Enterovirus 71 induces apoptosis of SH‑SY5Y human neuroblastoma cells through stimulation of endogenous microRNA let-7b expression.

Enterovirus 71 (EV71) is a pathogenic microorganism that causes hand， foot and mouth disease. However， the epigenetic mechanisms behind how EV71 regulates host cell proliferation and apoptosis are unclear. In the present study， the ability of EV71 to induce apoptosis was analyzed in the SH-SY5Y human neuroblastoma cell line and the effect of this virus on the mRNA expression levels of various apoptotic markers， miRNA let-7b and cyclin D1 (CCND1)， was also investigated. The results demonstrated that EV71 induced SH-SY5Y cell apoptosis. An MTT assay revealed a significant inhibitory effect of EV71 on cell proliferation between 12-72 h post injection， compared with the control group. Furthermore， quantitative polymerase chain reaction and western blot analyses demonstrated that expression level of the apoptosis inhibitor Bcl-2 was markedly reduced， but the expression levels of the apoptosis-promoting factors Bax， caspase-7， caspase‑3 and active caspase-3 were markedly higher in the SH-SY5Y cells 12-48 h after EV71 infection， compared with the non-infected cells. In addition， flow cytometric assays revealed that EV71 arrested the cell cycle of host SH-SY5Y cells. Northern blot analysis revealed a marked miRNA let-7b hybridization signal in the EV71 virus-infected group compared with the non-infected group. Furthermore， western blotting confirmed that the CCND1 protein expression levels were significantly reduced in EV71-infected SH-SY5Y cells. EV71-inhibited SH-SY5Y proliferation was abrogated using let-7b specific 2'-O-Methyl-RNA， which inhibited endogenous miRNA let-7b expression. Thus， EV71 regulated the host SH‑SY5Y cell cycle and cell proliferation via stimulating endo-genous miRNA let-7b and directly targeting CCND1， therefore EV71 is a potential candidate for antiviral therapy.