Indiana University-Purdue University Indianapolis (IUPUI) / The function(s) of the intracellular form of HBeAg, previously reported as the
preCore protein intermediate (p22) without the N-terminal signal peptide, remains elusive.
Here, we propose to elucidate the translocation of p22 during its formation from
endoplasmic reticulum (ER) to cytosol, how it differs from core in its inability to form a
capsid and the biological functions of cytoplasmic and nuclear p22. Firstly, we have
identified that a portion of p22, after the cleavage of its signal peptide in ER, is released
back into the cytosol through an ERAD-independent mechanism, as neither wildtype nor
dominant-negative p97 affected the ER-to-cytosol translocation of p22 or ER-Golgi
secretion of HBeAg. Secondly, despite sharing the same sequence with core protein except
for the extended 10 amino acid precore region at the N-terminus, we observed that p22
wildtype and C-7Q mutant are unable to form a capsid. Thirdly, we report that p22 but not
the secreted HBeAg significantly reduced interferon stimulated response element (ISRE)
activity and expression of interferon stimulated genes (ISGs) upon interferon-alpha (IFN-
α) stimulation. Furthermore, in line with this, RNA-seq analysis of ISG induction profile
from IFN-α treated patients showed that HBeAg(+) patients exhibited reduced and weak
antiviral ISG upregulations compared to HBeAg(-) patients. Further, mechanistic study
indicated that while p22 did not alter the total STAT1 or p-STAT1 levels in IFN-α treated
cells, it blocked the nuclear translocation of p-STAT1 by interacting with karyopherin α1,
indicating that the cytoplasmic p22 may impede JAK-STAT signaling to help the virus
evade host innate immune response and cause resistance to IFN therapy in patients.
Additionally, nuclear p22 and nuclear core were found to interact with the promoter regions (ISRE – containing) of ISGs, suggesting a new mechanism of inhibition of ISG expression
upon stimulation. Finally, we found that the nuclear p22 can bind to cccDNA
minichromosome and affects cccDNA maintenance and/or transcription. Thus, our results
indicate that there is a novel ER sorting mechanism for the distribution of the intracellular
and secretory HBeAg, and the intracellular HBeAg may contribute to HBV persistence by
interfering with IFN-α elicited JAK-STAT signaling and regulating cccDNA metabolism.
| Identifer | oai:union.ndltd.org:IUPUI/oai:scholarworks.iupui.edu:1805/21091 |
| Date | 09 1900 |
| Creators | Mitra, Bidisha |
| Contributors | Guo, Haitao, Androphy, Elliot J., Kaplan, Mark, Yu, Andy, Lu, Tao |
| Source Sets | Indiana University-Purdue University Indianapolis |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
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