-1H-pyrrole-2,5-dione (YQ36) is a novel analogue of bisindolylmaleimide, which has been reported to overcome multidrug resistance. Here, we dedicated to investigate the anticancer activity of YQ36 on KB/VCR cells. The results revealed that YQ36 exhibited great antiproliferative activity on three parental cell lines and MDR1 overexpressed cell lines. Moreover, the hypersensitivity of YQ36 was confirmed on the base of great apoptosis induction and unaltered intracellular drug accumulation in KB/VCR cells. Further results suggested that YQ36 could not be considered as a substrate of P-gp, which contributed to its successfully escaping from the efflux mediated by P-gp. Interestingly, we observed that YQ36 could accumulate in nucleus and induce DNA damage. YQ36 could also induce the activation of caspase-3, imposing effects on the mitochondrial function. Collectively, our data demonstrated that YQ36 exhibited potent activities against MDR cells, inducing DNA damage and triggering subsequent apoptosis via mitochondrial pathway.

Dihydrotestosterone activates CREB signaling in cultured hippocampal neurons

Although androgens induce numerous actions in brain, relatively little is known about which cell signaling pathways androgens activate in neurons. Recent work in our laboratory showed that the androgens testosterone and dihydrotestosterone (DHT) activate androgen receptor (AR)-dependent mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signaling. Since the transcription factor cyclic AMP response element binding protein (CREB) is a downstream effector of MAPK/ERK and androgens activate CREB in non-neuronal cells, we investigated whether androgens activate CREB signaling in neurons. First, we observed that DHT rapidly activates CREB in cultured hippocampal neurons, as evidenced by CREB phosphorylation. Further, we observed that DHT-induced CREB phosphorylation is AR-dependent, as it occurs in PC12 cells stably transfected with AR but in neither wild-type nor empty vector-transfected cells. Next, we sought to identify the signal transduction pathways upstream of CREB phosphorylation using pharmacological inhibitors. DHT-induced CREB phosphorylation in neurons was found to be dependent upon protein kinase C (PKC) signaling but independent of MAPK/ERK, phosphatidylinositol 3-kinase, protein kinase A, and Ca(2+)/calmodulin-dependent protein kinase IV. These results demonstrate that DHT induces PKC-dependent CREB signaling, which may contribute to androgen-mediated neural functions.

Eradication of CD19+ leukemia by targeted calicheamicin θ

Children with relapsed and refractory acute lymphoblastic leukemia (ALL) still face a critical prognosis. We tested the hypothesis that targeted calicheamicin theta (θ) using an anti-CD19-immunoconjugate may provide an effective treatment strategy for CD19(+) ALL. Calicheamicin θ is a rationally designed prodrug of the natural enediyene calicheamicin γ, obtained by total synthesis. It offers the advantage of increased in vivo stability and 1000-fold higher antitumor potency over calicheamicin γ. First, we demonstrate efficacy of calicheamicin θ against primary pre-B leukemic cells and multidrug-resistant leukemia cell lines (IC(50) = 10(-9) to 10(-12) M). Second, conjugation of calicheamicin θ to an internalizing murine anti-CD19 monoclonal antibody was demonstrated to affect neither calicheamicin θ mediated cytotoxicity nor binding of the antibody to the target molecule. Third, anti-CD19-calicheamicin θ immunoconjugate revealed a maximum tolerated dose of 10 μg/kg and CD19-specific and long-lasting eradication of established leukemia was demonstrated in a xenograft model. Finally, we show that the antileukemic effect of anti-CD19-calicheamicin θ is mediated by induction of apoptosis proceeding through the caspase-mediated mitochondrial pathway. On the basis of these results, we conclude that anti-CD19-calicheamicin θ immunoconjugates may offer a novel and effective approach for the treatment of relapsed CD19(+) ALL.

Excretory-secretory products from Paragonimus westermani increase nitric oxide production in microglia in PKC-dependent and -independent manners

Excretory-secretory products (ESP) from helminthic parasites may play pivotal roles in the immune regulation in hosts. Previously, we reported that ESP produced from Paragonimus westermani induced morphological activation of microglial cells and markedly stimulated nitric oxide (NO) production via activation of mitogen-activated protein kinases (MAPKs). In the present study, we investigated the role of protein kinase C and protein kinase A in MAPKs-dependent NO production by ESP. We found that treatment with protein kinase C inhibitor Go6976 strongly inhibited the phosphorylation of p38 and JNK, but not ERK, of MAPKs and decreased the production of NO in ESP-stimulated microglial cells. Inhibition of ERK, p38 or PKC decreased the ESP-induced activation of NF-kappaB, an important transcription factor for iNOS expression. Furthermore, ESP increased the level of p-CREB in microglial cells. However, adenylyl cyclase activator (forskolin), adenylyl cyclase inhibitor (SQ22536), cAMP analogue (db-cAMP) or protein kinase A inhibitor (H89) was not able to change iNOS expression and NO production in ESP-treated microglial cells. It implies that the cAMP-PKA-CREB pathway is not implicated in the ESP-evoked NO production in microglial cells. Thus, our results indicate that ESP stimulates microglial expression of iNOS via both PKC-dependent and -independent MAPKs phosphorylation and NF-kappaB activation.

Multifunctional neuroprotective derivatives of rasagiline as anti-Alzheimer's disease drugs

The recent therapeutic approach in which drug candidates are designed to possess diverse pharmacological properties and act on multiple targets has stimulated the development of the multimodal drugs, ladostigil (TV3326) [(N-propargyl-(3R) aminoindan-5yl)-ethyl methyl carbamate] and the newly designed multifunctional antioxidant iron chelator, M-30 (5-[N-methyl-N-propargylaminomethyl]-8-hydroxyquinoline). Ladostigil combines, in a single molecule, the neuroprotective/neurorestorative effects of the novel anti-Parkinsonian drug and selective monoamine oxidase (MAO)-B inhibitor, rasagiline (Azilect, Teva Pharmaceutical Co.) with the cholinesterase (ChE) inhibitory activity of rivastigmine. A second derivative of rasagiline, M-30 was developed by amalgamating the propargyl moiety of rasagiline into the skeleton of our novel brain permeable neuroprotective iron chelator, VK-28. Preclinical experiments showed that both compounds have anti-Alzheimer's disease activities and thus, the clinical development is oriented toward treatment of this type of dementia. This review discusses the multimodal effects of two rasagiline-containing hybrid molecules, namely ladostigil and M-30, concerning their neuroprotective molecular mechanisms in vivo and in vitro, including regulation of amyloid precursor protein processing, activation of protein kinase C, and mitogen-activated protein kinase signaling pathways, inhibition of cell death markers and upregulation of neurotrophic factors. Altogether, these scientific findings make these multifunctional compounds potentially valuable drugs for the treatment of Alzheimer's disease.

Distinct requirements for activation-induced cell surface expression of preformed Fas/CD95 ligand and cytolytic granule markers in T cells

Fas (CD95/Apo-1) ligand is a potent inducer of apoptosis and one of the major killing effector mechanisms of cytotoxic T cells. Thus, Fas ligand activity has to be tightly regulated, involving various transcriptional and post-transcriptional processes. For example, preformed Fas ligand is stored in secretory lysosomes of activated T cells, and rapidly released by degranulation upon reactivation. In this study, we analyzed the minimal requirements for activation-induced degranulation of Fas ligand. T cell receptor activation can be mimicked by calcium ionophore and phorbol ester. Unexpectedly, we found that stimulation with phorbol ester alone is sufficient to trigger Fas ligand release, whereas calcium ionophore is neither sufficient nor necessary. The relevance of this process was confirmed in primary CD4(+) and CD8(+) T cells and NK cells. Although the activation of protein kinase(s) was absolutely required for Fas ligand degranulation, protein kinase C or A were not involved. Previous reports have shown that preformed Fas ligand co-localizes with other markers of cytolytic granules. We found, however, that the activation-induced degranulation of Fas ligand has distinct requirements and involves different mechanisms than those of the granule markers CD63 and CD107a/Lamp-1. We conclude that activation-induced degranulation of Fas ligand in cytotoxic lymphocytes is differently regulated than other classical cytotoxic granule proteins.

Bisindolylmaleimides in anti-cancer therapy - more than PKC inhibitors

Bisindolylmaleimide derivatives were originally described as protein kinase C inhibitors. However, several studies have shown that bisindolylmaleimides target several other signaling molecules. The review presents bisindolylmaleimide-mediated PKC-dependent and PKC-independent biological effects, such as reversal of MDR and modulation of Wnt signaling through GSK-3b and b-catenin. Importantly, the potent proapoptotic properties of bisindolylmaleimides are also described. Bis-IX appears as the most efficient activator of intrinsic apoptotic pathway and additionally, facilitates extrinsic apoptosis. Presented molecular mechanisms indicate that bisindolylmaleimides could be useful agents in anticancer therapy. They repress uncontrolled proliferation and restore the sensitivity to chemotherapy which allows eradication of cancer cells.

Prostanoid F receptors elicit an inotropic effect in rat left ventricle by enhancing myosin light chain phosphorylation

AIMS

The aims of this study were to determine if the prostanoid F receptor (FPR)-mediated inotropic effect in rat ventricle is mediated by increased phosphorylation of myosin light chain-2 (MLC-2) and to elucidate the signalling pathway(s) activated by FPRs to regulate MLC-2 phosphorylation.

METHODS AND RESULTS

Contractility was measured in left ventricular strips from adult male rats. Strips were also snap-frozen, and changes in the phosphorylation level of both MLC-2 and myosin phosphatase targeting subunit-2 (MYPT-2) were quantified. FPR stimulation with fluprostenol increased contractility by approximately 100% above basal and increased phosphorylation of both MLC-2 (by approximately 30%) and MYPT-2 (by approximately 50%). The FPR-mediated inotropic effect and MLC-2 phosphorylation were reduced by a similar magnitude in the presence of the myosin light chain kinase (MLCK) inhibitor ML-7 (approximately 60-70%) and an inhibitor of Ca(2+)/calmodulin, W-7 (approximately 35%). Inhibition of Rho-associated kinase by Y-27632 reduced the FPR-mediated inotropic effect and MLC-2 phosphorylation by approximately 40-45% and MYPT-2 phosphorylation by approximately 70%. ML-7 and Y-27632 together reduced contractility and MLC-2 phosphorylation by approximately 70-80%. The FPR-mediated inotropic effect was only modestly affected by high concentrations of the inositol tris-phosphate (IP(3)) receptor blocker 2-APB, but not by the protein kinase C (PKC) inhibitor bisindolylmaleimide.

CONCLUSION

The FPR-evoked inotropic effect is mediated by increasing the phosphorylation of MLC-2 through regulation of both MLCK and myosin light chain phosphatase activities. The second messenger IP(3) and PKC are unlikely to be involved in the signalling cascade of the FPR-mediated positive inotropic effect. Therefore, FPR signalling mechanism(s) regulating MLC-2 phosphorylation likely extend beyond those classically established for G(q/11)-coupled receptors.

The tumour suppressor RASSF1A is a novel substrate of PKC

Ras association domain family 1A (RASSF1A) is a tumour suppressor that contains an amino-terminal cysteine-rich region, similar to the diacylglycerol (DAG)-binding domain (C1 domain) found in the protein kinase C (PKC) family of proteins, and a carboxy-terminal Ras-association (RA) domain. In the present study, RASSF1A was identified as a substrate for PKC. Using classical biochemical approaches, it was established that S197 and S203 within the RA domain of RASSF1A are phosphorylated by PKC in vitro and in vivo. Unlike the WT protein, the S197, 203D double mutant of RASSF1A failed to modulate microtubule organization and perinuclear vimentin collapse. By contrast, the equivalent AA mutant of RASSF1A phenocopied the WT protein. These findings indicate that PKC phosphorylation of RASSF1A regulates its ability to reorganize the microtubule network.

Aminoindan and hydroxyaminoindan, metabolites of rasagiline and ladostigil, respectively, exert neuroprotective properties in vitro

The anti-Parkinson, selective irreversible monoamine oxidase B inhibitor drug, rasagiline (Azilect), recently approved by the US Food and Drug Administration, has been shown to possess neuroprotective-neurorescue activities in in vitro and in vivo models. Recent preliminary studies indicated the potential neuroprotective effect of the major metabolite of rasagiline, 1-(R)-aminoindan. In the current study, the neuroprotective properties of 1-(R)-aminoindan were assessed employing a cytotoxic model of human neuroblastoma SK-N-SH cells in high-density culture-induced neuronal death. We show that aminoindan (0.1-1 mumol/L) significantly reduced the apoptosis-associated phosphorylated protein, H2A.X (Ser139), decreased the cleavage of caspase 9 and caspase 3, while increasing the anti-apoptotic proteins, Bcl-2 and Bcl-xl. Protein kinase C (PKC) inhibitor, GF109203X, prevented the neuroprotection, indicating the involvement of PKC in aminoindan-induced cell survival. Aminoindan markedly elevated pPKC(pan) and specifically that of the pro-survival PKC isoform, PKCepsilon. Additionally, hydroxyaminoindan, a metabolite of a novel bifunctional drug, ladostigil [(N-propargyl-(3R) aminoindan-5yl)-ethyl methyl carbamate], combining cholinesterase and monoamine oxidase inhibitor activity, exerted similar neuroprotective properties. Aminoindan and hydroxyaminoindan also protected rat pheochromacytoma PC-12 cells against the neurotoxin, 6-hydroxydopamine. Our findings suggest that both metabolites may contribute to the overall neuroprotective activity of their respective parent compounds, further implicating rasagiline and ladostigil as potentially valuable drugs for treatment of a wide variety of neurodegenerative disorders of aging.

Inhibition of ABCG2-mediated transport by protein kinase inhibitors with a bisindolylmaleimide or indolocarbazole structure

ABCG2 is a transporter with potential importance in cancer drug resistance, drug oral absorption, and stem cell biology. In an effort to identify novel inhibitors of ABCG2, we examined the ability of commercially available bisindolylmaleimides (BIM) and indolocarbazole protein kinase inhibitors (PKI) to inhibit ABCG2, given the previous demonstration that the indolocarbazole PKI UCN-01 interacted with the transporter. At a concentration of 10 micromol/L, all of the compounds tested increased intracellular fluorescence of the ABCG2-specific substrate pheophorbide a in ABCG2-transfected HEK-293 cells by 1.3- to 6-fold as measured by flow cytometry; the ABCG2-specific inhibitor fumitremorgin C increased intracellular fluorescence by 6.6-fold. In 4-day cytotoxicity assays, wild-type ABCG2-transfected cells were not more than 2-fold resistant to any of the compounds, suggesting that the PKIs are not significantly transported by ABCG2. BIMs I, II, III, IV, and V, K252c, and arcyriaflavin A were also able to inhibit [(125)I]iodoarylazidoprazosin labeling of ABCG2 by 65% to 80% at 20 micromol/L, compared with a 50% to 70% reduction by 20 micromol/L fumitremorgin C. K252c and arcyriaflavin A were the most potent compounds, with IC(50) values for inhibition of [(125)I]iodoarylazidoprazosin labeling of 0.37 and 0.23 micromol/L, respectively. K252c and arcyriaflavin A did not have any effect on the ATPase activity of ABCG2. Four minimally toxic compounds--BIM IV, BIM V, arcyriaflavin A, and K252c-reduced the relative resistance of ABCG2-transfected cells to SN-38 in cytotoxicity assays. We find that indolocarbazole and BIM PKIs directly interact with the ABCG2 protein and may thus increase oral bioavailability of ABCG2 substrates.

Altered expression of connexin43 in the inhibition of gap junctional intercellular communication by chlorohydroxyfuranones in WB-F344 rat liver epithelial cells

3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), 3,4-dichloro-5-hydroxy-2(5H)-furanone (MCA), and 3-chloro-4-methyl-5-hydroxy-2(5H)-furanone (MCF) promote foci formation in the two-stage cell transformation assay in vitro. These chlorohydroxyfuranones (CHFs) and their structural congener 3-chloro-4-(chloromethyl)-5-hydroxy-2(5H)-furanone (CMCF) inhibit gap junctional intercellular communication (GJIC) in Balb/c 3T3 mouse fibroblast cells. In the present study, the effects of MX, MCA, CMCF, and MCF on GJIC were evaluated in liver cells (WB-F344 rat liver epithelial cells), the target cells of MX-induced carcinogenicity, using the scrape-loading dye transfer technique. The CHFs inhibited GJIC after 1 h exposure in a concentration-dependent fashion. The order of potency was MX>CMCF approximately MCA>MCF. In terms of the lowest observed effective concentrations, the difference in the potency was about 27-fold (MX 1.875 microM, MCF 50 microM). After a prolonged exposure period (12 h), the inhibition of GJIC by MX and CMCF remained stable, but MCA and MCF exhibited increasing inhibitory effects. After removal of the CHFs, the GJIC slowly recovered. At the transcriptional level, CHFs caused essentially no change in the level of connexin43 (Cx43) mRNA. Preincubation of cells with the protein kinase C (PKC) inhibitor did not modify the response, but the specific MEK 1 inhibitor PD98059 decreased substantially the inhibition of GJIC by all four CHFs. Activation of the mitogen-activated protein kinases (MAPKs) signaling pathway was necessary for inhibition of GJIC. CHFs did not increase the basal phosphorylation state of the Cx43 protein, but all CHFs caused a concentration-dependent degradation of the Cx43 protein. The results indicate that all the studied CHFs inhibit GJIC in WB-F344 cells by altering Cx43 expression.

Involvement of multiple survival signal transduction pathways in the neuroprotective, neurorescue and APP processing activity of rasagiline and its propargyl moiety

Our recent studies aimed to elucidate the molecular and biochemical mechanism of actions of the novel anti-Parkinson's drug, rasagiline, an irreversible and selective monoamine oxidase (MAO)-B inhibitor and its propargyl moiety, propargylamine. In cell death models induced by serum withdrawal in rat PC12 cells and human SH-SY5Y neuroblastoma cells, both rasagiline and propargylamine exerted neuroprotective and neurorescue activities via multiple survival pathways, including: stimulation of protein kinase C (PKC) phosphorylation; up-regulation of protein and gene levels of PKCalpha, PKCepsilon and the anti-apoptotic Bcl-2, Bcl-xL, and Bcl-w; and up-regulation of the neurotrophic factors, BDNF and GDNF mRNAs. Rasagiline and propargylamine inhibited the cleavage and subsequent activation of pro-caspase-3 and poly ADP-ribose polymerase. Additionally, these compounds significantly down-regulated PKCgamma mRNA and decreased the level of the pro-apoptotic proteins, Bax, Bad, Bim and H2A.X. Rasagiline and propargylamine both regulated amyloid precursor protein (APP) processing towards the non-amyloidogenic pathway. These structure-activity studies have provided evidence that propargylamine promoted neuronal survival via neuroprotective/neurorescue pathways similar to that of rasagiline. In addition, recent study demonstrated that chronic low doses of rasagiline administered to mice subsequently to 1 methyl-4 phenyl 1,2,3,6 tetrahydropyridine (MPTP), rescued dopaminergic neurons in the substantia nigra pars compacta via activation of the Ras-PI3K-Akt survival pathway, suggesting that rasagiline may possess a disease modifying activity.

Multidrug reverting activity toward leukemia cells in a group of new verapamil analogues with low cardiovascular activity

The development of refractory disease is often associated with the overexpression of multidrug resistance (MDR) proteins, especially in several hematological malignancies, such as acute myeloid leukemias (AML), multiple myeloma (MM) and non-Hodgkin's lymphomas (NHL). Since the recognition of these proteins, several attempts have been made to modulate their expression and activity (protein kinase C inhibitors, anti-MDR-1 oligonucleotides, pharmacological competitors and transcriptional inhibitors). Six new compounds (MM 36, CTS 4, CTS 9, CTS 12, CTS 27 and CTS 41), derived from verapamil (VRP), were designed and synthesized to improve their MDR-reverting activity and reduce cardiovascular effects. Cytotoxicity (WST-1 methods) and functional (calcein-acetoxymethyl (Calcein-AM)) assays were performed on a resistant cell line K-562/doxR and on the mononuclear cells (MNCs) of patients with AML. Furthermore, the six molecules were tested for their vasodilator, inotropic and chronotropic activity on guinea pig aortic strip and isolated atrium preparations, respectively. Comparison between survival plots and relative ID50, obtained from the K-562/doxR cells treated with Idarubicin (IDA), in the presence or absence of inhibitors, showed that these compounds function well. All the resistance modifying agents potentiated IDA activity inducing a significant reduction (P<0.01) in ID(50) values in comparison to VRP at each of the concentrations tested, but MM 36, CTS 27 and CTS 41 demonstrated the strongest activity. Results obtained from the MNCs were superimposible to K-562/doxR. Further studies on pump functional analysis confirmed the cytotoxic test results: MM 36, CTS 27 and CTS 41 showed a striking inhibition of P-glycoprotein (Pgp) efflux in K-562/doxR and MNCs. Cardiovascular activity of MM 36, CTS 27 and CTS 41, that are the most interesting compounds as MDR inhibitors, followed this course: MM 36>CTS 27>CTS 41, the last one presenting no cardiovascular activity. Chemosensivity to IDA in K-562/doxR cells and AML blasts could be enhanced in vitro by the adjuvant use of the six new VRP analogues. Compared to VRP, all the new compounds presented good MDR-reverting- and reduced cardiovascular activities along with no vasorelaxant effects. The particularly favourable results in some cases (MM 36, CTS 27 and CTS 41) suggests that anti-MDR activity should be further evaluated in clinical trials in patients with myeloid malignancies.

Comparative study of respiratory burst induced by phorbol ester and zymosan in human granulocytes

OBJECTIVES

We have comparatively evaluated respiratory burst and some steps of its signaling in human granulocytes towards different stimuli.

MATERIALS AND METHODS

An alternative method to remove erythrocytes by dextran differential sedimentation was employed. Respiratory burst (RB) was assessed in a flow cytometer by the oxidation of a fluorescent probe (dichlorodihydrofluorescein). Stimuli were phorbol ester (PMA) and zymosan.

RESULTS

Granulocytes obtained with dextran sedimentation mounted a normal RB for the two stimuli but cells obtained by erythrocyte lysis were ineffective to respond to zymosan (P < 0.05). EGTA did not affect PMA-induced, but inhibited zymosan-induced RB (P < 0.05). PMA-induced RB was blocked by a protein kinase C inhibitor (P < 0.05), whereas zymosan was not. Microfilament integrity was essential for zymosan but not for PMA, whereas microtubule depolymerization does not seem to be essential for both stimuli. Granulocytes obtained from recently diagnosed leukemia patients responded relatively well to both stimuli but after chemotherapy, the response to zymosan was increased whereas cells were unable to respond to PMA.

CONCLUSION

The use of the proposed method allows the study of both RB and phagocytosis, making it useful to study these granulocyte responses in the clinical and experimental settings.

Ca2+-dependent PKC activation mediates menthol-induced desensitization of transient receptor potential M8

In 1950, Hensel and Zotterman reported cooling-induced desensitization of cold receptors by extracellular discharge recordings of cold fibers. Since then, however, its intracellular mechanism has remained unresolved. We studied menthol-induced desensitization of cold/menthol receptors (TRPM8, transient receptor potential M8) expressed in HEK cells. TRPM8 desensitization depended on extracellular Ca2+ ions, indicating that Ca2+ influx-induced [Ca2+]i elevation caused the desensitization. We studied whether Ca2+-dependent kinase, PKC, mediated TRPM8 desensitization. PMA, a PKC activator, desensitized TRPM8. Inhibitor of Ca2+-dependent PKC isozymes specifically abolished PMA-induced TRPM8 desensitization. PMA similarly desensitized wild type TRPM8 and mutant TRPM8, in which serine or threonine residues in some putative PKC phosphorylation sites were replaced by alanine. PMA treatment did not induce internalization of TRPM8. As the basis of cooling-induced desensitization of cold receptors, we conclude that cooling-activated TRPM8 causes Ca2+-dependent PKC isozymes to desensitize TRPM8 itself.

Role of protein kinase C-Ras-MAPK p44/42 in ethanol and transforming growth factor-beta3-induced basic fibroblast growth factor release from folliculostellate cells

In the present study, we determined the interactive effects of ethanol and transforming growth factor beta-3 (TGF-beta3) on basic fibroblast growth factor (bFGF) release from folliculostellate (FS) cells and the role of the mitogen-activated protein kinase (MAPK) pathway in this interaction. We found that TGF-beta3 and ethanol alone increased release of bFGF from FS cells, but together they showed markedly increased levels of bFGF compared with the individual effect. Ethanol and TGF-beta3 alone moderately increased activation of MAPK p44/42, but together they produced marked activation of MAPK p44/42. TGF-beta3 alone increased the activation of smad2. Ethanol did not activate smad2 or alter TGF-beta3 activation of smad2. Pretreatment of FS cells with a mitogen-activated protein kinase kinase 1/2 inhibitor or with a protein kinase C (PKC) inhibitor suppressed the TGF-beta3 and ethanol actions on MAPK p44/42 activation and bFGF release. Ethanol and TGF-beta3, either alone or in combination, increased the levels of active Ras. Furthermore, the MAPK p44/42 activation by TGF-beta3 and ethanol was blocked by overexpression of Ras N17, a dominant negative mutant of Ras p21. These data suggest that the PKC-activated Ras-dependent MAPK p44/42 pathway is involved in the cross talk between TGF-beta3 and ethanol to increase bFGF release from FS cells.

Influence of protein kinase C on transcription of the tight junction elements ZO-1 and occludin

Tight junctions as an epithelial barrier against paracellular diffusion have mainly been investigated on the protein level with particular respect to subcellular localization. In this study, real-time PCR has been established to investigate the influence of protein kinase C (PKC) modulation on the transcription of tight junction elements occludin and ZO-1 in the cell line T84. Activation of PKC by the phorbol ester TPA induced ZO-1 and occludin transcription, whereas PKC inhibition lead to decreased expression levels. Activation of PKC exerted its effect on transcript level directly. PKC signal was partially transduced via MEK1/MEK2 but depended strongly on MAPK independent pathways probably involving nuclear localized PKC, whereas p38 signaling was not implicated. TPA induced loss of function concomitant with a dislocation of ZO-1 and occludin could be prevented by inhibition of MEK1 by PD98059. Overall ZO-1 and occludin seem to be identically regulated in colonic epithelium on the transcript level.

Protein kinase C epsilon regulates tumor necrosis factor-alpha-induced stannin gene expression

Stannin (Snn) is a highly conserved vertebrate protein that has been closely linked to trimethyltin (TMT) toxicity. We have previously demonstrated that Snn is required for TMT-induced cell death. Others have shown that TMT exposure results in tumor necrosis factor-alpha (TNFalpha) production and that TNFalpha treatment induces Snn gene expression in human umbilical vein endothelial cells (HUVECs). In this study, we investigated a signaling mechanism by which Snn gene expression is regulated by TMT and demonstrated that TNFalpha stimulates Snn gene expression in a protein kinase C epsilon-dependent manner in HUVECs in response to TMT exposure. Supporting this, we show that TMT-induced toxicity is significantly blocked by pretreatment with an anti-TNFalpha antibody in HUVECs. Using a quantitative real-time polymerase chain reaction assay, we also show that the level of Snn gene expression is significantly increased in HUVECs in response to either TMT or TNFalpha treatment. This TNFalpha-induced Snn gene expression is blocked when HUVECs were pretreated with bisindolylmaleimide I, an inhibitor of protein kinase C (PKC). In contrast, when HUVECs were treated with phorbol 12-myristate 13-acetate, a PKC activator, we observed a significant increase in Snn gene expression. Using isotype-specific siRNA against PKC, we further show that knockdown of PKC epsilon, but not PKC delta or PKC zeta, significantly blocked TNFalpha-induced Snn gene expression. Together, these results indicate that TNFalpha-induced, PKC epsilon-dependent Snn expression may be a critical factor in TMT-induced cytotoxicity.

New 4-aryl-1,4-dihydropyridines and 4-arylpyridines as P-glycoprotein inhibitors

Efflux of cytotoxic agents mediated by P-glycoprotein is believed to be an important mechanism of multidrug resistance, which remains a serious limitation to successful chemotherapy in cancers such as metastatic breast cancer. A series of 4-aryl-1,4-dihydropyridines and corresponding aromatized 4-arylpyridines have been synthesized based on structure modifications of niguldipine to enhance multidrug resistance reversal activity, while minimizing calcium channel binding. Thirty new compounds were characterized. [(3)H]Vinblastine accumulation studies indicated that at a concentration level of 3 muM, 15 of 18 4-aryl-1,4-dihydropyridines and all 4-arylpyridines can successfully restore intracellular accumulation of vinblastine in a resistant human breast adenocarcinoma cell line, MCF-7/adr, which overexpresses P-glycoprotein. The most potent compounds led to an approximately 15-fold increase of vinblastine accumulation. All of the test compounds that significantly increased vinblastine accumulation in MCF/adr cells were able to substantially reduce IC(50) values of daunomycin and increase its cytotoxicity in MCF-7/adr-resistant cells, confirming the results of the vinblastine accumulation studies. Calcium channel binding assays for these newly synthesized compounds were conducted using rat cerebral cortex membrane. All but eight compounds demonstrated negligible calcium channel binding over the concentration range from 15 to 2500 nM. The results demonstrate that the newly synthesized series of 1,4-dihydropyridines and pyridines represent P-glycoprotein modulators with negligible calcium channel blocking activity.

Translation modulation of acid beta-glucosidase in HepG2 cells: participation of the PKC pathway

Acid beta-glucosidase (GCase) is the enzyme deficient in Gaucher disease, a prototypical inherited metabolic error for enzyme and gene therapy. An 80 kDa mammalian cytoplasmic translational control protein (TCP80) modulates GCase translation in vitro and ex vivo by interacting with the 5' coding region of GCase RNA. Ten predicted PKC phosphorylation sites (Ser- or Thr-) are in the TCP80 protein. Phosphorylation of TCP80 in vitro by PKC greatly enhanced its translational inhibitory function using in vitro translation assays; binding of GCase mRNA to TCP80 was unaltered. Conversely, de-phosphorylation of TCP80 reduced its translational inhibitory function. Phosphorylation-related modulation of GCase mRNA translation also was studied in HepG2 cells. GCase expression (protein and activity levels) in HepG2 cells increased (>2-fold) in cells treated with bisindolylmaleimide (BIM), a highly selective PKC specific inhibitor. This correlated with a 90% reduction in TCP80 phosphorylation in the presence of BIM. The amount of TCP80 protein in cytoplasm and its RNA-binding activity were unchanged. These experiments indicate that GCase mRNA translation is modulated by PKC signaling pathways that are mediated through TCP80. These findings indicate potential broader impacts of the TCP/PKC system on expression of this and other genes of therapeutic interest.

Metabolites of benzene are potent inhibitors of gap-junction intercellular communication

Chronic exposure to benzene has been shown to lead to bone marrow depression and the development of leukemia. The mechanism underlying the carcinogenicity of benzene is unknown, although a number of genetic changes including chromosomal aberrations have been associated with benzene toxicity. Metabolism of benzene is required for the induced toxicological effects. We have investigated the effect of trans,trans-muconaldehyde (MUC), hydroquinone (HQ), and four MUC metabolites on gap-junction intercellular communication (GJIC). Inhibition of GJIC has been considered a possible predictor of tumor promoters and non-genotoxic carcinogens, and shown to result in perturbation of hematopoiesis. MUC was found to be a strong inhibitor of GJIC (EC50=12 micromol L(-1)) in rat liver epithelial cells IAR20, with potency similar to that of chlordane (EC50=7 micromol L(-1)). HQ inhibited GJIC with an EC50 of 25 micromolmol L(-1), and the metabolite OH/CHO with an EC50 of 58 micromol L(-1). The other MUC metabolites tested, CHO/COOH and OH/COOH were weak inhibitors of GJIC whereas COOH/COOH had no effect. Benzene itself had no effect on GJIC when tested in concentrations up to 20 micromol L(-1). The relative potency observed for the metabolites on GJIC is similar to their hematotoxic effects. The effect of MUC on GJIC was observed to take place concordant with a dramatic loss of connexin 43 (Cx43) from the cells as visualized by Western blotting. Substances with the ability to inhibit Cx43-dependent GJIC have previously been observed to interfere with normal hematopoietic development. The ability of benzene metabolites to interfere with gap-junction functionality, and especially the dramatic loss of Cx43 induced by MUC, should therefore be considered as a possible mechanism for benzene-induced hematotoxicity and development of leukemia.

Protein Kinase C Blockade Inhibits Differentiation of Myeloid Blasts into Dendritic Cells by Calcium Ionophore A23187

Direct differentiation of myeloid leukemia blasts into antigen-presenting dendritic cells (DCs) for use as cellular vaccines is unique in that identification of tumor-specific antigens may not be necessary because the antigens should already be endogenously expressed. We hypothesized that signaling through protein kinase C (PKC) is required for differentiation of HL-60 promyeloblasts into DCs upon stimulation with calcium ionophore A23187. To demonstrate the inhibitory effect of PKC blockade, we pretreated HL-60 myeloid blasts with the protein kinase inhibitor bisindolylmaleimide I (Bis-1) for 24 hours and then treated the cells with calcium ionophore A23187 for an additional 24 hours. Controls consisted of HL-60 blasts treated with A23187, Bis-1 alone, or media. We noted that blasts cultured in media, Bis-1, or Bis-1 then A23187 did not develop the morphologic and phenotypic DC characteristics, up-regulate Rel B, or activate allogeneic T-cells. Our findings suggested that PKC blockade inhibits morphologic, phenotypic, and functional differentiation of HL-60 promyeloblasts into antigen-presenting DCs. Our findings supported the role of PKC as an obligatory pathway for calcium ionophore A23187-induced differentiation of HL-60 myeloblasts into antigen-presenting DCs.

Disruption of hepatocellular tight junctions by vascular endothelial growth factor (VEGF): a novel mechanism for tumor invasion

BACKGROUND/AIMS

Vascular endothelial growth factor (VEGF) is expressed by many tumors, including hepatocellular carcinoma (HCC) and is involved in tumor angiogenesis. Little is known about its role for HCC infiltration into normal liver parenchyma.

METHODS

The effects of VEGF on the integrity of tight junctions were studied in HepG2 cells and human HCC by means of confocal laser scanning microscopy.

RESULTS

VEGF induced within 45 min a marked loss of pseudocanaliculi and disruption of occludin-delineated tight junctions. This effect of VEGF was mimicked by phorbol-12-myristate-13-acetate (PMA) and was sensitive to protein kinase C (PKC) inhibition by Gö6850. VEGF induced within 15 min the translocation of the PKC alpha-isoform to the plasma-membrane, but had no effect on the activity of Erks and p38(MAPK). Sections from surgically removed HCC showed expression of VEGF in the tumor and occludin disassembly in normal liver parenchyma next to the tumor.

CONCLUSIONS

VEGF induces disruption of tight junctions in a PKC-alpha dependent manner. In addition to its known angioneogenic properties, VEGF may promote HCC spreading into normal liver parenchyma. The data may provide another rationale for the use of VEGF antagonists for tumor therapy.

Neuroprotection via pro‐survival protein kinase C isoforms associated with Bcl‐2 family members

This study provides new insights into neuroprotection involving interaction of protein kinase C (PKC) pathway with Bcl-2 family proteins. Using a model of serum deprivation, we investigated the mechanism by which the anti-Parkinson/monoamine oxidase (MAO)-B inhibitor drug, rasagiline, exerts its neuroprotective effect in rat pheochromocytoma PC12 cells. Here, we report that rasagiline (0.1-10 microM) decreased apoptosis via multiple protection mechanisms, including the stimulation of PKC phosphorylation; up-regulation of PKCalpha and PKC mRNAs, induction of Bcl-xL, Bcl-w, and brain-derived neurotrophic factor (BDNF) mRNAs; and down-regulation of Bad and Bax mRNAs. Moreover, rasagiline inhibited the cleavage and activation of procaspase-3 and poly (ADP-ribose) polymerase (PARP), whereas the PKC inhibitor, GF109203X, reversed these actions. Similarly, rasagiline decreased serum-free-induced levels of the important regulator of cell death, Bad, which was also blocked by GF109203X, indicating the involvement of PKC in rasagiline-induced cell survival. Furthermore, these studies have established that PKC- and Bcl-2-dependent neuroprotective activity of rasagiline is dependent on its propargyl moiety, because propargylamine had similar effects with the same potency.

Calmodulin-mediated activation of Akt regulates survival of c-Myc-overexpressing mouse mammary carcinoma cells

c-Myc-overexpressing mammary epithelial cells are proapoptotic; their survival is strongly promoted by epidermal growth factor (EGF). We now demonstrate that EGF-induced Akt activation and survival in transgenic mouse mammary tumor virus-c-Myc mouse mammary carcinoma cells are both calcium/calmodulin-dependent. Akt activation is abolished by the phospholipase C-gamma inhibitor U-73122, by the intracellular calcium chelator BAPTA-AM, and by the specific calmodulin antagonist W-7. These results implicate calcium/calmodulin in the activation of Akt in these cells. In addition, Akt activation by serum and insulin is also inhibited by W-7. EGF-induced and calcium/calmodulin-mediated Akt activation occurs in both tumorigenic and non-tumorigenic mouse and human mammary epithelial cells, independent of their overexpression of c-Myc. These results imply that calcium/calmodulin may be a common regulator of Akt activation, irrespective of upstream receptor activator, mammalian species, and transformation status in mammary epithelial cells. However, only c-Myc-overexpressing mouse mammary carcinoma cells (but not normal mouse mammary epithelial cells) undergo apoptosis in the presence of the calmodulin antagonist W-7, indicating the vital selective role of calmodulin for survival of these cells. Calcium/calmodulin-regulated Akt activation is mediated directly by neither calmodulin kinases nor phosphatidylinositol 3-kinase (PI-3 kinase). Pharmacological inhibitors of calmodulin kinase kinase and calmodulin kinases II and III do not inhibit EGF-induced Akt activation, and calmodulin antagonist W-7 does not inhibit phosphotyrosine-associated PI-3 kinase activation. Akt is, however, co-immunoprecipitated with calmodulin in an EGF-dependent manner, which is inhibited by calmodulin antagonist W-7. We conclude that calmodulin may serve a vital regulatory function to direct the localization of Akt to the plasma membrane for its activation by PI-3 kinase.

Protein kinase C inhibition differentially affects 3,4-methylenedioxymethamphetamine-induced dopamine release in the striatum and prefrontal cortex of the rat

The acute administration of 3,4-methylenedioxymethamphetamine (MDMA) elevates extracellular concentrations of dopamine (DA) and serotonin (5-HT) in the rat striatum and medial prefrontal cortex (mPFC). The release of DA induced by MDMA is thought to involve both transporter and impulse-mediated processes. Furthermore, the impulse-dependent release of DA in the striatum elicited by MDMA appears to involve 5-HT2 receptor activation. Since 5-HT2 receptors are known to utilize protein kinase C (PKC) for intracellular signaling, we examined the effects of modulators of PKC activity on DA release stimulated by MDMA. Reverse dialysis of the PKC inhibitors bisindolylmaleimide I (BIM; 30 microM) or chelerythrine chloride (100 microM) through a microdialysis probe significantly attenuated the MDMA (10 mg/kg, i.p.)-induced increase in the extracellular concentration of DA in the striatum. In contrast, BIM did not significantly alter the increase in the extracellular concentration of DA in the striatum elicited by amphetamine (5 mg/kg, i.p.). Reverse dialysis of a PKC activator, phorbol 12,13-dibutyrate (PDBu) (0.5 microM), through the microdialysis probe into the striatum, significantly increased MDMA-induced DA release. In contrast to the inhibitory effects of the PKC inhibitors on MDMA-induced DA release in the striatum, intracortical infusion of BIM enhanced MDMA-induced release of DA in the mPFC. These data suggest that PKC-mediated signaling pathways differentially modulate MDMA-induced DA release from mesocorticolimbic and nigrostriatal neurons.

Mechanical Strain Inhibits Airway Smooth Muscle Gene Transcription via Protein Kinase C Signaling

Mechanical strain affects airway myocyte phenotype, cytoskeletal architecture, proliferation, and contractile function. We hypothesized that (i) short-term mechanical strain modulates transcription of smooth muscle-specific gene promoters for SM22 and smooth muscle myosin heavy chain (smMHC); and (ii) strain-induced change is mediated by altered actin polymerization in association with activation of protein kinase C (PKC). Primary cultured canine tracheal myocytes were transiently transfected with luciferase reporter plasmids harboring a murine SM22, human smMHC, or artificial serum response factor (SRF)-specific gene promoter and then subjected to cyclic strain for 48 h. This strain protocol significantly reduced transcriptional activity of SM22 and smMHC promoters and an artificial SRF-dependent promoter by 55 +/- 5.9%, 57 +/- 6.4%, and 75 +/- 7.9%, respectively, with concomitant reduction in F/G actin ratio by 31 +/- 8%. PKC inhibitors, GF109203X or Gö6976, significantly attenuated these affects. Similar to strain, strain-independent activation of PKC inhibited SM22, smMHC, and SRF-dependent promoter activity by 61 +/- 4%, 66 +/- 5%, and 28 +/- 15%, respectively, and reduced the F/G actin ratio by 30 +/- 5%. Gel shift assay revealed that PKC activation led to decreased binding of the required transcription factor, SRF, to CArG elements in the SM22 promoter. These data suggest a previously unknown role for PKC isoforms in mechanosensitive signaling in airway myocytes that is associated with coordinated regulation of actin cytoskeletal dynamics and smooth muscle-specific gene transcription.

CREB regulates AChE-R-induced proliferation of human glioblastoma cells

The cyclic adenosine monophosphate (AMP) response element-binding protein, CREB, often modulates stress responses. Here, we report that CREB suppresses the glioblastoma proliferative effect of the stress-induced acetylcholinesterase variant, AChE-R. In human U87MG glioblastoma cells, AChE-R formed a triple complex with protein kinase C (PKC) epsilon and the scaffold protein RACK1, enhanced PKCepsilon phosphorylation, and facilitated BrdU incorporation. Either overexpressed CREB, or antisense destruction of AChE-R mRNA, PKC, or protein kinase A (PKA) inhibitors-but not CREB combined with PKC inhibition suppressed-this proliferation, suggesting that CREB's repression of this process involves a PKC-mediated pathway, whereas impaired CREB regulation allows AChE-R-induced, PKA-mediated proliferation of glioblastoma tumors.