Gene expression profiling study by RNA-seq to identify gene signature resposed to chemo-radiotherapy in colorectal cancers.

The objective of this study is to assess gene expression changes and identify gene sets associated with chemo-radiotherapy (CRT) in colorectal cancer (CRC) patients. We performed RNA-seq based transcriptome profiling using primary tumor samples obtained from 22 CRC patients. By a number of statistical tests, a total of 575 genes were statistically significant, indicating a gene set profoundly responded to chemo-radiotherapy in CRC. To select the genes showing strong gene expression intensities and critically validate the differences between treatment-responded and non-responded patients, we applied more rigorous cut-off for gene selection, revealing a total of 8 final gene candidates. These genes were applied to the downstream experimental assays. RNA-seq data of 22 CRC samples were generated. Total RNA was isolated by RNeasy Mini Kit (Qiagen, CA, USA), according to the manufacturer's protocol. The quality and integrity of the RNA were confirmed by agarose gel electrophoresis and ethidium bromide staining, followed by visual examination under ultraviolet light. Sequencing library was prepared using TruSeq RNA Sample Preparation kit v2 (Illumina, CA, USA) according to the manufacturer’s protocols. Briefly, mRNA was purified from total RNA using poly-T oligo-attached magnetic beads, fragmented, and converted into cDNAs. Then, adapters were ligated and the fragments were amplified on a PCR. Sequencing was performed in paired end reads (2x100 bp) using Hiseq-2000 (Illumina).