Kinase-dependent Mechanism Research Articles

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Mitochondria and AMP-activated Protein Kinase-dependent Mechanism of Efferocytosis

Defective clearance of apoptotic cells is frequently associated with perpetuation of inflammatory conditions. Our results show a rapid activation of AMP-activated kinase (AMPK) in macrophages upon exposure to apoptotic cells or lysophosphatidylcholine, a specific phospholipid that is produced and released from dying cells. AMPK activation resulted from inhibition of mitochondrial oxygen consumption and ATP production and further depended on Ca(2+) mobilization and mitochondrial reactive oxygen species generation. Once activated, AMPK increased microtubule synthesis and chemokinesis and provided adaptation to energy demand during tracking and engulfment. Uptake of apoptotic cells was increased in lungs of mice that received lysophosphatidylcholine. Furthermore, inhibition of AMPK diminished clearance of apoptotic thymocytes in vitro and in dexamethasone-treated mice. Taken together, we conclude that the mitochondrial AMPK axis is a sensor and enhancer of tracking and removal of apoptotic cell, processes crucial to resolution of inflammatory conditions and a return to tissue homeostasis.

A bidirectional crosstalk between iNKT cells and adipocytes mediated by leptin modulates susceptibility for T cell mediated hepatitis

Immunometabolism is an emerging field of clinical investigation due to the obesity epidemic worldwide. A reciprocal involvement of immune mediators in the body energy metabolism has been recognized for years, but is only partially understood. We hypothesized that the adipokine leptin could provide an important modulator of iNKT cells. The expression of leptin receptor (LR) on resting and activated iNKT cells was measured by flow cytometry. FACS-sorted hepatic iNKT cells were stimulated with anti-CD3/CD28Ab coated beads in the absence or presence of a neutralizing anti-leptin Ab. Furthermore, we evaluated the outcome of LR blocking nanobody treatment in ConA induced hepatitis and towards metabolic parameters in WT and iNKT cell deficient mice. The LR is expressed on iNKT cells and leptin suppresses iNKT cell proliferation and cytokine production in vitro. LR deficient iNKT cells are hyper-responsive further enforcing the role of leptin as an important inhibitor of iNKT cell function. Consistently, in vivo blockade of LR signaling exacerbated ConA hepatitis in wild-type but not in iNKT cell deficient mice, through both Janus kinase (JAK)2 and mitogen-activated protein kinase (MAPK) dependent mechanisms. Moreover, LR inhibition altered fat pad features and was accompanied by insulin resistance, only in wild-type mice. Curiously, this interaction was strictly dependent on MAPK mediated LR signaling in iNKT cells and uncoupled from the more central effects of leptin. Our data support a new concept of immune regulation by which leptin protects towards T cell mediated hepatitis via modulation of iNKT cells.

Oncogenic PAK4 regulates Smad2/3 axis involving gastric tumorigenesis

The alteration of p21-activated kinase 4 (PAK4) and transforming growth factor-beta (TGF-β) signaling effector Smad2/3 was detected in several types of tumors, which acts as oncogenic factor and tumor suppressor, but the relationship between these events has not been explored. Here, we demonstrate that PAK4 interacts with and modulates phosphorylation of Smad2/3 via both kinase-dependent and kinase-independent mechanisms, which attenuate Smad2/3 axis transactivation and TGF-β-mediated growth inhibition in gastric cancer cells. First, PAK4 interaction with Smad2/3, which is independent of PAK4 kinase activity, blocks TGF-β1-induced phosphorylation of Smad2 Ser465/467 or Smad3 Ser423/425 and the consequent activation. In addition, PAK4 phosphorylates Smad2 on Ser465, leading to the degradation of Smad2 through ubiquitin-proteasome-dependent pathway under hepatocyte growth factor (HGF) stimulation. Interestingly, PAK4 expression correlates negatively with phospho-Ser465/467 Smad2 but positively with phospho-Ser465 Smad2 in gastric cancer tissues. Furthermore, the expressions of HGF, phospho-Ser474 PAK4 and phospho-Ser465 Smad2 are markedly increased in gastric cancer tissues, and the expression of Smad2 is decreased in gastric cancer tissues. Our results document an oncogenic role of PAK4 in repression of Smad2/3 transactivation that involved in tumorigenesis, and suggest PAK4 as a potential therapeutic target for gastric cancer.

Immunoglobulin E induces VEGF production in mast cells and potentiates their pro-tumorigenic actions through a Fyn kinase-dependent mechanism

BackgroundHigh concentrations of plasmatic IgE have been related to distinct systemic inflammatory conditions that frequently predispose individuals to hypersensitivity reactions. Although effects of IgE have been suggested to relay on the low-intensity activation of distinct effector elements of the immune system, such as mast cells (MC), experimental evidence on the role of IgE-induced production of inflammatory mediators on specific pathologies is scarce. MC are an important component in tumor microenvironment where they seem to secrete a number of immunomodulatory and angiogenic mediators, such as the Vascular Endothelial Growth Factor (VEGF) by not well-described mechanisms. In this work, we investigated the effect of monomeric IgE (in the absence of antigen) on the production of VEGF in MC, analyzed if monomeric IgE could exacerbate the pro-tumorigenic properties of that cell type and characterized some of the molecular mechanisms behind the effects of IgE on VEGF production and tumor growth.MethodsFor in vitro studies, murine bone marrow-derived mast cells (BMMCs) were used. Pharmacological inhibitors and phosphorylation of key elements controlling VEGF secretion and protein translation were used to characterize the mechanism of VEGF production triggered by IgE.In vivo, the effect of a single i.v. administration of monomeric IgE on B16 melanoma tumor weight, intratumoral blood vessel formation and tumor-associated MC was assessed in four groups of mice: MC-proficient (WT), MC-deficient (Wsh), Wsh reconstituted with MC derived from WT mice (Wsh Rec WT) and Wsh reconstituted with MC derived from Fyn −/− mice (Wsh Rec Fyn −/−).ResultsMonomeric IgE induced VEGF secretion through a Fyn kinase-dependent mechanism and modulated de novo protein synthesis modifying the activity of the translational regulator 4E-BP1 in BMMCs. In vivo, monomeric IgE increased melanoma tumor growth, peritumoral MC and blood vessel numbers in WT but not in Wsh mice. The positive effects of IgE on melanoma tumor growth were reproduced after reconstitution of Wsh mice with WT but not with Fyn −/− BMMCs.ConclusionOur data suggest that monomeric IgE, in the absence of antigen, induces VEGF production in MC and in vivo contributes to melanoma tumor growth through a Fyn kinase-dependent mechanism.

Oxidized low-density lipoproteins induce rapid platelet activation and shape change through tyrosine kinase and Rho kinase–signaling pathways

AbstractOxidized low-density lipoproteins (oxLDL) generated in the hyperlipidemic state may contribute to unregulated platelet activation during thrombosis. Although the ability of oxLDL to activate platelets is established, the underlying signaling mechanisms remain obscure. We show that oxLDL stimulate platelet activation through phosphorylation of the regulatory light chains of the contractile protein myosin IIa (MLC). oxLDL, but not native LDL, induced shape change, spreading, and phosphorylation of MLC (serine 19) through a pathway that was ablated under conditions that blocked CD36 ligation or inhibited Src kinases, suggesting a tyrosine kinase–dependent mechanism. Consistent with this, oxLDL induced tyrosine phosphorylation of a number of proteins including Syk and phospholipase C γ2. Inhibition of Syk, Ca2+ mobilization, and MLC kinase (MLCK) only partially inhibited MLC phosphorylation, suggesting the presence of a second pathway. oxLDL activated RhoA and RhoA kinase (ROCK) to induce inhibitory phosphorylation of MLC phosphatase (MLCP). Moreover, inhibition of Src kinases prevented the activation of RhoA and ROCK, indicating that oxLDL regulates contractile signaling through a tyrosine kinase–dependent pathway that induces MLC phosphorylation through the dual activation of MLCK and inhibition of MLCP. These data reveal new signaling events downstream of CD36 that are critical in promoting platelet aggregation by oxLDL.

DIDS inhibits Na-K-ATPase activity in porcine nonpigmented ciliary epithelial cells by a Src family kinase-dependent mechanism

The anion transport inhibitor DIDS is known to reduce aqueous humor secretion but questions remain about anion dependence of the effect. In some tissues, DIDS is reported to cause Na-K-ATPase inhibition. Here, we report on the ability of DIDS to inhibit Na-K-ATPase activity in nonpigmented ciliary epithelium (NPE) and investigate the underlying mechanism. Porcine NPE cells were cultured to confluence on permeable supports, treated with drugs added to both sides of the membrane, and then used for (86)Rb uptake measurements or homogenized to measure Na-K-ATPase activity or to detect protein phosphorylation. DIDS inhibited ouabain-sensitive (86)Rb uptake, activated Src family kinase (SFK), and caused a reduction of Na-K-ATPase activity. PP2, an SFK inhibitor, prevented the DIDS responses. In BCECF-loaded NPE, DIDS was found to reduce cytoplasmic pH (pHi). PP2-sensitive Na-K-ATPase activity inhibition, (86)Rb uptake suppression, and SFK activation were observed when a similar reduction of pHi was imposed by low-pH medium or an ammonium chloride withdrawal maneuver. PP2 and the ERK inhibitor U0126 prevented robust ERK1/2 activation in cells exposed to DIDS or subjected to pHi reduction, but U0126 did not prevent SFK activation or the Na-K-ATPase activity response. The evidence points to an inhibitory influence of DIDS on NPE Na-K-ATPase activity by a mechanism that hinges on SFK activation associated with a reduction of cytoplasmic pH.

DIDS and the Janus-faced Na+-K+-activated ATPase. Focus on “DIDS inhibits Na-K-ATPase activity in porcine nonpigmented ciliary epithelial cells by a Src family kinase-dependent mechanism”

the maintenance of mammalian cell volume fundamentally rests on net cation extrusion through Na+-K+-activated ATPase, the Na+ pump. The publication by Shahidullah et al. ([11][1]) persuasively identifies the series of events by which a widely used inhibitor of anion transport, DIDS, can reduce Na+

G protein‐coupled receptors engage the mammalian Hippo pathway through F‐actin

The Hippo pathway, a cascade of protein kinases that inhibits the oncogenic transcriptional coactivators YAP and TAZ, was discovered in Drosophila as a major determinant of organ size in development. Known modes of regulation involve surface proteins that mediate cell-cell contact or determine epithelial cell polarity which, in a tissue-specific manner, use intracellular complexes containing FERM domain and actin-binding proteins to modulate the kinase activities or directly sequester YAP. Unexpectedly, recent work demonstrates that GPCRs, especially those signaling through Galpha12/13 such as the protease activated receptor PAR1, cause potent YAP dephosphorylation and activation. This response requires active RhoA GTPase and increased assembly of filamentous (F-)actin. Morever, cell architectures that promote F-actin assembly per se also activate YAP by kinase-dependent and independent mechanisms. These findings unveil the ability of GPCRs to activate the YAP oncogene through a newly recognized signaling function of the actin cytoskeleton, likely to be especially important for normal and cancerous stem cells.

Systems Modelling of NHEJ Reveals the Importance of Redox Regulation of Ku70/80 in the Dynamics of DNA Damage Foci

The presence of DNA double-stranded breaks in a mammalian cell typically activates the Non-Homologous End Joining (NHEJ) pathway to repair the damage and signal to downstream systems that govern cellular decisions such as apoptosis or senescence. The signalling system also stimulates effects such as the generation of reactive oxygen species (ROS) which in turn feed back into the damage response. Although the overall process of NHEJ is well documented, we know little of the dynamics and how the system operates as a whole. We have developed a computational model which includes DNA Protein Kinase (DNA-PK) dependent NHEJ (D-NHEJ) and back-up NHEJ mechanisms (B-NHEJ) and use it to explain the dynamic response to damage induced by different levels of gamma irradiation in human fibroblasts. Our work suggests that the observed shift from fast to slow repair of DNA damage foci at higher levels of damage cannot be explained solely by inherent stochasticity in the NHEJ system. Instead, our model highlights the importance of Ku oxidation which leads to increased Ku dissociation rates from DNA damage foci and shifts repair in favour of the less efficient B-NHEJ system.

STAT1 expression and activation is increased in lesional psoriatic skin

The JAK (Janus kinase)/STAT (signal transducer and activator of transcription) signalling pathway is known to play an important role in many cellular processes including inflammation. The activation of STAT1 is dependent on tyrosine 701 and serine 727 phosphorylation, which leads to the formation of the STAT dimer and modulation of STAT1 activity, respectively. To determine STAT1 expression and activation in psoriatic skin. Biopsies were collected from patients with psoriasis. mRNA expression was evaluated by quantitative polymerase chain reaction, whereas the protein and phosphorylation level of STAT1 were evaluated by Western blotting. STAT1 localization was determined by immunofluorescence analysis and STAT1-induced transcriptional activity was analysed in cultured human keratinocytes using a reporter assay. The expression of STAT1 was demonstrated to be significantly increased at both mRNA and protein level in lesional psoriatic skin. In addition, the phosphorylation level of STAT1(Tyr701) and STAT1(Ser727) was significantly increased in lesional compared with nonlesional psoriatic skin. Luciferase assays showed a significant induction of the STAT1-induced transcriptional activity when cultured human keratinocytes were stimulated with either interferon (IFN)-α or IFN-γ. STAT1(Ser727) phosphorylation induced by IFN-α, IFN-γ or ultraviolet B was mediated by a protein kinase C (PKC)-δ- and p38 mitogen-activated protein kinase-dependent mechanism in human keratinocytes, whereas IFN-α-induced STAT1(Tyr701) phosphorylation was mediated by a PKC-δ-dependent mechanism. This study demonstrates for the first time that the phosphorylation level of STAT1(Tyr701) and STAT1(Ser727) is increased in lesional psoriatic skin. In addition, specific signalling pathways leading to this phosphorylation have been identified. Together, our data indicate an important role of STAT1 in the pathogenesis of psoriasis.

Astrocytes Modulate a Postsynaptic NMDA–GABAA-Receptor Crosstalk in Hypothalamic Neurosecretory Neurons

A dynamic balance between the excitatory and inhibitory neurotransmitters glutamate and GABA is critical for maintaining proper neuronal activity in the brain. This balance is partly achieved via presynaptic interactions between glutamatergic and GABA(A)ergic synapses converging into the same targets. Here, we show that in hypothalamic magnocellular neurosecretory neurons (MNCs), a direct crosstalk between postsynaptic NMDA receptors (NMDARs) and GABA(A) receptors (GABA(A)Rs) contributes to the excitatory/inhibitory balance in this system. We found that activation of NMDARs by endogenous glutamate levels controlled by astrocyte glutamate transporters, evokes a transient and reversible potentiation of postsynaptic GABA(A)Rs. This inter-receptor crosstalk is calcium-dependent and involves a kinase-dependent phosphorylation mechanism, but does not require nitric oxide as an intermediary signal. Finally, we found the NMDAR-GABA(A)R crosstalk to be blunted in rats with heart failure, a pathological condition in which the hypothalamic glutamate-GABA balance is tipped toward an excitatory predominance. Together, our findings support a novel form of glutamate-GABA interactions in MNCs, which involves crosstalk between NMDA and GABA(A) postsynaptic receptors, whose strength is controlled by the activity of local astrocytes. We propose this inter-receptor crosstalk to act as a compensatory, counterbalancing mechanism to dampen glutamate-mediated overexcitation. Finally, we propose that an uncoupling between NMDARs and GABA(A)Rs may contribute to exacerbated neuronal activity and, consequently, sympathohumoral activation in such disease conditions as heart failure.

Lysophosphatidic acid-stimulated phosphorylation of PKD2 is mediated by PI3K p110β and PKCδ in myoblasts

Context: G-protein coupled receptor (GPCR) signaling in skeletal muscle is incompletely understood; in particular, the signaling pathways that regulate GPCR-mediated signaling in skeletal muscle are only beginning to be established. Lysophosphatidic acid (LPA) is a GPCR agonist that has previously been shown to activate protein kinase D (PKD) in non-muscle cells; however, whether PKD is activated in response to LPA in skeletal muscle myoblasts, and the identities of signaling intermediates that regulate this activation, have not been defined. Objective: To determine whether PKD is activated in response to LPA administration in myoblasts, and to define the signaling pathways that mediate LPA-stimulated PKD phosphorylation. Methods: C2C12 myoblasts were treated with LPA and signaling pathways examined by means of Western immunoblotting and real-time PCR (RT-PCR). Pharmacological inhibition and RNA-interference were used to target specific molecules to determine their involvement in LPA-induced PKD phosphorylation. Results: Treatment of myoblasts with exogenous LPA revealed that PI3K p110β mediated PKD phosphorylation at Ser 748 and at Ser 916 through kinase-dependent and kinase-independent mechanisms. Loss of PKCδ, but not the loss of PKCα, prevented LPA-induced PKD phosphorylation. The PKD isoform responsive to LPA treatment was identified as PKD2. Conclusion: These results indicate that LPA-stimulated PKD2 phosphorylation requires PKCδ and non-catalytic actions of PI3K p110β, and provide new information with respect to GPCR-mediated signal transduction in myoblasts.

A Glucagon-Like Peptide-1 Analog Reverses the Molecular Pathology and Cardiac Dysfunction of a Mouse Model of Obesity

Cardiac consequences of obesity include inflammation, hypertrophy, and compromised energy metabolism. Glucagon-like peptide-1 is an incretin hormone capable of cytoprotective actions that reduces inflammation and endoplasmic reticulum stress in other tissues. Here we examine the cardiac effects of the glucagon-like peptide-1 analog liraglutide in a model of obesity, independent of changes in body weight. C57Bl6 mice were placed on a 45% high-fat diet (HFD) or a regular chow diet. Mice on HFD developed 46±2% and 60±2% greater body weight relative to regular chow diet-fed mice at 16 and 32 weeks, respectively (both P<0.0001), manifesting impaired glucose tolerance, insulin resistance, and cardiac ceramide accumulation by 16 weeks. One-week treatment with liraglutide (30 µg/kg twice daily) did not reduce body weight, but reversed insulin resistance, cardiac tumor necrosis factor-α expression, nuclear factor kappa B translocation, obesity-induced perturbations in cardiac endothelial nitric oxide synthase, connexin-43, and markers of hypertrophy and fibrosis, in comparison with placebo-treated HFD controls. Liraglutide improved the cardiac endoplasmic reticulum stress response and also improved cardiac function in animals on HFD by an AMP-activated protein kinase-dependent mechanism. Supporting a direct mechanism of action, liraglutide (100 nmol/L) prevented palmitate-induced lipotoxicity in isolated mouse cardiomyocytes and primary human coronary smooth muscle cells and prevented adhesion of human monocytes to tumor necrosis factor-α-activated human endothelial cells in vitro. Weight-neutral treatment with a glucagon-like peptide-1 analog activates several cardioprotective pathways, prevents HFD-induced insulin resistance and inflammation, reduces monocyte vascular adhesion, and improves cardiac function in vivo by activating AMP-activated protein kinase. These data support a role for glucagon-like peptide-1 analogs in limiting the cardiovascular risks of obesity.

Posttranslational regulation of thioredoxin-interacting protein

Thioredoxin-interacting protein (Txnip) is a metabolic regulator, which modulates insulin sensitivity and likely plays a role in type 2 diabetes. We studied the regulation of Txnip in 3T3-L1 adipocytes. Cells were incubated under different conditions and Txnip was measured by immunoblotting. We confirmed that high glucose markedly increases Txnip expression by promoting transcription. Insulin decreases Txnip protein levels. Rapamycin under most conditions decreased Txnip, suggesting that mTOR complex-1 is involved. The acute effects of insulin are mainly posttranscriptional; insulin (100 nM) accelerates Txnip degradation more than tenfold. This effect is cell type specific. It works in adipocytes, preadipocytes and in L6 myotubes but not in HepG2 or in HEK 293 cells or in a pancreatic β-cell line. The ubiquitin/proteasome pathway is involved. Degradation of Txnip occurred within 15 min in the presence of 3 nM insulin and overnight with 0.6 nM insulin. Proteasomal Txnip degradation is not mediated by a cysteine protease or an anti-calpain enzyme. Okadaic acid (OKA), an inhibitor of phosphoprotein phosphatases (pp), markedly reduced Txnip protein and stimulated its further decrease by insulin. The latter occurred after incubation with 1 or 1000 nM OKA, suggesting that insulin enhances the phosphorylation of a pp2A substrate. Incubation with 0.1 μM Wortmannin, a PI3 kinase inhibitor, increased Txnip protein twofold and significantly inhibited its insulin-induced decrease. Thus, while OKA mimics the effect of insulin, Wortmannin opposes it. In summary, insulin stimulates Txnip degradation by a PI3 kinase-dependent mechanism, which activates the ubiquitin/proteasome pathway and likely serves to mitigate insulin resistance.

Neuroprotective Effects of Reactive Oxygen Species Mediated by BDNF-Independent Activation of TrkB

Reactive oxygen species (ROS) have diverse biological consequences in the mammalian CNS, but the molecular targets mediating these pleiotropic effects are incompletely understood. Like ROS, the neurotrophin receptor, TrkB receptor tyrosine kinase, has diverse effects in the developing and mature mammalian brain. Our discovery that zinc can transactivate TrkB, together with the finding that ROS can trigger zinc release from cytosolic zinc binding proteins, led us to hypothesize that ROS can transactivate TrkB in CNS neurons by a zinc-dependent mechanism. We found that both exogenous H(2)O(2) and endogenous ROS activate TrkB signaling by a Src family kinase-dependent but brain-derived neurotrophic factor-independent mechanism in cultured rat cortical neurons. Exogenous H(2)O(2) enhances cytosolic zinc content in a metallothionein-3 (MT-3)-requiring manner. Both exogenous H(2)O(2) and endogenous ROS mediated transactivation of TrkB requires intracellular zinc and MT-3. The ROS-triggered transactivation of TrkB exerts neuroprotective effects, because inhibition of TrkB kinase activity or uncoupling Shc signaling from TrkB exacerbates neuronal cell death induced by H(2)O(2). Thus, we propose a molecular signaling event whereby ROS induce release of zinc from cytosolic MT-3, the increased cytosolic zinc transactivates TrkB, and the enhanced Shc signaling downstream from TrkB promotes prosurvival effects. We suggest that such neuroprotective effects mediated by ROS are operative in diverse acute and chronic neurological disorders.

Phosphorylation of 4E-BP1 in the Mammalian Brain Is Not Altered by LRRK2 Expression or Pathogenic Mutations

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are a common cause of autosomal dominant familial Parkinson's disease (PD). LRRK2 encodes a multi-domain protein containing GTPase and kinase enzymatic domains. Disease-associated mutations in LRRK2 variably influence enzymatic activity with the common G2019S variant leading to enhanced kinase activity. Mutant LRRK2 induces neuronal toxicity through a kinase-dependent mechanism suggesting that kinase activity is important for mediating the pathogenic effects of LRRK2 mutations. A number of LRRK2 kinase substrates have been identified in vitro but whether they represent authentic physiological substrates in mammalian cells or tissues is not yet clear. The eukaryotic initiation factor 4E (eIF4E)-binding protein, 4E-BP1, was recently identified as a potential substrate of LRRK2 kinase activity in vitro and in Drosophila with phosphorylation occurring at Thr37 and Thr46. Here, we explore a potential interaction of LRRK2 and 4E-BP1 in mammalian cells and brain. We find that LRRK2 can weakly phosphorylate 4E-BP1 in vitro but LRRK2 overexpression is not able to alter endogenous 4E-BP1 phosphorylation in mammalian cells. In mammalian neurons LRRK2 and 4E-BP1 display minimal co-localization, whereas the subcellular distribution, protein complex formation and covalent post-translational modification of endogenous 4E-BP1 are not altered in the brains of LRRK2 knockout or mutant LRRK2 transgenic mice. In the brain, the phosphorylation of 4E-BP1 at Thr37 and Thr46 does not change in LRRK2 knockout or mutant LRRK2 transgenic mice, nor is 4E-BP1 phosphorylation altered in idiopathic or G2019S mutant PD brains. Collectively, our results suggest that 4E-BP1 is neither a major nor robust physiological substrate of LRRK2 in mammalian cells or brain.

Targeting blood-brain barrier sphingolipid signaling reduces basal P-glycoprotein activity and improves drug delivery to the brain

P-glycoprotein, an ATP-driven drug efflux pump, is a major obstacle to the delivery of small-molecule drugs across the blood-brain barrier and into the CNS. Here we test a unique signaling-based strategy to overcome this obstacle. We used a confocal microscopy-based assay with isolated rat brain capillaries to map a signaling pathway that within minutes abolishes P-glycoprotein transport activity without altering transporter protein expression or tight junction permeability. This pathway encompasses elements of proinflammatory- (TNF-α) and sphingolipid-based signaling. Critical to this pathway was signaling through sphingosine-1-phosphate receptor 1 (S1PR1). In brain capillaries, S1P acted through S1PR1 to rapidly and reversibly reduce P-glycoprotein transport activity. Sphingosine reduced transport by a sphingosine kinase-dependent mechanism. Importantly, fingolimod (FTY720), a S1P analog recently approved for treatment of multiple sclerosis, also rapidly reduced P-glycoprotein activity; similar effects were found with the active, phosphorylated metabolite (FTY720P). We validated these findings in vivo using in situ brain perfusion in rats. Administration of S1P, FTY720, or FTY729P increased brain uptake of three radiolabeled P-glycoprotein substrates, (3)H-verapamil (threefold increase), (3)H-loperamide (fivefold increase), and (3)H-paclitaxel (fivefold increase); blocking S1PR1 abolished this effect. Tight junctional permeability, measured as brain (14)C-sucrose accumulation, was not altered. Therefore, targeting signaling through S1PR1 at the blood-brain barrier with the sphingolipid-based drugs, FTY720 or FTY720P, can rapidly and reversibly reduce basal P-glycoprotein activity and thus improve delivery of small-molecule therapeutics to the brain.

Early intravenous cyclosporine treatment attenuates necrotizing enterocolitis-like intestinal injury compared to delayed treatment during resuscitation of asphyxiated newborn piglets

INTRODUCTION: P-glycoprotein (Pgp) is a transmembrane protein expressed in many cell types. We identified a protein in human breast milk that cross-reacts with Pgp antibody. This Pgp-like factor (Pgp-F) binds to intestinal epithelial cells. p38 MAP Kinase has multiple roles in inflammation and may have a role in binding of protective factors. We hypothesize that Pgp-F binding protects against bacteria-induced inflammation via a p38 MAP kinasedependent mechanism.

Nuclear-Cytoplasmic Trafficking of NTF2, the Nuclear Import Receptor for the RanGTPase, Is Subjected to Regulation

NTF2 is a cytosolic protein responsible for nuclear import of Ran, a small Ras-like GTPase involved in a number of critical cellular processes, including cell cycle regulation, chromatin organization during mitosis, reformation of the nuclear envelope following mitosis, and controlling the directionality of nucleocytoplasmic transport. Herein, we provide evidence for the first time that translocation of the mammalian NTF2 from the nucleus to the cytoplasm to collect Ran in the GDP form is subjected to regulation. Treatment of mammalian cells with polysorbitan monolaurate was found to inhibit nuclear export of tRNA and proteins, which are processes dependent on RanGTP in the nucleus, but not nuclear import of proteins. Inhibition of the export processes by polysorbitan monolaurate is specific and reversible, and is caused by accumulation of Ran in the cytoplasm because of a block in translocation of NTF2 to the cytoplasm. Nuclear import of Ran and the nuclear export processes are restored in polysorbitan monolaurate treated cells overproducing NTF2. Moreover, increased phosphorylation of a phospho-tyrosine protein and several phospho-threonine proteins was observed in polysorbitan monolaurate treated cells. Collectively, these findings suggest that nucleocytoplasmic translocation of NTF2 is regulated in mammalian cells, and may involve a tyrosine and/or threonine kinase-dependent signal transduction mechanism(s).