Stabilization of E2-EPF UCP protein is implicated in hepatitis B virus-associated hepatocellular carcinoma progression

Knockout of UBE2S inhibits the proliferation of gastric cancer cells and induces apoptosis by FAS-mediated death receptor pathway

Ubiquitin binding enzyme E2S (UBE2S) is a member of ubiquitin binding enzyme family involved in a variety of biological functions, including cell cycle regulation, apoptosis, and regulation of the ubiquitination of proteins, which are closely correlated with the development of various tumors. However, its role in gastric cancer (GC) remains unknown. In this study, we found that UBE2S was upregulated in GC tissues and cells. Further, its high expression positively correlated with the tumor stage and indicated a poor prognosis. Knockout of UBE2S by CRISPR/Cas9-mediated strategy suppressed the growth of GC in vitro and in vivo. Moreover, RNA-Seq-based transcriptome analysis and tandem mass tag (TMT)-based quantitative proteomics analysis was performed for exploring the underlying mechanism. The multi-omics and verification results showed that UBE2S knockout-induced apoptosis and proliferation inhibition of GC cells was related to upregulation of FAS and the activation of the FAS-mediated apoptotic pathway. Moreover, a negative correlation between UBE2S and FAS expression was observed in GC tissue samples. Finally, the ubiquitination assay confirmed that knockout of UBE2S might activate endogenous FAS by inhibiting ubiquitination and degradation of p53 in GC cells. Collectively, UBE2S is expected to be a novel prognostic biomarker and potential therapeutic target for GC.

The Functions of Hepatitis B Virus Encoding Proteins: Viral Persistence and Liver Pathogenesis

About 250 million people worldwide are chronically infected with Hepatitis B virus (HBV), contributing to a large burden on public health. Despite the existence of vaccines and antiviral drugs to prevent infection and suppress viral replication respectively, chronic hepatitis B (CHB) cure remains a remote treatment goal. The viral persistence caused by HBV is account for the chronic infection which increases the risk for developing liver cirrhosis and hepatocellular carcinoma (HCC). HBV virion utilizes various strategies to escape surveillance of host immune system therefore enhancing its replication, while the precise mechanisms involved remain elusive. Accumulating evidence suggests that the proteins encoded by HBV (hepatitis B surface antigen, hepatitis B core antigen, hepatitis B envelope antigen, HBx and polymerase) play an important role in viral persistence and liver pathogenesis. This review summarizes the major findings in functions of HBV encoding proteins, illustrating how these proteins affect hepatocytes and the immune system, which may open new venues for CHB therapies.

Molecular Insights into the Oxygen-Sensing Pathway and Erythropoietin Expression Regulation in Erythropoiesis

Erythropoiesis is regulated by several factors, including the oxygen-sensing pathway as the main regulator of erythropoietin (EPO) synthesis in the kidney. The release of EPO from the kidney and its binding to the EPO receptor (EPOR) on erythrocyte progenitor cells in the bone marrow results in increased erythropoiesis. Any imbalance in these homeostatic mechanisms can lead to dysregulated erythropoiesis and hematological disorders. For example, mutations in genes encoding key players of oxygen-sensing pathway and regulation of EPO production (HIF-EPO pathway), namely VHL, EGLN, EPAS1 and EPO, are well known causative factors that contribute to the development of erythrocytosis. We aimed to investigate additional molecular mechanisms involved in the HIF-EPO pathway that correlate with erythropoiesis. To this end, we conducted an extensive literature search and used several in silico tools. We identified genes encoding transcription factors and proteins that control transcriptional activation or repression; genes encoding kinases, deacetylases, methyltransferases, conjugating enzymes, protein ligases, and proteases involved in post-translational modifications; and genes encoding nuclear transport receptors that regulate nuclear transport. All these genes may modulate the stability or activity of HIF2α and its partners in the HIF-EPO pathway, thus affecting EPO synthesis. The theoretical information we provide in this work can be a valuable tool for a better understanding of one of the most important regulatory pathways in the process of erythropoiesis. This knowledge is necessary to discover the causative factors that may contribute to the development of hematological diseases and improve current diagnostic and treatment solutions in this regard.

Hepatitis B Virus preS/S Truncation Mutant rtM204I/sW196* Increases Carcinogenesis through Deregulated HIF1A, MGST2, and TGFbi

Inevitable long-term therapy with nucleos(t)ide analogs in patients with chronic hepatitis B virus (HBV) infection has selected reverse-transcriptase (rt) mutants in a substantial proportion of patients. Some of these mutants introduce premature stop codons in the overlapping surface (s) gene, including rtA181T/sW172*, which has been shown to enhance oncogenicity. The oncogenicity of another drug-resistant mutant, rtM204I/sW196*, has not been studied. We constructed plasmids harboring rtM204I/sW196* and assessed the in vitro cell transformation, endoplasmic reticulum (ER) stress response, and xenograft tumorigenesis of the transformants. Cellular gene expression was analyzed by cDNA microarray and was validated. The rtM204I/sW196* transformants, compared with the control or wild type, showed enhanced transactivation activities for c-fos, increased cell proliferation, decreased apoptosis, more anchorage-independent growth, and enhanced tumor growth in mouse xenografts. X box-binding protein-1 (XBP1) splicing analysis showed no ER stress response. Altered gene expressions, including up-regulated MGST2 and HIF1A, and downregulated transforming growth factor beta-induced (TGFbi), were unveiled by cDNA microarray and validated by RT-qPCR. The TGFbi alteration occurred in transformants with wild type or mutated HBV. The altered MGST2 and HIF1A were found only with mutated HBV. The rtM204I/sW196* preS/S truncation may endorse the cell transformation and tumorigenesis ability via altered host gene expressions, including MGST2, HIF1A, and TGFbi. Downregulated TGFbi may be a common mechanism for oncogenicity in HBV surface truncation mutants.

Deubiquitylase OTUD6B Governs pVHL Stability in an Enzyme-Independent Manner and Suppresses Hepatocellular Carcinoma Metastasis

Hypoxia inducible factors (HIFs) are the key transcription factors that allow cancer cells to survive hypoxia. HIF's stability is mainly controlled by von Hippel-Lindau (pVHL)-mediated ubiquitylation. Unlike sporadic clear-cell renal carcinomas, VHL mutation is rarely observed in hepatocellular carcinoma (HCC) and the regulatory mechanisms of pVHL-HIF signaling remain elusive. Here, it is shown that deubiquitylase ovarian tumor domain-containing 6B (OTUD6B) suppresses HCC metastasis through inhibiting the HIF activity. OTUD6B directly interacts with pVHL, decreases its ubiquitylation and proteasomal degradation to reduce HIF-1α accumulation in HCC cells under hypoxia. Surprisingly, OTUD6B limits the ubiquitylation of pVHL independent of its deubiquitylase activity. OTUD6B couples pVHL and elongin B/C to form more CBCVHL ligase complex, which protects pVHL from proteasomal degradation. Depletion of OTUD6B results in the dissociation of CBCVHL complex and the degradation of pVHL by Trp Asp repeat and suppressors of cytokine signaling box-containing protein 1 (WSB1). In human HCC tissues, the protein level of OTUD6B is positively correlated with pVHL, but negatively with HIF-1α and vascular endothelial growth factor. Low expression of OTUD6B predicts poor patient survival. Furthermore, OTUD6B gene is a direct transcriptional target of HIF-1α and upregulated upon hypoxia. These results indicate a previously unrecognized feedback loop consisting of OTUD6B, pVHL, and HIF-1α, and provide insights into the targeted hypoxic microenvironment for HCC therapy.