Obesity-dependent changes in interstitial ECM mechanics promote breast tumorigenesis.

Obesity and extracellular matrix (ECM) density are considered independent risk and prognostic factors for breast cancer. Whether they are functionally linked is uncertain. We investigated the hypothesis that obesity enhances local myofibroblast content in mammary adipose tissue and that these stromal changes increase malignant potential by enhancing interstitial ECM stiffness. Indeed, mammary fat of both diet- and genetically induced mouse models of obesity were enriched for myofibroblasts and stiffness-promoting ECM components. These differences were related to varied adipose stromal cell (ASC) characteristics because ASCs isolated from obese mice contained more myofibroblasts and deposited denser and stiffer ECMs relative to ASCs from lean control mice. Accordingly, decellularized matrices from obese ASCs stimulated mechanosignaling and thereby the malignant potential of breast cancer cells. Finally, the clinical relevance and translational potential of our findings were supported by analysis of patient specimens and the observation that caloric restriction in a mouse model reduces myofibroblast content in mammary fat. Collectively, these findings suggest that obesity-induced interstitial fibrosis promotes breast tumorigenesis by altering mammary ECM mechanics with important potential implications for anticancer therapies.

Estrogen Protects against Obesity-Induced Mammary Gland Inflammation in Mice.

Obesity is a risk factor for the development of hormone receptor (HR)-positive breast cancer in postmenopausal women. Obesity causes subclinical inflammation in white adipose tissue (WAT), characterized by macrophages surrounding dead or dying adipocytes forming crown-like structures (CLS). Estrogen synthesis is catalyzed by aromatase. Previously, we demonstrated CLS and elevated levels of proinflammatory mediators and aromatase in the mammary glands of obese mice and breast tissue of obese women. Here, we tested the hypothesis that supplemental estrogen could prevent or reverse WAT inflammation (WATi) and related molecular changes in the mammary gland. C57BL/6J mice were ovariectomized (OVX) to simulate the postmenopausal state. Supplementation with 17ß-estradiol (E2) protected against high fat diet (HFD)-induced weight gain and mammary glands WATi. Expression of proinflammatory mediators (Cox-2, TNFα, IL1ß) and aromatase were also reduced in the mammary glands of mice that received supplemental E2. Next, to determine whether E2 supplementation can reverse WATi, obese OVX mice were treated with E2 or placebo and then continued on HFD. E2 supplementation induced weight loss, reversed mammary gland inflammation, and downregulated expression of proinflammatory mediators and aromatase. Finally, we determined whether the protective effects of E2 were mediated by estrogen receptor-α (ERα). Knocking out ERα in ovary intact mice fed a HFD led to weight gain, WATi and elevated levels of proinflammatory mediators and aromatase mimicking the effects of OVX. Taken together, our findings indicate that estrogen via ERα protects against weight gain, WATi and associated increases in proinflammatory mediators and aromatase in the mammary gland.

Dietary polyphenols suppress elevated levels of proinflammatory mediators and aromatase in the mammary gland of obese mice.

In postmenopausal women, obesity is a risk factor for the development of hormone receptor-positive breast cancer driven by estrogen. After menopause, aromatization of androgen precursors in adipose tissue is a major synthetic source of estrogen. Recently, in mouse models and women, we identified an obesity-inflammation-aromatase axis. This obesity-induced inflammation is characterized by crown-like structures (CLS) consisting of dead adipocytes encircled by macrophages in breast white adipose tissue. CLS occur in association with NF-κB activation, elevated levels of proinflammatory mediators, and increased aromatase expression. Saturated fatty acids released from adipocytes have been linked to obesity-related white adipose tissue inflammation. Here we found that stearic acid, a prototypic saturated fatty acid, stimulated Akt-dependent activation of NF-κB resulting in increased levels of proinflammatory mediators [TNF-α, interleukin (IL)-1ß, COX-2] in macrophages leading, in turn, to the induction of aromatase. Several polyphenols (resveratrol, curcumin, epigallocatechin gallate) blocked these inductive effects of stearic acid. Zyflamend, a widely used polyherbal preparation that contains numerous polyphenols, possessed similar suppressive effects. In a mouse model of obesity, treatment with Zyflamend suppressed levels of phospho-Akt, NF-κB binding activity, proinflammatory mediators, and aromatase in the mammary gland. Collectively, these results suggest that targeting the activation of NF-κB is a promising approach for reducing levels of proinflammatory mediators and aromatase in inflamed mouse mammary tissue. Further investigation in obese women is warranted.

Caloric restriction reverses obesity-induced mammary gland inflammation in mice.

Obesity is a risk factor for the development of hormone receptor-positive breast cancer in postmenopausal women. Estrogen synthesis is catalyzed by aromatase. Recently, we identified an obesity→inflammation→aromatase axis in mouse models and women. In mouse models of obesity, inflammatory foci characterized by crown-like structures (CLS) consisting of dead adipocytes encircled by macrophages were found in the mammary gland. CLS of the breast were found in most overweight and obese women. CLS were associated with adipocyte hypertrophy, activation of NF-κB, elevated levels of proinflammatory mediators and aromatase, and increased expression of the progesterone receptor (PR). Collectively, these findings provide a plausible explanation for the link between obesity, chronic inflammation, and postmenopausal breast cancer. Here, we investigated whether caloric restriction (CR) reversed the inflammatory state and related molecular changes in the mammary gland of obese mice. Obese ovariectomized C57BL/6J mice were subjected to 30% CR for 7 or 14 weeks. Findings in CR mice were compared with the results in mice fed a high-fat diet ad libitum or with control mice fed a low-fat diet. CR was associated with more than a 75% decrease in mammary CLS/cm(2). Reduced histologic inflammation following CR was associated with decreased adipocyte diameter and monocyte chemoattractant protein-1 (MCP-1) levels, reduced NF-κB binding activity, and normalization of levels of proinflammatory mediators, aromatase, and PR. In summary, obesity-related inflammation of the mammary gland and elevated aromatase and PR levels were reversed with CR. Our results provide a rationale for determining whether weight loss can reverse breast inflammation associated with obesity in women.

Increased levels of COX-2 and prostaglandin E2 contribute to elevated aromatase expression in inflamed breast tissue of obese women.

UNLABELLED: Obesity is a risk factor for hormone receptor-positive breast cancer in postmenopausal women. Estrogen synthesis is catalyzed by aromatase, which is encoded by CYP19. We previously showed that aromatase expression and activity are increased in the breast tissue of overweight and obese women in the presence of characteristic inflammatory foci [crown-like structures of the breast (CLS-B)]. In preclinical studies, proinflammatory prostaglandin E(2) (PGE(2)) is a determinant of aromatase expression. We provide evidence that cyclooxygenase (COX)-2-derived PGE(2) stimulates the cyclic AMP (cAMP) → PKA signal transduction pathway that activates CYP19 transcription, resulting in increased aromatase expression and elevated progesterone receptor levels in breast tissues from overweight and obese women. We further demonstrate that a measure of in-breast inflammation (CLS-B index) is a better correlate of these biologic end points than body mass index. The obesity → inflammation → aromatase axis is likely to contribute to the increased risk of hormone receptor-positive breast cancer and the worse prognosis of obese patients with breast cancer. SIGNIFICANCE: We show that obesity-associated inflammatory foci in the human breast are associated with elevated COX-2 levels and activation of the PGE2 → cAMP → PKA signal transduction pathway resulting in increased aromatase expression. These findings help to explain the link among obesity, low-grade chronic inflammation, and breast cancer with important clinical implications.

Matrix metalloproteinase-dependent microsomal prostaglandin E synthase-1 expression in macrophages: role of TNF-α and the EP4 prostanoid receptor.

Matrix metalloproteinase (MMP)-9 contributes to the pathogenesis of chronic inflammatory diseases and cancer. Thus, identifying targetable components of signaling pathways that regulate MMP-9 expression may have broad therapeutic implications. Our previous studies revealed a nexus between metalloproteinases and prostanoids whereby MMP-1 and MMP-3, commonly found in inflammatory and neoplastic foci, stimulate macrophage MMP-9 expression via the release of TNF-α and subsequent induction of cyclooxygenase-2 and PGE(2) engagement of EP4 receptor. In the current study, we determined whether MMP-induced cyclooxygenase-2 expression was coupled to the expression of prostaglandin E synthase family members. We found that MMP-1- and MMP-3-dependent release of TNF-α induced rapid and transient expression of early growth response protein 1 in macrophages followed by sustained elevation in microsomal prostaglandin synthase 1 (mPGES-1) expression. Metalloproteinase-induced PGE(2) levels and MMP-9 expression were markedly attenuated in macrophages in which mPGES-1 was silenced, thereby identifying mPGES-1 as a therapeutic target in the regulation of MMP-9 expression. Finally, the induction of mPGES-1 was regulated, in part, through a positive feedback loop dependent on PGE(2) binding to EP4. Thus, in addition to inhibiting macrophage MMP-9 expression, EP4 antagonists emerge as potential therapy to reduce mPGES-1 expression and PGE(2) levels in inflammatory and neoplastic settings.

The effect of HIV and HPV coinfection on cervical COX-2 expression and systemic prostaglandin E2 levels.

Human immunodeficiency virus (HIV-1) infection causes chronic inflammation. COX-2-derived prostaglandin E(2) (PGE(2)) has been linked to both inflammation and carcinogenesis. We hypothesized that HIV-1 could induce COX-2 in cervical tissue and increase systemic PGE(2) levels and that these alterations could play a role in AIDS-related cervical cancer. Levels of cervical COX-2 mRNA and urinary PGE-M, a biomarker of systemic PGE(2) levels, were determined in 17 HIV-negative women with a negative cervical human papilloma virus (HPV) test, 18 HIV-infected women with a negative HPV test, and 13 HIV-infected women with cervical HPV and high-grade squamous intraepithelial lesions on cytology. Cervical COX-2 levels were significantly associated with HIV and HPV status (P = 0.006 and 0.002, respectively). Median levels of urinary PGE-M were increased in HIV-infected compared with uninfected women (11.2 vs. 6.8 ng/mg creatinine, P = 0.02). Among HIV-infected women, urinary PGE-M levels were positively correlated with plasma HIV-1 RNA levels (P = 0.003). Finally, levels of cervical COX-2 correlated with urinary PGE-M levels (P = 0.005). This study shows that HIV-1 infection is associated with increased cervical COX-2 and elevated systemic PGE(2) levels. Drugs that inhibit the synthesis of PGE(2) may prove useful in reducing the risk of cervical cancer or systemic inflammation in HIV-infected women.

Inflammation and increased aromatase expression occur in the breast tissue of obese women with breast cancer.

Obesity is a risk factor for the development of hormone receptor-positive breast cancer in postmenopausal women and has been associated with an increased risk of recurrence and reduced survival. In humans, obesity causes subclinical inflammation in visceral and subcutaneous adipose tissue, characterized by necrotic adipocytes surrounded by macrophages forming crown-like structures (CLS). Recently, we found increased numbers of CLS, activation of the NF-κB transcription factor, and elevated aromatase levels and activity in the mammary glands of obese mice. These preclinical findings raised the possibility that the obesity → inflammation axis is important for the development and progression of breast cancer. Here, our main objective was to determine if the findings in mouse models of obesity translated to women. Breast tissue was obtained from 30 women who underwent breast surgery. CLS of the breast (CLS-B) was found in nearly 50% (14 of 30) of patient samples. The severity of breast inflammation, defined as the CLS-B index, correlated with both body mass index (P < 0.001) and adipocyte size (P = 0.01). Increased NF-κB binding activity and elevated aromatase expression and activity were found in the inflamed breast tissue of overweight and obese women. Collectively, our results suggest that the obesity → inflammation → aromatase axis is present in the breast tissue of most overweight and obese women. The presence of CLS-B may be a biomarker of increased breast cancer risk or poor prognosis.

Obesity is associated with inflammation and elevated aromatase expression in the mouse mammary gland.

Elevated circulating estrogen levels are associated with increased risk of breast cancer in obese postmenopausal women. Following menopause, the biosynthesis of estrogens through CYP19 (aromatase)-mediated metabolism of androgen precursors occurs primarily in adipose tissue, and the resulting estrogens are then secreted into the systemic circulation. The potential links between obesity, inflammation, and aromatase expression are unknown. In both dietary and genetic models of obesity, we observed necrotic adipocytes surrounded by macrophages forming crown-like structures (CLS) in the mammary glands and visceral fat. The presence of CLS was associated with activation of NF-κB and increased levels of proinflammatory mediators (TNF-α, IL-1ß, Cox-2), which were paralleled by elevated levels of aromatase expression and activity in the mammary gland and visceral fat of obese mice. Analyses of the stromal-vascular and adipocyte fractions of the mammary gland suggested that macrophage-derived proinflammatory mediators induced aromatase and estrogen-dependent gene expression (PR, pS2) in adipocytes. Saturated fatty acids, which have been linked to obesity-related inflammation, stimulated NF-κB activity in macrophages leading to increased levels of TNF-α, IL-1ß, and Cox-2, each of which contributed to the induction of aromatase in preadipocytes. The discovery of the obesity → inflammation → aromatase axis in the mammary gland and visceral fat and its association with CLS may provide insight into mechanisms underlying the increased risk of hormone receptor-positive breast cancer in obese postmenopausal women, the reduced efficacy of aromatase inhibitors in the treatment of breast cancer in these women, and their generally worse outcomes. The presence of CLS may be a biomarker of increased breast cancer risk or poor prognosis.

UV radiation inhibits 15-hydroxyprostaglandin dehydrogenase levels in human skin: evidence of transcriptional suppression.

Elevated levels of prostaglandins (PG) have been detected in the skin following UV radiation (UVR). PGs play an important role in mediating both the acute and the chronic consequences of UVR exposure. UVR-mediated induction of cyclooxygenase-2 (COX-2) contributes to increased PG synthesis. In theory, reduced catabolism might also contribute to increased PG levels. 15-Hydroxyprostaglandin deyhdrogenase (15-PGDH), a tumor suppressor gene, plays a major role in PG catabolism. In this study, we investigated whether UVR exposure suppressed 15-PGDH while inducing COX-2 in keratinocytes and in human skin. UVR exposure caused dose-dependent induction of COX-2, suppression of 15-PGDH, and increased prostaglandin E(2) (PGE(2)) production in HaCaT cells. Exposure to UVR suppressed the transcription of 15-PGDH, resulting in reduced 15-PGDH mRNA, protein, and enzyme activities. UVR exposure induced Slug, a repressive transcription factor that bound to the 15-PGDH promoter. Silencing Slug blocked UVR-mediated downregulation of 15-PGDH. The effects of UVR were also evaluated in the EpiDerm skin model, a three-dimensional model of human epidermis. Here too, COX-2 levels were induced and 15-PGDH levels suppressed following UVR exposure. Next, the effects of UVR were evaluated in human subjects. UVR treatment induced COX-2 while suppressing 15-PGDH mRNA in the skin of 9 of 10 subjects. Collectively, these data suggest that reduced expression of 15-PGDH contributes to the elevated levels of PGs found in the skin following UVR exposure. Possibly, agents that prevent UVR-mediated downregulation of 15-PGDH will affect the acute or the long-term consequences of UVR exposure, including nonmelanoma skin cancer.

Effects of cigarette smoke on the human oral mucosal transcriptome.

Use of tobacco is responsible for approximately 30% of all cancer-related deaths in the United States, including cancers of the upper aerodigestive tract. In the current study, 40 current and 40 age- and gender-matched never smokers underwent buccal biopsies to evaluate the effects of smoking on the transcriptome. Microarray analyses were carried out using Affymetrix HGU133 Plus 2 arrays. Smoking altered the expression of numerous genes: 32 genes showed increased expression and 9 genes showed reduced expression in the oral mucosa of smokers versus never smokers. Increases were found in genes involved in xenobiotic metabolism, oxidant stress, eicosanoid synthesis, nicotine signaling, and cell adhesion. Increased numbers of Langerhans cells were found in the oral mucosa of smokers. Interestingly, smoking caused greater induction of aldo-keto reductases, enzymes linked to polycyclic aromatic hydrocarbon-induced genotoxicity, in the oral mucosa of women than men. Striking similarities in expression changes were found in oral compared with the bronchial mucosa. The observed changes in gene expression were compared with known chemical signatures using the Connectivity Map database and suggested that geldanamycin, a heat shock protein 90 inhibitor, might be an antimimetic of tobacco smoke. Consistent with this prediction, geldanamycin caused dose-dependent suppression of tobacco smoke extract-mediated induction of CYP1A1 and CYP1B1 in vitro. Collectively, these results provide new insights into the carcinogenic effects of tobacco smoke, support the potential use of oral epithelium as a surrogate tissue in future lung cancer chemoprevention trials, and illustrate the potential of computational biology to identify chemopreventive agents.

Matrix metalloproteinase (MMP)-1 and MMP-3 induce macrophage MMP-9: evidence for the role of TNF-alpha and cyclooxygenase-2.

Matrix metalloproteinase (MMP)-9 (gelatinase B) participates in a variety of diverse physiologic and pathologic processes. We recently characterized a cyclooxygenase-2 (COX-2)-->PGE(2)-->EP4 receptor axis that regulates macrophage MMP-9 expression. In the present studies, we determined whether MMPs, commonly found in inflamed and neoplastic tissues, regulate this prostanoid-EP receptor axis leading to enhanced MMP-9 expression. Results demonstrate that exposure of murine peritoneal macrophages and RAW264.7 macrophages to MMP-1 (collagenase-1) or MMP-3 (stromelysin-1) lead to a marked increase in COX-2 expression, PGE(2) secretion, and subsequent induction of MMP-9 expression. Proteinase-induced MMP-9 expression was blocked in macrophages preincubated with the selective COX-2 inhibitor celecoxib or transfected with COX-2 small interfering RNA (siRNA). Likewise, proteinase-induced MMP-9 was blocked in macrophages preincubated with the EP4 antagonist ONO-AE3-208 or transfected with EP4 siRNA. Exposure of macrophages to MMP-1 and MMP-3 triggered the rapid release of TNF-alpha, which was blocked by MMP inhibitors. Furthermore, both COX-2 and MMP-9 expression were inhibited in macrophages preincubated with anti-TNF-alpha IgG or transfected with TNF-alpha siRNA. Thus, proteinase-induced MMP-9 expression by macrophages is dependent on the release of TNF-alpha, induction of COX-2 expression, and PGE(2) engagement of EP4. The ability of MMP-1 and MMP-3 to regulate macrophage secretion of PGE(2) and expression of MMP-9 defines a nexus between MMPs and prostanoids that is likely to play a role in the pathogenesis of chronic inflammatory diseases and cancer. These data also suggest that this nexus is targetable utilizing anti-TNF-alpha therapies and/or selective EP4 antagonists.

Pilot randomized phase II study of celecoxib in oral premalignant lesions.

PURPOSE: Cyclooxygenase-2 (COX-2)-specific inhibition suppresses carcinogenesis in preclinical models and is a promising strategy for preventing oral cancer. In this pilot randomized phase II study, we evaluated the efficacy and safety of the COX-2 inhibitor celecoxib in patients with oral premalignant lesions (OPL). EXPERIMENTAL DESIGN: Patients were randomly assigned to placebo (n=18), celecoxib 100 mg twice daily (n=17), or celecoxib 200 mg twice daily (n=15) for 12 weeks. Six additional patients received celecoxib (400 mg twice daily) in an unblinded extension of the study. Biopsies were obtained at baseline and week 12. All patients entering the study were required to have at least one histologically confirmed early (atypical hyperplasia, atypical hyperkeratosis, or mild dysplasia) or advanced (moderate to severe dysplasia) OPL. RESULTS: Forty-nine patients (46 of 50 randomized and 3 of 6 open label) were evaluable for efficacy analyses. There were no statistically significant differences between the response rates of the randomly assigned arms: placebo, 33.3% (6 of 18); celecoxib 100 mg twice daily, 41.2% (7 of 17); and celecoxib 200 mg twice daily, 20.0% (3 of 15). Two patients responded on celecoxib 400 mg twice daily. Celecoxib was generally well tolerated. Patients with higher baseline COX-2 mRNA levels had an increased risk of disease progression within 3 months. CONCLUSIONS: Celecoxib at 100 or 200 mg twice daily was ineffective in controlling OPLs in this randomized controlled trial. This result and cardiovascular toxicity results of other (large scale) randomized controlled trials of selective COX-2 inhibitors have discouraged the continued investigation of these agents in oral cancer chemoprevention. Better methods for identifying high-risk patients and more active interventions are needed for future oral cancer chemoprevention trials.

Effects of tobacco smoke on gene expression and cellular pathways in a cellular model of oral leukoplakia.

In addition to being causally linked to the formation of multiple tumor types, tobacco use has been associated with decreased efficacy of anticancer treatment and reduced survival time. A detailed understanding of the cellular mechanisms that are affected by tobacco smoke (TS) should facilitate the development of improved preventive and therapeutic strategies. We have investigated the effects of a TS extract on the transcriptome of MSK-Leuk1 cells, a cellular model of oral leukoplakia. Using Affymetrix HGU133 Plus 2 arrays, 411 differentially expressed probe sets were identified. The observed transcriptome changes were grouped according to functional information and translated into molecular interaction network maps and signaling pathways. Pathways related to cellular proliferation, inflammation, apoptosis, and tissue injury seemed to be perturbed. Analysis of networks connecting the affected genes identified specific modulated molecular interactions, hubs, and key transcription regulators. Thus, TS was found to induce several epidermal growth factor receptor (EGFR) ligands forming an EGFR-centered molecular interaction network, as well as several aryl hydrocarbon receptor-dependent genes, including the xenobiotic metabolizing enzymes CYP1A1 and CYP1B1. Notably, the latter findings in vitro are consistent with our parallel finding that CYP1A1 and CYP1B1 levels were increased in oral mucosa of smokers. Collectively, these results offer insights into the mechanisms underlying the procarcinogenic effects of TS and raise the possibility that inhibitors of EGFR or aryl hydrocarbon receptor signaling will prevent or delay the development of TS-related tumors. Moreover, the inductive effects of TS on xenobiotic metabolizing enzymes may help explain the reduced efficacy of chemotherapy, and suggest targets for chemopreventive agents in smokers.

Inhibition of Jun NH2-terminal kinases suppresses the growth of experimental head and neck squamous cell carcinoma.

PURPOSE: This study was carried out to investigate whether c-Jun NH2-terminal kinases (JNK) are potential targets for treating head and neck squamous cell carcinoma (HNSCC). EXPERIMENTAL DESIGN: JNK activity was first evaluated in 20 paired samples of human HNSCC. The antitumor activity of SP600125, a reversible nonselective ATP-competitive inhibitor of JNKs, was then investigated both in an HNSCC xenograft model and in vitro using immunohistochemistry, immunoblotting, enzyme immunoassay, flow cytometry, and a Matrigel assay of capillary tube formation. Complementary studies were carried out using small interfering RNA to JNK1/2. RESULTS: JNK activity was increased in human HNSCC compared with normal-appearing epithelium. Treatment of mice bearing HNSCC xenografts with SP600125 resulted in >60% inhibition of tumor growth relative to vehicle-treated animals. Inhibition of tumor growth was associated with significant reductions in both cell proliferation and microvessel density. SP600125 inhibited tumor cell proliferation by causing delays in both the S and G2-M phases of the cell cycle. Inhibition of angiogenesis seemed to reflect effects on both tumor and endothelial cells. The JNK inhibitor suppressed the production of vascular endothelial growth factor and interleukin-8 by tumor cells and also inhibited endothelial cell proliferation and capillary tube formation. Reduced amounts and phosphorylation of epidermal growth factor receptor were found in tumor cells after treatment with SP600125. Small interfering RNA-mediated suppression of JNK1/2 led to reduced tumor cell proliferation and decreased levels of epidermal growth factor receptor, vascular endothelial growth factor, and interleukin-8. CONCLUSIONS: JNK activity is commonly increased in HNSCC. Our preclinical results provide a rationale for evaluating JNK inhibition as an approach to treating HNSCC.

Tobacco smoke induces urokinase-type plasminogen activator and cell invasiveness: evidence for an epidermal growth factor receptor dependent mechanism.

Multiple tobacco smoke-related premalignant and malignant lesions develop synchronously or metachronously in various organ sites, including the oral cavity. Both field cancerization and clonal migration seem to contribute to the occurrence of multiple tumors. Although the importance of endogenous factors (e.g., oncogenes) in regulating clonal migration is well established, little is known about the role of exogenous factors. Hence, the main objective of this study was to elucidate the mechanism by which tobacco smoke stimulated the migration of cells through extracellular matrix (ECM). Treatment of MSK-Leuk1 cells with a saline extract of tobacco smoke induced the migration of cells through ECM. Tobacco smoke induced the expression of urokinase-type plasminogen activator (uPA), resulting in plasmin-dependent degradation of ECM and increased cell migration. AG1478, a small-molecule inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase, a neutralizing antibody to EGFR, or an antibody to amphiregulin, an EGFR ligand, also blocked tobacco smoke-mediated induction of uPA and cell migration through ECM. PD98059, an inhibitor of mitogen-activated protein kinase (MAPK) kinase activity, caused similar inhibitory effects. Taken together, these results suggest that tobacco smoke activated the EGFR-->extracellular signal-regulated kinase 1/2 MAPK pathway, causing induction of uPA. This led, in turn, to increased plasmin-dependent degradation of matrix proteins and enhanced cell migration through ECM. These data strongly suggest that chemicals in tobacco smoke can mimic the effects of oncogenes in regulating uPA-dependent cell invasion through ECM. These findings also strengthen the rationale for determining whether inhibitors of EGFR tyrosine kinase reduce the risk of tobacco smoke-related second primary tumors.