Virus Meets Host MicroRNA: the Destroyer, the Booster, the Hijacker

Virus-host interactions highlight key regulatory steps in the control of gene expression. MicroRNAs (miRNAs) are small non-coding RNAs that regulate protein production via base pairing with mRNAs. Both DNA and RNA viruses have evolved mecha-nisms to degrade, boost, or hijack cellular miRNAs to benefit the viral life cycle. This minireview focuses on recent discoveries in virus-host miRNA interactions. Viruses are masters of gene regulation. Their parasitic life styleemploys host machinery to carry out basic biological pro-cesses, from transcription to protein synthesis. Thus, viruses can dramatically downsize their genomes to the minimum number of genes essential for successful infection (1). Even though some vi-ruses, such as pandoravirus (2) and mimivirus (3, 4), encode as many as several thousand proteins—more than some free-living bacteria—they are exceptions to the rule. Typical mammalian herpesviruses possess from 70 to 200 genes in 120,000 to 250,000 base pairs of viral genomic DNA (5). These viral genomes are remarkably compacted compared to those of the host. For exam-ple, of the 3.2 billion base pairs in the human genome, more tha