Generation of an inducible colon-specific Cre enzyme mouse line for colon cancer research

Abstract

Current mouse models for colorectal cancer often differ significantly from human colon cancer, being largely restricted to the small intestine. Here, we aim to develop a colon-specific inducible mouse model that can faithfully recapitulate human colon cancer initiation and progression. Carbonic anhydrase I (Car1) is a gene expressed uniquely in colonic epithelial cells. We generated a colon-specific inducible Car1 CreER knock-in (KI) mouse with broad Cre activity in epithelial cells of the proximal colon and cecum. Deletion of the tumor suppressor gene Apc using the Car1 CreER KI caused tumor formation in the cecum but did not yield adenomas in the proximal colon. Mutation of both Apc and Kras yielded microadenomas in both the cecum and the proximal colon, which progressed to macroadenomas with significant morbidity. Aggressive carcinomas with some invasion into lymph nodes developed upon combined induction of oncogenic mutations of Apc, Kras, p53, and Smad4. Importantly, no adenomas were observed in the small intestine. Additionally, we observed tumors from differentiated Car1-expressing cells with Apc/Kras mutations, suggesting that a top-down model of intestinal tumorigenesis can occur with multiple mutations. Our results establish the Car1 CreER KI as a valuable mouse model to study colon-specific tumorigenesis and metastasis as well as cancer-cell-of-origin questions.

TGFβ pathway limits dedifferentiation following WNT and MAPK pathway activation to suppress intestinal tumourigenesis

“… 6 , 30 An excellent study using a carbonic anhydrase Cre recombinase to target colonic enterocytes showed that Apc loss and Kras activation, but not Apc loss alone, can drive tumour growth in differentiated cells and generate ‘top-down’ tumours. 31 Apart from these studies, very little is known about the pathways that confer plasticity in adult intestinal epithelium. Here, we show that loss of the TGF β signalling pathway induces the formation of more aggressive tumours, which are mainly responsible for the significant reduction of the overall survival.…”

WNT Signaling and Colorectal Cancer

“…These transgenic and knock-in alleles including Fabp-Cre [51], Cdx2-Cre [52], Cdx2-CreER [53], CAC [54], and Car1-CreER [55], all enable reproducible, colon-restricted gene inactivation or activation, depending on the genetic context. One recent publication describes the development of the Car1-CreER strain, which outlines an extremely complex model to generate oncogenic mutations in the four most common CRC-associated alterations ( Apc, Kras, Trp53 and Smad4 ) [55]. This is an impressive example of what can be accomplished with traditional genetically engineered mouse models (GEMMs), but also a cautionary tale.…”

DNA Methylation Analysis Validates Organoids as a Viable Model for Studying Human Intestinal Aging

“…The majority of data on stem cells in the mammalian digestive tract are derived from studying the mouse SI; however, a major caveat to using mice to investigate intestinal physiology relevant to human beings is species-specific differences in regional biology. 2 It is imperative that we use reliable in vitro models to study human gut stem cell behavior because human in vivo analyses generally are impractical. Three-dimensional organoids, self-organizing cultures of ISCs, and their progeny have transformed our ability to study human intestinal physiology and stem cell function.…”