The MxAL612K and the MxAΔC mutants, which are unable to self-assemble, retain the ability to interact with HBcAg, suggesting that the self-assembly of MxA is not required for the recruitment of HBcAg. This supports the current model in which high molecular weight MxA oligomers are a storage form, whereas MxA monomers are the active form of MxA,24 at least in terms of its anti-HBV buy PD0325901 action. Using distinct intracellular membrane structural markers, we identified the large perinuclear complexes

in which MxA and HBcAg aggregate. It is reasonable to speculate that the MxA sequesters the viral nucleocapsid protein to form complexes at sites where either MxA assembles or the viral particles form. Recently, it has been found that MxA self-assembles into rings and associates with the smooth ER.25 On the other hand, the envelopment and budding of the mature capsids of HBV enclosed with HBcAg also occurs in the ER.26 Nevertheless, our colocalization and BFA experiments clearly excluded association of the large MxA-HBcAg complexes with either the ER or the Golgi apparatus. Rather, our results showed that the perinuclear location of the complexes is dependent on the stability of microtubules. The dependence on microtubules supports the recently proposed concept of aggresomes,27 implying that either HBV capsids assemble in aggresomes buy GDC-0449 or MxA takes the HBcAg to the aggresomes for degradation.

It has been proposed that

association of MxA with viral nucleoproteins may hijack the nucleoproteins, preventing them from transcription of the viral genome or the assembly of new viral particles; however, so far, no direct evidence has been provided. Real-time imaging and photobleaching techniques allowed us to investigate the mobility of nucleoprotein in living cells. Our data indicate that the formation of MxA-HBcAg complexes immobilizes the HBcAg. Although this mechanism may be involved in both the inhibition of nucleocapsid assembly and the enveloping of viral nucleocapsids, our data suggest that MxA-HBcAg interaction interferes in the early stage of core particle formation, based on the decrease in cytoplasmic encapsidated pgRNA and the RC-DNA. Our data is consistent with previous studies showing that IFN prevents MCE the formation of replication-competent HBV capsids.28, 29 Although the anti-HBV activity of MxA has been defined, in view of the antagonistic effects of HBcAg on the antiviral activity of MxA and the lack of global efficiency of IFNα in clinical treatment, the discovery of methods that either strengthen the trapping of HBcAg or disrupt the binding of HBcAg to the MxA promoter is a practical strategy. In this context, the findings of our present study suggest that small molecules based on the MxA CID domain may be a promising choice. Additional Supporting Information may be found in the online version of this article.