Background and Aims: Hepatic ischemia‐reperfusion (HIR) injury, a common clinical complication of liver transplantation and resection, affects patient prognosis. Ring finger protein 5 (RNF5) is an E3 ubiquitin ligase that plays important roles in endoplasmic reticulum stress, unfolded protein reactions, and inflammatory responses; however, its role in HIR is unclear. Approach and Results: RNF5 expression was significantly down‐regulated during HIR in mice and hepatocytes. Subsequently, RNF5 knockdown and overexpression of cell lines were subjected to hypoxia‐reoxygenation challenge. Results showed that RNF5 knockdown significantly increased hepatocyte inflammation and apoptosis, whereas RNF5 overexpression had the opposite effect. Furthermore, hepatocyte‐specific RNF5 knockout and transgenic mice were established and subjected to HIR, and RNF5 deficiency markedly aggravated liver damage and cell apoptosis and activated hepatic inflammatory responses, whereas hepatic RNF5 transgenic mice had the opposite effect compared with RNF5 knockout mice. Mechanistically, RNF5 interacted with phosphoglycerate mutase family member 5 (PGAM5) and mediated the degradation of PGAM5 through K48‐linked ubiquitination, thereby inhibiting the activation of apoptosis‐regulating kinase 1 (ASK1) and its downstream c‐Jun N‐terminal kinase (JNK)/p38. This eventually suppresses the inflammatory response and cell apoptosis in HIR. Conclusions: We revealed that RNF5 protected against HIR through its interaction with PGAM5 to inhibit the activation of ASK1 and the downstream JNK/p38 signaling cascade. Our findings indicate that the RNF5‐PGAM5 axis may be a promising therapeutic target for HIR.

Background and Aims: Hepatic ischemia‐reperfusion (I/R) injury, which mainly involves inflammatory responses and apoptosis, is a common cause of organ dysfunction in liver transplantation (LT). As a critical mediator of inflammation and apoptosis in various cell types, the role of tripartite motif‐containing (TRIM) 27 in hepatic I/R injury remains worthy of study. Approach and Results: This study systemically evaluated the putative role of TRIM27/transforming growth factor β–activated kinase 1 (TAK1)/JNK (c‐Jun N‐terminal kinase)/p38 signaling in hepatic I/R injury. TRIM27 expression was significantly down‐regulated in liver tissue from LT patients, mice subjected to hepatic I/R surgery, and hepatocytes challenged by hypoxia/reoxygenation (H/R) treatment. Subsequently, using global Trim27 knockout mice (Trim27‐KO mice) and hepatocyte‐specific Trim27 transgenic mice (Trim27‐HTG mice), TRIM27 functions to ameliorate liver damage, reduce the inflammatory response, and prevent cell apoptosis. In parallel in vitro studies, activating TRIM27 also prevented H/R‐induced hepatocyte inflammation and apoptosis. Mechanistically, TRIM27 constitutively interacted with the critical components, TAK1 and TAK1 binding protein 2/3 (TAB2/3), and promoted the degradation of TAB2/3, leading to inactivation of TAK1 and the subsequent suppression of downstream JNK/p38 signaling. Conclusions: TRIM27 is a key regulator of hepatic I/R injury by mediating the degradation of TAB2/3 and suppression of downstream TAK1‐JNK/p38 signaling. TRIM27 may be a promising approach to protect the liver against I/R‐mediated hepatocellular damage in transplant recipients.

Background and Aims: Hepatic ischemia‐reperfusion (I/R) injury remains a major challenge affecting the morbidity and mortality of liver transplantation. Effective strategies to improve liver function after hepatic I/R injury are limited. Six‐transmembrane epithelial antigen of the prostate 3 (Steap3), a key regulator of iron uptake, was reported to be involved in immunity and apoptotic processes in various cell types. However, the role of Steap3 in hepatic I/R‐induced liver damage remains largely unclear. Approach and Results: In the present study, we found that Steap3 expression was significantly up‐regulated in liver tissue from mice subjected to hepatic I/R surgery and primary hepatocytes challenged with hypoxia/reoxygenation insult. Subsequently, global Steap3 knockout (Steap3‐KO) mice, hepatocyte‐specific Steap3 transgenic (Steap3‐HTG) mice, and their corresponding controls were subjected to partial hepatic warm I/R injury. Hepatic histology, the inflammatory response, and apoptosis were monitored to assess liver damage. The molecular mechanisms of Steap3 function were explored in vivo and in vitro. The results demonstrated that, compared with control mice, Steap3‐KO mice exhibited alleviated liver damage after hepatic I/R injury, as shown by smaller necrotic areas, lower serum transaminase levels, decreased apoptosis rates, and reduced inflammatory cell infiltration, whereas Steap3‐HTG mice had the opposite phenotype. Further molecular experiments showed that Steap3 deficiency could inhibit transforming growth factor‐β–activated kinase 1 (TAK1) activation and downstream c‐Jun N‐terminal kinase (JNK) and p38 signaling during hepatic I/R injury. Conclusions: Steap3 is a mediator of hepatic I/R injury that functions by regulating inflammatory responses as well as apoptosis through TAK1‐dependent activation of the JNK/p38 pathways. Targeting hepatocytes, Steap3 may be a promising approach to protect the liver against I/R injury.

Liver resection and liver transplantation are the treatment modalities with the greatest potential for curing hepatocellular carcinoma (HCC). Tumor recurrence after resection for HCC is, however, a major problem, and an increased rate of recurrence after living donor transplantation versus cadaveric whole liver transplantation has been suggested. Factors involved in liver regeneration may stimulate the growth of occult tumors. The aim of this project was to test the hypothesis that a microscopic HCC tumor in the setting of partial hepatectomy would show enhanced growth and signs of increased invasiveness corresponding to the size of the liver resection. Hepatectomy was performed to various degrees in groups of Buffalo rats with the concomitant implantation of a fixed number of hepatoma cells in the remnant liver; a control group underwent only resection. After 21 days, the sizes and numbers of the tumors and the expression of alpha-fetoprotein (AFP), cyclin D1, calpain small subunit 1 (CAPNS1), CD34 (a microvessel density marker), vascular endothelial growth factor (VEGF), and vascular endothelial growth factor receptor 2 (VEGFR2) were evaluated and compared between the groups. The tumor volume and number increased significantly with the size of the partial hepatectomy (P< 0.05). The largest resections were also associated with increased hepatoma cell infiltration in the lungs and significant up-regulation of cyclin D1, AFP, CAPNS1, CD34, VEGF, and VEGFR2. The results suggest that liver regeneration after partial hepatectomy facilitates the growth and malignant transformation of microscopic HCC, and this could be significant for liver resection and partial liver transplantation strategies for HCC. Liver Transpl 17:866-874, 2011. © 2011 AASLD.

Background: The ERBB2 oncogene hypothesis is challenged in hepatocellular carcinoma (HCC) with the conflicting evidences of human epidermal growth factor receptor 2 (HER2) overexpression. HER2 could be a new target as a treatment option for HCC as well as tumor recurrence after surgery. HER2 in HCC biology needs further explorations.Methods: Clinical and mRNA data of HCC patients were obtained from TCGA HCC cohort, GSE89377 and GSE115018. Western Blotting and immunohistochemistry were employed to test expression of HER2, E‐cadherin, and Vimentin. In HepG2, JM1, HER2‐transfected McA cells, and TGF‐β cocultured JM1 cells, HCC biology, including cell survival, proliferation, and epithelial‐to‐mesenchymal transition (EMT) phenotypes were evaluated.Results: ERBB2 mRNA amplification was found in HCC datasets, and its expression was downregulated in high grade HCC with a worse overall survival. HER2 overexpression was identified in H4IIE, HepG2, JM1 cells, and 82% (14/17) HCC samples, and tumor stage was correlated with expression of HER2, E‐cadherin, and Vimentin (P < 0.05). Trastuzumab with the high concentrations suppressed proliferation of HER2‐positive hepatoma cells (P < 0.05); in the coculture model to induce EMT of JM1 cells, HER2 expression increased with downregulated E‐cadherin and upregulated Vimentin. Trastuzumab intravenous injection inhibited in vivo tumor size and metastases (P < 0.05). Signal analysis revealed that HER2 functioned through upregulation of β‐catenin and inhibition of SMAD3.Conclusion: HER2 expression pattern is linked with tumor stage and overall survival; the transforming function of HER2 is found more relevant through β‐catenin and SMAD3. HER2‐targeted treatment is recommended to suppress the HER2‐mediated tumor growth during postoperative liver regeneration.

Liver regeneration after major surgery may activate occult micrometastases and facilitate tumor growth, leading to liver tumor recurrence. Molecular changes during liver regeneration can provide a microenvironment that stimulates intrahepatic tumor propagation through alterations in cellular signaling pathways, where activation and proliferation of mature hepatocytes, hepatic progenitor cells, non-parenchymal liver cells might favor both liver regeneration and tumor growth. This review highlights recent advances of tumor growth and development in the regenerating liver, possible mechanisms and clinical implications.