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Exon level expression profiling of colorectal cancer tissue samples (test sample series).

ABSTRACT: Colorectal cancer is a heterogeneous disease molecularly characterized by inherent genomic instabilities, chromosome instability and microsatellite instability. In the present study we propose transcriptome instability as an analogue to genomic instability on the transcriptome level. Exon microarray data from two independent series of altoghether 160 colorectal cancer tissue samples was used for global alternative splicing detection using the FIRMA algorithm (aroma.affymetrix). The sample-wise amounts of these alternative splicing scores exceeding a defined threshold (deviating exon usage amounts) were summarized to provide the basis for description of transcriptome instability. This characteristic was shown to be associated with splicing factor expression levels and patient survival in both independent sample series. Overall design: We analyzed genome-wide expression at the exon-level for two independent series of colorectal cancer tissue biopsies using the Affymetrix Human Exon 1.0 ST platform. This series of samples represents the test series.

INSTRUMENT(S): [HuEx-1_0-st] Affymetrix Human Exon 1.0 ST Array [transcript (gene) version]

ORGANISM(S): Homo Sapiens

SUBMITTER: Anita Sveen

PROVIDER: GSE24549 | GEO |

SECONDARY ACCESSION(S): PRJNA133513

REPOSITORIES: GEO

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	GSE24549_RAW.tar	Raw
	filelist.txt	Txt

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Project description:BACKGROUND: Colorectal cancer (CRC) is a heterogeneous disease that, on the molecular level, can be characterized by inherent genomic instabilities; chromosome instability and microsatellite instability. In the present study we analyze genome-wide disruption of pre-mRNA splicing, and propose transcriptome instability as a characteristic that is analogous to genomic instability on the transcriptome level. METHODS: Exon microarray profiles from two independent series including a total of 160 CRCs were investigated for their relative amounts of exon usage differences. Each exon in each sample was assigned an alternative splicing score calculated by the FIRMA algorithm. Amounts of deviating exon usage per sample were derived from exons with extreme splicing scores. RESULTS: There was great heterogeneity within both series in terms of sample-wise amounts of deviating exon usage. This was strongly associated with the expression levels of approximately half of 280 splicing factors (54% and 48% of splicing factors were significantly correlated to deviating exon usage amounts in the two series). Samples with high or low amounts of deviating exon usage, associated with overall transcriptome instability, were almost completely separated into their respective groups by hierarchical clustering analysis of splicing factor expression levels in both sample series. Samples showing a preferential tendency towards deviating exon skipping or inclusion were associated with skewed transcriptome instability. There were significant associations between transcriptome instability and reduced patient survival in both sample series. In the test series, patients with skewed transcriptome instability showed the strongest prognostic association (P = 0.001), while a combination of the two characteristics showed the strongest association with poor survival in the validation series (P = 0.03). CONCLUSIONS: We have described transcriptome instability as a characteristic of CRC. This transcriptome instability has associations with splicing factor expression levels and poor patient survival.

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Exon level expression profiling of colorectal cancer tissue samples (test sample series).

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