Inter-laboratory comparison of human renal proximal tubule (HK-2) transcriptome alterations due to Cyclosporine A exposure and medium exhaustion

There is an acknowledged need to promote and further develop in vitro techniques in order to achieve the goal of improved risk assessment of chemicals and pharmaceuticals to humans. The EU 6th framework project "PREDICTOMICS" was established in order to contribute to the further development of in vitro toxicology, with a particular focus on emerging techniques including toxicogenomics. DNA microarray technology is being used more frequently in the in vitro field, however, only very few studies have assessed the reproducibility of this technique with respect to in vitro toxicology. To this end we conducted an interlaboratory comparison to test the reproducibility of transcriptomic changes induced by the immunosuppressive agent, Cyclosporine A (CsA) on the human renal proximal tubular cell line, HK-2 cell. Four European laboratories took part in this study. Under standardised conditions, each laboratory treated HK-2 cells with 5 mu M CsA for 12 and 48 h. RNA was isolated and hybridised to Affymetrix HGU-133 plus two arrays at three different sites. Analysis of the transcription profiles demonstrated that one laboratory clustered away from the other laboratories, potentially due to an inclusion of a trypsinisation step by this laboratory. Once the genes responsible for this separate clustering were removed all laboratories showed similar expression profiles. There was a major impact of time since feed, due to medium exhaustion in the 48 h arrays compared to the 12 h arrays, regardless of CsA treatment. Biological processes including general vesicle transport, amino acid metabolism, amino acid transport and amino acid biosynthesis were over-represented due to time since feed, while cell cycle, DNA replication, mitosis and DNA metabolism were under-represented. CsA responsive genes were involved in cell cycle, the p53 pathway and Wnt signaling. Additionally there was an overlap of differentially expressed genes due to CsA and medium exhaustion which is most likely due to CsA induced glycolysis. The glucose deprivation dependent genes HspA5 and GP96 and the Hsp70 chaperones DNAJ/Hsp40, DNAJ/HspB9, DNAJ/HspC3 DNAJ/HspC10 were induced by both CsA and medium exhaustion. We conclude that under standardised conditions the application of Affymetrix DNA microarrays to in vitro toxiciological studies are satisfactorily reproducible. However, confounding factors such as medium exhaustion must also be considered in such analyses.