Adhesion contact kinetics of HepG2 cells during Hepatitis B virus replication: Involvement of SH3-binding motif in HBX

It has been shown that Hepatitis B virus (HBV) replication directly alters the expression of key cytoskeleton-associated proteins which play key roles in mechanochemical signal transduction. Nevertheless, little is known on the correlation between HBV replication and the subsequent adhesion mechanism of HBV-replicating cells. In this study, it is demonstrated that the lag time of adhesion contact evolution of HepG2 cells with HBV replication is significantly increased by two times compared to that of normal HepG2 cell on collagen coated substrate. During the initial 20 min of cell seeding, only diffuse forms of vinculin was detected in HBV replicating cells while vinculin-associated focal complexes were found in normal and control cells. Similar delay in cell adhesion in HBV-replicating cells was observed in cells transfected with HBX, the smallest HBV protein, suggesting its involvement in this cellular process. In addition, a proline rich region found in many SH3 binding proteins was identified in HBX. HBX was found to interact with the focal adhesion protein, vinexin-β, through the SH3 binding. Furthermore, HepG2 cells with HBV replication showed evidence of cell rounding up, possibly resulting from cytoskeletal reorganizations associated with interaction between HBX and vinexin-β. Taken together, our results suggest that HBX is involved in the cytoskeletal reorganization in response to HBV replication.