Mossman University of Vermont College of Medicine, University of Vermont CONTENTS 10.1 Preface ...197 10.2 Relevance of Cell Proliferation in Lung to Disease ...198 10.3 Importance of Un
Trang 110 Cell-Signaling Pathways Elicited
by Particulates
Jamie E Levis and Brooke T Mossman
University of Vermont College of Medicine, University of Vermont
CONTENTS
10.1 Preface 197
10.2 Relevance of Cell Proliferation in Lung to Disease 198
10.3 Importance of Understanding Cell-Signaling Pathways Leading to Inflammatory Alterations in Lung Disease 199
10.4 Signaling Pathways Activated by Particulates 200
10.4.1 Mitogen-Activated Protein Kinases, Fos/Jun Family Members, and Activator Protein-1 200
10.4.2 Nuclear Factor-kB 202
10.4.3 Other Signaling Pathways Induced by Particulates 204
10.5 Conclusions 204
References 204
10.1 PREFACE
Inhaled particles impinge upon epithelial cells of the respiratory tract after inhalation, facilitating an inflammatory response In addition to causing epithelial cell injury through mechanisms involving DNA damage, pathogenic particles such as silica or asbestos elicit toxic and proliferative responses
in lung cells through cell signaling pathways that can be triggered by direct interactions of fibers with the plasma membrane (Rom et al 1991; Adamson 1997; Mossman and Churg 1998) or indirectly via reactive oxygen species (ROS) (Shukla et al 2003a) At high concentrations of particles, exposures result in cell death and repair or compensatory proliferation of surrounding epithelial cells If this phenomenon occurs subsequent to DNA damage, a situation could arise whereby the replicating population, including initiated cells that have an increased propensity towards further genetic instability, could continue on the route towards malignancy, i.e., lung cancers The elucidation of the molecular mechanisms of cell injury and proliferation by inhaled particles is therefore critically important for understanding mechanisms of lung cancer and mesothelioma, a tumor unique to asbestos fibers, as well as pulmonary or pleural fibrosis In these diseases, proliferation of epithelial cells or mesothelial cells may play dual roles: (1) repair
of damaged epithelium, and (2) production of cytokines and chemokines that encourage inflam-mation and proliferation In this chapter, we focus on cell signaling pathways controlling these processes Although these cascades were first characterized in epithelial and mesothelial cells after exposure to asbestos or silica, several of these pathways have now been documented in various cell types after exposure to airborne particulate matter (PM), diesel exhaust, and/or ultrafine particles from a variety of sources Because cell-signaling pathways initiated by particulates are studied in an
197
Trang 2effort to understand how to control proliferative and inflammatory alterations intrinsic to particu-late-associated lung diseases, we first present the relevance of these processes to the pathogenesis of fibrogenic, carcinogenic, and inflammatory diseases such as asthma We then describe relevant signaling cascades impinging upon the activator protein-1 (AP-1) and nuclear factor-kB (NF-kB) transcription factors and what is known about their activation by various particulates Lastly, we provide a perspective on how these pathways can be verified in lung tissue after inhalation or instillation of particles for screening and therapy of particle-associated diseases
10.2 RELEVANCE OF CELL PROLIFERATION IN LUNG TO DISEASE
In asbestosis and idiopathic pulmonary fibrosis (IPF), the histological sequence leading to disease is believed to occur in the following fashion: an initial alveolitis, which may involve polymorpho-nuclear (PMN) leukocytes but is predominately monocytic, occurs before fibrotic changes become evident (Rom et al 1987; Spurzem et al 1987; Mossman and Gee 1989) Proliferation is noted in alveolar macrophages, fibroblasts, and epithelial cells of the bronchioles Importantly, there is evidence to suggest that smooth muscle cells, as well as endothelial cells of the arterioles near alveolar duct bifurcations, undergo proliferation in response to inhalation of chrysotile asbestos (McGavran et al 1990) This initial inflammatory response is followed by an accumulation of PMNs in the alveoli and lung interstitium, followed by an influx of interstitial macrophages and fibroblast proliferation, which leads to interstitial thickening and eventual irreversible architectural distortion, particularly in the terminal bronchioles and alveolar ducts (Brody et al 1981) Damage
to the basement membrane occurs, with loss of endothelial and type I alveolar epithelial cells and epithelial integrity, allowing access of growth factors, cytokines, and chemokines into the inter-stitium (Rom et al 1987; Chang et al 1988; Mossman and Marsh 1989) Type II epithelial cell hyperplasia develops along with interstitial fibrosis as typified by deposition of collagen and other extracellular matrix proteins Finally, fibrosis of the peribronchiolar and interstitial tissues develops and becomes the hallmark of advanced asbestosis (Becklake 1976; Craighead et al 1982; Rom et al
1987, 1991; Mossman and Churg 1998)
Injury to cells is often followed by compensatory cell proliferation Alveolar type II and bronchiolar epithelial cells in rat lungs undergo proliferation in response to high exposures to crocidolite and chrysotile asbestos (Be´ruBe´ et al 1996) It is known that proliferation of these cell types is a prominent repercussion of lung injury, such as that occurring in pulmonary fibrosis
well as immunodetection of proliferating cell nuclear antigen (PCNA), have shown that areas of developing fibrotic foci in lung in response to chrysotile asbestos are characterized by proliferation
of alveolar type II as well as bronchiolar epithelial cells (Dixon et al 1995; Quinlan et al 1995; Be´ruBe´ et al 1996; Robledo et al 2000) As noted above, the degree of injury in asbestos exposed animals is dose-dependant and followed by epithelial cell proliferation with a more intense and protracted inflammatory response, and eventually, fibrosis Observations suggest that the increases
in epithelial cell proliferation may be important in lung remodeling following injury, but if allowed
to proceed unchecked and unregulated, can culminate in fibrogenesis or carcinogenesis A logical conclusion stemming from these data would be that early responses of lung epithelial cells are instrumental to the development of fibrogenesis
Other data support this view For example, a study using bleomycin instillation into lung (a well characterized model of fibrosis in rodents) shows that early injury and repair of epithelial cells can govern whether fibrosis develops (Nomoto et al 1997) Interestingly, this work provides evidence that programmed cell death, i.e., apoptosis of epithelial cells, is sustained during fibrogenesis, and that glucocorticoids administered to rodents block the apoptotic response of these cells and the accompanying fibrogenesis A further study by this group has demonstrated that inhalation of an
Trang 3anti-Fas antibody (mimicking Fas/Fas-ligand interaction) induces apoptosis of epithelial cells and results in fibrogenesis (Kuwano et al 1999)
As cited above, the proliferative responses of epithelial cells to asbestos are well documented, but is there evidence that asbestos really causes apoptosis in epithelial cells in vivo? Recent studies have in fact demonstrated apoptotic effects of asbestos on epithelial cells in vitro (Aljandali et al 2001; Yuan et al 2004; Upadhyay et al 2005) and in vivo following intratracheal instillation of asbestos (Aljandali et al 2001), but apoptosis has not been reported after inhalation of asbestos Taken together, these data certainly suggest that functional responses of epithelial cells are crucial
in the development of fibrosis, carcinogenesis, and lung remodeling Epithelial cell injury is also a prominent feature of asthma, a disease often associated with the development of airway fibrosis (Comhair et al 2005)
When compared with normal subjects, asbestos-exposed individuals demonstrate increased numbers of macrophages undergoing mitosis (Takemura et al 1989), and the surfaces of alveolar macrophages from individuals with fibrosis show a striking increase in blebs, ruffling, and filopodia, presumably reflecting the enhanced phagocytic capability of these cells (Bitterman et al 1984)
In summary, understanding the cell signaling pathways controlling death and cell proliferation
of epithelial cells and macrophages is critical to modulation of these processes which may be important in both disease prevention and therapy
10.3 IMPORTANCE OF UNDERSTANDING CELL-SIGNALING PATHWAYS LEADING TO INFLAMMATORY ALTERATIONS IN LUNG DISEASE
The initial and protracted inflammatory response, which characterizes a number of models of pulmonary fibrosis, is believed to be important in asbestosis as well In a study using Fisher 344 rats, lower-dose exposure to crocidolite asbestos resulted in a transient inflammation in bronchoalveolar lavage fluid and reversible inflammatory foci in lung with a maintenance of normal lung architecture (Quinlan et al 1994) At higher concentrations of asbestos, neutrophil infiltration into lung and focal fibrotic lesions were noted, along with increased levels of the collagen marker, hydroxyproline Interestingly, we also noted that changes in levels of expression
of genes involved in antioxidant defense (manganese superoxide dismutase and copper–zinc super-oxide dismutase) as well as cell proliferation (ornithine decarboxylase and c-jun) correlated with histopathologic findings, inflammatory cell influx, and lung hydroxyproline levels The increase in c-jun levels in response to asbestos inhalation in this fibrosis model is particularly significant in light of the changes in the expression of this gene in response to asbestos and its association with altered cellular proliferation in carcinogenesis (Schutte et al 1989)
The development of asbestosis has been linked to oxidants which are either generated directly from asbestos fibers induced by cells contacting asbestos fibers or are associated with inflammation (Robledo and Mossman 1999) On high iron-containing particles or fibers, ROS generated by the Fenton reaction can produce reactive oxygen intermediates, which directly participate in cell damage at high concentrations or cell proliferation at low concentrations Generation of ROS during frustrated phagocytosis, i.e., an oxidative burst, can also initiate cell signaling and inflam-mation (Shukla et al 2003a) More recently, attention has been focused on the interaction of ROS and reactive nitrogen species (RNS) This interaction can result in the generation of peroxynitrite, which has been shown to nitrate macromolecules, including proteins in vitro, thereby critically altering their function (MacMillan-Crow et al 1998) Inhalation of asbestos induces RNS in rat lungs (Tanaka et al 1998), and tyrosine nitration resulting from asbestos inhalation is associated with increased activation of signaling pathways in rat lungs (Iwagaki et al 2003) It is conceivable that RNS, acting alone or with ROS, contribute to cell death and proliferation seen following asbestos exposure, thereby contributing to the development of fibrosis
Trang 4The inflammatory cascade, involving paracrine and autocrine events, is believed to be crucial in the pathology of asbestos-induced lung injury (Robledo and Mossman 1999) The protracted pulmonary inflammation noted in animal models of asbestosis can be correlated with the fibropro-liferative responses, and cytokines, a major class of inflammatory modulators, are implicated in clinical asbestosis and animal models of this disease (Mossman and Churg 1998) Tumor necrosis factor a (TNFa) and its interaction with cytokines and growth factors has been the most extensively studied factor in the pathogenesis of asbestosis (Mossman and Churg 1998; Robledo and Mossman 1999) For example, crocidolite and chrysotile asbestos cause increased production of TNFa in alveolar macrophages (Driscoll et al 1995b) Transgenic mice that overexpress TNFa in alveolar type II epithelial cells develop pulmonary fibrosis independent of pathogenic stimuli (Miyazaki
et al 1995) Conversely, mice that lack the TNF receptor produce TNF in response to a fibrogenic dose of chrysotile, but do not demonstrate markers for cellular proliferation nor develop fibrotic lesions (Liu et al 1998) Increased expression and production of TNF was noted in the lungs of inducible nitric oxide synthase (iNOS) knockout mice exposed to asbestos, and this increase was correlated with an increase in neutrophil influx into the alveolar space (Dorger et al 2002) Interes-tingly, this study provides evidence that iNOS-derived nitric oxide exerts a dual role in this model—it results in an exacerbated inflammatory response but attenuates oxidant-promoted tissue damage
An exhaustive elucidation of the inflammatory mediators downstream from TNFa in asbestos-induced fibrosis is beyond the scope of this review It should be noted, however, that TNFa is not directly chemotactic for neutrophils and macrophages (Robledo and Mossman 1999), thus work has focused on TNF-inducible chemotactic cytokines as effectors of asbestos induced lung damage, or fibrosis These include interleukins 1, 6, and 8 (IL-1, IL-6, and IL-8), and transforming growth factor a and b (TGFa and TGFb) These factors may be of particular importance in fibrogenesis, as they induce production of extracellular matrix proteins, induce epithelial cell proliferation, and are chemotactic for lung fibroblasts (Robledo and Mossman 1999) There is evidence to show that TGFb is produced in the lungs following exposure to asbestos, and that macrophages showing strong positive staining for this peptide are found at sites of developing fibrotic lesions (Perdue and Brody 1994) A recent study has shown that expression of TGFb-1 is noticeably absent in the lungs
of TNFa receptor mice, and, importantly, these mice do not develop fibrosis following asbestos exposure (Liu and Brody 2001) This finding supports the contention that TNFa is an integral part
of a pathway that is important in the fibrotic process resulting from asbestos exposure, and that it is exerting at least part of its effect through inducing the expression of downstream effectors and signaling pathways (see below)
10.4 SIGNALING PATHWAYS ACTIVATED BY PARTICULATES
10.4.1 MITOGEN-ACTIVATEDPROTEINKINASES, FOS/JUNFAMILYMEMBERS,ANDACTIVATOR
The mitogen-activated protein kinases (MAPK) cascades consist of a series of phosphorylated serine threonine kinases that are divided into three major pathways: extracellular signal-regulated kinases (ERKs), of which ERKs1 and 2 represent the major mammalian kinases of this group;
(SAPKs); and p38 kinases (Karin 1995; Shukla et al 2003b) MAPK cascades can be initiated
by receptor tyrosine kinases or factors stimulating phosphorylation of upstream MAPKKK or MAPKK Alternatively, factors inhibiting the phosphatases that normally check these pathways will also cause net increases in phosphorylation of these proteins
Specific MAPKs control the activation of fos and jun family proto-oncogene and their protein products that have been implicated in both apoptotic and proliferative responses to asbestos (Manning et al 2002) In mesothelial and pulmonary epithelial cells, asbestos preferentially
Trang 5activates the ERK1/2 pathway via an oxidant-dependant mechanism involving phosphorylation of the epidermal growth factor receptor (EGFR) (Figure 10.1) (Zanella et al 1996; Jimenez et al 1997) In rat pleural mesothelial (RPM) cells, addition of either chrysotile or crocidolite asbestos, in contrast to a number of other particles and synthetic fibers, induces phosphorylation and increased kinase activity of ERK1 and ERK2 Asbestos induced activation can be blocked by treating these cells with tyrphostin AG1478, a specific inhibitor of the tyrosine kinase activity of EGFR (Zanella
et al 1996) Treatment with this inhibitor prevents the induction of c-fos and apoptosis in these cell types (Zanella et al 1999), further strengthening the case for interaction of asbestos fibers with the EGFR (Pache et al 1998a) These finding are of particular relevance regarding the pathobiology of mesothelioma, as EGF is a growth factor required by human mesothelial cells (Gabrielson et al 1988) EGFR and ERK1/2 activation by asbestos have also been associated with initiating cell cycle alterations in a murine alveolar type II epithelial cell line (C10), suggesting that EGFR and ERK may play a role in aberrant proliferation in lung epithelial cells (Buder-Hoffmann et al 2001) ERK1 and 2 phosphorylation by crocidolite asbestos can also be inhibited by administration of catalase in RPM cells, suggesting that this is an oxidant-dependent process Moreover, integrins appear to be integral to stimulation of ERK1/2 by asbestos in mesothelial cells (Berken et al 2003) ERK5 is also induced in C10 alveolar epithelial cells by crocidolite asbestos fibers through an oxidant-dependent process that is not dependent on EGFR activation, unlike ERK1/2 (Scapoli et al 2004) Moreover, both ERK1/2 and ERK5 activation by asbestos involves Src activation, and activation of all three pathways are essential for initiation of cell proliferation An intriguing line of investigation regarding fiber length and activation of cellular pathways which can lead to cell proliferation, apoptosis, and cell survival has shown that EGFR activity in human mesothelial cells exposed to crocidolite is greatest in areas where the cell contacts the fiber, and that fibers longer than 60 mm are associated with increased EGFR immunoreactivity in contrast to shorter fibers (Pache et al 1998b) Shorter fibers are also less apt to cause frustrated phagocytosis, a process releasing large amounts of oxidants from cells due to a phagocytic burst, and these reactive species are known to alter EGFR activation (Goldkorn et al 2005)
28S
Cytosol
Asbestos fibers
EGFR P
Nucleus
P
Gene expression
Proliferation/survival Cell death
Tumor development Cytokines
Ras Raf1 MEK1/2 ERK1/2 ERK1/2
P P P P
Oxidants
Ras
ERK5 ERK5 MEK5
P P P
IKK
Particulate matter
O2.−
OH. NOX
TLR
p50/p65
Transcription factors
O 2 −
Src
FIGURE 10.1 A diagram illustrating the primary signaling pathways stimulated by particulates such as asbestos fibers and airborne particulate matter in lung epithelium and mesothelium All abbreviations and definitions are provided in the text
Trang 6It has been known for over a decade that asbestos fibers activate the early response protoonco-genes, c-fos and c-jun, in rodent mesothelial and tracheal epithelial cells in vitro (Heintz et al 1993; Janssen et al 1994) Activation is not seen with nonpathogenic synthetic fibers or particles, suggesting a link to the pathobiology of lung cancers and mesothelioma This viewpoint has been reinforced with observations that erionite, the most potent mesotheliomagenic fiber in man and rodents, causes potent and prolonged c-fos/c-jun activation in mesothelial cells (Janssen et al 1994) Moreover, ultrafine airborne particles (uPM) cause increases in c-jun, junB, fra-1, and fra-2
at proliferative concentrations in C10 epithelial cells whereas increased concentrations of uPM-causing apoptosis are associated with upregulation of genes involved in Fas-associated and TNFR-associated death pathways (Timblin et al 1998b)
Early response genes encode proteins that form AP-1, a redox sensitive transcription factor that activates a variety of genes that are involved in DNA synthesis AP-1 also has been shown to be of paramount importance in tumor promotion in skin carcinogenesis (Young et al 1999) The induction of these protooncogenes in response to asbestos is persistent in in vitro models (Heintz
et al 1993; Janssen et al 1994), and may be a chronic source of aberrant cell proliferation in asbestos exposed lung via activation of EGFR-mediated signaling (Timblin et al 1995) Although overexpression of c-jun has been shown to cause proliferative changes in tracheal epithelial cells (Reddy and Mossman 2002), the function of other AP-1 family members in carcinogenesis is unclear, and may in fact be cell type- and AP-1 partner type-specific (Reddy and Mossman 2002)
We have also shown that a signature of asbestos inhalation and coal dust instillation is increased expression of phosphorylated ERK1/2 using immunohistochemistry (IHC) (Robledo et al 2000; Albrecht et al 2002; Cummins et al 2002) This is most striking in distal bronchiolar epithelium and the alveolar duct region, sites of asbestos fiber and particle impaction after inhalation Phospho-ERK1/2 is translocated to the nucleus of C10 alveolar epithelial cells after addition of crocidolite asbestos in vitro, which eventually determines cell fate after exposure At low concentrations of asbestos fibers, there is initial nuclear accumulation of phospho-ERK1/2, which diminishes over time and results in expression of cyclin D1, an AP-1 regulated gene, and entry of cells into S phase
At higher concentrations of fibers, phospho-ERK1/2 accumulates in the nucleus where apoptosis-inducing factor (AIF) is detected and precedes apoptosis (Yuan et al 2004) These events correlate with nuclear accumulation of Fos (Burch et al 2004), whereas we have linked ERK1/2 dependent Fra-1 expression to proliferation and transformation of RPM cells (Ramos-Nino et al 2002, 2003) Most recently, we have linked asbestos-induced EGFR activation, fra-1 transactivation, expression of AP-1 family members, and AP-1 to DNA binding cells to intracellular levels of glutathione and y-glutamylcysteine synthetase levels, suggesting again a critical role of particle-induced oxidative stress (Shukla et al 2004) The recent observation that diesel exhaust, a known source of particles and other agents inducing oxidative stress, activates redox-sensitive transcrip-tion factors, and kinases in human airways (Pourazar et al 2005), confirms the relevance of these signaling pathways to human lung responses Using gene profiling, we have confirmed that expression of more than 38 signal transduction genes and oxidative-stress genes, including the AP-1 regulated gene, heme oxygenase, is altered in mouse lungs after inhalation of chrysotile asbestos over a 40-day period (Sabo-Attwood et al 2005)
10.4.2 NUCLEARFACTOR-kB
Of the many signaling cascades activated in airway epithelium in response to oxidant or particle stimulation, NF-kB has been implicated as one of the most important in both regulation of inflam-mation and cell survival NF-kB is a ubiquitous transcription factor that can be activated by cytokines, ROS, growth factors, bacteria and viruses, ultraviolet irradiation, airborne PM and inorganic minerals such as asbestos or silica (Janssen et al 1995, 1997; Ghosh et al 1998; Janssen-Heininger et al 2000; Shukla et al 2000; Ding et al 2002) NF-kB activity is tightly controlled by the inhibitory protein, IkBa, that is normally present in the cytosol complexed
Trang 7to NF-kB dimers, thereby preventing the nuclear localization of NF-kB and ensuring low basal
becomes phosphorylated at serines 32 and 36 by the activity of the IkB kinase (IKK) complex, then
is ubiquinated and degraded through the 26S proteasome pathway This exposes the nuclear locali-zation sequence of NF-kB, allowing its entry into the nucleus and thus facilitating DNA binding and the transcriptional up-regulation of NF-kB regulated genes The regulation of NF-kB and its degradation products are topics of contemporary interest, as many NF-kB inducible genes encode inflammatory chemokines and cytokines, adhesion molecules, growth factors, enzymes, and trans-cription factors (Sanceau et al 1995) For example, interleukin-6 (IL-6) (Harant et al 1996), interleukin-8 (IL-8) (Driscoll et al 1995a), and macrophage inflammatory protein-2 (MIP-2) (Poynter et al 1999), three putative mediators of inflammation and fibrogenesis in lung, have NF-kB binding sequences in their promoter regions which are critical to their transcriptional activation
We have shown previously that asbestos and silica fibers cause activation of the NF-kB signaling pathway in vitro (Hubbard et al 2002) and in lung epithelium after inhalation of crocidolite asbestos by rats (Hubbard et al 2001) In vivo, striking increases in nuclear translocation
of p65 (Rel A), the subunit causing transcriptional activation of NF-kB, occur in distal bronchiolar and alveolar epithelial cells after brief exposures to fibers (Hubbard et al 2001) Thus, the induction
of NF-kB in airway epithelium by asbestos or other particles may be a critical initial event promoting epithelial cell alterations, inflammation, and lung disease
regulated genes in lung homogenates, including TNFa (Shukla et al 2000) Transcriptional activation of NF-kB-dependent gene expression was also observed by PM in an alveolar epithelial NF-kB luciferase reporter cell line and was inhibited by catalase admini-stration.These findings support the concept that NF-kB is redox-sensitive transcription factor, like AP-1 (Janssen-Heininger et al 2000) A recent report establishes that Ottawa Urban Air
uptake by rat tracheal explants in vitro (Churg et al 2005) Both dusts and an iron-containing citrate extract from them caused phosphorylation of the EGFR and activated NF-kB through a pathway involving oxidative stress and Src activation These studies imply that extracellular stimulation of NF-kB by oxidants elaborated by particles occurs through the EGFR (see Figure 10.1) We have shown previously that NF-kB activation in C10 lung epithelial cells by asbestos fibers does not require EGFR phosphorylation by crocidolite asbestos fibers (Ramos-Nino et al 2002) However, frustrated phagocytosis involving stimulation of NADPH oxidases (NOX) and elaboration of intracellular oxidants occurs in response to iron-containing asbestos types, such as crocidolite, in these and other cell types (Shukla et al 2003a), and these processes might activate NF-kB Cell signaling and cytokine production by ambient and diesel sources of PM have been studied extensively in human alveolar macrophages (HAM) and human airway epithelial cells (NHBE)
in vitro (Becker et al 2005) These studies reveal that oxidant-induced stress plays a major role in production of cytokines by both coarse and fine particles in HAM, can be blocked by a toll like receptor 4 (TLR4) agonist involved in the recognition of LPS, and Gram negative bacteria-exposure
to PM decreases the expression of TLR4 associated with hyperesponsiveness to LPS, i.e., tolerance NHBE also recognize PM through TLR2, a receptor with preference for recognition of Gram-positive bacteria TLRs have been linked to LPS-stimulation of the NF-kB signaling pathways, and
it is highly likely that they modulate PM-induced NF-kB signaling responses and cytokine production
NF-kB activation is also induced by silica in various cell types (Ding et al 2002), and unlike asbestos, PM and silica induce JNK activation by lung epithelial cells in vitro (Timblin et al 1998a; Shukla et al 2001) Although JNK activation is classically associated with cell death (Yanase et al 2005), crosstalk mediated between the JNK signaling pathway and NF-kB, a transcription factor
Trang 8promoting survival as opposed to cell death (Wang et al 2005), may dictate eventual proliferative
or apoptotic responses to particulates For example, inhibition of JNK activation may occur through NF-kB target genes, GADD45b, and c-IAP (an inhibitor of apoptosis protein) (Tang et al 2001)
10.4.3 OTHERSIGNALINGPATHWAYSINDUCED BYPARTICULATES
Other signaling pathways that impact upon the MAPK/AP-1 and or NF-kB pathways have been shown to be activated by asbestos in a variety of cell types (Shukla et al 2003b) These include members of the Protein Kinase C family (Lounsbury et al 2002; Shukla et al 2003c), nuclear factor
of activated T cells (NFAT) (Li et al 2002), calcium-dependent pathways leading to activation of the CREB transcription factor (Barlow et al 2006), and the phosphatidylinositol-3 kinase (PI3-K)/ AKT pathway leading to mTOR activation (Swain et al submitted) The interplay between these pathways will likely prove critical in determining phenotypic and inflammatory outcomes of particulate exposures in epithelial and other lung cell types
10.5 CONCLUSIONS
In vitro studies have shed light on mechanisms of cell signaling by pathogenic particulates, including asbestos fibers, silica particles and most recently, airborne PM from a variety of sources While initial work has shown that redox-associated transcription factors are activated
by these particulates in several cell types, the significance of these pathways in terms of lung responses and remodeling remains to be determined in vivo The fact that many of these pathways can be demonstrated in rodent and human lungs in vivo using cell imaging after inhalation of particulates (Poynter et al 1999; Taatjes and Mossman 2005) is encouraging and validates
in vitro investigations Moreover, microarray analysis and in situ hybridization studies now allow profiling and localization of genes regulated by AP-1 and NF-kB transcription factors in rodent and human cells of the lung (Sabo-Attwood et al 2005) Transgenic targeting of genes and proteins modulating cell signaling using lung epithelial and other cell-specific promoters are exciting developments that will verify the functional ramifications of signaling pathways in animal models of particulate-induced lung diseases
REFERENCES
Adamson, I Y., Early mesothelial cell proliferation after asbestos exposure: in vivo and in vitro studies, Environ Health Perspect., 105 (suppl 5), 1205–1208, 1997
Albrecht, C., Borm, P J., Adolf, B., Timblin, C R., and Mossman, B T., In vitro and in vivo activation of extracellular signal-regulated kinases by coal dusts and quartz silica, Toxicol Appl Pharmacol., 184, 37–45, 2002
Aljandali, A., Pollack, H., Yeldandi, A., Li, Y., Weitzman, S A., and Kamp, D W., Asbestos causes apoptosis
in alveolar epithelial cells: role of iron-induced free radicals, J Lab Clin Med., 137, 330–339, 2001 Barlow, C A., Shukla, A., Mossman, B T., and Lounsbury, K M., Oxidant-mediated cAMP response element binding protein activation: calcium regulation and role in apoptosis of lung epithelial cells, Am
J Respir Cell Mol Biol., 34, 7–14, 2006
Becker, S., Mundandhara, S., Devlin, R B., and Madden, M., Regulation of cytokine production in human alveolar macrophages and airway epithelial cells in response to ambient air pollution particles: further mechanistic studies, Toxicol Appl Pharmacol., 207, 269–275, 2005
Becklake, M R., Asbestos-related diseases of the lung and other organs: their epidemiology and implications for clinical practice, Am Rev Respir Dis., 114, 187–227, 1976
Berken, A., Abel, J., and Unfried, K., beta1-integrin mediates asbestos-induced phosphorylation of AKT and ERK1/2 in a rat pleural mesothelial cell line, Oncogene, 22, 8524–8528, 2003
Trang 9Be´ruBe´, K A., Quinlan, T R., Moulton, G., Hemenway, D., O’Shaughnessy, P., Vacek, P., and Mossman, B T., Comparative proliferative and histopathologic changes in rat lungs after inhalation
of chrysotile or crocidolite asbestos, Toxicol Appl Pharmacol., 137, 67–74, 1996
Bitterman, P B., Saltzman, L E., Adelberg, S., Ferrans, V J., and Crystal, R G., Alveolar macrophage replication one mechanism for the expansion of the mononuclear phagocyte population in the chroni-cally inflamed lung, J Clin Invest., 74, 460–469, 1984
Brody, A R., Hill, L H., Adkins, B., Jr., and O’Connor, R W., Chrysotile asbestos inhalation in rats: deposition pattern and reaction of alveolar epithelium and pulmonary macrophages, Am Rev Respir Dis., 123, 670–679, 1981
Buder-Hoffmann, S., Palmer, C., Vacek, P., Taatjes, D., and Mossman, B., Different accumulation of activated extracellular signal-regulated kinases (ERK 1/2) and role in cell-cycle alterations by epidermal growth factor, hydrogen peroxide, or asbestos in pulmonary epithelial cells, Am J Respir Cell Mol Biol., 24, 405–413, 2001
Burch, P M., Yuan, Z., Loonen, A., and Heintz, N H., An extracellular signal-regulated kinase 1- and 2-dependent program of chromatin trafficking of c-Fos and Fra-1 is required for cyclin D1 expression during cell cycle reentry, Mol Cell Biol., 24, 4696–4709, 2004
Chang, L Y., Overby, L H., Brody, A R., and Crapo, J D., Progressive lung cell reactions and extracellular matrix production after a brief exposure to asbestos, Am J Pathol., 131, 156–170, 1988
Churg, A., Xie, C., Wang, X., Vincent, R., and Wang, R D., Air pollution particles activate NF-kB on contact with airway epithelial cell surfaces, Toxicol Appl Pharmacol., 208, 37–45, 2005
Comhair, S A., Xu, W., Ghosh, S., Thunnissen, F B., Almasan, A., Calhoun, W J., Janocha, A J., Zheng, L., Hazen, S L., and Erzurum, S C., Superoxide dismutase inactivation in pathophysiology of asthmatic airway remodeling and reactivity, Am J Pathol., 166, 663–674, 2005
Craighead, J E., Abraham, J L., Churg, A., Green, F H., Kleinerman, J., Pratt, P C., Seemayer, T A., Vallyathan, V., and Weill, H., The pathology of asbestos-associated diseases of the lungs and pleural cavities: diagnostic criteria and proposed grading schema Report of the Pneumoconiosis Committee
of the College of American Pathologists and the National Institute for Occupational Safety and Health, Arch Pathol Lab Med., 106, 544–596, 1982
Crouch, E., Pathobiology of pulmonary fibrosis, Am J Physiol., 259, L159–L184, 1990
Cummins, M M., O’Mullane, L M., Barden, J A., Cook, D I., and Poronnik, P., Antisense co-suppression of G(alpha)(q) and G(alpha)(11) demonstrates that both isoforms mediate M(3)-receptor-activated Ca(2C) signaling in intact epithelial cells, Pflugers Arch., 444, 644–653, 2002
Ding, M., Chen, F., Shi, X., Yucesoy, B., Mossman, B., and Vallyathan, V., Diseases caused by silica: mechanisms of injury and disease development, Int Immunopharmacol., 2, 173–182, 2002 Dixon, D., Bowser, A D., Badgett, A., Haseman, J K., and Brody, A R., Incorporation of bromode-oxyuridine (BrdU) in the bronchiolar-alveolar regions of the lungs following two inhalation exposures to chrysotile asbestos in strain A/J mice, J Environ Pathol Toxicol Oncol., 14, 205–213, 1995
Dorger, M., Allmeling, A M., Kiefmann, R., Munzing, S., Messmer, K., and Krombach, F., Early inflam-matory response to asbestos exposure in rat and hamster lungs: role of inducible nitric oxide synthase, Toxicol Appl Pharmacol., 181, 93–105, 2002
Driscoll, K E., Hassenbein, D G., Howard, B W., Isfort, R J., Cody, D., Tindal, M H., Suchanek, M., and Carter, J M., Cloning, expression, and functional characterization of rat MIP-2: a neutrophil chemoat-tractant and epithelial cell mitogen, J Leukoc Biol., 58, 359–364, 1995
Driscoll, K E., Maurer, J K., Higgins, J., and Poynter, J., Alveolar macrophage cytokine and growth factor production in a rat model of crocidolite-induced pulmonary inflammation and fibrosis, J Toxicol Environ Health, 46, 155–169, 1995
Gabrielson, E W., Gerwin, B I., Harris, C C., Roberts, A B., Sporn, M B., and Lechner, J F., Stimulation of DNA synthesis in cultured primary human mesothelial cells by specific growth factors, Faseb J., 2, 2717–2721, 1988
Ghosh, S., May, M J., and Kopp, E B., NF-kB and Rel proteins: evolutionarily conserved mediators of immune responses, Annu Rev Immunol., 16, 225–260, 1998
Goldkorn, T., Ravid, T., and Khan, E M., Life and death decisions: ceramide generation and EGF receptor trafficking are modulated by oxidative stress, Antioxid Redox Signal., 7, 119–128, 2005
Trang 10Harant, H., de Martin, R., Andrew, P J., Foglar, E., Dittrich, C., and Lindley, I J., Synergistic activation of interleukin-8 gene transcription by all-trans-retinoic acid and tumor necrosis factor-alpha involves the transcription factor NF-kappa B, J Biol Chem., 271, 26954–26961, 1996
Heintz, N H., Janssen, Y M., and Mossman, B T., Persistent induction of c-fos and c-jun expression by asbestos, Proc Natl Acad Sci U S A, 90, 3299–3303, 1993
Hubbard, A K., Timblin, C R., Rincon, M., and Mossman, B T., Use of transgenic luciferase reporter mice to determine activation of transcription factors and gene expression by fibrogenic particles, Chest, 120, 24S–25S, 2001
Hubbard, A K., Timblin, C R., Shukla, A., Rincon, M., and Mossman, B T., Activation of NF-kappa B-dependent gene expression by silica in lungs of luciferase reporter mice, Am J Physiol Lung Cell Mol Physiol., 282, L968–L975, 2002
Iwagaki, A., Choe, N., Li, Y., Hemenway, D R., and Kagan, E., Asbestos inhalation induces tyrosine nitration associated with extracellular signal-regulated kinase 1/2 activation in the rat lung, Am J Respir Cell Mol Biol., 28, 51–60, 2003
Janssen, Y M., Heintz, N H., Marsh, J P., Borm, P J., and Mossman, B T., Induction of c-fos and c-jun proto-oncogenes in target cells of the lung and pleura by carcinogenic fibers, Am J Respir Cell Mol Biol.,
11, 522–530, 1994
Janssen, Y M., Barchowsky, A., Treadwell, M., Driscoll, K E., and Mossman, B T., Asbestos induces nuclear factor kB (NF-kB) DNA-binding activity and NF-kB-dependent gene expression in tracheal epithelial cells, Proc Natl Acad Sci U S A, 92, 8458–8462, 1995
Janssen, Y M., Driscoll, K E., Howard, B., Quinlan, T R., Treadwell, M., Barchowsky, A., and Mossman, B T., Asbestos causes translocation of p65 protein and increases NF-kB DNA binding activity in rat lung epithelial and pleural mesothelial cells, Am J Pathol., 151, 389–401, 1997 Janssen-Heininger, Y M., Poynter, M E., and Baeuerle, P A., Recent advances towards understanding redox mechanisms in the activation of nuclear factor kappaB, Free Radic Biol Med., 28, 1317–1327, 2000 Jimenez, L A., Zanella, C., Fung, H., Janssen, Y M., Vacek, P., Charland, C., Goldberg, J., and Mossman, B T., Role of extracellular signal-regulated protein kinases in apoptosis by asbestos and H2O2, Am J Physiol., 273, L1029–L1035, 1997
Karin, M., The regulation of AP-1 activity by mitogen-activated protein kinases, J Biol Chem., 270, 16483–16486, 1995
Kuwano, K., Hagimoto, N., Kawasaki, M., Yatomi, T., Nakamura, N., Nagata, S., Suda, T et al., Essential roles of the Fas–Fas ligand pathway in the development of pulmonary fibrosis, J Clin Invest., 104, 13–19, 1999
Li, J., Huang, B., Shi, X., Castranova, V., Vallyathan, V., and Huang, C., Involvement of hydrogen peroxide in asbestos-induced NFAT activation, Mol Cell Biochem., 234–235, 161–168, 2002
Liu, J Y and Brody, A R., Increased TGF-beta1 in the lungs of asbestos-exposed rats and mice: reduced expression in TNF-alpha receptor knockout mice, J Environ Pathol Toxicol Oncol., 20, 97–108, 2001 Liu, J Y., Brass, D M., Hoyle, G W., and Brody, A R., TNF-alpha receptor knockout mice are protected from the fibroproliferative effects of inhaled asbestos fibers, Am J Pathol., 153, 1839–1847, 1998 Lounsbury, K M., Stern, M., Taatjes, D., Jaken, S., and Mossman, B T., Increased localization and substrate activation of protein kinase C delta in lung epithelial cells following exposure to asbestos, Am
J Pathol., 160, 1991–2000, 2002
MacMillan-Crow, L A., Crow, J P., and Thompson, J A., Peroxynitrite-mediated inactivation of manganese superoxide dismutase involves nitration and oxidation of critical tyrosine residues, Biochemistry, 37, 1613–1622, 1998
Manning, C B., Cummins, A B., Jung, M W., Berlanger, I., Timblin, C R., Palmer, C., Taatjes, D J., Hemenway, D., Vacek, P., and Mossman, B T., A mutant epidermal growth factor receptor targeted to lung epithelium inhibits asbestos-induced proliferation and proto-oncogene expression, Cancer Res.,
62, 4169–4175, 2002
McGavran, P D., Moore, L B., and Brody, A R., Inhalation of chrysotile asbestos induces rapid cellular proliferation in small pulmonary vessels of mice and rats, Am J Pathol., 136, 695–705, 1990 Miyazaki, Y., Araki, K., Vesin, C., Garcia, I., Kapanci, Y., Whitsett, J A., Piguet, P F., and Vassalli, P., Expression of a tumor necrosis factor-alpha transgene in murine lung causes lymphocytic and fibrosing alveolitis A mouse model of progressive pulmonary fibrosis, J Clin Invest., 96, 250–259, 1995