Transmissible Gastroenteritis Virus Infection Up-Regulates FcRn Expression via Nucleocapsid Protein and Secretion of TGF-ß in Porcine Intestinal Epithelial Cells

Qian, Shaoju; Gao, Zitong; Cao, Rui; Yang, Kang; Cui, Yijie; Li, Shaowen; Meng, Xianrong; He, Qigai; Li, Zili

In order to further explore N functional domains, N protein truncations were expressed in this study. According to the Lasergene DNASTAR Protean 9.0 software prediction, the N-protein contains two nuclear export signal (NES) sequences at aa 221-236 (NES-1), aa 330-353 (NES-2), an RNA-binding region at aa 33-159, a specific SR-rich region at aa 156-198 and a ZnF region at aa 137-219 ( Figure 5A ). TGEV N protein is mainly located at aa 128-252 and this region has high hydrophilicity and flexibility. In order to study the TGEV N protein, the structure of which is essential for FcRn activation, four truncation mutants were cloned into the eukaryotic expression plasmid, pCAGGS-HA, named as N1(1-128), N2(128-382), N3(252-382), and N4(128-252). The relationship between these mutants and FcRn activation was analyzed through luciferase reporter assays and Western blot. As shown in Figure 5 , N4, which contains NES1 and the immune dominant area, compared with the total length of the TGEV N protein, increased the FcRn activation and expression (Figures 5B,C) . The result showed that the central region (128-252) of N protein is critical for FcRn activation.