Background: Shift work that involves circadian disruption has been deemed by IARC to be "probably carcinogenic" to humans. Although several theories have been put forth to explain the connection between shift work and cancer, including suppression of melatonin production and deregulation of circadian genes involved in cancer-related pathways, other potential cancer-relevant pathways remain unexplored. In this study, we test the hypothesis that aberrant methylation events in the CpG islands of specific miRNA promoters may be induced by prolonged exposure to shift work in an all-female population, which in turn can lead to cancer development.

Material and Methods: We performed a genome-wide methylation assay of miRNA promoters using DNA extracted from 10 pairs of long-term shift workers and day workers selected from participants of the Danish “Diet, Cancer and Health” prospective cohort. A genome-wide expression microarray analysis was then carried out using a miR-219-overexpressed MCF-7 breast cancer cell line. Differentially expressed transcripts were then analyzed for network and functional interrelatedness using the Ingenuity Pathway Analysis (IPA) software.

Result: The genome-wide methylation analysis indicated that 50 CpG loci of 30 miRNAs, including miR-10a, miR-219, miR-7-3, miR34b/c, and 25 other newly discovered miRNAs, were differentially methylated in shift workers compared to day workers. Of these, miR-219 has previously been implicated in circadian-related pathways. Genome-wide expression microarray analysis identified 319 differentially expressed transcripts in miR-219-overexpressed MCF-7 cells, which were subsequently analyzed by IPA. The most statistically significant network formed from these transcripts suggests that overexpression of miR-219 induced apoptotic and tumor-suppressive activities in MCF-7. Additional analysis indicated that a number of signaling pathways were affected following miR-219 overexpression, including interferon-α/β (IFN-α/β) singnaling, interferon-gamma (IFN-γ) singnaling, and JAK/STAT signaling. In addition, miR-219 appears to also be involved in the initiation of apoptosis signaling via the increase of TRAIL expression and induction of the caspase cascade.

Conclusion: Our results suggest that long-term shift work can lead to aberrant methylation patterns in miRNAs, including miR-219. Hypermethylation of the miR-219 promoter, as observed in our long-term shift workers, may suppress the expression of miR-219, potentially leading to downregulation of miR-219-mediated apoptosis and increased risk for cancer. This study may help us develop a more complete understanding of a potential mechanism for the increased risk of breast cancer observed in female long-term shift workers, which could be useful for providing additional insight in the development of preventative and therapeutic strategies.

Citation Format: Fengqin Shi, Yong Zhu, Alan Fu, Johnni Hansen, Richard Stevens, Ronghua Wang. Aberrant DNA methylation of miR-219 is associated with long-term shift work and cancer-relevant biological pathways. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4156. doi:10.1158/1538-7445.AM2013-4156

©2013 American Association for Cancer Research
2013