Title: A Polymorphism in MAPKAPK3 Affects Response to Interferon Therapy for Chronic Hepatitis C Short Title: MAPKAPK3 and IFN therapy for HCV infection

Background & Aims: This study aimed to identify host single nucleotide polymorphisms (SNPs) that are associated with the efficacy of interferon (IFN) therapy in patients with chronic hepatitis C. Methods: We examined whether 116 tagging-SNPs from 13 genes which are involved in Type I IFN signaling associate with the outcome of IFN therapy in Japanese case-control groups; the study included 468 sustained responders and 587 non-responders. Results: We identified 2 SNPs (rs3792323 [A/T] and rs616589 [G/A]), located in intron 2 of mitogen-activated protein kinase-activated protein kinase 3 (MAPKAPK3), that were associated with the outcome of IFN therapy in patients infected with hepatitis C virus (HCV) genotype 1b (P=4.6×10-5 and 4.8×10-5, respectively). The 2 SNPs were in strong linkage disequilibrium and multivariate logistic regression analysis showed that rs3792323 is an independent factor associated with the IFN efficacy (genotype 1b, P=0.0011). MAPKAPK3 is a kinase involved in the mitogen and stress responses, but the biological significance of MAPKAPK3 in IFN responses is poorly understood. Using an allele-specific transcript quantification assay in liver biopsy, we demonstrated that allele-specific expression of MAPKAPK3 mRNA, corresponding to the risk allele for non-response, was significantly higher than that of the other allele. Luciferase reporter assay data indicated that overexpression of MAPKAPK3 inhibits IFN-α-induced gene transcription via IFN-stimulated response element and IFN-γ activated site. Conclusions: The SNP rs3792323 in MAPKAPK3 associates with the outcome of IFN Tsukada H et al., Page 5 therapy in patients with HCV genotype 1b. Our functional analyses indicate that MAPKAPK3 inhibits IFN-α-induced antiviral activity. Tsukada H et al., Page 6