Proteomic analyses indicate induction of hepatic carbonyl reductase/20β-hydroxysteroid dehydrogenase B in rainbow trout exposed to sewage effluent

Proteomic analyses were performed to identify regulated liver proteins in rainbow trout (Oncorhynchus mykiss) caged upstream and downstream from a sewage treatment works (STW). Two-dimensional gel electrophoresis, image analysis and FT-ICR mass-spectrometry revealed four regulated protein spots. The three down-regulated spots contained betaine aldehyde dehydrogenase, lactate dehydrogenase and an unidentified protein respectively. The only up-regulated spot consisted of both mitochondrial ATP synthase alpha-subunit and carbonyl reductase/20β-hydroxysteroid dehydrogenase (CR/20β-HSD). Further studies using quantitative PCR revealed a 13.5-fold induction of CR/20β-HSD B mRNA following STW effluent exposure. The CR/20β-HSD B gene was not regulated by 17α-ethinylestradiol, suggesting that its induction downstream from the STW is due to other factors than exposure to estrogens. Image analysis was initially performed on four gels from each group. These analyses suggested 15 regulated spots. However, validation of the 15 spots by increasing the number of replicates confirmed only four regulated spots. Hence, the present study also demonstrates the need for sufficient biological/technical replication in the interpretation of proteomic data.