Synthetic double-stranded RNA induces retinoic acid-inducible gene-I in mouse osteoblastic cells

Retinoic acid inducible gene-I (RIG-I) is a member of the DExH box family of proteins. RIG-I acts as a sensor of viral infections through the recognition of viral double-stranded RNA (dsRNA). Recently, it was demonstrated that polyinosinic acid:polycytidylic acid [poly(I):poly(C)], a synthetic dsRNA analogue, induced the expression of RIG-I in various cell types, such as vascular endothelial cells and gingival fibroblasts. However, it remains unclear whether RIG-I is induced in osteoblasts in response to poly(I):poly(C). In the present study, we investigated the effects of poly(I):poly(C) on the expression of RIG-I in mouse osteoblastic MC3T3-E1(E1) cells. We found that poly(I):poly(C) increased the expression level of RIG-I in E1 cells, and that recombinant interferon-β (IFN-β) induced the expression of RIG-I mRNA in E1 cells. An anti-IFN-β neu-tralizing antibody partially inhibited poly(I):poly(C)-induced RIG-I expression. These results indicate that RIG-I production is induced by poly(I):poly(C)-provoked IFN-β in mouse osteoblastic E1 cells. We suggest that osteoblasts are involved in antiviral defense as well as in bone metabolism. Results of further studies will provide more clues regarding the molecular function of osteoblasts in viral infection.