Curcumin assists anti-EV71 activity of IFN-alpha by inhibiting IFNAR1 reduction in SH-SY5Y cells

Background and aim: Enterovirus 71(EV71) can cause severe hand, foot, and mouth disease (HFMD) with brain tissue involvement. Few effective anti-EV71 drugs are presently available in clinical practice. Interferon-alpha (IFN-alpha) was ineffective while Curcumin was effective in restricting EV71 replication in non-neuronal cells. Ubiquitin-proteasome-mediated degradation of interferon-alpha receptor 1 (IFNAR1) protein contributes to IFN-alpha resistance. Current study aimed to determine synergistic inhibition of EV71 by Curcumin and IFN-alpha in human neuroblastoma SH-SY5Y cells. Methods: SH-SY5Y cells were infected with mock-/Curcumin-pre-incubated EV71 or transfected with plasmid containing interferon-stimulated response element (ISRE) or mRNA containing viral internal ribosomal entry site (IRES) following by post-treatment with Curcumin with or without IFN-alpha. Supernatant IFN-alpha/beta was detected by ELISA. ISRE, IRSE, proteasome and deubiquitinating activity were measured by luciferase assay. EV71 RNA and viral protein or IFNAR1 were determined by qPCR and western blot, respectively. Results: EV71 flailed to completely block IFN-alpha/beta production but inhibited IFN-alpha signal. Curcumin only slightly inhibited EV71 proliferation without modulating virus attachment and internalization. However, Curcumin addition restored IFN-alpha-mediated ISRE activity thus significantly inhibiting EV71 replication. Furthermore, EV71 also reduced IFNAR1 protein with proteasome-dependence in SH-SY5Y cells, which can be reversed by Curcumin addition with the evidence that it lowered proteasome activity. Conclusion: These data demonstrate that Curcumin assists anti-EV71 activity of IFN-alpha by inhibiting IFNAR1 reduction via ubiquitin-proteasome disruption in SH-SY5Y cells.