Differential contributions of porcine bocavirus NP1 protein N- and C-terminal regions to its nuclear localization and immune regulation

Porcine bocavirus (PBoV), a newly identified parvovirus in the family Parvoviridae, has been reported worldwide in swine with post-weaning multisystemic wasting syndrome, respiratory disease or diarrhoea and in asymptomatic swine. NP1 is a protein unique to the genus Bocavirus and its function is not fully understood. In this study, we show that the N-terminal region of PBoV NP1 contains two classical nuclear localization signals (cNLSs) and a non-classical NLS. The N-terminal region also inhibits the promoter activity of IFN-β and IFN-stimulated response element activity the same as full-length NP1 protein, but the PBoV NP1 C-terminal region does not. PBoV NP1 also induces NFκB activation by increasing the phosphorylation of p65, and we demonstrate that the C-terminal region (aa 168–218) is responsible for the induction of NFκB, although the cNLS region of NP1 enhances this activation. The data suggest that PBoV NP1 contains two functionally independent domains in its N- and C-terminal regions. Thus, the N-terminal region of PBoV NP1 is critical for its nuclear localization and IFN-related promoter inhibition, and the C-terminal region is critical for its induction of NFκB.