Persistent prion infection disturbs the function of Oct-1, resulting in the down-regulation of murine interferon regulatory factor-3

Homma, Takujiro; Ishibashi, Daisuke; Nakagaki, Takehiro; Fuse, Takayuki; Sano, Kazunori; Satoh, Katsuya; Atarashi, Ryuichiro; Nishida, Noriyuki

We have investigated the promotion of the murine IRF-3 gene and found promoter activity within the region nt -119 to -1 ( Fig. 1a and 1b), which contains 3 different promoter binding sites. It has been shown that E2F1 negatively regulates human IRF-3 gene expression 13 . Although the E2F1 site was also present in the murine promoter, the E2F1 site mutation had little effect on promoter activity ( Fig. 3h and 3i ). Mach et al. have shown that Oct-1 also bound to the human IRF-3 promoter 14 . Importantly, the putative transcription factor binding sites in 59 flanking region are very similar between human and murine IRF-3 promoter (Supplementary Fig. S5 ). However, the contribution of Oct-1 in human IRF-3 promoter remains controversial and elusive. In our experimental study, mutations in the Oct-1 binding site lost their promoter activity (Fig. 3c to 3f) and exogenous Oct-1 enhanced the activity (Fig. 4b) . In conclusion, Oct-1 positively regulates the IRF-3 promoter activity, while E2F1 and AML1 are not involved in murine IRF-3 gene regulation. Intriguingly, Oct-1 expression was significantly reduced in two distinct prion strains-infected cells and mice brains ( Fig. 5 and Supplementary Fig. S6 ). Although we are not able to exclude yet the possibility that the accumulation of abnormal prion protein may directly impair the function of Oct-1, prion infection might alter the expression of Oct-1 as a result of its destructive effect on protein synthesis in the host cell. It has recently been reported that prion infection could impair the host's ability to synthesize protein by means of inhibition of double-stranded RNA-activated protein kinase (PKR)-dependent eIF-2a phosphorylation 15, 16 . Another study revealed that the global alteration of gene expression has occurred in prion-infected mouse brains by unknown mechanisms 17 .