Inhibition of Herpes Simplex Virus Type 1 by Human Salivary Cystatin SN and its Proteinase Inhibitory Regions

다국어 초록 (Multilingual Abstract)

Cystatins are a family cysteine proteinase inhibitors, many of which possess antiviral properties. Previous studies demonstrated that human cystatin C and salivary cystatin SN inhibit herpes simplex virus type 1〔HSV-1〕replication. The full-length cystatin C and SN do not function as serine proteinase inhibitors, but contain serine proteinase inhibitory regions. The goal of this study was to evaluate whether the inhibition of HSV-1 by cystatin SN occurs through its cysteine or serine proteinase inhibitory regions. using viral yield reduction assays, our results demonstrated that the N-truncated cystatin SN〔a deletion of one of the conserved cysteine proteinase inhibitory region〕was not able to effectively inhibit HSV-1〔20% versus 90% by the full-length cystatin SN〕. The results also showed that a circular peptide to the serine proteinase inhibitory region of cystatin SN inhibited HSV-1 by only 20%, while the linear peptide to the same region failed to inhibit HSV-1. Previous studies indicated that the inhibition of HSV-1 replicatin by cystatin SN occurred during the later stages of the viral infection. Thus, we have examined, by western blot analysis, the effect of cystatin SN on specific HSV-1 structural proteins 〔VP5, VP19, VP23, VP21/VP22a〕, as well as its effect on a non-structural DNA binding protein produced at an earlier stage in the viral life cycle〔ICP8〕. We report that cystatin SN reduced the production of total HSV-1 proteins, as well as all the individual proteins tested, while the circular peptide inhibited only two of the proteins tested, VP5 and VP19. In conclusion, the role of cystatin SN in HSV-1 inhibition appears to involve both ist cysteine and serine proteinase inhibitory regions.