Tumor metastasis is responsible for the high mortality rates in patients with hepatocellular carcinoma (HCC). Absent in melanoma 2 (AIM2) has been implicated in inflammation and carcinogenesis, although its role in HCC metastasis remains unknown. In the present study, we show that AIM2 protein expression was noticeably reduced in HCC cell lines and clinical samples. A reduction in AIM2 was closely associated with higher serum AFP levels, vascular invasion, poor tumor differentiation, an incomplete tumor capsule and unfavorable postsurgical survival odds. In vitro studies demonstrated that AIM2 expression was modulated by hepatitis B virus X protein (HBx) at transcriptional and post‐translational levels. HBx overexpression markedly blocked the expression of AIM2 at mRNA and protein levels by enhancing the stability of Enhancer of zeste homolog 2 (EZH2). Furthermore, HBx interacted with AIM2, resulting in an increase of AIM2 degradation via ubiquitination induction. Functionally, knockdown of AIM2 enhanced cell migration, formation of cell pseudopodium, wound healing and tumor metastasis, whereas reintroduction of AIM2 attenuated these functions. The loss of AIM2 induced the activation of epithelial‐mesenchymal transition (EMT). Fibronectin 1 (FN1) was found to be a downstream effector of AIM2, with its expression reversely modulated by AIM2. Silencing of FN1 significantly halted cell migration induced by AIM2 depletion. These data demonstrate that HBx‐induced loss of AIM2 is associated with poor outcomes and facilitates HCC metastasis by triggering the EMT process. The results of the present study therefore suggest that AIM2 is a potential prognostic biomarker in hepatitis B virus‐related HCC, as well as a possible therapeutic target for tumor metastasis.

The bacterial phosphotriesterase (PTE) from Pseudomonas diminuta catalyzes the hydrolysis of organophosphate esters at rates close to the diffusion limit. X-ray diffraction studies have shown that a binuclear metal center is positioned in the active site of PTE and that this complex is responsible for the activation of the nucleophilic water from solvent. In this paper the three dimensional structure of PTE was determined in the presence of the hydrolysis product, diethyl phosphate (DEP), and a product analogue, cacodylate. In the structure of the PTE-diethyl phosphate complex the DEP product is found symmetrically bridging the two divalent cations. The DEP displaces the hydroxide from solvent that normally bridges the two divalent cations in structures determined in the presence or absence of substrate analogues. One of the phosphoryl oxygen atoms in the PTE-DEP complex is 2.0 Å away from the α-metal ion while the other oxygen is 2.2 Å away from the β-metal ion. The two metal ions are separated by a distance of 4.0 Å. A similar structure is observed in the presence of cacodylate. Analogous complexes have previously been observed for the product complexes of isoaspartyl dipeptidase, D-aminoacylase, and dihydroorotase from the amidohydrolase superfamily of enzymes. The experimentally determined structure of the PTE-diethyl phosphate product complex is inconsistent with a recent proposal based upon QM/MM simulations which postulated the formation of an asymmetrical product complex bound exclusively to the β-metal ion with a metalmetal separation of 5.3 Å. This structure is also inconsistent with a chemical mechanism for substrate hydrolysis that utilizes the bridging hydroxide as a base to abstract a proton from a water molecule loosely associated with the α-metal ion. Density functional theory (DFT) calculations support a reaction mechanism that utilizes the bridging hydroxide as the direct nucleophile in the hydrolysis of organophosphate esters by PTE. † This work was supported in part by the NIH (GM71790 and GM68550) and the Robert A. Welch Foundation (A-840). JK was supported by GM76988. Supporting information available Electron density for cacodylate bound to the active site of G60A ( Figure S1) and for diethyl phosphate bound to wild type PTE ( Figures S2A and S2B). This material is available free of charge via the Internet at

Deregulation of polycomb proteins influences the development and progression of hepatocellular carcinoma. Here we show that chromobox 8 (CBX8) expression is increased in hepatocellular carcinoma and correlates with poor outcome in two independent cohorts containing a total of 879 cases. Ectopic expression of CBX8 facilitated tumor growth and metastasis, whereas CBX8 silencing suppressed these effects. CBX8 efficiently activated AKT/β-catenin signaling via upregulation of the transcription factor EGR1 and miR-365-3p in a noncanonical manner: CBX8 directly bound the EGR1 promoter to enhance its activity. In the nucleus, CBX8 also interacted with EGR1 to prevent its degradation. Furthermore, CBX8 increased the transcription of miR-365a-3p, which promoted the nuclear localization of β-catenin by targeting the 3'-UTR ZNRF1. Inhibiting either EGR1 or miR-365a-3p partially rescued CBX8-mediated malignant phenotypes. In clinical samples, CBX8 expression closely correlated with EGR1, miR-365a-3p, and nuclear β-catenin. Collectively, our results show that CBX8 functions as an oncogene to upregulate EGR1 and miR-365-3p to stimulate the AKT/β-catenin pathway. This newly identified signaling axis may suggest new therapeutic strategies against hepatocellular carcinoma. Elucidation of a key new element of the β-catenin signaling pathway in liver cancer may suggest new therapeutic targets. .