A genetic mouse model for metastatic lung cancer with gender differences in survival

DMXAA causes tumor site-specific vascular disruption in murine non-small cell lung cancer, and like the endogenous non-canonical cyclic dinucleotide STING agonist, 2'3'-cGAMP, induces M2 macrophage repolarization

The vascular disrupting agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA), a murine agonist of the stimulator of interferon genes (STING), appears to target the tumor vasculature primarily as a result of stimulating pro-inflammatory cytokine production from tumor-associated macrophages (TAMs). Since there were relatively few reports of DMXAA effects in genetically-engineered mutant mice (GEMM), and models of non-small cell lung cancer (NSCLC) in particular, we examined both the effectiveness and macrophage dependence of DMXAA in various NSCLC models. The DMXAA responses of primary adenocarcinomas in K-rasLA1/+ transgenic mice, as well as syngeneic subcutaneous and metastatic tumors, generated by a p53R172HΔg/+; K-rasLA1/+ NSCLC line (344SQ-ELuc), were assessed both by in vivo bioluminescence imaging as well as by histopathology. Macrophage-dependence of DMXAA effects was explored by clodronate liposome-mediated TAM depletion. Furthermore, a comparison of the vascular structure between subcutaneous tumors and metastases was carried out using micro-computed tomography (micro-CT). Interestingly, in contrast to the characteristic hemorrhagic necrosis produced by DMXAA in 344SQ-ELuc subcutaneous tumors, this agent failed to cause hemorrhagic necrosis of either 344SQ-ELuc-derived metastases or autochthonous K-rasLA1/+ NSCLCs. In addition, we found that clodronate liposome-mediated depletion of TAMs in 344SQ-ELuc subcutaneous tumors led to non-hemorrhagic necrosis due to tumor feeding-vessel occlusion. Since NSCLC were comprised exclusively of TAMs with anti-inflammatory M2-like phenotype, the ability of DMXAA to re-educate M2-polarized macrophages was examined. Using various macrophage phenotypic markers, we found that the STING agonists, DMXAA and the non-canonical endogenous cyclic dinucleotide, 2'3'-cGAMP, were both capable of re-educating M2 cells towards an M1 phenotype. Our findings demonstrate that the choice of preclinical model and the anatomical site of a tumor can determine the vascular disrupting effectiveness of DMXAA, and they also support the idea of STING agonists having therapeutic utility as TAM repolarizing agents.

ZEB1 sensitizes lung adenocarcinoma to metastasis suppression by PI3K antagonism

Epithelial tumor cells that have undergone epithelial-to-mesenchymal transition (EMT) are typically prone to metastasis and drug resistance and contribute to a poor clinical outcome. The transcription factor ZEB1 is a known driver of EMT, and mediators of ZEB1 represent potential therapeutic targets for metastasis suppression. Here, we have shown that phosphatidylinositol 3-kinase-targeted (PI3K-targeted) therapy suppresses metastasis in a mouse model of Kras/Tp53-mutant lung adenocarcinoma that develops metastatic disease due to high expression of ZEB1. In lung adenocarcinoma cells from Kras/Tp53-mutant animals and human lung cancer cell lines, ZEB1 activated PI3K by derepressing miR-200 targets, including amphiregulin (AREG), betacellulin (BTC), and the transcription factor GATA6, which stimulated an EGFR/ERBB2 autocrine loop. Additionally, ZEB1-dependent derepression of the miR-200 and miR-183 target friend of GATA 2 (FOG2) enhanced GATA3-induced expression of the p110α catalytic subunit of PI3K. Knockdown of FOG2, p110α, and RHEB ameliorated invasive and metastatic propensities of tumor cells. Surprisingly, FOG2 was not required for mesenchymal differentiation, suggesting that mesenchymal differentiation and invasion are distinct and separable processes. Together, these results indicate that ZEB1 sensitizes lung adenocarcinoma cells to metastasis suppression by PI3K-targeted therapy and suggest that treatments to selectively modify the metastatic behavior of mesenchymal tumor cells are feasible and may be of clinical value.

Obligate progression precedes lung adenocarcinoma dissemination

Despite its clinical importance, very little is known about the natural history and molecular underpinnings of lung cancer dissemination and metastasis. Here, we used a genetically engineered mouse model of metastatic lung adenocarcinoma in which cancer cells are fluorescently marked to determine whether dissemination is an inherent ability or a major acquired phenotype during lung adenocarcinoma metastasis. We find very little evidence for dissemination from oncogenic KRAS-driven hyperplasias or most adenocarcinomas. p53 loss is insufficient to drive dissemination but rather enables rare cancer cells in a small fraction of primary adenocarcinomas to gain alterations that drive dissemination. Molecular characterization of disseminated tumor cells indicates that downregulation of the transcription factor Nkx2-1 precedes dissemination. Finally, we show that metastatic primary tumors possess a highly proliferative subpopulation of cells with characteristics matching those of disseminating cells. We propose that dissemination is a major hurdle during the natural course of lung adenocarcinoma metastasis.

SIGNIFICANCE

Because of its aggressively metastatic nature, lung cancer is the top cancer killer of both men and women in the United States. We show that, unlike in other cancer types, lung cancer dissemination is a major initial barrier to metastasis. Our findings provide insight into the effect of p53 deficiency and downregulation of Nkx2-1 during lung adenocarcinoma progression.

Sex-specific lung diseases: effect of oestrogen on cultured cells and in animal models

Sex prevalence in lung disease suggests that sex-specific hormones may contribute to the pathogenesis and/or progression of at least some lung diseases, such as lung adenocarcinoma, lymphangioleiomyomatosis (LAM) and benign metastasising leiomyoma (BML). Oestrogen is an important hormone in normal lung development and in the pathogenesis of female predominant pulmonary diseases. In vivo and in vitro studies have facilitated our understanding of disease pathogenesis and discovery of potential therapeutic targets. Oestrogen promoted disease progression in cell and animal models of lung adenocarcinoma, LAM and BML. Specifically, oestrogen enhanced tumour growth and metastasis in animal models of these diseases. Furthermore, 17β-estradiol (E2), the most abundant form of oestrogen in humans, increased the size and proliferation of cultured cells of lung adenocarcinoma and LAM. Coupled with the known mechanisms of oestrogen metabolism and signalling, these model systems may provide insights into the diverse effects of oestrogen and other hormones on lung diseases. Anti-oestrogen treatments that target key events of oestrogen synthesis or signalling, such as aromatase activity, oestrogen receptors and signalling pathways, may offer additional opportunities for clinical trials.

Smoking, p53 mutation, and lung cancer

This issue marks the 50th anniversary of the release of the U.S. Surgeon General's Report on Smoking and Health. Perhaps no other singular event has done more to highlight the effects of smoking on the development of cancer. Tobacco exposure is the leading cause of cancers involving the oral cavity, conductive airways, and the lung. Owing to the many carcinogens in tobacco smoke, smoking-related malignancies have a high genome-wide burden of mutations, including in the gene encoding for p53. The p53 protein is the most frequently mutated tumor suppressor in cancer, responsible for a range of critical cellular functions that are compromised by the presence of a mutation. Herein, we review the epidemiologic connection between tobacco exposure and cancer, the molecular basis of p53 mutation in lung cancer, and the normal molecular and cellular roles of p53 that are abrogated during lung tumor development and progression as defined by in vitro and in vivo studies. We also consider the therapeutic potential of targeting mutant p53 in a clinical setting based upon the cellular role of mutant p53 and data from genetic murine models.

ARF inhibits the growth and malignant progression of non-small-cell lung carcinoma

Non-small-cell lung carcinoma (NSCLC) is among the deadliest of human cancers. The CDKN2A locus, which houses the INK4a and ARF tumor suppressor genes, is frequently altered in NSCLC. However, the specific role of ARF in pulmonary tumorigenesis remains unclear. KRAS and other oncogenes induce the expression of ARF, thus stabilizing p53 activity and arresting cell proliferation. To address the role of ARF in Kras-driven NSCLC, we compared the susceptibility of NIH/Ola strain wild-type and Arf-knockout mice to urethane-induced lung carcinogenesis. Lung tumor size, malignancy and associated morbidity were significantly increased in Arf(-/-) compared with Arf(+/+) animals at 25 weeks after induction. Pulmonary tumors from Arf-knockout mice exhibited increased cell proliferation and DNA damage compared with wild-type mice. A subgroup of tumors in Arf(-/-) animals presented as dedifferentiated and metastatic, with many characteristics of pulmonary sarcomatoid carcinoma, a neoplasm previously undocumented in mouse models. Our finding of a role for ARF in NSCLC is consistent with the observation that benign adenomas from Arf(+/+) mice robustly expressed ARF, while ARF expression was markedly reduced in malignant adenocarcinomas. ARF expression also frequently colocalized with the expression of p21(CIP1), a transcriptional target of p53, arguing that ARF induces the p53 checkpoint to arrest cell proliferation in vivo. Taken together, these findings demonstrate that induction of ARF is an early response in lung tumorigenesis that mounts a strong barrier against tumor growth and malignant progression.

Estrogen metabolism within the lung and its modulation by tobacco smoke

Although estrogen and the enzymes responsible for its metabolism have been detected within the lung, the ability of this tissue to metabolize estrogen has not been demonstrated previously. The goal of this study was to characterize the profile of estrogen metabolites within the murine lung and to determine the effect of tobacco smoke exposure on metabolite levels. Use of liquid chromatography-tandem mass spectrometry led to the detection of three estrogens (E1, E2 and E3) and five estrogen metabolites (2-OHE1, 4-OHE1, 4-OHE2, 2-OMeE1 and 2-OMeE2) within the perfused lung, with 4-OHE1 being the most abundant species. Levels of 4-OHEs, carcinogenic derivatives produced primarily by cytochrome P450 1B1 (Cyp1b1), were 2-fold higher in females than males. Deletion of Cyp1b1 in females led to a dramatic reduction (21-fold) in 4-OHEs, whereas levels of 2-OHE1 and the putative protective estrogen metabolite 2-OMeE2 were increased (2.4- and 5.0-fold, respectively) (P = 0.01). Similar quantitative differences in estrogen metabolite levels were observed between Cyp1b1 null and wild-type males. Exposure of female mice to tobacco smoke for 8 weeks (2h per day, 5 days per week) increased the levels of 4-OHE1 (4-fold) and 2-OHE2 (2-fold) within the lung while reducing the total concentration of 2-OMeEs to 70% of those of unexposed controls. These data suggest that tobacco smoke accelerates the production of 4-OHEs within the lung; carcinogenic metabolites that could potentially contribute to lung tumor development. Thus, inhibition of CYP1B1 may represent a promising strategy for the prevention and treatment of lung cancer.

Ikaros is a critical target during simultaneous exposure to X-rays and N-ethyl-N-nitrosourea in mouse T-cell lymphomagenesis

Cancer risk associated with radiation exposure is considered the result of concurrent exposure to other natural and manmade carcinogens. Available data on the molecular characteristics of cancer after simultaneous exposure to radiation and chemicals are insufficient. In our study, we used a mouse thymic lymphoma (TL) model that was synergistically induced by simultaneous exposure to X-rays and N-ethyl-N-nitrosourea (ENU) at subcarcinogenic doses and analyzed the mutation frequency and spectrum of the TL-associated genes Ikaros, Notch1, p53 and Kras. We found that the point mutation frequency in Ikaros was significantly increased to 47% for simultaneous exposure compared to 13 and 0% for X-ray and ENU exposure alone, respectively. These mutations were mostly G:C > A:T at non-CpG sites and T:A > C:G, both of which are characteristic of ENU mutagenesis. About half of the point mutations were accompanied by loss of heterozygosity (LOH), typical of X-irradiation. The remaining half did not include LOH, which suggests that they were dominant-negative mutations. In Notch1, the frequency of abnormalities was high (>58%) regardless of the treatment, suggesting that Notch1 aberration may be important for T-cell lymphomagenesis. The p53 and Kras mutation frequencies were low for all treatments (<23%). Importantly, the frequency of TLs containing mutations in multiple genes, especially both Ikaros and Notch1, increased after simultaneous exposure. Thus, after simultaneous exposure, Ikaros is a critical target and is inactivated by ENU-induced point mutations and/or X-ray-induced LOH in T-cell lymphomagenesis. Furthermore, concomitant alterations of multiple tumor-associated genes may contribute to enhanced lymphomagenesis after simultaneous exposure.

CXCR2 expression in tumor cells is a poor prognostic factor and promotes invasion and metastasis in lung adenocarcinoma

CXCR2 in non-small cell lung cancer (NSCLC) has been studied mainly in stromal cells and is known to increase tumor inflammation and angiogenesis. Here, we examined the prognostic importance of CXCR2 in NSCLC and the role of CXCR2 and its ligands in lung cancer cells. The effect of CXCR2 expression on tumor cells was studied using stable knockdown clones derived from a murine KRAS/p53-mutant lung adenocarcinoma cell line with high metastatic potential and an orthotopic syngeneic mouse model and in vitro using a CXCR2 small-molecule antagonist (SB225002). CXCR2 protein expression was analyzed in tumor cells from 262 NSCLC. Gene expression profiles for CXCR2 and its ligands (CXCR2 axis) were analyzed in 52 human NSCLC cell lines and 442 human lung adenocarcinomas. Methylation of CXCR2 axis promoters was determined in 70 human NSCLC cell lines. Invasion and metastasis were decreased in CXCR2 knockdown clones in vitro and in vivo. SB225002 decreased invasion in vitro. In lung adenocarcinomas, CXCR2 expression in tumor cells was associated with smoking and poor prognosis. CXCR2 axis gene expression profiles in human NSCLC cell lines and lung adenocarcinomas defined a cluster driven by CXCL5 and associated with smoking, poor prognosis, and RAS pathway activation. Expression of CXCL5 was regulated by promoter methylation. The CXCR2 axis may be an important target in smoking-related lung adenocarcinoma.

A synthetic matrix with independently tunable biochemistry and mechanical properties to study epithelial morphogenesis and EMT in a lung adenocarcinoma model

Better understanding of the biophysical and biochemical cues of the tumor extracellular matrix environment that influence metastasis may have important implications for new cancer therapeutics. Initial exploration into this question has used naturally derived protein matrices that suffer from variability, poor control over matrix biochemistry, and inability to modify the matrix biochemistry and mechanics. Here, we report the use of a synthetic polymer-based scaffold composed primarily of poly(ethylene glycol), or PEG, modified with bioactive peptides to study murine models of lung adenocarcinoma. In this study, we focus on matrix-derived influences on epithelial morphogenesis of a metastatic cell line (344SQ) that harbors mutations in Kras and p53 (trp53) and is prone to a microRNA-200 (miR-200)-dependent epithelial-mesenchymal transition (EMT) and metastasis. The modified PEG hydrogels feature biospecific cell adhesion and cell-mediated proteolytic degradation with independently adjustable matrix stiffness. 344SQ encapsulated in bioactive peptide-modified, matrix metalloproteinase-degradable PEG hydrogels formed lumenized epithelial spheres comparable to that seen with three-dimensional culture in Matrigel. Altering both matrix stiffness and the concentration of cell-adhesive ligand significantly influenced epithelial morphogenesis as manifest by differences in the extent of lumenization, in patterns of intrasphere apoptosis and proliferation, and in expression of epithelial polarity markers. Regardless of matrix composition, exposure to TGF-β induced a loss of epithelial morphologic features, shift in expression of EMT marker genes, and decrease in mir-200 levels consistent with EMT. Our findings help illuminate matrix-derived cues that influence epithelial morphogenesis and highlight the potential utility that this synthetic matrix-mimetic tool has for cancer biology.

ZEB1 drives prometastatic actin cytoskeletal remodeling by downregulating miR-34a expression

Metastatic cancer is extremely difficult to treat, and the presence of metastases greatly reduces a cancer patient's likelihood of long-term survival. The ZEB1 transcriptional repressor promotes metastasis through downregulation of microRNAs (miRs) that are strong inducers of epithelial differentiation and inhibitors of stem cell factors. Given that each miR can target multiple genes with diverse functions, we posited that the prometastatic network controlled by ZEB1 extends beyond these processes. We tested this hypothesis using a mouse model of human lung adenocarcinoma metastasis driven by ZEB1, human lung carcinoma cells, and human breast carcinoma cells. Transcriptional profiling studies revealed that ZEB1 controls the expression of numerous oncogenic and tumor-suppressive miRs, including miR-34a. Ectopic expression of miR-34a decreased tumor cell invasion and metastasis, inhibited the formation of promigratory cytoskeletal structures, suppressed activation of the RHO GTPase family, and regulated a gene expression signature enriched in cytoskeletal functions and predictive of outcome in human lung adenocarcinomas. We identified several miR-34a target genes, including Arhgap1, which encodes a RHO GTPase activating protein that was required for tumor cell invasion. These findings demonstrate that ZEB1 drives prometastatic actin cytoskeletal remodeling by downregulating miR-34a expression and provide a compelling rationale to develop miR-34a as a therapeutic agent in lung cancer patients.

ZEB1 drives prometastatic actin cytoskeletal remodeling by downregulating miR-34a expression

Metastatic cancer is extremely difficult to treat, and the presence of metastases greatly reduces a cancer patient's likelihood of long-term survival. The ZEB1 transcriptional repressor promotes metastasis through downregulation of microRNAs (miRs) that are strong inducers of epithelial differentiation and inhibitors of stem cell factors. Given that each miR can target multiple genes with diverse functions, we posited that the prometastatic network controlled by ZEB1 extends beyond these processes. We tested this hypothesis using a mouse model of human lung adenocarcinoma metastasis driven by ZEB1, human lung carcinoma cells, and human breast carcinoma cells. Transcriptional profiling studies revealed that ZEB1 controls the expression of numerous oncogenic and tumor-suppressive miRs, including miR-34a. Ectopic expression of miR-34a decreased tumor cell invasion and metastasis, inhibited the formation of promigratory cytoskeletal structures, suppressed activation of the RHO GTPase family, and regulated a gene expression signature enriched in cytoskeletal functions and predictive of outcome in human lung adenocarcinomas. We identified several miR-34a target genes, including Arhgap1, which encodes a RHO GTPase activating protein that was required for tumor cell invasion. These findings demonstrate that ZEB1 drives prometastatic actin cytoskeletal remodeling by downregulating miR-34a expression and provide a compelling rationale to develop miR-34a as a therapeutic agent in lung cancer patients.

Quantitative ex-vivo micro-computed tomographic imaging of blood vessels and necrotic regions within tumors

Techniques for visualizing and quantifying the microvasculature of tumors are essential not only for studying angiogenic processes but also for monitoring the effects of anti-angiogenic treatments. Given the relatively limited information that can be gleaned from conventional 2-D histological analyses, there has been considerable interest in methods that enable the 3-D assessment of the vasculature. To this end, we employed a polymerizing intravascular contrast medium (Microfil) and micro-computed tomography (micro-CT) in combination with a maximal spheres direct 3-D analysis method to visualize and quantify ex-vivo vessel structural features, and to define regions of hypoperfusion within tumors that would be indicative of necrosis. Employing these techniques we quantified the effects of a vascular disrupting agent on the tumor vasculature. The methods described herein for quantifying whole tumor vascularity represent a significant advance in the 3-D study of tumor angiogenesis and evaluation of novel therapeutics, and will also find potential application in other fields where quantification of blood vessel structure and necrosis are important outcome parameters.

Acquisition order of Ras and p53 gene alterations defines distinct adrenocortical tumor phenotypes

Sporadic adrenocortical carcinomas (ACC) are rare endocrine neoplasms with a dismal prognosis. By contrast, benign tumors of the adrenal cortex are common in the general population. Whether benign tumors represent a separate entity or are in fact part of a process of tumor progression ultimately leading to an ACC is still an unresolved issue. To this end, we have developed a mouse model of tumor progression by successively transducing genes altered in adrenocortical tumors into normal adrenocortical cells. The introduction in different orders of the oncogenic allele of Ras (H-Ras^G12V) and the mutant p53^DD that disrupts the p53 pathway yielded tumors displaying major differences in histological features, tumorigenicity, and metastatic behavior. Whereas the successive expression of Ras^G12V and p53^DD led to highly malignant tumors with metastatic behavior, reminiscent of those formed after the simultaneous introduction of p53^DD and Ras^G12V, the reverse sequence gave rise only to benign tumors. Microarray profiling revealed that 157 genes related to cancer development and progression were differentially expressed. Of these genes, 40 were up-regulated and 117 were down-regulated in malignant cell populations as compared with benign cell populations. This is the first evidence-based observation that ACC development follows a multistage progression and that the tumor phenotype is directly influenced by the order of acquisition of genetic alterations.

A sequential acquisition of genetic events is critical in tumorigenesis, and a dysregulation of a limited set of pathways has been demonstrated as sufficient to progressively transform normal cells into tumor cells in several human tissues. However, in the case of adrenocortical tumorigenesis, whether benign tumors represent a separate entity or are in fact part of a process of tumor progression leading ultimately to an adrenal carcinoma is still an unresolved issue. Moreover, the importance of the order in which these genetic events must occur to transform a cell has not been established. Here, we developed a tissue reconstruction model in mice that allows direct comparison of cells modified with sequential introduction of two genetic events. This revealed that adrenocortical tumor development follows a multistage progression and that the tumor phenotype, including histopathology and metastatic behavior, is directly influenced by the order of acquisition of genetic alterations.

Targets of the tumor suppressor miR-200 in regulation of the epithelial-mesenchymal transition in cancer

The microRNA-200 (miR-200) family restricts epithelial-mesenchymal transition (EMT) and metastasis in tumor cell lines derived from mice that develop metastatic lung adenocarcinoma. To determine the mechanisms responsible for EMT and metastasis regulated by this microRNA, we conducted a global liquid chromatography/tandem mass spectrometry analysis to compare metastatic and nonmetastatic murine lung adenocarcinoma cells which had undergone EMT because of loss of miR-200. An analysis of syngeneic tumors generated by these cells identified multiple novel proteins linked to metastasis. In particular, the analysis of conditioned media, cell surface proteins, and whole-cell lysates from metastatic and nonmetastatic cells revealed large-scale modifications in the tumor microenvironment. Specific increases were documented in extracellular matrix (ECM) proteins, peptidases, and changes in distribution of cell adhesion proteins in the metastatic cell lines. Integrating proteomic data from three subproteomes, we defined constituents of a multilayer protein network that both regulated and mediated the effects of TGFβ. Lastly, we identified ECM proteins and peptidases that were directly regulated by miR-200. Taken together, our results reveal how expression of miR-200 alters the tumor microenvironment to inhibit the processes of EMT and metastasis.

Multiple stress signals activate mutant p53 in vivo

p53 levels are tightly regulated in normal cells, and thus, the wild-type p53 protein is nearly undetectable until stimulated through a variety of stresses. In response to stress, p53 is released from its negative regulators, mainly murine double minute 2 (Mdm2), allowing p53 to be stabilized to activate cell-cycle arrest, senescence, and apoptosis programs. Many of the upstream signals that regulate wild-type p53 are known; however, limited information for the regulation of mutant p53 exists. Previously, we showed that wild-type and mutant p53R172H are regulated in a similar manner in the absence of Mdm2 or p16. In addition, this stabilization of mutant p53 is responsible for the gain-of-function metastatic phenotype observed in the mouse. In this report, we examined the role of oncogenes, DNA damage, and reactive oxygen species, signals that stabilize wild-type p53, on the stabilization of mutant p53 in vivo and the consequences of this expression on tumor formation and survival. These factors stabilized mutant p53 protein which oftentimes contributed to exacerbated tumor phenotypes. These findings, coupled with the fact that patients carry p53 mutations without stabilization of p53, suggest that personalized therapeutic schemes may be needed for individual patients depending on their p53 status.

Myc, Aurora Kinase A, and mutant p53(R172H) co-operate in a mouse model of metastatic skin carcinoma

Clinical observations, as well as data obtained from the analysis of genetically engineered mouse models, firmly established the gain-of-function (GOF) properties of certain p53 mutations. However, little is known about the underlying mechanisms. We have used two independent microarray platforms to perform a comprehensive and global analysis of tumors arising in a model of metastatic skin cancer progression, which compares the consequences of a GOF p53(R172H) mutant vs p53 deficiency. DNA profiling revealed a higher level of genomic instability in GOF vs loss-of-function (LOF) p53 squamous cell carcinomas (SCCs). Moreover, GOF p53 SCCs showed preferential amplification of Myc with a corresponding increase in its expression and deregulation of Aurora Kinase A. Fluorescent in situ hybridization confirmed amplification of Myc in primary GOF p53 SCCs and its retention in metastatic tumors. We also identified by RNA profiling distinct gene expression profiles in GOF p53 tumors, which included enriched integrin and Rho signaling, independent of tumor stage. Thus, the progression of GOF p53 papillomas to carcinoma was marked by the acquisition of epithelial-to-mesenchymal transition and metastatic signatures. In contrast, LOF p53 tumors showed enrichment of genes associated with cancer proliferation and chromosomal instability. Collectively, these observations suggest that genomic instability has a prominent role in the early stages of GOF p53 tumor progression (that is, papillomas), whereas it is implicated at a later stage in LOF p53 tumors (that is, SCCs). This model will allow us to identify specific targets in mutant p53 SCCs, which may lead to the development of new therapeutic agents for the treatment of metastatic SCCs.

Map2k4 functions as a tumor suppressor in lung adenocarcinoma and inhibits tumor cell invasion by decreasing peroxisome proliferator-activated receptor γ2 expression

MAP2K4 encodes a dual-specificity kinase (mitogen-activated protein kinase kinase 4, or MKK4) that is mutated in a variety of human malignancies, but the biochemical properties of the mutant kinases and their roles in tumorigenesis have not been fully elucidated. Here we showed that 8 out of 11 cancer-associated MAP2K4 mutations reduce MKK4 protein stability or impair its kinase activity. On the basis of findings from bioinformatic studies on human cancer cell lines with homozygous MAP2K4 loss, we posited that MKK4 functions as a tumor suppressor in lung adenocarcinomas that develop in mice owing to expression of mutant Kras and Tp53. Conditional Map2k4 inactivation in the bronchial epithelium of mice had no discernible effect alone but increased the multiplicity and accelerated the growth of incipient lung neoplasias induced by oncogenic Kras. MKK4 suppressed the invasion and metastasis of Kras-Tp53-mutant lung adenocarcinoma cells. MKK4 deficiency increased peroxisomal proliferator-activated receptor γ2 (PPARγ2) expression through noncanonical MKK4 substrates, and PPARγ2 enhanced tumor cell invasion. We conclude that Map2k4 functions as a tumor suppressor in lung adenocarcinoma and inhibits tumor cell invasion by decreasing PPARγ2 levels.

Identification of fat4 and tsc22d1 as novel candidate genes for spontaneous pulmonary adenomas

Genetic influences that underlie spontaneous lung oncogenesis are poorly understood. The objective of this study was to determine the genetic influences on spontaneous pulmonary adenoma frequency and severity in 28 strains of mice as part of a large-scale aging study conducted at the Jackson Aging Center (http://agingmice.jax.org/). Genome-wide association studies were conducted in these strains with both low-density (132,000) and high-density (4,000,000) panel of single-nucleotide polymorphisms (SNP). Our analysis revealed that adenomas were relatively less frequent and less severe in females than males, and that loci implicated in frequency and severity were often different between male and female mice. While some of the significant loci identified mapped to genomic locations known to be responsible for carcinogen-induced cancers (e.g., Pas1), others were unique to our study. In particular, Fat4 was influential in males and Tsc22d1 was influential in females. SNPs implicated were predicted to alter amino acid sequence and change protein function. In summary, our results suggested that genetic influences that underlie pulmonary adenoma frequency are dependent on gender, and that Fat4 and Tsc22d1 are likely candidate genes to influence formation of spontaneous pulmonary adenoma in aging male and female mice, respectively.

The Notch ligand Jagged2 promotes lung adenocarcinoma metastasis through a miR-200-dependent pathway in mice

Epithelial tumor cells transit to a mesenchymal state in response to extracellular cues, in a process known as epithelial-to-mesenchymal transition (EMT). The precise nature of these cues has not been fully defined, an important issue given that EMT is an early event in tumor metastasis. Here, we have found that a population of metastasis-prone mouse lung adenocarcinoma cells expresses Notch and Notch ligands and that the Notch ligand Jagged2 promotes metastasis. Mechanistically, Jagged2 was found to promote metastasis by increasing the expression of GATA-binding (Gata) factors, which suppressed expression of the microRNA-200 (miR-200) family of microRNAs that target the transcriptional repressors that drive EMT and thereby induced EMT. Reciprocally, miR-200 inhibited expression of Gata3, which reversed EMT and abrogated metastasis, suggesting that Gata3 and miR-200 are mutually inhibitory and have opposing effects on EMT and metastasis. Consistent with this, high levels of Gata3 expression correlated with EMT in primary tumors from 2 cohorts of lung adenocarcinoma patients. These findings reveal what we believe to be a novel Jagged2/miR-200-dependent pathway that mediates lung adenocarcinoma EMT and metastasis in mice and may have implications for the treatment of human epithelial tumors.

miR-200 Inhibits lung adenocarcinoma cell invasion and metastasis by targeting Flt1/VEGFR1

The microRNA-200 (miR-200) family is part of a gene expression signature that predicts poor prognosis in lung cancer patients. In a mouse model of K-ras/p53-mutant lung adenocarcinoma, miR-200 levels are suppressed in metastasis-prone tumor cells, and forced miR-200 expression inhibits tumor growth and metastasis, but the miR-200 target genes that drive lung tumorigenesis have not been fully elucidated. Here, we scanned the genome for putative miR-200 binding sites and found them in the 3'-untranslated region (3'-UTR) of 35 genes that are amplified in human cancer. Mining of a database of resected human lung adenocarcinomas revealed that the levels of one of these genes, Flt1/VEGFR1, correlate inversely with duration of survival. Forced miR-200 expression suppressed Flt1 levels in metastasis-prone lung adenocarcinoma cells derived from K-ras/p53-mutant mice, and negatively regulated the Flt1 3'-UTR in reporter assays. Cancer-associated fibroblasts (CAFs) isolated from murine lung adenocarcinomas secreted abundant VEGF and enhanced tumor cell invasion in coculture studies. CAF-induced tumor cell invasion was abrogated by VEGF neutralization or Flt1 knockdown in tumor cells. Flt1 knockdown decreased the growth and metastasis of tumor cells in syngeneic mice. We conclude that miR-200 suppresses lung tumorigenesis by targeting Flt1.

Novel insights into the molecular origins and treatment of lung cancer

Lung cancer is the most common and most deadly cancer worldwide. Because of the aggressive and metastatic nature of many forms of the disease, it is frequently diagnosed late and responds poorly to the therapies currently available. Although our understanding of the molecular origins and evolution of lung cancer is still incomplete, recent research has yielded several developments that may offer opportunities for new, targeted and effective therapy. In this review we first discuss the prevalence and origins of lung cancer, with emphasis on non-small-cell lung cancer and adenocarcinoma, together with current treatments and their efficacy. We then look at a selection of recent papers which between them shed new light on possible therapeutic opportunities, including a novel synthetic interaction with the Kras gene and genomic or proteomic profiling studies that may pave the way for personalized treatment for lung cancer based on specific "signatures" of protein and gene expression. Lung cancer remains the foremost cause of cancer deaths worldwide. Despite advances in both detection and treatment, diagnosis is often late and the prognosis for patients poor. Our understanding of the molecular basis and progression of lung cancer remains incomplete, hampering the design and development of more effective diagnostic tools and therapies for this devastating disease. However, the last twelve months have witnessed the publication of several studies that represent significant advances in our knowledge of lung cancer, and may represent important steps on the road to effective new therapies. In this review we aim to summarize these recent developments, and give our perspectives on the therapeutic possibilities they may offer in the future.

You can win by losing: p53 mutations in rhabdomyosarcomas

Rhabdomyosarcomas are soft tissue sarcomas of mesenchymal origin. Unlike rhabdomyosarcomas observed in paediatric patients which typically respond well to chemotherapeutic treatment, adults generally present with pleomorphic rhabdomyosarcomas that are typically associated with poor prognosis. Therefore, understanding the molecular biology that gives rise to pleomorphic rhabdomyosarcomas is critical. In this issue of The Journal of Pathology, Doyle and colleagues have generated elegant tissue-specific Cre/loxP-dependent mouse models that mimic pleomorphic rhabdomyosarcoma development in humans. In this report, the authors employed KRas(G12V)-expressing mouse models that concomitantly either express mutant p53 (p53R172H) or have deleted the p53 gene. Mice that express mutant p53 have decreased survival with development of aggressive metastases as compared to mice that have simply lost wild-type p53. The data presented herein provide the first in vivo evidence that in rhabdomyosarcomas, expression of mutant p53 results in a more aggressive p53R172H-dependent gain-of-function phenotype.

Contextual extracellular cues promote tumor cell EMT and metastasis by regulating miR-200 family expression

Metastatic disease is a primary cause of cancer-related death, and factors governing tumor cell metastasis have not been fully elucidated. Here, we address this question by using tumor cell lines derived from mice that develop metastatic lung adenocarcinoma owing to expression of mutant K-ras and p53. Despite having widespread somatic genetic alterations, the metastasis-prone tumor cells retained a marked plasticity. They transited reversibly between epithelial and mesenchymal states, forming highly polarized epithelial spheres in three-dimensional culture that underwent epithelial-to-mesenchymal transition (EMT) following treatment with transforming growth factor-beta or injection into syngeneic mice. This transition was entirely dependent on the microRNA (miR)-200 family, which decreased during EMT. Forced expression of miR-200 abrogated the capacity of these tumor cells to undergo EMT, invade, and metastasize, and conferred transcriptional features of metastasis-incompetent tumor cells. We conclude that tumor cell metastasis is regulated by miR-200 expression, which changes in response to contextual extracellular cues.

Contextual extracellular cues promote tumor cell EMT and metastasis by regulating miR-200 family expression

Metastatic disease is a primary cause of cancer-related death, and factors governing tumor cell metastasis have not been fully elucidated. Here, we address this question by using tumor cell lines derived from mice that develop metastatic lung adenocarcinoma owing to expression of mutant K-ras and p53. Despite having widespread somatic genetic alterations, the metastasis-prone tumor cells retained a marked plasticity. They transited reversibly between epithelial and mesenchymal states, forming highly polarized epithelial spheres in three-dimensional culture that underwent epithelial-to-mesenchymal transition (EMT) following treatment with transforming growth factor-beta or injection into syngeneic mice. This transition was entirely dependent on the microRNA (miR)-200 family, which decreased during EMT. Forced expression of miR-200 abrogated the capacity of these tumor cells to undergo EMT, invade, and metastasize, and conferred transcriptional features of metastasis-incompetent tumor cells. We conclude that tumor cell metastasis is regulated by miR-200 expression, which changes in response to contextual extracellular cues.

WNT/TCF signaling through LEF1 and HOXB9 mediates lung adenocarcinoma metastasis

Metastasis from lung adenocarcinoma can occur swiftly to multiple organs within months of diagnosis. The mechanisms that confer this rapid metastatic capacity to lung tumors are unknown. Activation of the canonical WNT/TCF pathway is identified here as a determinant of metastasis to brain and bone during lung adenocarcinoma progression. Gene expression signatures denoting WNT/TCF activation are associated with relapse to multiple organs in primary lung adenocarcinoma. Metastatic subpopulations isolated from independent lymph node-derived lung adenocarcinoma cell lines harbor a hyperactive WNT/TCF pathway. Reduction of TCF activity in these cells attenuates their ability to form brain and bone metastases in mice, independently of effects on tumor growth in the lungs. The WNT/TCF target genes HOXB9 and LEF1 are identified as mediators of chemotactic invasion and colony outgrowth. Thus, a distinct WNT/TCF signaling program through LEF1 and HOXB9 enhances the competence of lung adenocarcinoma cells to colonize the bones and the brain. For a video summary of this article, see the PaperFlick file available with the online Supplemental Data.

Expression signatures of metastatic capacity in a genetic mouse model of lung adenocarcinoma

Background

Non-small cell lung cancer (NSCLC) is the foremost cause of cancer-related death in Western countries, which is due partly to the propensity of NSCLC cells to metastasize. The biologic basis for NSCLC metastasis is not well understood.

Methodology/Principal Findings

Here we addressed this deficiency by transcriptionally profiling tumors from a genetic mouse model of human lung adenocarcinoma that develops metastatic disease owing to the expression of K-ras^G12D and p53^R172H. We identified 2,209 genes that were differentially expressed in distant metastases relative to matched lung tumors. Mining of publicly available data bases revealed this expression signature in a subset of NSCLC patients who had a poorer prognosis than those without the signature.

Conclusions/Significance

These findings provide evidence that K-ras^G12D; p53^R172H mice recapitulate features of human NSCLC metastasis and will provide a useful platform on which to study the biologic basis for lung adenocarcinoma metastasis and its prevention by novel agents.