Rustgi Lab

Tumor cell progression is illustrated by invasion into the extracellular matrix (ECM) or stroma. This then involves interrelated networks between tumor cells and diverse cell types in the tumor microenvironment. This cross-talk triggers a necessary cascade of events prior to dissemination of tumor cells into blood and lymphatic vessels, as well as local and distant metastasis. These include, but are not restricted to, immune cells/inflammatory cells, fibroblasts, endothelial cells, pericytes, neurons, and adipocytes. We investigate how the p53 tumor suppressor protein modulates

The exocrine pancreas has a remarkable ability to regenerate after injury, as illustrated in acute pancreatitis, and subsets of chronic pancreatitis. Acinar-ductal metaplasia (ADM) is critical in the ability of the exocrine pancreas to regenerate or permit progression to a preneoplastic state (pancreatic intraepithelial neoplasia or PanIN).  In mouse models of pancreatic cancer, induction of either acute or chronic pancreatitis results in tissue-wide ADM that is followed by rapid repair (we designate this as “Adaptive” ADM). However, in the presence of oncogenic Kras, repair is impaired and ADM progresses to PanIN lesions (we designate this as “Oncogenic” ADM). Currently, the mechanisms underlying the formation of ADM and how ADM progresses to PanIN in the presence of mutant Kras remain unknown. Recently, our group performed gene expression analysis of murine ductal cells isolated from the developing pancreas, acute pancreatitis (ADM), and PanIN expressing oncogenic KrasG12D, and compared the expression profiles to that of normal pancreatic ductal cells, resulting in nearly 80 potential genes of interest. Prrx1 (paired-related homeobox 1) was the most differentially regulated transcription factor in all three processes, followed by Etv5, a member of the Ets family of transcriptional factors. We believe that Etv5 and Prrx1 are involved in the initiation and maintenance of ADM, respectively, following pancreatitis. Furthermore, we hypothesize that this regulation allows for subsequent transformation by oncogenic Kras, thereby promoting progression to PanIN. More recently, we have focused on the Fra1 protein as being a master regulator along the continuum from normal pancreas to ADM to PanIN to PDAC.

The intestinal epithelium is in a dynamic equilibrium of proliferation, differentiation and apoptosis along the crypt-villus gradient. Normal intestinal homeostasis is disturbed during states of infection, inflammation and malignant transformation (adenomatous polyps, colorectal cancer). The pathogenesis of sporadic colorectal cancer involves distinct pathways with characteristic genomic and genetic alterations. Despite significant advances in leveraging our understanding of these pathways for diagnostic, prognostic, and therapeutic strategies, colorectal cancer (CRC) remains a leading cause of cancer-related mortality. This underscores a specific need to identify and understand novel, therapeutically tractable pathways in intestinal homeostasis that may drive CRC. Our work has introduced and elucidated the novel role of mRNA binding proteins in intestinal/colonic epithelial homeostasis, as well as aberrations including hyperproliferation, altered metabolism and transformation. LIN28B, an mRNA binding protein, also critical in embryonic stem cells, post- transcriptionally regulates the let-7 microRNA family and results in suppression of differentiation. In turn, Let-7 microRNAs have diverse mRNA targets, including IMP1 (Igf2 mRNA binding protein-1), another mRNA binding protein. We have demonstrated that LIN28B and IMP1 separately drive tumor-initiating cell phenotypes associated with their roles in regulating proliferation and differentiation during normal homeostasis; however, it remains unclear if LIN28B-mediated hyperproliferation, altered differentiation, and associated tumorigenesis requires IMP1. Currently, we are focused on LIN28B contributes to metastasis in the background of APC, KRAS and p53 mutations, using mouse models and 3D organoids.

The esophageal lumen is lined by a stratified squamous epithelium comprised of proliferative basal cells that differentiate while migrating toward the luminal surface and eventually desquamate. Rapid epithelial renewal occurs, but the specific cell of origin that supports this high proliferative demand remains unknown. Herein, we have described a long-lived progenitor cell population in the mouse esophageal epithelium that is characterized by expression of keratin 15 (Krt15). Genetic in vivo lineage tracing revealed that the Krt15 promoter marks a long-lived basal cell population able to self-renew, proliferate, and generate differentiated cells, consistent with a progenitor/stem cell population. Transcriptional profiling demonstrated that Krt15+ basal cells are molecularly distinct from Krt15- basal cells. Depletion of Krt15-derived cells resulted in decreased proliferation, thereby leading to atrophy of the esophageal epithelium. Further, Krt15+ cells were radioresistant and contributed to esophageal epithelial regeneration following radiation-induced injury. These results establish the presence of a long-lived and indispensable Krt15+ progenitor cell population that provides additional perspective on esophageal epithelial biology and the widely prevalent diseases that afflict this epithelium.

Metastatic organotropism, a phenomenon defined by the intrinsic propensity of tumor cells to selectively metastasize to different organs, is poorly understood despite being first described in Stephen Paget’s famous 1889 “seed and soil” hypothesis. Using novel mouse models of pancreatic cancer, we have demonstrated that liver and lung metastatic organotropism is dependent on the E-CADHERIN regulating protein p120 catenin (p120ctn). Complete loss of p120ctn destabilizes membranous E-CAD leading to a preference towards lung metastases. In contrast, heterozygous deletion of p120ctn, a state sufficient for E-CAD-mediated cellular adhesion, allows for both lung and liver metastases. Collectively, these results suggest that cells undergo epithelial-to-mesenchymal transition (EMT) and are thus in a mesenchymal state favor lung metastastasis, while those that are able to undergo the reverse mesenchymal-to-epithelial transition (MET) and thus return to an epithelial state can metastasize to either liver or lung. Our work here is connected to how mutant p53 contributes to metastasis/organotropism in various GI cancers as well as how LIN28B cooperates with other genes in colon cancer induced liver metastasis.