Eri Tanaka

DHX9 regulates production of hepatitis B virus-derived circular RNA and viral protein levels

Hepatitis B virus (HBV) infection, which is a major health concern worldwide, can lead to liver cirrhosis and hepatocellular carcinoma. Although current nucleos(t)ide analogs efficiently inhibit viral reverse transcription and viral DNA load clinically, episomal viral covalently closed circular DNA (cccDNA) minichromosomes and transcripts from cccDNA continue to be expressed over the long term. We hypothesized that, under these conditions, viral transcripts may have biological functions involved in pathogenesis. Here, we show that the host protein DExH-box helicase 9 (DXH9) is associated with viral RNAs. We also show that viral-derived circular RNA is produced during HBV replication, and the amount is increased by knockdown of the DHX9 protein, which, in turn, results in decreased viral protein levels but does not affect the levels of HBV DNA. These phenomena were observed in the HBV-producing cell culture model and HBV mini-circle model mimicking HBV cccDNA, as well as in human primary hepatocytes infected with HBV. Based on these results, we conclude that, in HBV infection, the RNA binding factor DHX9 is a novel regulator of viral circular RNA and viral protein levels.

Satellite RNA Increases DNA Damage and Accelerates Tumor Formation in Mouse Models of Pancreatic Cancer

Highly repetitive tandem arrays such as satellite sequences in the centromeric and pericentromeric regions of chromosomes, which were previously considered to be silent, are actively transcribed in various biological processes, including cancers. In the pancreas, this aberrant expression occurs even in Kras-mutated pancreatic intraepithelial neoplasia (PanIN) tissues, which are precancerous lesions. To determine the biological role of satellite RNAs in carcinogenesis in vivo, we constructed mouse major satellite (MajSAT) RNA-expressing transgenic mice. However, these transgenic mice did not show spontaneous malignant tumor formation under normal breeding. Importantly, however, DNA damage was increased in pancreatic tissues induced by caerulein treatment or high-fat diet, which may be due to impaired nuclear localization of Y-Box Binding Protein 1 (YBX1), a component of the DNA damage repair machinery. In addition, when crossed with pancreas-specific Kras-mutant mice, MajSAT RNA expression resulted in an earlier increase in PanIN formation. These results suggest that aberrant MajSAT RNA expression accelerates oncogenesis by increasing the probability of a second driver mutation, thus accelerating cells to exit from the breakthrough phase to the expansion phase. Implications: Aberrant expression of satellite RNAs accelerates oncogenesis through a mechanism involving increased DNA damage. Mol Cancer Res; 16(8); 1255–62. ©2018 AACR.

Hepatitis B virus pathogenesis: Fresh insights into hepatitis B virus RNA

Hepatitis B virus (HBV) is still a worldwide health concern. While divergent factors are involved in its pathogenesis, it is now clear that HBV RNAs, principally templates for viral proteins and viral DNAs, have diverse biological functions involved in HBV pathogenesis. These functions include viral replication, hepatic fibrosis and hepatocarcinogenesis. Depending on the sequence similarities, HBV RNAs may act as sponges for host miRNAs and may deregulate miRNA functions, possibly leading to pathological consequences. Some parts of the HBV RNA molecule may function as viral-derived miRNA, which regulates viral replication. HBV DNA can integrate into the host genomic DNA and produce novel viral-host fusion RNA, which may have pathological functions. To date, elimination of HBV-derived covalently closed circular DNA has not been achieved. However, RNA transcription silencing may be an alternative practical approach to treat HBV-induced pathogenesis. A full understanding of HBV RNA transcription and the biological functions of HBV RNA may open a new avenue for the development of novel HBV therapeutics.

Circular RNA and exosomes in pancreatic cancer progression

Circular RNA (circRNA) is a type of noncoding RNA that forms a covalently closed continuous loop. CircRNAs were discovered in the 1980s but were thought to be an artifact of aberrant RNA splicing or specific to a few pathogens such as hepatitis delta virus (1). The development of next-generation sequencing and bioinformatics tools has led to the discovery of numerous endogenous circRNAs, the expression of which is considerably higher than previously thought.

Invasive Pulmonary Aspergillosis in the Epidural Space in a Patient with Acute Myelogenous Leukemia with Myelodysplasia-related Changes: A Case Study and Literature Review of Vertebral Aspergillosis in Japan

Vertebral aspergillosis is a rare infectious disease with a high mortality rate. We herein report a 70-year-old woman with acute myelogenous leukemia with myelodysplasia-related changes, nontuberculous mycobacteriosis, and bronchiectasis who presented with a fever and cough. Her clinical symptoms and laboratory test results suggested febrile neutropenia and pneumonia. However, her clinical course was further complicated by lower extremity weakness. Magnetic resonance imaging of the spine showed consolidation contiguously spreading toward the epidural space between the T4 and T5. Cytological testing of the pleural effusion revealed Aspergillus fumigatus. We also review and summarize previously reported cases of vertebral aspergillosis in Japan.

Atraumatic Splenic Rupture due to Ectopic Extramedullary Hematopoiesis after Autologous Stem Cell Transplantation in a Patient with AL Amyloidosis

A 50-year-old man was diagnosed with multiple myeloma complicating AL amyloidosis. Splenic rupture was complicated during autologous stem cell transplantation (auto-SCT). Granulocyte colony-stimulating factor (G-CSF) was not administered. A pathological examination of the spleen revealed that CD34-positive cells were concentrated in the ruptured part of the splenic capsule. Hematopoietic cells were engrafted in the small gap between the capsule and amyloid protein deposition area of the spleen, which might have caused the splenic rupture in the absence of G-CSF administration. Special attention is thus required for amyloidosis patients undergoing auto-SCT, even when G-CSF is not administered.

Cholangitis complicated by infection of a simple hepatic cyst

An 87-year-old man was admitted to our hospital due to fever and elevated liver enzymes. Computed tomography (CT) scan revealed bile duct stones with a dilated biliary system, which confirmed the diagnosis of cholangitis. A 12-cm simple hepatic cyst was also seen in the right liver, which had been detected on CT scan 5xa0years before, and did not change in size. Fever did not subside even after endoscopic biliary drainage and a repeated CT scan showed an enlarged cyst up to 14xa0cm, suggesting cyst infection. An enlarged hepatic cyst collapsed after percutaneous transhepatic drainage, along with resolution of fever. Simple hepatic cysts are common and most of them are asymptomatic. Infection of simple hepatic cysts is a rare condition and the major entry route is considered as the biliary tract as communication between the biliary tract and cysts is reportedly observed in those cases. However, in our case, no communication was seen on cholangiogram or cystogram on fluoroscopy and bilirubin level of the cyst aspirate was low. Given the fact that patients with cholangitis are rarely complicated by hepatic cyst infection, other routes of bacterial entry to simple hepatic cysts should also be considered.

Invasive tracheobronchial aspergillosis developed during radioimmunotherapy for malignant lymphoma

Invasive pulmonary aspergillosis (IPA) often occurs during the treatment of malignant lymphoma. However, invasive tracheobronchial aspergillosis (ITBA) is a rare form of IPA. Particularly, due to the decrease in immunity associated with chemotherapy, it is difficult to diagnose ITBA only by CT imaging and serological findings. Pathologic diagnosis by bronchoscopy is important.

Inhibition of HBV transcription from cccDNA with nitazoxanide by targeting the HBx–DDB1 interaction

Background & Aims Hepatitis B virus (HBV) infection is a major health concern worldwide. Although currently used nucleos(t)ide analogs efficiently inhibit viral replication, viral proteins transcribed from the episomal viral covalently closed circular DNA (cccDNA) minichromosome continue to be expressed long-term. Because high viral RNA or antigen loads may play a biological role during this chronicity, the elimination of viral products is an ultimate goal of HBV treatment. HBV regulatory protein X (HBx) was recently found to promote transcription of cccDNA with degradation of Smc5/6 through the interaction of HBx with the host protein DDB1. Here, this protein–protein interaction was considered as a new molecular target of HBV treatment. Methods To identify candidate compounds that target the HBx–DDB1 interaction, a newly constructed split luciferase assay system was applied to comprehensive compound screening. The effects of the identified compounds on HBV transcription and cccDNA maintenance were determined using HBV minicircle DNA, which mimics HBV cccDNA, and the natural HBV infection model of human primary hepatocytes. Results We show that nitazoxanide (NTZ), a thiazolide anti-infective agent that has been approved by the FDA for protozoan enteritis, efficiently inhibits the HBx–DDB1 protein interaction. NTZ significantly restores Smc5 protein levels and suppresses viral transcription and viral protein production in the HBV minicircle system and in human primary hepatocytes naturally infected with HBV. Conclusions These results indicate that NTZ, which targets an HBV-related viral–host protein interaction, may be a promising new therapeutic agent and a step toward a functional HBV cure.

A tiny but crucial player bridging microbes and colonic carcinogenesis

Colorectal cancer (CRC) is one of the most common malignancies in the world (1). The probability of suffering from CRC is approximately 4–5%, and the risk of developing CRC is associated with characteristics such as age, chronic disease history, and lifestyle (2). CRC is caused by mutations in oncogenes, tumor-suppressor genes, and genes related to DNA repair mechanisms. The underlying pathogenic mechanisms are threefold; namely, chromosomal instability (CIN), microsatellite instability (MSI), and CpG island methylator phenotype (CIMP). In CRC, common mutations, chromosomal changes, and translocations reportedly affect important intracellular signaling pathways [WNT, mitogen activated protein kinase (MAPK)/phosphoinositide 3-kinase (PI3K), transforming growth factor (TGF)-β, and TP53] (2). In addition to genetic mutations, alterations in non-coding RNAs, such as microRNAs, also contribute to carcinogenesis.