Measles Virus Nonstructural C Protein Modulates Viral RNA Polymerase Activity by Interacting with Host Protein SHCBP1

Abstract

cMost viruses possess strategies to circumvent host immune responses. The measles virus (MV) nonstructural C protein suppresses the interferon response, thereby allowing efficient viral growth, but its detailed mechanism has been unknown. We identified Shc Src homology 2 domain-binding protein 1 (SHCBP1) as one of the host proteins interacting with the C protein. Knockdown of SHCBP1 using a short-hairpin RNA greatly reduced MV growth. SHCBP1 was found to be required for viral RNA synthesis in the minigenome assay and to bind to the MV phosphoprotein, a subunit of the viral RNA polymerase. A stretch of 12 amino acid residues in the C protein were sufficient for SHCBP1 binding, and the peptide containing these 12 residues could suppress MV RNA synthesis, like the full-length C protein. The central region of SHCBP1 was found to bind to the C protein, as well as the phosphoprotein, but the two viral proteins did not compete for SHCBP1 binding. Our results indicate that the C protein modulates MV RNA polymerase activity by binding to the host protein SHCBP1. SHCBP1 may be exploited as a target of antiviral compounds. Measles, an acute human disease characterized by high fever and a generalized maculopapular rash, is still a major cause of morbidity and mortality of children worldwide (1). Measles virus (MV), the causative agent of the disease, is an enveloped virus classified as a member of the genus Morbillivirus in the family Paramyxoviridae. The virus contains a nonsegmented negativestrand RNA genome ϳ16 kb in length, with six genes encoding the nucleocapsid (N), phospho-(P), matrix (M), fusion, hemagglutinin, and large (L) proteins, respectively. The P gene encodes two additional nonstructural proteins, the V and C proteins, via the RNA editing and alternative translational initiation in a different reading frame, respectively (2, 3).The V and C proteins have been shown to counteract the host interferon (IFN) response by various mechanisms. The V protein interacts with several molecules involved in the induction or signal transduction of IFN-␣ and IFN-␤ (type I IFNs), including the RNA helicases melanoma differentiation-associated gene 5 (MDA5) and LGP2 (4), IB kinase ␣ (5), signal transducer and activator of transcription 1 (STAT1) (6), STAT2 (7,8), and Janus kinase 1 (6), and interferes with their activity. The function of the C protein is less clear. A recombinant MV lacking the C protein (MV⌬C) neither propagates nor causes symptoms such as Koplik spot and rash in experimentally infected nonhuman primates (9, 10). Furthermore, MV⌬C exhibits attenuated growth in cells possessing the intact type I IFN system (11-14), partly through protein kinase PKR-mediated translation inhibition (13) and . Since the C protein downregulates viral RNA synthesis (12, 15, 16), it was proposed that the C protein allows the virus to escape detection by the cytosolic RNA sensors retinoic acid-inducible gene I (RIG-I) and MDA5 and prevents IFN production (12). A recent study reported that the transfected C protein can interfere with...

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