CK2beta gene silencing increases cell susceptibility to influenza A virus infection resulting in accelerated virus entry and higher viral protein content

BACKGROUND: Influenza A virus (IVA) exploits diverse cellular gene products to support its replication in the host. The significance of the regulatory (β) subunit of casein kinase 2 (CK2β) in various cellular mechanisms is well established, but less is known about its potential role in IVA replication. We studied the role of CK2β in IVA-infected A549 human epithelial lung cells. RESULTS: Activation of CK2β was observed in A549 cells during virus binding and internalization but appeared to be constrained as replication began. We used small interfering RNAs (siRNAs) targeting CK2β mRNA to silence CK2β protein expression in A549 cells without affecting expression of the CK2α subunit. CK2β gene silencing led to increased virus titers, consistent with the inhibition of CK2β during IVA replication. Notably, virus titers increased significantly when CK2β siRNA-transfected cells were inoculated at a lower multiplicity of infection. Virus titers also increased in cells treated with a specific CK2 inhibitor but decreased in cells treated with a CK2β stimulator. CK2β absence did not impair nuclear export of viral ribonucleoprotein complexes (6 h and 8 h after inoculation) or viral polymerase activity (analyzed in a minigenome system). The enhancement of virus titers by CK2β siRNA reflects increased cell susceptibility to influenza virus infection resulting in accelerated virus entry and higher viral protein content. CONCLUSION: This study demonstrates the role of cellular CK2β protein in the viral biology. Our results are the first to demonstrate a functional link between siRNA-mediated inhibition of the CK2β protein and regulation of influenza A virus replication in infected cells. Overall, the data suggest that expression and activation of CK2β inhibits influenza virus replication by regulating the virus entry process and viral protein synthesis.