MEK inhibition impairs influenza B virus propagation without emergence of resistant variants.

Influenza A and B viruses are still a major worldwide threat. We demonstrate that influenza B virus infection induces signaling via the Raf/MEK/ERK cascade, a process required for efficient virus production. Expression of dominant-negative Raf and ERK mutants or treatment with a MEK inhibitor (U0126) strongly impaired viral propagation, while selective activation of the pathway resulted in increased virus titers. MEK inhibition appears to interfere with a distinct viral nuclear export process. Most importantly, no resistant virus variants emerged in the presence of U0126 demonstrating that influenza viruses cannot easily adapt to the missing cellular function.