Human cytomegalovirus miR-US4-5p promotes apoptosis via downregulation of p21-activated kinase 2 in cultured cells.

The human cytomegalovirus (HCMV) encodes >= 26 microRNAs (miRNAs). These miRNAs are utilized by HCMV to regulate its own genes in addition to the genes of the host cell, during infection. The present study first identified p21-activated kinase 2 (PAK2) as a target of hcmv-miR-US4-5p, via hybrid polymerase chain reaction, which was further verified using a luciferase reporter assay. The protein expression level of PAK2, detected via western blotting, was demonstrated to be directly downregulated by overexpression of hcmv-miR-US4-5p in HEK293, HELF and THP-1 cells. Furthermore, it was demonstrated that the PAK2 protein level in naturally infected HELF cells was gradually decreased at 24, 48 and 72 h post infection with increased hcmv-miR-US4-5p expression. The use of PAK2-specific small interfering RNA and an inhibitor for hcmv-miR-US4-5p, demonstrated that the promotion of apoptosis by hcmv-miR-US4-5p in these cells was specifically mediated via inhibition of PAK2 expression. These results indicated that hcmv-miR-US4-5p may exhibit this activity during natural HCMV infection, in order to establish a balance between the host cell and virus.