1 3865 130 JAK2 REGULATES MISMATCH REPAIR PROTEIN-MEDIATED EPIGENETIC ALTERATIONS IN RESPONSE TO OXIDATIVE DAMAGE. AT SITES OF CHRONIC INFLAMMATION EPITHELIAL CELLS UNDERGO ABERRANT DNA METHYLATION THAT CONTRIBUTES TO TUMORIGENESIS. INFLAMMATION IS ASSOCIATED WITH AN INCREASE IN REACTIVE OXYGEN SPECIES (ROS) THAT CAUSE OXIDATIVE DNA DAMAGE, WHICH HAS ALSO BEEN LINKED TO EPIGENETIC ALTERATIONS. WE PREVIOUSLY DEMONSTRATED THAT IN RESPONSE TO ROS, MISMATCH REPAIR PROTEINS MSH2 AND MSH6 RECRUIT EPIGENETIC SILENCING PROTEINS DNA METHYLTRANSFERASE 1 (DNMT1) AND POLYCOMB REPRESSIVE COMPLEX 2 (PRC2) MEMBERS TO SITES OF DNA DAMAGE, RESULTING IN TRANSCRIPTIONAL REPRESSION OF TUMOR SUPPRESSOR GENES (TSGS). HOWEVER, IT WAS UNCLEAR WHAT SIGNAL IS UNIQUE TO ROS THAT RESULTS IN THE CHROMATIN BINDING OF MSH2 AND MSH6. HEREIN, WE DEMONSTRATE THAT IN RESPONSE TO HYDROGEN PEROXIDE (H(2) O(2) ), JAK2 LOCALIZES TO THE NUCLEUS AND INTERACTS WITH MSH2 AND MSH6. INHIBITION OR KNOCKDOWN OF JAK2 REDUCES THE H(2) O(2) -INDUCED CHROMATIN INTERACTION OF MSH2, MSH6, DNMT1, AND PRC2 MEMBERS, REDUCES H(2) O(2) -INDUCED GLOBAL INCREASE IN TRIMETHYLATION OF LYSINE 27 OF HISTONE H3 (H3K27ME3), AND ABROGATES OXIDATIVE DAMAGE-INDUCED TRANSCRIPTIONAL REPRESSION OF CANDIDATE TSGS. MOREOVER, JAK2 MRNA EXPRESSION IS ASSOCIATED WITH CPG ISLAND METHYLATOR PHENOTYPE (CIMP) STATUS IN HUMAN COLORECTAL CANCER. OUR FINDINGS PROVIDE NOVEL INSIGHT INTO THE CONNECTION BETWEEN KINASE ACTIVATION AND EPIGENETIC ALTERATIONS DURING OXIDATIVE DAMAGE AND INFLAMMATION. ENVIRON. MOL. MUTAGEN. 60:308-319, 2019. (C) 2018 WILEY PERIODICALS, INC. 2019 2 4997 36 PERINATAL LEAD (PB) EXPOSURE RESULTS IN SEX AND TISSUE-DEPENDENT ADULT DNA METHYLATION ALTERATIONS IN MURINE IAP TRANSPOSONS. EPIDEMIOLOGICAL AND ANIMAL DATA SUGGEST THAT ADULT CHRONIC DISEASE IS INFLUENCED BY EARLY-LIFE EXPOSURE-INDUCED CHANGES TO THE EPIGENOME. PREVIOUSLY, WE OBSERVED THAT PERINATAL LEAD (PB) EXPOSURE RESULTS IN PERSISTENT MURINE METABOLIC- AND ACTIVITY-RELATED EFFECTS. USING PHYLOGENETIC AND DNA METHYLATION ANALYSIS, WE HAVE ALSO IDENTIFIED NOVEL INTRACISTERNAL A PARTICLE (IAP) RETROTRANSPOSONS EXHIBITING REGIONS OF VARIABLE METHYLATION AS CANDIDATE LOCI FOR ENVIRONMENTAL EFFECTS ON THE EPIGENOME. HERE, WE NOW EVALUATE BRAIN AND KIDNEY DNA METHYLATION PROFILES OF FOUR REPRESENTATIVE IAPS IN ADULT MICE EXPOSED TO HUMAN PHYSIOLOGICALLY RELEVANT LEVELS OF PB TWO WEEKS PRIOR TO MATING THROUGH LACTATION. WHEN IAPS ACROSS THE GENOME WERE EVALUATED GLOBALLY, AVERAGE (SD) METHYLATION LEVELS WERE 92.84% (3.74) DIFFERING BY TISSUE (P < 0.001), BUT NOT SEX OR DOSE. BY CONTRAST, THE FOUR INDIVIDUAL IAPS DISPLAYED TISSUE-SPECIFIC PB AND SEX EFFECTS. MEDIUM PB-EXPOSED MICE HAD 3.86% LESS BRAIN METHYLATION AT IAP 110 (P < 0.01), WHILE HIGH PB-EXPOSED MICE HAD 2.83% LESS BRAIN METHYLATION AT IAP 236 (P = 0.01) AND 1.77% LESS AT IAP 506 (P = 0.05). INDIVIDUAL IAP DNA METHYLATION DIFFERED BY SEX FOR IAP 110 IN THE BRAIN AND KIDNEY, IAP 236 IN THE KIDNEY, AND IAP 1259 IN THE KIDNEY. USING TOMTOM, WE IDENTIFIED THREE BINDING MOTIFS THAT MATCHED TO EACH OF OUR NOVEL IAPS IMPACTED BY PB, ONE OF WHICH (HMGA2) HAS BEEN LINKED TO METABOLIC-RELATED CONDITIONS IN BOTH MICE AND HUMANS. THUS, THESE RECENTLY IDENTIFIED IAPS DISPLAY TISSUE-SPECIFIC ENVIRONMENTAL LABILITY AS WELL AS SEX-SPECIFIC DIFFERENCES SUPPORTING AN EPIGENETIC LINK BETWEEN EARLY EXPOSURE TO PB AND LATER-IN-LIFE HEALTH OUTCOMES. ENVIRON. MOL. MUTAGEN. 58:540-550, 2017. (C) 2017 WILEY PERIODICALS, INC. 2017 3 6663 36 UPREGULATION OF HISTONE-LYSINE METHYLTRANSFERASES PLAYS A CAUSAL ROLE IN HEXAVALENT CHROMIUM-INDUCED CANCER STEM CELL-LIKE PROPERTY AND CELL TRANSFORMATION. WHILE HEXAVALENT CHROMIUM [CR(VI)] IS GENERALLY CONSIDERED AS A GENOTOXIC ENVIRONMENTAL CARCINOGEN, STUDIES SHOWED THAT CR(VI) EXPOSURE ALSO CAUSES EPIGENETIC CHANGES. HOWEVER, WHETHER CR(VI)-CAUSED EPIGENETIC DYSREGULATIONS PLAYS AN IMPORTANT ROLE IN CR(VI) CARCINOGENICITY REMAIN LARGELY UNKNOWN. THE AIM OF THIS STUDY WAS TO DETERMINE IF CHRONIC LOW DOSE CR(VI) EXPOSURE CAUSES EPIGENETIC CHANGES, THE UNDERLYING MECHANISM AND WHETHER CHRONIC LOW DOSE CR(VI) EXPOSURE-CAUSED EPIGENETIC DYSREGULATION CONTRIBUTES CAUSALLY TO CR(VI)-INDUCED CANCER STEM CELL (CSC)-LIKE PROPERTY AND CELL TRANSFORMATION. TWO IMMORTALIZED HUMAN BRONCHIAL EPITHELIAL CELL LINES (BEAS-2B AND 16HBE) WERE EXPOSED TO 0.25 MUM OF K(2)CR(2)O(7) FOR 20 AND 40 WEEKS TO INDUCE CELL TRANSFORMATION, RESPECTIVELY. CR(VI)-INDUCED EPIGENETIC CHANGES WERE EXAMINED IN CR(VI)-TRANSFORMED CELLS AND CR(VI) EXPOSURE-CAUSED HUMAN LUNG CANCER TISSUES. PHARMACOLOGICAL INHIBITORS AND GENE KNOCKDOWN EXPERIMENTS WERE USED TO DETERMINE THE ROLE OF EPIGENETIC DYSREGULATION IN CR(VI) CARCINOGENICITY. WE FOUND THAT CHRONIC CR(VI) EXPOSURE CAUSES EPIGENETIC DYSREGULATION AS EVIDENCED BY THE INCREASED LEVELS OF HISTONE H3 REPRESSIVE METHYLATION MARKS (H3K9ME2 AND H3K27ME3) AND THE RELATED HISTONE-LYSING METHYLTRANSFERASES (HMTASES). PHARMACOLOGICAL INHIBITION OR KNOCKDOWN OF HMTASES REDUCES H3 REPRESSIVE METHYLATION MARKS AND MALIGNANT PHENOTYPES OF CR(VI)-TRANSFORMED CELLS. MOREOVER, KNOCKDOWN OF HMTASES IN PARENTAL CELLS SIGNIFICANTLY REDUCES CHRONIC CR(VI) EXPOSURE-INDUCED CSC-LIKE PROPERTY AND CELL TRANSFORMATION. FURTHER MECHANISTIC STUDY REVEALED THAT KNOCKDOWN OF HMTASES DECREASES CR(VI) EXPOSURE-CAUSED DNA DAMAGE. OUR FINDINGS INDICATE THAT CHRONIC CR(VI) EXPOSURE INCREASES H3 REPRESSIVE METHYLATION MARKS BY INCREASING THE RELATED HMTASES EXPRESSION; AND THAT INCREASED EXPRESSION OF HMTASES PLAYS A CAUSAL ROLE IN CR(VI)-INDUCED CSC-LIKE PROPERTY AND CELL TRANSFORMATION. 2018 4 3942 30 LNCRNA DUXAP10 UPREGULATION AND THE HEDGEHOG PATHWAY ACTIVATION ARE CRITICALLY INVOLVED IN CHRONIC CADMIUM EXPOSURE-INDUCED CANCER STEM CELL-LIKE PROPERTY. CADMIUM (CD) IS A WELL-KNOWN LUNG CARCINOGEN. HOWEVER, THE MECHANISM OF CD CARCINOGENESIS REMAINS TO BE CLEARLY DEFINED. CD HAS BEEN SHOWN TO ACT AS A WEAK MUTAGEN, SUGGESTING THAT IT MAY EXERT TUMORIGENIC EFFECT THROUGH NONGENOTOXIC WAYS, SUCH AS EPIGENETIC MECHANISMS. LONG NONCODING RNAS (LNCRNAS) REFER TO RNA MOLECULES THAT ARE LONGER THAN 200 NUCLEOTIDES IN LENGTH BUT LACK PROTEIN-CODING CAPACITIES. REGULATION OF GENE EXPRESSIONS BY LNCRNAS IS CONSIDERED AS ONE OF IMPORTANT EPIGENETIC MECHANISMS. THE GOAL OF THIS STUDY IS TO INVESTIGATE THE MECHANISM OF CD CARCINOGENESIS FOCUSING ON THE ROLE OF LNCRNA DYSREGULATIONS. CD-INDUCED MALIGNANT TRANSFORMATION OF HUMAN BRONCHIAL EPITHELIA BEAS-2B CELLS WAS ACCOMPLISHED BY A 9-MONTH LOW-DOSE CD (CDCL2, 2.5 MICROM) EXPOSURE. THE CD-EXPOSED CELLS FORMED SIGNIFICANTLY MORE COLONIES IN SOFT AGAR, DISPLAYED CANCER STEM CELL (CSC)-LIKE PROPERTY, AND FORMED TUMORS IN NUDE MICE. MECHANISTICALLY, CHRONIC LOW-DOSE CD EXPOSURE DID NOT CAUSE SIGNIFICANT GENOTOXIC EFFECTS BUT DYSREGULATED LNCRNA EXPRESSIONS. FURTHER Q-PCR ANALYSIS CONFIRMED THE SIGNIFICANT UPREGULATION OF THE ONCOGENIC LNCRNA DUXAP10 IN CD-TRANSFORMED CELLS. DUXAP10 KNOCKDOWN IN CD-TRANSFORMED CELLS SIGNIFICANTLY REDUCED THEIR CSC-LIKE PROPERTY. FURTHER MECHANISTIC STUDIES SHOWED THAT THE HEDGEHOG PATHWAY IS ACTIVATED IN CD-TRANSFORMED CELLS AND INHIBITION OF THIS PATHWAY REDUCES CD-INDUCED CSC-LIKE PROPERTY. DUXAP10 KNOCKDOWN CAUSED THE HEDGEHOG PATHWAY INACTIVATION IN CD-TRANSFORMED CELLS. FURTHERMORE, PAX6 EXPRESSION WAS UPREGULATED IN CD-TRANSFORMED CELLS AND PAX6 KNOCKDOWN SIGNIFICANTLY REDUCED THEIR DUXAP10 LEVELS AND CSC-LIKE PROPERTY. IN SUMMARY, THESE FINDINGS SUGGEST THAT THE LNCRNA DUXAP10 UPREGULATION MAY PLAY AN IMPORTANT ROLE IN CD CARCINOGENESIS. 2021 5 6086 42 THE EFFECTS OF ACETALDEHYDE EXPOSURE ON HISTONE MODIFICATIONS AND CHROMATIN STRUCTURE IN HUMAN LUNG BRONCHIAL EPITHELIAL CELLS. AS THE PRIMARY METABOLITE OF ALCOHOL AND THE MOST ABUNDANT CARCINOGEN IN TOBACCO SMOKE, ACETALDEHYDE IS LINKED TO A NUMBER OF HUMAN DISEASES ASSOCIATED WITH CHRONIC ALCOHOL CONSUMPTION AND SMOKING INCLUDING CANCERS. IN ADDITION TO DIRECT DNA DAMAGE AS A RESULT OF THE FORMATION OF ACETALDEHYDE-DNA ADDUCTS, ACETALDEHYDE MAY ALSO INDIRECTLY IMPACT PROPER GENOME FUNCTION THROUGH THE FORMATION OF PROTEIN ADDUCTS. HISTONE PROTEINS ARE THE MAJOR COMPONENT OF THE CHROMATIN. POST-TRANSLATIONAL HISTONE MODIFICATIONS (PTMS) ARE CRITICALLY IMPORTANT FOR THE MAINTENANCE OF GENETIC AND EPIGENETIC STABILITY. HOWEVER, LITTLE IS KNOWN ABOUT HOW ACETALDEHYDE-HISTONE ADDUCTS AFFECT HISTONE MODIFICATIONS AND CHROMATIN STRUCTURE. THE RESULTS OF PROTEIN CARBONYL ASSAYS SUGGEST THAT ACETALDEHYDE FORMS ADDUCTS WITH HISTONE PROTEINS IN HUMAN BRONCHIAL EPITHELIAL BEAS-2B CELLS. THE LEVEL OF ACETYLATION FOR N-TERMINAL TAILS OF CYTOSOLIC HISTONES H3 AND H4, AN IMPORTANT MODIFICATION FOR HISTONE NUCLEAR IMPORT AND CHROMATIN ASSEMBLY, IS SIGNIFICANTLY DOWNREGULATED FOLLOWING ACETALDEHYDE EXPOSURE IN BEAS-2B CELLS, POSSIBLY DUE TO THE FORMATION OF HISTONE ADDUCTS AND/OR THE DECREASE IN THE EXPRESSION OF HISTONE ACETYLTRANSFERASES. NOTABLY, THE LEVEL OF NUCLEOSOMAL HISTONES IN THE CHROMATIN FRACTION AND AT MOST OF THE GENOMIC LOCI WE TESTED ARE LOW IN ACETALDEHYDE-TREATED CELLS AS COMPARED WITH THE CONTROL CELLS, WHICH IS SUGGESTIVE OF INHIBITION OF CHROMATIN ASSEMBLY. MOREOVER, ACETALDEHYDE EXPOSURE PERTURBS CHROMATIN STRUCTURE AS EVIDENCED BY THE INCREASE IN GENERAL CHROMATIN ACCESSIBILITY AND THE DECREASE IN NUCLEOSOME OCCUPANCY AT GENOMIC LOCI FOLLOWING ACETALDEHYDE TREATMENT. OUR RESULTS INDICATE THAT REGULATION OF HISTONE MODIFICATIONS AND CHROMATIN ACCESSIBILITY MAY PLAY IMPORTANT ROLES IN ACETALDEHYDE-INDUCED PATHOGENESIS. ENVIRON. MOL. MUTAGEN. 59:375-385, 2018. (C) 2018 WILEY PERIODICALS, INC. 2018 6 714 28 CADMIUM IS A MUTAGEN THAT ACTS BY INHIBITING MISMATCH REPAIR. MOST ERRORS THAT ARISE DURING DNA REPLICATION CAN BE CORRECTED BY DNA POLYMERASE PROOFREADING OR BY POST-REPLICATION MISMATCH REPAIR (MMR). INACTIVATION OF BOTH MUTATION-AVOIDANCE SYSTEMS RESULTS IN EXTREMELY HIGH MUTABILITY THAT CAN LEAD TO ERROR CATASTROPHE. HIGH MUTABILITY AND THE LIKELIHOOD OF CANCER CAN BE CAUSED BY MUTATIONS AND EPIGENETIC CHANGES THAT REDUCE MMR. HYPERMUTABILITY CAN ALSO BE CAUSED BY EXTERNAL FACTORS THAT DIRECTLY INHIBIT MMR. IDENTIFYING SUCH FACTORS HAS IMPORTANT IMPLICATIONS FOR UNDERSTANDING THE ROLE OF THE ENVIRONMENT IN GENOME STABILITY. WE FOUND THAT CHRONIC EXPOSURE OF YEAST TO ENVIRONMENTALLY RELEVANT CONCENTRATIONS OF CADMIUM, A KNOWN HUMAN CARCINOGEN, CAN RESULT IN EXTREME HYPERMUTABILITY. THE MUTATION SPECIFICITY ALONG WITH RESPONSES IN PROOFREADING-DEFICIENT AND MMR-DEFICIENT MUTANTS INDICATE THAT CADMIUM REDUCES THE CAPACITY FOR MMR OF SMALL MISALIGNMENTS AND BASE-BASE MISMATCHES. IN EXTRACTS OF HUMAN CELLS, CADMIUM INHIBITED AT LEAST ONE STEP LEADING TO MISMATCH REMOVAL. TOGETHER, OUR DATA SHOW THAT A HIGH LEVEL OF GENETIC INSTABILITY CAN RESULT FROM ENVIRONMENTAL IMPEDIMENT OF A MUTATION-AVOIDANCE SYSTEM. 2003 7 6562 29 TRANSIENT AND PERMANENT CHANGES IN DNA METHYLATION PATTERNS IN INORGANIC ARSENIC-MEDIATED EPITHELIAL-TO-MESENCHYMAL TRANSITION. CHRONIC LOW DOSE INORGANIC ARSENIC EXPOSURE CAUSES CELLS TO TAKE ON AN EPITHELIAL-TO-MESENCHYMAL PHENOTYPE, WHICH IS A CRUCIAL PROCESS IN CARCINOGENESIS. INORGANIC ARSENIC IS NOT A MUTAGEN AND THUS EPIGENETIC ALTERATIONS HAVE BEEN IMPLICATED IN THIS PROCESS. INDEED, DURING THE EPITHELIAL-TO-MESENCHYMAL TRANSITION, MORPHOLOGIC CHANGES TO CELLS CORRELATE WITH CHANGES IN CHROMATIN STRUCTURE AND GENE EXPRESSION, ULTIMATELY DRIVING THIS PROCESS. HOWEVER, STUDIES ON THE EFFECTS OF INORGANIC ARSENIC EXPOSURE/WITHDRAWAL ON THE EPITHELIAL-TO-MESENCHYMAL TRANSITION AND THE IMPACT OF EPIGENETIC ALTERATIONS IN THIS PROCESS ARE LIMITED. IN THIS STUDY WE USED HIGH-RESOLUTION MICROARRAY ANALYSIS TO MEASURE THE CHANGES IN DNA METHYLATION IN CELLS UNDERGOING INORGANIC ARSENIC-INDUCED EPITHELIAL-TO-MESENCHYMAL TRANSITION, AND ON THE REVERSAL OF THIS PROCESS, AFTER REMOVAL OF THE INORGANIC ARSENIC EXPOSURE. WE FOUND THAT CELLS EXPOSED TO CHRONIC, LOW-DOSE INORGANIC ARSENIC EXPOSURE SHOWED 30,530 SITES WERE DIFFERENTIALLY METHYLATED, AND WITH INORGANIC ARSENIC WITHDRAWAL SEVERAL DIFFERENTIAL METHYLATED SITES WERE REVERSED, ALBEIT NOT COMPLETELY. FURTHERMORE, THESE CHANGES IN DNA METHYLATION MAINLY CORRELATED WITH CHANGES IN GENE EXPRESSION AT MOST SITES TESTED BUT NOT AT ALL. THIS STUDY SUGGESTS THAT DNA METHYLATION CHANGES ON GENE EXPRESSION ARE NOT CLEAR-CUT AND PROVIDE A PLATFORM TO BEGIN TO UNCOVER THE RELATIONSHIP BETWEEN DNA METHYLATION AND GENE EXPRESSION, SPECIFICALLY WITHIN THE CONTEXT OF INORGANIC ARSENIC TREATMENT. 2017 8 1122 32 COMPARISON OF GENE EXPRESSION PROFILES IN CHROMATE TRANSFORMED BEAS-2B CELLS. BACKGROUND: HEXAVALENT CHROMIUM [CR(VI)] IS A POTENT HUMAN CARCINOGEN. OCCUPATIONAL EXPOSURE HAS BEEN ASSOCIATED WITH INCREASED RISK OF RESPIRATORY CANCER. MULTIPLE MECHANISMS HAVE BEEN SHOWN TO CONTRIBUTE TO CR(VI) INDUCED CARCINOGENESIS, INCLUDING DNA DAMAGE, GENOMIC INSTABILITY, AND EPIGENETIC MODULATION, HOWEVER, THE MOLECULAR MECHANISM AND DOWNSTREAM GENES MEDIATING CHROMIUM'S CARCINOGENICITY REMAIN TO BE ELUCIDATED. METHODS/RESULTS: WE ESTABLISHED CHROMATE TRANSFORMED CELL LINES BY CHRONIC EXPOSURE OF NORMAL HUMAN BRONCHIAL EPITHELIAL BEAS-2B CELLS TO LOW DOSES OF CR(VI) FOLLOWED BY ANCHORAGE-INDEPENDENT GROWTH. THESE TRANSFORMED CELL LINES NOT ONLY EXHIBITED CONSISTENT MORPHOLOGICAL CHANGES BUT ALSO ACQUIRED ALTERED AND DISTINCT GENE EXPRESSION PATTERNS COMPARED WITH NORMAL BEAS-2B CELLS AND CONTROL CELL LINES (UNTREATED) THAT AROSE SPONTANEOUSLY IN SOFT AGAR. INTERESTINGLY, THE GENE EXPRESSION PROFILES OF SIX CR(VI) TRANSFORMED CELL LINES WERE REMARKABLY SIMILAR TO EACH OTHER YET DIFFERED SIGNIFICANTLY FROM THAT OF EITHER CONTROL CELL LINES OR NORMAL BEAS-2B CELLS. A TOTAL OF 409 DIFFERENTIALLY EXPRESSED GENES WERE IDENTIFIED IN CR(VI) TRANSFORMED CELLS COMPARED TO CONTROL CELLS. GENES RELATED TO CELL-TO-CELL JUNCTION WERE UPREGULATED IN ALL CR(VI) TRANSFORMED CELLS, WHILE GENES ASSOCIATED WITH THE INTERACTION BETWEEN CELLS AND THEIR EXTRACELLULAR MATRICES WERE DOWN-REGULATED. ADDITIONALLY, EXPRESSION OF GENES INVOLVED IN CELL PROLIFERATION AND APOPTOSIS WERE ALSO CHANGED. CONCLUSION: THIS STUDY IS THE FIRST TO REPORT GENE EXPRESSION PROFILING OF CR(VI) TRANSFORMED CELLS. THE GENE EXPRESSION CHANGES ACROSS INDIVIDUAL CHROMATE EXPOSED CLONES WERE REMARKABLY SIMILAR TO EACH OTHER BUT DIFFERED SIGNIFICANTLY FROM THE GENE EXPRESSION FOUND IN ANCHORAGE-INDEPENDENT CLONES THAT AROSE SPONTANEOUSLY. OUR ANALYSIS IDENTIFIED MANY NOVEL GENE EXPRESSION CHANGES THAT MAY CONTRIBUTE TO CHROMATE INDUCED CELL TRANSFORMATION, AND COLLECTIVELY THIS TYPE OF INFORMATION WILL PROVIDE A BETTER UNDERSTANDING OF THE MECHANISM UNDERLYING CHROMATE CARCINOGENICITY. 2011 9 192 34 ACETYLATED H4K16 BY MYST1 PROTECTS UROTSA CELLS FROM ARSENIC TOXICITY AND IS DECREASED FOLLOWING CHRONIC ARSENIC EXPOSURE. ARSENIC, A HUMAN CARCINOGEN THAT IS ASSOCIATED WITH AN INCREASED RISK OF BLADDER CANCER, IS COMMONLY FOUND IN DRINKING WATER. AN IMPORTANT MECHANISM BY WHICH ARSENIC IS THOUGHT TO BE CARCINOGENIC IS THROUGH THE INDUCTION OF EPIGENETIC CHANGES THAT LEAD TO ABERRANT GENE EXPRESSION. PREVIOUSLY, WE REPORTED THAT THE SAS2 GENE IS REQUIRED FOR OPTIMAL GROWTH OF YEAST IN THE PRESENCE OF ARSENITE (AS(III)). YEAST SAS2P IS ORTHOLOGOUS TO HUMAN MYST1, A HISTONE 4 LYSINE 16 (H4K16) ACETYLTRANSFERASE. HERE, WE SHOW THAT H4K16 ACETYLATION IS NECESSARY FOR THE RESISTANCE OF YEAST TO AS(III) THROUGH THE MODULATION OF CHROMATIN STATE. WE FURTHER EXPLORED THE ROLE OF MYST1 AND H4K16 ACETYLATION IN ARSENIC TOXICITY AND CARCINOGENESIS IN HUMAN BLADDER EPITHELIAL CELLS. THE EXPRESSION OF MYST1 WAS KNOCKED DOWN IN UROTSA CELLS, A MODEL OF BLADDER EPITHELIUM THAT HAS BEEN USED TO STUDY ARSENIC-INDUCED CARCINOGENESIS. SILENCING OF MYST1 REDUCED ACETYLATION OF H4K16 AND INDUCED SENSITIVITY TO AS(III) AND TO ITS MORE TOXIC METABOLITE MONOMETHYLARSONOUS ACID (MMA(III)) AT DOSES RELEVANT TO HIGH ENVIRONMENTAL HUMAN EXPOSURES. IN ADDITION, BOTH AS(III) AND MMA(III) TREATMENTS DECREASED GLOBAL H4K16 ACETYLATION LEVELS IN A DOSE- AND TIME-DEPENDENT MANNER. THIS INDICATES THAT ACETYLATED H4K16 IS REQUIRED FOR RESISTANCE TO ARSENIC AND THAT A REDUCTION IN ITS LEVELS AS A CONSEQUENCE OF ARSENIC EXPOSURE MAY CONTRIBUTE TO TOXICITY IN UROTSA CELLS. BASED ON THESE FINDINGS, WE PROPOSE A NOVEL ROLE FOR THE MYST1 GENE IN HUMAN SENSITIVITY TO ARSENIC. 2009 10 1993 31 EPIGENETIC AND EPITRANSCRIPTOMIC MECHANISMS OF CHROMIUM CARCINOGENESIS. HEXAVALENT CHROMIUM [CR(VI)], A GROUP I CARCINOGEN CLASSIFIED BY THE INTERNATIONAL AGENCY FOR RESEARCH ON CANCER (IARC), REPRESENTS ONE OF THE MOST COMMON OCCUPATIONAL AND ENVIRONMENTAL POLLUTANTS. THE FINDINGS FROM HUMAN EPIDEMIOLOGICAL AND LABORATORY ANIMAL STUDIES SHOW THAT LONG-TERM EXPOSURE TO CR(VI) CAUSES LUNG CANCER AND OTHER CANCER. ALTHOUGH CR(VI) IS A WELL-RECOGNIZED CARCINOGEN, THE MECHANISM OF CR(VI) CARCINOGENESIS HAS NOT BEEN WELL UNDERSTOOD. DUE TO THE FACT THAT CR(VI) UNDERGOES A SERIES OF METABOLIC REDUCTIONS ONCE ENTERING CELLS TO GENERATE REACTIVE CR METABOLITES AND REACTIVE OXYGEN SPECIES (ROS) CAUSING GENOTOXICITY, CR(VI) IS GENERALLY CONSIDERED AS A GENOTOXIC CARCINOGEN. HOWEVER, MORE AND MORE STUDIES HAVE DEMONSTRATED THAT ACUTE OR CHRONIC CR(VI) EXPOSURE ALSO CAUSES EPIGENETIC DYSREGULATIONS INCLUDING CHANGING DNA METHYLATION, HISTONE POSTTRANSLATIONAL MODIFICATIONS AND REGULATORY NON-CODING RNA (MICRORNA AND LONG NON-CODING RNA) EXPRESSIONS. MOREOVER, EMERGING EVIDENCE SHOWS THAT CR(VI) EXPOSURE IS ALSO CAPABLE OF ALTERING CELLULAR EPITRANSCRIPTOME. GIVEN THE INCREASINGLY RECOGNIZED IMPORTANCE OF EPIGENETIC AND EPITRANSCRIPTOMIC DYSREGULATIONS IN CANCER INITIATION AND PROGRESSION, IT IS BELIEVED THAT CR(VI) EXPOSURE-CAUSED EPIGENETIC AND EPITRANSCRIPTOMIC CHANGES COULD PLAY IMPORTANT ROLES IN CR(VI) CARCINOGENESIS. THE GOAL OF THIS CHAPTER IS TO REVIEW THE EPIGENETIC AND EPITRANSCRIPTOMIC EFFECTS OF CR(VI) EXPOSURE AND DISCUSS THEIR ROLES IN CR(VI) CARCINOGENESIS. BETTER UNDERSTANDING THE MECHANISM OF CR(VI) CARCINOGENESIS MAY IDENTIFY NEW MOLECULAR TARGETS FOR MORE EFFICIENT PREVENTION AND TREATMENT OF CANCER RESULTING FROM CR(VI) EXPOSURE. 2023 11 2961 37 GENETIC AND EPIGENETIC MECHANISMS IN METAL CARCINOGENESIS AND COCARCINOGENESIS: NICKEL, ARSENIC, AND CHROMIUM. CHRONIC EXPOSURE TO NICKEL(II), CHROMIUM(VI), OR INORGANIC ARSENIC (IAS) HAS LONG BEEN KNOWN TO INCREASE CANCER INCIDENCE AMONG AFFECTED INDIVIDUALS. RECENT EPIDEMIOLOGICAL STUDIES HAVE FOUND THAT CARCINOGENIC RISKS ASSOCIATED WITH CHROMATE AND IAS EXPOSURES WERE SUBSTANTIALLY HIGHER THAN PREVIOUSLY THOUGHT, WHICH LED TO MAJOR REVISIONS OF THE FEDERAL STANDARDS REGULATING AMBIENT AND DRINKING WATER LEVELS. GENOTOXIC EFFECTS OF CR(VI) AND IAS ARE STRONGLY INFLUENCED BY THEIR INTRACELLULAR METABOLISM, WHICH CREATES SEVERAL REACTIVE INTERMEDIATES AND BYPRODUCTS. TOXIC METALS ARE CAPABLE OF POTENT AND SURPRISINGLY SELECTIVE ACTIVATION OF STRESS-SIGNALING PATHWAYS, WHICH ARE KNOWN TO CONTRIBUTE TO THE DEVELOPMENT OF HUMAN CANCERS. DEPENDING ON THE METAL, ASCORBATE (VITAMIN C) HAS BEEN FOUND TO ACT EITHER AS A STRONG ENHANCER OR SUPPRESSOR OF TOXIC RESPONSES IN HUMAN CELLS. IN ADDITION TO GENETIC DAMAGE VIA BOTH OXIDATIVE AND NONOXIDATIVE (DNA ADDUCTS) MECHANISMS, METALS CAN ALSO CAUSE SIGNIFICANT CHANGES IN DNA METHYLATION AND HISTONE MODIFICATIONS, LEADING TO EPIGENETIC SILENCING OR REACTIVATION OF GENE EXPRESSION. IN VITRO GENOTOXICITY EXPERIMENTS AND RECENT ANIMAL CARCINOGENICITY STUDIES PROVIDED STRONG SUPPORT FOR THE IDEA THAT METALS CAN ACT AS COCARCINOGENS IN COMBINATION WITH NONMETAL CARCINOGENS. COCARCINOGENIC AND COMUTAGENIC EFFECTS OF METALS ARE LIKELY TO STEM FROM THEIR ABILITY TO INTERFERE WITH DNA REPAIR PROCESSES. OVERALL, METAL CARCINOGENESIS APPEARS TO REQUIRE THE FORMATION OF SPECIFIC METAL COMPLEXES, CHROMOSOMAL DAMAGE, AND ACTIVATION OF SIGNAL TRANSDUCTION PATHWAYS PROMOTING SURVIVAL AND EXPANSION OF GENETICALLY/EPIGENETICALLY ALTERED CELLS. 2008 12 4267 26 MICROARRAY DATASET OF TRANSIENT AND PERMANENT DNA METHYLATION CHANGES IN HELA CELLS UNDERGOING INORGANIC ARSENIC-MEDIATED EPITHELIAL-TO-MESENCHYMAL TRANSITION. THE NOVEL DATASET PRESENTED HERE REPRESENTS THE RESULTS OF THE CHANGING PATTERN OF DNA METHYLATION PROFILES IN HELA CELLS EXPOSED TO CHRONIC LOW DOSE (0.5 MICROM) SODIUM ARSENITE, RESULTING IN EPITHELIAL-TO-MESENCHYMAL TRANSITION, AS WELL AS DNA METHYLATION PATTERNS IN CELLS WHERE INORGANIC ARSENIC HAS BEEN REMOVED. INORGANIC ARSENIC IS A KNOWN CARCINOGEN, THOUGH NOT MUTAGENIC. SEVERAL MECHANISMS HAVE BEEN PROPOSED AS TO HOW INORGANIC ARSENIC DRIVES CARCINOGENESIS SUCH AS REGULATION OF THE CELL?S REDOX POTENTIAL AND/OR EPIGENETICS. IN FACT, THERE ARE GENE SPECIFIC STUDIES AND LIMITED GENOME-WIDE STUDIES THAT HAVE IMPLICATED EPIGENETIC FACTORS SUCH AS DNA METHYLATION IN INORGANIC ARSENIC-MEDIATED EPITHELIAL-TO-MESENCHYMAL TRANSITION (EMT). HOWEVER, GENOME-WIDE STUDIES ABOUT THE IMPACT OF 1) CHRONIC, LOW-DOSE INORGANIC ARSENIC EXPOSURE ON DNA METHYLATION PATTERNS DURING INORGANIC ARSENIC-INDUCED EPITHELIAL-TO-MESENCHYMAL TRANSITION, AND 2) THE REMOVAL INORGANIC ARSENIC (REVERSAL) ON DNA METHYLATION PATTERNS, IS LACKING. FOR THIS DATASET, TWO REPLICATES WERE PERFORMED WITH EACH OF THE SAMPLES - NON-TREATED, INORGANIC ARSENIC-TREATED, AND REVERSE-TREATED CELLS. WE PROVIDE NORMALIZED AND PROCESSED DATA, AND LOG2 FOLD CHANGE IN DNA METHYLATION. THE RAW MICROARRAY DATA ARE AVAILABLE THROUGH NCBI GEO, ACCESSION NUMBER GSE95232 AND A RELATED RESEARCH PAPER HAS BEEN ACCEPTED FOR PUBLISHED IN TOXICOLOGY AND APPLIED PHARMACOLOGY (ECKSTEIN ET AL., 2017) [1]. 2017 13 4208 21 METAL CARCINOGEN EXPOSURE INDUCES CANCER STEM CELL-LIKE PROPERTY THROUGH EPIGENETIC REPROGRAMING: A NOVEL MECHANISM OF METAL CARCINOGENESIS. ARSENIC, CADMIUM, NICKEL AND HEXAVALENT CHROMIUM ARE AMONG THE MOST COMMON ENVIRONMENTAL POLLUTANTS AND POTENT CARCINOGENS. CHRONIC EXPOSURE TO THESE METALS CAUSES VARIOUS TYPES OF CANCER IN HUMANS, REPRESENTING A SIGNIFICANT ENVIRONMENTAL HEALTH ISSUE. ALTHOUGH UNDER ACTIVE INVESTIGATION, THE MECHANISMS OF METAL CARCINOGENESIS HAVE NOT BEEN CLEARLY DEFINED. ONE COMMON FEATURE OF THESE METAL CARCINOGENS IS THAT THEY ARE ALL ABLE TO CAUSE VARIOUS EPIGENETIC DYSREGULATIONS, WHICH ARE BELIEVED TO PLAY IMPORTANT ROLES IN THEIR CARCINOGENICITY. HOWEVER, HOW METAL CARCINOGEN-CAUSED EPIGENETIC DYSREGULATION CONTRIBUTES TO METAL CARCINOGENESIS REMAINS LARGELY UNKNOWN. THE EVOLUTION OF CANCER STEM CELL (CSC) THEORY HAS OPENED EXCITING NEW AVENUES FOR STUDYING THE MECHANISM OF METAL CARCINOGENESIS. INCREASING EVIDENCE INDICATES THAT CHRONIC METAL CARCINOGEN EXPOSURE PRODUCES CSC-LIKE CELLS THROUGH DYSREGULATED EPIGENETIC MECHANISMS. THIS REVIEW WILL FIRST PROVIDE SOME BRIEF INTRODUCTIONS ABOUT CSC, EPIGENETICS AND EPIGENETIC REGULATION OF CSCS; THEN SUMMARIZE PROGRESSES IN RECENT STUDIES ON METAL CARCINOGEN-INDUCED CSC-LIKE PROPERTY THROUGH EPIGENETIC REPROGRAMING AS A NOVEL MECHANISM OF METAL CARCINOGENESIS. SOME PERSPECTIVES FOR FUTURE STUDIES IN THIS FIELD ARE ALSO PRESENTED. 2019 14 6733 20 WHAT CAN CHEMICAL CARCINOGENESIS SHED LIGHT ON THE LNT HYPOTHESIS IN RADIATION CARCINOGENESIS? TO PROTECT THE PUBLIC'S HEALTH FROM EXPOSURE TO PHYSICAL, CHEMICAL, AND MICROBIOLOGICAL AGENTS, IT IS IMPORTANT THAT ANY POLICY BE BASED ON RIGOROUS SCIENTIFICALLY BASED RESEARCH. THE CONCEPT OF "LINEAR NO-THRESHOLD" (LNT) HAS BEEN IMPLEMENTED TO PROVIDE GUIDELINE EXPOSURES TO THESE AGENTS. THE PRACTICAL LIMITATION TO TESTING THIS HYPOTHESIS IS TO PROVIDE SUFFICIENT SAMPLES FOR EXPERIMENTAL OR EPIDEMIOLOGICAL STUDIES. WHILE THERE IS NO UNIVERSALLY ACCEPTED UNDERSTANDING OF MOST HUMAN DISEASES, THERE SEEMS TO BE BETTER UNDERSTANDING OF CANCER THAT MIGHT HELP RESOLVE THE "LNT" MODEL. THE PUBLIC'S CONCERN, AFTER BEING EXPOSED TO RADIATION, IS THE POTENTIAL OF PRODUCING CANCER. THE MOST RIGOROUS HYPOTHESIS OF HUMAN CARCINOGENESIS IS THE "MULTISTAGE, MULTIMECHANISM" CHEMICAL CARCINOGENESIS MODEL. THE RADIATION CARCINOGENESIS LNT MODEL, RARELY, IF EVER, BUILT IT INTO THEIR SUPPORT. IT WILL BE ARGUED THAT THIS MULTISTAGE, MULTIMECHANISM MODEL OF CARCINOGENESIS, INVOLVING THE "INITIATION" OF A SINGLE CELL BY A MUTAGEN EVENT, FOLLOWED BY CHRONIC EXPOSURE TO THRESHOLD LEVELS OF EPIGENETIC AGENTS OR CONDITIONS THAT STIMULATE THE CLONAL EXPANSION OF THE "INITIATED" CELL, CAN CONVERT THESE BENIGN CELLS TO BECOME INVASIVE AND METASTATIC. THIS "PROMOTION" PROCESS CAN BE INTERRUPTED, THEREBY PREVENTING THESE INITIATED CELLS FROM TRANSITIONING TO THE "PROGRESSION" PROCESS OF INVASION AND METASTASIS. 2019 15 323 28 ALKBH4 STABILIZATION IS REQUIRED FOR ARSENIC-INDUCED 6MA DNA METHYLATION INHIBITION, KERATINOCYTE MALIGNANT TRANSFORMATION, AND TUMORIGENICITY. INORGANIC ARSENIC IS ONE OF THE WELL-KNOWN HUMAN SKIN CARCINOGENS. HOWEVER, THE MOLECULAR MECHANISM BY WHICH ARSENIC PROMOTES CARCINOGENESIS REMAINS UNCLEAR. PREVIOUS STUDIES HAVE ESTABLISHED THAT EPIGENETIC CHANGES, INCLUDING CHANGES IN DNA METHYLATION, ARE AMONG THE CRITICAL MECHANISMS THAT DRIVE CARCINOGENESIS. N(6)-METHYLADENINE (6MA) METHYLATION ON DNA IS A WIDESPREAD EPIGENETIC MODIFICATION THAT WAS INITIALLY FOUND ON BACTERIAL AND PHAGE DNA. ONLY RECENTLY HAS 6MA BEEN IDENTIFIED IN MAMMALIAN GENOMES. HOWEVER, THE FUNCTION OF 6MA IN GENE EXPRESSION AND CANCER DEVELOPMENT IS NOT WELL UNDERSTOOD. HERE, WE SHOW THAT CHRONIC LOW DOSES OF ARSENIC INDUCE MALIGNANT TRANSFORMATION AND TUMORIGENESIS IN KERATINOCYTES AND LEAD TO THE UPREGULATION OF ALKBH4 AND DOWNREGULATION OF 6MA ON DNA. WE FOUND THAT REDUCED 6MA LEVELS IN RESPONSE TO LOW LEVELS OF ARSENIC WERE MEDIATED BY THE UPREGULATION OF THE 6MA DNA DEMETHYLASE ALKBH4. MOREOVER, WE FOUND THAT ARSENIC INCREASED ALKBH4 PROTEIN LEVELS AND THAT ALKBH4 DELETION IMPAIRED ARSENIC-INDUCED TUMORIGENICITY IN VITRO AND IN MICE. MECHANISTICALLY, WE FOUND THAT ARSENIC PROMOTED ALKBH4 PROTEIN STABILITY THROUGH REDUCED AUTOPHAGY. TOGETHER, OUR FINDINGS REVEAL THAT THE DNA 6MA DEMETHYLASEALKBH4 PROMOTES ARSENIC TUMORIGENICITY AND ESTABLISHES ALKBH4 AS A PROMISING TARGET FOR ARSENIC-INDUCED TUMORIGENESIS. 2022 16 979 27 CHRONIC OXIDATIVE STRESS INCREASES RESISTANCE TO DOXORUBICIN-INDUCED CYTOTOXICITY IN RENAL CARCINOMA CELLS POTENTIALLY THROUGH EPIGENETIC MECHANISM. RENAL CELL CARCINOMA IS THE MOST COMMON FORM OF KIDNEY CANCER AND IS HIGHLY RESISTANT TO CHEMOTHERAPY. ALTHOUGH THE ROLE OF OXIDATIVE STRESS IN KIDNEY CANCER IS KNOWN, THE CHEMOTHERAPEUTIC RESPONSE OF CANCER CELLS ADAPTED TO CHRONIC OXIDATIVE STRESS IS NOT CLEAR. HENCE, THE EFFECT OF OXIDATIVE STRESS ON SENSITIVITY TO DOXORUBICIN-INDUCED CYTOTOXICITY WAS EVALUATED USING AN IN VITRO MODEL OF HUMAN KIDNEY CANCER CELLS ADAPTED TO CHRONIC OXIDATIVE STRESS. RESULTS OF MTT- AND ANCHORAGE-INDEPENDENT GROWTH ASSAYS AND CELL CYCLE ANALYSIS REVEALED SIGNIFICANT DECREASE IN SENSITIVITY TO DOXORUBICIN IN CAKI-1 CELLS ADAPTED TO OXIDATIVE STRESS. CHANGES IN THE EXPRESSION OF GENES INVOLVED IN DRUG TRANSPORT, CELL SURVIVAL, AND DNA REPAIR-DEPENDENT APOPTOSIS FURTHER CONFIRMED INCREASED RESISTANCE TO DOXORUBICIN-INDUCED CYTOTOXICITY IN THESE CELLS. DECREASED EXPRESSION OF MISMATCH REPAIR (MMR) GENE MSH2 IN CELLS EXPOSED TO OXIDATIVE STRESS SUGGESTS THAT LOSS OF MMR-DEPENDENT APOPTOSIS COULD BE A POTENTIAL MECHANISM FOR INCREASED RESISTANCE TO DOXORUBICIN-INDUCED CYTOTOXICITY. ADDITIONALLY, DOWNREGULATION OF HDAC1, AN INCREASE IN THE LEVEL OF HISTONE H3 ACETYLATION, AND HYPERMETHYLATION OF MSH2 PROMOTER WERE ALSO OBSERVED IN CAKI-1 CELLS ADAPTED TO CHRONIC OXIDATIVE STRESS. DNA-DEMETHYLATING AGENT 5-AZA-2DC SIGNIFICANTLY RESTORED THE EXPRESSION OF MSH2 AND DOXORUBICIN-INDUCED CYTOTOXICITY IN CAKI-1 CELLS ADAPTED TO CHRONIC OXIDATIVE STRESS, SUGGESTING THE ROLE OF DNA HYPERMETHYLATION IN INACTIVATION OF MSH2 EXPRESSION AND CONSEQUENTLY MMR-DEPENDENT APOPTOSIS IN THESE CELLS. IN SUMMARY, THIS STUDY FOR THE FIRST TIME PROVIDES DIRECT EVIDENCE FOR THE ROLE OF OXIDATIVE STRESS IN CHEMOTHERAPEUTIC RESISTANCE IN RENAL CARCINOMA CELLS POTENTIALLY THROUGH EPIGENETIC MECHANISM. 2016 17 482 25 ARSENITE BINDS TO THE ZINC FINGER MOTIF OF TIP60 HISTONE ACETYLTRANSFERASE AND INDUCES ITS DEGRADATION VIA THE 26S PROTEASOME. ARSENIC IS A UBIQUITOUS ENVIRONMENTAL CONTAMINANT WITH WIDESPREAD PUBLIC HEALTH CONCERN. EPIDEMIOLOGICAL STUDIES HAVE REVEALED THAT CHRONIC HUMAN EXPOSURE TO ARSENIC IN DRINKING WATER IS ASSOCIATED WITH THE PREVALENCE OF SKIN, LUNG, AND BLADDER CANCERS. ABERRANT HISTONE MODIFICATIONS (E.G., METHYLATION, ACETYLATION, AND UBIQUITINATION) WERE PREVIOUSLY FOUND TO BE ACCOMPANIED BY ARSENIC EXPOSURE; THUS, PERTURBATION OF EPIGENETIC PATHWAYS IS THOUGHT TO CONTRIBUTE TO ARSENIC CARCINOGENESIS. ARSENITE IS KNOWN TO INTERACT WITH ZINC FINGER MOTIFS OF PROTEINS, AND ZINC FINGER MOTIF IS PRESENT IN AND INDISPENSABLE FOR THE ENZYMATIC ACTIVITIES OF CRUCIAL HISTONE-MODIFYING ENZYMES ESPECIALLY THE MYST FAMILY OF HISTONE ACETYLTRANSFERASES (E.G., TIP60). HENCE, WE REASONED THAT TRIVALENT ARSENIC MAY TARGET THE ZINC FINGER MOTIF OF THESE ENZYMES, DISTURB THEIR ENZYMATIC ACTIVITIES, AND ALTER HISTONE ACETYLATION. HEREIN, WE FOUND THAT AS(3+) COULD BIND DIRECTLY TO THE ZINC-FINGER MOTIF OF TIP60 IN VITRO AND IN CELLS. IN ADDITION, EXPOSURE TO AS(3+) COULD LEAD TO A DOSE-DEPENDENT DECREASE IN TIP60 PROTEIN LEVEL VIA THE UBIQUITIN-PROTEASOME PATHWAY. THUS, THE RESULTS FROM THE PRESENT STUDY REVEALED, FOR THE FIRST TIME, THAT ARSENITE MAY TARGET CYSTEINE RESIDUES IN THE ZINC-FINGER MOTIF OF THE TIP60 HISTONE ACETYLTRANSFERASE, THEREBY ALTERING THE H4K16AC HISTONE EPIGENETIC MARK. OUR RESULTS ALSO SHED SOME NEW LIGHT ON THE MECHANISMS UNDERLYING THE ARSENIC-INDUCED EPIGENOTOXICITY AND CARCINOGENESIS IN HUMANS. 2017 18 1557 15 DNA METHYLATION MODIFICATIONS INDUCED BY HEXAVALENT CHROMIUM. HEXAVALENT CHROMIUM [CR (VI)] CONTRIBUTES A SIGNIFICANT HEALTH RISK AND CAUSES A NUMBER OF CHRONIC DISEASES AND CANCERS. WHILE THE GENOTOXIC AND CARCINOGENIC EFFECTS OF HEXAVALENT CHROMIUM EXPOSURE ARE EXPLICIT AND BETTER-CHARACTERIZED, THE EXACT MECHANISM UNDERLYING THE CARCINOGENIC PROCESS OF CR (VI) IS STILL A MATTER OF DEBATE. IN RECENT YEARS, STUDIES HAVE SHOWN THAT EPIGENETIC MODIFICATIONS, ESPECIALLY DNA METHYLATION, MAY PLAY A SIGNIFICANT ROLE IN CR (VI)-INDUCED CARCINOGENESIS. THE AIM OF THIS REVIEW IS TO SUMMARIZE OUR UNDERSTANDING REGARDING THE EFFECTS OF CR (VI) ON GLOBAL AND GENE-SPECIFIC DNA METHYLATION. 2019 19 567 27 BASIC PROPERTIES AND MOLECULAR MECHANISMS OF EXOGENOUS CHEMICAL CARCINOGENS. EXOGENOUS CHEMICAL CARCINOGENESIS IS AN EXTREMELY COMPLEX MULTIFACTORIAL PROCESS DURING WHICH GENE-ENVIRONMENT INTERACTIONS INVOLVING CHRONIC EXPOSURE TO EXOGENOUS CHEMICAL CARCINOGENS (ECCS) AND POLYMORPHISMS OF CANCER SUSCEPTIBILITY GENES ADD FURTHER COMPLEXITY. WE DESCRIBE THE PROPERTIES AND MOLECULAR MECHANISMS OF ECCS THAT CONTRIBUTE TO INDUCE AND GENERATE CANCER. A BASIC AND SPECIFIC PROPERTY OF MANY LIPOPHILIC ORGANIC ECCS INCLUDING POLYCYCLIC AROMATIC HYDROCARBONS AND POLYHALOGENATED AROMATIC HYDROCARBONS IS THEIR ABILITY TO BIOACCUMULATE IN THE ADIPOSE TISSUE FROM WHERE THEY MAY BE RELEASED IN THE BLOOD CIRCULATION AND TARGET PERIPHERAL TISSUES FOR CARCINOGENESIS. MANY ORGANIC ECCS ARE PROCARCINOGENS AND CONSEQUENTLY NEED TO BE ACTIVATED BY THE CYTOCHROME P450 (CYP) SYSTEM AND/OR OTHER ENZYMES BEFORE THEY CAN ADDUCT DNA AND PROTEINS. BECAUSE THEY CONTRIBUTE NOT ONLY TO THE COCARCINOGENIC AND PROMOTING EFFECTS OF MANY AROMATIC POLLUTANTS BUT ALSO TO THEIR MUTAGENIC EFFECTS, THE ARYL HYDROCARBON RECEPTOR-ACTIVATING AND THE INDUCIBLE CYP SYSTEMS ARE CENTRAL TO EXOGENOUS CHEMICAL CARCINOGENESIS. ANOTHER BASIC PROPERTY OF ECCS IS THEIR ABILITY TO INDUCE STABLE AND BULKY DNA ADDUCTS THAT CANNOT BE SIMPLY REPAIRED BY THE DIFFERENT REPAIR SYSTEMS. IN ADDITION, FOLLOWING ECC EXPOSURE, MUTAGENESIS MAY ALSO BE CAUSED INDIRECTLY BY FREE-RADICAL PRODUCTION AND BY EPIGENETIC ALTERATIONS. AS A RESULT OF COMPLEX MOLECULAR INTERPLAYS, DIRECT AND/OR INDIRECT MUTAGENESIS MAY ESPECIALLY ACCOUNT FOR THE CARCINOGENIC EFFECTS OF MANY EXOGENOUS METALS AND METALLOIDS. BECAUSE OF THESE MOLECULAR PROPERTIES AND ACTION MECHANISMS, WE CONCLUDE THAT ECCS COULD BE MAJOR CONTRIBUTORS TO HUMAN CANCER, WITH OBVIOUSLY GREAT PUBLIC HEALTH CONSEQUENCES. 2010 20 474 23 ARSENIC BIOTRANSFORMATION AS A CANCER PROMOTING FACTOR BY INDUCING DNA DAMAGE AND DISRUPTION OF REPAIR MECHANISMS. CHRONIC EXPOSURE TO ARSENIC IN DRINKING WATER POSES A MAJOR GLOBAL HEALTH CONCERN. POPULATIONS EXPOSED TO HIGH CONCENTRATIONS OF ARSENIC-CONTAMINATED DRINKING WATER SUFFER SERIOUS HEALTH CONSEQUENCES, INCLUDING ALARMING CANCER INCIDENCE AND DEATH RATES. ARSENIC IS BIOTRANSFORMED THROUGH SEQUENTIAL ADDITION OF METHYL GROUPS, ACQUIRED FROM S-ADENOSYLMETHIONINE (SAM). METABOLISM OF ARSENIC GENERATES A VARIETY OF GENOTOXIC AND CYTOTOXIC SPECIES, DAMAGING DNA DIRECTLY AND INDIRECTLY, THROUGH THE GENERATION OF REACTIVE OXIDATIVE SPECIES AND INDUCTION OF DNA ADDUCTS, STRAND BREAKS AND CROSS LINKS, AND INHIBITION OF THE DNA REPAIR PROCESS ITSELF. SINCE SAM IS THE METHYL GROUP DONOR USED BY DNA METHYLTRANSFERASES TO MAINTAIN NORMAL EPIGENETIC PATTERNS IN ALL HUMAN CELLS, ARSENIC IS ALSO POSTULATED TO AFFECT MAINTENANCE OF NORMAL DNA METHYLATION PATTERNS, CHROMATIN STRUCTURE, AND GENOMIC STABILITY. THE BIOLOGICAL PROCESSES UNDERLYING THE CANCER PROMOTING FACTORS OF ARSENIC METABOLISM, RELATED TO DNA DAMAGE AND REPAIR, WILL BE DISCUSSED HERE. 2011