Influenza A virus is a cytolytic virus that induces apoptosis in numerous cell types. However, molecular mechanism of cell apoptosis induced by influenza A virus is not well understood. The present study was aimed to investigate the molecular mechanism of miR-34a involved in influenza A virus induced apoptosis.

Firstly, microRNA array was used to select miRNAs involved in influenza A virus infection. Then, Luciferase reporter assay and western blot were carried to determine the target gene of miR-34a. Finally, miR-34a mimic was transfected in influenza A virus-infected A549 cells, and western blot was used to test the function of miR-34a and its target gene in in influenza A virus infection.

miR-34a was found significantly down-regulated in influenza A virus-infected A549 cells and was further confirmed by qRT-PCR in vitro and in vivo (P < 0.01). Next, transfection miR-34 mimic/inhibitor in influenza A virus-infected A549 cells showed that overexpression of miR-34a could inhibit influenza virus-induced apoptosis. Furthermore, target prediction analysis revealed that miR-34a complemented to the 3′-UTR of Bax mRNA. Luciferase reporter assay and western blot confirm that miR-34a directly targeted Bax. Moreover, we detected influenza virus infection enhanced the luciferase reporter translational activity in A549 cells transfected with the construct with Bax 3′-UTR encoding miR-34a binding site. However, western blot analysis showed that the up-regulation of Bax protein level was significantly reversed by overexpression miR-34a.

It is, therefore, concluded that influenza virus infection regulated pro-apoptotic Bax expression through miR-34a downregulation, which might be the partial mechanism of influenza virus-induced cell apoptosis.