Activation of extracellular signal-regulated kinase in lung tissues of mice treated with carcinogen

Regulatory role of heme oxygenase-1 in silica-induced lung injury

Background

Silicosis, a progressive inflammatory lung disease attributed mainly to occupational exposure to silica dust, shows loss of lung function even after cessation of exposure. In addition to conventional evaluation methods such as chest X-ray, computed tomography, and spirometry, we identified heme oxygenase (HO)-1, an inducible antioxidant, as a potential biomarker to identify at-risk patients. We found that HO-1 was critical in attenuating the disease progression of silicosis; however, the key signaling pathway has not yet been elucidated. Here, we report the critical pathway after silica exposure, focusing on the role of silica-derived reactive oxygen species (ROS) signaling and its attenuation, which is mediated by HO-1 induction, in vivo and in vitro.

Methods

Normal bronchial epithelial cells and a macrophage cell line, as well as a murine silicosis model generated by intratracheal administration of 2.5 mg of crystalline silica, were used in this study. The pathways activated in response to silica exposure, including the mitogen-activated protein kinase (MAPK) signaling pathway, were examined and compared with or without super-induction of HO-1.

Results

The murine silicosis model was first assessed for the evaluation of activated pathways after silica exposure, focusing on ROS-MAPK activation. In the murine model, increased expression of HO-1 in the lungs was observed after silica-instillation. Moreover, silica-medicated activation of extracellular signal-regulated kinase (ERK) in the lungs was attenuated in response to silica-induced HO-1 upregulation. Activation of other MAPKs, such as p38 and c-Jun N-terminal kinase pathways, after silica exposure was not significantly different irrespective of HO-1 induction. Further in vitro studies showed that 1) silica-induced HO-1 was significantly attenuated by inhibiting ERK activation, and 2) carbon monoxide and bilirubin as final byproducts of HO-1 could inhibit ERK activation. Taken together, silica-induced HO-1 upregulation was mediated by ERK activation, and HO-1 further regulates ERK activation via its final byproducts, carbon monoxide and bilirubin.

Conclusions

This is the first study to demonstrate the regulatory role of HO-1 in silicosis. This finding could contribute to the development of a treatment strategy of monitoring HO-1 levels as a marker of therapeutic intervention.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0852-6) contains supplementary material, which is available to authorized users.

Altered tumor biology and tumorigenesis in irradiated and chemical carcinogen-treated single and combined connexin32/p27Kip1-deficient mice

Connexin32 knockout mice (Cx32-KO) exhibit increased chemical and radiation-induced liver and lung tumorigenesis. This increased tumor incidence is associated with altered tumor biology including enhanced tumor progression and an increased percent of MAPK-active tumors. Likewise, mice lacking the tumor suppressor/cell cycle regulator p27Kip1 exhibit increased tumorigenesis in a variety of tissues following chemical and radiation induction. Interestingly, in a double-deficient mouse model (DKO), additional loss of p27Kip1 in a Cx32-KO background results in attenuation of liver and lung tumorigenesis as well as MAPK activation profiles, suggesting pathway interaction. While these mouse strains exhibit altered liver and lung tumor susceptibility following both chemical (DEN) and radiation (X-ray) induction protocols, comparisons of the resulting tumor incidence, multiplicity, tumor progression, and MAPK activation in response to these two distinct carcinogens underscores the separate influence of each individual gene on both tumor formation and activation of specific oncogenic pathways. Furthermore, these studies demonstrate that different carcinogens interact disparately with Cx32/p27Kip1 genotypic backgrounds in situ resulting in varied tumorigenic response.

Mice deficient for the gap junction protein Connexin32 exhibit increased radiation-induced tumorigenesis associated with elevated mitogen-activated protein kinase (p44/Erk1, p42/Erk2) activation

Loss of connexin expression/gap junction intercellular communication (GJIC) has been correlated with decreased growth control and increased tumorigenesis. Studies utilizing Connexin32 (Cx32)-deficient knockout mice have demonstrated that loss of Cx32 increases susceptibility to chemically induced liver tumorigenesis. Here, in addition to dramatically increased liver tumorigenesis, we show that tumor induction utilizing X-ray radiation resulted in a statistically significant increase in overall tumor burden in Cx32-deficient mice compared with wild-type mice due to tumorigenesis in several other tissues (lung, adrenal, lymph and small intestine) even when excluding prevalent liver tumors. Irradiated Cx32-deficient mice were particularly sensitive to liver tumorigenesis (46% incidence compared with 18% in wild-type mice, P = 0.007) demonstrating that Cx32 functions as a hepatic tumor suppressor in response to radiation-associated mutation events. Cx32-deficient mice also exhibited increased lung tumorigenesis (bronchioloalveolar) with an increased progression to carcinoma when compared with wild-type mice. Two Cx32-deficient mice developed an uncommon, invasive medullary adrenal tumor type (pheochromocytoma) not observed in irradiated wild-type mice. Immunohistochemical analysis revealed increased levels of activated mitogen-activated protein kinase (MAPK) (p44/Erk1, p42/Erk2) in Cx32-deficient mouse liver tumors (P = 0.006), lung tumors (P = 0.056) and adrenal tumors (primary and metastases) compared with wild-type counterparts implicating elevated activation of MAPK-interacting pathways in Cx32-deficient tumorigenesis. Interestingly, lung tumors from Cx32-deficient mice also demonstrated decreased p27Kip1 levels compared with wild-type lung tumors (P = 0.05). This study demonstrates that loss of Cx32/GJIC plays a significant role in radiation-induced tumorigenesis of the liver and importantly that Cx32 may also play a role in tumor suppression and/or tumor progression in other tissue types such as lung and adrenal gland. Additionally, this mouse model suggests that MAPK-related pathways may be preferentially activated or conversely that tumors harboring activated MAPK pathways may selectively progress towards more advanced tumor states in the absence of Cx32-mediated GJIC.

pRB2/p130 target genes in non-small lung cancer cells identified by microarray analysis

The retinoblastoma gene family consisting of RB/p105, p107, and RB2/p130 cooperate to regulate cell-cycle progression through the G1 phase of the cell cycle. Previous data demonstrated an independent role for the reduction or loss of pRb2/p130 expression in the formation and/or progression of lung carcinoma. Rb2/p130 is mutated in a human cell line of lung small cell carcinoma as well as in primary lung tumors. To identify potential pRb2/p130 target genes in an unbiased manner, we have utilized an adenovirus-mediated expression system of pRb2/p130 in a non-small lung cancer cell line to identify specific genes that are regulated by pRb2/p130. Using oligonucleotide arrays, a number of Rb2/p130 downregulated genes were identified and their regulation was confirmed by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis. As a result, 40 genes showed greater than 2.0-fold modification in their expression level after the RB2/p130 viral transduction. In conclusion, coupling adenoviral overexpression with microarray and semiquantitative RT-PCR analyses proved to be a versatile strategy for identifying pRb2/p130 target genes and for better understanding the expression profiles of these genes. Our results may also contribute to identifying novel therapeutic biomarkers in lung carcinoma.

Persistent localization of activated extracellular signal-regulated kinases (ERK1/2) is epithelial cell-specific in an inhalation model of asbestosis

Asbestos fibers up-regulate the extracellular signal-regulated kinase (ERK1/2) pathway in mesothelial and pulmonary epithelial cells in vitro, but the cell-type expression patterns and intracellular localization of activated, ie, phosphorylated, ERK in the lung after inhalation of asbestos are unclear. C57/BL6 mice were exposed to 7-mg/m(3) air of crocidolite asbestos for 5 and 30 days, the times required for the development of epithelial cell hyperplasia and fibrotic lesions, respectively. Exposure to asbestos caused striking increases in both unphosphorylated and phosphorylated ERK (p-ERK), which were most marked at 30 days and co-localized in bronchiolar and alveolar epithelial cells using an antibody to cytokeratin. Alveolar macrophages, detected with an anti-macrophage antibody, did not express p-ERK. p-ERK was localized at the apical cell surface of bronchiolar and alveolar type II epithelial cells exposed to asbestos fibers, and was most marked in areas of epithelial hyperplasia in association with fibrotic lesions. Because translocation of p-ERK to the nucleus is associated with activation of early response genes and transcription factors, laser scanning cytometry was used to determine the kinetics of activation and nuclear translocation of p-ERK in an alveolar type II epithelial cell line in vitro after exposure to asbestos or the ERK stimuli, epidermal growth factor, or H(2)O(2). Results showed that cytoplasmic to nuclear translocation of p-ERK occurred in a protracted manner in cells exposed to asbestos. The immunolocalization of p-ERK at the membrane surface, a site of initial exposure to asbestos fibers, and the chronic activation of p-ERK in epithelial cells at sites of fibrogenesis are consistent with the concept that epithelial cell signaling through the ERK pathway contributes to remodeling of the lung during the development of pulmonary fibrosis.

High oleic acid oil suppresses lung tumorigenesis in mice through the modulation of extracellular signal-regulated kinase cascade

This study was undertaken to estimate the effect of dietary high oleic acid oil (OA) on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumorigenesis in mice. Diet containing 10% oil was fed to mice through experimental periods. On day 30 after NNK injection (100 mg/kg body weight, i.p.), the treatment increased the level of prostaglandin E2 (PGE2) as well as proliferating cell nuclear antigen, a marker of cell proliferation in a high linoleic acid oil (LA)-fed group but not in an OA-fed group. The NNK treatment also induced the activation of an extracellular signal-regulated kinase (Erk) cascade (Erk, Mek and Raf-1) in an LA-fed group. On the other hand, OA feeding abolished the NNK-induced activation of the Erk cascade. In conjugation with these events, OA feeding reduced lung tumor incidence and tumor multiplicity (percentage of mice with tumors) in mice compared with LA feeding at the 20th experimental week. These results suggest that OA suppresses lung tumorigenesis and that this suppression is correlated with the inhibition of PGE2 production and inactivation of the Erk cascade.

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

The extracellular signal-regulated kinase (ERK) pathway is induced by cytokines and oxidative stress. In this study we examined the patterns of localization of phosphorylated ERK proteins in relationship to subsequent phenotypic responses by the mitogenic agent epidermal growth factor (EGF) (5 ng/ ml); hydrogen peroxide (H(2)O(2)) (100 to 300 microM), an inducer of apoptosis; and crocidolite asbestos (5 microg/cm(2) dish) in a nontransformed murine alveolar type II epithelial cell line (C10). Laser scanning cytometry and flow cytometry were used to determine: (1) whether expression of phosphorylated ERKs was cell cycle-related; and (2) whether cell-cycle alterations by agents could be modified after addition of the mitogen-activated protein kinase/ERK kinase (MEK) 1 inhibitor PD98059. In contrast to other stimuli which induced transient increases in phosphorylated ERKs, asbestos caused fiber-associated localization of phosphorylated ERKs that were elevated from 1 to 24 h (P < or = 0.05), and striking apoptosis followed by increased numbers of cells in the S phase at 72 h. In both control and asbestos-exposed cells, the percentage of phosphorylated ERK-positive cells was greatest in cells in the G(2)/M and S phases of the cell cycle. All stimuli caused increased proportions of cells in G(2)/M at 24 h that were inhibited by PD98059 (30 microM). Increases in G(2)/M cells by H(2)O(2) and asbestos also were decreased at 48 h by the MEK1 inhibitor. In addition, PD98059 abrogated elevations in S-phase cells by EGF and H(2)O(2) at 24 h and by asbestos at 72 h. Our results suggest that ERKs mediate cell-cycle alterations during the development of epithelial cell apoptosis or proliferation by diverse ERK stimuli.

Ki-ras and the characteristics of mouse lung tumors

Codon 12 mutations are frequent in the Ki-ras oncogene in human lung adenocarcinomas, but the effects of these alterations have not been well characterized in lung epithelial cells. Murine primary lung tumors derived from peripheral epithelial cells also may present Ki-ras mutations and are useful models for study of early phases of tumor development. One hypothesis is that Ki-ras mutation and/or a Ki-ras p21 increase could enhance Ki-ras p21-GTP and cell-cycle stimulation through raf-1 and extracellularly regulated protein kinases (Erks). We examined lung tumors 1-7 mm in largest dimension initiated in male Swiss mice by N-nitrosodimethylamine for pathologic type, Ki-ras mutations and levels of total Ki-ras p21, Ki-ras p21 bound to GTP, raf-1, Erk1 and Erk2 and their phosphorylated (activated) forms, and proliferating cell nuclear antigen. Total Ki-ras p21 and activated ras-GTP were not significantly greater in tumors than in normal lung or in tumors with versus those without Ki-ras mutations. Carcinomas with Ki-ras mutations were significantly smaller than those without mutations. Carcinomas were significantly larger than adenomas only for tumors without mutations. High levels of Erk2 and correlation of Erk2 amount with ras-GTP were specific characteristics of tumors with Ki-ras mutations. Size of all tumors correlated with ras-GTP but not with proliferating cell nuclear antigen. Raf-1 was expressed mainly in alveolar macrophages in normal lung but was focally upregulated in papillary areas of some tumors. The results indicate that Ki-ras influences the characteristics of lung tumors, but a linear ras-raf-Erk-cell-cycle control sequence does not adequately characterize tumorigenic events in this model. Mol. Carcinog. 28:156-167, 2000.

Increased phosphorylated extracellular signal-regulated kinase immunoreactivity associated with proliferative and morphologic lung alterations after chrysotile asbestos inhalation in mice

Activation of extracellular signal-regulated kinases (ERK) has been associated with the advent of asbestos-associated apoptosis and proliferation in mesothelial and alveolar epithelial cells and may be linked to the development of pulmonary fibrosis. The objective of studies here was to characterize the development of inflammation, cellular proliferation, and fibrosis in asbestos-exposed C57Bl/6 mice in relationship to patterns of ERK phosphorylation. Inflammation occurred after 10 and 20 days of asbestos exposure as evidenced by increases in total protein and neutrophils in bronchoalveolar lavage fluid. Increases in cell proliferation were observed at 30 days in bronchiolar epithelia and at 4, 14, and 30 days in the alveolar compartment of the lung. Trichrome-positive focal lesions of pulmonary fibrosis developed at 30 days in the absence of elevations in lung hydroxyproline or procollagen mRNA levels. Striking increases in ERK phosphorylation were observed within pulmonary epithelial cells at sites of developing fibrotic lesions after 14 and 30 days of inhalation. In addition to characterizing a murine inhalation model of asbestosis, we provide the first evidence showing activation of ERK signaling within lung epithelium in vivo, following inhalation of asbestos fibers.