Overview of viral and host miRNA functions related to Polyomavirus infection. Polyomavirus encoded miRNAs exert an autoregulatory role through targeting of LTAg, which plays an essential role in viral replication. This viral miRNA also plays a role in regulating the host immune response by targeting host factors, such as the stress-induced ligand ULBP3, that are essential for recognition of infected cells by the immune system. Host miRNAs can mimic the polyomavirus miRNA, thereby also influencing the expression of LTAg and consequently viral replication, but they might also affect viral protein synthesis by targeting the viral transcripts through binding at the 3′UTR of the viral transcripts. Next to this virus specific role, miRNAs are also shown to play a more general role in the immune response upon viral infection.