Phosphoinositide 3-kinase activity leads to silica-induced NF-kappaB activation through interacting with tyrosine-phosphorylated I(kappa)B-alpha and contributing to tyrosine phosphorylation of p65 NF-kappaB

Evaluation of the association of chronic inflammation and cancer: Insights and implications

Among the most extensively researched processes in the development and treatment of cancer is inflammatory condition. Although acute inflammation is essential for the wound healing and reconstruction of tissues that have been damaged, chronic inflammation may contribute to the onset and growth of a number of diseases, including cancer. By disrupting the signaling processes of cells, which result in cancer induction, invasion, and development, a variety of inflammatory molecules are linked to the development of cancer. The microenvironment surrounding the tumor is greatly influenced by inflammatory cells and their subsequent secretions, which also contribute significantly to the tumor's growth, survivability, and potential migration. These inflammatory variables have been mentioned in several publications as prospective diagnostic tools for anticipating the onset of cancer. Targeting inflammation with various therapies can reduce the inflammatory response and potentially limit or block the proliferation of cancer cells. The scientific medical literature from the past three decades has been studied to determine how inflammatory chemicals and cell signaling pathways related to cancer invasion and metastasis are related. The current narrative review updates the relevant literature while highlighting the specifics of inflammatory signaling pathways in cancer and their possible therapeutic possibilities.

Bioreactivity of the crystalline silica polymorphs, quartz and cristobalite, and implications for occupational exposure limits (OELs)

Silica or silicon dioxides (SiO₂) are naturally occurring substances that comprise the vast majority of the earth's crust. Because of their prevalence and commercial applications, they have been widely studied for their potential to induce pulmonary fibrosis and other disorders. Historically, the focus in the workplace has been on the development of inflammation and fibrotic lung disease, the basis for promulgating workplace standards to protect workers. Crystalline silica (CS) polymorphs, predominantly quartz and cristobalite, are used in industry but are different in their mineralogy, chemistry, surface features, size dimensions and association with other elements naturally and during industrial applications. Epidemiologic, clinical and experimental studies in the literature historically have predominantly focused on quartz polymorphs. Thus, in this review, we summarize past scientific evaluations and recent peer-reviewed literature with an emphasis on cristobalite, in an attempt to determine whether quartz and cristobalite polymorphs differ in their health effects, toxicity and other properties that may dictate the need for various standards of protection in the workplace. In addition to current epidemiological and clinical reports, we review in vivo studies in rodents as well as cell culture studies that shed light on mechanisms intrinsic to the toxicity, altered cell responses and protective or defense mechanisms in response to these minerals. The medical and scientific literature indicates that the mechanisms of injury and potential causation of inflammation and fibrotic lung disease are similar for quartz and cristobalite. Our analysis of these data suggests similar occupational exposure limits (OELs) for these minerals in the workplace.

Silica induces cell cycle changes through PI-3K/AP-1 pathway in human embryo lung fibroblast cells

Exposure to silica is associated with progressive pulmonary inflammation and fibrosis. Our previous study had demonstrated silica exposure could cause cell cycle alternation and activator protein-1 (AP-1) activation. This study showed that silica exposure induced phosphorylation of p70S6 kinase (p70S6K) and Akt in human embryo lung fibroblasts (HELFs). These changes were blocked by overexpression of dominant-negative mutants of phosphatidylinositol-3 kinase (Δp85) or Akt (DN-Akt), respectively. Moreover, pretreatment of cells with rapamycin, a specific p70S6K inhibitor, could inhibit silica-induced cell cycle alteration, AP-1 activation, and phosphorylation of p70S6K, but had no effect on Akt phosphorylation. This suggested that phosphatidylinositol-3 kinase (PI-3K)/AP-1 pathway was likely responsible for cell cycle changes. Furthermore, we observed the effect of the pathway on cell cycle regulatory proteins. Our results indicated that inactivation of PI-3K, Akt, or p70S6K could inhibit silica-induced overexpression of cyclin D1 and cyclin-dependent kinase 4 (CDK4) and decreased expression of E2F-4. Taken together, silica could induce cell cycle changes through PI-3K/ AP-1 pathway in HELFs.

Correlation of NF-kappaB signal pathway with tumor metastasis of human head and neck squamous cell carcinoma

Background

Nuclear factor-kappa B (NF-κB) signaling constitutes a key event in the multistep process of carcinogenesis, progression and treatment in many cancer types. However, the significance of NF-κB pathway for complex and tissue-specific aspects of head and neck cancer progression, such as invasion and metastasis, is less understood.

Methods

The expression of NF-κB p65 in squamous cell carcinoma of the head and neck (SCCHN) clinical specimens by immunohistochemistry. The role of NF-κB activity in head and neck squamous cell carcinoma was determined by western blot, reporter assay and EMSA analysis in vitro and metastasis assays in vivo in different metastatic potential tumor cells. Furthermore, the apoptosis rate and expression of metastasis-related protein such as MMP9 and VEGF were examined by Annexin V/PI staining and Western blot, respectively.

Results

A higher level of active nuclear-localized NF-κB was observed in the metastatic SCCHN specimens group (p < 0.01). The NF-κB activities of SCCHN cell lines with different metastatic potentials were then determined and in excellent agreement with results found in SCCHN specimens, highly metastatic SCCHN cell lines expressed high level of NF-κB activity. The treatment of highly metastatic SCCHN cells with NF-κB inhibitors reduced the in vitro cell invasion capacity of the cells without affecting the apoptotic rate. Additionally, the NF-κB inhibitors significantly inhibited the experimental lung metastasis of Tb cells and lymph node metastasis of TL cells in nude mice. Furthermore, the expression of metastasis-related proteins, such as matrix metalloproteinase 9 and vascular endothelial growth factor, was inhibited by pyrrolidine dithiocarbonate.

Conclusions

This study suggests that NF-κB activity significantly contributes to tumor hematologic and lymphatic metastases and may aid in the development of early detection methods or therapies targeting non-conventional molecular targets.

Targeting the NF-kappa B pathway in estrogen receptor negative MDA-MB-231 breast cancer cells using small inhibitory RNAs

Cancer cells in order to survive are often mutated to block apoptosis. One chemotherapeutic option is the re-establishment of apoptosis. An example of such a therapy is the PKC inhibitor Gö6976, which activates apoptosis and shrinks in vivo tumors in estrogen receptor-negative breast cancers. We proposed as a mechanism blockage of activation of the transcription factor NF-kappaB, which is anti-apoptotic and often elevated in cancers. Over recent years, questions have arisen regarding the specificity of these "small-molecule inhibitors." We have therefore explored the role of NF-kappaB inhibition in MDA-MB-231 breast cancer cells using small inhibitory RNAs (siRNA). siRNAs designed against NF-kappaB protein p65 (RelA) and IKKalpha, IKKbeta, and IKKgamma, strongly decreased the target proteins. But, unlike Gö6976, they did not decrease basal NF-kappaB or cause apoptosis. In particular, the decrease in p65 protein had no effects on apoptosis or cell proliferation, thus questioning the importance of NF-kappaB alone in the maintenance of these cells. Furthermore, the proteasome inhibitor MG-132 caused loss of IkappaBalpha, and an increase of it is phosphorylated form, but basal NF-kappaB was unchanged, whilst activation of NF-kappaB by TNFalpha was completely inhibited, suggesting that MG-132 activity is independent of constitutive NF-kappaB activation. We ascribe these differences to the specificity of inhibition by siRNAs as compared to the well-known non-specificity of small-molecule inhibitors. We conclude that the mutations in these cancer cells made them resistant to apoptosis, by elevating their NF-kappaB and activating other basal pathways that are blocked by Gö6976 but not by IKK and p65 siRNAs.

Post-translational modifications regulating the activity and function of the nuclear factor kappa B pathway

The diverse cellular and biological functions of the nuclear factor kappa B (NF-kappaB) pathway, together with the catastrophic consequences of its aberrant regulation, demand specific and highly regulated control of its activity. As described in this review, regulation of the NF-kappaB pathway is brought about through multiple post-translational modifications that control the activity of the core components of NF-kappaB signaling: the IkappaB kinase (IKK) complex, the IkappaB proteins and the NF-kappaB subunits themselves. These regulatory modifications, which include phosphorylation, ubiquitination, acetylation, sumoylation and nitrosylation, can vary, depending on the nature of the NF-kappaB-inducing stimulus. Moreover, they frequently have distinct, sometimes antagonistic, functional consequences and the same modification can have different effects depending on the context. Given the important role of NF-kappaB in human health and disease, understanding these pathways will not only provide valuable insights into mechanism and function, but could also lead to new drug targets and the development of diagnostic and prognostic biomarkers for many pathological conditions.

p38 mitogen-activated protein kinase up-regulates LPS-induced NF-κB activation in the development of lung injury and RAW 264.7 macrophages

Clarification of the key regulatory steps that lead to nuclear factor-kappa B (NF-kappaB) under cellular and pathological conditions is very important. The action of p38 mitogen-activated protein kinase (MAPK) on the upstream of NF-kappaB activation remains controversial. To examine this issue using an in vivo lung injury model, SB203580, a p38 MAPK inhibitor was given intraorally 1h prior to lipopolysaccharide (LPS) treatment (intratracheally). The mice were sacrificed 4 h after LPS treatment. SB203580 substantially suppressed LPS-induced rises in p38 MAPK phosphorylation, neutrophil recruitment, total protein content in bronchoalveolar lavage fluid, and apoptosis of bronchoalveolar cells. Furthermore, SB203580 blocked LPS-induced NF-kappaB activation in lung tissue through down-regulation of serine phosphorylation, degradation of IkappaB-alpha, and consequent translocation of the p65 subunit of NF-kappaB to the nucleus. It is likely that, in cultured RAW 264.7 macrophages, SB203580 also blocked LPS-induced NF-kappaB activation in a dose-dependent manner. SB203580 inhibited LPS-induced serine phosphorylation, degradation of IkappaB-alpha, and tyrosine phosphorylation of p65 NF-kappaB. These data indicate that p38 MAPK acts upstream of LPS-induced NF-kappaB activation by modulating the phosphorylation of IkappaB-alpha and p65 NF-kappaB during acute lung injury. Because LPS-stimulated macrophages may contribute to inflammatory lung injury, the inhibition of the p38 MAPK-mediated intracellular signaling pathway leading to NF-kappaB activation represents a target for the attenuation of lung inflammation and parenchymal damage.

TRAF6 activation of PI 3-kinase-dependent cytoskeletal changes is cooperative with Ras and is mediated by an interaction with cytoplasmic Src

Interleukin 1 (IL-1) has been implicated in the reorganization of the actin cytoskeleton. An expression vector encoding a PKB/Akt pleckstrin-homology domain fused to a fluorescent protein was used to detect phosphoinositide 3-kinase (PI 3-kinase) products. It was observed that PI 3-kinase was activated either by treatment with IL-1 or by expression of either TRAF6, Src, MyD88 or dominant-positive PI 3-kinase, and resulted in the formation of long filopodia-like cellular protrusions that appeared to branch at membrane sites consisting of clusters of phosphoinositide. This depended upon a TRAF6 polyproline motif and Src catalytic activity, and was blocked by inhibitors of PI 3-kinase, Src and Ras. Using both conventional and split fluorescent protein probes fused to expressed TRAF6 and Src in living cells, the polyproline sequence of TRAF6 and the Src-homology 3 (SH3) domain of Src were shown to be required for interaction between these two proteins. Interaction occurred within the cytoplasm, and not at either the cell membrane or cytoplasmic sequestosomes. In addition, co-transfection of vectors expressing fluorescent-protein-fused TRAF6 and non-fluorescent MyD88, IRAK1 and IRAK2 revealed an inverse correlation between increased sequestosome formation and activation of both PI 3-kinase and NF-kappaB. Although a key factor in TRAF6-dependent activation of PI 3-kinase, ectopic expression of Src was insufficient for NF-kappaB activation and, in contrast to NF-kappaB, was not inhibited by IRAK2.

Src Tyrosine Kinases Mediate Crystalline Silica-Induced NF-κB Activation through Tyrosine Phosphorylation of IκB-α and p65 NF-κB in RAW 264.7 Macrophages

Protein tyrosine kinases (PTKs) and mitogen-activated protein kinases (MAPKs) have been demonstrated to play a crucial role in the signaling pathways induced by silica. In the present study, we investigated whether Src family TKs play a role in crystalline silica-induced NF-kappaB activation and whether NF-kappaB activation requires Src TK-dependent MAPK activity in RAW 264.7 cells, a mouse peritoneal macrophage cell line. Selective Src TK inhibitors, damnacanthal or PP1, inhibited silica-induced NF-kappaB activation in a dose-dependent manner. Furthermore, these kinase inhibitors suppressed silica-induced tyrosine phosphorylation of IkappaB-alpha and p65 NF-kappaB. Within a similar time frame, c-Src and Lck were physically associated with IkappaB-alpha and with p65 NF-kappaB. Silica stimulated the phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2), but not p38 MAPK and c-Jun NH(2)-terminal kinase 1 and 2 (JNK1/2). Damnacanthal or PP1 substantially blocked the silica-induced activation of ERK1/2. Moreover, PD98059, an inhibitor of ERK1/2, or SB203580, an inhibitor of p38 MAPK, failed to inhibit silica-induced NF-kappaB activation. These results suggest that c-Src and Lck act for silica-induced NF-kappaB activation by mediating the tyrosine phosphorylations of IkappaB-alpha and p65 NF-kappaB. However, the Src TK-dependent activation of ERK1/2 may not be involved in the silica signaling pathway leading to NF-kappaB activation.

Respiratory burst: role in signal transduction in alveolar macrophages

Alveolar macrophages play an important role in defense against airborne pathogens and particles. These macrophages respond through both the adaptive and acquired immune responses, and through the activation of a multitude of signaling pathways. One major macrophage defense mechanism is respiratory burst, the production of reactive oxygen species (ROS). While the ROS produced may act directly in pathogen killing, they may also be involved as secondary signaling messengers. This review focuses on the activation of four main signaling pathways following the production of reactive oxygen species. These pathways include the nuclear factor kappa beta (NFkB), activating protein-1 (AP-1), mitogen-activating protein kinase (MAPK), and phosphotidyl inositol-3 kinase (PI3K) pathways. This review also briefly examines the role of ROS in DNA damage, in particular looking at the base excision repair pathway (BER), the main pathway involved in repair of oxidative DNA damage. This review highlights many of the studies in the field of ROS, signal transduction, and DNA damage; however, work still remains to further elucidate the role of ROS in disease.

Blocking anti-apoptosis as a strategy for cancer chemotherapy: NF-kappaB as a target

Critical processes underlying cancers must be better understood to develop strategies for treatment and prevention. A chemotherapeutic strategy is proposed that is based upon re-establishment, with a drug, of nullified programmed cell death (apoptosis) in cancer cells, which to survive have mutated to block apoptosis. A chemotherapy that is specific against tumors implanted in mice demonstrated the feasibility of this principle. This therapy is specific because it affects a process unique to cancer cells. It also has the advantage of killing these cells, in contrast to reversibly blocking their proliferation. The anti-apoptotic transcription factor NF-kappaB provides a potential therapeutic target in estrogen receptor negative (ER-) breast cancers that over-express the epidermal growth factor family of receptors (EGFR). Further investigations of the pathways utilize dominant negative protein inhibitory peptide, and small inhibitory RNAs (siRNAs) to block the production of relevant enzymes.

Signaling pathways controlling the production of inflammatory mediators in response to crystalline silica exposure: role of reactive oxygen/nitrogen species

Occupational exposure to crystalline silica has been linked to pulmonary fibrosis and lung cancer. Surface properties of crystalline silica are critical to the production of oxidant species, chemokines, inflammatory cytokines, and proliferative factors involved in the initiation and progression of silica-induced damage, inflammation, alveolar type II cell hyperplasia, fibroblast activation, and disease. The transcription factors nuclear factor kappaB (NF-kappaB) and activator protein 1 (AP-1) have been shown to play key roles in gene promotion for inflammatory mediators, oncogenes, and growth factors. This review summarizes evidence that in vitro and in vivo exposure to crystalline silica results in activation of NF-kappaB and AP-1. Signaling pathways for activation of these transcription factors are described. In addition, the role of silica-induced reactive oxygen species and nitric oxide in the activation of these signaling events is presented. Last, the generalizability of mechanisms regulating silica-induced pulmonary responses to pulmonary reactions to other occupational particles is discussed.