Supplementary Data Materials And
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Supplementary Data Materials and methods Cell culture HepG2 human hepatoblastoma cells were obtained from ATCC (HB-8065, Rockville, MD, USA). Cells were grown in a humidified incubator (20% O2, 5% CO2 at 37°C) (Sanyo MCO-18M O2/CO2 incubator, Osaka, Japan) in Williams Medium E (WEM, InVitrogen) supplemented with 10% fetal calf serum, 2 mM L- glutamine, 20 mU/ml insulin, 50 nM dexamethasone, 100 U/ml penicillin, 100 µg/ml streptomycin, 2.5 µg fungizone, 50 µg/ml gentamycin and 100 µg/ml vancomycin (=WEM-C). For the microarray analysis two experiments were executed in parallel. Cells 6 were seeded at 3x10 in 75 cm² tissue culture flasks (n=4) at 20% O2 and were grown until 70% confluence. After reaching near-confluence, 2 flasks were placed in a humidified incubator with hypoxic conditions (2% O2, 5% CO2 at 37°C), while the other flasks (n=2) remained in normoxic conditions (20% O2). Cells were cultured for 72hrs in these different oxygen conditions and after three days cells were harvested after trypsin treatment, mixed with Trizol (InVitrogen, Merelbeke, Belgium) and stored in -80°C for further analysis. Sample Collection and Microarray Target Synthesis and Processing Samples in Trizol were homogenized in a Dounce homogenizer for RNA extraction. Thereafter, RNA was isolated with the RNeasy Kit (Qiagen, Chatsworth, CA) according to the manufacturer’s instructions. The quality of all RNA samples was monitored with a NanoDrop spectrophotometer (NanoDrop Technologies, Centreville, DE) and by means of the Agilent 2100 BioAnalyzer (Agilent, Palo Alto, CA). Only RNA showing no signs of degradation or impurities (260/280 and 260/230 nm ratios, >1.8) was considered suitable for microarray analysis and used for labeling. Briefly, from 1 μg of cellular RNA, poly-A RNA was reversed transcribed using a poly dT-T7 primer. The resulting cDNA was immediately used for one round of amplification by T7 in vitro transcription reaction in the presence of Cyanine 3-CTP or Cyanine 5-CTP. The amplified and labeled RNA probes were purified separately with RNeasy purification columns (Qiagen, Belgium). Probes were verified for amplification yield and incorporation efficiency by measuring the RNA concentration at 280 nm, Cy3 incorporation at 550 nm and Cy5 incorporation at 650 nm using a Nanodrop spectrophotometer. Samples were hybridized on dual color Agilent's Human Whole Genome Oligo Microarray (Cat# G4112F, Agilent, Diegem, Belgium) that contained 44k 60-mer oligonucleotide probes representing around 41,000 well-characterized human transcripts. Agilent technology utilizes one glass array for the simultaneous hybridization of two populations of labeled, antisense cRNAs obtained from two samples (reference and assay). Primary data analysis Statistical data analysis was performed on the processed Cy3 and Cy5 intensities, as provided by the Feature Extraction Software version 9.1. Probes with none of the eight signals flagged as positive and significant (by the Feature Extraction Software) were omitted from all subsequent analyses as well as the various controls. Further analysis was performed in the R programming environment, in conjunction with the packages developed within the Bioconductor project (http://www.bioconductor.org).(1) In a first analysis the differential expression of the 2% versus 20% oxygen samples was assessed via the moderated t-statistic, described in Smyth (2004).(2) This moderated statistic applies an empirical Bayesian strategy to compute the gene-wise residual standard deviations and thereby increases the power of the test, especially beneficial for smaller data sets. To control the false discovery rate, multiple testing correction was performed and probes with a corrected p-value below 0.05 and a fold change of >2 were selected.(3) To determine the highly significant differentially expressed genes under chronic hypoxic conditions we used higher stringency of p-value below 0.01. Finally, the remaining differentially expressed genes were designated as the liver in vitro hypoxia gene set and with these genes we could further investigate the relevance of chronic hypoxia in primary human liver cancer. Quantitative RT-PCR - Hypoxia score at different oxygen tension To investigate the expression of the 7 genes from the in vitro hypoxia gene set at different oxygen concentrations a number of parallel experiments were performed. HepG2 cells were seeded in 25cm³ culture flasks (106 cells/flask) that were placed in either reduced O2 (5% O2, 2% O2 and 1%O2) or 20% O2 in parallel. All culture conditions were performed in triplicate and cells were collected for RNA isolation. Samples were processed for RT-PCR as described below (for primers see Table 1A). - Confirmation array results To investigate the dynamics of hypoxia related gene expression and to confirm the array findings, we performed RT-PCR at different time points for an additional set of 6 genes (Table 1B) using beta-2-microglobulin as housekeeping gene. HepG2 cells were seeded in 25cm³ culture flasks (106 cells/flask), using the same culture conditions as were used for the microarray experiment. Flasks were placed in either 2% O2 or 20% O2 and gene expression was tested at 0 hr, 10 hrs, 24 hrs and up to 72 hrs. All culture conditions were performed in triplicate and cells were collected for RNA isolation. RNA was isolated with the RNeasy Kit (Qiagen, Chatsworth, CA) according to the manufacturer’s instructions. One microgram of cellular RNA was reverse transcribed into cDNA using SuperScript II reverse transcriptase and random hexamer primers (Invitrogen Life Technologies, USA). The PCR reaction was carried out in a volume of 10 µl in a mixture that contained appropriate sense- and anti-sense primers and a probe in TaqMan Universal PCR Master Mixture (Applied Biosystems, Foster City, California). We used the Assays-on-DemandTM Gene Expression products, which consist of a 20x mix of unlabeled PCR primers and TaqMan MGB probe (FAMTM dye-labeled). These assays are designed for the detection and quantification of specific human genetic sequences in RNA samples converted to cDNA. The primers used are listed in Table 1. Real-time PCR amplification and data analysis were performed using the A7500 Fast Real-Time PCR System (Applied Biosystems). Each sample was assayed in duplicate in a MicroAmp optical 96-well plate. The thermo-cycling condition consisted of 2 minutes at 50°C and 10 min incubations at 95°C, followed by 40 two-temperature cycles of 15 seconds at 95°C and 1 min at 60°C. The ΔΔCt- method was used to determine relative gene expression levels. Gene Gene Name Chromosome Assay ID Applied symbol Biosystems A Hypoxia score at different oxygen tension B2M Beta-2-microglobulin 15 Hs99999907_m1 CCNG2 cyclin G2 4 Hs00171119_m1 EGLN3 egl nine homolog 3 (C. elegans) 14 Hs00222966_m1 ERO1L ERO1-like (S. cerevisiae) 14 Hs00969232_m1 FGF21 fibroblast growth factor 21 19 Hs00173927_m1 MAT1A methionine adenosyltransferase I, alpha 10 Hs01547962_m1 RCL1 RNA terminal phosphate cyclase-like 1 9 Hs00195050_m1 WDR45L WDR45-like 17 Hs00750495_s1 B Confirmation array results CDO1 Cysteine dioxygenase, type I 5 Hs00156447_m1 EGLN1 Egl nine homolog 1 (C. elegans) 1 Hs00254392_m1 HIF-1α Hypoxia-inducible factor 1, alpha subunit 14 Hs00936368_m1 FIH Hypoxia-inducible factor 1 alpha inhibitor 10 Hs00215495_m1 IGFBP3 Insulin-like growth factor binding protein 3 7 Hs00181211_m1 VEGF-A Vascular endothelial growth factor A 6 Hs00173626_m1 Table 1. List of genes and RT-PCR assay IDs (Applied Biosystems) used in this study. Immunohistochemistry on Hif-1α and VEGF HepG2 cells were grown on Thermanox plastic cover slips (Nalgene Nunc international, Rochester, NY USA, 13 mm diameter) placed in a 24 well plate with 1 mL William’s Medium E (WEM-C, InVitrogen). After one day of incubation and attachment, cells were either exposed to hypoxia (2% O2) or normal oxygen conditions for 0, 24, or 72 hours. Subsequently cells were washed once with PBS and fixed in acetone for 15 minutes. When dry, the cover slides were stored at - 20°C. For immunohistochemistry we used the Envision technique of Dako. Cover slips collected at the different time points were stained in duplicate. Cells were incubated for 45 minutes with a primary antibody against Hif-1α (1:250 anti-Hif- 1α monoclonal mouse antibody, BD Biosciences) or against VEGF (1:100 anti- VEGF A-20 polyclonal rabbit antibody, Santa Cruz). As secondary antibody Envision monoclonal antibodies were used (for Hif-1α; Envision monoclonal mouse antibody, Dako and for VEGF; Envision monoclonal rabbit antibody, Dako). Finally, the staining was performed with 3-amino-9-ethylcarbazole (AEC) and a contra-staining with haematoxylin. The thermanox cover slips were mounted with glycergel. To evaluate the staining we used a semi-quantative quickscore,(4) which combines positivity (P) and intensity (I). Positivity was scored as: 1= 0-4%, 2= 5-19%, 3= 20-39%, 4= 40-59%, 5= 60-79% and 6= 80- 100%. Intensity was scored as: 0= negative, 1= weak, 2= intermediate and 3= strong. The final score was the total of P+I and has a range of 1-9. All slides were scored independently by two researchers. Results Microarray We started with the cell culture as model and determined the differentially expressed genes in HepG2 cells that were cultured for 72 hours at either 20% oxygen or in hypoxic conditions at 2% oxygen. We used the Agilent technology with color flip on two independent experiments in duplicate resulting in 8 ratio values. A total of 37,707 spots showed a representative signal of which 3,592 (8%) with a fold change above 2 and an uncorrected p-value <0.05 (1,879 up- regulated and 1,713 down-regulated). To control the false discovery rate, multiple testing correction was performed and the highly significant genes with a corrected p-value below 0.01 and a fold change of >2 were selected.