Abstract 292: Aberrant methylation of miR-34b as a potential mechanism for increased shiftwork-mediated breast cancer susceptibility
Authors: Jacobs Daniel I. , Liu Ran , Hansen Johnni , Fu Alan , Stevens Richard G. , Zhu Yong 
Published: May 2015

Background: The molecular mechanisms underlying the association between exposure to light at night (LAN) and breast cancer risk remain to be fully elucidated. Previously, we have observed that long-term exposure to LAN through shiftwork may result in dysregulated patterns of methylation at promoter regions of cancer-related genes and microRNAs (miRNAs). In this study, we investigate the link between a miRNA suggested to be an important tumor suppressor, miR-34b, and shiftwork-related breast cancer.

Methods: miR-34b promoter methylation was evaluated in blood-derived DNA of 10 female long-term shiftworkers and 10 folate intake- and age-matched female dayworkers participating in the Danish “Diet, Cancer, and Health” prospective cohort study using an Illumina Infinium 27K Methylation Assay. Subsequently, a genome-wide expression array analysis was performed in a miR-34b-overexpressed MCF-7 breast cancer cell line and a network analysis was conducted using Ingenuity Pathway Analysis software in order to determine the expression impact of miR-34b on individual genes and cellular networks.

Results: In a comparison of miR-34b promoter methylation, we observed a 49.1% increase in methylation (β=0.055 to β=0.082, P=0.016) among shiftworkers relative to dayworkers at CpG site cg22879515, which is located 148 bp upstream of the 5’ end of the miR-34b gene within a CpG island. To further explore the role of miR-34b in breast cancer, a miR-34b mimic was transfected into MCF-7 cells, and induced differential expression of 230 transcripts (≥2-fold expression change) that were analyzed for functional and network interrelatedness using Ingenuity Pathway Analysis software. The analysis revealed a robust upregulation of transcripts involved in the interferon-mediated antiviral response as well as apoptotic and antiproliferative gene networks. Notably, three of the top five overexpressed transcripts (IFIT3, IFIT2, and RARRES3) encode proteins with potential tumor suppressive features, while three of the top five underexpressed transcripts (S100A8, S100A9, and IGFBP5) encode proteins with potential oncogenic features.

Conclusion: These results suggest that long-term shiftwork may induce methylation of the miR-34b promoter region. Given the tumor suppressive role of miR-34b as demonstrated by our genome-wide expression analysis and as suggested by previous work, methylation-based suppression of miR-34b expression may correspond to diminished immunomediated anti-tumor capacity and accordingly an increased risk of breast cancer development. Taken together, our findings suggest that the epigenetic silencing of miR-34b warrants further exploration as a potential mechanism explaining the increased risk of breast cancer among long-term shiftworkers.

Citation Format: Daniel I. Jacobs, Ran Liu, Johnni Hansen, Alan Fu, Richard G. Stevens, Yong Zhu. Aberrant methylation of miR-34b as a potential mechanism for increased shiftwork-mediated breast cancer susceptibility. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 292. doi:10.1158/1538-7445.AM2014-292