Unknown,Transcriptomics,Genomics,Proteomics

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Genome position and gene amplification - expressional profiling of methotrexate resistant colonies

ABSTRACT: We investigated the influence of genome position on propensity to amplify. First, we integrated a mutant form of DHFR into different positions in the human genome, challenged cells with methotrexate and then studied the genomic alterations arising in drug resistant cells. We observed site specific differences in methotrexate sensitivity, organization of amplicons and amplification frequency. One site was uniquely associated with a significantly enhanced propensity to amplify and recurrent amplicon boundaries, possibly implicating a rare folate sensitive fragile site in initiating amplification. Hierarchical clustering of gene expression patterns and subsequent gene enrichment analysis revealed two clusters differing significantly in expression of MYC target genes independent of integration site. We introduced a mutant form of DHFR (L22F), which confers greater resistance to methotrexate than the wild type (endogenous) gene into HCT116+chr3 cells and isolated independent clones containing DHFR* at different positions in the genome and identified genome sequences flanking the integration site of DHFR* using inverse PCR. For further analysis, we selected only clones, which were considered to have a single insertion of DHFR* by inverse PCR (13 independent insertion sites). The individual insertion site clones were further characterized with respect to genome copy number profiles. To select methotrexate resistant colonies, we exposed cells to a concentration of methotrexate that was three to four times the IC-50 for each integration site. Genomic copy number profiles were obtained for isolated resistant colonies (GSE6262) by using UCSF HumArray platform (GPL4421). Twelve methotrexate resistant colonies (four different integration sites) were selected for microarray analysis of gene expression at the mRNA level. The untreated integration site clone was used as the reference (Cy5 labeled cDNA) for each of the hybridizations with its respective resistant colonies (Cy3 labeled cDNA). Hybridizations were carried out on arrays of printed long oligonucleotides (70mers) containing 21,000 elements (Operon V2.0, printed in J. David Gladstone Institutes, Genomics Core Laboratory).

ORGANISM(S): Homo sapiens

SUBMITTER: Donna Albertson

PROVIDER: E-GEOD-6361 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Genome position and gene amplification.

Gajduskova Pavla P Snijders Antoine M AM Kwek Serena S Roydasgupta Ritu R Fridlyand Jane J Tokuyasu Taku T Pinkel Daniel D Albertson Donna G DG

Genome biology 20070101 6

<h4>Background</h4>Amplifications, regions of focal high-level copy number change, lead to overexpression of oncogenes or drug resistance genes in tumors. Their presence is often associated with poor prognosis; however, the use of amplification as a mechanism for overexpression of a particular gene in tumors varies. To investigate the influence of genome position on propensity to amplify, we integrated a mutant form of the gene encoding dihydrofolate reductase into different positions in the hum ...[more]

PMID: 17584934

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Project description:A summary of the work associated to these microarrays is the following:; Methotrexate (MTX) is one of the earliest cytotoxic drugs used in cancer therapy, and despite the isolation of multiple other folate antagonists, methotrexate maintains its significant role as a treatment for different types of cancer and other disorders. The usefulness of treatment with methotrexate is limited by the development of drug resistance, which may be acquired through different ways. To get insights into the mechanisms associated with drug resistance and sensitization we have performed a functional analysis of genes deregulated in methotrexate resistant cells, either due to its co-amplification with the DHFR gene or as a result of a transcriptome screening using microarrays. Genes adjacent to dhfr locus and included in the 5q14 amplicon were overexpressed in HT29 MTX-resistant cells. Treatment with siRNAs against those genes caused a slight reduction in cell viability in both HT29 sensitive and resistant cells. On the other hand, microarray analysis of HT29 and HT29 MTX resistant cells unveiled overexpression of caveolin 1, enolase 2 and PKCa genes in treated cells without concomitant copy number gain. siRNAs against these three genes effectively reduced cell viability and caused a decreased MTX resistance capacity. Moreover, overexpression of E-cadherin, which was found underexpressed in MTX-resistant cells, also sensitized the cells toward the chemotherapeutic agent. We provide functional evidences indicating that caveolin 1 and E-cadherin may play a critical role in cell survival and may constitute potential targets for coadjuvant therapy. Experiment Overall Design: Two cell lines are compared in the study, which are HT29 colon cancer cells sensitive to methotrexate and HT29 cells resistant to 10e-5M MTX. Six samples are provided which correspond to triplicated of each cell line. The samples provided were subsequently normalyzed and analyzed using the specific software GeneSpring GX v7.3.1.

Dataset Information

Genome position and gene amplification - expressional profiling of methotrexate resistant colonies

Publications

Genome position and gene amplification.

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