California researchers have found a previously unrecognized role for microRNAs: aiding and abeting hepatitis C virus in the liver. Peter Sarnow and colleagues at Stanford University School of Medicine found that a liver-specific microRNA interacts with the 5' noncoding region of viral RNA to enhance replication.1 The authors looked at miR-122, which accounts for 70% of microRNAs found in the liver, to see if hepatitis C might be using the host microRNA "for its own good," says Sarnow.

Hepatitis C RNA in Huh7 liver cell lines was reduced by about 80% when the researchers inactivated miR-122. And with miR-122 active, viral RNA with mutations in the 5' noncoding region failed to accumulate. Ectopically expressed miR-122 containing corresponding 5' mutations restored hepatitis C RNA levels, arguing against the possibility that the 5' mutation lowered levels through misfolding.

Previous work has shown that microRNAs can repress translation by binding an mRNA's...

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