Abstract
Abstract DICER1 is required for generation of mature microRNAs (miRNAs) and other short noncoding RNAs. Reduced DICER1 levels are associated with adverse outcomes in a variety of cancers and multiple lines of evidence suggest DICER1 is a tumor suppressor. The effects of reduced DICER1 on mRNA transcript abundance in tumor cells remain largely unknown. To determine how reduced DICER1 levels contribute to tumor phenotypes we used shRNA to stably knock down DICER1 in endometrial cancer cell lines for extended periods (up to 25 passages). Reduced DICER1 levels had no effect on cell proliferation but were associated with enhanced cell migration and increased growth in soft agar. MiRNA profiling for the KLE cancer cell line DICER1 knockdowns (two different DICER1 shRNA constructs) revealed that miRNA levels were decreased overall. Not surprisingly, many mRNA transcripts were upregulated in the DICER1 knockdowns. A striking number of interferon stimulated genes (ISGs) showed upregulation. Upregulation of six ISG transcripts was validated by qRT-PCR in three independent knockdowns of DICER1 in KLE cells. IFNα, a key upstream regulator of the interferon response, was significantly increased in DICER1 knockdowns (KLE and additional endometrial cancer cell lines). IFNα protein secreted in media of DICER1 knockdown cells activated an interferon response in HT29 colon carcinoma cells. The majority of ISGs with increased transcript levels lacked miRNA target sequences and as such it seemed unlikely that the increase in expression levels was secondary to reduced miRNA levels. We tested the hypothesis that defects in miRNA processing could trigger an interferon response. We showed that DICER1 knockdowns in which miRNA processing is reduced have increased levels of pre-microRNAs in the cytoplasm. Pre-microRNAs are double-stranded molecules and long enough (60-100 nt) to activate the dsRNA sensors in the cytoplasm, such as Mda5/IFIH1, that typically sense viral dsRNA (> 30 nt) and stimulate the interferon response. Knockdown of DROSHA, necessary for processing of pri-miRNAs to pre-miRNAs, did not result in accumulation of pre-miRNAs and did not cause an interferon response. Our findings suggest elevated pre-microRNA levels trigger the interferon response to double stranded RNA (incompletely processed miRNA and other species). Rescue experiments (restoring DICER1 function) are currently underway to shed additional light on how reduced double-stranded RNA processing might elicit an interferon response. Work is ongoing to determine the relationship between the observed interferon response and the migration and soft agar phenotypes. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2312. doi:1538-7445.AM2012-2312
Published Version
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