Nuclear Import of Epstein-Barr virus BLLF2 is Mediated by an Importin β1-Dependent Mechanism

Abstract

Background: Epstein-Barr virus (EBV), the pathogen of several human malignancies, encodes many proteins that require to be transported into the nucleus for viral DNA reproduction and nucleocapsids assembly in the lytic replication cycle. A nuclear membrane phosphoprotein encoded by EBV BLLF2, is believed to associate with viral DNA packaging and primary egress across the nuclear membrane. Results: Here, fluorescence microscope, mutation analysis, interspecies heterokaryon assays, co-immunoprecipitation assays and western blot were performed to explore the nuclear import mechanism of BLLF2. As results, BLLF2 was shown to be a nucleocytoplasmic shuttling protein, which was mediated neither by chromosomal region maintenance 1 (CRM1)- nor transporter associated with antigen processing (TAP)-dependent pathway. Yet, two functional nuclear localization signals (NLSs) of BLLF2, NLS1 (16KRQALETVPHPQNRGR31) and NLS2 (48PPVAKRRR58), were identified, whereas the predicted NES was nonfunctional. Finally, BLLF2 was proved to transport into the nucleus via Ran-dependent and importin β1-dependent pathway. Conclusions: This mechanism may contribute to a more extensive insight of the assembly and synthesis of EB virions in the nucleus, thus affording a new direction for the treatment of viruses.