Unknown,Transcriptomics,Genomics,Proteomics

Dataset Information

Gene expression signature reflects differentiation differences rather than telomere maintenance mechanism

ABSTRACT: A gene expression signature purporting to distinguish between telomerase and ALT immortalization has recently been described (Lafferty-Whyte et al., 2009). This was obtained as the intersection of two independent signatures, one obtained from cell lines and the other from a panel of liposarcomas, which utilize different telomere maintenance mechanisms (TMMs). To assess the utility of this signature we used Affymetrix U133plus2.0 arrays to undertake a similar analysis of an independent collection of liposarcomas of defined TMM. In our dataset, the 297 gene signature causes the liposarcomas to cluster not on the basis of TMM, but rather on the basis of tumor histological subtype [Figure 1], consistent with the signatures reported by others (Matushansky et al., 2008). Expression analyses were performed on 38 liposarcoma tumors using Affymetrix U133plus2.0 arrays. Using cosine distance as a distance metric, hierarchical clustering of these samples was performed according to the expression levels of the 297 genes identified in the study by Lafferty-Whyte et al.

ORGANISM(S): Homo sapiens

SUBMITTER: David Kipling

PROVIDER: E-GEOD-20559 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Publications

Validating a gene expression signature proposed to differentiate liposarcomas that use different telomere maintenance mechanisms.

Doyle K R KR Mitchell M A MA Roberts C L CL James S S Johnson J E JE Zhou Y Y von Mehren M M Lev D D Kipling D D Broccoli D D

Oncogene 20110627 2

PMID: 21706060

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Project description:Soft tissue sarcomas are a diverse set of fatal human tumors where few agents have demonstrable clinical efficacy, with the standard therapeutic combination of doxorubicin and ifosfamide showing only a 25-30% response rate in large multi-institutional trials. Although liposarcomas are the most common histological form of adult soft tissue sarcomas, research in this area is severely hampered by the lack of experimentally tractable in vitro model systems. To this end, here we describe a novel in vitro model for human pleomorphic liposarcoma. The cell line (LS2) is derived from a pleomorphic liposarcoma that utilizes Alternative Lengthening of Telomeres (ALT) mechanism of telomere maintenance, which may be particularly important in modulating the response of this tumor type to DNA damaging agents. We present detailed baseline molecular and genomic data, including genome wide copy number and transcriptome profiles, for this model compared to its parental tumor and a panel of liposarcomas covering multiple histologies. The model has retained essentially all of the detectable alterations in copy number that are seen in the parental tumor, and shows molecular karyotypic and expression profiles consistent with pleomorphic liposarcomas. We also demonstrate the utility of this model, together with two additional human liposarcoma cell lines, to investigate the relationship between topoisomerase 2A expression and the sensitivity of ALT-positive liposarcomas to doxorubicin. This model, together with its associated baseline data, provide a powerful new tool to develop treatments for this clinically poorly-tractable tumor, and to investigate the contribution that ALT makes to modulating sensitivity to DNA damaging chemotherapeutic agents such as doxorubicin. Affymetrix U133 2.0 expression analyses were performed for 30 liposarcoma tumors, including 2 recurrences of 2 tumors. In addition, analyses were performed for three replicates of a tumor-derived cell line, LS2, as well as the tumor from which it was derived (5228). Finally, the Affymetrix Human Genome 50K DNA Mapping Array was used to determine copy number profiles for two Passages of LS2, as well as tumor 5228.

Project description:The human Werner and Bloom syndromes (WS and BS) are caused by deficiencies in the WRN and BLM RecQ helicases, respectively. WRN, BLM and their S. cerevisiae homologue Sgs1, are particularly active in vitro in unwinding G-quadruplex DNA (G4-DNA), a family of non-canonical nucleic acid structures formed by certain G-rich sequences. Recently, mRNA levels from loci containing potential G-quadruplex-forming sequences (PQS) were found to be preferentially altered in sgs1 mutants, suggesting that G4-DNA targeting by Sgs1 directly affects gene expression. Here, we extend these findings to human cells. Using microarrays to measure mRNAs obtained from human fibroblasts deficient for various RecQ family helicases, we observe significant associations between loci that are upregulated in WS or BS cells and loci that have PQS. No such PQS associations were observed for control expression datasets, however. Furthermore, upregulated genes in WS and BS showed no or dramatically reduced associations with sequences similar to PQS but that have considerably reduced potential to form intramolecular G4-DNA. These findings indicate that, like Sgs1, WRN and BLM can regulate transcription globally by targeting G4-DNA. Cell culture conditions and media Human fibroblast cell strains (WS: AG05229, AG12795, AG12797; BS: GM02932, GM03402, GM16891; RTS: AG18371, AG18375, AG05013; Normal/Wild-type: AG04054, AG06310, AG09975) were obtained from the Coriell Repository (Camden, NJ), from donors matched for gender and of similar ages, and were at similar passage levels. Cells were cultured in MEM supplemented with Earle’s salts, 20% fetal bovine serum, 1x penicillin/streptomycin, and 1x fungizone in 3% O2 at 37oC and harvested for RNA extraction during active growth and at ~ 80% confluence. GeneChip microarray expression Total RNA from the 12 fibroblast cell strains was isolated by extraction with TRIzol (Invitrogen) and purified using the RNeasy system (Qiagen). Total RNA was amplified by in vitro transcription using the Ovation RNA Amplification System V2 (NuGen). The resultant cDNA was fragmented and labeled using the FL-Ovation cDNA Biotin Module V2 (NuGen), and then purified using QIAquick columns (Qiagen), as specified by the Ovation System manual. Labeled probe was hybridized to Affymetrix U133A 2.0 GeneChips, and ultimately scanned using an Axon GenePix array scanner. Statistical analysis of microarray expression experiment The output files were normalized by Robust Multiarray Average (RMA), using the R package GCRMA and gene expression levels were log2-transformed.

Dataset Information

Gene expression signature reflects differentiation differences rather than telomere maintenance mechanism

Publications

Validating a gene expression signature proposed to differentiate liposarcomas that use different telomere maintenance mechanisms.

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