Background: Herpes simplex virus type 1 (HSV-1) is a potent inducer of nuclear factor-KB (NF-kappaB), a cellular transcription factor with a crucial role in promoting inflammation and controlling cell proliferation and survival.
Objectives: On the basis of the recent demonstration that HSV-1-induced NF-kappaB is actively recruited to KB-binding sites in the HSV-1 infected-cell protein 0 (ICPO) promoter enhancing viral transcription and replication, we investigated the effect of proteasome inhibitors MG132, MG115 and epoxomicin, which block NF-kappaB function by preventing the degradation of the inhibitory proteins IkappaBalpha, on HSV-1-induced NF-kappaB activation and viral replication.
Methods: Antiviral activity of proteasome inhibitors was analysed in HSV-1-infected HEp2 cells by determining infective virus titres by CPE50%, viral RNA synthesis by RT-PCR, and viral protein synthesis by immunoblot analysis or immunofluorescence. ICPO transcription was studied in transient transfection experiments using the ICPO promoter-luciferase IE1-Luc construct. IkappaBalpha degradation and NF-kappaB activity were determined by immunoblot analysis and EMSA, respectively.
Results: Proteasome inhibitors were found to prevent HSV-1-induced NF-kappaB activation in the early phase of infection. Block of virus-induced NF-kappaB activation resulted in inhibiting HSV-1 ICPO gene expression, in decreasing the level of immediate-early and late viral proteins, and ultimately in greatly suppressing viral replication. The antiviral effect was lost if treatment was started after NF-kappaB activation, and appeared to be independent of the HSV-1-induced activation of the JNK pathway.
Conclusions: Proteasome inhibitors possess NF-kappaB-dependent antiherpetic activity. The results described further identify the IKK/NF-kappaB pathway as a suitable target for novel antiherpetic drugs.