There is one specific microRNA called miR-122 which is specific to human liver. This is absolutely required for Hepatitis C virus (HCV) replication. If you take it away, the virus can't replicate. This is why HCV is hepatotropic (hepato- means special affinity to liver). Drugs that target miR-122 would be a good anti-viral therapy. Reduced miR-122 levels in the liver is associated with a rare liver cancer called hepatocellular carcinoma. HCV is a small enveloped + single-stranded RNA virus. miRs, generally, bind to 3'UTR repressing gene expression. But, miR-122 binds to 5'UTR of the viral mRNA stimulating viral proteins. It is amazing how viruses use host machinery for their own replication. When host cells (human) recognize a viral infection they induce apoptosis (programmed cell death or suicide) but viruses block apoptosis. Host cells tend to stop dividing upon infection, but viruses prevent cell cycle arrest. Human cells have numerous mechanisms to reduce and stop ...