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Progressive genomic instability in the FVB/KrasLA2 mouse model of lung cancer

ABSTRACT: Alterations in DNA copy number contribute to the development and progression of cancers and are common in epithelial tumors. We have used array Comparative Genomic Hybridization (aCGH) to visualize DNA copy number alterations across the genomes of lung tumors in the KrasLA2 model of lung cancer. Copy number gain involving the Kras locus, as focal amplification or whole chromosome gain, is the most common alteration in these tumors, and with a prevalence that increased significantly with increasing tumor size. Furthermore, Kras amplification was the only major genomic event among the smallest lung tumors, suggesting that this alteration occurs early during the development of mutant Kras driven lung cancers. Recurring gains and deletions of other chromosomes occur progressively more frequently among larger tumors. These results are in contrast to a previous aCGH analysis of lung tumors from KrasLA2 mice on a mixed genetic background, in which relatively few DNA copy alterations were observed regardless of tumor size. Our model features the KrasLA2 allele on the inbred FVB/N mouse strain, and in this genetic background there is a highly statistically significant increase in level of genomic instability with increasing tumor size. These data suggest that recurring DNA copy alterations are important for tumor progression in the KrasLA2 model of lung cancer, and that the requirement for these alterations may be dependent on the genetic background of the mouse strain.

ORGANISM(S): Mus musculus

PROVIDER: GSE29230 | GEO | 2011/11/22

SECONDARY ACCESSION(S): PRJNA139937

REPOSITORIES: GEO

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Project description:The success of targeted therapies creates a need to discriminate tumors accurately by their histological and genetic characteristics. Here, we used cDNA microarray analysis to identify gene expression profiles and single markers that recapitulate the pathological and genetic background (i.e., BRAF, EGFR, KRAS, LKB1, PIK3CA, and TP53 gene alterations) of non-small cell lung cancer (NSCLC). Gene expression profiles were determined for 6 normal lung tissues and 69 lung tumors from patients diagnosed with NSCLC. We performed an unsupervised hierarchical clustering with the most variably expressed transcript to investigate whether there was evidence for natural grouping samples based on similarity in gene expression profiles. We examined the relationship between the clusters of tumors and patient and tumor characteristics such as gender, smoking status, histological type, degree of differentiation, tumor size, lymph node involvement and genetic background. We used a supervised analysis to identify the genes that are important for distinguishing subgroups of tumors defined by histological type. Moreover, we used this supervised approach to search for markers that characterize those tumors carrying EGFR, KRAS, PIK3CA and TP53 alterations. We identify several genes with characteristic patterns of expression in each tumor histological type (adenocarcinoma and squamous cell carcinoma) and we found that the presence of EGFR mutations result in a particular expression profile. Keywords: Transciption profiling of tumors with different histological and genetic background. We analyzed 69 NSCLC tumors. All the samples were characterized by histological type and by the presence of alterations at genes that are known to be involved in lung carcinogenesis. Mutational analysis of BRAF, EGFR, KRAS, and LKB1 is provided only for adenocarcinomas and analysis of alterations at PIK3CA gene (mutational analysis or gene amplification by FISH analysis) is provided only for 47 of the tumors. We analyzed gene expression profiles to identify those genes that are differentially expressed between two subgroups by t-test: 1) adenocarcinomas vs. squamous cell carcinomas; 2) tumors with mutation at EGFR gene vs. wild type tumors; 3) tumors with mutation at KRAS gene vs. wild type tumors; 4) tumors with mutation at TP53 gene vs. wild type tumors; 5) tumors with alterations (mutation or gene amplification) at PIK3CA gene vs. wild type tumors.

Project description:Background: LKB1 is among the most frequently altered tumor suppressors in lung adenocarcinoma. Inactivation of Lkb1 accelerates the growth and progression of oncogenic KRAS-driven lung tumors in mouse models. However, the molecular mechanisms by which LKB1 constrains lung tumorigenesis and whether the aggressive cancer state that stems from Lkb1 deficiency can be reverted remains unknown. Purpose: To assess the impact of CRISPR/Cas9-mediated targeting of a subset of LKB1-dependent genes and C/EBP factors on tumor size in the context of a genetically engineered mouse model of oncogenic KRAS-driven lung adenocarcinoma. Approach: Measurements of tumor size across genetic perturbations were obtained by tumor barcode sequencing (Tuba-seq; Rogers et al., 2017 Nature Methods). Briefly, lung tumors were initiated in KrasLSL-G12D/+;R26LSL-tdTomato (KT) and KT;H11LSL-Cas9 mice using a pool of Lenti-sgRNA/Cre vectors that are each modified with two-component barcodes composed of sgRNA-specific and clonal identifiers. This particular pool of Lenti-sgRNA/Cre vectors was composed of vectors targeting a series of LKB1-dependent genes as well a subset of C/EBP transciription factors. Following tumor development, the two-component lentiviral barcodes integrated within transduced populations were amplified from genomic DNA of whole-lung homogenates. The resulting amplicons were then subjected to next-generation sequencing. From the resulting reads, barcode pileups were generated and filtered prior to conversion to absolute numbers of neoplastic cells via normalization to spiked-in samples of known quantities of barcoded neoplastic cells. The resulting tumor size distributions were then analyzed by multiple statistical measures as described previously (Rogers et al., 2017 Nature Methods). Results: Targeting of Lkb1 dramatically increased lung tumor size relative to inert sgRNAs. Little to no impact on tumor size was observed upon targeting LKB1-dependent genes. However, simultaneous targeting of Cebpa/b/d resulted in a significant increase in tumor size. Conclusions: A subset of C/EBP transcription factors constrain oncogenic KRAS-driven lung tumor growth.

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Progressive genomic instability in the FVB/KrasLA2 mouse model of lung cancer

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