Hepatitis B virus upregulates host expression of a-1,2-mannosidases via the PPARa pathway

Hu, Song; Jiang, Li-Bin; Zou, Xiao-Jing; Yi, Wei; Tian, De-Ying

To further confirm the effect of HBV on α-1,2mannosidase expression, plasmids containing seven individual viral genes of HBV (PTT22-HBx, PTT22-HBs, PTT22-preS2, PTT22-preS1, PTT22-HBc, PTT22-HBe, and PTT22-HBp) or control plasmids (PTT22-vector) were transfected into HepG2 cells. Western blot was used to determine the expression of HBx ( Figure 3A ), HBp ( Figure 3B ), HBc ( Figure 3C) , HBs, preS2, and preS1 ( Figure 3D ); whereas ELISA was used to estimate the expression of HBe ( Figure 3E ). The kifunensine did not affect the production or secretion of HBV virus particles, it did increase its recognition by DC-SIGN, resulting in activation of the immune response [8, 9] . Moreover, in our previous studies, we found that demannosylation is beneficial to HBV to escape DC-SIGN recognition [10] . Therefore, the upregulation of host α-mannosidases by HBV, as observed in this study, appears to contribute to viral escape [10] . HBV contains three envelope proteins made up of the preS1, preS2, and S domains: the large (L, preS1/preS2/S), middle (M, preS2/S), and small (S) envelope proteins [24] . The L and S proteins can only be singly glycosylated (P39 and GP42 for the L protein, and P24 and GP27 for S protein). There is also a N-glycosylation site (NXS/T) at N146 of the S region. On the other hand, the M protein can be bi-glycosylated (at the GP33 and GP36 sites) [25] . We used plasmids encoding different HBV proteins, including the L, M, and S proteins, to transfect HepG2 cells. Surprisingly, we found that only the L, M, and S proteins could increase the expression of MAN1C1; however, such an effect was not found for the other HBV proteins. As all the L, M, and S proteins include the S domain, we hypothesized that it was this region that induced the increase of MAN1C1. Therefore, the S protein was used to represent the envelope protein in the consequent experiments.