The role of the microbiome in cancer development and therapy.

Answer questions and earn CME/CNE The human body harbors enormous numbers of microbiota that influence cancer susceptibility, in part through their prodigious metabolic capacity and their profound influence on immune cell function. Microbial pathogens drive tumorigenesis in 15% to 20% of cancer cases. Even larger numbers of malignancies are associated with an altered composition of commensal microbiota (dysbiosis) based on microbiome studies using metagenomic sequencing. Although association studies cannot distinguish whether changes in microbiota are causes or effects of cancer, a causative role is supported by rigorously controlled preclinical studies using gnotobiotic mouse models colonized with one or more specific bacteria. These studies demonstrate that microbiota can alter cancer susceptibility and progression by diverse mechanisms, such as modulating inflammation, inducing DNA damage, and producing metabolites involved in oncogenesis or tumor suppression. Evidence is emerging that microbiota can be manipulated for improving cancer treatment. By incorporating probiotics as adjuvants for checkpoint immunotherapy or by designing small molecules that target microbial enzymes, microbiota can be harnessed to improve cancer care. CA Cancer J Clin 2017;67:326-344. © 2017 American Cancer Society.

Targeted inhibition of gut bacterial ß-glucuronidase activity enhances anticancer drug efficacy.

Irinotecan treats a range of solid tumors, but its effectiveness is severely limited by gastrointestinal (GI) tract toxicity caused by gut bacterial ß-glucuronidase (GUS) enzymes. Targeted bacterial GUS inhibitors have been shown to partially alleviate irinotecan-induced GI tract damage and resultant diarrhea in mice. Here, we unravel the mechanistic basis for GI protection by gut microbial GUS inhibitors using in vivo models. We use in vitro, in fimo, and in vivo models to determine whether GUS inhibition alters the anticancer efficacy of irinotecan. We demonstrate that a single dose of irinotecan increases GI bacterial GUS activity in 1 d and reduces intestinal epithelial cell proliferation in 5 d, both blocked by a single dose of a GUS inhibitor. In a tumor xenograft model, GUS inhibition prevents intestinal toxicity and maintains the antitumor efficacy of irinotecan. Remarkably, GUS inhibitor also effectively blocks the striking irinotecan-induced bloom of Enterobacteriaceae in immune-deficient mice. In a genetically engineered mouse model of cancer, GUS inhibition alleviates gut damage, improves survival, and does not alter gut microbial composition; however, by allowing dose intensification, it dramatically improves irinotecan's effectiveness, reducing tumors to a fraction of that achieved by irinotecan alone, while simultaneously promoting epithelial regeneration. These results indicate that targeted gut microbial enzyme inhibitors can improve cancer chemotherapeutic outcomes by protecting the gut epithelium from microbial dysbiosis and proliferative crypt damage.

The CRCbiome study: a large prospective cohort study examining the role of lifestyle and the gut microbiome in colorectal cancer screening participants.

BACKGROUND: Colorectal cancer (CRC) screening reduces CRC incidence and mortality. However, current screening methods are either hampered by invasiveness or suboptimal performance, limiting their effectiveness as primary screening methods. To aid in the development of a non-invasive screening test with improved sensitivity and specificity, we have initiated a prospective biomarker study (CRCbiome), nested within a large randomized CRC screening trial in Norway. We aim to develop a microbiome-based classification algorithm to identify advanced colorectal lesions in screening participants testing positive for an immunochemical fecal occult blood test (FIT). We will also examine interactions with host factors, diet, lifestyle and prescription drugs. The prospective nature of the study also enables the analysis of changes in the gut microbiome following the removal of precancerous lesions. METHODS: The CRCbiome study recruits participants enrolled in the Bowel Cancer Screening in Norway (BCSN) study, a randomized trial initiated in 2012 comparing once-only sigmoidoscopy to repeated biennial FIT, where women and men aged 50-74 years at study entry are invited to participate. Since 2017, participants randomized to FIT screening with a positive test result have been invited to join the CRCbiome study. Self-reported diet, lifestyle and demographic data are collected prior to colonoscopy after the positive FIT-test (baseline). Screening data, including colonoscopy findings are obtained from the BCSN database. Fecal samples for gut microbiome analyses are collected both before and 2 and 12 months after colonoscopy. Samples are analyzed using metagenome sequencing, with taxonomy profiles, and gene and pathway content as primary measures. CRCbiome data will also be linked to national registries to obtain information on prescription histories and cancer relevant outcomes occurring during the 10 year follow-up period. DISCUSSION: The CRCbiome study will increase our understanding of how the gut microbiome, in combination with lifestyle and environmental factors, influences the early stages of colorectal carcinogenesis. This knowledge will be crucial to develop microbiome-based screening tools for CRC. By evaluating biomarker performance in a screening setting, using samples from the target population, the generalizability of the findings to future screening cohorts is likely to be high. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT01538550 .

The Warburg effect dictates the mechanism of butyrate-mediated histone acetylation and cell proliferation.

Widespread changes in gene expression drive tumorigenesis, yet our knowledge of how aberrant epigenomic and transcriptome profiles arise in cancer cells is poorly understood. Here, we demonstrate that metabolic transformation plays an important role. Butyrate is the primary energy source of normal colonocytes and is metabolized to acetyl-CoA, which was shown to be important not only for energetics but also for HAT activity. Due to the Warburg effect, cancerous colonocytes rely on glucose as their primary energy source, so butyrate accumulated and functioned as an HDAC inhibitor. Although both mechanisms increased histone acetylation, different target genes were upregulated. Consequently, butyrate stimulated the proliferation of normal colonocytes and cancerous colonocytes when the Warburg effect was prevented from occurring, whereas it inhibited the proliferation of cancerous colonocytes undergoing the Warburg effect. These findings link a common metabolite to epigenetic mechanisms that are differentially utilized by normal and cancerous cells because of their inherent metabolic differences.

Personalized Nutrition in Disrupting Cancer - Proceedings From the 2017 American College of Nutrition Annual Meeting.

Cancer is a major public health problem and is the second leading cause of death in the United States and worldwide; nearly one in six deaths are attributable to cancer. Approximately 20% of all cancers diagnosed in the United States are attributable to unhealthy diet, excessive alcohol consumption, physical inactivity, and body fatness. Individual cancers are distinct disease states that are multifactorial in their causation, making them exceedingly cumbersome to study from a nutrition standpoint. Genetic influences are a major piece of the puzzle and personalized nutrition is likely to be most effective in disrupting cancer during all stages. Increasing evidence shows that after a cancer diagnosis, continuing standard dietary recommendations may not be appropriate. This is because powerful dietary interventions such as short-term fasting and carbohydrate restriction can disrupt tumor metabolism, synergizing with standard therapies such as radiation and drug therapy to improve efficacy and ultimately, cancer survival. The importance of identifying dietary interventions cannot be overstated, and the American College of Nutrition's commitment to advancing knowledge and research is evidenced by dedication of the 2017 ACN Annual Meeting to "Disrupting Cancer: The Role of Personalized Nutrition" and this resulting proceedings manuscript, which summarizes the meeting's findings.

BRG1 and BRM function antagonistically with c-MYC in adult cardiomyocytes to regulate conduction and contractility.

RATIONALE: The contractile dysfunction that underlies heart failure involves perturbations in multiple biological processes ranging from metabolism to electrophysiology. Yet the epigenetic mechanisms that are altered in this disease state have not been elucidated. SWI/SNF chromatin-remodeling complexes are plausible candidates based on mouse knockout studies demonstrating a combined requirement for the BRG1 and BRM catalytic subunits in adult cardiomyocytes. Brg1/Brm double mutants exhibit metabolic and mitochondrial defects and are not viable although their cause of death has not been ascertained. OBJECTIVE: To determine the cause of death of Brg1/Brm double-mutant mice, to test the hypothesis that BRG1 and BRM are required for cardiac contractility, and to identify relevant downstream target genes. METHODS AND RESULTS: A tamoxifen-inducible gene-targeting strategy utilizing αMHC-Cre-ERT was implemented to delete both SWI/SNF catalytic subunits in adult cardiomyocytes. Brg1/Brm double-mutant mice were monitored by echocardiography and electrocardiography, and they underwent rapidly progressive ventricular dysfunction including conduction defects and arrhythmias that culminated in heart failure and death within 3weeks. Mechanistically, BRG1/BRM repressed c-Myc expression, and enforced expression of a DOX-inducible c-MYC trangene in mouse cardiomyocytes phenocopied the ventricular conduction defects observed in Brg1/Brm double mutants. BRG1/BRM and c-MYC had opposite effects on the expression of cardiac conduction genes, and the directionality was consistent with their respective loss- and gain-of-function phenotypes. To support the clinical relevance of this mechanism, BRG1/BRM occupancy was diminished at the same target genes in human heart failure cases compared to controls, and this correlated with increased c-MYC expression and decreased CX43 and SCN5A expression. CONCLUSION: BRG1/BRM and c-MYC have an antagonistic relationship regulating the expression of cardiac conduction genes that maintain contractility, which is reminiscent of their antagonistic roles as a tumor suppressor and oncogene in cancer.

Brahma is required for cell cycle arrest and late muscle gene expression during skeletal myogenesis.

Although the two catalytic subunits of the SWI/SNF chromatin-remodeling complex--Brahma (Brm) and Brg1--are almost invariably co-expressed, their mutually exclusive incorporation into distinct SWI/SNF complexes predicts that Brg1- and Brm-based SWI/SNF complexes execute specific functions. Here, we show that Brg1 and Brm have distinct functions at discrete stages of muscle differentiation. While Brg1 is required for the activation of muscle gene transcription at early stages of differentiation, Brm is required for Ccnd1 repression and cell cycle arrest prior to the activation of muscle genes. Ccnd1 knockdown rescues the ability to exit the cell cycle in Brm-deficient myoblasts, but does not recover terminal differentiation, revealing a previously unrecognized role of Brm in the activation of late muscle gene expression independent from the control of cell cycle. Consistently, Brm null mice displayed impaired muscle regeneration after injury, with aberrant proliferation of satellite cells and delayed formation of new myofibers. These data reveal stage-specific roles of Brm during skeletal myogenesis, via formation of repressive and activatory SWI/SNF complexes.

PPARα inhibition modulates multiple reprogrammed metabolic pathways in kidney cancer and attenuates tumor growth.

Kidney cancer [renal cell carcinoma (RCC)] is the sixth-most-common cancer in the United States, and its incidence is increasing. The current progression-free survival for patients with advanced RCC rarely extends beyond 1-2 yr due to the development of therapeutic resistance. We previously identified peroxisome proliferator-activating receptor-α (PPARα) as a potential therapeutic target for this disease and showed that a specific PPARα antagonist, GW6471, induced apoptosis and cell cycle arrest at G0/G1 in RCC cell lines associated with attenuation of cell cycle regulatory proteins. We now extend that work and show that PPARα inhibition attenuates components of RCC metabolic reprogramming, capitalizing on the Warburg effect. The specific PPARα inhibitor GW6471, as well as a siRNA specific to PPARα, attenuates the enhanced fatty acid oxidation and oxidative phosphorylation associated with glycolysis inhibition, and PPARα antagonism also blocks the enhanced glycolysis that has been observed in RCC cells; this effect did not occur in normal human kidney epithelial cells. Such cell type-specific inhibition of glycolysis corresponds with changes in protein levels of the oncogene c-Myc and has promising clinical implications. Furthermore, we show that treatment with GW6471 results in RCC tumor growth attenuation in a xenograft mouse model, with minimal obvious toxicity, a finding associated with the expected on-target effects on c-Myc. These studies demonstrate that several pivotal cancer-relevant metabolic pathways are inhibited by PPARα antagonism. Our data support the concept that targeting PPARα, with or without concurrent inhibition of glycolysis, is a potential novel and effective therapeutic approach for RCC that targets metabolic reprogramming in this tumor.

Emerging roles of the microbiome in cancer.

Gene-environment interactions underlie cancer susceptibility and progression. Yet, we still have limited knowledge of which environmental factors are important and how they function during tumorigenesis. In this respect, the microbial communities that inhabit our gastrointestinal tract and other body sites have been unappreciated until recently. However, our microbiota are environmental factors that we are exposed to continuously, and human microbiome studies have revealed significant differences in the relative abundance of certain microbes in cancer cases compared with controls. To characterize the function of microbiota in carcinogenesis, mouse models of cancer have been treated with antibiotics. They have also been maintained in a germfree state or have been colonized with specific bacteria in specialized (gnotobiotic) facilities. These studies demonstrate that microbiota can increase or decrease cancer susceptibility and progression by diverse mechanisms such as by modulating inflammation, influencing the genomic stability of host cells and producing metabolites that function as histone deacetylase inhibitors to epigenetically regulate host gene expression. One might consider microbiota as tractable environmental factors because they are highly quantifiable and relatively stable within an individual compared with our exposures to external agents. At the same time, however, diet can modulate the composition of microbial communities within our gut, and this supports the idea that probiotics and prebiotics can be effective chemoprevention strategies. The trajectory of where the current work is headed suggests that microbiota will continue to provide insight into the basic mechanisms of carcinogenesis and that microbiota will also become targets for therapeutic intervention.

The BRG1 chromatin remodeler regulates widespread changes in gene expression and cell proliferation during B cell activation.

Widespread changes in gene expression underlie B cell development and activation, yet our knowledge of which chromatin-remodeling factors are essential is limited. Here, we demonstrate that the BRG1 catalytic subunit of SWI/SNF complexes was dispensable for murine B cell development but played an important, albeit selective, role during activation. Although BRG1 was dispensable for CD69 induction and differentiation into plasma cells based on the ability of mutant B cells to undergo hypertrophy and secrete IgM antibodies, it was required for robust cell proliferation in response to activation. Accordingly, BRG1 was required for only ∼100 genes to be expressed at normal levels in naïve B cells but >1,000 genes during their activation. BRG1 upregulated fivefold more genes than it downregulated, and the toll-like receptor pathway and JAK/STAT cytokine-signaling pathways were particularly dependent on BRG1. The importance of BRG1 in B cell activation was underscored by the occurrence of opportunistic Pasteurella infections in conditionally mutant mice. B cell activation has long served as a model of inducible gene expression, and the results presented here identify BRG1 as a chromatin-remodeling factor that upregulates the transcriptome of B cells during their activation to promote rapid cell proliferation and to mount an effective immune response.

Functional redundancy of SWI/SNF catalytic subunits in maintaining vascular endothelial cells in the adult heart.

RATIONALE: Mating type switching/sucrose non-fermenting (SWI/SNF) chromatin-remodeling complexes utilize either BRG1 or BRM as a catalytic subunit to alter nucleosome position and regulate gene expression. BRG1 is required for vascular endothelial cell (VEC) development and embryonic survival, whereas BRM is dispensable. OBJECTIVE: To circumvent embryonic lethality and study Brg1 function in adult tissues, we used conditional gene targeting. To evaluate possible Brg1-Brm redundancy, we analyzed Brg1 mutant mice on wild-type and Brm-deficient backgrounds. METHODS AND RESULTS: The inducible Mx1-Cre driver was used to mutate Brg1 in adult mice. These conditional-null mutants exhibited a tissue-specific phenotype and unanticipated functional compensation between Brg1 and Brm. Brg1 single mutants were healthy and had a normal lifespan, whereas Brg1/Brm double mutants exhibited cardiovascular defects and died within 1 month. BRG1 and BRM were required for the viability of VECs but not other cell types where both genes were also knocked out. The VEC phenotype was most evident in the heart, particularly in the microvasculature of the outer myocardium, and was recapitulated in primary cells ex vivo. VEC death resulted in vascular leakage, cardiac hemorrhage, secondary death of cardiomyocytes due to ischemia, and ventricular dissections. CONCLUSIONS: BRG1-catalyzed SWI/SNF complexes are particularly important in cardiovascular tissues. However, in contrast to embryonic development, in which Brm does not compensate, Brg1 is required in adult VECs only when Brm is also mutated. These results demonstrate for the first time that Brm functionally compensates for Brg1 in vivo and that there are significant changes in the relative importance of BRG1- and BRM-catalyzed SWI/SNF complexes during the development of an essential cell lineage.

Combined gene dosage requirement for SWI/SNF catalytic subunits during early mammalian development.

Mammalian SWI/SNF complexes utilize either BRG1 or BRM as alternative catalytic subunits with DNA-dependent ATPase activity to remodel chromatin. Although the two proteins are 75 % identical, broadly expressed, and have similar biochemical activities in vitro, BRG1 is essential for mouse embryonic development, while BRM is dispensable. To investigate whether BRG1 and BRM have overlapping functions during mouse embryogenesis, we performed double-heterozygous intercrosses using constitutive null mutations previously created by gene targeting. The progeny of these crosses had a distribution of genotypes that was significantly skewed relative to their combined gene dosage. This was most pronounced at the top and bottom of the gene dosage hierarchy, with a 1.5-fold overrepresentation of Brg1 (+/+) ;Brm (+/+) mice and a corresponding 1.6-fold underrepresentation of Brg1 (+/-) ;Brm (-/-) mice. To account for the underrepresentation of Brg1 (+/-) ;Brm (-/-) mice, timed matings and blastocyst outgrowth assays demonstrated that ~50 % of these embryos failed to develop beyond the peri-implantation stage. These results challenge the idea that BRG1 is the exclusive catalytic subunit of SWI/SNF complexes in ES cells and suggest that BRM also interacts with the pluripotency transcription factors to facilitate self-renewal of the inner cell mass. In contrast to implantation, the Brm genotype did not influence an exencephaly phenotype that arises because of Brg1 haploinsufficiency during neural tube closure and that results in peri-natal lethality. Taken together, these results support the idea that BRG1 and BRM have overlapping functions for certain developmental processes but not others during embryogenesis.

Metaboloepigenetics: interrelationships between energy metabolism and epigenetic control of gene expression.

Diet and energy metabolism affect gene expression, which influences human health and disease. Here, we discuss the role of epigenetics as a mechanistic link between energy metabolism and control of gene expression. A number of key energy metabolites including SAM, acetyl-CoA, NAD(+), and ATP serve as essential co-factors for many, perhaps most, epigenetic enzymes that regulate DNA methylation, posttranslational histone modifications, and nucleosome position. The relative abundance of these energy metabolites allows a cell to sense its energetic state. And as co-factors, energy metabolites act as rheostats to modulate the activity of epigenetic enzymes and upregulate/downregulate transcription as appropriate to maintain homeostasis.

BRG1 co-localizes with DNA replication factors and is required for efficient replication fork progression.

For DNA replication to occur, chromatin must be remodeled. Yet, we know very little about which proteins alter nucleosome occupancy at origins and replication forks and for what aspects of replication they are required. Here, we demonstrate that the BRG1 catalytic subunit of mammalian SWI/SNF-related complexes co-localizes with origin recognition complexes, GINS complexes, and proliferating cell nuclear antigen at sites of DNA replication on extended chromatin fibers. The specific pattern of BRG1 occupancy suggests it does not participate in origin selection but is involved in the firing of origins and the process of replication elongation. This latter function is confirmed by the fact that Brg1 mutant mouse embryos and RNAi knockdown cells exhibit a 50% reduction in replication fork progression rates, which is associated with decreased cell proliferation. This novel function of BRG1 is consistent with its requirement during embryogenesis and its role as a tumor suppressor to maintain genome stability and prevent cancer.

BRG1 requirement for long-range interaction of a locus control region with a downstream promoter.

The dynamic packaging of DNA into chromatin is a fundamental step in the control of diverse nuclear processes. Whereas certain transcription factors and chromosomal components promote the formation of higher-order chromatin loops, the co-regulator machinery mediating loop assembly and disassembly is unknown. Using mice bearing a hypomorphic allele of the BRG1 chromatin remodeler, we demonstrate that the Brg1 mutation abrogated a cell type-specific loop between the beta-globin locus control region and the downstream beta major promoter, despite trans-acting factor occupancy at both sites. By contrast, distinct loops were insensitive to the Brg1 mutation. Molecular analysis with a conditional allele of GATA-1, a key regulator of hematopoiesis, in a novel cell-based system provided additional evidence that BRG1 functions early in chromatin domain activation to mediate looping. Although the paradigm in which chromatin remodelers induce nucleosome structural transitions is well established, our results demonstrating an essential role of BRG1 in the genesis of specific chromatin loops expands the repertoire of their functions.

BRG1 directly regulates nucleosome structure and chromatin looping of the alpha globin locus to activate transcription.

Alpha globin expression must be regulated properly to prevent the occurrence of alpha-thalassemias, yet many questions remain unanswered regarding the mechanism of transcriptional activation. Identifying factors that regulate chromatin structure of the endogenous alpha globin locus in developing erythroblasts will provide important mechanistic insight. Here, we demonstrate that the BRG1 catalytic subunit of SWI/SNF-related complexes co-immunoprecipitates with GATA-1 and EKLF in murine fetal liver cells in vivo and is recruited to the far-upstream major-regulatory element (MRE) and alpha2 promoter. Furthermore, based on our analysis of Brg1(null/ENU1) mutant mice, BRG1 regulates DNase I sensitivity, H3ac, and H3K4me2 but not CpG methylation at both sites. Most importantly, BRG1 is required for chromatin loop formation between the MRE and alpha2 promoter and for maximal RNA Polymerase II occupancy at the alpha2 promoter. Consequently, Brg1 mutants express alpha globin mRNA at only 5-10% of wild-type levels and die at mid-gestation. These data identify BRG1 as a chromatin-modifying factor required for nucleosome remodeling and transcriptional activation of the alpha globin locus. These data also demonstrate that chromatin looping between the MRE and alpha2 promoter is required as part of the transcriptional activation mechanism.

The role of Brg1, a catalytic subunit of mammalian chromatin-remodeling complexes, in T cell development.

Mammalian SWI-SNF-related complexes use brahma-related gene 1 (Brg1) as a catalytic subunit to remodel nucleosomes and regulate transcription. Recent biochemical data has linked Brg1 function to genes important for T lymphocyte differentiation. To investigate the role of SWI-SNF-related complexes in this lineage, we ablated Brg1 function in T lymphocytes. T cell-specific Brg1-deficient mice showed profound thymic abnormalities, CD4 derepression at the double negative (DN; CD4- CD8-) stage, and a developmental block at the DN to double positive (CD4+ CD8+) transition. 5'-bromo-2'-deoxyuridine incorporation and annexin V staining establish a role for Brg1 complexes in the regulation of thymocyte cell proliferation and survival. This Brg1-dependent cell survival is specific for developing thymocytes as indicated by the presence of Brg1-deficient mature T lymphocytes that have escaped the developmental block in the thymus. However, reductions in peripheral T cell populations lead to immunodeficiency and compromised health of mutant mice. These results highlight the importance of chromatin-remodeling complexes at different stages in the development of a mammalian cell lineage.

Dissecting molecular steps in chromatin domain activation during hematopoietic differentiation.

GATA factors orchestrate hematopoiesis via multistep transcriptional mechanisms, but the interrelationships and importance of individual steps are poorly understood. Using complementation analysis with GATA-1-null cells and mice containing a hypomorphic allele of the chromatin remodeler BRG1, we dissected the pathway from GATA-1 binding to cofactor recruitment, chromatin loop formation, and transcriptional activation. Analysis of GATA-1-mediated activation of the beta-globin locus, in which GATA-1 assembles dispersed complexes at the promoters and the distal locus control region (LCR), revealed molecular intermediates, including GATA-1-independent and GATA-1-containing LCR subcomplexes, both defective in promoting loop formation. An additional intermediate consisted of an apparently normal LCR complex and a promoter complex with reduced levels of total RNA polymerase II (Pol II) and Pol II phosphorylated at serine 5 of the carboxy-terminal domain. Reduced BRG1 activity solely compromised Pol II and serine 5-phosphorylated Pol II occupancy at the promoter, phenocopying the LCR-deleted mouse. These studies defined a hierarchical order of GATA-1-triggered events at a complex locus and establish a novel mechanism of long-range gene regulation.

Reversible epigenetic modifications of the two cardiac myosin heavy chain genes during changes in expression.

The two genes of the cardiac myosin heavy chain (MHC) locus-alpha-MHC (aMHC) and beta-MHC (bMHC)--are reciprocally regulated in the mouse ventricle during development and in adult conditions such as hypothyroidism and pathological cardiac hypertrophy. Their expressions are under the control of thyroid hormone T3 levels. To gain insights into the epigenetic mechanisms that underlie this inducible and reversible switching of the aMHC and bMHC isoforms, we have investigated the histone modification patterns that occur over the two cardiac MHC promoters during T3-mediated reversible switching of gene expression. Mice fed a diet of propylthiouracil (PTU, an inhibitor of T3 synthesis) for 2 weeks dramatically reduce aMHC mRNA expression and increase bMHC mRNA levels to high levels, while a subsequent withdrawal of PTU diet for 2 weeks completely reverses the T3-mediated changes in MHC expression. Using hearts from mice treated in this way, we carried out chromatin immunoprecipitation-qPCR assays with antibodies against acetylated histone H3 (H3ac) and trimethylated histone (H3K4me3)-two well-documented markers of activation. Our results show that the reexpression of bMHC is associated at the bMHC promoter with increased H3ac but not H3K4me3. In contrast, the silencing of aMHC is associated at its promoter with decreased H3K4me3, but not decreased H3ac. The epigenetic changes at the two MHC promoters are completely reversed when the gene expression returns to initial levels. These data indicate that during reciprocal and inducible gene expression H3ac parallels bMHC isoform expression while H3K4me3 parallels expression of the tightly linked aMHC isoform.

The failure of two major formaldehyde catabolism enzymes (ADH5 and ALDH2) leads to partial synthetic lethality in C57BL/6 mice.

BACKGROUND: Exogenous formaldehyde is classified by the IARC as a Category 1 known human carcinogen. Meanwhile, a significant amount of endogenous formaldehyde is produced in the human body; as such, formaldehyde-derived DNA and protein adducts have been detected in animals and humans in the absence of major exogenous formaldehyde exposure. However, the toxicological effects of endogenous formaldehyde on individuals with normal DNA damage repair functions are not well understood. In this study, we attempted to generate C57BL/6 mice deficient in both Adh5 and Aldh2, which encode two major enzymes that metabolize endogenous formaldehyde, in order to understand the effects of endogenous formaldehyde on mice with normal DNA repair function. RESULTS: Due to deficiencies in both ADH5 and ALDH2, few mice survived past post-natal day 21. In fact, the survival of pups within the first few days after birth was significantly decreased. Remarkably, two Aldh2 -/- /Adh5 -/- mice survived for 25 days after birth, and we measured their total body weight and organ weights. The body weight of Aldh2 -/- /Adh5 -/- mice decreased significantly by almost 37% compared to the Aldh2 -/- /Adh5 +/- and Aldh2 -/- /Adh5 +/+ mice of the same litter. In addition, the absolute weight of each organ was also significantly reduced. CONCLUSION: Mice deficient in both formaldehyde-metabolizing enzymes ADH5 and ALDH2 were found to develop partial synthetic lethality and mortality shortly after birth. This phenotype may be due to the accumulation of endogenous formaldehyde. No serious phenotype has been reported in people with dysfunctional, dominant-negative ALDH2*2 alleles, but it has been reported that they may be highly susceptible to osteoporosis and neurodegenerative diseases. It is important to further investigate these diseases in individuals with ALDH2*2 alleles, including an association with decreased metabolism, and thus accumulation, of formaldehyde.