Eukaryotic Transcriptional Regulation

National Institute Of Environmental Health Sciences

Investigators

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Abstract

Our research program is divided into two different subject areas. One section of the laboratory is engaged in basic science questions related to how transcription factors function in a chromatin context. The remainder of the laboratory studies how environmental factors influence epigenetic information in a manner that influences disease risk. Our work on transcription factor function centers on how the zinc-finger transcription factor GATA3 invades chromatin to nucleate enhancer formation. We utilize a system wherein GATA3 is exogenously expressed at modest levels in basal breast cancer cells that do not normally express this protein. Introduction of GATA3 reprograms cell phenotype from mesenchymal to epithelial. Concomitant with a change in phenotype is a dramatic reprogramming of the transcriptome. As expected, genes integral to the epithelial phenotype are upregulated, genes integral to the mesenchymal phenotype are downregulated. We have used this system to map GATA3 binding sites in the genome and to ask basic science questions about how nucleosome position (relative to the GATA3 binding motif) and local chromatin features influence the ability of GATA3 to bind and productively nucleate new enhancers which activate nearby genes. A conditional GATA3 expression system has enabled us to ask about kinetics of binding, chromatin alterations and gene activation. We are pursuing forward genetic screens using CRISPR and related technologies to catalog genes that are required for GATA3-dependent enhancer formation as well as genes that oppose this process. We also study how cells respond to changes in environment. For these studies, we employ mouse models and vary diet as an experimental variable. We find that mice fed a diet rich in energy, with the majority of calories derived from fat, become obese and their colon epithelial cells undergo moderate reprogramming of the enhancer landscape. We observe that enhancers activated in obese animals versus lean counterparts are enriched for enhancers implicated in cancer progression. As obesity represents a principal disease risk for colorectal cancer development in humans, we interpret this data to suggest that environmental factors, such as diet, can influence disease risk in part through epigenetic alteration in target tissue. Current experiments in the lab are aimed at dissection of specific components of diet, interrogation of the role of the microbiome, and testing of disease risk using animal models of tumor development and/or progression.