p21-activated kinase 1 activates the nuclear factor kappa B (NF-kappa B)-inducing kinase-Ikappa B kinases NF-kappa B pathway and proinflammatory cytokines in Helicobacter pylori infection

Natural PAK1 inhibitors: potent anti-inflammatory effectors for prevention of pulmonary fibrosis in COVID-19 therapy

One of the main efforts of scientists to study drug development is the discovery of novel antiviral agents that could be beneficial in the struggle against viruses that cause diseases in humans. Natural products are complex metabolites that are designed and synthesised by different sources in an attempt to optimise nature. Recently, natural products are still a source of biologically active molecules, facilitating drug discovery. A p21-activating kinase PAK1 is a key regulator of cytoskeletal actin assembly, phenotypic signalling, and transcription process which affects a wide range of cellular processes such as cell motility, invasion, metastasis, cell growth, angiogenesis, and cell cycle progression. Most recently, PAK1 was shown to be involved in the progression of coronavirus-caused pulmonary inflammation (lung fibrosis), but clinical data is not currently available yet. This review highlights the naturally occurring compounds that inhibit the oncogenic, melanogenic, and ageing kinase PAK1. Additionally, the potent anti-inflammatory effects of natural products in an attempt to prevent pulmonary fibrosis in COVID-19 have also been discussed.

Helicobacter pylori triggers inflammation and oncogenic transformation by perturbing the immune microenvironment

The immune microenvironment plays a critical regulatory role in the pathogenesis of Helicobacter pylori (H. pylori). Understanding the mechanisms that drive the transition from chronic inflammation to cancer may provide new insights for early detection of gastric cancer. Although chronic inflammation is frequent in precancerous gastric conditions, the monitoring function of the inflammatory microenvironment in the progression from H. pylori-induced chronic inflammation to gastric cancer remains unclear. This literature review summarizes significant findings on how H. pylori triggers inflammatory responses and facilitates cancer development through the immune microenvironment. Furthermore, the implications for future research and clinical applications are also addressed. The review is divided into four main sections: inflammatory response and immune evasion mechanisms induced by H. pylori, immune dysregulation associated with gastric cancer, therapeutic implications, and future perspectives on H. pylori-induced gastric carcinogenesis with a focus on the immune microenvironment.

Ellagitannins from Castanea sativa Mill. Leaf Extracts Impair H. pylori Viability and Infection-Induced Inflammation in Human Gastric Epithelial Cells

Helicobacter pylori (H. pylori) is an etiologic factor of peptic ulcer disease and gastric cancer. Virulent strains of H. pylori are correlated with the severity of gastritis, due to NF-κB activation and IL-8 expression at the epithelial level. Ellagitannins have been documented for antibacterial and anti-inflammatory activities, thus suggesting their potential use in gastritis. Recently, several authors, including our group, demonstrated that tannin-rich extracts from chestnut byproducts, at present considered agricultural waste, display promising biological activities. In this work, we detected high levels of polyphenols in hydroalcoholic extracts from chestnut leaves (Castanea sativa L.). Among polyphenols, the ellagitannin isomers castalagin and vescalagin (about 1% w/w of dry extract) were identified as potential bioactive compounds. In GES-1 cells infected by H. pylori, leaf extract and pure ellagitannins inhibited IL-8 release (IC₅₀ ≈ 28 µg/mL and 11 µM, respectively). Mechanistically, the anti-inflammatory activity was partly due to attenuation of NF-κB signaling. Moreover, the extract and pure ellagitannins reduced bacterial growth and cell adhesion. A simulation of the gastric digestion suggested that the bioactivity might be maintained after oral administration. At the transcriptional level, castalagin downregulated genes involved in inflammatory pathways (NF-κB and AP-1) and cell migration (Rho GTPase). To the best of our knowledge, this is the first investigation in which ellagitannins from plant extracts have demonstrated a potential role in the interaction among H. pylori and human gastric epithelium.

p21-Activated Kinase: Role in Gastrointestinal Cancer and Beyond

Simple Summary

Gastrointestinal tumors are the most common tumors with a high mortality rate worldwide. Numerous protein kinases have been studied in anticipation of finding viable tumor therapeutic targets, including PAK. PAK is a serine/threonine kinase that plays an important role in the malignant phenotype of tumors. The function of PAK in tumors is highlighted in cell proliferation, survival, motility, tumor cell plasticity and the tumor microenvironment, therefore providing a new possible target for clinical tumor therapy. Based on the current research works of PAK, we summarize and analyze the PAK features and signaling pathways in cells, especially the role of PAK in gastrointestinal tumors, thereby hoping to provide a theoretical basis for both the future studies of PAK and potential tumor therapeutic targets.

Abstract

Gastrointestinal tumors are the most common tumors, and they are leading cause of cancer deaths worldwide, but their mechanisms are still unclear, which need to be clarified to discover therapeutic targets. p21-activating kinase (PAK), a serine/threonine kinase that is downstream of Rho GTPase, plays an important role in cellular signaling networks. According to the structural characteristics and activation mechanisms of them, PAKs are divided into two groups, both of which are involved in the biological processes that are critical to cells, including proliferation, migration, survival, transformation and metabolism. The biological functions of PAKs depend on a large number of interacting proteins and the signaling pathways they participate in. The role of PAKs in tumors is manifested in their abnormality and the consequential changes in the signaling pathways. Once they are overexpressed or overactivated, PAKs lead to tumorigenesis or a malignant phenotype, especially in tumor invasion and metastasis. Recently, the involvement of PAKs in cellular plasticity, stemness and the tumor microenvironment have attracted attention. Here, we summarize the biological characteristics and key signaling pathways of PAKs, and further analyze their mechanisms in gastrointestinal tumors and others, which will reveal new therapeutic targets and a theoretical basis for the clinical treatment of gastrointestinal cancer.

The Role of p21-Activated Kinases in Cancer and Beyond: Where Are We Heading?

The p21-activated kinases (PAKs), downstream effectors of Ras-related Rho GTPase Cdc42 and Rac, are serine/threonine kinases. Biologically, PAKs participate in various cellular processes, including growth, apoptosis, mitosis, immune response, motility, inflammation, and gene expression, making PAKs the nexus of several pathogenic and oncogenic signaling pathways. PAKs were proved to play critical roles in human diseases, including cancer, infectious diseases, neurological disorders, diabetes, pancreatic acinar diseases, and cardiac disorders. In this review, we systematically discuss the structure, function, alteration, and molecular mechanisms of PAKs that are involved in the pathogenic and oncogenic effects, as well as PAK inhibitors, which may be developed and deployed in cancer therapy, anti-viral infection, and other diseases. Furthermore, we highlight the critical questions of PAKs in future research, which provide an opportunity to offer input and guidance on new directions for PAKs in pathogenic, oncogenic, and drug discovery research.

p21-Activated Kinases in Thyroid Cancer

The family of p21-activated kinases (PAKs) are oncogenic proteins that regulate critical cellular functions. PAKs play central signaling roles in the integrin/CDC42/Rho, ERK/MAPK, PI3K/AKT, NF-κB, and Wnt/β-catenin pathways, functioning both as kinases and scaffolds to regulate cell motility, mitosis and proliferation, cytoskeletal rearrangement, and other cellular activities. PAKs have been implicated in both the development and progression of a wide range of cancers, including breast cancer, pancreatic melanoma, thyroid cancer, and others. Here we will discuss the current knowledge on the structure and biological functions of both group I and group II PAKs, as well as the roles that PAKs play in oncogenesis and progression, with a focus on thyroid cancer and emerging data regarding BRAF/PAK signaling.

NF-κB/miR-223-3p/ARID1A axis is involved in Helicobacter pylori CagA-induced gastric carcinogenesis and progression

Infection with Helicobacter pylori (H. pylori) and the resulting gastric inflammation is regarded as the strongest risk factor for gastric carcinogenesis and progression. NF-κB plays an important role in linking H. pylori-mediated inflammation to cancer. However, the underlying mechanisms are poorly understood. In this study, we find that H. pylori infection induces miR-223-3p expression in H. pylori CagA-dependent manner. NF-κB stimulates miR-223-3p expression via directly binding to the promoter of miR-223-3p and is required for H. pylori CagA-mediated upregulation of miR-223-3p. miR-223-3p promotes the proliferation and migration of gastric cancer cells by directly targeting ARID1A and decreasing its expression. Furthermore, miR-223-3p/ARID1A axis is involved in CagA-induced cell proliferation and migration. In the clinical setting, the level of miR-223-3p is upregulated, while ARID1A is downregulated significantly in human gastric cancer tissues compared with the corresponding noncancerous tissues. The expression level of miR-223-3p is significantly higher in H. pylori-positive gastric cancer tissues than that in H. pylori-negative tissues. Moreover, a negative correlation between miR-223-3p and ARID1A expression is found in the gastric cancer tissues. Taken together, our findings suggested NF-κB/miR-223-3p/ARID1A axis may link the process of H. pylori-induced chronic inflammation to gastric cancer, thereby providing a new insight into the mechanism underlying H. pylori-associated gastric diseases.

PAKs in the brain: Function and dysfunction

p21-Activated kinases (PAKs) comprise a family of proteins covering a central role in signal transduction. They are downstream effectors of Rho GTPases and can affect a variety of processes in different cell types and tissues by remodeling the cytoskeleton and by promoting gene transcription and cell survival. Given the relevance of cytoskeletal organization in neuronal development as well as synaptic function and the importance of pro-survival signals in controlling neuronal cell fate, accumulating studies investigated the role of PAKs in the nervous system. In this review, we provide a critical overview of the role of PAKs in the nervous system, both in neuronal and non-neuronal cells, and discuss their potential link with neurodegenerative diseases.

Subverting Host Cell P21-Activated Kinase: A Case of Convergent Evolution across Pathogens

Intracellular pathogens have evolved a wide range of strategies to not only escape from the immune systems of their hosts, but also to directly exploit a variety of host factors to facilitate the infection process. One such strategy is to subvert host cell signalling pathways to the advantage of the pathogen. Recent research has highlighted that the human serine/threonine kinase PAK, or p21-activated kinase, is a central component of host-pathogen interactions in many infection systems involving viruses, bacteria, and eukaryotic pathogens. PAK paralogues are found in most mammalian tissues, where they play vital roles in a wide range of functions. The role of PAKs in cell proliferation and survival, and their involvement in a number of cancers, is of great interest in the context of drug discovery. In this review we discuss the latest insights into the surprisingly central role human PAK1 plays for the infection by such different infectious disease agents as viruses, bacteria, and parasitic protists. It is our intention to open serious discussion on the applicability of PAK inhibitors for the treatment, not only of neoplastic diseases, which is currently the primary objective of drug discovery research targeting these enzymes, but also of a wide range of infectious diseases.

Growth hormone-releasing hormone receptor antagonists inhibit human gastric cancer through downregulation of PAK1-STAT3/NF-κB signaling

Gastric cancer (GC) ranks as the fourth most frequent in incidence and second in mortality among all cancers worldwide. The development of effective treatment approaches is an urgent requirement. Growth hormone-releasing hormone (GHRH) and GHRH receptor (GHRH-R) have been found to be present in a variety of tumoral tissues and cell lines. Therefore the inhibition of GHRH-R was proposed as a promising approach for the treatment of these cancers. However, little is known about GHRH-R and the relevant therapy in human GC. By survival analyses of multiple cohorts of GC patients, we identified that increased GHRH-R in tumor specimens correlates with poor survival and is an independent predictor of patient prognosis. We next showed that MIA-602, a highly potent GHRH-R antagonist, effectively inhibited GC growth in cultured cells. Further, this inhibitory effect was verified in multiple models of human GC cell lines xenografted into nude mice. Mechanistically, GHRH-R antagonists target GHRH-R and down-regulate the p21-activated kinase 1 (PAK1)-mediated signal transducer and activator of transcription 3 (STAT3)/nuclear factor-κB (NF-κB) inflammatory pathway. Overall, our studies establish GHRH-R as a potential molecular target in human GC and suggest treatment with GHRH-R antagonist as a promising therapeutic intervention for this cancer.

p21-activated kinase 1 determines stem-like phenotype and sunitinib resistance via NF-κB/IL-6 activation in renal cell carcinoma

The p21-activated kinase 1 (PAK1), a serine/threonine kinase that orchestrates cytoskeletal remodeling and cell motility, has been shown to function as downstream node for various oncogenic signaling pathways to promote cell proliferation, regulate apoptosis and accelerate mitotic abnormalities, resulting in tumor formation and invasiveness. Although alterations in PAK1 expression and activity have been detected in various human malignancies, its potential biological and clinical significance in renal cell carcinoma (RCC) remains obscure. In this study, we found increased PAK1 and phosphorylated PAK1 levels in tumor tissues according to TNM stage progression. Elevated phosphorylated PAK1 levels associated with progressive features and indicated unfavorable overall survival (OS) as an independent adverse prognosticator for patients with RCC. Moreover, PAK1 kinase activation with constitutive active PAK1 mutant T423E promoted growth, colony formation, migration, invasion and stem-like phenotype of RCC cells, and vice versa, in PAK1 inhibition by PAK1 kinase inactivation with specific PAK1 shRNA, dead kinase PAK1 mutant K299R or allosteric inhibitor IPA3. Stem-like phenotype due to sunitinib administration via increased PAK1 kinase activation could be ameliorated by PAK1 shRNA, PAK1 mutant K299R and IPA3. Furthermore, nuclear factor-κB (NF-κB)/interleukin-6 (IL-6) activation was found to be responsible for PAK1-mediated stem-like phenotype following sunitinib treatment. Both IL-6 neutralizing antibody and IPA3 administration enhanced tumor growth inhibition effect of sunitinib treatment on RCC cells in vitro and in vivo. Our results unraveled that oncogenic activation of PAK1 defines an important mechanism for maintaining stem-like phenotype and sunitinib resistance through NF-κB/IL-6 activation in RCC, lending PAK1-mediated NF-κB/IL-6 activation considerable appeal as novel pharmacological therapeutic targets against sunitinib resistance.

Macrophage polarization drives granuloma outcome during Mycobacterium tuberculosis infection

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), induces formation of granulomas, structures in which immune cells and bacteria colocalize. Macrophages are among the most abundant cell types in granulomas and have been shown to serve as both critical bactericidal cells and targets for M. tuberculosis infection and proliferation throughout the course of infection. Very little is known about how these processes are regulated, what controls macrophage microenvironment-specific polarization and plasticity, or why some granulomas control bacteria and others permit bacterial dissemination. We take a computational-biology approach to investigate mechanisms that drive macrophage polarization, function, and bacterial control in granulomas. We define a "macrophage polarization ratio" as a metric to understand how cytokine signaling translates into polarization of single macrophages in a granuloma, which in turn modulates cellular functions, including antimicrobial activity and cytokine production. Ultimately, we extend this macrophage ratio to the tissue scale and define a "granuloma polarization ratio" describing mean polarization measures for entire granulomas. Here we coupled experimental data from nonhuman primate TB granulomas to our computational model, and we predict two novel and testable hypotheses regarding macrophage profiles in TB outcomes. First, the temporal dynamics of granuloma polarization ratios are predictive of granuloma outcome. Second, stable necrotic granulomas with low CFU counts and limited inflammation are characterized by short NF-κB signal activation intervals. These results suggest that the dynamics of NF-κB signaling is a viable therapeutic target to promote M1 polarization early during infection and to improve outcome.

PAK signaling in cancer

Transformation of a normal cell to a cancer cell is caused by mutations in genes that regulate proliferation, apoptosis, and invasion. Small GTPases such as Ras, Rho, Rac and Cdc42 orchestrate many of the signals that are required for malignant transformation. The p21-activated kinases (PAKs) are effectors of Rac and Cdc42. PAKs are a family of serine/threonine protein kinases comprised of six isoforms (PAK1–6), and they play important roles in cytoskeletal dynamics, cell survival and proliferation. They act as key signal transducers in several cancer signaling pathways, including Ras, Raf, NFκB, Akt, Bad and p53. Although PAKs are not mutated in cancers, they are overexpressed, hyperactivated or amplified in several human tumors and their role in cell transformation make them attractive therapeutic targets. This review discusses the evidence that PAK is important for cell transformation and some key signaling pathways it regulates. This review primarily discusses Group I PAKs (PAK1, PAK2 and PAK3) as Group II PAKs (PAK4, PAK5 and PAK6) are discussed elsewhere in this issue (by Minden).

Inhibition of p21-activated kinase 1 by IPA-3 attenuates secondary injury after traumatic brain injury in mice

The p21-activated kinase 1 (PAK1) is up-regulated in the brain following traumatic brain injury (TBI). Inhibition of PAK1 has been found to alleviate brain edema in a rat model of subarachnoid hemorrhage. Suppressing PAK1 activity might represent a novel therapeutics of attenuating secondary injury following TBI. Here we confirmed that the mRNA and protein levels of PAK1 and the protein level of p-PAK1 were significantly increased after inducing TBI in mice via M.A. Flierl's weight-drop model. A single intraperitoneal administration of IPA-3, a specific PAK1 inhibitor, immediately after TBI significantly reduced the protein level of p-PAK1, cleaved caspase-3 level, the number of apoptotic cells at the lesion sites of TBI mice. It also reduced brain water content and the blood-brain barrier permeability in TBI mice. Furthermore, the administration of IPA-3 significantly reduced the neurological severity score and increased the grip test score in TBI mice. Taken together, we demonstrate that PAK1 inhibition by IPA-3 may attenuate the secondary injury following TBI, suggesting it might be a promising neuroprotective strategy for preventing the development of secondary injury after TBI.

Therapeutic efficacy of the multi-epitope vaccine CTB-UE against Helicobacter pylori infection in a Mongolian gerbil model and its microRNA-155-associated immuno-protective mechanism

Vaccination is an effective means of preventing infectious diseases, including those caused by Helicobacter pylori. In this study, we constructed a novel multi-epitope vaccine, CTB-UE, composed of the cholera toxin B subunit and tandem copies of the B and Th cell epitopes from the H. pylori urease A and B subunits. We evaluated the therapeutic efficacy of the multi-epitope vaccine CTB-UE against H. pylori infection in a Mongolian gerbil model and studied its immuno-protective mechanisms. The experimental results indicated that urease activity, H. pylori colonisation density, the levels of IL-8 and TNF-α in the serum, and the levels of COX-2 and NAP in gastric tissue were significantly lower and the IgG level in the serum and the IFN-γ level in spleen lymphocytes were significantly higher in the vaccinated group compared with the model control group; additionally, gastric mucosal inflammation was notably alleviated following vaccination. The results showed that CTB-UE had a good therapeutic effect on H. pylori infection. The immuno-protective mechanism was closely related to the immune response mediated by microRNA-155, the expression of which was strongly up-regulated after CTB-UE administration. The expression levels of the microRNA-155 target proteins IFN-γRα, AID, and PU.1 were significantly down-regulated; these results indicated that CTB-UE induced an immune response biased towards Th1 cells by up-regulating microRNA-155 to inhibit IFN-γRα expression and induced a humoral immune response towards B cells by up-regulating microRNA-155 to inhibit PU.1 and AID expression. These results demonstrate that the multi-epitope vaccine CTB-UE may be a promising therapeutic vaccine against H. pylori infection and is a new therapeutic tool for human use.

MEKK3 and TAK1 synergize to activate IKK complex in Helicobacter pylori infection

Helicobacter pylori colonises the gastric epithelial cells of half of the world's population and represents a risk factor for gastric adenocarcinoma. In gastric epithelial cells H. pylori induces the immediate early response transcription factor nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-κB) and the innate immune response. We show that H. pylori induces in a type IV secretion system-dependent (T4SS) and cytotoxin associated gene A protein (CagA)-independent manner a transient activation of the inhibitor of NF-κB (IκBα) kinase (IKK)-complex. IKKα and IKKβ expression stabilises the regulatory IKK complex subunit NF-κB essential modulator (NEMO). We provide evidence for an intimate mutual control of the IKK complex by mitogen-activated protein kinase kinase kinase 3 (MEKK3) and transforming growth factor β activated kinase 1 (TAK1). TAK1 interacts transiently with the E3 ubiquitin ligase tumor necrosis factor receptor-associated factor 6 (TRAF6). Protein modifications in the TAK1 molecule, e.g. TAK1 autophosphorylation and K63-linked ubiquitinylation, administer NF-κB signalling including transient recruitment of the IKK-complex. Overall, our data uncover H. pylori-induced interactions and protein modifications of the IKK complex, and its upstream regulatory factors involved in NF-κB activation.

Helicobacter pylori induces type 4 secretion system-dependent, but CagA-independent activation of IκBs and NF-κB/RelA at early time points

Colonization of the gastric epithelium by Helicobacter pylori induces the transcription factor nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-κB) and the innate immune response. Virulent strains of H. pylori carry a cag pathogenicity island (cagPAI), which encodes a type IV secretion system (T4SS). Recent publications have shown controversial data regarding the role of the T4SS and the effector protein cytotoxin associated gene A (CagA), which becomes translocated by the T4SS into the eukaryotic epithelial cell, in H. pylori-induced NF-κB activation. Thus, this study analyses by using three different H. pylori strains (P1, B128 and G27) whether CagA is required to initiate activation of different molecules of inhibitors of kappa B (IκB) and the NF-κB transcription factor RelA. We provide experimental evidence that H. pylori induces phosphorylation of NF-κB inhibitors IκBα, IκBβ and IκBɛ, and degradation of IκBα. Further, H. pylori stimulates phosphorylation of RelA at amino acids S536, S468 and S276, promotes DNA binding of RelA, and interleukin 8 (IL-8) gene expression in a T4SS-, but CagA-independent manner at early time points.

Inhibition of nuclear factor-kappa B activation decreases survival of Mycobacterium tuberculosis in human macrophages

Nuclear factor-kappa B (NFκB) is a ubiquitous transcription factor that mediates pro-inflammatory responses required for host control of many microbial pathogens; on the other hand, NFκB has been implicated in the pathogenesis of other inflammatory and infectious diseases. Mice with genetic disruption of the p50 subunit of NFκB are more likely to succumb to Mycobacterium tuberculosis (MTB). However, the role of NFκB in host defense in humans is not fully understood. We sought to examine the role of NFκB activation in the immune response of human macrophages to MTB. Targeted pharmacologic inhibition of NFκB activation using BAY 11-7082 (BAY, an inhibitor of IκBα kinase) or an adenovirus construct with a dominant-negative IκBα significantly decreased the number of viable intracellular mycobacteria recovered from THP-1 macrophages four and eight days after infection. The results with BAY were confirmed in primary human monocyte-derived macrophages and alveolar macrophages. NFκB inhibition was associated with increased macrophage apoptosis and autophagy, which are well-established killing mechanisms of intracellular MTB. Inhibition of the executioner protease caspase-3 or of the autophagic pathway significantly abrogated the effects of BAY. We conclude that NFκB inhibition decreases viability of intracellular MTB in human macrophages via induction of apoptosis and autophagy.

Ca2+/calmodulin-dependent kinase II contributes to inhibitor of nuclear factor-kappa B kinase complex activation in Helicobacter pylori infection

Helicobacter pylori, a class I carcinogen, induces a proinflammatory response by activating the transcription factor nuclear factor-kappa B (NF-κB) in gastric epithelial cells. This inflammatory condition could lead to chronic gastritis, which is epidemiologically and biologically linked to the development of gastric cancer. So far, there exists no clear knowledge on how H. pylori induces the NF-κB-mediated inflammatory response. In our study, we investigated the role of Ca(2+) /calmodulin-dependent kinase II (CAMKII), calmodulin, protein kinases C (PKCs) and the CARMA3-Bcl10-MALT1 (CBM) complex in conjunction with H. pylori-induced activation of NF-κB via the inhibitor of nuclear factor-kappa B kinase (IKK) complex. We use specific inhibitors and/or RNA interference to assess the contribution of these components. Our results show that CAMKII and calmodulin contribute to IKK complex activation and thus to the induction of NF-κB in response to H. pylori infection, but not in response to TNF-α. Thus, our findings are specific for H. pylori infected cells. Neither the PKCs α, δ, θ, nor the CBM complex itself is involved in the activation of NF-κB by H. pylori. The contribution of CAMKII and calmodulin, but not PKCs/CBM to the induction of an inflammatory response by H. pylori infection augment the understanding of the molecular mechanism involved and provide potential new disease markers for the diagnosis of gastric inflammatory diseases including gastric cancer.

Helicobacter pylori-induced disruption of monolayer permeability and proinflammatory cytokine secretion in polarized human gastric epithelial cells

Helicobacter pylori infection of the stomach is related to the development of diverse gastric pathologies. The ability of H. pylori to compromise epithelial junctional complexes and to induce proinflammatory cytokines is believed to contribute to pathogenesis. The purpose of this study was to use an in vitro human gastric epithelial model to investigate the ability of H. pylori to affect permeability and the extent and polarity of the host inflammatory response. NCI-N87 monolayers were cocultured with live or heat-killed H. pylori or culture supernatants. Epithelial barrier function was measured by transepithelial electric resistance (TEER) analysis, diffusion of fluorescein isothiocyanate (FITC)-labeled markers, and immunostaining for tight junction proteins. Supernatants from both apical and basolateral chambers were tested for cytokine production by multiplex analysis. H. pylori caused a significant decrease in TEER, an increased passage of markers through the infected monolayer, and severe disruption and mislocalization of ZO-1 and claudin-1 proteins. Cell viability was not altered by H. pylori, indicating that loss of barrier function could be attributed to a breakdown of tight junction integrity. Significantly high levels of cytokine secretion were induced by either viable or heat-killed H. pylori. H. pylori affects monolayer permeability of polarized human gastric epithelial cells. Proinflammatory cytokines were secreted in a polarized manner, mostly basolaterally. Live bacteria are required for disruption of tight junctions but not for the induction of cytokine secretion. The NCI-N87 cell line provides an excellent model for the in vitro study of H. pylori pathogenesis and the epithelial cell host response to infection.

p21-activated kinases and gastrointestinal cancer

p21-activated kinases (PAKs) were initially identified as effector proteins downstream from GTPases of the Rho family. To date, six members of the PAK family have been discovered in mammalian cells. PAKs play important roles in growth factor signalling, cytoskeletal remodelling, gene transcription, cell proliferation and oncogenic transformation. A large body of research has demonstrated that PAKs are up-regulated in several human cancers, and that their overexpression is linked to tumour progression and resistance to therapy. Structural and biochemical studies have revealed the mechanisms involved in PAK signalling, and opened the way to the development of PAK-targeted therapies for cancer treatment. Here we summarise recent findings from biological and clinical research on the role of PAKs in gastrointestinal cancer, and discuss the current status of PAK-targeted anticancer therapies.

Rebamipide abolishes Helicobacter pylori CagA-induced phospholipase D1 expression via inhibition of NFκB and suppresses invasion of gastric cancer cells

Infection with cagA-positive Helicobacter pylori is a risk factor for the development of severe gastritis and gastric cancer (GC). CagA protein is injected into gastric epithelial cells and deregulates a variety of cellular signaling molecules. Phospholipase D (PLD) is elevated in many different types of human cancers and has been implicated as a critical factor in inflammation and carcinogenesis. In this study, we show that infection with cagA-positive H. pylori in GC cells significantly induces PLD1 expression via CagA-dependent activation of nuclear factor κB (NFκB). Interestingly, the level of PLD1 protein and IκBα phosphorylation is aberrantly upregulated in H. pylori-infected human GC tissues. Infection with cagA-positive H. pylori and expression of CagA enhanced the binding of NFκB to the PLD1 promoter, and two functional NFκB-binding sites were identified within the PLD1 promoter. Rebamipide, a mucosal-protective antiulcer agent, abolished H. pylori cagA-induced PLD1 expression via inhibition of binding of NFκB to the PLD1 promoter, and also inhibited PLD activity. Moreover, rebamipide suppressed H. pylori-induced matrix metalloproteinase-9, interleukin-8 and activation-induced cytidine deaminase expression as well as invasion of GC cells through downregulation of PLD1. Our data suggest that H. pylori cagA targets PLD1 for invasion of GC cells, and rebamipide might contribute to the antitumorigenic effect of GC cells via inhibition of the H. pylori cagA-NFκB-PLD1 signaling pathway.

Induction of CD69 expression by cagPAI-positive Helicobacter pylori infection

AIM: To investigate and elucidate the molecular mechanism that regulates inducible expression of CD69 by Helicobacter pylori (H. pylori) infection.

METHODS: The expression levels of CD69 in a T-cell line, Jurkat, primary human peripheral blood mononuclear cells (PBMCs), and CD4⁺ T cells, were assessed by immunohistochemistry, reverse transcription polymerase chain reaction, and flow cytometry. Activation of CD69 promoter was detected by reporter gene. Nuclear factor (NF)-κB activation in Jurkat cells infected with H. pylori was evaluated by electrophoretic mobility shift assay. The role of NF-κB signaling in H. pylori-induced CD69 expression was analyzed using inhibitors of NF-κB and dominant-negative mutants. The isogenic mutants with disrupted cag pathogenicity island (cagPAI) and virD4 were used to elucidate the role of cagPAI-encoding type IV secretion system and CagA in CD69 expression.

RESULTS: CD69 staining was detected in mucosal lymphocytes and macrophages in specimens of patients with H. pylori-positive gastritis. Although cagPAI-positive H. pylori and an isogenic mutant of virD4 induced CD69 expression, an isogenic mutant of cagPAI failed to induce this in Jurkat cells. H. pylori also induced CD69 expression in PBMCs and CD4⁺ T cells. The activation of the CD69 promoter by H. pylori was mediated through NF-κB. Transfection of dominant-negative mutants of IκBs, IκB kinases, and NF-κB-inducing kinase inhibited H. pylori-induced CD69 activation. Inhibitors of NF-κB suppressed H. pylori-induced CD69 mRNA expression.

CONCLUSION: The results suggest that H. pylori induces CD69 expression through the activation of NF-κB. cagPAI might be relevant in the induction of CD69 expression in T cells. CD69 in T cells may play a role in H. pylori-induced gastritis.

Helicobacter pylori-induced tyrosine phosphorylation of IKKβ contributes to NF-κB activation

Helicobacter pylori, the etiological agent of several human gastric diseases, induces the transcription factor nuclear factor-κB (NF-κB) in colonized epithelial cells leading to the release of proinflammatory mediators. Activation of NF-κB involves the IκB kinase (IKK)-complex composed of two catalytic subunits, IKKα and IKKβ, and a regulatory scaffold protein, IKKγ. IKKβ was shown to be essential for NF-κB activation in response to a variety of stimuli including H. pylori. In addition to the phosphorylation of serine residues, tyrosine phosphorylation could be crucial for IKKβ activation. Here we provide evidence that IKKβ phosphorylation is induced in lipid rafts (DRM fractions) of H. pylori-infected cells, but not TNFα-stimulated cells. Furthermore, H. pylori transiently induces binding of IKKβ to c-Src kinase. Inhibition of c-Src by specific inhibitors as well as knockdown of c-Src by small interfering RNA reduced phosphorylation of IκBα as well as of p65. Thus, tyrosine-phosphorylated IKKβ contributes at least in part to NF-κB activation in response to H. pylori infection.

What a disorder: proinflammatory signaling pathways induced by Helicobacter pylori

Infection of gastric epithelial cells with Helicobacter pylori induces strong proinflammatory responses by activating nuclear transcription factors NF-κB and AP-1. Several reports indicate that multiple bacterial factors and cellular molecules are involved in this signaling. Injected peptidoglycan, CagA or OipA and urease, and at least 16 different signaling cascades have been implicated in H. pylori-induced proinflammatory signaling. Many of these reports are contradictory, thus generating a highly puzzling scenario. Here we discuss the pros and cons of the multiple signaling activities in the induction of proinflammatory responses and associated problems, and give suggestions for finding ways out of this dilemma.

CagA(+) H. pylori induces Akt1 phosphorylation and inhibits transcription of p21(WAF1/CIP1) and p27(KIP1) via PI3K/Akt1 pathway

OBJECTIVE

Cytotoxin-associated protein (CagA) of H. pylori has been confirmed to be closely associated with gastric inflammation and tumorigenesis, but the mechanism behind it is little understood. In this study, we try to determine roles of CagA(+) strain in activating PI3K/Akt1 signaling pathway, and affecting expression of p21(WAF1/CIP1) and p27(KIP1), and also in releasing IL-8 in host cells.

METHODS

Akt1 phosphorylation and IL-8 levels of CagA(+) and CagA⁻ strain infected AGS cells were detected by ELISAs. Two quantitative RT-PCRs were established to measure p21(WAF1/CIP1) and p27(KIP1) mRNA levels in the CagA(+) and CagA⁻ strain infected cells. LY294002, an inhibitor of PI3K/Akt pathway, was used to define effect of the pathway in IL-8 release.

RESULTS

CagA(+) strain could induce an obvious elevation of Akt1 phosphorylation in the infected AGS cells while CagA? strain failed to do so. The CagA(+) H. pylori strain infected AGS cells showed significant drops both in p21(WAF1/CIP1) and p27(KIP1) mRNA levels, whereas the CagA⁻ H. pylori strain caused a remarkable increase in p21(WAF1/CIP1) mRNA without affecting p27(KIP1) gene transcription in the AGS cells. Both the CagA(+) and CagA⁻ H. pylori strains enabled AGS cells to produce close elevated levels of IL-8, and the LY294002 block resulted in unexpected elevations of IL-8 levels.

CONCLUSIONS

CagA can activate PI3K/Akt1 pathway that plays an inhibitory role in IL-8 release in H. pylori infected AGS cells. Activation of PI3K/Akt1 pathway and subsequent negative regulation of p21(WAF1/CIP1) and p27(KIP1) expression might be involved in CagA-associated carcinogenesis.

alphaPix interacts with Helicobacter pylori CagA to induce IL-8 expression in gastric epithelial cells

OBJECTIVE

Helicobacter pylori CagA, translocated into gastric epithelial cells, induces IL-8 expression through the signalling pathways, including extracellular signal-regulated kinase (ERK) and nuclear factor-kappaB (NF-kappaB). We previously demonstrated that CagA interacts with host alphaPix. The present study was purposed to determine the role of the interaction of alphaPix with CagA on the signalling pathways for IL-8 expression in H. pylori-infected gastric epithelial cells.

MATERIAL AND METHODS

H. pylori HP99 strain (CagA+, VacA+) was infected to gastric epithelial AGS cells transfected with non-targeting (NT) or alphaPix- targeting siRNA. Activation of signalling molecules including p21-activated kinase (PAK), ERK and NF-kappaB, and expression of IL-8 in the cells were assessed.

RESULTS

H. pylori CagA was delivered into AGS cells and then interacted with alphaPix at 4 h following H. pylori infection. PAK1, ERK and NF-kappaB were activated in the cells containing NT and alphaPix siRNA at 1-2 h following H. pylori infection. However, after 4 h, the time when CagA was delivered into the cells, the activations of PAK1, ERK and NF-kappaB were inhibited by down-regulation of alphaPix using siRNA but not by NT siRNA. The results indicate that alphaPix is required for H. pylori-mediated signalling of PAK1, ERK and NF-kappaB. Additionally, alphaPix siRNA suppressed IL-8 induction after translocation of CagA into the cells, indicating that interaction of CagA with alphaPix is critical for CagA-mediating signalling for IL-8 expression.

CONCLUSIONS

The interaction of alphaPix with CagA activates PAK1, ERK and NF-kappaB, which induces IL-8 expression in H. pylori-infected gastric epithelial cells.

Effect of resveratrol on Helicobacter pylori-induced interleukin-8 secretion, reactive oxygen species generation and morphological changes in human gastric epithelial cells

Inflammatory cytokine interleukin-8 (IL-8) and reactive oxygen species (ROS) overexpressed in the gastric mucosa when exposed to Helicobacter pylori, defined as a class I carcinogen. Moreover, infection with H. pylori leads to morphological changes in co-cultured cells known as hummingbird phenomenon along with increased motility. Resveratrol, a highly abundant polyphenol in red grapes, has shown anti-inflammatory, anti-cancer, cardioprotective and neuroprotective activities. However, the effect of resveratrol in H. pylori-infected cells has not been investigated. The present study was, therefore, aimed to evaluate the effect of resveratrol on the induction of IL-8, ROS and hummingbird morphology in H. pylori-infected gastric epithelial cells. The non-toxic concentration of resveratrol for both H. pylori and epithelial cells was determined by brucella broth dilution method and DNA fragmentation assay. The non-toxic resveratrol (< or =100 microM) treatment did not demonstrate any inhibitory effect against H. pylori adhesion to gastric epithelial cells. However, preincubation of the cells with 75 and 100 muM of resveratrol significantly (p<0.05 and p<0.01 respectively) inhibited the secretion of IL-8 from H. pylori-infected cells. In addition, resveratrol pretreatment at 1-100 muM suppressed H. pylori-induced ROS generation in a concentration dependent manner. Moreover, H. pylori-initiated morphological changes were markedly blocked by resveratrol. Hence, resveratrol can be considered as a potential candidate against various H. pylori related gastric pathogenic processes.

Downregulation of p21-activated kinase-1 inhibits the growth of gastric cancer cells involving cyclin B1

p21-Activated kinase 1 (Pak1), a serine/threonine kinase, has been implicated in cytoskeletal remodelling, cell motility, apoptosis and transformation. However, the role of Pak1 in gastric cancer remains unclear. In this study, we detected Pak1 expression in gastric cancer tissues from 40 patients by western blot. Overexpression of Pak1 was associated with progression, metastasis and prognosis of gastric cancer. In addition, we found that knockdown of Pak1 expression significantly inhibited anchorage-dependent and anchorage-independent growth in gastric cancer cells, and markedly inhibited gastric cancer cell xenograft tumor growth. In further study, data showed that Pak1 could regulate the expression of cyclin B1 at the mRNA and protein levels, and impact the subcellular distribution and the promoter activity of cyclin B1. Results from deletion and mutant analysis supplied a new NF-kappaB binding sites at position -321 of cyclin B1 promoter, and indicated that Pak1 regulated the transcription of cyclin B1 in gastric cancer through NF-kappaB. In conclusion, Pak1 may be a potential prognostic marker and therapeutic target in gastric cancer.

Helicobacter pylori CagA activates NF-kappaB by targeting TAK1 for TRAF6-mediated Lys 63 ubiquitination

Helicobacter pylori-initiated chronic gastritis is characterized by the cag pathogenicity island-dependent upregulation of proinflammatory cytokines, which is largely mediated by the transcription factor nuclear factor (NF)-kappaB. However, the cag pathogenicity island-encoded proteins and cellular signalling molecules that are involved in H. pylori-induced NF-kappaB activation and inflammatory response remain unclear. Here, we show that H. pylori virulence factor CagA and host protein transforming growth factor-beta-activated kinase 1 (TAK1) are essential for H. pylori-induced activation of NF-kappaB. CagA physically associates with TAK1 and enhances its activity and TAK1-induced NF-kappaB activation through the tumour necrosis factor receptor-associated factor 6-mediated, Lys 63-linked ubiquitination of TAK1. These findings show that polyubiquitination of TAK1 regulates the activation of NF-kappaB, which in turn is used by H. pylori CagA for the H. pylori-induced inflammatory response.

Tumor necrosis factor-alpha induced expression of matrix metalloproteinase-9 through p21-activated kinase-1

Background

Expressed in embryonic development, matrix metalloprotein-9 (MMP-9) is absent in most of developed adult tissues, but recurs in inflammation during tissue injury, wound healing, tumor formation and metastasis. Expression of MMP-9 is tightly controlled by extracellular cues including pro-inflammatory cytokines and extracellular matrix (ECM). While the pathologic functions of MMP-9 are evident, the intracellular signaling pathways to control its expression are not fully understood. In this study we investigated mechanism of cytokine induced MMP-9 with particular emphasis on the role of p21-activated-kinase-1 (PAK1) and the down stream signaling.

Results

In response to TNF-alpha or IL-1alpha, PAK1 was promptly activated, as characterized by a sequential phosphorylation, initiated at threonine-212 followed by at threonine-423 in the activation loop of the kinase, in human skin keratinocytes, dermal fibroblasts, and rat hepatic stellate cells. Ectopic expression of PAK1 variants, but not p38 MAP kinase, impaired the TNF-alpha-induced MMP-9 expression, while other MMPs such as MMP-2, -3 and -14 were not affected. Activation of Jun N-terminal kinase (JNK) and NF-kappaB has been demonstrated to be essential for MMP-9 expression. Expression of inactive PAK1 variants impaired JNK but not NF-kappaB activation, which consequently suppressed the 5'-promoter activities of the MMP-9 gene. After the cytokine-induced phosphorylation, both ectopically expressed and endogenous PAK1 proteins were promptly accumulated even in the condition of suppressing protein synthesis, suggesting the PAK1 protein is stabilized upon TNF-alpha stimulation. Stabilization of PAK1 protein by TNF-alpha treatment is independent of the kinase catalytic activity and p21 GTPase binding capacities. In contrast to epithelial cells, mesenchymal cells require 3-dimensional type-I collagen in response to TNF-alpha to massively express MMP-9. The collagen effect is mediated, in part, by boost JNK activation in a way to cooperate the cytokine signaling.

Conclusion

We identified a novel mechanism for MMP-9 expression in response to injury signals, which is mediated by PAK1 activation and stabilization leading JNK activation.

NF-kappaB activation by Helicobacter pylori requires Akt-mediated phosphorylation of p65

Background

The inflammatory response in Helicobacter pylori-infected gastric tissue is mediated by cag pathogenicity island (PAI)-dependent activation of nuclear factor-κB (NF-κB). Phosphatidylinositol 3-kinase (PI3K)/Akt signaling is known to play a role in NF-κB activation, but little information is available on the relationship between H. pylori and PI3K/Akt signaling in gastric epithelial cells. We examined whether H. pylori activates Akt in gastric epithelial cells, the role of cag PAI in this process and the role of Akt in regulating H. pylori-induced NF-κB activation.

Results

Phosphorylated Akt was detected in epithelial cells of H. pylori-positive gastric tissues. Although Akt was activated in MKN45 and AGS cells by coculture with cag PAI-positive H. pylori strains, a cag PAI-negative mutant showed no activation of Akt. H. pylori also induced p65 phosphorylation. PI3K inhibitor suppressed H. pylori-induced p65 phosphorylation and NF-κB transactivation, as well as interleukin-8 expression. Furthermore, transfection with a dominant-negative Akt inhibited H. pylori-induced NF-κB transactivation. Transfection with small interference RNAs for p65 and Akt also inhibited H. pylori-induced interleukin-8 expression.

Conclusion

The results suggest that cag PAI-positive H. pylori activates Akt in gastric epithelial cells and this may contribute to H. pylori-mediated NF-κB activation associated with mucosal inflammation and carcinogenesis.

Helicobacter pylori-induced interleukin-12 p40 expression

Interleukin-12 (IL-12) is a heterodimeric cytokine produced by antigen-presenting cells that promotes the development of T-helper lymphocyte 1 (Th1). Chronic gastritis induced by Helicobacter pylori is considered a Th1-mediated process. IL-12 levels in gastric biopsy samples of H. pylori-infected patients are higher than in those of uninfected individuals, but the cellular source of IL-12 remains elusive. IL-12 staining was detected in mucosal epithelial cells, lymphocytes, and macrophages in specimens of patients with H. pylori-positive gastritis. Therefore, we investigated IL-12 p40 mRNA induction by H. pylori in gastric epithelial cells and T cells. Although cag pathogenicity island (PAI)-positive H. pylori induced IL-12 p40 mRNA expression, an isogenic mutant of the cag PAI failed to induce it in both cell types. Supernatants from H. pylori cultures and H. pylori VacA induced IL-12 p40 mRNA expression in T cells but not in epithelial cells. The activation of the IL-12 p40 promoter by H. pylori was mediated through NF-kappaB. The transfection of IkappaB kinase and NF-kappaB-inducing kinase dominant-negative mutants inhibited H. pylori-induced IL-12 p40 activation. Inhibitors of NF-kappaB, phosphatidylinositol 3-kinase, p38 mitogen-activated protein kinase, and Hsp90 suppressed H. pylori- and VacA-induced IL-12 p40 mRNA expression. The results indicate that H. pylori induces IL-12 p40 expression by the activation of NF-kappaB, phosphatidylinositol 3-kinase, and p38 mitogen-activated protein kinase. Hsp90 is also a crucial regulator of H. pylori-induced IL-12 p40 expression. In addition to the cag PAI, VacA might be relevant in the induction of IL-12 expression and a Th1-polarized response only in T cells.

Metabolic actions of estrogen receptor beta (ERbeta) are mediated by a negative cross-talk with PPARgamma

Estrogen receptors (ER) are important regulators of metabolic diseases such as obesity and insulin resistance (IR). While ERα seems to have a protective role in such diseases, the function of ERβ is not clear. To characterize the metabolic function of ERβ, we investigated its molecular interaction with a master regulator of insulin signaling/glucose metabolism, the PPARγ, in vitro and in high-fat diet (HFD)-fed ERβ -/- mice (βERKO) mice. Our in vitro experiments showed that ERβ inhibits ligand-mediated PPARγ-transcriptional activity. That resulted in a blockade of PPARγ-induced adipocytic gene expression and in decreased adipogenesis. Overexpression of nuclear coactivators such as SRC1 and TIF2 prevented the ERβ-mediated inhibition of PPARγ activity. Consistent with the in vitro data, we observed increased PPARγ activity in gonadal fat from HFD-fed βERKO mice. In consonance with enhanced PPARγ activation, HFD-fed βERKO mice showed increased body weight gain and fat mass in the presence of improved insulin sensitivity. To directly demonstrate the role of PPARγ in HFD-fed βERKO mice, PPARγ signaling was disrupted by PPARγ antisense oligonucleotide (ASO). Blockade of adipose PPARγ by ASO reversed the phenotype of βERKO mice with an impairment of insulin sensitization and glucose tolerance. Finally, binding of SRC1 and TIF2 to the PPARγ-regulated adiponectin promoter was enhanced in gonadal fat from βERKO mice indicating that the absence of ERβ in adipose tissue results in exaggerated coactivator binding to a PPARγ target promoter. Collectively, our data provide the first evidence that ERβ-deficiency protects against diet-induced IR and glucose intolerance which involves an augmented PPARγ signaling in adipose tissue. Moreover, our data suggest that the coactivators SRC1 and TIF2 are involved in this interaction. Impairment of insulin and glucose metabolism by ERβ may have significant implications for our understanding of hormone receptor-dependent pathophysiology of metabolic diseases, and may be essential for the development of new ERβ-selective agonists.

In the present study, we demonstrate for the first time a pro-diabetogenic function of the ERβ. Our experiments indicate that ERβ impairs insulin sensitivity and glucose tolerance in mice challenged with a high fat diet (HFD). Loss of ERβ, studied in ERβ -/- mice (βERKO mice), results in increased body weight gain and fat deposition under HFD-treatment. Conversely, absence of ERβ averted accumulation of triglycerides and preserved regular insulin signaling in liver and skeletal muscle. This observation was associated with improved whole-body insulin sensitivity and glucose tolerance. Increased adipose tissue mass in the presence of improved insulin sensitivity and glucose tolerance is usually observed under chronic stimulation of the nuclear hormone receptor PPARγ. In consonance, we show that activation of PPARγ was markedly induced in gonadal fat from βERKO mice and blockade of adipose PPARγ signaling by antisense oligonucleotide injection reversed the metabolic phenotype. Moreover, our cell culture experiments indicate that ERβ is a negative regulator of ligand-induced PPARγ activity in vitro. Finally, we identify SRC1 and TIF2 as key players in the ERβ-PPARγ interaction. In summary, the present study demonstrates that ERβ impairs insulin and glucose metabolism, which may, at least in part, result from a negative cross-talk with adipose PPARγ.

The pathogenesis of Helicobacter pylori-induced gastro-duodenal diseases

Helicobacter pylori is the main cause of peptic ulceration, distal gastric adenocarcinoma, and gastric lymphoma. Only 15% of those colonized develop disease, and pathogenesis depends upon strain virulence, host genetic susceptibility, and environmental cofactors. Virulence factors include the cag pathogenicity island, which induces proinflammatory, pro-proliferative epithelial cell signaling; the cytotoxin VacA, which causes epithelial damage; and an adhesin, BabA. Host genetic polymorphisms that lead to high-level pro-inflammatory cytokine release in response to infection increase cancer risk. Pathogenesis is dependent upon inflammation, a Th-1 acquired immune response and hormonal changes including hypergastrinaemia. Antral-predominant inflammation leads to increased acid production from the uninflamed corpus and predisposes to duodenal ulceration; corpus-predominant gastritis leads to hypochlorhydria and predisposes to gastric ulceration and adenocarcinoma. Falling prevalence of H. pylori in developed countries has led to a falling incidence of associated diseases. However, whether there are disadvantages of an H. pylori-free stomach, for example increased risk of esosphageal adenocarcinoma, remains unclear.

JAK2 Tyrosine Kinase Phosphorylates PAK1 and Regulates PAK1 Activity and Functions

The serine-threonine kinase PAK1 is activated by small GTPase-dependent and -independent mechanisms and promotes cell survival. However, the role of tyrosyl phosphorylation in the regulation of PAK1 function is poorly understood. In this study, we have shown that the prolactin-activated tyrosine kinase JAK2 phosphorylates PAK1 in vivo. Wild type, but not kinase-dead, JAK2 directly phosphorylates PAK1 in cells and in an in vitro kinase assay. PAK1 tyrosines 153, 201, and 285 were identified as sites of JAK2 tyrosyl phosphorylation by mass spectrometry and two-dimensional peptide mapping. Mutation of PAK1 tyrosines 153, 201, and 285 to phenylalanines individually or in combination implicated these PAK1 tyrosines in the regulation of PAK1 kinase activity. Tyrosyl phosphorylation by JAK2 significantly increases PAK1 kinase activity, whereas similar phosphorylation of the PAK1 Y153F,Y201F,Y285F mutant has no effect on PAK1 activity. Tyrosyl phosphorylation of wild type PAK1 decreases apoptosis induced by serum deprivation and staurosporine treatment and increases cell motility. In contrast, these parameters are unaltered in the PAK1 Y153F,Y201F,Y285F mutant. Our findings indicate that JAK2 phosphorylates PAK1 at these specific tyrosines and that this phosphorylation plays an important role in cell survival and motility.

Helicobacter pylori induces CCL20 expression

CCL20 attracts immature dendritic cells and memory T cells and plays a role on mucosal surfaces in inflammation. However, whether Helicobacter pylori infection induces CCL20 in human gastric epithelial cells remains to be determined. The aim of this study was to analyze the molecular mechanism of H. pylori-induced CCL20 expression. Expression of CCL20 mRNA was assessed by reverse transcription-PCR. Five normal and five H. pylori-infected gastric tissue samples were stained immunohistochemically for CCL20. A luciferase assay was used to monitor activation of the CCL20 gene promoter, and an electrophoretic mobility shift assay was used to explore the binding of transcription factors to this promoter. The CCL20 expression in epithelial cells of H. pylori-positive tissues was higher than that in H. pylori-negative tissues. H. pylori induced CCL20 expression in gastric epithelial cell lines, and the induction was dependent on an intact cag pathogenicity island. Activation of the CCL20 promoter by H. pylori occurred through the action of NF-kappaB. Transfection of IkappaB kinase and NF-kappaB-inducing kinase dominant negative mutants inhibited H. pylori-mediated activation of CCL20. Treatment with an inhibitor of Hsp90 suppressed H. pylori-induced CCL20 mRNA due to deactivation of NF-kappaB. Collectively, these results suggest that H. pylori activates NF-kappaB through an intracellular signaling pathway that involves IkappaB kinase and NF-kappaB-inducing kinase, leading to CCL20 gene transcription, and that Hsp90 is a crucial regulator of H. pylori-induced CCL20 expression, presumably contributing to the immune response in H. pylori.

Apoptotic signaling in methylglyoxal-treated human osteoblasts involves oxidative stress, c-Jun N-terminal kinase, caspase-3, and p21-activated kinase 2

Methylglyoxal (MG) is a reactive dicarbonyl compound endogenously produced mainly from glycolytic intermediates. MG is cytotoxic through induction of cell death, and elevated MG levels in diabetes patients are believed to contribute to diabetic complications. In this report, we show for the first time that MG treatment triggers apoptosis in human osteoblasts. We further show that MG-induced apoptosis of osteoblasts involves specific apoptotic biochemical changes, including oxidative stress, c-Jun N-terminal kinase (JNK) activation, mitochondrial membrane potential changes, cytochrome C release, increased Bax/Bcl-2 protein ratios, and activation of caspases (caspase-9, caspase-3) and p21-activated protein kinase 2 (PAK2). Treatment of osteoblasts with SP600125, a JNK-specific inhibitor, led to a reduction in MG-induced apoptosis and decreased activation of caspase-3 and PAK2, indicating that JNK activity is upstream of these events. Experiments using anti-sense oligonucleotides against PAK2 further showed that PAK2 activation is required for MG-induced apoptosis in osteoblasts. Interestingly, we also found that MG treatment triggered nuclear translocation of NF-kappaB, although the precise regulatory role of NF-kappaB activation in MG-induced apoptosis remains unclear. Lastly, we examined the effect of MG on osteoblasts in vivo, and found that exposure of rats to dietary water containing 100-200 microM MG caused bone mineral density (BMD) loss. Collectively, these results reveal for the first time that MG treatment triggers apoptosis in osteoblasts via specific apoptotic signaling, and causes BMD loss in vivo.

The effect of Helicobacter felis and Helicobacter bizzozeronii on the gastric mucosa in Mongolian gerbils: a sequential pathological study

In contrast to Helicobacter(H.) pylori, little is known about the pathogenic mechanisms of gastric non-H. pylori Helicobacter species. Mongolian gerbils were inoculated intragastrically with H. felis or H. bizzozeronii and killed at different timepoints post-inoculation (p.i.), stomach tissue being taken for light and transmission electron microscopy (TEM) and polymerase chain reaction (PCR) analysis. Parietal cells (PCs), apoptosis, cell proliferation and nuclear factor-kappaB (NF-kappaB) activation were "visualized" immunohistochemically. Inflammation consisted of neutrophilic granulocytes, mainly in the antrum, and lymphocytic infiltrates around the limiting ridge and throughout the stomach mucosa and submucosa. From day 11 p.i. onwards, H. felis-inoculated animals showed moderate to severe loss of PCs extending from the limiting ridge into the fundus. Apoptotic cells, spiral bacteria, cell proliferation, and NF-kappaB activation were detected at the transition zone between affected and normal PCs. TEM revealed interaction of H. felis flagella with PCs and chief cells. Moreover, H. felis was seen in proximity to, and inside, necrotic cells. At 10 weeks p.i., some H. felis-infected gerbils showed complete loss of fundic glands, and mucous metaplasia of the epithelium. H. bizzozeronii, which made no flagellar contact with epithelial cells, was associated with only mild PC loss. The mechanism by which H. felis induces PC necrosis and apoptosis remains unclear. The observed flagellar contact and NF-kappaB activation may play an important role in H. felis-associated inflammation.

Anti-apoptotic signalling by the Dot/Icm secretion system of L. pneumophila

The Dot/Icm type IV secretion system of Legionella pneumophila triggers robust activation of caspase-3 during early and exponential stages of proliferation within human macrophages, but apoptosis is delayed till late stages of infection, which is novel. As caspase-3 is the executioner of the cell, we tested the hypothesis that L. pneumophila triggers anti-apoptotic signalling within the infected human macrophages to halt caspase-3 from dismantling the cells. Here we show that during early and exponential replication, L. pneumophila-infected human monocyte-derived macrophages (hMDMs) exhibit a remarkable resistance to induction of apoptosis, in a Dot/Icm-dependent manner. Microarray analyses and real-time PCR reveal that during exponential intracellular replication, L. pneumophila triggers upregulation of 12 anti-apoptotic genes that are linked to activation of the nuclear transcription factor kappa-B (NF-kappaB). Our data show that L. pneumophila induces a Dot/Icm-dependent sustained nuclear translocation of the p50 and p65 subunits of NF-kappaB during exponential intracellular replication. Bacterial entry is essential both for the anti-apoptotic phenotype of infected hMDMs and for nuclear translocation of the p65. Using p65-/- and IKKalpha-/- beta-/- double knockout mouse embryonic fibroblast cell lines, we show that nuclear translocation of NF-kappaB is required for the resistance of L. pneumophila-infected cells to apoptosis-inducing agents. In addition, the L. pneumophila-induced nuclear translocation of NF-kappaB requires the activity of IKKalpha and/or IKKbeta. We conclude that although the Dot/Icm secretion system of L. pneumophila elicits an early robust activation of caspase-3 in human macrophages, it triggers a strong anti-apoptotic signalling cascade mediated, at least in part by NF-kappaB, which renders the cells refractory to external potent apoptotic stimuli.

Helicobacter pylori induces IkappaB kinase alpha nuclear translocation and chemokine production in gastric epithelial cells

NF-kappaB is an important transcriptional factor that is involved in multiple cellular responses, such as inflammation and antiapoptosis. IkappaB kinase alpha (IKKalpha) and IKKbeta, which are critical regulators of NF-kappaB activity, possess various mechanisms for NF-kappaB activation. This variability in NF-kappaB signaling may be associated with distinct inflammatory responses in specific cell types. The gastric pathogen Helicobacter pylori is known to activate NF-kappaB. However, the role of IKK in H. pylori infection remains unclear. In this report, we show that H. pylori activates both IKKalpha and IKKbeta in gastric cancer cells and enhances NF-kappaB signaling in distinct manners. We found that IKKbeta acted as an IkappaBalpha kinase during H. pylori infection, whereas IKKalpha did not. H. pylori induced IKKalpha nuclear translocation in time-, multiplicity of infection-, and cag pathogenicity island-dependent manners. In contrast, p100 processing, which is a known IKKalpha activity induced by several cytokines, was not induced by H. pylori. Both IKKs were responsible for chemokine secretion by infected cells. However, the antiapoptotic effect of H. pylori was merely transduced by IKKbeta. Microarray analysis and real-time PCR indicated that both IKKs were involved in the transcriptional activation of genes associated with inflammation, antiapoptosis, and signal transduction. Our results indicate that H. pylori activates NF-kappaB via both IKKalpha and IKKbeta using distinct mechanisms. IKKalpha nuclear translocation induced by H. pylori is indispensable for appropriate inflammatory responses but not for antiapoptosis, which suggests a critical role for IKKalpha in gastritis development.

p21-activated kinases in cancer

The pivotal role of kinases in signal transduction and cellular regulation has lent them considerable appeal as pharmacological targets across a broad spectrum of cancers. p21-activated kinases (Paks) are serine/threonine kinases that function as downstream nodes for various oncogenic signalling pathways. Paks are well-known regulators of cytoskeletal remodelling and cell motility, but have recently also been shown to promote cell proliferation, regulate apoptosis and accelerate mitotic abnormalities, which results in tumour formation and cell invasiveness. Alterations in Pak expression have been detected in human tumours, which makes them an attractive new therapeutic target.

MyD88 and TNF receptor-associated factor 6 are critical signal transducers in Helicobacter pylori-infected human epithelial cells

Helicobacter pylori induces NF-kappaB activation, leading to mucosal inflammation via cag pathogenicity island. Although recent studies have implicated several candidate proteins of both H. pylori and host, the molecular mechanism by which H. pylori activates NF-kappaB remains unclear. The aim of this study was to analyze the mechanism of cag pathogenicity island-mediated NF-kappaB activation in epithelial cells. The responses of human cell lines and mouse embryonic fibroblasts to infection with wild-type H. pylori or cagE mutant were investigated. The effect of small interfering RNAs (siRNAs) for several NF-kappaB signaling intermediate molecules was evaluated in H. pylori-induced IkappaBalpha phosphorylation and IL-8 production. Protein interactions of exogenously expressed TNFR-associated factor 6 (TRAF6) and MyD88 or receptor-interacting protein 2 and nucleotide-binding oligomerization domain 1 or those of endogenous IkappaB kinase, TGF-beta-activated kinase 1 (TAK1), and TRAF6 were assessed by immunoprecipitation. Cag pathogenicity island-dependent NF-kappaB activation was observed in human cell lines, but not in mouse fibroblasts. In human epithelial cells, H. pylori-induced IkappaBalpha phosphorylation and IL-8 production were severely inhibited by siRNAs directed against TAK1, TRAF6, and MyD88. In contrast, siRNAs for TRAF2, IL-1R-associated kinases 1 and 4, and cell surface receptor proteins did not affect these responses. H. pylori infection greatly enhanced MyD88 and TRAF6 complex formation in a cag-dependent manner, but did not enhance Nod1 and receptor-interacting protein 2 complex formation. H. pylori also induced TAK1 and TRAF6 complexes. These results suggest that the cag pathogenicity island of H. pylori is a cell type-specific NF-kappaB activator. TAK1, TRAF6, and MyD88 are important signal transducers in H. pylori-infected human epithelial cells.

The PAK1 autoregulatory domain is required for interaction with NIK in Helicobacter pylori-induced NF-kappaB activation

Helicobacter pylori, the etiological agent of various human gastric diseases, induces the transcription factor nuclear factor kappaB (NF-kappaB) and proinflammatory cytokines/chemokines. We have characterised the direct interaction between p21-activated kinase 1 (PAK1) and NF-kappaB-inducing kinase (NIK) in H. pylori-infected epithelial cells. The dimerisation (DI) motif, which is part of the NH2-terminal autoregulatory domain of PAK1, is critical for this interaction, whereas NIK forms complexes with PAK1 through its carboxy-terminal IkappaB kinase alpha (IKKalpha) binding site. Since the identified interaction sites are also crucial for the binding of activator (Rac/Cdc42 in the case of PAK1) or effector molecules (IKKalpha in the case of NIK), sequential stepwise signalling is suggested. Furthermore, we show that mitogen-activated protein kinase kinase kinases (MAP3K), like TPL2 (tumour progression locus 2) and transforming growth factor beta-activated kinase 1 (TAK1), have no impact on H. pylori-induced activation of NF-kappaB. These results identify the roles of PAK1 and NIK in a unique pathway involved in H. pylori-induced NF-kappaB activation, which is crucial for the induction of the innate immune response.