1 4239 123 METHYLATION PROFILE OF HEPATITIS B VIRUS IS NOT INFLUENCED BY INTERFERON ALPHA IN HUMAN LIVER CANCER CELLS. INTERFERON (IFN) ALPHA IS USED FOR THE TREATMENT OF CHRONIC HEPATITIS B VIRUS (HBV) INFECTION, BUT THE MOLECULAR MECHANISMS UNDERLYING ITS ANTIVIRAL EFFECT HAVE NOT BEEN FULLY ELUCIDATED. EPIGENETIC MODIFICATIONS REGULATE THE TRANSCRIPTIONAL ACTIVITY OF COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) IN CELLS WITH CHRONIC HBV INFECTION. IFN?ALPHA HAS BEEN SHOWN TO MODIFY CCCDNA?BOUND HISTONES, BUT IT IS NOT KNOWN WHETHER THE ANTI?HBV EFFECT OF IFN?ALPHA INVOLVES METHYLATION OF CCCDNA. THE PRESENT STUDY AIMED TO DETERMINE WHETHER IFN?ALPHA INDUCED METHYLATION OF HBV CCCDNA IN A CELL?BASED MODEL IN WHICH HEPG2 CELLS WERE DIRECTLY INFECTED WITH WILD?TYPE HBV VIRIONS. METHYLATION STATUS OF HBV CCCDNA WAS ASSESSED USING GLOBAL DNA METHYLATION ELISA ASSAY, METHYLATION?SPECIFIC PCR AND BISULFITE SEQUENCING. IFN?ALPHA SUPPRESSED HBV DNA AND RNA TRANSCRIPTS, BUT METHYLATION PROFILES WERE SIMILAR BETWEEN THE CONTROL AND IFN?ALPHA TREATED GROUPS. CHROMATIN IMMUNOPRECIPITATION RESULTS REVEALED BINDING OF DNA METHYLTRANSFERASES (DNMT) 3A AND DNMT3B TO HBV CCCDNA AND TREATMENT WITH IFN?ALPHA SUPPRESSED THE RECRUITMENT OF DNMT3B TO CCCDNA. TAKEN TOGETHER, THESE RESULTS SUGGEST THAT IFN?ALPHA DOES NOT INDUCE METHYLATION OF HBV CCCDNA. THEREFORE, IT WAS CONCLUDED THAT METHYLATION IS UNLIKELY TO CONTRIBUTE TO THE ANTI?HBV EFFECT OF IFN?ALPHA IN HEPG2 CELLS, AND THAT ALTERNATIVE MECHANISMS NEED TO BE SOUGHT TO ENHANCE CCCDNA METHYLATION AS A NOVEL THERAPY AGAINST HBV. 2021 2 5689 41 SILENCING HEPATITIS B VIRUS COVALENTLY CLOSED CIRCULAR DNA: THE POTENTIAL OF AN EPIGENETIC THERAPY APPROACH. GLOBAL PROPHYLACTIC VACCINATION PROGRAMMES HAVE HELPED TO CURB NEW HEPATITIS B VIRUS (HBV) INFECTIONS. HOWEVER, IT IS ESTIMATED THAT NEARLY 300 MILLION PEOPLE ARE CHRONICALLY INFECTED AND HAVE A HIGH RISK OF DEVELOPING HEPATOCELLULAR CARCINOMA. AS SUCH, HBV REMAINS A SERIOUS HEALTH PRIORITY AND THE DEVELOPMENT OF NOVEL CURATIVE THERAPEUTICS IS URGENTLY NEEDED. CHRONIC HBV INFECTION HAS BEEN ATTRIBUTED TO THE PERSISTENCE OF THE COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) WHICH ESTABLISHES ITSELF AS A MINICHROMOSOME IN THE NUCLEUS OF HEPATOCYTES. AS THE VIRAL TRANSCRIPTION INTERMEDIATE, THE CCCDNA IS RESPONSIBLE FOR PRODUCING NEW VIRIONS AND PERPETUATING INFECTION. HBV IS DEPENDENT ON VARIOUS HOST FACTORS FOR CCCDNA FORMATION AND THE MINICHROMOSOME IS AMENABLE TO EPIGENETIC MODIFICATIONS. TWO HBV PROTEINS, X (HBX) AND CORE (HBC) PROMOTE VIRAL REPLICATION BY MODULATING THE CCCDNA EPIGENOME AND REGULATING HOST CELL RESPONSES. THIS INCLUDES VIRAL AND HOST GENE EXPRESSION, CHROMATIN REMODELING, DNA METHYLATION, THE ANTIVIRAL IMMUNE RESPONSE, APOPTOSIS, AND UBIQUITINATION. ELIMINATION OF THE CCCDNA MINICHROMOSOME WOULD RESULT IN A STERILIZING CURE; HOWEVER, THIS MAY BE DIFFICULT TO ACHIEVE. EPIGENETIC THERAPIES COULD PERMANENTLY SILENCE THE CCCDNA MINICHROMOSOME AND PROMOTE A FUNCTIONAL CURE. THIS REVIEW EXPLORES THE CCCDNA EPIGENOME, HOW HOST AND VIRAL FACTORS INFLUENCE TRANSCRIPTION, AND THE RECENT EPIGENETIC THERAPIES AND EPIGENOME ENGINEERING APPROACHES THAT HAVE BEEN DESCRIBED. 2021 3 3794 39 INTERLEUKIN-33 MEDIATES BOTH IMMUNE-RELATED AND NON-IMMUNE-RELATED INHIBITORY EFFECTS AGAINST HEPATITIS B VIRUS. CHRONIC INFECTION BY HEPATITIS B VIRUS (HBV) IS ASSOCIATED WITH HIGH RISKS OF LIVER FIBROSIS, CIRRHOSIS AND HEPATOCELLULAR CARCINOMA. HBV COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) IN THE NUCLEUS OF INFECTED HEPATOCYTE SERVES AS TRANSCRIPTION TEMPLATE. NEITHER NATURAL RESOLUTION OF ACUTE INFECTION NOR CURRENT TREATMENT OPTIONS FOR CHRONIC INFECTION ARE BELIEVED TO CAUSE CCCDNA CLEARANCE. WE PREVIOUSLY SHOWED THAT INJECTION OF IL-33-EXPRESSING PLASMID FACILITATED CLEARANCE OF INTRAHEPATIC HBV DNA IN A MOUSE MODEL OF HBV PERSISTENCE. IN THIS WORK, HBV-TARGETING THERAPEUTIC EFFECTS OF IL-33 WERE FURTHER EXPLORED. MURINE IL-33 DELIVERED BY RECOMBINANT ADENO-ASSOCIATED VIRUS (AAV-MIL-33) INDUCED CLEARANCE OF BOTH SERUM HBV MARKERS AND INTRAHEPATIC HBV DNA IN TWO MOUSE MODELS OF HBV PERSISTENCE BASED ON REPLICON PLASMID AND RECOMBINANT CCCDNA (RCCCDNA) RESPECTIVELY. CLEARANCE WAS ASSOCIATED WITH SERUM ALT ELEVATIONS AND LIVER INFILTRATIONS BY CD4(+) AND CD8(+) T CELLS, INDICATING IL-33-INDUCED CELLULAR IMMUNE RESPONSES AGAINST HBV-HARBORING CELLS. ADOPTIVE TRANSFER OF SPLENOCYTES FROM AAV-MIL-33-CURED MICE WAS INDEED SUFFICIENT TO ENGENDER SIMILAR CLEARANCE IN RECIPIENT MICE. IN VITRO, INTRACELLULAR, INSTEAD OF EXTRACELLULAR, IL-33 WAS MAINLY RESPONSIBLE FOR REPRESSING VIRAL TRANSCRIPTION, PROTEIN PRODUCTION AND GENOME REPLICATION IN HUH7 CELLS TRANSFECTED WITH HBV REPLICON OR RCCCDNA. IL-33 WAS SHOWN TO BE RECRUITED ONTO RCCCDNA MINICHROMOSOME ACCOMPANIED BY LOSS OF TRANSCRIPTIONAL ACTIVATION EPIGENETIC MARKS. FINALLY, TRANSFECTION OF IL-33 INTO HBV-INFECTED HEPG2/NTCP CELLS RESULTED IN REDUCED TRANSCRIPTION, ANTIGEN EXPRESSION AND GENOME REPLICATION, SUGGESTING REPRESSION OF CANONICAL CCCDNA. THESE DATA DEMONSTRATED DIVERSE INHIBITORY EFFECTS ON HBV AND HBV-INFECTED CELLS MEDIATED BY IL-33, AND SUGGEST IL-33 AS AN INTERESTING THERAPEUTIC CANDIDATE. 2022 4 442 23 ANTIVIRAL THERAPIES FOR HEPATITIS B VIRUS-RELATED HEPATOCELLULAR CARCINOMA. CHRONIC HEPATITIS B VIRUS (HBV) INFECTION IS A CRITICAL RISK FACTOR FOR THE CARCINOGENESIS AND PROGRESSION OF HEPATOCELLULAR CARCINOMA (HCC). IT PROMOTES HCC DEVELOPMENT BY INDUCING LIVER FIBROGENESIS, GENETIC AND EPIGENETIC ALTERATIONS, AND THE EXPRESSION OF ACTIVE VIRAL-CODED PROTEINS. EFFECTIVE ANTIVIRAL TREATMENTS INHIBIT THE REPLICATION OF HBV, REDUCE SERUM VIRAL LOAD AND ACCELERATE HEPATITIS B E ANTIGEN SERUM CONVERSION. TIMELY INITIATION OF ANTIVIRAL TREATMENT IS NOT ONLY ESSENTIAL FOR PREVENTING THE INCIDENCE OF HCC IN CHRONIC HEPATITIS B PATIENTS, BUT ALSO IMPORTANT FOR REDUCING HBV REACTIVATION, IMPROVING LIVER FUNCTION, REDUCING OR DELAYING HCC RECURRENCE, AND PROLONGING OVERALL SURVIVAL OF HBV-RELATED HCC PATIENTS AFTER CURATIVE AND PALLIATIVE THERAPIES. THE SELECTION OF ANTIVIRAL DRUGS, MONITORING OF INDICATORS SUCH AS HBV DNA AND HEPATITIS B SURFACE ANTIGEN, AND TIMELY RESCUE TREATMENT WHEN NECESSARY, ARE ESSENTIAL IN ANTIVIRAL THERAPIES FOR HBV-RELATED HCC. 2015 5 5936 23 TARGETING HEPATITIS B VIRUS COVALENTLY CLOSED CIRCULAR DNA AND HEPATITIS B VIRUS X PROTEIN: RECENT ADVANCES AND NEW APPROACHES. CHRONIC HEPATITIS B VIRUS (HBV) INFECTION REMAINS A WORLDWIDE CONCERN AND PUBLIC HEALTH PROBLEM. TWO KEY ASPECTS OF THE HBV LIFE CYCLE ARE ESSENTIAL FOR VIRAL REPLICATION AND THUS THE DEVELOPMENT OF CHRONIC INFECTIONS: THE ESTABLISHMENT OF THE VIRAL MINICHROMOSOME, COVALENTLY CLOSED CIRCULAR (CCC) DNA, WITHIN THE NUCLEUS OF INFECTED HEPATOCYTES AND THE EXPRESSION OF THE REGULATORY HEPATITIS B VIRUS X PROTEIN (HBX). INTERESTINGLY, NUCLEAR HBX REDIRECTS HOST EPIGENETIC MACHINERY TO ACTIVATE CCCDNA TRANSCRIPTION. IN THIS PERSPECTIVE, WE PROVIDE AN OVERVIEW OF RECENT ADVANCES IN UNDERSTANDING THE REGULATION OF CCCDNA AND THE MECHANISTIC AND FUNCTIONAL ROLES OF HBX. WE ALSO DESCRIBE THE PROGRESS TOWARD TARGETING BOTH CCCDNA AND HBX FOR THERAPEUTIC PURPOSES. FINALLY, WE OUTLINE STANDING QUESTIONS IN THE FIELD AND PROPOSE COMPLEMENTARY CHEMICAL BIOLOGY APPROACHES TO ADDRESS THEM. 2019 6 5368 31 RECENT ADVANCES IN THE STUDY OF HEPATITIS B VIRUS COVALENTLY CLOSED CIRCULAR DNA. CHRONIC HEPATITIS B INFECTION IS CAUSED BY HEPATITIS B VIRUS (HBV) AND A TOTAL CURE IS YET TO BE ACHIEVED. THE VIRAL COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) IS THE KEY TO ESTABLISH A PERSISTENT INFECTION WITHIN HEPATOCYTES. CURRENT ANTIVIRAL STRATEGIES HAVE NO EFFECT ON THE PRE-EXISTING CCCDNA RESERVOIR. THEREFORE, THE STUDY OF THE MOLECULAR MECHANISM OF CCCDNA FORMATION IS BECOMING A MAJOR FOCUS OF HBV RESEARCH. THIS REVIEW SUMMARIZES THE CURRENT ADVANCES IN CCCDNA MOLECULAR BIOLOGY AND THE LATEST STUDIES ON THE ELIMINATION OR INACTIVATION OF CCCDNA, INCLUDING THREE MAJOR AREAS: (1) EPIGENETIC REGULATION OF CCCDNA BY HBV X PROTEIN, (2) IMMUNE-MEDIATED DEGRADATION, AND (3) GENOME-EDITING NUCLEASES. ALL THESE ASPECTS PROVIDE CLUES ON HOW TO FINALLY ATTAIN A CURE FOR CHRONIC HEPATITIS B INFECTION. 2017 7 4055 46 MAPPING OF HISTONE MODIFICATIONS IN EPISOMAL HBV CCCDNA UNCOVERS AN UNUSUAL CHROMATIN ORGANIZATION AMENABLE TO EPIGENETIC MANIPULATION. CHRONIC HEPATITIS B VIRUS (HBV) INFECTION AFFECTS 240 MILLION PEOPLE WORLDWIDE AND IS A MAJOR RISK FACTOR FOR LIVER FAILURE AND HEPATOCELLULAR CARCINOMA. CURRENT ANTIVIRAL THERAPY INHIBITS CYTOPLASMIC HBV GENOMIC REPLICATION, BUT IS NOT CURATIVE BECAUSE IT DOES NOT DIRECTLY AFFECT NUCLEAR HBV CLOSED CIRCULAR DNA (CCCDNA), THE GENOMIC FORM THAT TEMPLATES VIRAL TRANSCRIPTION AND SUSTAINS VIRAL PERSISTENCE. NOVEL APPROACHES THAT DIRECTLY TARGET CCCDNA REGULATION WOULD THEREFORE BE HIGHLY DESIRABLE. CCCDNA IS ASSEMBLED WITH CELLULAR HISTONE PROTEINS INTO CHROMATIN, BUT LITTLE IS KNOWN ABOUT THE REGULATION OF HBV CHROMATIN BY HISTONE POSTTRANSLATIONAL MODIFICATIONS (PTMS). HERE, USING A NEW CCCDNA CHIP-SEQ APPROACH, WE REPORT, TO OUR KNOWLEDGE, THE FIRST GENOME-WIDE MAPS OF PTMS IN CCCDNA-CONTAINING CHROMATIN FROM DE NOVO INFECTED HEPG2 CELLS, PRIMARY HUMAN HEPATOCYTES, AND FROM HBV-INFECTED LIVER TISSUE. WE FIND HIGH LEVELS OF PTMS ASSOCIATED WITH ACTIVE TRANSCRIPTION ENRICHED AT SPECIFIC SITES WITHIN THE HBV GENOME AND, SURPRISINGLY, VERY LOW LEVELS OF PTMS LINKED TO TRANSCRIPTIONAL REPRESSION EVEN AT SILENT HBV PROMOTERS. WE SHOW THAT TRANSCRIPTION AND ACTIVE PTMS IN HBV CHROMATIN ARE REDUCED BY THE ACTIVATION OF AN INNATE IMMUNITY PATHWAY, AND THAT THIS EFFECT CAN BE RECAPITULATED WITH A SMALL MOLECULE EPIGENETIC MODIFYING AGENT, OPENING THE POSSIBILITY THAT CHROMATIN-BASED REGULATION OF CCCDNA TRANSCRIPTION COULD BE A NEW THERAPEUTIC APPROACH TO CHRONIC HBV INFECTION. 2015 8 3186 45 HBV COVALENTLY CLOSED CIRCULAR DNA MINICHROMOSOMES IN DISTINCT EPIGENETIC TRANSCRIPTIONAL STATES DIFFER IN THEIR VULNERABILITY TO DAMAGE. BACKGROUND AND AIMS: HBV COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) IS A MAJOR OBSTACLE FOR A CURE OF CHRONIC HEPATITIS B. ACCUMULATING EVIDENCE SUGGESTS THAT EPIGENETIC MODIFICATIONS REGULATE THE TRANSCRIPTIONAL ACTIVITY OF CCCDNA MINICHROMOSOMES. HOWEVER, IT REMAINS UNCLEAR HOW THE EPIGENETIC STATE OF CCCDNA AFFECTS ITS STABILITY. APPROACHES AND RESULTS: BY USING HBV INFECTION CELL MODELS AND IN VITRO AND IN VIVO RECOMBINANT CCCDNA (RCCCDNA) AND HBVCIRCLE MODELS, THE REDUCTION RATE OF HBV CCCDNA AND THE EFFICACY OF APOLIPOPROTEIN B MRNA EDITING ENZYME CATALYTIC SUBUNIT 3A (APOBEC3A)-MEDIATED AND CRISPR/CRISPR-ASSOCIATED 9 (CAS9)-MEDIATED CCCDNA TARGETING WERE COMPARED BETWEEN CCCDNAS WITH DISTINCT TRANSCRIPTIONAL ACTIVITIES. INTERFERON-ALPHA TREATMENT AND HEPATITIS B X PROTEIN (HBX) DELETION WERE APPLIED AS TWO STRATEGIES FOR CCCDNA REPRESSION. CHROMATIN IMMUNOPRECIPITATION AND MICROCOCCAL NUCLEASE ASSAYS WERE PERFORMED TO DETERMINE THE EPIGENETIC PATTERN OF CCCDNA. HBV CCCDNA LEVELS REMAINED STABLE IN NONDIVIDING HEPATOCYTES; HOWEVER, THEY WERE SIGNIFICANTLY REDUCED DURING CELL DIVISION, AND THE REDUCTION RATE WAS SIMILAR BETWEEN CCCDNAS IN TRANSCRIPTIONALLY ACTIVE AND TRANSCRIPTIONALLY REPRESSED STATES. STRIKINGLY, HBV RCCCDNA WITHOUT HBX EXPRESSION EXHIBITED A SIGNIFICANTLY LONGER PERSISTENCE IN MICE. THE CCCDNA WITH LOW TRANSCRIPTIONAL ACTIVITY EXHIBITED AN EPIGENETICALLY INACTIVE PATTERN AND WAS MORE DIFFICULT TO ACCESS BY APOBEC3A AND ENGINEERED CRISPR-CAS9. THE EPIGENETIC REGULATOR ACTIVATING CCCDNA INCREASED ITS VULNERABILITY TO APOBEC3A. CONCLUSIONS: HBV CCCDNA MINICHROMOSOMES IN DISTINCT EPIGENETIC TRANSCRIPTIONAL STATES SHOWED A SIMILAR REDUCTION RATE DURING CELL DIVISION BUT SIGNIFICANTLY DIFFERED IN THEIR ACCESSIBILITY AND VULNERABILITY TO TARGETED NUCLEASES AND ANTIVIRAL AGENTS. EPIGENETIC SENSITIZATION OF CCCDNA MAKES IT MORE SUSCEPTIBLE TO DAMAGE AND MAY POTENTIALLY CONTRIBUTE TO AN HBV CURE. 2022 9 2240 40 EPIGENETIC MODULATION IN CHRONIC HEPATITIS B VIRUS INFECTION. THE HUMAN HEPATITIS B VIRUS (HBV) IS A SMALL-ENVELOPED DNA VIRUS CAUSING ACUTE AND CHRONIC HEPATITIS. DESPITE THE EXISTENCE OF AN EFFECTIVE PROPHYLACTIC VACCINE AND THE STRONG CAPACITY OF APPROVED ANTIVIRAL DRUGS TO SUPPRESS VIRAL REPLICATION, CHRONIC HBV INFECTION (CHB) CONTINUES TO BE A MAJOR HEALTH BURDEN WORLDWIDE. BOTH THE INABILITY OF THE IMMUNE SYSTEM TO RESOLVE CHB AND THE UNIQUE REPLICATION STRATEGY EMPLOYED BY HBV, WHICH FORMS A STABLE VIRAL COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) MINICHROMOSOME IN THE HEPATOCYTE NUCLEUS, ENABLE INFECTION PERSISTENCE. KNOWLEDGE OF THE COMPLEX NETWORK OF INTERACTIONS THAT HBV ENGAGES WITH ITS HOST IS STILL LIMITED BUT ACCUMULATING EVIDENCE INDICATES THAT EPIGENETIC MODIFICATIONS OCCURRING BOTH ON THE CCCDNA AND ON THE HOST GENOME IN THE COURSE OF INFECTION ARE ESSENTIAL TO MODULATE VIRAL ACTIVITY AND LIKELY CONTRIBUTE TO PATHOGENESIS AND CANCER DEVELOPMENT. THUS, A DEEPER UNDERSTANDING OF EPIGENETIC REGULATORY PROCESSES MAY OPEN NEW VENUES TO CONTROL AND EVENTUALLY CURE CHB. THIS REVIEW SUMMARIZES MAJOR FINDINGS IN HBV EPIGENETIC RESEARCH, FOCUSING ON THE EPIGENETIC MECHANISMS REGULATING CCCDNA ACTIVITY AND THE MODIFICATIONS DETERMINED IN INFECTED HOST CELLS AND TUMOR LIVER TISSUES. 2020 10 3806 51 INTRACELLULAR INTERFERON SIGNALLING PATHWAYS AS POTENTIAL REGULATORS OF COVALENTLY CLOSED CIRCULAR DNA IN THE TREATMENT OF CHRONIC HEPATITIS B. INFECTION WITH THE HEPATITIS B VIRUS (HBV) IS STILL A MAJOR GLOBAL HEALTH THREAT AS 250 MILLION PEOPLE WORLDWIDE CONTINUE TO BE CHRONICALLY INFECTED WITH THE VIRUS. WHILE PATIENTS MAY BE TREATED WITH NUCLEOSIDE/NUCLEOTIDE ANALOGUES, THIS ONLY SUPPRESSES HBV TITRE TO SUB-DETECTION LEVELS WITHOUT ELIMINATING THE PERSISTENT HBV COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) GENOME. AS A RESULT, HBV INFECTION CANNOT BE CURED, AND THE VIRUS REACTIVATES WHEN CONDITIONS ARE FAVORABLE. INTERFERONS (IFNS) ARE CYTOKINES KNOWN TO INDUCE POWERFUL ANTIVIRAL MECHANISMS THAT CLEAR VIRUSES FROM INFECTED CELLS. THEY HAVE BEEN SHOWN TO INDUCE CCCDNA CLEARANCE, BUT THEIR USE IN THE TREATMENT OF HBV INFECTION IS LIMITED AS HBV-TARGETING IMMUNE CELLS ARE EXHAUSTED AND HBV HAS EVOLVED MULTIPLE MECHANISMS TO EVADE AND SUPPRESS IFN SIGNALLING. THUS, TO FULLY UTILIZE IFN-MEDIATED INTRACELLULAR MECHANISMS TO EFFECTIVELY ELIMINATE HBV, INSTEAD OF DIRECT IFN ADMINISTRATION, NOVEL STRATEGIES TO SUSTAIN IFN-MEDIATED ANTI-CCCDNA AND ANTIVIRAL MECHANISMS NEED TO BE DEVELOPED. THIS REVIEW WILL CONSOLIDATE WHAT IS KNOWN ABOUT HOW IFNS ACT TO ACHIEVE ITS INTRACELLULAR ANTIVIRAL EFFECTS AND HIGHLIGHT THE CRITICAL INTERFERON-STIMULATED GENE TARGETS AND EFFECTOR MECHANISMS WITH POTENT ANTI-CCCDNA FUNCTIONS. THESE INCLUDE CCCDNA DEGRADATION BY APOBECS AND CCCDNA SILENCING AND TRANSCRIPTION REPRESSION BY EPIGENETIC MODIFICATIONS. IN ADDITION, THE MECHANISMS THAT HBV EMPLOYS TO DISRUPT IFN SIGNALLING WILL BE DISCUSSED. DRUGS THAT HAVE BEEN DEVELOPED OR ARE IN THE PIPELINE FOR COMPONENTS OF THE IFN SIGNALLING PATHWAY AND HBV TARGETS THAT DETRACT IFN SIGNALLING MECHANISMS WILL ALSO BE IDENTIFIED AND DISCUSSED FOR UTILITY IN THE TREATMENT OF HBV INFECTIONS. TOGETHER, THESE WILL PROVIDE USEFUL INSIGHTS INTO DESIGN STRATEGIES THAT SPECIFICALLY TARGET CCCDNA FOR THE ERADICATION OF HBV. 2021 11 6115 36 THE EPIGENETIC CONTROL OF HEPATITIS B VIRUS MODULATES THE OUTCOME OF INFECTION. EPIGENETIC MODIFICATIONS ARE STABLE ALTERATIONS IN GENE EXPRESSION THAT DO NOT INVOLVE MUTATIONS OF THE GENETIC SEQUENCE ITSELF. IT HAS BECOME INCREASINGLY CLEAR THAT EPIGENETIC FACTORS CONTRIBUTE TO THE OUTCOME OF CHRONIC HEPATITIS B VIRUS (HBV) INFECTION BY AFFECTING CELLULAR AND VIRION GENE EXPRESSION, VIRAL REPLICATION AND THE DEVELOPMENT OF HEPATOCELLULAR CARCINOMA. HBV PERSISTS IN THE NUCLEUS OF INFECTED HEPATOCYTES AS A STABLE NON-INTEGRATED COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) WHICH FUNCTIONS AS A MINICHROMOSOME. THERE ARE TWO MAJOR FORMS OF HBV EPIGENETIC REGULATION: POSTTRANSLATIONAL MODIFICATION OF HISTONE PROTEINS ASSOCIATED WITH THE CCCDNA MINICHROMOSOME AND DNA METHYLATION OF VIRAL AND HOST GENOMES. THIS REVIEW EXPLORES HOW HBV CAN INTERPHASE WITH HOST EPIGENETIC REGULATION IN ORDER TO EVADE HOST DEFENCES AND TO PROMOTE ITS OWN SURVIVAL AND PERSISTENCE. WE FOCUS ON THE EFFECT OF CCCDNA BOUND-HISTONE MODIFICATIONS AND THE METHYLATION STATUS OF HBV DNA IN REGULATING VIRAL REPLICATION. INVESTIGATION OF HBV EPIGENETIC CONTROL HAS IMPORTANT CLINICAL CORRELATES WITH REGARDS TO THE DEVELOPMENT OF POTENTIAL THERAPEUTIC REGIMENS THAT WILL SUCCESSFULLY ERADICATE HBV INFECTION AND DEAL WITH HBV REACTIVATION IN THOSE UNDERGOING TREATMENT WITH DEMETHYLATING AGENTS. 2015 12 6271 31 THE ONCOGENIC ROLE OF HEPATITIS B VIRUS. THE HEPATITIS B VIRUS (HBV) IS A SMALL ENVELOPED DNA VIRUS THAT CAUSES ACUTE AND CHRONIC HEPATITIS. HBV INFECTION IS A WORLD HEALTH PROBLEM, WITH 350 MILLION CHRONICALLY INFECTED PEOPLE AT INCREASED RISK OF DEVELOPING LIVER DISEASE AND HEPATOCELLULAR CARCINOMA (HCC). HBV HAS BEEN CLASSIFIED AMONG HUMAN TUMOR VIRUSES BY VIRTUE OF A ROBUST EPIDEMIOLOGIC ASSOCIATION BETWEEN CHRONIC HBV CARRIAGE AND HCC OCCURRENCE. IN THE ABSENCE OF CYTOPATHIC EFFECT IN INFECTED HEPATOCYTES, THE ONCOGENIC ROLE OF HBV MIGHT INVOLVE A COMBINATION OF DIRECT AND INDIRECT EFFECTS OF THE VIRUS DURING THE MULTISTEP PROCESS OF LIVER CARCINOGENESIS. LIVER INFLAMMATION AND HEPATOCYTE PROLIFERATION DRIVEN BY HOST IMMUNE RESPONSES ARE RECOGNIZED DRIVING FORCES OF LIVER CELL TRANSFORMATION. GENETIC AND EPIGENETIC ALTERATIONS CAN ALSO RESULT FROM VIRAL DNA INTEGRATION INTO HOST CHROMOSOMES AND FROM PROLONGED EXPRESSION OF VIRAL GENE PRODUCTS. NOTABLY, THE TRANSCRIPTIONAL REGULATORY PROTEIN HBX ENCODED BY THE X GENE IS ENDOWED WITH TUMOR PROMOTER ACTIVITY. HBX HAS PLEIOTROPIC ACTIVITIES AND PLAYS A MAJOR ROLE IN HBV PATHOGENESIS AND IN LIVER CARCINOGENESIS. BECAUSE HEPATIC TUMORS CARRY A DISMAL PROGNOSIS, THERE IS URGENT NEED TO DEVELOP EARLY DIAGNOSTIC MARKERS OF HCC AND EFFECTIVE THERAPIES AGAINST CHRONIC HEPATITIS B. DECIPHERING THE ONCOGENIC MECHANISMS THAT UNDERLIE HBV-RELATED TUMORIGENESIS MIGHT HELP DEVELOPING ADAPTED THERAPEUTIC STRATEGIES. 2014 13 3779 54 INTERFERON ALPHA INDUCES MULTIPLE CELLULAR PROTEINS THAT COORDINATELY SUPPRESS HEPADNAVIRAL COVALENTLY CLOSED CIRCULAR DNA TRANSCRIPTION. COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) OF HEPADNAVIRUSES EXISTS AS AN EPISOMAL MINICHROMOSOME IN THE NUCLEUS OF AN INFECTED HEPATOCYTE AND SERVES AS THE TEMPLATE FOR THE TRANSCRIPTION OF VIRAL MRNAS. IT HAD BEEN DEMONSTRATED BY OTHERS AND US THAT INTERFERON ALPHA (IFN-ALPHA) TREATMENT OF HEPATOCYTES INDUCED A PROLONGED SUPPRESSION OF HUMAN AND DUCK HEPATITIS B VIRUS CCCDNA TRANSCRIPTION, WHICH IS ASSOCIATED WITH THE REDUCTION OF CCCDNA-ASSOCIATED HISTONE MODIFICATIONS SPECIFYING ACTIVE TRANSCRIPTION (H3K9(AC) OR H3K27(AC)), BUT NOT THE HISTONE MODIFICATIONS MARKING CONSTITUTIVE (H3K9(ME3)) OR FACULTATIVE (H3K27(ME3)) HETEROCHROMATIN FORMATION. IN OUR EFFORTS TO IDENTIFY IFN-INDUCED CELLULAR PROTEINS THAT MEDIATE THE SUPPRESSION OF CCCDNA TRANSCRIPTION BY THE CYTOKINE, WE FOUND THAT DOWNREGULATING THE EXPRESSION OF SIGNAL TRANSDUCER AND ACTIVATOR OF TRANSCRIPTION 1 (STAT1), STRUCTURAL MAINTENANCE OF CHROMOSOMES FLEXIBLE HINGE DOMAIN CONTAINING 1 (SMCHD1), OR PROMYELOCYTIC LEUKEMIA (PML) PROTEIN INCREASED BASAL LEVEL OF CCCDNA TRANSCRIPTION ACTIVITY AND PARTIALLY ATTENUATED IFN-ALPHA SUPPRESSION OF CCCDNA TRANSCRIPTION. IN CONTRAST, ECTOPIC EXPRESSION OF STAT1, SMCHD1, OR PML SIGNIFICANTLY REDUCED CCCDNA TRANSCRIPTION ACTIVITY. SMCHD1 IS A NONCANONICAL SMC FAMILY PROTEIN AND IMPLICATED IN EPIGENETIC SILENCING OF GENE EXPRESSION. PML IS A COMPONENT OF NUCLEAR DOMAIN 10 (ND10) AND IS INVOLVED IN SUPPRESSING THE REPLICATION OF MANY DNA VIRUSES. MECHANISTIC ANALYSES DEMONSTRATED THAT STAT1, SMCHD1, AND PML WERE RECRUITED TO CCCDNA MINICHROMOSOMES AND PHENOCOPIED THE IFN-ALPHA-INDUCED POSTTRANSLATIONAL MODIFICATIONS OF CCCDNA-ASSOCIATED HISTONES. WE THUS CONCLUDE THAT STAT1, SMCHD1, AND PML MAY PARTLY MEDIATE THE SUPPRESSIVE EFFECT OF IFN-ALPHA ON HEPADNAVIRAL CCCDNA TRANSCRIPTION.IMPORTANCE PEGYLATED IFN-ALPHA IS THE ONLY THERAPEUTIC REGIMEN THAT CAN INDUCE A FUNCTIONAL CURE OF CHRONIC HEPATITIS B IN A SMALL, BUT SIGNIFICANT, FRACTION OF TREATED PATIENTS. UNDERSTANDING THE MECHANISMS UNDERLYING THE ANTIVIRAL FUNCTIONS OF IFN-ALPHA IN HEPADNAVIRAL INFECTION MAY REVEAL MOLECULAR TARGETS FOR DEVELOPMENT OF NOVEL ANTIVIRAL AGENTS TO IMPROVE THE THERAPEUTIC EFFICACY OF IFN-ALPHA. BY A LOSS-OF-FUNCTION GENETIC SCREENING OF INDIVIDUAL IFN-STIMULATED GENES (ISGS) ON HEPADNAVIRAL MRNAS TRANSCRIBED FROM CCCDNA, WE FOUND THAT DOWNREGULATING THE EXPRESSION OF STAT1, SMCHD1, OR PML SIGNIFICANTLY INCREASED THE LEVEL OF VIRAL RNAS WITHOUT ALTERING THE LEVEL OF CCCDNA. MECHANISTIC ANALYSES INDICATED THAT THOSE CELLULAR PROTEINS ARE RECRUITED TO CCCDNA MINICHROMOSOMES AND INDUCE THE POSTTRANSLATIONAL MODIFICATIONS OF CCCDNA-ASSOCIATED HISTONES SIMILAR TO THOSE INDUCED BY IFN-ALPHA TREATMENT. WE HAVE THUS IDENTIFIED THREE IFN-ALPHA-INDUCED CELLULAR PROTEINS THAT SUPPRESS CCCDNA TRANSCRIPTION AND MAY PARTLY MEDIATE IFN-ALPHA SILENCING OF HEPADNAVIRAL CCCDNA TRANSCRIPTION. 2020 14 3782 40 INTERFERON THERAPY OF CHRONIC HEPATITIS B. CHRONIC HEPATITIS B (CHB) RESULTS FROM THE INABILITY OF THE HOST'S IMMUNE SYSTEM TO CONTROL VIRAL REPLICATION. INTERFERON-ALPHA (IFN-ALPHA) THERAPY CAN CONVERT CHB INTO INACTIVE HEPATITIS B VIRUS (HBV) INFECTION IN 20-30% OF THE TREATED PATIENTS. IN SPITE OF THE LOW RESPONSE RATE, IFN-ALPHA THERAPY HAS THE ADVANTAGE OF HAVING A LIMITED DURATION AND BEING EFFECTIVE EVEN AFTER THERAPY, AS DEMONSTRATED BY A MUCH HIGHER INCIDENCE OF HBSAG CLEARANCE IN RESPONDERS TO IFN-ALPHA THAN IN NATURALLY OCCURRING INACTIVE HBSAG CARRIERS. IFN-ALPHA HAS MULTIPLE ANTIVIRAL, ANTIPROLIFERATIVE, AND IMMUNOMODULATORY ACTIVITIES AND TARGETS: CELLULAR GENES (IFN-STIMULATED GENES) ACTIVATING DIFFERENT PATHWAYS OF ANTIVIRAL DEFENSE IN INFECTED AND NONINFECTED CELLS, HBV REPLICATION BLOCKING THE RNA-CONTAINING CORE PARTICLE FORMATION AND ACCELERATING THEIR DECAY, DEGRADING PREGENOMIC RNA, AND MODULATING THE NUCLEAR VIRAL MINICHROMOSOME (COVALENTLY CLOSED CIRCULAR DNA) ACTIVITY BY TARGETING ITS EPIGENETIC REGULATION AND BOTH INNATE AND ADAPTIVE IMMUNE RESPONSE. THE INTERFERENCE OF VIRAL HETEROGENEITY AND GENETIC POLYMORPHISMS OF THE HOST ON IFN-ALPHA SUSCEPTIBILITY IS UNDER INVESTIGATION. ONLY A BETTER UNDERSTANDING OF THE COMPLEX INTERPLAY BETWEEN THE DIFFERENT ACTIVITIES OF IFN-ALPHA WOULD WARRANT THE AMELIORATION OF CURRENT THERAPEUTIC STRATEGIES AND THE DESIGN OF NEW THERAPEUTIC APPROACHES. THE STUDY OF ON-TREATMENT DYNAMICS OF HBV INFECTION BY MEANS OF COMBINED QUANTITATIVE MONITORING OF SERUM HBV DNA AND HBSAG WARRANT TAILORING TREATMENT AT THE SINGLE-PATIENT LEVEL AND CAN HELP TO MAKE TREATMENT MORE COST-EFFECTIVE BY USING THE DIFFERENT COMBINATIONS OF CURRENTLY AVAILABLE ANTIVIRALS, INCLUDING IFN, MORE APPROPRIATELY. INTEGRATED MOLECULAR AND CLINICAL KNOWLEDGE IN A SYSTEMS MEDICINE FASHION IS MANDATORY TO FURTHER IMPROVE ANTIVIRAL THERAPY IN CHB. 2014 15 4816 34 OCCULT HEPATITIS B VIRUS INFECTION: A COMPLEX ENTITY WITH RELEVANT CLINICAL IMPLICATIONS. OCCULT HEPATITIS B VIRUS (HBV) INFECTION IS A WORLD-WIDE ENTITY, FOLLOWING THE GEOGRAPHICAL DISTRIBUTION OF DETECTABLE HEPATITIS B. THIS ENTITY IS DEFINED AS THE PERSISTENCE OF VIRAL GENOMES IN THE LIVER TISSUE AND IN SOME INSTANCES ALSO IN THE SERUM, ASSOCIATED TO NEGATIVE HBV SURFACE ANTIGEN SEROLOGY. THE MOLECULAR BASIS OF THE OCCULT INFECTION IS RELATED TO THE LIFE CYCLE OF HBV, WHICH PRODUCES A COVALENTLY CLOSED CIRCULAR DNA THAT PERSISTS IN THE CELL NUCLEI AS AN EPISOME, AND SERVES AS A TEMPLATE FOR GENE TRANSCRIPTION. THE MECHANISM RESPONSIBLE FOR THE HBSAG NEGATIVE STATUS IN OCCULT HBV CARRIERS IS A STRONG SUPPRESSION OF VIRAL REPLICATION, PROBABLY DUE TO THE HOST'S IMMUNE RESPONSE, CO-INFECTION WITH OTHER INFECTIOUS AGENTS AND EPIGENETIC FACTORS. THERE IS EMERGING EVIDENCE OF THE POTENTIAL CLINICAL RELEVANCE OF OCCULT HBV INFECTION, SINCE THIS COULD BE INVOLVED IN OCCULT HBV TRANSMISSION THROUGH ORTHOTOPIC LIVER TRANSPLANT AND BLOOD TRANSFUSION, REACTIVATION OF HBV INFECTION DURING IMMUNOSUPPRESSION, IMPAIRING CHRONIC LIVER DISEASE OUTCOME AND ACTING AS A RISK FACTOR FOR HEPATOCELLULAR CARCINOMA. THEREFORE IT IS IMPORTANT TO BEAR IN MIND THIS ENTITY IN CRYPTOGENETIC LIVER DISEASES, HEPATITIS C VIRUS/HIV INFECTED PATIENTS AND IMMUNOSUPRESSED INDIVIDUALS. IT IS ALSO NECESSARY TO INCREASE OUR KNOWLEDGE IN THIS FASCINATING FIELD TO DEFINE BETTER STRATEGIES TO DIAGNOSE AND TREAT THIS INFECTION. 2011 16 3255 32 HEPATITIS B VIRUS X PROTEIN MEDIATED EPIGENETIC ALTERATIONS IN THE PATHOGENESIS OF HEPATOCELLULAR CARCINOMA. CHRONIC HEPATITIS B VIRUS (HBV) INFECTION IS A WORLDWIDE HEALTH PROBLEM. HEPATITIS B VIRUS X PROTEIN (HBX), A PLEIOTROPIC REGULATORY PROTEIN ENCODED BY HBV, IS NECESSARY FOR THE TRANSCRIPTION OF HBV COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) MINICHROMOSOMES, AND AFFECTS THE EPIGENETIC REGULATION OF HOST CELLS. THE EPIGENETIC REPROGRAMMING OF HBX ON HOST CELL GENOME IS STRONGLY INVOLVED IN HBV-RELATED HCC CARCINOGENESIS. HERE, WE REVIEW THE LATEST FINDINGS OF THE EPIGENETIC REGULATION INDUCED BY HBX PROTEIN IN HEPATOCELLULAR CARCINOMA (HCC), INCLUDING DNA METHYLATION, HISTONE MODIFICATION AND NON-CODING RNA EXPRESSION. THE INFLUENCE OF HBX ON THE EPIGENETIC REGULATION OF CCCDNA IS ALSO SUMMARIZED. IN ADDITION, PRELIMINARY STUDIES OF TARGETED DRUGS FOR EPIGENETIC CHANGES INDUCED BY HBX ARE ALSO DISCUSSED. THE EXPLORATION OF EPIGENETIC MARKERS AS POTENTIAL TARGETS WILL HELP TO DEVELOP NEW PREVENTION AND/OR TREATMENT METHODS FOR HBX-RELATED HCC. 2022 17 2324 34 EPIGENETIC REGULATION OF HEPATITIS B VIRUS COVALENTLY CLOSED CIRCULAR DNA: IMPLICATIONS FOR EPIGENETIC THERAPY AGAINST CHRONIC HEPATITIS B. HEPATITIS B VIRUS (HBV) INFECTION REPRESENTS A SIGNIFICANT PUBLIC HEALTH BURDEN WORLDWIDE. ALTHOUGH CURRENT THERAPEUTICS MANAGE TO CONTROL THE DISEASE PROGRESSION, LIFELONG TREATMENT AND SURVEILLANCE ARE REQUIRED BECAUSE DRUG RESISTANCE DEVELOPS DURING TREATMENT AND REACTIVATIONS FREQUENTLY OCCUR FOLLOWING MEDICATION CESSATION. THUS, THE OCCURRENCE OF HEPATOCELLULAR CARCINOMA IS DECREASED, BUT NOT ELIMINATED. ONE MAJOR REASON FOR FAILURE OF HBV TREATMENT IS THE INABILITY TO ERADICATE OR INACTIVATE THE VIRAL COVALENTLY CLOSED CIRCULAR DNA (CCCDNA), WHICH IS A STABLE EPISOMAL FORM OF THE VIRAL GENOME DECORATED WITH HOST HISTONES AND NONHISTONE PROTEINS. ACCUMULATING EVIDENCE SUGGESTS THAT EPIGENETIC MODIFICATIONS OF CCCDNA CONTRIBUTE TO VIRAL REPLICATION AND THE OUTCOME OF CHRONIC HBV INFECTION. HERE, WE SUMMARIZE CURRENT PROGRESS ON HBV EPIGENETICS RESEARCH AND THE THERAPEUTIC IMPLICATIONS FOR CHRONIC HBV INFECTION BY LEARNING FROM THE EPIGENETIC THERAPIES FOR CANCER AND OTHER VIRAL DISEASES, WHICH MAY OPEN A NEW VENUE TO CURE CHRONIC HEPATITIS B. (HEPATOLOGY 2017;66:2066-2077). 2017 18 1178 33 CONTROL OF CCCDNA FUNCTION IN HEPATITIS B VIRUS INFECTION. THE TEMPLATE OF HEPATITIS B VIRUS (HBV) TRANSCRIPTION, THE COVALENTLY CLOSED CIRCULAR DNA (CCCDNA), PLAYS A KEY ROLE IN THE LIFE CYCLE OF THE VIRUS AND PERMITS THE PERSISTENCE OF INFECTION. NOVEL MOLECULAR TECHNIQUES HAVE OPENED NEW POSSIBILITIES TO INVESTIGATE THE ORGANIZATION AND THE ACTIVITY OF THE CCCDNA MINICHROMOSOME IN VIVO, AND RECENT ADVANCES HAVE STARTED TO SHED LIGHT ON THE COMPLEXITY OF THE MECHANISMS CONTROLLING CCCDNA FUNCTION. NUCLEAR CCCDNA ACCUMULATES IN HEPATOCYTE NUCLEI AS A STABLE MINICHROMOSOME ORGANIZED BY HISTONE AND NON-HISTONE VIRAL AND CELLULAR PROTEINS. IDENTIFICATION OF THE MOLECULAR MECHANISMS REGULATING CCCDNA STABILITY AND ITS TRANSCRIPTIONAL ACTIVITY AT THE RNA, DNA AND EPIGENETIC LEVELS IN THE COURSE OF CHRONIC HEPATITIS B (CH-B) INFECTION MAY REVEAL NEW POTENTIAL THERAPEUTIC TARGETS FOR ANTI-HBV DRUGS AND HENCE ASSIST IN THE DESIGN OF STRATEGIES AIMED AT SILENCING AND EVENTUALLY DEPLETING THE CCCDNA RESERVOIR. 2009 19 3185 31 HBC BINDS TO THE CPG ISLANDS OF HBV CCCDNA AND PROMOTES AN EPIGENETIC PERMISSIVE STATE. HBV COVALENTLY CLOSED CIRCULAR DNA (CCCDNA) IS THE TEMPLATE FOR THE TRANSCRIPTION OF HBV. HBV CORE PROTEIN (HBC) IS A MAIN COMPONENT OF THE HBV CCCDNA MINICHROMOSOME. HOWEVER, THE FUNCTION OF HBC IN CCCDNA IS NOT FULLY UNDERSTOOD. IN LIGHT OF RECENT FINDINGS THAT HBV CCCDNA MAY BE REGULATED EPIGENETICALLY, WE ANALYZED THE BINDING OF HBC TO CCCDNA AND THE IMPACT OF HBC ON CCCDNA EPIGENETIC PROFILE IN THE LIVER BIOPSY SAMPLES OF 22 PATIENTS WITH CHRONIC HEPATITIS B (CHB). WE FOUND THAT HBC BINDING TO HBV CCCDNA OCCURRED PREFERENTIALLY AT CPG ISLAND 2, AN IMPORTANT REGION FOR THE REGULATION OF HBV TRANSCRIPTION. FURTHERMORE, THE RELATIVE ABUNDANCES OF HBC BINDING TO CPG ISLAND 2 WERE POSITIVELY CORRELATED WITH THE RATIOS OF RELAXED CIRCULAR DNA TO CCCDNA AND THE LEVELS OF SERUM HBV DNA IN THOSE PATIENTS. INTERESTINGLY, THE RELATIVE ABUNDANCES OF HBC BINDING TO CPG ISLAND 2 WERE ASSOCIATED WITH THE BINDING OF CREB BINDING PROTEIN (CBP) AND WITH HYPOMETHYLATION IN CPG ISLAND 2 OF HBV CCCDNA MINICHROMOSOMES. HOWEVER, RELATIVELY HIGHER AMOUNTS OF HBC BINDING TO CPG ISLAND 2 OF CCCDNA WERE ACCOMPANIED BY LOWER AMOUNTS OF HDAC1 BINDING. MULTIVARIATE ANALYSIS REVEALED THAT THE ABUNDANCES OF HBC BINDING TO CPG ISLAND 2 OF CCCDNA AND POSITIVE HBEAG WERE INDEPENDENT FACTORS ASSOCIATED WITH THE REPLICATION OF HBV (P = 0.001 FOR BOTH). APPARENTLY, HBC IS A POSITIVE REGULATOR OF HBV TRANSCRIPTION AND REPLICATION, MAINTAINING THE PERMISSIVE EPIGENETIC STATE IN THE CRITICAL REGION OF THE HBV CCCDNA MINICHROMOSOMES. 2011 20 3394 28 HOST EPIGENETIC ALTERATIONS AND HEPATITIS B VIRUS-ASSOCIATED HEPATOCELLULAR CARCINOMA. HEPATOCELLULAR CARCINOMA (HCC) IS THE MOST FREQUENT PRIMARY MALIGNANCY OF THE LIVER AND A LEADING CAUSE OF CANCER-RELATED DEATHS WORLDWIDE. ALTHOUGH MUCH PROGRESS HAS BEEN MADE IN HCC DRUG DEVELOPMENT IN RECENT YEARS, TREATMENT OPTIONS REMAIN LIMITED. THE MAJOR CAUSE OF HCC IS CHRONIC HEPATITIS B VIRUS (HBV) INFECTION. DESPITE THE EXISTENCE OF A VACCINE, MORE THAN 250 MILLION INDIVIDUALS ARE CHRONICALLY INFECTED BY HBV. CURRENT ANTIVIRAL THERAPIES CAN REPRESS VIRAL REPLICATION BUT TO DATE THERE IS NO CURE FOR CHRONIC HEPATITIS B. OF NOTE, INHIBITION OF VIRAL REPLICATION REDUCES BUT DOES NOT ELIMINATE THE RISK OF HCC DEVELOPMENT. HBV CONTRIBUTES TO LIVER CARCINOGENESIS BY DIRECT AND INDIRECT EFFECTS. THIS REVIEW SUMMARIZES THE CURRENT KNOWLEDGE OF HBV-INDUCED HOST EPIGENETIC ALTERATIONS AND THEIR ASSOCIATION WITH HCC, WITH AN EMPHASIS ON THE INTERACTIONS BETWEEN HBV PROTEINS AND THE HOST CELL EPIGENETIC MACHINERY LEADING TO MODULATION OF GENE EXPRESSION. 2021