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1.  Reduced NF1 expression confers resistance to EGFR inhibition in lung cancer 
Cancer discovery  2014;4(5):606-619.
Activating mutations in the EGF receptor (EGFR) are associated with clinical responsiveness to EGFR tyrosine kinase inhibitors (TKIs), such as erlotinib and gefitinib. However, resistance eventually arises, often due to a second EGFR mutation, most commonly T790M. Through a genome-wide siRNA screen in a human lung cancer cell line and analyses of murine mutant EGFR-driven lung adenocarcinomas, we found that erlotinib resistance was associated with reduced expression of neurofibromin, the RAS GTPase activating protein encoded by the NF1 gene. Erlotinib failed to fully inhibit RAS-ERK signaling when neurofibromin levels were reduced. Treatment of neurofibromin-deficient lung cancers with a MEK inhibitor restored sensitivity to erlotinib. Low levels of NF1 expression were associated with primary and acquired resistance of lung adenocarcinomas to EGFR TKIs in patients. These findings identify a subgroup of patients with EGFR mutant lung adenocarcinoma who might benefit from combination therapy with EGFR and MEK inhibitors.
PMCID: PMC4011693  PMID: 24535670
NF1; EGFR; KRAS; MAPK pathway; drug resistance; erlotinib; gefitinib; lung adenocarcinoma
2.  Reduced NF1 expression confers resistance to EGFR inhibition in lung cancer 
Cancer discovery  2014;4(5):606-619.
Activating mutations in the EGF receptor (EGFR) are associated with clinical responsiveness to EGFR tyrosine kinase inhibitors (TKIs), such as erlotinib and gefitinib. However, resistance eventually arises, often due to a second EGFR mutation, most commonly T790M. Through a genome-wide siRNA screen in a human lung cancer cell line and analyses of murine mutant EGFR-driven lung adenocarcinomas, we found that erlotinib resistance was associated with reduced expression of neurofibromin, the RAS GTPase activating protein encoded by the NF1 gene. Erlotinib failed to fully inhibit RAS-ERK signaling when neurofibromin levels were reduced. Treatment of neurofibromin-deficient lung cancers with a MEK inhibitor restored sensitivity to erlotinib. Low levels of NF1 expression were associated with primary and acquired resistance of lung adenocarcinomas to EGFR TKIs in patients. These findings identify a subgroup of patients with EGFR mutant lung adenocarcinoma who might benefit from combination therapy with EGFR and MEK inhibitors.
PMCID: PMC4011693  PMID: 24535670
NF1; EGFR; KRAS; MAPK pathway; drug resistance; erlotinib; gefitinib; lung adenocarcinoma
3.  DOK2 Inhibits EGFR-Mutated Lung Adenocarcinoma 
PLoS ONE  2013;8(11):e79526.
Somatic mutations in the EGFR proto-oncogene occur in ~15% of human lung adenocarcinomas and the importance of EGFR mutations for the initiation and maintenance of lung cancer is well established from mouse models and cancer therapy trials in human lung cancer patients. Recently, we identified DOK2 as a lung adenocarcinoma tumor suppressor gene. Here we show that genomic loss of DOK2 is associated with EGFR mutations in human lung adenocarcinoma, and we hypothesized that loss of DOK2 might therefore cooperate with EGFR mutations to promote lung tumorigenesis. We tested this hypothesis using genetically engineered mouse models and find that loss of Dok2 in the mouse accelerates lung tumorigenesis initiated by oncogenic EGFR, but not that initiated by mutated Kras. Moreover, we find that DOK2 participates in a negative feedback loop that opposes mutated EGFR; EGFR mutation leads to recruitment of DOK2 to EGFR and DOK2-mediated inhibition of downstream activation of RAS. These data identify DOK2 as a tumor suppressor in EGFR-mutant lung adenocarcinoma.
PMCID: PMC3821857  PMID: 24255704
4.  Epstein-Barr Virus: An Important Vaccine Target for Cancer Prevention 
Science translational medicine  2011;3(107):107fs7.
Participants at the February 2011 meeting at the U.S. National Institutes of Health on Epstein-Barr virus (EBV) vaccine research recommend that future clinical trials have two goals: prevention of infectious mononucleosis and EBV-associated cancers, facilitated by identification of disease-predictive surrogate markers.
PMCID: PMC3501269  PMID: 22049067
5.  Identification and preliminary characterization of novel small molecules that inhibit growth of human lung adenocarcinoma cells 
Journal of biomolecular screening  2009;14(10):1176-1184.
Drug treatment for human lung cancers remains unsatisfactory, despite the identification of many potential therapeutic targets (such as mutant KRAS protein) and the approval of agents that inhibit the tyrosine kinase activity of mutant epidermal growth factor receptor (EGFR). To seek new therapeutic strategies against lung tumors, we have screened 189, 290 small molecules for their ability to retard growth of human lung adenocarcinoma cell lines, which harbor mutations in EGFR or KRAS. Four candidates that are structurally different from common tyrosine kinase inhibitors were selected for further study. We describe one small molecule (designated lung cancer screen-1, LCS-1) in detail here. Identification of the targets of LCS-1 and other growth inhibitors found in this screen may help to develop new agents for treatment of lung adenocarcinomas, including those driven by mutant EGFR and KRAS.
PMCID: PMC3146390  PMID: 19887599
high throughput drug screen; lung cancer; EGFR; KRAS
8.  Cell-Specific Transduction of Prdm1-Expressing Lineages Mediated by a Receptor for Avian Leukosis Virus Subgroup B▿ †  
Journal of Virology  2009;83(10):4835-4843.
The transcription factor Blimp-1 has emerged as a regulator of cell fate in embryonic (germ cell) and adult (B- and T-cell immune effector and epithelial) lineages. It has also been proposed to act as a tumor suppressor in B-cell malignancy. Here, we present a novel in vivo system enabling the targeted genetic manipulation of cells expressing Prdm1, the gene encoding Blimp-1. We created bacterial artificial chromosome-transgenic mice expressing the avian leukosis virus (ALV) receptor TVB, fused to monomeric red fluorescent protein, under regulation by Prdm1 transcriptional elements, and we achieved transduction of TVB-expressing lymphocytes by ALV vectors bearing a subgroup B envelope. The system presented here incorporates a number of innovations. First, it is the first mammalian transgenic system that employs the ALV receptor TVB, thus expanding the flexibility and scope of ALV-mediated gene delivery. Second, it represents the first ALV-based system that allows gene transfer and expression into in vivo-activated mature lymphocytes, a cell type that has traditionally presented formidable challenges to efficient retroviral transduction. Third, Prdm1:TVB-mRFP transgenic animals could provide an invaluable tool for exploring the diverse roles of Blimp-1 in lineage commitment, immune regulation, and tumorigenesis.
PMCID: PMC2682090  PMID: 19279099
9.  MYC-induced myeloid leukemogenesis is accelerated by all six members of the anti-apoptotic BCL family 
Oncogene  2009;28(9):1274-1279.
Signals that control the fine balance between cell death and cell survival are altered in cells during tumorigenesis. Understanding the mechanisms by which this balance is perturbed, leading to excessive cell survival, is important for designing effective therapies. Proteins belonging to the BCL family are known to regulate death responses to apoptotic signals, especially those originating within cells. A subset of BCL family members capable of inhibiting cell death is known to contribute to tumorigenesis; however, it is not known whether all six anti-apoptotic BCL family members play a causal role in tumor development. Using a mouse model of MYC-driven leukemia we demonstrate that, in addition to the well characterized BCL2 and BCLxl (BCL2L1), the other four family members- BCLw (BCL2L2), BCLb (BCL2L10), BFL1 (BCL2A1), and MCL1- also cooperate with MYC to accelerate leukemogenesis. In addition, high levels of each family member are found in either solid human tumors or cell lines derived from human leukemias or lymphomas.
PMCID: PMC2743088  PMID: 19137012
10.  Activation of PyMT in β Cells Induces Irreversible Hyperplasia, but Oncogene-Dependent Acinar Cell Carcinomas When Activated in Pancreatic Progenitors 
PLoS ONE  2009;4(9):e6932.
It is unclear whether the cellular origin of various forms of pancreatic cancer involves transformation or transdifferentiation of different target cells or whether tumors arise from common precursors, with tumor types determined by the specific genetic alterations. Previous studies suggested that pancreatic ductal carcinomas might be induced by polyoma middle T antigen (PyMT) expressed in non-ductal cells. To ask whether PyMT transforms and transdifferentiates endocrine cells toward exocrine tumor phenotypes, we generated transgenic mice that carry tetracycline-inducible PyMT and a linked luciferase reporter. Induction of PyMT in β cells causes β-cell hyperplastic lesions that do not progress to malignant neoplasms. When PyMT is de-induced, β cell proliferation and growth cease; however, regression does not occur, suggesting that continued production of PyMT is not required to maintain the viable expanded β cell population. In contrast, induction of PyMT in early pancreatic progenitor cells under the control of Pdx1 produces acinar cell carcinomas and β-cell hyperplasia. The survival of acinar tumor cells is dependent on continued expression of PyMT. Our findings indicate that PyMT can induce exocrine tumors from pancreatic progenitor cells, but cells in the β cell lineage are not transdifferentiated toward exocrine cell types by PyMT; instead, they undergo oncogene-dependent hyperplastic growth, but do not require PyMT for survival.
PMCID: PMC2758666  PMID: 19812721
11.  The Knockout Mouse Project 
Nature genetics  2004;36(9):921-924.
Mouse knockout technology provides a powerful means of elucidating gene function in vivo, and a publicly available genome-wide collection of mouse knockouts would be significantly enabling for biomedical discovery. To date, published knockouts exist for only about 10% of mouse genes. Furthermore, many of these are limited in utility because they have not been made or phenotyped in standardized ways, and many are not freely available to researchers. It is time to harness new technologies and efficiencies of production to mount a high-throughput international effort to produce and phenotype knockouts for all mouse genes, and place these resources into the public domain.
PMCID: PMC2716027  PMID: 15340423
12.  Somatic mutations affect key pathways in lung adenocarcinoma 
Ding, Li | Getz, Gad | Wheeler, David A. | Mardis, Elaine R. | McLellan, Michael D. | Cibulskis, Kristian | Sougnez, Carrie | Greulich, Heidi | Muzny, Donna M. | Morgan, Margaret B. | Fulton, Lucinda | Fulton, Robert S. | Zhang, Qunyuan | Wendl, Michael C. | Lawrence, Michael S. | Larson, David E. | Chen, Ken | Dooling, David J. | Sabo, Aniko | Hawes, Alicia C. | Shen, Hua | Jhangiani, Shalini N. | Lewis, Lora R. | Hall, Otis | Zhu, Yiming | Mathew, Tittu | Ren, Yanru | Yao, Jiqiang | Scherer, Steven E. | Clerc, Kerstin | Metcalf, Ginger A. | Ng, Brian | Milosavljevic, Aleksandar | Gonzalez-Garay, Manuel L. | Osborne, John R. | Meyer, Rick | Shi, Xiaoqi | Tang, Yuzhu | Koboldt, Daniel C. | Lin, Ling | Abbott, Rachel | Miner, Tracie L. | Pohl, Craig | Fewell, Ginger | Haipek, Carrie | Schmidt, Heather | Dunford-Shore, Brian H. | Kraja, Aldi | Crosby, Seth D. | Sawyer, Christopher S. | Vickery, Tammi | Sander, Sacha | Robinson, Jody | Winckler, Wendy | Baldwin, Jennifer | Chirieac, Lucian R. | Dutt, Amit | Fennell, Tim | Hanna, Megan | Johnson, Bruce E. | Onofrio, Robert C. | Thomas, Roman K. | Tonon, Giovanni | Weir, Barbara A. | Zhao, Xiaojun | Ziaugra, Liuda | Zody, Michael C. | Giordano, Thomas | Orringer, Mark B. | Roth, Jack A. | Spitz, Margaret R. | Wistuba, Ignacio I. | Ozenberger, Bradley | Good, Peter J. | Chang, Andrew C. | Beer, David G. | Watson, Mark A. | Ladanyi, Marc | Broderick, Stephen | Yoshizawa, Akihiko | Travis, William D. | Pao, William | Province, Michael A. | Weinstock, George M. | Varmus, Harold E. | Gabriel, Stacey B. | Lander, Eric S. | Gibbs, Richard A. | Meyerson, Matthew | Wilson, Richard K.
Nature  2008;455(7216):1069-1075.
Determining the genetic basis of cancer requires comprehensive analyses of large collections of histopathologically well-classified primary tumours. Here we report the results of a collaborative study to discover somatic mutations in 188 human lung adenocarcinomas. DNA sequencing of 623 genes with known or potential relationships to cancer revealed more than 1,000 somatic mutations across the samples. Our analysis identified 26 genes that are mutated at significantly high frequencies and thus are probably involved in carcinogenesis. The frequently mutated genes include tyrosine kinases, among them the EGFR homologue ERBB4; multiple ephrin receptor genes, notably EPHA3; vascular endothelial growth factor receptor KDR; and NTRK genes. These data provide evidence of somatic mutations in primary lung adenocarcinoma for several tumour suppressor genes involved in other cancers—including NF1, APC, RB1 and ATM—and for sequence changes in PTPRD as well as the frequently deleted gene LRP1B. The observed mutational profiles correlate with clinical features, smoking status and DNA repair defects. These results are reinforced by data integration including single nucleotide polymorphism array and gene expression array. Our findings shed further light on several important signalling pathways involved in lung adenocarcinoma, and suggest new molecular targets for treatment.
PMCID: PMC2694412  PMID: 18948947
13.  Seeding and Propagation of Untransformed Mouse Mammary Cells in the Lung 
Science (New York, N.Y.)  2008;321(5897):1841-1844.
The acquisition of metastatic ability by tumor cells is considered a late event in the evolution of malignant tumors. We report that untransformed mouse mammary cells that have been engineered to express the inducible oncogenic transgenes MYC and KrasD12, or polyoma middle T, and introduced into the systemic circulation of a mouse can bypass transformation at the primary site and develop into metastatic pulmonary lesions upon immediate or delayed oncogene induction. Therefore, previously untransformed mammary cells may establish residence in the lung once they have entered the bloodstream and may assume malignant growth upon oncogene activation. Mammary cells lacking oncogenic transgenes displayed a similar capacity for long-term residence in the lungs but did not form ectopic tumors.
PMCID: PMC2694414  PMID: 18755941
14.  Characterizing the cancer genome in lung adenocarcinoma 
Nature  2007;450(7171):893-898.
Somatic alterations in cellular DNA underlie almost all human cancers1. The prospect of targeted therapies2 and the development of high-resolution, genome-wide approaches3–8 are now spurring systematic efforts to characterize cancer genomes. Here we report a large-scale project to characterize copy-number alterations in primary lung adenocarcinomas. By analysis of a large collection of tumors (n = 371) using dense single nucleotide polymorphism arrays, we identify a total of 57 significantly recurrent events. We find that 26 of 39 autosomal chromosome arms show consistent large-scale copy-number gain or loss, of which only a handful have been linked to a specific gene. We also identify 31 recurrent focal events, including 24 amplifications and 7 homozygous deletions. Only six of these focal events are currently associated with known mutations in lung carcinomas. The most common event, amplification of chromosome 14q13.3, is found in ~12% of samples. On the basis of genomic and functional analyses, we identify NKX2-1 (NK2 homeobox 1, also called TITF1), which lies in the minimal 14q13.3 amplification interval and encodes a lineage-specific transcription factor, as a novel candidate proto-oncogene involved in a significant fraction of lung adenocarcinomas. More generally, our results indicate that many of the genes that are involved in lung adenocarcinoma remain to be discovered.
PMCID: PMC2538683  PMID: 17982442
15.  The Classic: Integration of Deoxyribonucleic Acid Specific for Rous Sarcoma Virus after Infection of Permissive and Nonpermissive Hosts 
A relatively simple but stringent technique was developed to detect the integration of virus-specific DNA into the genomes of higher organisms. In both permissive (duck) and nonpermissive (mammalian) cells which normally contain no nucleotide sequences specific for Rous sarcoma virus, transformation by the virus results in the appearance of DNA specific for Rous sarcoma virus covalently integrated into strands of host-cell DNA containing reiterated sequences. Early after infection of mouse or duck cells by Rous sarcoma virus, unintegrated DNA specific for the virus can be demonstrated.
PMCID: PMC2493013  PMID: 18597148
16.  Progress toward Public Access to Science 
PLoS Biology  2008;6(4):e101.
PLoS Chairman of the Board Harold Varmus applauds the newly enacted NIH public access policy as a positive step toward ensuring greater access to and better use of the scientific literature.
PMCID: PMC2288632  PMID: 18399723
17.  Induction of ovarian cancer by defined multiple genetic changes in a mouse model system 
Cancer cell  2002;1(1):53-62.
We have developed a mouse model for ovarian carcinoma by using an avian retroviral gene delivery technique for the introduction of multiple genes into somatic ovarian cells of adult mice. Ovarian cells from transgenic mice engineered to express the gene encoding the avian receptor TVA were efficiently infected in vitro with multiple vectors carrying coding sequences for oncogenes and marker genes. When target cells were derived from TVA transgenic mice deficient for p53, the addition of any two of the oncogenes c-myc, K-ras, and Akt were sufficient to induce ovarian tumor formation when infected cells were injected at subcutaneous, intraperitoneal, or ovarian sites. We demonstrated that the ovarian surface epithelium is the precursor tissue for these ovarian carcinomas, and that introduction of oncogenes causes phenotypic changes in the ovarian surface epithelial cells. The induced ovarian tumors in mice resembled human ovarian carcinomas in their rapid progression and intraperitoneal metastatic spread.
PMCID: PMC2267863  PMID: 12086888
18.  Assessing Tumor Progression Factors by Somatic Gene Transfer into a Mouse Model: Bcl-xL Promotes Islet Tumor Cell Invasion 
PLoS Biology  2007;5(10):e276.
Tumors develop through multiple stages, implicating multiple effectors, but the tools to assess how candidate genes contribute to stepwise tumor progression have been limited. We have developed a novel system in which progression of phenotypes in a mouse model of pancreatic islet cell tumorigenesis can be used to measure the effects of genes introduced by cell-type-specific infection with retroviral vectors. In this system, bitransgenic mice, in which the rat insulin promoter (RIP) drives expression of both the SV40 T antigen (RIP-Tag) and the receptor for subgroup A avian leukosis virus (RIP-tva), are infected with avian viral vectors carrying cDNAs encoding candidate progression factors. Like RIP-Tag mice, RIP-Tag; RIP-tva bitransgenic mice develop isolated carcinomas by ∼14 wk of age, after progression through well-defined stages that are similar to aspects of human tumor progression, including hyperplasia, angiogenesis, adenoma, and invasive carcinoma. When avian retroviral vectors carrying a green fluorescent protein marker were introduced into RIP-Tag; RIP-tva mice by intra-cardiac injection at the hyperplastic or early dysplastic stage of tumorigenesis, approximately 20% of the TVA-positive cells were infected and expressed green fluorescent proteins as measured by flow cytometry. Similar infection with vectors carrying cDNA encoding either of two progression factors, a dominant-negative version of cadherin 1 (dnE-cad) or Bcl-xL, accelerated the formation of islet tumors with invasive properties and pancreatic lymph node metastasis. To begin studying the mechanism by which Bcl-xL, an anti-apoptotic protein, promotes invasion and metastasis, RIP-Tag; RIP-tva pancreatic islet tumor cells were infected in vitro with RCASBP-Bcl-xL. Although no changes were observed in rates of proliferation or apoptosis, Bcl-xL altered cell morphology, remodeled the actin cytoskeleton, and down-regulated cadherin 1; it also induced cell migration and invasion, as evaluated using two-chamber transwell assays. In addition, myosin Va was identified as a novel Bcl-xL-interacting protein that might mediate the effects of Bcl-xL on tumor cell migration and invasion.
Author Summary
Cancer cells accumulate multiple genetic alterations. Some of these contribute to tumor development while others are a mere by-product of genomic instability. To determine whether a candidate gene can promote tumor development, we have developed a novel experimental system using engineered viruses to deliver genes into premalignant lesions. We used genetically engineered mice in which both an oncogene (SV40 T antigen) and a specific docking molecule for the virus are produced in β cells in the pancreatic islets of Langerhans. Tumors form in only a subset of the islets expressing this oncogene, indicating that tumor development requires other events. Since these precancerous cells also express the virus docking molecule, we could deliver candidate progression genes via the virus to see whether they contributed to tumor progression. We show that genes encoding two proteins (a survival factor, Bcl-xL, and an inhibitory form of the cell adhesion molecule cadherin 1) can be delivered into premalignant β cells and thereby enhance tumorigenesis. Both of these proteins were previously implicated in tumor progression, confirming that our technique can identify such progression genes. Moreover, we find that Bcl-xL promotes tumor cell migration and invasion by a mechanism distinct from its known role in cell survival.
A new technique using lentivirus to deliver genes into targeted cell types reveals that the tumor progression geneBcl-xL not only promotes cell survival in premalignant cells but also promotes tumor cell invasion.
PMCID: PMC2020504  PMID: 17941720
19.  Mutational Analysis of EGFR and Related Signaling Pathway Genes in Lung Adenocarcinomas Identifies a Novel Somatic Kinase Domain Mutation in FGFR4 
PLoS ONE  2007;2(5):e426.
Fifty percent of lung adenocarcinomas harbor somatic mutations in six genes that encode proteins in the EGFR signaling pathway, i.e., EGFR, HER2/ERBB2, HER4/ERBB4, PIK3CA, BRAF, and KRAS. We performed mutational profiling of a large cohort of lung adenocarcinomas to uncover other potential somatic mutations in genes of this signaling pathway that could contribute to lung tumorigenesis.
Methodology/Principal Findings
We analyzed genomic DNA from a total of 261 resected, clinically annotated non-small cell lung cancer (NSCLC) specimens. The coding sequences of 39 genes were screened for somatic mutations via high-throughput dideoxynucleotide sequencing of PCR-amplified gene products. Mutations were considered to be somatic only if they were found in an independent tumor-derived PCR product but not in matched normal tissue. Sequencing of 9MB of tumor sequence identified 239 putative genetic variants. We further examined 22 variants found in RAS family genes and 135 variants localized to exons encoding the kinase domain of respective proteins. We identified a total of 37 non-synonymous somatic mutations; 36 were found collectively in EGFR, KRAS, BRAF, and PIK3CA. One somatic mutation was a previously unreported mutation in the kinase domain (exon 16) of FGFR4 (Glu681Lys), identified in 1 of 158 tumors. The FGFR4 mutation is analogous to a reported tumor-specific somatic mutation in ERBB2 and is located in the same exon as a previously reported kinase domain mutation in FGFR4 (Pro712Thr) in a lung adenocarcinoma cell line.
This study is one of the first comprehensive mutational analyses of major genes in a specific signaling pathway in a sizeable cohort of lung adenocarcinomas. Our results suggest the majority of gain-of-function mutations within kinase genes in the EGFR signaling pathway have already been identified. Our findings also implicate FGFR4 in the pathogenesis of a subset of lung adenocarcinomas.
PMCID: PMC1855985  PMID: 17487277
20.  Changes in gene expression during the development of mammary tumors in MMTV-Wnt-1 transgenic mice 
Genome Biology  2005;6(10):R84.
cDNA microarray-derived expression profiles of MMTV-Wnt-1 and MMTV-Neu transgenic mice reveal several hundred genes to be differentially expressed at each stage of breast tumor development.
In human breast cancer normal mammary cells typically develop into hyperplasia, ductal carcinoma in situ, invasive cancer, and metastasis. The changes in gene expression associated with this stepwise progression are unclear. Mice transgenic for mouse mammary tumor virus (MMTV)-Wnt-1 exhibit discrete steps of mammary tumorigenesis, including hyperplasia, invasive ductal carcinoma, and distant metastasis. These mice might therefore be useful models for discovering changes in gene expression during cancer development.
We used cDNA microarrays to determine the expression profiles of five normal mammary glands, seven hyperplastic mammary glands and 23 mammary tumors from MMTV-Wnt-1 transgenic mice, and 12 mammary tumors from MMTV-Neu transgenic mice. Adipose tissues were used to control for fat cells in the vicinity of the mammary glands. In these analyses, we found that the progression of normal virgin mammary glands to hyperplastic tissues and to mammary tumors is accompanied by differences in the expression of several hundred genes at each step. Some of these differences appear to be unique to the effects of Wnt signaling; others seem to be common to tumors induced by both Neu and Wnt-1 oncogenes.
We described gene-expression patterns associated with breast-cancer development in mice, and identified genes that may be significant targets for oncogenic events. The expression data developed provide a resource for illuminating the molecular mechanisms involved in breast cancer development, especially through the identification of genes that are critical in cancer initiation and progression.
PMCID: PMC1257467  PMID: 16207355
21.  The Absence of p53 Promotes Metastasis in a Novel Somatic Mouse Model for Hepatocellular Carcinoma†  
Molecular and Cellular Biology  2005;25(4):1228-1237.
We have generated a mouse model for hepatocellular carcinoma using somatic delivery of oncogene-bearing avian retroviral vectors to the liver cells of mice expressing the viral receptor TVA under the control of the albumin gene promoter (Alb-TVA mice). Viruses encoding mouse polyoma virus middle T antigen (PyMT) induced tumors, which can be visualized with magnetic resonance imaging, in 65% of TVA-positive animals. While these tumors can exceed 10 mm in diameter, they do not invade locally or metastasize to the lungs. Delivery of PyMT-expressing viruses to Alb-TVA mice lacking an intact p53 gene does not increase tumor incidence. However, the resulting tumors are poorly differentiated, invasive, and metastatic to the lungs. Gene expression microarrays identified over 100 genes that are differentially expressed between tumors found in p53 wild-type and p53 null mice. Some of these genes, such as cathepsin E and Igf2, have been previously implicated in tumor cell migration and invasion. Tumors induced in p53 null, TVA transgenic mice by PyMT mutants with changes in specific tyrosine residues fail to form metastases, indicating that metastasis is dependent on both the oncogene and the absence of p53.
PMCID: PMC548003  PMID: 15684377
22.  KRAS Mutations and Primary Resistance of Lung Adenocarcinomas to Gefitinib or Erlotinib 
PLoS Medicine  2005;2(1):e17.
Somatic mutations in the gene for the epidermal growth factor receptor (EGFR) are found in adenocarcinomas of the lung and are associated with sensitivity to the kinase inhibitors gefitinib (Iressa) and erlotinib (Tarceva). Lung adenocarcinomas also harbor activating mutations in the downstream GTPase, KRAS, and mutations in EGFR and KRAS appear to be mutually exclusive.
Methods and Findings
We sought to determine whether mutations in KRAS could be used to further enhance prediction of response to gefitinib or erlotinib. We screened 60 lung adenocarcinomas defined as sensitive or refractory to gefitinib or erlotinib for mutations in EGFR and KRAS. We show that mutations in KRAS are associated with a lack of sensitivity to either drug.
Our results suggest that treatment decisions regarding use of these kinase inhibitors might be improved by determining the mutational status of both EGFR and KRAS.
Mutational analysis of the KRAS gene in lung cancer patients treated with two different kinase inhibitors suggests that tumors with KRAS mutations do not respond to these drugs
PMCID: PMC545207  PMID: 15696205
23.  Evolution of somatic mutations in mammary tumors in transgenic mice is influenced by the inherited genotype 
BMC Medicine  2004;2:24.
MMTV-Wnt1 transgenic mice develop mammary hyperplasia early in development, followed by the appearance of solitary mammary tumors with a high proportion of cells expressing early lineage markers and many myoepithelial cells. The occurrence of tumors is accelerated in experiments that activate FGF proto-oncogenes or remove the tumor suppressor genes Pten or P53, implying that secondary oncogenic events are required for progression from mammary hyperplasia to carcinoma. It is not known, however, which oncogenic pathways contribute to Wnt1-induced tumorigenesis – further experimental manipulation of these mice is needed. Secondary events also appear to be required for mammary tumorigenesis in MMTV-Neu transgenic mice because the transgene in the tumors usually contains an acquired mutation that activates the Neu protein-tyrosine kinase.
cDNA or DNA from the mammary glands and mammary tumors from MMTV-Wnt1, MMTV-Wnt1/p53-/-, MMTV-Neu transgenic mice, and newly generated MMTV-Wnt1/MMTV-Neu bitransgenic mice, was sequenced to seek activating mutations in H-Ras, K-Ras, and N-Ras genes, or in the MMTV-Neu transgene. In addition, tumors from bitransgenic animals were examined to determine the cellular phenotype.
We found activating mutations at codons 12, 13, and 61 of H-Ras in just over half of the mammary tumors in MMTV-Wnt1 transgenic mice, and we confirmed the high frequency of activating mutations of Neu in tumors in MMTV-Neu transgenic mice. Tumors appeared earlier in bitransgenic MMTV-Wnt1/MMTV-Neu mice, but no Ras or MMTV-Neu mutations were found in these tumors, which were phenotypically similar to those arising in MMTV-Wnt1 mice. In addition, no Ras mutations were found in the mammary tumors that arise in MMTV-Wnt1 transgenic mice lacking an intact P53 gene.
Tumorigenic properties of cells undergoing functionally significant secondary mutations in H-Ras or the MMTV-Neu transgene allow selection of those cells in MMTV-Wnt1 and MMTV-Neu transgenic mice, respectively. Alternative sources of oncogenic potential, such as a second transgenic oncogene or deficiency of a tumor suppressor gene, can obviate the selective power of those secondary mutations. These observations are consistent with the notion that somatic evolution of mouse mammary tumors is influenced by the specific nature of the inherited cancer-promoting genotype.
PMCID: PMC446228  PMID: 15198801
24.  Casein Kinase Iɛ Modulates the Signaling Specificities of Dishevelled 
Molecular and Cellular Biology  2004;24(5):2000-2011.
Wnt signaling is critical to many aspects of development, and aberrant activation of the Wnt signaling pathway can cause cancer. Dishevelled (Dvl) protein plays a central role in this pathway by transducing the signal from the Wnt receptor complex to the β-catenin destruction complex. Dvl also plays a pivotal role in the planar cell polarity pathway that involves the c-Jun N-terminal kinase (JNK). How functions of Dvl are regulated in these two distinct pathways is not clear. We show that deleting the C-terminal two-thirds of Dvl, which includes the PDZ and DEP domains and is essential for Dvl-induced JNK activation, rendered the molecule a much more potent activator of the β-catenin pathway. We also found that casein kinase Iɛ (CKIɛ), a previously identified positive regulator of Wnt signaling, stimulated Dvl activity in the Wnt pathway, but dramatically inhibited Dvl activity in the JNK pathway. Consistent with this, overexpression of CKIɛ in Drosophila melanogaster stimulated Wnt signaling and disrupted planar cell polarity. We also observed a correlation between the localization and the signaling activity of Dvl in the β-catenin pathway and the JNK pathway. Furthermore, by using RNA interference, we demonstrate that the Drosophila CKIɛ homologue Double time positively regulates the β-catenin pathway through Dvl and negatively regulates the Dvl-induced JNK pathway. We suggest that CKIɛ functions as a molecular switch to direct Dvl from the JNK pathway to the β-catenin pathway, possibly by altering the conformation of the C terminus of Dvl.
PMCID: PMC350543  PMID: 14966280
25.  Requirement for a Nuclear Function of β-Catenin in Wnt Signaling 
Molecular and Cellular Biology  2003;23(23):8462-8470.
Wnt signaling stabilizes β-catenin, which in turn influences the transcription of Wnt-responsive genes in conjunction with T-cell factor (TCF) transcription factors. At present, there are two models for the actions of β-catenin. The conventional nuclear model suggests that β-catenin acts in the nucleus to form a heterodimeric transcriptional factor complex with TCF, with TCF providing DNA-specific binding and the C and N termini of β-catenin stimulating transcription. The alternative cytoplasmic model postulates that β-catenin exports TCF from the nucleus to relieve its repressive activity or activates it in the cytoplasm. We have generated modified forms of β-catenin and used RNA interference against endogenous β-catenin to distinguish between these models in cultured mammalian and Drosophila cells. We show that the VP16 transcriptional activation domain can replace the C terminus of β-catenin without loss of function and that the function of β-catenin is compromised by fusion to a transcriptional repressor domain from histone deacetylase, favoring the direct effects of β-catenin in the nucleus. Furthermore, membrane-tethered β-catenin requires interaction with the adenomatous polyposis coli protein but not with TCF for its function, whereas untethered β-catenin requires binding to TCF for its signaling activity. Importantly, by using RNA interference, we show that the signaling activity of membrane-tethered β-catenin, but not free β-catenin, requires the presence of endogenous β-catenin, which is able to accumulate in the nucleus when stabilized by the binding of the β-catenin degradation machinery to the membrane-tethered form. All of these data support a nuclear model for the normal function of β-catenin.
PMCID: PMC262677  PMID: 14612392

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