%0 Journal Article %A Yeom, Sujeong %A Kim, Soo Shin %A Jeong, Hyerin %A Jang, Kyung Lib %T Hepatitis B virus X protein activates E3 ubiquitin ligase Siah-1 to control virus propagation via a negative feedback loop %D 2017 %J Journal of General Virology, %V 98 %N 7 %P 1774-1784 %@ 1465-2099 %R https://doi.org/10.1099/jgv.0.000856 %K Siah-1 %K ubiquitin-proteasome system %K HBx %K Hepatitis B virus %K p53 %I Microbiology Society, %X The seven in absentia homologue 1 (Siah-1) protein is an E3 ubiquitin ligase that induces ubiquitin-dependent proteasomal degradation of HBx, the principal regulatory protein of hepatitis B virus (HBV); however, its role in HBV propagation remains unknown. Here, we found that HBx upregulates Siah-1 levels in HepG2 but not in Hep3B cells, in which p53 is absent. For this effect, HBx sequentially activated ataxia telangiectasia mutated kinase and checkpoint kinase 2 via phosphorylation at the Ser-1981 and Thr-68 residues, respectively, which led to the activation of p53 via phosphorylation at the Ser-15 and Ser-20 residues. As a result, HBx was heavily ubiquitinated by Siah-1 and degraded by the ubiquitin–proteasome system in HepG2 cells, whereas this effect was marginal or undetectable in Hep3B cells. Knock-down of p53 in HepG2 cells downregulated Siah-1 levels and subsequently upregulated HBx levels, whereas ectopic p53 expression in Hep3B cells upregulated Siah-1 levels and subsequently downregulated HBx levels. In addition, Siah-1 knock-down impaired the ubiquitination and proteasomal degradation of HBx in HepG2 cells, whereas ectopic Siah-1 expression induced ubiquitin-dependent proteasomal degradation of HBx in Hep3B cells. The effects of HBx on p53 and Siah-1 were exactly reproduced in a 1.2-mer HBV replicon system, mimicking the natural course of HBV infection. In particular, Siah-1 knock-down upregulated the levels of HBx derived from the HBV replicon, resulting in an increase in HBV production. In conclusion, HBx modulates its own protein level via a negative feedback loop involving p53 and Siah-1 to control HBV propagation. %U https://www.microbiologyresearch.org/content/journal/jgv/10.1099/jgv.0.000856