Exosome-associated tetraspanin CD63 is a potential target for the inhibition of infectious envelope formation of hepatitis B virus

【Background/aim】The intraluminal vesicles (ILVs) generated within multivesicular bodies (MVBs) have been implicated in the late synthesis stages of HBV. In this study, we tried to clarify the association between HBV and the tetraspanin protein CD63, which is known to be a prominent and essential component of ILVs.
【Methods】Using HBV-expressing cells, we observed colocalization of CD63 and HBV proteins with immunofluorescent microscopy. After the depletion of CD63 with siRNA, intracellular/extracellular viral components were quantified generally. 
【Results】siRNA-mediated depletion of CD63 induced a substantial accumulation of intracellular LHBs protein but did not alter the levels of either intra- or extracellular HBV DNA, nor pregenomic RNA. Consistent with these findings, we found that markedly less LHBs protein was associated with the released HBV particles from CD63 siRNA-treated cells. Therefore, it was considered that CD63 is required for the efficient incorporation of LHBs to the envelope. Additionally, after the CD63 depletion, the amount of 2.4/2.1 kb mRNA was increased, suggesting that CD63 might affect the transcription of envelope proteins. Importantly, the HBV viral particles that were shed from CD63-depleted cells were substantially less infective than those collected from control cells. 
【Conclusion】These findings implicate CD63 might be an important component in the formation of infectious HBV particles. The inhibition of a potential interaction between CD63 and LHBs might be an option for a novel antiviral approach.