Pyridinyl Imidazole Research Articles

Unexpected inhibition of the lipid kinase PIKfyve reveals an epistatic role for p38 MAPKs in endolysosomal fission and volume control

p38 mitogen-activated protein kinases (MAPKs) participate in autophagic signaling; and previous reports suggest that pyridinyl imidazole p38 MAPK inhibitors, including SB203580 and SB202190, induce cell death in some cancer cell-types through unrestrained autophagy. Subsequent studies, however, have suggested that the associated cytoplasmic vacuolation resulted from off-target inhibition of an unidentified enzyme. Herein, we report that SB203580-induced vacuolation is rapid, reversible, and relies on the class III phosphatidylinositol 3-kinase (PIK3C3) complex and the production of phosphatidylinositol 3-phosphate [PI(3)P] but not on autophagy per se. Rather, vacuolation resulted from the accumulation of Rab7 on late endosome and lysosome (LEL) membranes, combined with an osmotic imbalance that triggered severe swelling in these organelles. Inhibition of PIKfyve, the lipid kinase that converts PI(3)P to PI(3,5)P2 on LEL membranes, produced a similar phenotype in cells; therefore, we performed in vitro kinase assays and discovered that both SB203580 and SB202190 directly inhibited recombinant PIKfyve. Cancer cells treated with either drug likewise displayed significant reductions in the endogenous levels of PI(3,5)P2. Despite these results, SB203580-induced vacuolation was not entirely due to off-target inhibition of PIKfyve, as a drug-resistant p38α mutant suppressed vacuolation; and combined genetic deletion of both p38α and p38β dramatically sensitized cells to established PIKfyve inhibitors, including YM201636 and apilimod. The rate of vacuole dissolution (i.e., LEL fission), following the removal of apilimod, was also significantly reduced in cells treated with BIRB-796, a structurally unrelated p38 MAPK inhibitor. Thus, our studies indicate that pyridinyl imidazole p38 MAPK inhibitors induce cytoplasmic vacuolation through the combined inhibition of both PIKfyve and p38 MAPKs, and more generally, that p38 MAPKs act epistatically to PIKfyve, most likely to promote LEL fission.

Anthracycline cardiotoxicity is exacerbated by global p38b genetic ablation in a sexually dimorphic manner but unaltered by cardiomyocyte-specific p38a loss.

Severe cardiotoxic effects limit the efficacy of doxorubicin (DOX) as a chemotherapeutic agent. Activation of intracellular stress signaling networks, including p38 mitogen-activated protein kinase (MAPK), have been implicated in DOX-induced cardiotoxicity (DIC). However, the roles of the individual p38 isoforms in DIC remain incompletely elucidated. We recently reported that global p38d deletion protected female but not male mice from DIC, while global p38g deletion did not significantly modulate it. Here we studied the in vivo roles of p38a and p38b in acute DIC. Male and female mice with cardiomyocyte-specific deletion of p38a or global deletion of p38b and their wild-type counterparts were injected with DOX. Survival and health were tracked for 10 days post-injection. Cardiac function was assessed by echocardiography and electrocardiography, and fibrosis by Picro Sirius Red staining. Expression and activation of signaling proteins and inflammatory markers were measured by western blot, phosphorylation array and chemokine/cytokine array, respectively. Global p38b deletion significantly aggravated DIC and worsened cardiac electrical and mechanical function deterioration in female mice. Mechanistically, DIC in p38b-null female mice correlated with increased autophagy, sustained hyperactivation of pro-apoptotic JNK signaling, as well as remodeling of myocardial inflammatory environment. In contrast, cardiomyocyte-specific deletion of p38a improved survival of DOX30-treated male mice 5 days post-treatment but did not influence cardiac function in DOX-treated male or female mice. Our data highlight the sex- and isoform-specific roles of p38a and p38b MAPKs in DOX-induced cardiac injury and suggest a novel in vivo function of p38b in protecting female mice from DIC.

Computer-aided drug design applied to a series of pyridinyl imidazole derivatives targeting p38α MAP kinase: 2D-QSAR, docking, MD simulation, and ADMET investigations

The p38 mitogen-activated protein kinase (MAPK) is a crucial target for chronic inflammation.

Dual Targeting of BRAF and mTOR Signaling in Melanoma Cells with Pyridinyl Imidazole Compounds.

BRAF inhibitors can delay the progression of metastatic melanoma, but resistance usually emerges, leading to relapse. Drugs simultaneously targeting two or more pathways essential for cancer growth could slow or prevent the development of resistant clones. Here, we identified pyridinyl imidazole compounds SB202190, SB203580, and SB590885 as dual inhibitors of critical proliferative pathways in human melanoma cells bearing the V600E activating mutation of BRAF kinase. We found that the drugs simultaneously disrupt the BRAF V600E-driven extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) activity and the mechanistic target of rapamycin complex 1 (mTORC1) signaling in melanoma cells. Pyridinyl imidazole compounds directly inhibit BRAF V600E kinase. Moreover, they interfere with the endolysosomal compartment, promoting the accumulation of large acidic vacuole-like vesicles and dynamic changes in mTOR signaling. A transient increase in mTORC1 activity is followed by the enrichment of the Ragulator complex protein p18/LAMTOR1 at contact sites of large vesicles and delocalization of mTOR from the lysosomes. The induced disruption of the endolysosomal pathway not only disrupts mTORC1 signaling, but also renders melanoma cells sensitive to endoplasmic reticulum (ER) stress. Our findings identify new activities of pharmacologically relevant small molecule compounds and provide a biological rationale for the development of anti-melanoma therapeutics based on the pyridinyl imidazole core.

PO-073 Dual targeting of proliferative pathways in BRAF-mutant melanoma cells by PYRIDINYL IMIDAZOLE compounds

IntroductionCarmofur (1-hexylcarbamoyl-5-fluorouracil, HCFU, Mifurol) is one of the masked forms of 5-fluorouracil widely used as an antineoplastic agent. The carmofur molecule contains an active core of 5-fluorouracil and hexylcarbamoyl substituent as a transport form, and it helps 5-FU to penetrate into the cell. In the last years the interest in using of 5-fluorouracil derivatives in cancer research was increased. Therefore, the aim of the present study is to evaluate the potential cytotoxic effect of carmofur on the breast cancer cell line, MCF-7.Material and methodsMTT assay, was used to detect cytotoxicity. For MTT assay, MCF-7 cells were treated with different concentrations of carmofur for 24 hours in 96-well plates. Incubated cells were quantifiend by spectrophotometry using a plate reader ar 570 nm wave lenght. Viability percentages were calculated from the obtained absorbances and IC50 value was determined.Results and discussionsTreatment of MCF-7 cells with different concentrations of carmofur resulted in a significant increase in the cell death in 24 hours. As conclusion, this study has shown that applied dose of carmofur in MCF-7 cells has an cytotoxic effect in concentration dependent manner.ConclusionThe calculated IC50 value was low enough for decreasing the viability of breast cancer cells in 24 hours. This result underline the potential cytotoxic effect of carmofur for MCF-7 cells and is a initial further investigation in manner of drug developing for cancer treatment.

Role of p38/MAPKs in Alzheimer's disease: implications for amyloid beta toxicity targeted therapy.

A myriad of environmental and genetic factors, as well as the physiologic process of aging, contribute to Alzheimer's disease (AD) pathology. Neuroinflammation is and has been a focus of interest, as a common gateway for initiation of many of the underlying pathologies of AD. Amyloid beta (Aβ) toxicity, increasing RAGE expression, tau hyperphosphorylation, induction of apoptosis, and deregulated autophagy are among other mechanisms, partly entangled and being explained by activation of mitogen-activated protein kinase (MAPK) and MAPK signaling. p38 MAPK is the most essential regulator of Aβ induced toxicity from this family. p38 induces NF-κB activation, glutamate excitotoxicity, and disruption of synaptic plasticity, which are other implications of all justifying the p38 MAPK as a potential target to break the vicious Aβ toxicity cycle. Until recently, many in vivo and in vitro studies have investigated the effects of p38 MAPK inhibitors in AD. The pyridinyl imidazole compounds SB202190 and SB203580 have shown promising anti-apoptotic results in vivo. MW108 inhibits activation of p38 and is able to postpone cognitive decline in animal models. The PD169316, with anti-inflammatory, anti-oxidative, and anti-apoptotic features, has improved spatial memory in vivo. Natural compounds from Camellia sinensis (green tea), polyphenols from olive oil, pinocembrin from propolis, and the puerarine extract isoflavones, have shown strong anti-apoptotic features, mediated by p38 MAPK inhibition. Use of these drug targets is limited due to central nervous system side effects or cross-reactivity with other kinases, predicting the low efficacy of these drugs in clinical trials.

Role of p38alpha/beta MAP Kinase in Cell Susceptibility to Clostridium sordellii Lethal Toxin and Clostridium difficile Toxin B.

Lethal Toxin from Clostridium sordellii (TcsL), which is casually involved in the toxic shock syndrome and in gas gangrene, enters its target cells by receptor-mediated endocytosis. Inside the cell, TcsL mono-O-glucosylates and thereby inactivates Rac/Cdc42 and Ras subtype GTPases, resulting in actin reorganization and an activation of p38 MAP kinase. While a role of p38 MAP kinase in TcsL-induced cell death is well established, data on a role of p38 MAP kinase in TcsL-induced actin reorganization are not available. In this study, TcsL-induced Rac/Cdc42 glucosylation and actin reorganization are differentially analyzed in p38alpha−/− MSCV empty vector MEFs and the corresponding cell line with reconstituted p38alpha expression (p38alpha−/− MSCV p38alpha MEFs). Genetic deletion of p38alpha results in reduced susceptibility of cells to TcsL-induced Rac/Cdc42 glucosylation and actin reorganization. Furthermore, SB203580, a pyridinyl imidazole inhibitor of p38alpha/beta MAP kinase, also protects cells from TcsL-induced effects in both p38−/− MSCV empty vector MEFs and in p38alpha−/− MSCV p38alpha MEFs, suggesting that inhibition of p38beta contributes to the protective effect of SB203580. In contrast, the effects of the related C. difficile Toxin B are responsive neither to SB203580 treatment nor to p38alpha deletion. In conclusion, the protective effects of SB203580 and of p38alpha deletion are likely not based on inhibition of the toxins’ glucosyltransferase activity rather than on inhibited endocytic uptake of specifically TcsL into target cells.

Comparative chemical array screening for p38γ/δ MAPK inhibitors using a single gatekeeper residue difference between p38α/β and p38γ/δ.

Mammalian p38 mitogen activated protein kinases (MAPKs) are responsive to a variety of cellular stresses. The development of specific pyridinyl imidazole inhibitors has permitted the characterization of the p38 MAPK isoform p38α, which is expressed in most cell types, whereas the physiological roles of p38γ and p38δ are poorly understood. In this study, we report an approach for identifying selective inhibitors against p38γ and p38δ by focusing on the difference in gatekeeper residues between p38α/β and p38γ/δ. Using GST-fused p38α wild type and T106M mutant constructs, wherein the p38α gatekeeper residue (Thr-106) was substituted by the p38γ/δ-type (Met), we performed comparative chemical array screening to identify specific binders of the mutant and identified SU-002 bound to p38αT106M specifically. SU-002 was found to inhibit p38αT106M but not p38α kinase activity in in vitro kinase assays. SU-005, the analog of SU-002, had inhibitory effects against the kinase activity of p38γ and p38δ in vitro but not p38α. In addition, SU-005 inhibited both p38γ and p38δ auto-phosphorylation in HeLa and HEK293T cells. These results demonstrate that the comparative chemical array screening approach is a powerful technique to explore specific inhibitors for mutant proteins with even single amino-acid substitutions in a high-throughput manner.

Pyridinyl imidazole inhibitors of p38 MAP kinase impair viral entry and reduce cytokine induction by Zaire ebolavirus in human dendritic cells

Antigen presenting cells (APCs), including macrophages and dendritic cells, are early and sustained targets of Ebola virus (EBOV) infection in vivo. Because EBOV activates mitogen-activated protein kinase (MAPK) signaling upon infection of APCs, we evaluated the effect of pyridinyl imidazole inhibitors of p38 MAPK on EBOV infection of human APCs and EBOV mediated cytokine production from human DCs. The p38 MAPK inhibitors reduced viral replication in PMA-differentiated macrophage-like human THP-1 cells with an IC50 of 4.73μM (SB202190), 8.26μM (p38kinhIII) and 8.21μM (SB203580) and primary human monocyte-derived dendritic cells (MDDCs) with an IC50 of 2.67μM (SB202190). Furthermore, cytokine production from EBOV-treated MDDCs was inhibited in a dose-dependent manner. A control pyridinyl imidazole compound failed to inhibit either EBOV infection or cytokine induction. Using an established EBOV virus-like particle (VLP) entry assay, we demonstrate that inhibitor pretreatment blocked VLP entry suggesting that the inhibitors blocked infection and replication at least in part by blocking EBOV entry. Taken together, our results indicate that pyridinyl imidazole p38 MAPK inhibitors may serve as leads for the development of therapeutics to treat EBOV infection.

Pyridinyl imidazole compounds interfere with melanosomes sorting through the inhibition of Cyclin G-associated Kinase, a regulator of cathepsins maturation

Transfer of melanin-containing melanosomes from melanocytes to neighboring keratinocytes results in skin pigmentation. Pharmacological modulation of melanosomal transfer has recently gained much attention as a strategy for modifying normal or abnormal pigmentation. In this study, while investigating the impact of pyridinyl imidazole (PI) compounds, a class of p38 MAPK inhibitors, on melanocyte differentiation we observed that some, but not all PIs interfere with the physiological melanosome sorting producing a strong retention of melanin in the intracellular compartment associated with a general reduction of melanin synthesis. Electron microscopy studies illustrated an accumulation of melanosomes inside melanocytes with enrichment in immature melanosome at stages II and III at the end of dendrites. We identified cyclin G-associated kinase GAK, a protein expressed ubiquitously in various tissues, as the off-target responsible of intracellular melanin accumulation and we report evidence that reduced GAK-dependent cathepsin maturation is implicated in melanosome sorting deficiency. The co-regulation of GAK and cathepsin B and L expression with the melanogenic biosynthetic pathway in normal human melanocytes as well as in B16-F0 melanoma cells strengthen the idea that these proteins represent new possible targets for prevention and treatment of irregular pigmentation.

Phosphorylation of Human Cytochrome P450c17 by p38α Selectively Increases 17,20 Lyase Activity and Androgen Biosynthesis

Cytochrome P450c17, a steroidogenic enzyme encoded by the CYP17A1 gene, catalyzes the steroid 17α-hydroxylation needed for glucocorticoid synthesis, which may or may not be followed by 17,20 lyase activity needed for sex steroid synthesis. Whether or not P450c17 catalyzes 17,20 lyase activity is determined by three post-translational mechanisms influencing availability of reducing equivalents donated by P450 oxidoreductase (POR). These are increased amounts of POR, the allosteric action of cytochrome b5 to promote POR-P450c17 interaction, and Ser/Thr phosphorylation of P450c17, which also appears to promote POR-P450c17 interaction. The kinase(s) that phosphorylates P450c17 is unknown. In a series of kinase inhibition experiments, the pyridinyl imidazole drugs SB202190 and SB203580 inhibited 17,20 lyase but not 17α-hydroxylase activity in human adrenocortical HCI-H295A cells, suggesting an action on p38α or p38β. Co-transfection of non-steroidogenic COS-1 cells with P450c17 and p38 expression vectors showed that p38α, but not p38β, conferred 17,20 lyase activity on P450c17. Antiserum to P450c17 co-immunoprecipitated P450c17 and both p38 isoforms; however, knockdown of p38α, but not knockdown of p38β, inhibited 17,20 lyase activity in NCI-H295A cells. Bacterially expressed human P450c17 was phosphorylated by p38α in vitro at a non-canonical site, conferring increased 17,20 lyase activity. This phosphorylation increased the maximum velocity, but not the Michaelis constant, of the 17,20 lyase reaction. p38α phosphorylates P450c17 in a fashion that confers increased 17,20 lyase activity, implying that the production of adrenal androgens (adrenarche) is a regulated event.

In Vitro Effects of SB202190 on Echinococcus granulosus

Spillage of cyst contents during surgical operation is the major cause of recurrence after hydatid cyst surgery. Instillation of a scolicidal agent into a hepatic hydatid cyst is the most commonly employed measure to prevent this complication. SB202190 is a pyridinyl imidazole derivative and is known to be a specific inhibitor of p38 MAPK. In the present study, the scolicidal effect of SB202190 was investigated. Freshly isolated Echinococcus granulosus protoscolices were subjected to SB202190 treatment (10, 20, 40, and 80 µM), and the effects on parasite viability were monitored by trypan blue staining. Corresponding effects were visualized by scanning and transmission electron microscopy. Dose-dependent protoscolex death within a few days of SB202190 treatment was observed. Although the in vitro scolicidal effect of SB202190 was satisfactory, the in vivo efficacy of this drug and also possible side effects remain to be further investigated.

Synthesis and Evaluation of Pyridinyltriazoles as Inhibitors of p38 MAP Kinase.

Inhibitors of p38 MAP kinase are considered as suitable target in the treatment of inflammatory diseases such as rheumatoid arthritis and bowel inflammatory diseases. The development of 5-alkylthio-1-aryl-2-(4-pyridinyl) triazoles as inhibitors of p38 MAP kinase is described. These are analogues of 4- pyridinyl imidazole p38 MAP kinase inhibitor reported by Merck Research Laboratories, in which imidazole ring has been replaced with triazole. Reaction of pyridine-4-carboxylic acid hydrazide 1 and arylisothiocyanate (2a, b) gave the intermediate thiourea derivative 3a, b (Figure 2). Refluxing of the latter in aqueous saturated sodium carbonate gave 1-aryl-5-mercapto-2-(4-pyridinyl) triazoles 4a, b. Treatment of 4a, b with alkyl iodide afforded the desired 5-alkylthio-1-aryl-2-(4-pyridinyl) triazoles (5a-d). P38 MAP kinase inhibitory activity of the synthesized compounds was evaluated in vitro by ELISA method and also by molecular docking. Compound 5c at 1 µM concentration and compound 5d at 1 µM and 10 µM significantly inhibited the p38 phosphorylation. These inhibitory effects are equal to those of standard compound SB202190 and no significant differences were observed. We demonstrated that both tested compounds have inhibitory effect on p38 MAP kinase and we did not find significant difference between their inhibitory effects and those of standard inhibitor SB202190.

Inhibition of Melanogenesis by the Pyridinyl Imidazole Class of Compounds: Possible Involvement of the Wnt/β-Catenin Signaling Pathway

While investigating the role of p38 MAPK in regulating melanogenesis, we found that pyridinyl imidazole inhibitors class compounds as well as the analog compound SB202474, which does not inhibit p38 MAPK, suppressed both α-MSH-induced melanogenesis and spontaneous melanin synthesis. In this study, we demonstrated that the inhibitory activity of the pyridinyl imidazoles correlates with inhibition of the canonical Wnt/β-catenin pathway activity. Imidazole-treated cells showed a reduction in the level of Tcf/Lef target genes involved in the β-catenin signaling network, including ubiquitous genes such as Axin2, Lef1, and Wisp1 as well as cell lineage-restricted genes such as microphthalmia-associated transcription factor and dopachrome tautomerase. Although over-expression of the Wnt signaling pathway effector β-catenin slightly restored the melanogenic program, the lack of complete reversion suggested that the imidazoles interfered with β-catenin-dependent transcriptional activity rather than with β-catenin expression. Accordingly, we did not observe any significant change in β-catenin protein expression. The independence of p38 MAPK activity from the repression of Wnt/β-catenin signaling pathway was confirmed by small interfering RNA knockdown of p38 MAPK expression, which by contrast, stimulated β-catenin-driven gene expression. Our data demonstrate that the small molecule pyridinyl imidazoles possess two distinct and opposite mechanisms that modulate β-catenin dependent transcription: a p38 inhibition-dependent effect that stimulates the Wnt pathway by increasing β-catenin protein expression and an off-target mechanism that inhibits the pathway by repressing β-catenin protein functionality. The p38-independent effect seems to be dominant and, at least in B16-F0 cells, results in a strong block of the Wnt/β-catenin signaling pathway.

A redox microenvironment is essential for MAPK-dependent secretion of pro-inflammatory cytokines: Modulation by glutathione (GSH/GSSG) biosynthesis and equilibrium in the alveolar epithelium

The characterization of oxidant (glutathione)-dependent regulation of MAPK p38/RK-mediated TNF-α secretion was undertaken in vitro, and the ramifications of the influence of a redox microenvironment were unraveled. Intermittent exposure of alveolar epithelial cells (FATEII) to LPS (endotoxin) transiently and temporally induced the expression of MAPK p38/RK. This upregulation was associated with the activation of MAPKAP-K 2, manifested by the specific phosphorylation of the downstream heat-shock protein (Hsp)-27. Selective blockading of the MAPK p38/RK pathway using the pyridinyl imidazole SB-203580 abrogated the LPS-dependent release of TNF-α. N-acetyl- l-cysteine (NAC), a precursor of glutathione, reduced TNF-α secretion and increased [GSH]. Conversely, l-buthionine-( S,R)-sulfoximine (BSO), an irreversible inhibitor of γ-glutamylcysteine synthetase (γ-GCS), the rate-limiting enzyme in the pathway mediating GSH biosynthesis, augmented the secretion of TNF-α and [GSSG] accumulation. Whereas NAC abrogated the phosphorylation of MAPK p38/RK, BSO reversibly amplified this effect. Furthermore, intermittent exposure of FATEII cells to the exogenous oxidants X/XO and H 2O 2 upregulated the secretion of pro-inflammatory cytokines IL-1β, IL-6 and TNF-α; this upregulation was correlated with increasing activity of key glutathione-related enzymes, closely involved with maintaining the cyclic GSH/GSSG equilibrium. These results indicate that a redox microenvironment plays a major role in regulating MAPK-dependent production of cytokines in the alveolar epithelium.

The Major Phagocyte Peroxidase-Derived Oxidant HOSCN Stimulates Gene-Specific p38 MAPK- Dependent, NF-κb-Mediated Activation of Tissue Factor, VCAM-1 and ICAM-1 Expression In Endothelium.

AbstractAbstract 1481Thiocyanate (SCN-) is, unexpectedly, the principal physiologic substrate for eosinophil peroxidase (EPO) and a major (i.e., accounting for 50% of H2O2 consumed) substrate for myeloperoxidase (MPO). The product of these reactions is HOSCN, a weak, exclusively sulfhydryl-reactive oxidant that we have previously shown to be a uniquely potent (up to 100-fold) oxidant transcriptional inducer of human umbilical vein endothelial cell (HUVEC) tissue factor (TF), ICAM-1 and VCAM-1 expression via a mechanism dependent upon NF-κB p65/p50 activation. We hypothesized that oxidative activation of p38 MAPK is a necessary and proximal step in the activation of NF-κB p65/p50 at the TF, VCAM-1 and ICAM-1 promoters. To test this we utilized the p38 MAPK-specific pyridinyl imidazole inhibitor SB 203580 (SB). In HUVEC monolayers exposed 4h to 150 μM HOSCN in M199 medium containing 10% FCS, SB strongly inhibited (>90%, ED50 300 nM) TF activity, decreased VCAM-1 expression assessed by western blot by > 50% but had no discernible effect upon ICAM-1 expression. qRT-PCR analysis confirmed that the effects of SB on these three molecules was transcriptionally mediated. Immunoprecipitation of HOSCN-treated HUVEC whole cell extracts with a polyclonal anti-phospho-p38 MAPK reagent showed rapid (within 1 min) phosphorylation of p38 MAPK that lasted >30 min with consequent kinase activity documented by detection of the downstream target product phospho HSP27. Confocal immunofluorescence confirmed the rapid and durable induction of phospho p38 MAPK from undetectable to abundant, primarily cytoplasmic, but also some nuclear localization. We further hypothesized that the disparate effects of SB on these three molecules reflects differences in the sequences of their NF-κB-binding sites that affect their ability to bind the p65 NF-kB subunit. Chromatin immunoprecipitation (ChIP) analysis of HUVEC treated for 3h with HOSCN using an anti-p65 antibody revealed that SB inhibited by 75% the 10-fold increase in binding of p65 to the authentic endogenous VCAM-1 and NF-κB binding loci but had no discernible effect on p65 binding to the ICAM-1 locus. An identical pattern was seen in HUVEC exposed 30 min to the prototypical inflammatory cytokine TNF. To test the physiologic significance of these findings we assessed the effect of SB upon PMN and eosinophil binding to HOSCN-exposed HUVEC monolayers treated as described above. SB pretreatment of HUVEC blocked by > 80% the 3–8-fold increase in binding of PMN and eosinophils that occurs in HOSCN-exposed monolayers. Blocking antibodies to ICAM-1 and VCAM-1 demonstrate that both of the adhesion molecules contribute to HOSCN-induced PMN and eosinophil adhesion. We conclude that HOSCN generated by PMN and eosinophils attached or subjacent to vascular endothelium has the capacity to rapidly activate endothelial p38 MAPK-dependent activation of p65 binding to the TF and VCAM-1, but not ICAM-1, NF-κB binding loci; and these differences manifest in physiologically relevant transcriptional regulation of protein expression. Therefore, p38 MAPK inhibitors may have anti-thrombotic and anti-inflammatory potential, the latter particularly in states, such as allergic inflammation, that are most dependent on VCAM-1. Disclosures:No relevant conflicts of interest to declare.

P38 Regulates Pigmentation via Proteasomal Degradation of Tyrosinase

The synthesis of melanin pigments, or melanogenesis, is regulated by the balance of a variety of signal transduction pathways. Among these pathways, p38 MAPK signaling was found to be involved in stress-induced melanogenesis and to be activated by alpha-melanocyte-stimulating hormone (alpha-MSH) and ultraviolet irradiation. Previous studies have shown that alpha-MSH-stimulated melanogenesis can be inhibited by blocking p38 MAPK activity with SB203580, a pyridinyl imidazole compound. Consistent with this, we observed that pyridinyl imidazoles (SB203580 and SB202190) inhibited both basal and alpha-MSH-induced melanogenesis in B16 melanoma cells. However, SB202474, which has no ability to inhibit p38 MAPK activity and is usually used as a negative control compound in p38 MAPK studies, also suppressed melanin synthesis induction. Furthermore, the independence of the p38 kinase pathway from the repression of melanogenesis by pyridinyl imidazole compounds was also confirmed by small interfering RNA experiments. Interfering with p38 MAPK expression surprisingly stimulated melanogenesis and tyrosinase family protein expression. Although the molecular mechanism(s) by which p38 promotes the degradation of melanogenic enzymes remain to be determined, the involvement of the ubiquitin-proteasome pathway was demonstrated by co-treatment with the proteasome-specific inhibitor MG132 and the relative decrease in the ubiquitination of tyrosinase in cells transfected with p38-specific small interfering RNA.

Fluorescence polarization binding assay to develop inhibitors of inactive p38α mitogen-activated protein kinase

Development of inhibitors that target inactive kinase conformations is becoming a more attractive approach to kinase inhibitor research. The major advantage of this methodology is that targeting the inactive conformation reduces competition with high intracellular adenosine triphosphate (ATP) concentrations. p38α Mitogen-activated protein kinase (MAPK) signaling has been identified as the principal mediator of inflammation associated with a spectrum of disorders (e.g., arthritis, Alzheimer’s disease, various malignancies). To allow identification and development of p38α MAPK inhibitors that preferentially bind to the inactive conformation, a novel fluorescence polarization-based binding assay is presented. The assay is homogeneous, requires low amounts of the kinase and fluoroprobe, and does not rely on radioactivity. It may, therefore, offer an inexpensive alternative to current p38α MAPK inhibitor screening methods. The validation of the system with known p38α MAPK inhibitors confirmed that the binding assay, rather than the conventional enzyme activity assay, correlates with cellular efficacy. Finally, we show that pyridinyl imidazoles that potently bind to the inactive p38α MAPK prevent activation of p38 MAPK in living cells, suggesting that pyridinyl imidazoles other than SB203580 are able to induce the DFG-out conformation that is incompatible with activation (where DFG is a single-letter amino acid code for the aspartate–phenylalanine–glycine sequence at the start of the activation loop).

Modulation of p38 MAPK Activity in Regulatory T Cells after Tolerance with Anti-DNA Ig Peptide in (NZB × NZW)F1 Lupus Mice

Treatment of (NZB x NZW)F(1) (NZB/W) lupus-prone mice with the anti-DNA Ig-based peptide pConsensus prolongs the survival of treated animals and effectively delays the appearance of autoantibodies and glomerulonephritis. We have previously shown that part of these protective effects associated with the induction of CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) that suppressed autoantibody responses. Because the effects of pConsensus appeared secondary to qualitative rather than quantitative changes in Tregs, we investigated the molecular events induced by tolerance in Tregs and found that signaling pathways including ZAP70, p27, STAT1, STAT3, STAT6, SAPK, ERK, and JNK were not significantly affected. However, peptide tolerization affected in Tregs the activity of the MAPK p38, whose phosphorylation was reduced by tolerance. The pharmacologic inhibition of p38 with the pyridinyl imidazole inhibitor SB203580 in naive NZB/W mice reproduced in vivo the effects of peptide-induced tolerance and protected mice from lupus-like disease. Transfer experiments confirmed the role of p38 in Tregs on disease activity in the NZB/W mice. These data indicate that the modulation of p38 activity in lupus Tregs can significantly influence the disease activity.

Non-specific in vivo inhibition of CK1 by the pyridinyl imidazole p38 inhibitors SB 203580 and SB 202190

Small-molecule inhibitors of protein kinases have contributed immensely to our understanding of biological signaling pathways and have been exploited therapeutically for the treatment of cancers and other disease states. The pyridinyl imidazole compounds SB 203580 and SB 202190 were identified as ATP competitive antagonists of the p38 stress-activated protein kinases and have been widely used to elucidate p38-dependent cellular processes. Here, we identify SB 203580 and SB 202190 as potent inhibitors of stress-induced CREB phosphorylation on Serine 111 (Ser-111) in intact cells. Unexpectedly, we found that the inhibitory activity of SB 203580 and SB 202190 on CREB phosphorylation was independent of p38, but instead correlated with inhibition of casein kinase 1 (CK1) in vitro. The inhibition of CK1-mediated CREB phosphorylation by concentrations of pyridinyl imidazoles commonly employed to suppress p38, suggests that in some cases conclusions of p38-dependence derived solely from the use of these inhibitors may be invalid.