Diversity in function and regulation of MAP kinase pathways

Oligodendrocyte progenitor cells in Alzheimer's disease: from physiology to pathology

Oligodendrocyte progenitor cells (OPCs) play pivotal roles in myelin formation and phagocytosis, communicating with neighboring cells and contributing to the integrity of the blood-brain barrier (BBB). However, under the pathological circumstances of Alzheimer's disease (AD), the brain's microenvironment undergoes detrimental changes that significantly impact OPCs and their functions. Starting with OPC functions, we delve into the transformation of OPCs to myelin-producing oligodendrocytes, the intricate signaling interactions with other cells in the central nervous system (CNS), and the fascinating process of phagocytosis, which influences the function of OPCs and affects CNS homeostasis. Moreover, we discuss the essential role of OPCs in BBB formation and highlight the critical contribution of OPCs in forming CNS-protective barriers. In the context of AD, the deterioration of the local microenvironment in the brain is discussed, mainly focusing on neuroinflammation, oxidative stress, and the accumulation of toxic proteins. The detrimental changes disturb the delicate balance in the brain, impacting the regenerative capacity of OPCs and compromising myelin integrity. Under pathological conditions, OPCs experience significant alterations in migration and proliferation, leading to impaired differentiation and a reduced ability to produce mature oligodendrocytes. Moreover, myelin degeneration and formation become increasingly active in AD, contributing to progressive neurodegeneration. Finally, we summarize the current therapeutic approaches targeting OPCs in AD. Strategies to revitalize OPC senescence, modulate signaling pathways to enhance OPC differentiation, and explore other potential therapeutic avenues are promising in alleviating the impact of AD on OPCs and CNS function. In conclusion, this review highlights the indispensable role of OPCs in CNS function and their involvement in the pathogenesis of AD. The intricate interplay between OPCs and the AD brain microenvironment underscores the complexity of neurodegenerative diseases. Insights from studying OPCs under pathological conditions provide a foundation for innovative therapeutic strategies targeting OPCs and fostering neurodegeneration. Future research will advance our understanding and management of neurodegenerative diseases, ultimately offering hope for effective treatments and improved quality of life for those affected by AD and related disorders.

Mitogen-activated protein kinase (MAPK) cascades-A yeast perspective

Discovery of the class of protein kinase now dubbed a mitogen (or messenger)-activated protein kinase (MAPK) is an illustrative example of how disparate lines of investigation can converge and reveal an enzyme family universally conserved among eukaryotes, from single-celled microbes to humans. Moreover, elucidation of the circuitry controlling MAPK function defined a now overarching principle in enzyme regulation-the concept of an activation cascade mediated by sequential phosphorylation events. Particularly ground-breaking for this field of exploration were the contributions of genetic approaches conducted using several model organisms, but especially the budding yeast Saccharomyces cerevisiae. Notably, examination of how haploid yeast cells respond to their secreted peptide mating pheromones was crucial in pinpointing genes encoding MAPKs and their upstream activators. Fully contemporaneous biochemical analysis of the activities elicited upon stimulation of mammalian cells by insulin and other growth- and differentiation-inducing factors lead eventually to the demonstration that components homologous to those in yeast were involved. Continued studies of these pathways in yeast were integral to other foundational discoveries in MAPK signaling, including the roles of tethering, scaffolding and docking interactions.

A community challenge for a pancancer drug mechanism of action inference from perturbational profile data

The Columbia Cancer Target Discovery and Development (CTD2) Center is developing PANACEA, a resource comprising dose-responses and RNA sequencing (RNA-seq) profiles of 25 cell lines perturbed with ∼400 clinical oncology drugs, to study a tumor-specific drug mechanism of action. Here, this resource serves as the basis for a DREAM Challenge assessing the accuracy and sensitivity of computational algorithms for de novo drug polypharmacology predictions. Dose-response and perturbational profiles for 32 kinase inhibitors are provided to 21 teams who are blind to the identity of the compounds. The teams are asked to predict high-affinity binding targets of each compound among ∼1,300 targets cataloged in DrugBank. The best performing methods leverage gene expression profile similarity analysis as well as deep-learning methodologies trained on individual datasets. This study lays the foundation for future integrative analyses of pharmacogenomic data, reconciliation of polypharmacology effects in different tumor contexts, and insights into network-based assessments of drug mechanisms of action.

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Drug-perturbed RNA sequencing data can be used to identify drug targets

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Technology-based drug-target definitions often subsume literature definitions

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Literature and screening datasets provide complementary information on drug mechanisms

Glycyrrhizic acid suppresses early stage of adipogenesis through repression of MEK/ERK-mediated C/EBPβ and C/EBPδ expression in 3T3-L1 cells

Glycyrrhizic acid (GA), a major constituent of the root of licorice (Glycyrrhiza glabra), and has various biological activities, including anti-obesity property. However, the molecular mechanism of anti-adipogenic effect of GA is still unclear. In this study, we investigated the anti-adipogenic effects of GA in mouse adipocytic 3T3-L1 cells and elucidated its underlying molecular mechanism. GA decreased the intracellular triglyceride level. The expression levels of the adipogenic and lipogenic genes were lowered by treatment with GA in a concertation-dependent manner. In contrast, GA did not affect the lipolytic gene expression and the released glycerol level. GA suppressed the early stage of adipogenesis when it was added for 0-3 h after initiation of adipogenesis. Moreover, GA reduced the mRNA levels of CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ, both of which activate the early stage of adipogenesis. Furthermore, GA decreased phosphorylation of extracellular signal-regulated kinase [ERK: p44/42 mitogen-activated protein kinase (MAPK)] in the early stage of adipogenesis. In addition, a MAPK kinase (MEK) inhibitor, PD98059 reduced the C/EBPβ and C/EBPδ gene expression. These results indicate that GA suppressed the early stage of adipogenesis through repressing the MEK/ERK-mediated C/EBPβ and C/EBPδ expression in 3T3-L1 cells. Thus, GA has an anti-adipogenic ability and a possible agent for treatment of obesity.

Understanding the impact of anticancer halogenated inhibitors and various functional groups (X = Cl, F, CF3, CH3, NH2, OH, H) of casein kinase 2 (CK2)

Main focus of study is to understand potency of halogen (X = Br) atom that exists in tetrabromobenzotriazole (TBB) derivatives of crystal CK2 ligand along with hinge region amino acids (VAL45, PHE113, GLU114, VAL116, ASN118) through interaction energy analysis. In turn to attain profound insight on nature of stabilization of core CK2 ligands: 1ZOE-L1, 1ZOG-L2, 1ZOH-L3, 2OXX-L4, 2OXY-L5, 3KXG-L6, 3KXH-L7 -L7 and 3KXM-L8, having four bromine atoms, we attempted to mutate all bromine (X = Br) atoms by various functional groups (X = Cl, F, CF₃, CH₃, NH₂, OH, H) and binding strength along with amino acids was calculated. Most stable ligands exist in mutated NH₂ functional groups: 1ZOG-L2, 1ZOH-L3, 2OXX-L4, 3KXM-L8 having interaction energy as -5.21, -14.87, -6.69 and -11.72 kcal/mol respectively, revealing strong binding strength. Second most stable mutated Cl functional group ligands also play a major role in 1ZOH-L3, 2OXX-L4 and 3KXM-L8 having interaction energy as -6.89, -5.37, and -10.48 kcal/mol respectively. Overall, this study will pave way for crystal growth and medicinal chemist to have cleared perceptive about structural properties of CK2 halogenated ligands with new insight on CK2 mutated functional group ligands. Further, it insists us to reuse existing CK2 crystal ligand with more preferable suggested binding contacts in course of new functional groups that lead to anticancer affinity.Communicated by Ramaswamy H. Sarma.

Oxidative damage mechanism in Saccharomyces cerevisiae cells exposed to tetrachlorobisphenol A

Tetrachlorobisphenol A (TCBPA) can promote intracellular reactive oxygen species (ROS) accumulation. However, limited attention has been given to mechanisms underlying TCBPA exposure-associated ROS accumulation. Here, such mechanisms were explored in the simple eukaryotic model organism Saccharomyces cerevisiae exposed to multiple concentrations of TCBPA. Addition of diphenyleneiodonium, a specific inhibitor of NADPH oxidase, blocked TCBPA treatment-associated intracellular ROS accumulation. NADPH oxidase can be activated by calcineurin, mitogen-activated protein kinase (MAPK), and tyrosine kinase. Therefore, corresponding specific inhibition respectively on these three kinases was performed and results suggested that the Ca²⁺ signaling pathway, MAPK pathway, and tyrosine kinase pathway all contributed to the TCBPA exposure-associated intracellular ROS accumulation. In addition, TCBPA exposure-associated up-regulation of genes involved in ROS production and down-regulation of catalase promoted ROS accumulation in S. cerevisiae. To sum up, our current results provide insights into the understanding of TCBPA exposure-associated ROS accumulation.

Transcriptome analysis of Artemia sinica in response to Micrococcus lysodeikticus infection

To enhance genomic resources and understand the molecular immune mechanisms underlying the response topathogens, we first performed a comparative gene transcription analysis from Micrococcus lysodeikticus-immunized Artemia sinica and from a control group through RNA-Seq technology, meanwhile the differentially expressed genes (DEGs) were investigated. In total, 80, 113, 984 clean reads were obtained and then assembled into 71,536 unigenes with an average length of 1115 bp and an N50 of 1783 bp. Unigenes were annotated by comparing against nr, Swiss-Prot\KEGG\ COG\ KOG\ GO and Pfam databases, and 27,689 unigenes (38.7%) were annotated in at least one database. After bacterial challenge, 183 and 298 genes were identified as remarkably up-regulated or down-regulated, respectively, amongst 481 were associated with 168 pathways, including classical immune-related pathways, such as 'Toll-like receptor signaling', 'the complement cascades', 'MAPK signaling pathway' and 'Apoptosis'. Besides, eight genes which were differently expressed immune-related were confirmed by using quantitative real-time PCR. This study characterized a gene expression pattern for normal and M. lysodeikticus -immunized A. sinica for the first time and sheds new light on the molecular mechanisms thus enabling future efforts on disease control programs in this valuable aquaculture species.

Cyclophilin A as a target in the treatment of cytomegalovirus infections

BACKGROUND

Viruses are obligate parasites that depend on the cellular machinery of the host to regenerate and manufacture their proteins. Most antiviral drugs on the market today target viral proteins. However, the more recent strategies involve targeting the host cell proteins or pathways that mediate viral replication. This new approach would be effective for most viruses while minimizing drug resistance and toxicity.

METHODS

Cytomegalovirus replication, latency, and immune response are mediated by the intermediate early protein 2, the main protein that determines the effectiveness of drugs in cytomegalovirus inhibition. This review explains how intermediate early protein 2 can modify the action of cyclosporin A, an immunosuppressive, and antiviral drug. It also links all the pathways mediated by cyclosporin A, cytomegalovirus replication, and its encoded proteins.

RESULTS

Intermediate early protein 2 can influence the cellular cyclophilin A pathway, affecting cyclosporin A as a mediator of viral replication or anti-cytomegalovirus drug.

CONCLUSION

Cyclosporin A has a dual function in cytomegalovirus pathogenesis. It has the immunosuppressive effect that establishes virus replication through the inhibition of T-cell function. It also has an anti-cytomegalovirus effect mediated by intermediate early protein 2. Both of these functions involve cyclophilin A pathway.

Functional Selectivity and Antidepressant Activity of Serotonin 1A Receptor Ligands

Serotonin (5-HT) is a monoamine neurotransmitter that plays an important role in physiological functions. 5-HT has been implicated in sleep, feeding, sexual behavior, temperature regulation, pain, and cognition as well as in pathological states including disorders connected to mood, anxiety, psychosis and pain. 5-HT1A receptors have for a long time been considered as an interesting target for the action of antidepressant drugs. It was postulated that postsynaptic 5-HT1A agonists could form a new class of antidepressant drugs, and mixed 5-HT1A receptor ligands/serotonin transporter (SERT) inhibitors seem to possess an interesting pharmacological profile. It should, however, be noted that 5-HT1A receptors can activate several different biochemical pathways and signal through both G protein-dependent and G protein-independent pathways. The variables that affect the multiplicity of 5-HT1A receptor signaling pathways would thus result from the summation of effects specific to the host cell milieu. Moreover, receptor trafficking appears different at pre- and postsynaptic sites. It should also be noted that the 5-HT1A receptor cooperates with other signal transduction systems (like the 5-HT1B or 5-HT2A/2B/2C receptors, the GABAergic and the glutaminergic systems), which also contribute to its antidepressant and/or anxiolytic activity. Thus identifying brain specific molecular targets for 5-HT1A receptor ligands may result in a better targeting, raising a hope for more effective medicines for various pathologies.

Resveratrol exerts growth inhibitory effects on human SZ95 sebocytes through the inactivation of the PI3-K/Akt pathway

Resveratrol is known to be a naturally produced polyphenol that is able to reduce cell proliferation in several types of cancer cells and adipocytes. However, the antiproliferative effects of resveratrol on the growth of human sebocytes are not yet clear. In the present study, we investigated possible cellular pathways associated with these growth inhibitory effects on human SZ95 sebocytes. Our results revealed that resveratrol inhibited the proliferation of sebocytes, and that this resulted in disruption of the cell cycle. The inactivation of extracellular signal-regulated protein kinase (ERK), Akt and peroxisome proliferator-activated receptor (PPAR)-γ was also shown to be involved in the inhibition of sebocyte growth by resveratrol. To examine the antiproliferative effects of resveratrol, we determined the levels of cell cycle control proteins. Resveratrol inhibited cyclin D1 synthesis, whereas it stimulated p21WAF1/CIP1 (p21) and p27KIP1 (p27) synthesis. In addition, we demonstrated that the resveratrol-mediated cell cycle arrest resulted in an increase in the proportion of cells in the sub-G0/G1 phase. Moreover, we found that the growth inhibitory effects of resveratrol were enhanced by treatment with LY294002 [a phosphatidylinositol 3-kinase (PI3-K) inhibitor] more so than by treatment with PD98059 (a MEK inhibitor), which indicates that resveratrol exerts its inhibitory effects on sebocyte proliferation through the inhibition of Akt. Linoleic acid (LA) is a well-established lipid inducer in sebocytes and is known to stimulate sebocyte differentiation through the upregulation of PPAR-γ. In this study, resveratrol was found to decrease the lipid content and PPAR-γ expression during LA-stimulated lipogenesis. Our results indicate that resveratrol plays a critical role in the inhibition of sebocyte growth through the inactivation of the Akt pathway. The present data suggest that resveratrol may be used as a therapeutic agent for the treatment of acne vulgaris.

A CXCR1 haplotype hampers HIV-1 matrix protein p17 biological activity

OBJECTIVE

Monocyte inflammatory processes are fundamental events in AIDS pathogenesis. HIV-1 matrix protein p17, released from infected cells, was found to exert an interleukin (IL)-8 chemokine-like activity on human monocytes, promoting their trafficking and sustaining inflammatory processes, after binding to CXCR1. A haplotype of the CXCR1 gene (CXCR1_300_142) has been associated with slow HIV disease progression. Here, we determine how CXCR1 genetic variations impact on p17 biological activity.

DESIGN/METHODS/RESULTS

Our results show that Jurkat cells overexpressing CXCR1 or the receptor carrying single polymorphism CXCR1_300 or CXCR1_142 are able to adhere and migrate in response to both IL-8 and p17. On the contrary, Jurkat cells overexpressing CXCR1_300_142 and monocytes of individuals with such CXCR1 polymorphisms lose the capacity to adhere and migrate in response to p17, but not to their physiological ligand IL-8. Surface plasmon resonance (SPR) and multispectral imaging flow cytometry showed that p17 bound with similar affinity to CXCR1 and CXCR1_300_142. Moreover, whereas p17 was able to activate CXCR1, it was incapable of functionally interacting with CXCR1_300_142 by phosphorylating extracellular signal-regulated kinase 1/2, which regulates chemokine-induced cellular responses. Finally, mutagenesis studies showed that, unlike IL-8, p17 does not use Glu-Leu-Arg-like motifs to activate CXCR1.

CONCLUSIONS

Our results, showing the inability of p17 to activate CXCR1_300_142, a receptor found to be expressed on immune cells of patients with a low progression of HIV disease, point to a crucial role of p17 in AIDS pathogenesis. Our findings herein call for an exploration of the therapeutic potential of blocking the p17/CXCR1 axis in HIV infection.

Modulating vascular intimal hyperplasia using HSV-1 mutant requires activated MEK

Outcomes of cardiovascular procedures, such as angioplasty and stent or bypass grafting are limited by failure, predominantly caused by pathological smooth muscle cell (SMC) proliferation, known as intimal hyperplasia. Local delivery of a genetically engineered herpes simplex virus (HSV) is known to block vascular SMC proliferation while allowing for re-endothelialization. However, the mechanism this mutant virus uses to prevent SMC hyperplasia is unknown. The Ras signaling cascade is activated in SMCs undergoing hyperplasia leading to phosphorylation of the mitogen-activated protein kinase (MAPK). In this study we tested the hypothesis that MAPK kinase (MEK) activity is the molecular basis by which SMCs are susceptible to mutant HSV. We show that genetically engineered herpes simplex-1 viruses (HSV-1) can target proliferating SMCs. We demonstrate that the molecular basis of this HSV-1 anti-proliferative effect is MEK activation in SMCs. We demonstrate efficacy and practicality of the MEK-dependent HSV-1 for the treatment of intimal hyperplasia in a clinically relevant in vivo model. Important to this strategy is the ability to modulate the effects by controlling viral dose. These results propel genetically engineered HSV-1 therapy towards clinical evaluation in treatment of intimal hyperplasia.

The molecular events involved in oligodendrocyte precursor cell proliferation induced by the conditioned medium from b104 neuroblastoma cells

The conditioned medium from B104 neuroblastoma cells (B104CM) induces proliferation of oligodendrocyte progenitor cells (OPCs) in vitro. However, the molecular events that occur during B104CM-induced proliferation of OPCs has not been well clarified. In the present study, using OPCs immunopanned from embryonic day 14 Sprague-Dawley rat spinal cords, we explored the activation of several signaling pathways and the expression of several important immediate early genes (IEGs) and cyclins in OPCs in response to B104CM. We found that B104CM can induce OPC proliferation through the activation of the extracellular signal-regulated kinases 1 and 2 (Erk1/2), but not PI3K or p38 MAPK signaling pathways in vitro. The IEGs involved in B104CM-induced OPC proliferation include c-fos, c-jun and Id2, but not c-myc, fyn, or p21. The cyclins D1, D2 and E are also involved in B104CM-stimulated proliferation of OPCs. The activation of Erk results in subsequent expression of IEGs (such as c-fos, c-jun and Id-2) and cyclins (including cyclin D1, D2 and E), which play key roles in cell cycle initiation and OPC proliferation. Collectively, these results suggest that the phosphorylation of Erk1/2 is an important molecular event during OPC proliferation induced by B104CM.

A MAP kinase gene, Clk1, is required for conidiation and pathogenicity in the phytopathogenic fungus Curvularia lunata

Mitogen-activated protein kinase (MAPK) cascades are highly conserved signal transduction pathways, which play a wide variety of important roles in extracellular signal transduction. The first MAPK gene of the maize pathogen Curvularia lunata, Clk1, was isolated via a PCR-based approach with a primer pair designed on the basis of conserved regions of known MAPKs. Southern blot analysis showed that the gene existed in the genome as a single copy. The predicted amino acid sequence (352 amino acids) was highly homologous with MAP kinases of other phytopathogenic fungi. Flanking regions of Clk1 were obtained through RACE and genomic walking technology. To understand the role of Clk1 in C. lunata, targeted gene disruption was adopted to construct Clk1 mutants. It was found that mutants lacking functional domain of Clk1 were not able to produce conidia but tended to form a few special chlamydospore-shaped structures. Clk1 mutants grew slower in adverse environments (at 24°C), produced less cell degrading enzymes (CWDEs) than the wild type, and they were almost unable to infect maize leaves via artificial wounds.

Fluoxetine upregulates phosphorylated-AKT and phosphorylated-ERK1/2 proteins in neural stem cells: evidence for a crosstalk between AKT and ERK1/2 pathways

Fluoxetine is a widely used antidepressant drug which inhibits the reuptake of serotonin in the central nervous system (CNS). Recent studies have shown that fluoxetine can promote neurogenesis and improve the survival rate of neurons. However, whether fluoxetine modulates the neuroprotection of neural stem cells (NSCs) needs to be elucidated. In this study, we demonstrated that 50 μM fluoxetine significantly upregulated expression of the phosphorylated-AKT and ERK1/2 proteins in NSCs derived from rats. Besides, expression of phosphorylated-AKT and phosphorylated-ERK1/2 in fluoxetine-treated NSCs was effectively blocked (P<0.05) by both PI3-K inhibitor (LY294002) and MEK inhibitor (PD98059). It was, therefore, concluded that the crosstalk between PI3K/AKT and MAPK/ERK pathways involved AKT and ERK1/2 phosphorylation by fluoxetine treatment. This study points to a novel role of fluoxetine in neuroprotection as an antidepressant drug and also unravels the crosstalk mechanism between the two signaling pathways.

Signaling regulation of fetoplacental angiogenesis

During normal pregnancy, dramatically increased placental blood flow is critical for fetal growth and survival as well as neonatal birth weights and survivability. This increased blood flow results from angiogenesis, vasodilatation, and vascular remodeling. Locally produced growth factors including fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor A (VEGFA) are key regulators of placental endothelial functions including cell proliferation, migration, and vasodilatation. However, the precise signaling mechanisms underlying such regulation in fetoplacental endothelium are less well defined, specifically with regard to the interactions amongst protein kinases (PKs), protein phosphatase, and nitric oxide (NO). Recently, we and other researchers have obtained solid evidence showing that different signaling mechanisms participate in FGF2- and VEGFA-regulated fetoplacental endothelial cell proliferation and migration as well as NO production. This review will briefly summarize currently available data on signaling mediating fetoplacental angiogenesis with a specific emphasis on PKs, ERK1/2, AKT1, and p38 MAPK and protein phosphatases, PPP2 and PPP3.

PDGF-AA mediates B104CM-induced oligodendrocyte precursor cell differentiation of embryonic neural stem cells through Erk, PI3K, and p38 signaling

The conditioned medium from B104 neuroblastoma cells (B104CM) induces neural stem cells (NSCs) to differentiate into OPCs in vitro, which indicates that certain factor(s) contained within the B104CM must give instructional signals that direct OPC differentiation of NSCs. However, the OPC-inductive factor(s) present within the B104CM has not been well identified yet. Platelet-derived growth factor AA (PDGF-AA) was not only known to be a potent mitogen for OPC proliferation but also to act as a regulator of oligodendrocyte differentiation from multipotent embryonic NSCs. This raises the possibility that B104CM induces OPC differentiation of NSCs through secretion of PDGF-AA. In the present study, we detected the expression of PDGF-AA mRNA in B104 cells and the high level of PDGF-AA protein in B104CM. Most importantly, B104CM-induced OPC differentiation of NSCs could be completely blocked by AG1295, a specific inhibitor of PDGFR signal pathway, suggesting that the PDGF-AA in B104CM is the key factor that induces NSCs to differentiate into OPCs. Moreover, such B104CM-induced OPC differentiation appears to be mediated by the extracellular signal-regulated kinases 1 and 2 (Erk1/2), phosphatidylinositol-3 kinase (PI3K), and p38 signal pathway because B104CM elicited the activation of Erk1/2, PI3K, and p38, which could be markedly blocked by U0126, LY294002, and SB203580, several specific inhibitors of these signal pathway, respectively. These inhibitors also abolished OPC differentiation of NSCs completely. Together our study suggests that PDGF-AA contained in B104CM is the key regulating molecule that instructs OPC differentiation from embryonic NSCs through the activation of Erk, PI3K, and p38 signal pathway in vitro.

Delayed neuroprotection induced by sevoflurane via opening mitochondrial ATP-sensitive potassium channels and p38 MAPK phosphorylation

This study aimed to investigate the role of p38 MAPK phosphorylation and opening of the mitoK(ATP) channels in the sevoflurane-induced delayed neuroprotection in the rat brain. Adult male Sprague-Dawley rats (250-300 g) were randomly assigned into four groups: ischemia/reperfusion (Control), sevoflurane (Sevo), 5-hydroxydecanoate (5-HD) + sevoflurane (5-HD + Sevo) and 5-HD groups and were subjected to right middle cerebral artery occlusion (MCAO) for 2 h. Sevoflurane preconditioning was induced 24 h before MCAO in sevoflurane and 5-HD + sevoflurane groups by exposing the animals to 2.4% sevoflurane in oxygen for 60 min. In control and 5-HD groups: animals were exposed to oxygen for 60 min at 24 h before MCAO. A selective mitoK(ATP) channel antagonist, 5-hydroxydecanoate (5-HD, 40 mg/kg, i.p.), was administered 30 min before sevoflurane/oxygen exposure in the 5-HD + sevoflurane and 5-HD groups, respectively. Neurological deficits scores and the protein expression of phosphorylated p38 mitogen-activated protein kinase (p-p38 MAPK) were evaluated at 24 and 72 h after reperfusion. Cerebral infarct size was evaluated at 72 h after reperfusion by 2,3,5-triphenyltetrazolium chloride staining. Sevoflurane preconditioning produced marked improvement neurological functions and a reduction in brain infarct volumes than animals with brain ischemia only. Sevoflurane treatment also caused increased phosphorylation of p38 MAPK at 24 and 72 h after reperfusion. These beneficial effects were attenuated by 5-HD. Blockade of cerebral protection with 5-HD concomitant with decrease in p38 phosphorylation suggests that mitoK(ATP) channels opening and p38 phosphorylation participate signal transduction cascade of sevoflurane preconditioning and p38 MAPK activation may be a downstream of opening mitoK(ATP) channels.

Potential down-regulation of salivary gland AQP5 by LPS via cross-coupling of NF-kappaB and p-c-Jun/c-Fos

The mRNA and protein levels of aquaporin (AQP)5 in the parotid gland were found to be potentially decreased by lipopolysaccharide (LPS) in vivo in C3H/HeN mice, but only weakly in C3H/HeJ, a TLR4 mutant mouse strain. In the LPS-injected mice, pilocarpine-stimulated saliva production was reduced by more than 50%. In a tissue culture system, the LPS-induced decrease in the AQP5 mRNA level was blocked completely by pyrrolidine dithiocarbamate, MG132, tyrphostin AG126, SP600125, and partially by SB203580, which are inhibitors for IkappaB kinase, 26S proteasome, ERK1/2, JNK, and p38 MAPK, respectively. In contrast, the expression of AQP1 mRNA was down-regulated by LPS and such down-regulation was blocked only by SP600125. The transcription factors NF-kappaB (p65 subunit), p-c-Jun, and c-Fos were increased by LPS given in vivo, whereas the protein-binding activities of the parotid gland extract toward the sequences for NF-kappaB but not AP-1-responsive elements present at the promoter region of the AQP5 gene were increased by LPS injection. Co-immunoprecipitation by using antibody columns suggested the physical association of the three transcription factors. These results suggest that LPS-induced potential down-regulation of expression of AQP5 mRNA in the parotid gland is mediated via a complex(es) of these two classes of transcription factors, NF-kappaB and p-c-Jun/c-Fos.

Signaling mechanisms of sphingosine 1-phosphate-induced ERK1/2 activation in cultured feline esophageal smooth muscle cells

Sphingosine 1-phosphate (S1P) is a bioactive lipid, stored and released from activated platelets, macrophages, and other mammalian cells. We previously reported that S1P induces esophageal smooth muscle contraction in freshly isolated intact cells. Here, we measured S1P-induced ERK1/2 activation and upstream signaling in cultured feline esophageal smooth muscle cells. Activation of ERK1/2 by S1P peaked at 5 min, was sustained up to 30 min, and was blocked by PTX. In contrast, S1P did not activate p38 MAPK or JNK. PTX inhibited S1P-induced ERK1/2 activation. We then used phospholipase inhibitors, DEDA for PLA(2), U73122 for PLC, and rhoCMB for PLD, to determine that ERK1/2 activation was downstream of PLC activation. The PKC inhibitors, GF109203X and chelerythrine, also suppressed ERK1/2 activation. Whereas the PTK inhibitor, genistein, partially inhibited ERK1/2 activation, the EGFR tyrosine kinase inhibitor, tyrphostin 51, had no effect. Taken together, S1P-induced ERK1/2 activation in cultured ESMCs requires a PTX-sensitive G protein, stimulation of the PLC pathway, and subsequent activation of the PKC and PTK pathways.

Intracerebral development of transplanted glioblastoma C6 cells in rats after preliminary exposure to neuropeptides and an MAPK inhibitor

The invasive growth, proliferation, and transcriptional regulation of glioma C6 cells treated with endothelin-1 and PD98059, a specific inhibitor of ERK1/2 were studied. The proliferation of glioma C6 cells was assessed in different growth conditions by prior in vitro treatment with endothelin-1 followed by implantation into the brain. In vitro studies showed that PD98059 inhibited the proliferation of cultured glioma C6 cells and activated transcription factors E2F1 and Myc-Max. Endothelin-1 significantly increased the proliferation of glioma C6 cells. The model used in this study was experimental and may allow the specific features of the in vitro behavior of cultured invasive cells to be identified.

Phosphoinositide Signaling in Unicellular Eukaryotes

The review considers the up to date achievements in the role of membrane phosphoinositides and keys enzymes of the lipid branch of the phosphoinositide signal pathway (PI-pathway) in unicellular eukaryotes. Particular attention is paid to mechanisms of phospholipase C (PLC) activation and the PLC interaction both with cell surface receptors and with the effector cytoplasm targets. The role of protein kinase C (PKC) in intracellular signaling and the relationship of the PI-pathway key enzymes with protein tyrosine kinases (PTK)-signaling and cAMP-protein kinase A (PKA) pathway are discussed.

Naringin-induced p21WAF1-mediated G(1)-phase cell cycle arrest via activation of the Ras/Raf/ERK signaling pathway in vascular smooth muscle cells

The flavonoid naringin has been shown to play a role in preventing the development of cardiovascular disease. However, the exact molecular mechanisms underlying the roles of integrated cell cycle regulation and MAPK signaling pathways in the regulation of naringin-induced inhibition of cell proliferation in vascular smooth muscle cells (VSMCs) remain to be identified. Naringin treatment resulted in significant growth inhibition and G(1)-phase cell cycle arrest mediated by induction of p53-independent p21WAF1 expression; expression of cyclins and CDKs in VSMCs was also down-regulated. In addition, among the pathways examined, blockade of ERK function inhibited naringin-dependent p21WAF1 expression, reversed naringin-mediated inhibition of cell proliferation and decreased cell cycle proteins. Moreover, naringin treatment increased both Ras and Raf activations. Transfection of cells with dominant negative Ras (RasN17) and Raf (RafS621A) mutant genes suppressed naringin-induced ERK activity and p21WAF1 expression. Finally, naringin-induced reduction in cell proliferation and cell cycle protein was abolished in the presence of RasN17 and RafS621A mutant genes. The Ras/Raf/ERK pathway participates in p21WAF1 induction, leading to a decrease in cyclin D1/CDK4 and cyclin E/CDK2 complexes and in naringin-dependent inhibition of cell growth. These novel and unexpected findings provide a theoretical basis for preventive use of flavonoids to the atherosclerosis disease.

Thrombin induces fibroblast CCL2/JE production and release via coupling of PAR1 to Galphaq and cooperation between ERK1/2 and Rho kinase signaling pathways

Uncontrolled activation of the coagulation cascade after tissue injury has been implicated in both inflammation and tissue fibrosis. Thrombin exerts pluripotent cellular effects via its high-affinity receptor, proteinase-activated receptor-1 (PAR(1)) and signaling via Galpha(i/o), Galpha(q), or Galpha(12/13). Activation of PAR(1) on fibroblasts, a key effector cell in fibrosis, results in the induction of several mediators, including the potent monocyte and fibrocyte chemoattractant CCL2. The aim of this study was to identify the G protein and signaling pathway involved in PAR(1)-mediated CCL2 production and release. Using a novel PAR(1) antagonist that blocks the interaction between PAR(1) and Galpha(q), we report for the first time that PAR(1) coupling to Galpha(q) is essential for thrombin-induced CCL2 gene expression and protein release in murine lung fibroblasts. We further demonstrate that these effects are mediated via the cooperation between ERK1/2 and Rho kinase signaling pathways: a calcium-independent protein kinase C (PKC), c-Raf, and ERK1/2 pathway was found to mediate PAR(1)-induced CCL2 gene transcription, whereas a phospholipase C, calcium-dependent PKC, and Rho kinase pathway influences CCL2 protein release. We propose that targeting the interaction between PAR(1) and Galpha(q) may allow us to selectively interfere with PAR(1) proinflammatory and profibrotic signaling, while preserving the essential role of other PAR(1)-mediated cellular responses.

Requirement for Ras/Raf/ERK pathway in naringin-induced G1-cell-cycle arrest via p21WAF1 expression

Naringin, an active flavonoid found in citrus fruit extracts, has pharmacological utility. The present study identified a novel mechanism of the anticancer effects of naringin in urinary bladder cancer cells. Naringin treatment resulted in significant dose-dependent growth inhibition together with G(1)-phase cell-cycle arrest at a dose of 100 microM (the half maximal inhibitory concentration) in 5637 cells. In addition, naringin treatment strongly induced p21WAF1 expression, independent of the p53 pathway, and downregulated expression of cyclins and cyclin dependent kinases (CDKs). Moreover, treatment with naringin induced phosphorylation of extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase and c-Jun N-terminal kinase. Among the pathways examined, only PD98059, an ERK-specific inhibitor, blocked naringin-dependent p21WAF1 expression. Consistently, blockade of ERK function reversed naringin-mediated inhibition of cell proliferation and decreased cell-cycle proteins. Furthermore, naringin treatment increased both Ras and Raf activation. Transfection of cells with dominant-negative Ras (RasN17) and Raf (RafS621A) mutant genes suppressed naringin-induced ERK activity and p21WAF1 expression. Finally, the naringin-induced reduction in cell proliferation and cell-cycle proteins also was abolished in the presence of RasN17 and RafS621A mutant genes. These data demonstrate that the Ras/Raf/ERK pathway participates in p21WAF1 induction, subsequently leading to a decrease in the levels of cyclin D1/CDK4 and cyclin E-CDK2 complexes and naringin-dependent inhibition of cell growth. Overall, these unexpected findings concerning the molecular mechanisms of naringin in 5637 cancer cells provide a theoretical basis for the therapeutic use of flavonoids to treat malignancies.

Platelet-derived growth factor-AA mediates oligodendrocyte lineage differentiation through activation of extracellular signal-regulated kinase signaling pathway

Platelet-derived growth factor-AA (PDGF-AA) has been used as a potent mitogen for the proliferation of oligodendrocyte progenitor cells (OPCs). Whether it plays a role in oligodendrocyte lineage differentiation of neural stem cells (NSCs) is unclear. Here we report that PDGF-AA is an instructional signal required for the differentiation of embryonic forebrain NSCs into O4-positive oligodendrocytes. Moreover, such PDGF-AA-induced oligodendrocyte differentiation appears to be mediated by the extracellular signal-regulated kinases 1 and 2 (Erk1/2) but not phosphatidylinositol-3 kinase (PI3K) pathway. Finally, PDGF-AA treatment resulted in a significant increase in the expression of the oligodendrocyte-specific transcriptional factor Olig2 in an Erk1/2-dependent mechanism at early stages of oligodendrogliogenesis. Together, our studies provide cellular and molecular evidence to suggest that PDGF-AA is a key molecule that regulates the differentiation of embryonic NSCs into oligodendrocytes. The action of PDGF-AA is mediated by the activation of Erk pathway which involves the downstream upregulation of transcriptional factor Olig2.

The Slt2-type MAP kinase Bmp3 of Botrytis cinerea is required for normal saprotrophic growth, conidiation, plant surface sensing and host tissue colonization

SUMMARY Mitogen-activated protein kinases (MAPKs) play important roles in signal transduction and regulation of various aspects of saprotrophic and pathogenic growth in plant pathogenic fungi. We have generated a Botrytis cinerea knock-out mutant in the bmp3 gene encoding a homologue of the yeast Slt2 cell wall integrity MAPK. The Deltabmp3 mutant showed reduced vegetative growth on various media, strongly impaired conidiation and loss of sclerotia formation. Growth retardation of the mutant was enhanced in media with low osmolarity, whereas nearly wild-type growth rates were observed under high osmolarity conditions. The Deltabmp3 mutant did not show increased susceptibility to cell wall damage induced by glucanase, Calcofluor White or Nikkomycin Z, but was more susceptible to the oxidizing agent paraquat and the phenylpyrrole fungicide fludioxonil. Deltabmp3 conidia showed normal germination and germ tube growth on agar, but excessive germ tube elongation on hard surfaces and reduced penetration efficiency, indicating a defect in surface sensing. After penetration, development of necrotic lesions induced by the Deltabmp3 mutant was retarded. All these defects were restored by genetic complementation of the mutant with the wild-type bmp3 gene.

The role of voltage-gated calcium channels in pancreatic beta-cell physiology and pathophysiology

Voltage-gated calcium (CaV) channels are ubiquitously expressed in various cell types throughout the body. In principle, the molecular identity, biophysical profile, and pharmacological property of CaV channels are independent of the cell type where they reside, whereas these channels execute unique functions in different cell types, such as muscle contraction, neurotransmitter release, and hormone secretion. At least six CaValpha1 subunits, including CaV1.2, CaV1.3, CaV2.1, CaV2.2, CaV2.3, and CaV3.1, have been identified in pancreatic beta-cells. These pore-forming subunits complex with certain auxiliary subunits to conduct L-, P/Q-, N-, R-, and T-type CaV currents, respectively. beta-Cell CaV channels take center stage in insulin secretion and play an important role in beta-cell physiology and pathophysiology. CaV3 channels become expressed in diabetes-prone mouse beta-cells. Point mutation in the human CaV1.2 gene results in excessive insulin secretion. Trinucleotide expansion in the human CaV1.3 and CaV2.1 gene is revealed in a subgroup of patients with type 2 diabetes. beta-Cell CaV channels are regulated by a wide range of mechanisms, either shared by other cell types or specific to beta-cells, to always guarantee a satisfactory concentration of Ca2+. Inappropriate regulation of beta-cell CaV channels causes beta-cell dysfunction and even death manifested in both type 1 and type 2 diabetes. This review summarizes current knowledge of CaV channels in beta-cell physiology and pathophysiology.

Cohesion-defective mutants of Myxococcus xanthus

Cohesion of Myxococcus xanthus cells involves interaction of a cell surface cohesin with a component of the extracellular matrix. In this work, two previously isolated cohesion-defective (fbd) mutants were characterized. The fbdA and fbdB genes do not encode the cohesins but are necessary for their production. Both mutants produce type IV pili, suggesting that PilA is not a major cohesin.

MgSlt2, a cellular integrity MAP kinase gene of the fungal wheat pathogen Mycosphaerella graminicola, is dispensable for penetration but essential for invasive growth

Among expressed sequence tag libraries of Mycosphaerella graminicola isolate IPO323, we identified a full-length cDNA clone with high homology to the mitogen-activated protein (MAP) kinase Slt2 in Saccharomyces cerevisiae. This MAP kinase consists of a 1242-bp open reading frame, and encodes a 414-amino-acid protein. We designated this homolog MgSlt2, generated MgSlt2 knockout strains in M. graminicola isolate IPO323, and found several altered phenotypes in vitro as well as in planta. In yeast glucose broth, MgSlt2 disruptants showed a defective polarized growth in the tip cells upon aging, causing substantial local enlargements culminating in large swollen cells containing two to four nuclei. The MgSlt2 disruptants showed a significantly increased sensitivity to several fungicides, including miconazole (2x), bifonazole (>4x), imazalil (5x), and cyproconazole (10x), and were hypersensitive to glucanase. Unlike the wild type, MgSlt2 disruptants did not produce aerial mycelia and did not melanize on potato dextrose agar. Although cytological analysis in planta showed normal penetration of wheat stomata by the germ tubes of the MgSlt2 disruptants, subsequently formed hyphal filaments frequently were unable to branch out and establish invasive growth resulting in highly reduced virulence, and prevented pycnidia formation. Therefore, we conclude that MgSlt2 is a new pathogenicity factor in M. graminicola.

Src family kinases regulate p38 MAPK-mediated IL-6 production in Kupffer cells following hypoxia

Tissue hypoxia is a common sequel of trauma-hemorrhage but can occur even without blood loss under hypoxic conditions. Although hypoxia is known to upregulate Kupffer cells (KC) to release cytokines, the precise mechanism of release remains unknown. We hypothesized that Src family kinases play a role in mediating KC mitogen-activated protein kinase (MAPK) signaling and their cytokine production after hypoxia. Male C3H/HeN mice received either Src inhibitor PP1 (1.5 mg/kg body wt) or vehicle 1 h before hypoxia. KCs were isolated 1 h after hypoxia, lysed, and immunoblotted with antibodies to Src, p38, ERK1/2, or JNK proteins. In addition, KCs were cultured to measure interleukin-6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1) production. Hypoxia produced a significant increase in KC Src and MAPK (p38, ERK, JNK) activity compared with normoxic controls. This was associated with an increase in IL-6 and MCP-1 production. Treatment with PP1 abolished the increase in KC Src activation as well as p38 activity. However, PP1 did not prevent the increase in KC ERK1/2 or JNK phosphorylation. Furthermore, administration of PP1 prevented the hypoxia-induced increase in IL-6 but not MCP-1 release by KC. Additional in vitro results suggest that p38 but not ERK1/2 or JNK are critical for KC IL-6 production. In contrast, the production of MCP-1 by KC was found to be independent of MAPK. Thus hypoxia increases KC IL-6 production by p38 MAPK activation via Src-dependent pathway. Src kinases may therefore be a novel therapeutic target for preventing immune dysfunction following low-flow conditions in trauma patients.

IL-2 induction by simian immunodeficiency virus involves MAP kinase signaling but is independent of calcineurin/NF-AT activity

The major T cell growth factor interleukin-2 (IL-2) is secreted by activated T cells in response to antigenic stimulation. This requires signal transduction via the CD3/TCR complex and the CD28 coreceptor, leading to activation of mitogen-activated protein kinase (MAPK) and calcineurin/NF-AT signaling pathways. We observed that simian immunodeficiency virus derived from African green monkeys (SIVagm3) is a potent activator of IL-2 gene expression. IL-2 promoter studies in A3.01 T cells demonstrated that SIVagm3 induced an up to 38-fold increased transcriptional activation of the IL-2 promoter. Inhibition of MAPK signaling pathways using inhibitors of MEK, JNK or p38 abolished SIVagm3-induced IL-2 activation in a dose-dependent manner. In contrast, the immunosuppressive drug cyclosporin A (CyA), a classical IL-2 inhibitor that blocks calcineurin activity, had no effect. Consistent with this finding, the nuclear factor of activated T cells (NF-AT), which is activated by calcineurin, was not induced by SIVagm3. Analyzing further transcription factor binding sites located on the IL-2 promoter we found that SIVagm3 did mainly promote transcriptional activation of the CD28/AP-1 and NF-kappaB responsive elements. These DNA elements were also induced by the viral transactivator protein (Tat) and expression of Tat was sufficient to activate IL-2 induction in stimulated cells. Our results show that SIVagm3 is capable of stimulating IL-2 gene expression via molecular mechanisms different from those induced during classical T cell activation.

Regulation of lipopolysaccharide-induced lung inflammation by plasminogen activator Inhibitor-1 through a JNK-mediated pathway

The neutrophil is of undoubted importance in lung inflammation after exposure to LPS. We have shown recently that systemic inhibition of JNK decreased neutrophil recruitment to the lung after exposure to LPS, although the mechanisms underlying this inhibition are incompletely understood. As plasminogen activator inhibitor-1 (PAI-1) accentuates cell migration, with JNK activation recently shown to up-regulate PAI-1 expression, this suggested that systemic JNK inhibition may down-regulate LPS-induced pulmonary neutrophil recruitment through a decrease in PAI-1 expression. We show in this study that exposure of mice to aerosolized LPS increased PAI-1 expression in the lung and alveolar compartment, which was decreased by pretreatment with the JNK inhibitor SP600125. Exogenous, intratracheally administered PAI-1 prevented the inhibition of pulmonary neutrophil recruitment in the setting of systemic JNK inhibition, thereby suggesting a role for PAI-1 in the JNK-mediated pathway regulating LPS-induced neutrophil recruitment. In addition, PAI-1(-/-) mice had a decrease in neutrophil recruitment to the alveolar compartment after exposure to LPS, compared with wild-type controls, further suggesting a role for PAI-1 in LPS-induced lung inflammation. An increase in the intravascular level of KC is a likely mechanism for the inhibition of pulmonary neutrophil recruitment after LPS exposure in the setting of decreased PAI-1 expression, as systemic KC levels after exposure to LPS were increased in PAI-1-deficient mice and in mice pretreated with SP600125, with augmentation of intravascular KC levels inhibiting neutrophil recruitment to the lung after exposure to LPS.

Macrophage inflammatory protein 1alpha inhibits postentry steps of human immunodeficiency virus type 1 infection via suppression of intracellular cyclic AMP

Primary isolates of human immunodeficiency virus type 1 (HIV-1) predominantly use chemokine receptor CCR5 to enter target cells. The natural ligands of CCR5, the beta-chemokines macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, and RANTES, interfere with HIV-1 binding to CCR5 receptors and decrease the amount of virions entering cells. Although the inhibition of HIV-1 entry by beta-chemokines is well documented, their effects on postentry steps of the viral life cycle and on host cell components that control the outcome of infection after viral entry are not well defined. Here, we show that all three beta-chemokines, and MIP-1alpha in particular, inhibit postentry steps of the HIV-1 life cycle in primary lymphocytes, presumably via suppression of intracellular levels of cyclic AMP (cAMP). Productive HIV-1 infection of primary lymphocytes requires cellular activation. Cell activation increases intracellular cAMP, which is required for efficient synthesis of proviral DNA during early steps of viral infection. Binding of MIP-1alpha to cognate receptors decreases activation-induced intracellular cAMP levels through the activation of inhibitory G proteins. Furthermore, inhibition of one of the downstream targets of cAMP, cAMP-dependent PKA, significantly inhibits synthesis of HIV-1-specific DNA without affecting virus entry. These data reveal that beta-chemokine-mediated inhibition of virus replication in primary lymphocytes combines inhibitory effects at the entry and postentry levels and imply the involvement of beta-chemokine-induced signaling in postentry inhibition of HIV-1 infection.

Attenuation of okadaic acid-induced hyperphosphorylation of cytoskeletal proteins by heat preconditioning and its possible underlying mechanisms

An imbalanced phosphorylation system is recognized to be one of the main reasons for Alzheimer-like hyperphosphorylation of cytoskeletal proteins. However, little is known about the strategies rectifying the lesions caused by this disrupted phosphorylation. To search for the means to arrest Alzheimer-like damages and explore the underlying mechanisms, in this study we treated N2a/peuht40 cells with okadaic acid (OA), a specific inhibitor of protein phosphatase-2A (PP-2A) and PP-1, to mimic an Alzheimer-like phosphatase-deficient system and then used heat preconditioning (42 degrees C for 1 hour) to induce the expression of inducible heat shock protein 70 (Hsp70) in the cells. We observed that heat preconditioning arrested OA-induced hyperphosphorylation of neurofilament (NF) protein at SMI34 and SMI33 epitopes as well as hyperphosphorylation of tau at Tau-1 and PHF-1 epitopes. It counteracted OA-induced decrease in PP-2A activity with a concurrent inhibition in constitutive activity of mitogen-activated protein kinases (MAPKs) and cyclic adenosine 5'-monophosphate-dependent protein kinase A (PKA). Conversely, quercetin, a recognized blocker of stress-responsive Hsp70 expression, diminished the effects caused by heat preconditioning. These results suggested that Hsp70 antagonized OA-induced Alzheimer-like NF and tau hyperphosphorylation, and the restoration of PP-2A and inhibition of MAPKs-PKA activity might be part of the underlying mechanisms for the rectification of OA-induced hyperphosphorylation.

Tetradecanoyl phorbol acetate induces expression of Toll-like receptor 2 in U937 cells: involvement of PKC, ERK, and NF-κB

Toll-like receptors (TLRs) have been identified recently as crucial signaling receptors mediating the innate immune recognition. Though induction of TLR2 or TLR4 by 12-O-tetradecanoyl phorbol 13-acetate (TPA) in leukemia cells has been reported, however, the mechanism by which TPA up-regulates TLR2 or TLR4 remains poorly understood. In this study, we investigated the effect of TPA on induction of TLR2 in U937 cells. TPA markedly induced TLR2 mRNA and protein expressions. TLR2 expression in response to TPA was attenuated by pretreatments with GF109203X and Go6976 (inhibitors of protein kinase C (PKC)) and PD98059 (an inhibitor of extracellular signal-regulated kinases (ERKs)), but not SB203580 (an inhibitor of p38s) and SP600125 (an inhibitor of c-Jun N-terminal kinases), suggesting involvement of PKC and ERKs in this response. Moreover, TPA-induced PKC activation was linked to generation of reactive oxygen species, which were dispensable for TLR2 expression in U937 cells. Pretreatments with GF109203X blocked TPA-induced phosphorylation of ERKs, suggesting activation of ERKs by PKC. In addition, TPA induced nuclear factor-kappaB (NF-kappaB) activation, which was shown by increased nuclear translocation of p65 NF-kappaB and degradation of IkappaB-alpha, a NF-kappaB inhibitory protein. Importantly, TPA-induced TLR2 expression was inhibited by blockage of NF-kappaB activation using NF-kappaB inhibitors, including MG132 and BAY11-7085. Specifically, TPA-induced nuclear translocation of NF-kappaB was effectively attenuated by GF109203X and PD98059, suggesting PKC and ERK regulation of NF-kappaB nuclear localization in response to TPA. Together, these results suggest that TPA-induced TLR2 expression in U937 cells may be at least in part mediated through activation of PKC and ERKs as well as NF-kappaB transcription factor, and that cross-talk between PKC or ERKs and NF-kappaB may exist.