Human bocavirus 1 (HBoV1) is an important pathogen causing lower respiratory tract infection. The VP1 unique region (VP1u), consisting of 129 amino acids at the N-terminus of the HBoV1 structural protein VP1, is an important component of virus infection. Bioinformatics analysis predicted that HBoV1 VP1u exhibits two bipartite nuclear localization signals (NLS) and contains four basic regions (BRs). The two potential bipartite NLSs consist of BR2 and 3 and BR3 and 4, respectively. In this study, we inserted the truncated vp1u sequences into a double EGFP fusion expression vector and confirmed the vimentin (VIM)-HBoV1 VP1u interaction by mass spectrometry and immunoprecipitation. The results of our IFA analysis showed that all four VP1u BRs displayed strong nuclear transport functions. We further demonstrated that VP1u interacted with VIM and that they colocalized in the cytoplasm. VP1u expression in the cells enhanced the VIM expression, and the VP1u expression also increased upon VIM overexpression, although it was not affected by VIM knockdown. Upon VIM overexpression, VP1u nucleation was significantly enhanced, but was inhibited by VIM downregulation. These results indicate that the VP1u-VIM interaction could be involved in the nuclear transport of VP1u. VP1u nucleation might further affect HBoV1 replication and infection. This study could potentially help clarify the function of VP1u by further revealing the HBoV1 nuclear transport mechanism and provide a new approach for elucidating the molecular mechanism of HBoV1 replication.
Keywords: HBoV1; NLS; VP1u; basic regions; nuclear transport; vimentin.