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.