Critical Role of K1685 and K1829 in the Large Protein of Rabies Virus in Viral Pathogenicity and Immune Evasion.

UNLABELLED: Rabies, one of the oldest infectious diseases, still presents a public health threat in most parts of the world today. Its pathogen, rabies virus (RABV), can utilize its viral proteins, such as the nucleoprotein and phosphorylation protein, to subvert the host innate immune system. For a long time, the large (L) protein was believed to be essential for RABV transcription and replication, but its role in viral pathogenicity and immune evasion was not known. Recent studies have found that the conserved K-D-K-E tetrad motif in the L protein is related to the methyltransferase (MTase) activity in the viral mRNA process. In the present study, a series of RABV mutations in this motif was constructed with the recombinant CVS-B2c (rB2c) virus. Two of these mutants, rB2c-K1685A and rB2c-K1829A, were found to be stable and displayed an attenuated phenotype in both in vitro growth and in vivo pathogenicity in adult and suckling mice. Further studies demonstrated that these two mutants were more sensitive to the expression of the interferon-stimulated gene product IFIT2 than the parent virus. Taken together, our results suggest that K1685 and K1829 in the L protein play important roles in pathogenicity and immune evasion during RABV infection. IMPORTANCE: Rabies continues to present a public health threat in most areas of the world, especially in the developing countries of Asia and Africa. The pathogenic mechanisms for rabies are not well understood. In the present study, it was found that the recombinant rabies viruses rB2c-K1685A and rB2c-K1829A, carrying mutations at the predicted MTase catalytic sites in the L protein, were highly attenuated both in vitro and in vivo. Further studies showed that these mutants were more sensitive to the expression of the interferon-stimulated gene product IFIT2 than the parent virus. These findings improve our understanding of rabies pathogenesis, which may help in developing potential therapeutics and an avirulent rabies vaccine.