A. KANNAN^1,2, M. SUOMALAINEN¹, M. AMSLER¹, H.V. TRINH³, A. FRANCESCHINI¹, C. VON MERING¹, S. HEMMI¹, U.F. GREBER<sup>1

1</sup>Institute of Molecular Life Sciences, University of Zurich, Switzerland, ²Life Science Zurich Graduate School, Molecular Life Sciences Program, Zurich, Switzerland, ³present address: US Military HIV Research Program, WRAIR and Henry M. Jackson Foundation for the Advancement of Military Medicine, MD, USA

Viruses elicit unprecedented complexities when they interact with their host cells. This involves changes in signalling, gene expressions, metabolites and lipids. Together these changes can drive the infected cell towards the state of a viral factory. For example adenovirus infected cancer cells produce thousands of progeny viruses in the nucleus, and release the virions in a poorly understood process of oncolysis. Adenoviruses are non- enveloped DNA viruses infecting many different vertebrates, including humans. They cause upper respiratory infections in children, and recurring infections in adults. For immune- compromised individuals, adenoviruses are a major risk factor, and can lead to severe health problems and fatalities. To better understand systems aspects of adenovirus infection, we carried out microRNA profiling with mirBase18 upon HAdV-C5 (species C) infection of human lung adenocarcinoma A549 cells. Cellular microRNAs are important regulators of gene expression in both normal and pathological processes. They are short ~22 nucleotide RNA sequences and bind to complementary sequences in the 3’ UTR of target mRNAs which can result in mRNA silencing. Using micro-array profiling and quantitative reverse transcription polymerase chain reaction (qRT-PCR), we found downregulated host miRNAs in HAdV-C5 infected cells, and also in HAdV-B3 infected cells. We show that chemically synthesized miRNA mimetics of the downregulated host microRNAs reduced HAdV-C5 infections of transformed and non-transformed cells. They also reduced Influenza A virus, Vesicular Stomatitis virus, and Semliki Forest virus infections of cultured cells. Transfected miRNA mimetics led to transcriptional activation of a range of interferon inducible genes. In silico analyses using canonical and noncanonical interaction models with potential target mRNAs revealed potential candidate target genes for expression modulation. Further studies on the mode of anti-viral action of the microRNA mimetics revealed the activation of dsRNA sensors and downstream innate immune responses, independent of canonical seed sequences recognizing target mRNAs. This study reveals new properties of host and viral regulatory networks and underlying mechanisms by which microRNA mimetics antagonize viral infections.