Alterations in promoter interaction landscape and transcriptional network underlying metabolic adaptation to diet.

Metabolic adaptation to nutritional state requires alterations in gene expression in key tissues. Here, we investigated chromatin interaction dynamics, as well as alterations in cis-regulatory loci and transcriptional network in a mouse model system. Chronic consumption of a diet high in saturated fat, when compared to a diet high in carbohydrate, led to dramatic reprogramming of the liver transcriptional network. Long-range interaction of promoters with distal regulatory loci, monitored by promoter capture Hi-C, was regulated by metabolic status in distinct fashion depending on diet. Adaptation to a lipid-rich diet, mediated largely by nuclear receptors including Hnf4α, relied on activation of preformed enhancer/promoter loops. Adaptation to carbohydrate-rich diet led to activation of preformed loops and to de novo formation of new promoter/enhancer interactions. These results suggest that adaptation to nutritional changes and metabolic stress occurs through both de novo and pre-existing chromatin interactions which respond differently to metabolic signals.

GATA3 zinc finger 2 mutations reprogram the breast cancer transcriptional network.

GATA3 is frequently mutated in breast cancer; these mutations are widely presumed to be loss-of function despite a dearth of information regarding their effect on disease course or their mechanistic impact on the breast cancer transcriptional network. Here, we address molecular and clinical features associated with GATA3 mutations. A novel classification scheme defines distinct clinical features for patients bearing breast tumors with mutations in the second GATA3 zinc-finger (ZnFn2). An engineered ZnFn2 mutant cell line by CRISPR-Cas9 reveals that mutation of one allele of the GATA3 second zinc finger (ZnFn2) leads to loss of binding and decreased expression at a subset of genes, including Progesterone Receptor. At other loci, associated with epithelial to mesenchymal transition, gain of binding correlates with increased gene expression. These results demonstrate that not all GATA3 mutations are equivalent and that ZnFn2 mutations impact breast cancer through gain and loss-of function.

Base-Resolution Analysis of DNA Methylation Patterns Downstream of Dnmt3a in Mouse Naïve B Cells.

The DNA methyltransferase, Dnmt3a, is dynamically regulated throughout mammalian B cell development and upon activation by antigenic stimulation. Dnmt3a inactivation in hematopoietic stem cells has been shown to drive B cell-related malignancies, including chronic lymphocytic leukemia, and associates with specific DNA methylation patterns in transformed cells. However, while it is clear that inactivation of Dnmt3a in hematopoietic stem cells has profound functional effects, the consequences of Dnmt3a inactivation in cells of the B lineage are unclear. To assess whether loss of Dnmt3a at the earliest stages of B cell development lead to DNA methylation defects that might impair function, we selectively inactivated Dnmt3a early in mouse B cell development and then utilized whole genome bisulfite sequencing to generate base-resolution profiles of Dnmt3a+/+ and Dnmt3a-/- naïve splenic B cells. Overall, we find that global methylation patterns are largely consistent between Dnmt3a+/+ and Dnmt3a-/- naïve B cells, indicating a minimal functional effect of DNMT3A in mature B cells. However, loss of Dnmt3a induced 449 focal DNA methylation changes, dominated by loss-of-methylation events. Regions found to be hypomethylated in Dnmt3a-/- naïve splenic B cells were enriched in gene bodies of transcripts expressed in B cells, a fraction of which are implicated in B cell-related disease. Overall, the results from this study suggest that factors other than Dnmt3a are the major drivers for methylome maintenance in B cell development.

An obesity-associated gut microbiome reprograms the intestinal epigenome and leads to altered colonic gene expression.

BACKGROUND: The gut microbiome, a key constituent of the colonic environment, has been implicated as an important modulator of human health. The eukaryotic epigenome is postulated to respond to environmental stimuli through alterations in chromatin features and, ultimately, gene expression. How the host mediates epigenomic responses to gut microbiota is an emerging area of interest. Here, we profile the gut microbiome and chromatin characteristics in colon epithelium from mice fed either an obesogenic or control diet, followed by an analysis of the resultant changes in gene expression. RESULTS: The obesogenic diet shapes the microbiome prior to the development of obesity, leading to altered bacterial metabolite production which predisposes the host to obesity. This microbiota-diet interaction leads to changes in histone modification at active enhancers that are enriched for binding sites for signal responsive transcription factors. These alterations of histone methylation and acetylation are associated with signaling pathways integral to the development of colon cancer. The transplantation of obesogenic diet-conditioned microbiota into germ free mice, combined with an obesogenic diet, recapitulates the features of the long-term diet regimen. The diet/microbiome-dependent changes are reflected in both the composition of the recipient animals' microbiome as well as in the set of transcription factor motifs identified at diet-influenced enhancers. CONCLUSIONS: These findings suggest that the gut microbiome, under specific dietary exposures, stimulates a reprogramming of the enhancer landscape in the colon, with downstream effects on transcription factors. These chromatin changes may be associated with those seen during colon cancer development.

Epigenetic Perturbations by Arg882-Mutated DNMT3A Potentiate Aberrant Stem Cell Gene-Expression Program and Acute Leukemia Development.

DNA methyltransferase 3A (DNMT3A) is frequently mutated in hematological cancers; however, the underlying oncogenic mechanism remains elusive. Here, we report that the DNMT3A mutational hotspot at Arg882 (DNMT3A(R882H)) cooperates with NRAS mutation to transform hematopoietic stem/progenitor cells and induce acute leukemia development. Mechanistically, DNMT3A(R882H) directly binds to and potentiates transactivation of stemness genes critical for leukemogenicity including Meis1, Mn1, and Hoxa gene cluster. DNMT3A(R882H) induces focal epigenetic alterations, including CpG hypomethylation and concurrent gain of active histone modifications, at cis-regulatory elements such as enhancers to facilitate gene transcription. CRISPR/Cas9-mediated ablation of a putative Meis1 enhancer carrying DNMT3A(R882H)-induced DNA hypomethylation impairs Meis1 expression. Importantly, DNMT3A(R882H)-induced gene-expression programs can be repressed through Dot1l inhibition, providing an attractive therapeutic strategy for DNMT3A-mutated leukemias.

Obesity, rather than diet, drives epigenomic alterations in colonic epithelium resembling cancer progression.

While obesity represents one of several risk factors for colorectal cancer in humans, the mechanistic underpinnings of this association remain unresolved. Environmental stimuli, including diet, can alter the epigenetic landscape of DNA cis-regulatory elements affecting gene expression and phenotype. Here, we explored the impact of diet and obesity on gene expression and the enhancer landscape in murine colonic epithelium. Obesity led to the accumulation of histone modifications associated with active enhancers at genomic loci downstream of signaling pathways integral to the initiation and progression of colon cancer. Meanwhile, colon-specific enhancers lost the same histone mark, poising cells for loss of differentiation. These alterations reflect a transcriptional program with many features shared with the program driving colon cancer progression. The interrogation of enhancer alterations by diet in colonic epithelium provides insights into the biology underlying high-fat diet and obesity as risk factors for colon cancer.

MT1-MMP and type II collagen specify skeletal stem cells and their bone and cartilage progeny.

Skeletal formation is dependent on timely recruitment of skeletal stem cells and their ensuing synthesis and remodeling of the major fibrillar collagens, type I collagen and type II collagen, in bone and cartilage tissues during development and postnatal growth. Loss of the major collagenolytic activity associated with the membrane-type 1 matrix metalloproteinase (MT1-MMP) results in disrupted skeletal development and growth in both cartilage and bone, where MT1-MMP is required for pericellular collagen dissolution. We show here that reconstitution of MT1-MMP activity in the type II collagen-expressing cells of the skeleton rescues not only diminished chondrocyte proliferation, but surprisingly, also results in amelioration of the severe skeletal dysplasia associated with MT1-MMP deficiency through enhanced bone formation. Consistent with this increased bone formation, type II collagen was identified in bone cells and skeletal stem/progenitor cells of wildtype mice. Moreover, bone marrow stromal cells isolated from mice expressing MT1-MMP under the control of the type II collagen promoter in an MT1-MMP-deficient background showed enhanced bone formation in vitro and in vivo compared with cells derived from nontransgenic MT1-MMP-deficient littermates. These observations show that type II collagen is not stringently confined to the chondrocyte but is expressed in skeletal stem/progenitor cells (able to regenerate bone, cartilage, myelosupportive stroma, marrow adipocytes) and in the chondrogenic and osteogenic lineage progeny where collagenolytic activity is a requisite for proper cell and tissue function.

Membrane-type MMPs enable extracellular matrix permissiveness and mesenchymal cell proliferation during embryogenesis.

Peri-cellular remodeling of mesenchymal extracellular matrices is considered a prerequisite for cell proliferation, motility and development. Here we demonstrate that membrane-type 3 MMP, MT3-MMP, is expressed in mesenchymal tissues of the skeleton and in peri-skeletal soft connective tissue. Consistent with this localization, MT3-MMP-deficient mice display growth inhibition tied to a decreased viability of mesenchymal cells in skeletal tissues. We document that MT3-MMP works as a major collagenolytic enzyme, enabling cartilage and bone cells to cleave high-density fibrillar collagen and modulate their resident matrix to make it permissive for proliferation and migration. Collectively, these data uncover a novel extracellular matrix remodeling mechanism required for proper function of mesenchymal cells. The physiological significance of MT3-MMP is highlighted in mice double deficient for MT1-MMP and MT3-MMP. Double deficiency transcends the combined effects of the individual single deficiencies and leads to severe embryonic defects in palatogenesis and bone formation incompatible with life. These defects are directly tied to loss of indispensable collagenolytic activities required in collagen-rich mesenchymal tissues for extracellular matrix remodeling and cell proliferation during embryogenesis.