For all experiments, cells were allowed to attach overnight, experienced 4 h of serum starvation and were subsequently treated with cisplatin for 24 h in IMDM medium without any supplements. The parental cells were treated with 11 µM cisplatin. The resistant sub-line was exposed to 11 µM cisplatin and additionally treated with 34 µM cisplatin. The control cells were treated with the drug-free medium.
Growth protocol
The human NSCLC cell line A549 was obtained from American Type Culture Collection (ATCC) (Manassas, VA, USA). Its cisplatin-resistant sub-line A549rCDDP2000 derived from the Resistant Cancer Cell Line (RCCL) collection (www.kent.ac.uk/stms/cmp/RCCL/RCCLabout.html) had been established by adapting the growth of A549 cells in the presence of increasing concentrations of cisplatin until a final concentration of 2000 ng/mL cisplatin. A549 cells were grown in IMDM medium (PAN-Biotech, Aidenbach, Germany) containing 4 mM L-glutamine supplemented with 10 % foetal calf serum, 100 I.E./mL penicillin and 0.1 mg/mL streptomycin. The medium of the A549rCDDP2000 cells additionally contained 2 µg/mL cisplatin. Cells were cultivated as monolayers in a humidified atmosphere at 37 °C and 5 % CO2.
Extracted molecule
total RNA
Extraction protocol
Total ribonucleic acid (RNA) was isolated from the cells with my-Budget RNA Mini Kit (Bio-Budget, Krefeld, Germany) through different spin columns according to the manufacturer’s instructions. Isolated RNA was stored at -80 °C until analysis was performed.
Label
Cy3
Label protocol
Transcriptome was then analysed using One-Color Whole Genome Array SurePrint G3 Human GE V2 8x60K Kit (Agilent Technologies, Santa Clara, CA, USA) according to the manufacturer’s instructions. Briefly, total RNA was transcribed to complementary deoxyribonucleic acid (cDNA) using AffinityScript-RT, Oligo dT-Promoter Primer and T7 RNA Polymerase and labelled using the One Colour RNA Spike-In Kit (positive controls) including Cyanin 3-CTP (Cy3) dye.
Hybridization protocol
After purifying the labelled/amplified complementary RNA (cRNA) using silica-membrane RNeasy spin columns from the RNeasy® Mini Kit (Qiagen, Venlo, the Netherlands), cRNA was quantified spectrophotometrically using NanoDropTM ND-1000 (Thermo Fisher Scientific Inc., Waltham, MA, USA). 40 µL of equivalent amounts of Cy3-labelled cRNA in 10x Blocking Agent and 25x Fragmentation Buffer, diluted with 2x GEx HI-RPM Hybridization Buffer were loaded on the gaskets of the microarray slide and kept at 65 °C for 17 h with 10 rpm of agitation.
Scan protocol
After washing twice with different washing buffers, the microarray was read out with the SureScan Microarray Scanner System (Agilent Technologies, Santa Clara, CA, USA) to obtain immunofluorescence intensity.
Description
gene expression in untreated res. cells
Data processing
Array data were pre-processed via background correction (exponential convolution method) and quantile normalization. Statistical significances of dose- and resistance-induced gene expression changes were analysed using limma, a linear model-based technique. Differential expression was declared at a 5 % false discovery rate (FDR) cut-off together with an at least twofold up- or downregulation. The overall significance of the signature of differentially expressed genes was assessed via a global test. VALUE contains quantile normalized data for probes with REFSEQ IDs only (29,729)
