miRNAs target complementary sequences in the 3′ untranslated region of specific mRNAs. As a result, target gene expression is repressed due either to translational inhibition and/or to mRNA degradation (reviewed

in Cannell et al., 2008, Fabian et al., 2010 and Jackson and Standart, 2007). Therefore, a small change in miRNA expression can have a profound effect on outcome making them an appealing area of research for the discovery of new mechanisms of action. The lack of hepatic miRNA response to BaP exposure as reported in Yauk et al. (2010) may be explained by: (1) few or no hepatic miRNAs under the transcriptional control of AHR or immediately responsive to DNA damage or (2) a high level of liver miRNA stability and lack of susceptibility to perturbation by BaP. Moreover, BaP exposure in rodents does not lead to liver cancer, but does cause cancer

in other tissues. Thus, we proposed that future experiments Etoposide concentration should investigate early miRNA response in a tissue that is susceptible to cancer development following BaP exposure. In the present work we investigate global pulmonary gene and miRNA expression from the same mice (Yauk et al., 2010) exposed by oral gavage for three days to BaP that exhibited no hepatic miRNA response (Yauk et al., 2010). The first goal of this work is to clarify the mechanisms of action that operate in lungs following BaP exposure via oral selleck screening library gavage. Lung transcriptomic profiles were compared to liver profiles to identify unique pulmonary responses that may contribute to tissue-specific carcinogenicity. Second, we test the hypothesis that liver miRNAs are less sensitive to perturbations than lungs following treatment ID-8 with BaP by oral gavage. The experimental samples used in the present work were generated as part of an earlier study described in detail in Yauk et al. (2010). Hepatic mRNA and miRNA profiles were analysed in that study. However, new DNA microarrays

were run in the present study because a higher exposure dose was included here. Age matched adult male B6C3F1 mice (27–30 d, Charles Rivers Laboratories, St Constant, Quebec, Canada) were housed individually under a 12:12 h light:dark cycle with food and water available ad libitum. Mice were randomly assigned (6/group) to a control or treatment group. Mice were treated with a daily dose of BaP in corn oil with 150 or 300 mg/kg (oral gavage, 10 ml/kg) for three consecutive days. Control mice received corn oil only. Mice were anaesthetized under isofluorane and sacrificed by exsanguination at 4 h after the last treatment. Right and left lung lobes were removed and immediately snap frozen and stored at −80 °C until use. Blood serum was collected as described below. Animals have been treated humanely with due consideration to the alleviation of distress and discomfort. All animal procedures (Approval ID: 2007-005) were in accordance with the guidelines of the Canadian Council for Animal Care and approved by the Health Canada Animal Care Committee.