Search

Mouse mammary tumor virus (MMTV) induces breast cancer in mice in the absence of known virally-encoded oncogenes. Tumorigenesis by MMTV is thought to occur primarily through insertional mutagenesis, leading to the activation of cellular proto-oncogenes and outgrowth of selected cells. Here we investigated whether MMTV encodes microRNAs (miRNAs) and/or modulates host miRNAs that could contribute to tumorigenesis. High throughput small RNA sequencing analysis of MMTV-infected cells and MMTV-induced mammary tumors demonstrates that MMTV does not encode miRNAs. However, infected tissues have altered levels of several host miRNAs, including increased expression of members of the oncogenic miRNA cluster, miR-17-92. Notably, similar changes in miRNA levels have been previously reported in human breast cancers. Combined, our results demonstrate that virally encoded miRNAs do not contribute to MMTV-mediated tumorigenesis, but that changes in specific host miRNAs in infected cells may contribute to virus replication and tumor biology., (Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.)

Many eukaryotes and some viruses encode microRNAs (miRNAs), small RNAs that post-transcriptionally regulate gene expression. While most miRNAs are generated through the activity of RNA Polymerase II (RNAP II) and subsequent processing by Drosha and Dicer, some viral miRNAs utilize alternative pathways of biogenesis. Some members of the herpesvirus and retrovirus families can direct synthesis of miRNAs through RNAP III transcription rather than RNAP II and can utilize atypical enzymes to generate miRNAs. Though the advantages of alternative miRNA biogenesis remain unclear for herpesviruses, the retroviral miRNA biogenesis routes allow the RNAP II transcribed retroviral genome to escape Drosha cleavage while still expressing abundant, biologically-active miRNAs. These RNAP III-derived miRNAs have unique characteristics that allow for their identification and characterization. In this article, we describe procedures to predict, validate, and characterize RNAP III-transcribed miRNAs and other small RNAs, while providing resources that are also useful for canonical miRNAs., (Copyright © 2015. Published by Elsevier Inc.)