Deborah C. Rubin, MD

Professor of Medicine

Washington University in St. Louis (WU)

Our laboratory’s major focus is in the study of gastrointestinal epithelial cell biology, specifically in examining molecular mechanisms regulating its proliferation and differentiation. Our two major projects are briefly described:
1. Epithelial-mesenchymal interactions in gut epithelial proliferation and carcinogenesis. Epithelial-mesenchymal interactions are required for normal intestinal morphogenesis and have a critical role in carcinogenesis in epithelial tissues. Epimorphin, a member of the syntaxin family of vesicle docking proteins, is a mesenchymal and myofibroblast protein with an important role in epithelial morphogenesis. To elucidate its biological function we generated epimorphin-/- (epi-/-) mice, which are viable yet manifest a phenotype including increased small bowel length, increased mucosal surface area, increased crypt cell proliferation and increased crypt fission. This phenotype derives, at least in part, from effects on bone morphogenetic protein (Bmp), Wnt-ß-catenin and Hedgehog (Hh) signaling pathways. These data are consistent with our observation that aged Epi-/- mice have a significantly increased incidence of spontaneous small bowel adenomatous polyps, and occasionally develop invasive cancer.
Our observations suggest that the net effect of stromal myofibroblast secretion mediated by epi in the intestine is to act as a “brake” on crypt cell proliferation and crypt fission. Thus, perturbing normal secretion by extinguishing epimorphin expression stimulates crypt cell proliferation and fission. Over time, we predict that this promotes adenomatous polyp formation and malignant transformation.
Our research focuses on determining the mechanisms by which epimorphin deletion leads to enhanced crypt cell proliferation and small intestinal polyp formation. The tumorigenic phenotype of Epi-/- mice is being assessed by determining the temporal, regional and histologic characteristics of the small bowel polyps and carcinomas. Effects of epi deletion on secretion of Bmps and other growth factors, and on Bmp, Hh and wnt-ß-catenin signaling pathways are being examined in the small bowel and colon of Epi-/- mice and in Epi-/- and WT myofibroblasts. In addition, we use using myofibroblast-epithelial co-culture models to examine the effects of epimorphin overexpression and inhibition on Bmp activity. Bmps modulate the wnt-ß-catenin pathway via effects on ß-catenin nuclear localization, and Bmp4 is a downstream target of the Hh signaling pathway. Thus we are determining how epimorphin overexpression and inhibition regulates these pathways, using in vitro model systems.
2. Molecular regulation of the proliferative and functional adaptive response of the small intestinal epithelium following loss of functional small bowel surface area. Following loss of functional small bowel surface area resulting from surgical resection or from ischemia, trauma, radiation or diseases such as Crohn’s disease, the remnant intestine undergoes a robust adaptive response. This is characterized by enhanced crypt cell proliferation, resulting in increased villus height, crypt depth and enterocyte migration as well as enhanced nutrient absorption. Our laboratory has been interested in determining the molecular regulation of this response, particularly focusing on mechanisms underlying enhanced epithelial function and crypt cell proliferation and apoptosis.
Recently we have elucidated the role of an immediate early gene, TIS7, in the gut during adaptation following resection. TIS7 is markedly upregulated during the early adaptive response. Transgenic mice that overexpress TIS7 in the small intestine have increased adiposity but lower growth rates compared to their normal littermates, and an enhanced rate of intestinal lipid absorption. In contrast, TIS7 null mice are protected from weight gain on a high fat diet. Studies presently focus on determining the mechanisms underlying the adiposity and alterations in fat absorption. We are also pursuing an extensive evaluation of gene expression regulation following resection, using Agilent chips for global gene profiling.