A highly specific inhibitor of human p38 MAP kinase binds in the ATP pocket

Mammary branch initiation and extension are inhibited by separate pathways downstream of TGFβ in culture

During the branching morphogenesis process that builds epithelial trees, signaling from stimulatory and inhibitory growth factors is integrated to control branch initiation and extension into the surrounding stroma. Here, we examined the relative roles played by these stimulatory and inhibitory signals in the patterning of branch initiation and extension of model mammary epithelial tubules in culture. We found that although several growth factors could stimulate branching, they did not determine the sites at which new branches formed or the lengths to which branches extended. Instead, branch initiation and extension were defined by two separate signals downstream of the inhibitory morphogen, transforming growth factor (TGF)-β. Branch initiation was controlled by signaling through p38 mitogen-activated protein kinase, whereas branch extension was controlled by Smad-mediated induction of a second diffusible inhibitor, Wnt5a. These data suggest that mammary epithelial branching is patterned predominately by repulsive signaling, and that TGFβ activates multiple inhibitory pathways to refine the architecture of the tree.

Parasite mitogen-activated protein kinases as drug discovery targets to treat human protozoan pathogens

Protozoan pathogens are a highly diverse group of unicellular organisms, several of which are significant human pathogens. One group of protozoan pathogens includes obligate intracellular parasites such as agents of malaria, leishmaniasis, babesiosis, and toxoplasmosis. The other group includes extracellular pathogens such as agents of giardiasis and amebiasis. An unfortunate unifying theme for most human protozoan pathogens is that highly effective treatments for them are generally lacking. We will review targeting protozoan mitogen-activated protein kinases (MAPKs) as a novel drug discovery approach towards developing better therapies, focusing on Plasmodia, Leishmania, and Toxoplasma, about which the most is known.

Human p38 mitogen-activated protein kinase inhibitor drugs inhibit Plasmodium falciparum replication

We recently demonstrated that human p38 mitogen-activated protein kinase (MAPK) inhibitors reduced in vitro and in vivo replication of the protozoan parasites Toxoplasma gondii and Encephalitozoon cuniculi. In this study, we assessed the efficacy of five p38 MAPK inhibitors to block the replication of Plasmodium falciparum in human erythrocytes cultured ex vivo and demonstrate that the pyridinylimidazole RWJ67657 and the pyrrolobenzimidazole RWJ68198 reduced P. falciparum replication, yielded trophozoites that were greatly diminished in size at 24h, and that these two agents interfered with stage differentiation. Interestingly, the chloroquine-resistant strain W2 was significantly more sensitive to these drugs than was the chloroquine-sensitive strain HB3. These results suggest that pyridinylimidazoles and pyrrolobenzimidazoles designed to inhibit human p38 MAPK activation can be developed to treat malaria.

T cell LFA-1 engagement induces HuR-dependent cytokine mRNA stabilization through a Vav-1, Rac1/2, p38MAPK and MKK3 signaling cascade

BACKGROUND

Engagement of the β2 integrin, lymphocyte function-associated antigen-1 (LFA-1), results in stabilization of T cell mRNA transcripts containing AU-rich elements (AREs) by inducing rapid nuclear-to-cytosolic translocation of the RNA-stabilizing protein, HuR. However, little is known regarding integrin-induced signaling cascades that affect mRNA catabolism. This study examines the role of the GTPases, Rac 1 and Rac 2, and their downstream effectors, in the LFA-1-induced effects on mRNA.

METHODOLOGY/PRINCIPAL FINDINGS

Engagement of LFA-1 to its ligand, ICAM-1, in human peripheral T cells resulted in rapid activation of Rac1 and Rac2. siRNA-mediated knockdown of either Rac1 or Rac2 prevented LFA-1-stimulated stabilization of the labile transcripts encoding IFN-γ and TNF-α, and integrin mediated IFN-γ mRNA stabilization was absent in T cells obtained from Rac2 gene-deleted mice. LFA-1 engagement-induced translocation of HuR and stabilization of TNF- α mRNA was lost in Jurkat cells deficient in the Rac guanine nucleotide exchange factor Vav-1 (J.Vav1). The transfection of J.Vav1 cells with constitutively active Rac1 or Rac2 stabilized a labile β-globin reporter mRNA, in a HuR-dependent manner. Furthermore, LFA-1-mediated mRNA stabilization and HuR translocation in mouse splenic T cells was dependent on the phosphorylation of the mitogen-activated protein kinase kinase, MKK3, and its target MAP kinase p38MAPK, and lost in T cells obtained from MKK3 gene-deleted mice.

CONCLUSIONS/SIGNIFICANCE

Collectively, these results demonstrate that LFA-1-induced stabilization of ARE-containing mRNAs in T cells is dependent on HuR, and occurs through the Vav-1, Rac1/2, MKK3 and p38MAPK signaling cascade. This pathway constitutes a molecular switch that enhances immune and pro-inflammatory gene expression in T cells undergoing adhesion at sites of activation and effector function.

Structural determinants of PERK inhibitor potency and selectivity

The unfolded protein response (UPR) is a coordinated program that promotes cell survival under conditions of endoplasmic reticulum stress and is required in tumor progression as well. To date, no specific small molecule inhibitor targeting this pathway has been identified. Pancreatic endoplasmic reticulum kinase (PERK), one of the UPR transducers, is an eIF2α kinase. Compromising PERK function inhibits tumor growth in mice, suggesting that PERK may be a cancer drug target, but identifying a specific inhibitor of any kinase is challenging. The goal of this study was to identify some pair-wise receptor-ligand atomic contacts that confer selective PERK inhibition. Compounds selectively inhibiting PERK-mediated phosphorylation in vitro were identified using an initial virtual library screen, followed by structure-activity hypothesis testing. The most potent PERK selective inhibitors utilize three specific kinase active site contacts that, when absent from chemically similar compounds, abrogates the inhibition: (i) a strong van der Waals contact with PERK residue Met7, (ii) interactions with the N-terminal portion of the activation loop, and (iii) groups providing electrostatic complementarity to Asp144. Interestingly, the activation loop contact is required for PERK selectivity to emerge. Understanding these structure-activity relationships may accelerate rational PERK inhibitor design.

Inhibitors of p38 suppress cytokine production in rheumatoid arthritis synovial membranes: does variable inhibition of interleukin-6 production limit effectiveness in vivo?

OBJECTIVE

The activity of p38 MAPK regulates lipopolysaccharide (LPS)-stimulated production of key proinflammatory cytokines such as tumor necrosis factor α (TNFα). Consequently, p38 MAPK inhibitors have attracted considerable interest as potential treatments of rheumatoid arthritis (RA), and studies in murine models of arthritis have yielded promising results. However, the performance of several compounds in human clinical trials has been disappointing. At present, the reason for this poor performance is unclear. The aim of this study was to examine the effects of p38 inhibitors on both diseased and normal human tissue and cells, in order to test whether this kinase still plays a critical role in cytokine production under conditions of chronic inflammation.

METHODS

Proinflammatory and antiinflammatory cytokine production was monitored after treatment of primary human monocytes, macrophages, and RA synovial membrane cultures with p38 MAPK inhibitor compounds. The following 3 inhibitors were used in these studies: SB-203580 (inhibits the α and β isoforms), BIRB-796 (inhibits the α, β, γ, and δ isoforms), and a novel, structurally distinct p38 MAPK inhibitor, SB-731445 (inhibits the α and β isoforms).

RESULTS

SB-731445 and SB-203580 produced profound inhibition of spontaneous production of proinflammatory cytokines (TNFα and interleukin-1 [IL-1]) in both RA membrane cultures and LPS-stimulated primary human monocytes. However, this and other p38 MAPK inhibitors produced a significant increase in IL-6 production by LPS-stimulated primary human macrophages and a decrease in IL-10 production by all cell types examined.

CONCLUSION

The potentially proinflammatory consequences of these activities (decreased IL-10 production and increased IL-6 production) may offer some explanation for the inability of p38 MAPK inhibitors to provide the therapeutic benefit that had been hoped for in RA.

A Single Amino Acid Substitution Makes WNK4 Susceptible to SB 203580 and SB 202190

Regulation of the SLC12 family of membrane transporters including NCCT involves a scaffold of interacting proteins including the STE 20 kinase SPAK and the WNK kinases, WNK 1 and WNK 4, which are mutated in the hypertensive syndrome of pseudohypoaldosteronism type 2 (PHAII). WNK4 regulates NCCT by affecting forward trafficking to the surface membrane. Studies in Xenopus using kinase dead WNK4 site mutants have produced inconsistent results with regard to the necessity of kinase function for NCCT regulation. Dynamic inhibition of WNK4 by small molecules may bring clarity to this issue however WNK4 is naturally resistant to commercial MAP kinase inhibitors owing to steric constraints prohibiting entry of small molecules to the active site. Using an approach similar to that used in p38 and ERK, we show that a single substitution in WNK4 (T261G) dramatically enhances its susceptibility to the inhibitors SB 202190 and SB 203580.

SB203580, a p38 inhibitor, improved cardiac function but worsened lung injury and survival during Escherichia coli pneumonia in mice

BACKGROUND

Supporting its therapeutic application in sepsis, p38 mitogen-activated protein kinase (MAPK) inhibition decreases cardiopulmonary injury and lethality with lipopolysaccharide challenge. However, only one preclinical study has reported the survival effects of a p38 inhibitor (SB203580, 100 mg/kg) during infection. We therefore tested SB203580 in mice (n = 763) challenged with intratracheal Escherichia coli and treated with antibiotics and fluids.

METHODS AND RESULTS

Compared with placebo, high dose SB203580 (100 mg/kg) pretreatment increased the hazards ratio of death (95% confidence interval) (3.6 [2.1, 6.1], p < 0.0001). Decreasing doses (10, 1, or 0.1 mg/kg) went from being harmful to having no significant effect (p < 0.0001 for the effect of decreasing dose). At 48 hours, but not 24 hours after E. coli, high and low dose SB203580 pretreatment decreased cardiac phosphorylated p38 MAPK levels and improved cardiac output either (p <or= 0.07). Low dose SB203580 did not alter lung neutrophils significantly but increased lung injury at 48 hours (p = 0.05). High dose decreased lung neutrophils and injury at 24 hours (p = 0.09 and 0.01, respectively) but then increased them at 48 hours (both p <or= 0.01). Lung injury was greater with high versus low dose at 48 hours (p = 0.002).

CONCLUSION

Thus, SB203580 had divergent effects on cardiac and lung function in E. coli challenged mice. Furthermore, high dose worsened survival and low dose did not improve it. Altogether, these findings suggest that clearly defining the risks and benefits of p38 MAPK inhibition is important before such treatment is applied in patients with or at risk of serious infection.

Targeting signaling pathways with small molecules to treat autoimmune disorders

Chronic activation of immune responses, mediated by inflammatory mediators and involving different effector cells of the innate and acquired immune system characterizes autoimmune disorders, such as rheumatoid arthritis, inflammatory bowel disease, psoriasis and septic shock syndrome. MAPKs are crucial intracellular mediators of inflammation. MAPK inhibitors are attractive anti-inflammatory drugs, because they are capable of reducing the synthesis of inflammation mediators at multiple levels and are effective in blocking proinflammatory cytokine signaling. Janus kinase (JAK)/signal transducers and activators of transcription (STAT) pathway converts cytokine signals into genomic responses regulating proliferation and differentiation of the immune cells. JAK inhibitors are a new class of immunomodulatory agents with immunosuppressive, anti-inflammatory and antiallergic properties. This review discusses the rationale behind current strategies of targeting MAPK and JAK/STAT signaling pathways, and the overall effects of signal transduction inhibitors in animal models of inflammatory disorders. Signal transduction inhibitors are small molecules that can be administered orally, and initial results of clinical trials have shown clinical benefits in patients with chronic inflammatory disorders.

Use of p38 MAPK Inhibitors for the Treatment of Werner Syndrome

Werner syndrome provides a convincing model for aspects of the normal ageing phenotype and may provide a suitable model for therapeutic interventions designed to combat the ageing process. Cultured primary fibroblast cells from Werner syndrome patients provide a powerful model system to study the link between replicative senescence in vitro and in vivo pathophysiology. Genome instability, together with an increased pro-oxidant state, and frequent replication fork stalling, all provide plausible triggers for intracellular stress in Werner syndrome cells, and implicates p38 MAPK signaling in their shortened replicative lifespan. A number of different p38 MAPK inhibitor chemotypes have been prepared rapidly and efficiently using microwave heating techniques for biological study in Werner syndrome cells, including SB203580, VX-745, RO3201195, UR-13756 and BIRB 796, and their selectivity and potency evaluated in this cellular context. Werner syndrome fibroblasts treated with a p38 MAPK inhibitor reveal an unexpected reversal of the accelerated ageing phenotype. Thus the study of p38 inhibition and its effect upon Werner pathophysiology is likely to provide new revelations into the biological mechanisms operating in cellular senescence and human ageing in the future.

Discovery of PDK1 kinase inhibitors with a novel mechanism of action by ultrahigh throughput screening

The phosphoinositide 3-kinase/AKT signaling pathway plays a key role in cancer cell growth, survival, and angiogenesis. Phosphoinositide-dependent protein kinase-1 (PDK1) acts at a focal point in this pathway immediately downstream of phosphoinositide 3-kinase and PTEN, where it phosphorylates numerous AGC kinases. The PDK1 kinase domain has at least three ligand-binding sites: the ATP-binding pocket, the peptide substrate-binding site, and a groove in the N-terminal lobe that binds the C-terminal hydrophobic motif of its kinase substrates. Based on the unique PDK1 substrate recognition system, ultrahigh throughput TR-FRET and Alphascreen screening assays were developed using a biotinylated version of the PDK1-tide substrate containing the activation loop of AKT fused to a pseudo-activated hydrophobic motif peptide. Using full-length PDK1, K(m) values were determined as 5.6 mum for ATP and 40 nm for the fusion peptide, revealing 50-fold higher affinity compared with the classical AKT(Thr-308)-tide. Kinetic and biophysical studies confirmed the PDK1 catalytic mechanism as a rapid equilibrium random bireactant reaction. Following an ultrahigh throughput screen of a large library, 2,000 compounds were selected from the reconfirmed hits by computational analysis with a focus on novel scaffolds. ATP-competitive hits were deconvoluted by dose-response studies at 1x and 10x K(m) concentrations of ATP, and specificity of binding was assessed in thermal shift assay. Inhibition studies using fusion PDK1-tide1 substrate versus AKT(Thr-308)-tide and kinase selectivity profiling revealed a novel selective alkaloid scaffold that evidently binds to the PDK1-interacting fragment pocket. Molecular modeling suggests a structural paradigm for the design of inhibitory versus activating allosteric ligands of PDK1.

Tumor necrosis factor-alpha regulates transforming growth factor-beta-dependent epithelial-mesenchymal transition by promoting hyaluronan-CD44-moesin interaction

Aberrant epithelial-mesenchymal transition (EMT) is involved in development of fibrotic disorders and cancer invasion. Alterations of cell-extracellular matrix interaction also contribute to those pathological conditions. However, the functional interplay between EMT and cell-extracellular matrix interactions remains poorly understood. We now show that the inflammatory mediator tumor necrosis factor-alpha (TNF-alpha) induces the formation of fibrotic foci by cultured retinal pigment epithelial cells through activation of transforming growth factor-beta (TGF-beta) signaling in a manner dependent on hyaluronan-CD44-moesin interaction. TNF-alpha promoted CD44 expression and moesin phosphorylation by protein kinase C, leading to the pericellular interaction of hyaluronan and CD44. Formation of the hyaluronan-CD44-moesin complex resulted in both cell-cell dissociation and increased cellular motility through actin remodeling. Furthermore, this complex was found to be associated with TGF-beta receptor II and clathrin at actin microdomains, leading to activation of TGF-beta signaling. We established an in vivo model of TNF-alpha-induced fibrosis in the mouse eye, and such ocular fibrosis was attenuated in CD44-null mice. The production of hyaluronan and its interaction with CD44, thus, play an essential role in TNF-alpha-induced EMT and are potential therapeutic targets in fibrotic disorders.

Global effects of kinase inhibitors on signaling networks revealed by quantitative phosphoproteomics

Aberrant signaling causes many diseases, and manipulating signaling pathways with kinase inhibitors has emerged as a promising area of drug research. Most kinase inhibitors target the conserved ATP-binding pocket; therefore specificity is a major concern. Proteomics has previously been used to identify the direct targets of kinase inhibitors upon affinity purification from cellular extracts. Here we introduce a complementary approach to evaluate the effects of kinase inhibitors on the entire cell signaling network. We used triple labeling SILAC (stable isotope labeling by amino acids in cell culture) to compare cellular phosphorylation levels for control, epidermal growth factor stimulus, and growth factor combined with kinase inhibitors. Of thousands of phosphopeptides, less than 10% had a response pattern indicative of targets of U0126 and SB202190, two widely used MAPK inhibitors. Interestingly, 83% of the growth factor-induced phosphorylation events were affected by either or both inhibitors, showing quantitatively that early signaling processes are predominantly transmitted through the MAPK cascades. In contrast to MAPK inhibitors, dasatinib, a clinical drug directed against BCR-ABL, which is the cause of chronic myelogenous leukemia, affected nearly 1,000 phosphopeptides. In addition to the proximal effects on ABL and its immediate targets, dasatinib broadly affected the downstream MAPK pathways. Pathway mapping of regulated sites implicated a variety of cellular functions, such as chromosome remodeling, RNA splicing, and cytoskeletal organization, some of which have been described in the literature before. Our assay is streamlined and generic and could become a useful tool in kinase drug development.

ERK and not p38 pathway is required for IL-12 restoration of T cell IL-2 and IFN-gamma in a rodent model of alcohol intoxication and burn injury

Previous studies from our laboratory have shown that acute alcohol/ethanol (EtOH) intoxication combined with burn injury suppresses T cell IL-2 and IFN-gamma production by inhibiting p38 and ERK activation. Because IL-12 plays a major role in Th1 differentiation and IFN-gamma production, we examined whether diminished IL-2 and IFN-gamma production after EtOH plus burn injury resulted from a decrease in IL-12. Furthermore, we investigated whether IL-12 utilizes the p38/ERK pathway to modulate T cell IL-2 and IFN-gamma production after EtOH and burn injury. Male rats ( approximately 250 g) were gavaged with 5 ml of 20% EtOH 4 h before approximately 12.5% total body surface area burn or sham injury. Rats were sacrificed on day 1 after injury, and mesenteric lymph node T cells were isolated. T cells were stimulated with anti-CD3 in the absence or presence of rIL-12 (10 ng/ml) for 5 min and lysed. Lysates were analyzed for p38/ERK protein and phosphorylation levels using specific Abs and Western blot. In some experiments, T cells were cultured for 48 h with or without the inhibitors of p38 (10 microM SB203580/SB202190) or ERK (50 microM PD98059) to delineate the role of p38 and ERK in IL-12-mediated restoration of IL-2 and IFN-gamma. Our findings indicate that IL-12 normalizes both p38 and ERK activation in T cells, but the results obtained using p38 and ERK inhibitors indicate that the restoration of ERK plays a predominant role in IL-12-mediated restoration of T cell IL-2 and IFN-gamma production after EtOH and burn injury.

p38alpha MAP kinase C-terminal domain binding pocket characterized by crystallographic and computational analyses

The mitogen-activated protein (MAP) kinase protein family has a critical role in cellular signaling events, with MAP kinase p38alpha acting in inflammatory processes and being an important drug discovery target. MAP kinase drug design efforts have focused on small-molecule inhibitors of the ATP catalytic site, which exhibit dose-limiting adverse effects. Therefore, characterizing other potential sites that bind substrates, inhibitors, or allosteric effectors is of great interest. Here, we present the crystal structure of human p38alpha MAP kinase, which has a lead compound bound both in the active site and in the lipid-binding site of the C-terminal cap. This C-terminal cap is formed from an extension to the kinase fold, unique to the MAP kinase and cyclin-dependent kinase families and glycogen synthase kinase 3. Binding of this lead, 4-[3-(4-fluorophenyl)-1H-pyrazol-4-yl]pyridine, to wild-type p38alpha induces movement of the C-terminal cap region, creating a hydrophobic pocket centered around residue Trp197. Computational analysis of this C-terminal domain pocket indicates notable flexibility for potentially binding different-shaped compounds, including lipids, oxidized arachidonic acid species such as leukotrienes, and small-molecule effectors. Furthermore, our structural results defining the open p38alpha C-lobe pocket provide a detailed framework for the design of novel small molecules with affinities comparable to active-site binders: to bind and potentially modulate the shape and activity of p38alpha in predetermined ways. Moreover, these results and analyses of p38alpha suggest strategies for designing specific binding compounds applicable to other MAP kinases, as well as the cyclin-dependent kinase family and glycogen synthase kinase 3beta that also utilize the C-terminal insert in their interactions.

Structural bioinformatics-based prediction of exceptional selectivity of p38 MAP kinase inhibitor PH-797804

PH-797804 is a diarylpyridinone inhibitor of p38alpha mitogen-activated protein (MAP) kinase derived from a racemic mixture as the more potent atropisomer (aS), first proposed by molecular modeling and subsequently confirmed by experiments. On the basis of structural comparison with a different biaryl pyrazole template and supported by dozens of high-resolution crystal structures of p38alpha inhibitor complexes, PH-797804 is predicted to possess a high level of specificity across the broad human kinase genome. We used a structural bioinformatics approach to identify two selectivity elements encoded by the TXXXG sequence motif on the p38alpha kinase hinge: (i) Thr106 that serves as the gatekeeper to the buried hydrophobic pocket occupied by 2,4-difluorophenyl of PH-797804 and (ii) the bidentate hydrogen bonds formed by the pyridinone moiety with the kinase hinge requiring an induced 180 degrees rotation of the Met109-Gly110 peptide bond. The peptide flip occurs in p38alpha kinase due to the critical glycine residue marked by its conformational flexibility. Kinome-wide sequence mining revealed rare presentation of the selectivity motif. Corroboratively, PH-797804 exhibited exceptionally high specificity against MAP kinases and the related kinases. No cross-reactivity was observed in large panels of kinase screens (selectivity ratio of >500-fold). In cellular assays, PH-797804 demonstrated superior potency and selectivity consistent with the biochemical measurements. PH-797804 has met safety criteria in human phase I studies and is under clinical development for several inflammatory conditions. Understanding the rationale for selectivity at the molecular level helps elucidate the biological function and design of specific p38alpha kinase inhibitors.

Inhibition of basal p38 or JNK activity enhances epithelial barrier function through differential modulation of claudin expression

Tight junctions (TJs) form a barrier to the paracellular diffusion of ions and solutes across epithelia. Although transmembrane proteins of the claudin family have emerged as critical determinants of TJ permeability, little is known about the signaling pathways that control their expression. The aim of this study was to assess the role of three mitogen-activated protein kinases (MAPKs), i.e., extracellular signal-regulated kinase-1/2 (ERK1/2), c-Jun NH(2)-terminal kinases (JNKs), and p38 kinases, in the regulation of epithelial barrier function and claudin expression in mammary epithelial cells. Addition of either PD169316 (a p38 inhibitor) or SP600125 (a JNK inhibitor) induced formation of domes (a phenomenon dependent on TJ barrier function) and enhanced transepithelial electrical resistance, whereas U0126 (an inhibitor of the ERK1/2 activators MEK1/MEK2) had no significant effect. Similar results were obtained using mechanistically unrelated p38 or JNK inhibitors. PD169316 increased the expression of claudin-4 and -8, whereas SP600125 increased claudin-4 and -9 and downregulated claudin-8. Silencing of p38alpha by isoform-specific small interfering RNAs increased claudin-4 and -8 mRNAs, whereas silencing of p38beta only increased claudin-4 mRNA. Silencing of either JNK1 or JNK2 increased claudin-9 mRNA expression while decreasing claudin-8 mRNA. Moreover, selective silencing of JNK2 increased claudin-4 and -7 mRNAs. Finally, both PD169316 and SP600125 inhibited the paracellular diffusion of Na(+) and Cl(-) across epithelial monolayers. Collectively, these results provide evidence that inhibition of either p38 or JNK enhances epithelial barrier function by selectively modulating claudin expression, implying that the basal activity of these MAPKs exerts a tonic effect on TJ ionic permeability.

Molecular signaling blockade as a new approach to inhibit leukocyte-endothelial interactions for inflammatory bowel disease treatment

Mitogen-activated protein kinases (MAPK) are among the major widespread transduction pathways in humans. They are involved in several inflammatory disorders, including the pathogenesis of inflammatory bowel disease (IBD). A recent paper showed that activated MAPK are upregulated on endothelium and fibroblasts from intestinal biopsies of active IBD patients. In vitro experiments demonstrated that MAPK activation on intestinal endothelial cells and fibroblasts are responsible for the production of certain chemokines, increased leukocyte adhesion and transmigration. Specific local inhibition of MAPK activity on endothelial cells and fibroblasts may provide a new mechanism to control mucosal inflammation and leukocyte recruitment into the intestine of active IBD patients.

Requirement of TLR4 and CD14 in dendritic cell activation by Hemagglutinin B from Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative anaerobic bacterium that is one of the causative agents of chronic adult periodontal disease. Among the potential virulence factors of P. gingivalis are the hemagglutinins. Recombinant Hemagglutinin B (rHagB) from P. gingivalis has been shown to activate the immune system by inducing specific antibodies that protect against experimental periodontal bone loss following P. gingivalis infection. Since different microbial products can stimulate dendritic cells (DC) through Toll-like receptors (TLRs), subsequently leading to T cell activation and antibody production, we wanted to investigate the immunostimulatory effect of rHagB on DC and the role of TLR signaling in this process. Using an endotoxin free rHagB preparation, our results show that stimulation of murine bone marrow-derived DC with rHagB leads to upregulation of the costimulatory molecules CD86 and CD40, activation of p38 and ERK MAP kinases, transcription factors NF-kappaB, CREB and IRF-3 and the production of IL-6, TNF-alpha, IL-12p40 and to a lesser extent IL-10 and IFN-beta. This activation process was absolutely dependent on TLR4 and CD14. While upregulation of CD86 was independent of the adaptor molecule MyD88, CD40 upregulation and optimal cytokine (IL-6, TNF-alpha, IL-12p40, IL-10 and IFN-beta) production required both MyD88 and TRIF molecules. These results are of importance since they are the first to provide insights into the interaction of rHagB with DC and TLRs. The information from this study will aid in the design of effective vaccines strategies against chronic adult periodontal disease.

Structure-activity relationships and X-ray structures describing the selectivity of aminopyrazole inhibitors for c-Jun N-terminal kinase 3 (JNK3) over p38

c-Jun N-terminal kinase 3alpha1 (JNK3alpha1) is a mitogen-activated protein kinase family member expressed primarily in the brain that phosphorylates protein transcription factors, including c-Jun and activating transcription factor-2 (ATF-2) upon activation by a variety of stress-based stimuli. In this study, we set out to design JNK3-selective inhibitors that had >1000-fold selectivity over p38, another closely related mitogen-activated protein kinase family member. To do this we employed traditional medicinal chemistry principles coupled with structure-based drug design. Inhibitors from the aminopyrazole class, such as SR-3576, were found to be very potent JNK3 inhibitors (IC(50) = 7 nm) with >2800-fold selectivity over p38 (p38 IC(50) > 20 microm) and had cell-based potency of approximately 1 microm. In contrast, indazole-based inhibitors exemplified by SR-3737 were potent inhibitors of both JNK3 (IC(50) = 12 nm) and p38 (IC(50) = 3 nm). These selectivity differences between the indazole class and the aminopyrazole class came despite nearly identical binding (root mean square deviation = 0.33 A) of these two compound classes to JNK3. The structural features within the compounds giving rise to the selectivity in the aminopyrazole class include the highly planar nature of the pyrazole, N-linked phenyl structures, which better occupied the smaller active site of JNK3 compared with the larger active site of p38.

Heat shock protein expression in diabetic nephropathy

Heat shock protein (HSP) HSP27, HSP60, HSP70, and HSP90 are induced by cellular stresses and play a key role in cytoprotection. Both hyperglycemia and glomerular hypertension are crucial determinants in the pathogenesis of diabetic nephropathy and impose cellular stresses on renal target cells. We studied both the expression and the phosphorylation state of HSP27, HSP60, HSP70, and HSP90 in vivo in rats made diabetic with streptozotocin and in vitro in mesangial cells and podocytes exposed to either high glucose or mechanical stretch. Diabetic and control animals were studied 4, 12, and 24 wk after the onset of diabetes. Immunohistochemical analysis revealed an overexpression of HSP25, HSP60, and HSP72 in the diabetic outer medulla, whereas no differences were seen in the glomeruli. Similarly, exposure neither to high glucose nor to stretch altered HSP expression in mesangial cells and podocytes. By contrast, the phosphorylated form of HSP27 was enhanced in the glomerular podocytes of diabetic animals, and in vitro exposure of podocytes to stretch induced HSP27 phosphorylation via a P38-dependent mechanism. In conclusion, diabetes and diabetes-related insults differentially modulate HSP27, HSP60, and HSP70 expression/phosphorylation in the glomeruli and in the medulla, and this may affect the ability of renal cells to mount an effective cytoprotective response.

Targeting the ribose and phosphate binding site of p38 mitogen-activated protein (MAP) kinase: synthesis and biological testing of 2-alkylsulfanyl-, 4(5)-aryl-, 5(4)-heteroaryl-substituted imidazoles

Three series of substituted 2-alkylsulfanyl-4-(4-fluorophenyl)imidazoles, 5-pyridinyl-, 1-methyl-5-pyridinyl-, and 5-(2-aminopyridin-4-yl)-imidazoles, were prepared and tested for their ability to inhibit p38 MAP kinase and TNF-alpha release. These compounds were prepared by using different synthetic routes. They were tested by applying a nonradioactive p38 MAP kinase assay and by measurement of TNF-alpha release in human whole blood. Potent inhibitors (IC50 values in the low nanomolar range, as low as 2 nM in the enzyme assay and 37 nM in the human whole blood test) were identified by variation of substituents at the imidazole- C2-thio position as well as at the 2-aminopyridinyl functionality. In contrast to other known kinase inhibitors, these novel imidazole derivatives with the substituents at the imidazole-C2-thio position may interact with the ribose as well as with the phosphate binding site of the p38 MAP kinase.

Quantitative structure-activity relationship study of benzylsulfanyl imidazoles as cytokine release inhibitors

Benzylsulfanyl imidazole derivatives (Figure 1) have shown their ability to inhibit the release of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) from peripheral blood mononuclear cells or human whole blood. Such anticytokine actions of these congeners are quantitatively studied using Fujita-Ban and Hansch type analyses. The Fujita-Ban study resulted in the contributions of different substituents and the parent moiety for the inhibitions of cytokines TNF-alpha and IL-1beta. The substituents that have a higher positive contribution to the given activity, relative to substituents of the parent moiety at different positions were then used to obtain a trend for the active analogues. None of the substituents present at X, Y, 2-R and 3-R, appears to be advantageous over the substituents of the parent moiety for inhibition of both the cytokines. However, the substituents at 4-R, 5-R and 6-R help to improve the inhibitory actions of the compounds for both cytokines. The optimal activities seem to be manifested by compounds in which 4-R, 5-R and 6-R are substituted respectively by OH (or SOCH3 and SO2CH3), Cl and OH for inhibition of TNF-alpha, whereas by SOCH3 (or SO2CH3 and OH), H and OH for inhibition of IL-1beta. The Hansch type analysis, on the other hand, revealed that the F-substituents of the X-position and a less bulky structural moiety such as--S(CH2)2--at the Y-incision are advantageous in improving the inhibitory action towards TNF-alpha. Similarly, a less bulky/polar substituent present at 2-R and not having a hydrogen-bond donor property, while a more hydrophobic substituent at 3-R and hydrogen-bond acceptor substituent at 4-R are helpful in augmenting inhibitory activity of a compound. However, for inhibition of cytokine IL-1beta, it emerged that the X-substituents that transmits a higher negative resonance effect, the Y-substituent that offers less molecular bulk are beneficial. The R-substituents, being more electron donors at the meta-position, less hydrophobic at the para-position and offering smaller refractivity (less bulky and or polar) at the ortho-position are likewise helpful in improving the activity of a compound.

Are MAP kinases drug targets? Yes, but difficult ones

Pharmaceutical companies are facing an increasing interest in new target identification and validation. In particular, extensive efforts are being made in the field of protein kinase inhibitors research and development, and the past ten years of effort in this field have altered our perception of the potential of kinases as drug targets. Therefore, in the drug discovery process, the selection of relevant, susceptible protein kinase targets combined with searches for leads and candidates have become a crucial approach. The success of recent launches of protein kinase inhibitors (Gleevec, Imatinib, Sutent, Iressa, Nexavar, Sprycel) gave another push to this field. Numerous other kinase inhibitors are currently undergoing clinical trials or clinical development. Some questions are nevertheless unanswered, mostly related to the great number of known kinases in the human genome, to their similarity with each other, to the existence of functionally redundant kinases for specific pathways, and also because the connection between particular pathways and diseases is not always clear. The review is leading the reader through a panoramic view of protein kinase inhibition with a major focus on MAPK, successful examples and clinical candidates.

Construction of 4D-QSAR models for use in the design of novel p38-MAPK inhibitors

The p38-mitogen-activated protein kinase (p38-MAPK) plays a key role in lipopolysaccharide-induced tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) release during the inflammatory process, emerging as an attractive target for new anti-inflammatory agents. Four-dimensional quantitative structure-activity relationship (4D-QSAR) analysis [Hopfinger et al., J. Am. Chem. Soc., 119 (1997) 10509] was applied to a series of 33 (a training set of 28 and a test set of 5) pyridinyl-imidazole and pyrimidinyl-imidazole inhibitors of p38-MAPK, with IC50 ranging from 0.11 to 2100 nM [Liverton et al., J. Med. Chem., 42 (1999) 2180]. Five thousand conformations of each analogue were sampled from a molecular dynamics simulation (MDS) during 50 ps at a constant temperature of 303 K. Each conformation was placed in a 2 angstroms grid cell lattice for each of three trial alignments. 4D-QSAR models were constructed by genetic algorithm (GA) optimization and partial least squares (PLS) fitting, and evaluated by leave-one-out cross-validation technique. In the best models, with three to six terms, the adjusted cross-validated squared correlation coefficients, Q2adj, ranged from 0.67 to 0.85. Model D (Q2adj = 0.84) was identified as the most robust model from alignment 1, and it is representative of the other best models. This model encompasses new molecular regions as containing pharmacophore sites, such as the amino-benzyl moiety of pyrimidine analogs and the N1-substituent in the imidazole ring. These regions of the ligands should be further explored to identify better anti-inflammatory inhibitors of p38-MAPK.

Supernatant from bifidobacterium differentially modulates transduction signaling pathways for biological functions of human dendritic cells

Background

Probiotic bacteria have been shown to modulate immune responses and could have therapeutic effects in allergic and inflammatory disorders. However, the signaling pathways engaged by probiotics are poorly understood. We have previously reported that a fermentation product from Bifidobacterium breve C50 (BbC50sn) could induce maturation, high IL-10 production and prolonged survival of DCs via a TLR2 pathway. We therefore studied the roles of mitogen-activated protein kinases (MAPK), glycogen synthase kinase-3 (GSK3) and phosphatidylinositol 3-kinase (PI3K) pathways on biological functions of human monocyte-derived DCs treated with BbC50sn.

Methodology/Principal Findings

DCs were differentiated from human monocytes with IL-4 and GM-CSF for 5 days and cultured with BbC50sn, lipopolysaccharide (LPS) or Zymosan, with or without specific inhibitors of p38MAPK (SB203580), ERK (PD98059), PI3K (LY294002) and GSK3 (SB216763). We found that 1) the PI3K pathway was positively involved in the prolonged DC survival induced by BbC50sn, LPS and Zymosan in contrast to p38MAPK and GSK3 which negatively regulated DC survival; 2) p38MAPK and PI3K were positively involved in DC maturation, in contrast to ERK and GSK3 which negatively regulated DC maturation; 3) ERK and PI3K were positively involved in DC-IL-10 production, in contrast to GSK3 that was positively involved in DC-IL-12 production whereas p38MAPK was positively involved in both; 4) BbC50sn induced a PI3K/Akt phosphorylation similar to Zymosan and a p38MAPK phosphorylation similar to LPS.

Conclusion/Significance

We report for the first time that a fermentation product of a bifidobacteria can differentially activate MAPK, GSK3 and PI3K in order to modulate DC biological functions. These results give new insights on the fine-tuned balance between the maintenance of normal mucosal homeostasis to commensal and probiotic bacteria and the specific inflammatory immune responses to pathogen bacteria.

Activation of p38 MAP kinase is involved in central neuropathic pain following spinal cord injury

Recent work regarding chronic central neuropathic pain (CNP) following spinal cord injury (SCI) suggests that activation of key signaling molecules such as members of the mitogen activated protein kinase (MAPK) family play a role in the expression of at-level mechanical allodynia. Previously, we have shown that the development of at-level CNP following moderate spinal cord injury is correlated with increased expression of the activated (and thus phosphorylated) forms of the MAPKs extracellular signal related kinase and p38 MAPK. The current study extends this work by directly examining the role of p38 MAPK in the maintenance of at-level CNP following spinal cord injury. Using a combination of behavioral, immunocytochemical, and electrophysiological measures we demonstrate that increased activation of p38 MAPK occurs in the spinal cord just rostral to the site of injury in rats that develop at-level mechanical allodynia after moderate SCI. Immunocytochemical analyses indicate that the increases in p38 MAPK activation occurred in astrocytes, microglia, and dorsal horn neurons in the spinal cord rostral to the site of injury. Inhibiting the enzymatic activity of p38 MAPK dose dependently reverses the behavioral expression of at-level mechanical allodynia and also decreases the hyperexcitability seen in thoracic dorsal horn neurons after moderate SCI. Taken together, these novel data are the first to demonstrate causality that increased activation of p38 MAPK in multiple cell types play an important role in the maintenance of at-level CNP following spinal cord injury.

Use of cell-permeable peptides to prevent neuronal degeneration

The loss of neurons is a hallmark of neurodegenerative disorders and evidence suggests that this occurs through an apoptotic mechanism. Following an insult, neuronal cells activate signal transduction pathways that lead to cell death and the establishment of the pathological state. The mechanisms underlying the cell-death response involve protein kinases, which phosphorylate many substrates and culminate in changes in gene expression. Traditionally, attempts at blocking such signaling targeted the phosphorylation of the substrates. However, preventing the interaction between two proteins using specific peptides might block the function of key mediators in signaling cascades. A cell-permeable peptide designed specifically to inhibit c-Jun N-terminal kinase action proved successful in in vivo models of neuronal degeneration following ischemia. Here, the recent findings that highlight the potential of this approach for therapeutic application are reviewed.

CD40-CD40 ligand interactions in human microglia induce CXCL8 (interleukin-8) secretion by a mechanism dependent on activation of ERK1/2 and nuclear translocation of nuclear factor-kappaB (NFkappaB) and activator protein-1 (AP-1)

CXCL8 is a CXC chemokine that recruits leukocytes to sites of inflammation. Expression of CXCL8 in the CNS has been demonstrated in neuroinflammatory diseases, including human immunodeficiency virus (HIV-1) encephalitis, but the mechanism of secretion of this chemokine is not fully understood. CD40 is a 50-kDa protein on the surface of microglia, and we have previously shown that it is increased in expression in HIV-1-infected brain tissue as well as by interferon-gamma (IFNgamma) in tissue culture. We examined the expression and regulation of CXCL8 in cultured human fetal microglia after ligation of CD40 with soluble trimeric CD40 ligand (sCD40L) as well as the expression of CXCL8 on microglia in HIV encephalitic brain tissue sections. Treatment of cultured microglia with IFNgamma + sCD40L resulted in significant induction of CXCL8. This expression was mediated by activation of the ERK1/2 MAPK pathway, as demonstrated by ELISA and Western blot using a specific inhibitor (U0126). Gel shift analyses demonstrated that NFkappaB and AP-1, but not C/EBPbeta, mediate microglial CXCL8 production. We also found increased colocalization of CXCL8 with CD68/CD40-positive cells in HIV encephalitic brain tissue compared with HIV-infected nonencephalitic and normal tissue. Thus, CD40-CD40L interactions facilitate chemokine expression, leading to the influx of inflammatory cells into the CNS. These events can lead to the pathology that is associated with neuroinflammatory diseases.

The design and synthesis of novel alpha-ketoamide-based p38 MAP kinase inhibitors

We have identified a novel series of potent p38 MAP kinase inhibitors through structure-based design which due to their extended molecular architecture bind, in addition to the ATP site, to an allosteric pocket. In vitro ADME and in vivo PK studies show these compounds to have drug-like characteristics which could result in the development of an oral treatment for inflammatory conditions.

Cardiotrophin-1 stimulates intercellular adhesion molecule-1 and monocyte chemoattractant protein-1 in human aortic endothelial cells

Intercellular adhesion molecule-1 (ICAM-1) and monocyte chemoattractant protein-1 (MCP-1) play critical roles in mediating monocyte adhesion to the vascular endothelium and monocyte migration into the subendothelial regions of the vessels. Inasmuch as cardiotrophin-1 (CT-1), an IL-6-type cytokine, was expressed in human atherosclerotic plaque, we examined whether CT-1 induces monocyte adhesion and migration by stimulating gene and protein expressions of ICAM-1 and MCP-1 in human aortic endothelial cells (HAECs). Immunocytochemistry revealed that CT-1 increased intensity of ICAM-1 and MCP-1 immunoreactivity in HAECs. Adhesion assay and chemotaxis assay revealed that CT-1 increased human monocytic THP-1 cell adhesion to HAECs and promoted chemotaxis in THP-1 cells, which were attenuated by anti-ICAM-1 and anti-MCP-1 antibody, respectively. Western blot analysis showed that CT-1 increased phosphorylation of ERK1/2 MAP kinase, p38 MAP kinase, and Akt and that their inhibitors, PD-98059, SB-203580, and LY-294002, respectively, inhibited phosphorylation. RNase protection assay and ELISA demonstrated that CT-1 increased gene and protein expressions of ICAM-1 and MCP-1. EMSA revealed that CT-1 enhanced NF-κB DNA-binding activity. CT-1-mediated upregulation of ICAM-1 and MCP-1 was suppressed by PD-98059, SB-203580, LY-294002, and parthenolide. The present study demonstrates that CT-1 promotes monocyte adhesion and migration by stimulating ICAM-1 and MCP-1 through mechanisms that involve ERK1/2 MAP kinase, p38 MAP kinase, phosphatidylinositol 3-kinase, and NF-κB pathways and suggests that CT-1 plays an important role in the pathophysiology of vascular inflammation and atherosclerosis.

Two adjacent docking sites in the yeast Hog1 mitogen-activated protein (MAP) kinase differentially interact with the Pbs2 MAP kinase kinase and the Ptp2 protein tyrosine phosphatase

Functional interactions between a mitogen-activated protein kinase (MAPK) and its regulators require specific docking interactions. Here, we investigated the mechanism by which the yeast osmoregulatory Hog1 MAPK specifically interacts with its activator, the MAPK kinase Pbs2, and its major inactivator, the protein phosphatase Ptp2. We found, in the N-terminal noncatalytic region of Pbs2, a specific Hog1-binding domain, termed HBD-1. We also defined two adjacent Pbs2-binding sites in Hog1, namely, the common docking (CD) domain and Pbs2-binding domain 2 (PBD-2). The PBD-2 docking site appears to be sterically blocked in the intact Hog1 molecule, but its affinity to Pbs2 is apparent in shorter fragments of Hog1. Both the CD and the PBD-2 docking sites are required for the optimal activation of Hog1 by Pbs2, and in the absence of both sites, Hog1 cannot be activated by Pbs2. These data suggest that the initial interaction of Pbs2 with the CD site might induce a conformational change in Hog1 so that the PBD-2 site becomes accessible. The CD and PBD-2 docking sites are also involved in the specific interaction between Hog1 and Ptp2 and govern the dynamic dephosphorylation of activated Hog1. Thus, the CD and the PBD-2 docking sites play critical roles in both the activation and inactivation of Hog1.

Transforming growth factor-beta-activated protein kinase 1-binding protein (TAB)-1alpha, but not TAB1beta, mediates cytokine-induced p38 mitogen-activated protein kinase phosphorylation and cell death in insulin-producing cells

Previous studies have indicated that the p38 MAPK participates in signaling events that lead to the death of the insulin-producing beta-cell. The aim of the present study was to elucidate the role of the TGF-beta-activated protein kinase 1-binding protein 1 (TAB1) in the cytokine-induced activation of p38. Levels of TAB1 mRNA and protein were analyzed by real-time PCR and immunoblotting, and TAB1 expression in mouse and human islet cells was down-regulated using lipofection of diced-small interfering RNA. TAB1 overexpression in beta-TC6 cells was achieved by transient transfections followed by fluorescence activated cell sorting. Phosphorylation of p38, c-Jun N-terminal kinase, and ERK was assessed by immunoblotting, and viability was determined using vital staining with bisbenzimide and propidium iodide. We observed that TAB1 is expressed in insulin-producing cells. Cytokine (IL-1beta + interferon-gamma)-stimulated p38 phosphorylation was significantly increased by TAB1alpha overexpression, but not TAB1beta overexpression, in beta-TC6 cells. The TAB1alpha-augmented p38 phosphorylation was paralleled by an increased cell death rate. Treatment of islet cells with diced-small interfering RNA specific for TAB1, but not for TGF-beta-activated kinase 1, resulted in lowered cytokine-induced p38 phosphorylation and protection against cell death. The cytokine-induced phosphorylation of c-Jun N-terminal kinase and ERK was not affected by changes in TAB1 levels. Finally, TAB1 phosphorylation was decreased by the p38 inhibitor SB203580. We conclude that TAB1alpha, but not TAB1beta, plays an important role in the activation of p38 in insulin-producing cells and therefore also in cytokine-induced beta-cell death.

Combined analysis of intracellular signalling and immunophenotype of human peripheral blood basophils by flow cytometry: a proof of concept

BACKGROUND

The signal transduction pathways and control mechanisms involved in IgE-mediated basophil activation remain incompletely understood.

OBJECTIVES

To investigate whether basophilic intracellular signal transduction and immunophenotype can be analysed simultaneously by flow cytometry.

METHODS

Basophils in whole blood were stimulated with anti-IgE and latex antigen at various concentrations and during different time courses. Phosphorylation of p38 mitogen-activated protein kinase (MAPK) as a representative of the intracellular signal transduction pathway and surface expression of CD63 was assessed simultaneously flow cytometrically. The effect of pre-incubation with IL-3 was assessed.

RESULTS

Stimulation of the basophils with anti-IgE and allergen induces a rapid phosphorylation of p38 MAPK that peaks between 1 and 5 min and returns to baseline levels after 60 min. In contrast, CD63 up-regulation demonstrates a maximal but more continuous expression that peaks approximately 5 min later than phosphorylation of p38 MAPK. Specific inhibition of p38 MAPK reduced or almost completely abrogated up-regulation of CD63. Pre-incubation of the basophils with IL-3 produces a rapid p38 MAPK phosphorylation over basal levels, but this was weaker and shorter than for anti-IgE stimulation. Pre-incubation of the basophils with IL-3 did not potentiate anti-IgE-induced phosphorylation of p38 MAPK and did affect spontaneous or IgE-mediated CD63 up-regulation.

CONCLUSIONS

This study provides the proof that the flow cytometer allows an integrated analysis of basophilic intracellular signalling and immunophenotyping. Owing to its technical simplicity, the low number of cells required and rapid analysis, the technique seems promising for use in the clinic as a diagnostic tool or to monitor therapy.

CAPSULE SUMMARY

This study is the first to provide evidence for a combined analysis of basophilic intracellular signalling and immunophenotyping by flow cytometry. Owing to its technical simplicity, the low number of cells required and rapid analysis, the technique seems promising for use in the clinic as a diagnostic tool or to monitor therapy.

Tagged fragment method for evolutionary structure-based de novo lead generation and optimization

Here we describe a computer-assisted de novo drug design method, EAISFD, which combines the de novo design engine EA-Inventor with a scoring function featuring the molecular docking program Surflex-Dock. This method employs tagged fragments, which are preserved substructures in EA-Inventor used for base fragment matching in Surflex-Dock, for constructing ligand structures under specific binding motifs. In addition, a target score mechanism is adopted that allows EAISFD to deliver a diverse set of desired structures. This method can be used to design novel ligand scaffolds (lead generation) or to optimize attachments on a fixed scaffold (lead optimization). EAISFD has successfully suggested many known inhibitor scaffolds as well as a number of new scaffold types when applied to p38 MAP kinase.

RIP2 mediates LPS-induced p38 and IkappaBalpha signaling including IL-12 p40 expression in human monocyte-derived dendritic cells

IL-12, the critical factor for the generation of the Th1 type immune response, is produced by dendritic cells (DC) upon stimulation with LPS. Different signal pathways mediate LPS-induced expression of IL-12 and involve PI3K, MAPK and the transcription factor NF-kappaB. Here, we show that the kinase Raf is involved in the expression of IL-12 in human DC stimulated by LPS. We demonstrate that Raf regulates the expression of the IL-12 subunit p40 not via the kinase MEK, the major effector of Raf in growth factor-dependent signaling, but via the receptor-interacting protein 2 (RIP2) using specific inhibitors for MAPK pathways. RIP2 is a kinase participating in LPS/Toll-like receptor 4 signaling. Knockdown of RIP2 by siRNA inhibited LPS-dependent expression of IL-12 p40. In addition, knockdown of RIP2 reduced phosphorylation of p38 MAPK, ERK and IkappaBalpha, which are known upstream regulators of IL-12 production. Thus, in human DC LPS stimulates a signal cascade that involves the Raf-dependent activation of RIP2 leading to expression of IL-12 p40.

Nicotinamide adenine dinucleotide metabolism as an attractive target for drug discovery

Nicotinamide adenine dinucleotide (NAD(+)) has crucial roles in many cellular processes, both as a coenzyme for redox reactions and as a substrate to donate ADP-ribose units. Enzymes involved in NAD(+) metabolism are attractive targets for drug discovery against a variety of human diseases, including cancer, multiple sclerosis, neurodegeneration and Huntington's disease. A small-molecule inhibitor of nicotinamide phosphoribosyltransferase, an enzyme in the salvage pathway of NAD(+) biosynthesis, is presently in clinical trials against cancer. An analog of a kynurenine pathway intermediate is efficacious against multiple sclerosis in an animal model. Indoleamine 2,3-dioxygenase plays an important role in immune evasion by cancer cells and other disease processes. Inhibitors against kynurenine 3-hydroxylase can reduce the production of neurotoxic metabolites while increasing the production of neuroprotective compounds. This review summarizes the existing knowledge on NAD(+) metabolic enzymes, with emphasis on their relevance for drug discovery.

Glycoprotein 120 binding to CXCR4 causes p38-dependent primary T cell death that is facilitated by, but does not require cell-associated CD4

HIV-1 infection causes the depletion of host CD4 T cells through direct and indirect (bystander) mechanisms. Although HIV Env has been implicated in apoptosis of uninfected CD4 T cells via gp120 binding to either CD4 and/or the chemokine receptor 4 (CXCR4), conflicting data exist concerning the molecular mechanisms involved. Using primary human CD4 T cells, we demonstrate that gp120 binding to CD4 T cells activates proapoptotic p38, but does not activate antiapoptotic Akt. Because ligation of the CD4 receptor alone or the CXCR4 receptor alone causes p38 activation and apoptosis, we used the soluble inhibitors, soluble CD4 (sCD4) or AMD3100, to delineate the role of CD4 and CXCR4 receptors, respectively, in gp120-induced p38 activation and death. sCD4 alone augments gp120-induced death, suggesting that CXCR4 signaling is principally responsible. Supporting that model, AMD3100 reduces death caused by gp120 or by gp120/sCD4. Finally, prevention of gp120-CXCR4 interaction with 12G5 Abs blocks p38 activation and apoptosis, whereas inhibition of CD4-gp120 interaction with Leu-3a has no effect. Consequently, we conclude that gp120 interaction with CXCR4 is required for gp120 apoptotic effects in primary human T cells.

Heat Shock Protein 27 Protects L929 Cells from Cisplatin-Induced Apoptosis by Enhancing Akt Activation and Abating Suppression of Thioredoxin Reductase Activity

PURPOSE

Heat shock protein 27 (Hsp27) is up-regulated in multiple malignancies and implicated in cisplatin resistance. It is attempted to know how Hsp27 endues cell with cisplatin resistance by interfering with upstream of both apoptosis signal-regulating kinase 1 (ASK1)/p38 mitogen-activated protein kinase-activated apoptotic signaling and serine/threonine kinase Akt-dependent survival signaling.

EXPERIMENTAL DESIGN

The mouse L929 cells stably transfected with human Hsp27 or its dominant-negative mutant and the human cervical cancer HeLa cells transfected with Hsp27 siRNA were used. The cisplatin-induced apoptosis and activation of ASK1, p38, and Akt were compared in control cells, cells overexpressing Hsp27, and cells with their endogenous Hsp27 knocked down.

RESULTS

Hsp27 effectively protected the cells from cisplatin-induced DNA fragmentation. The p38 inhibitors obviously decreased whereas Akt inhibitors markedly increased the apoptotic fraction in cisplatin-treated cells. Overexpression of Hsp27 doubly enhanced the drug-induced Akt activation while substantially depressing the drug-induced activation of ASK1 and p38. Knockdown of the endogenous Hsp27 in HeLa cells resulted in the effects opposite to that observed in the Hsp27-overexpressing cells. Enhancement of Akt activation is associated with complex formation between Akt and Hsp27, whereas depression of ASK1/p38 activation is attributed to a reversion of the drug-induced inhibition of thioredoxin reductase activity and subsequent oxidation of thioredoxin.

CONCLUSIONS

Hsp27 endues cells with cisplatin resistance via depression of the drug-induced ASK1/p38 activation and enhancement of the drug-induced Akt activation. This study revealed the intervention of Hsp27 in upstream of both ASK1/p38 apoptotic signaling and phosphatidylinositol 3-kinase/Akt survival signaling. Therefore, the inhibition of Hsp27 may be a novel strategy of cancer chemotherapy.