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.