The Receptor Tyrosine Kinase EPHB4 Has Tumor Suppressor Activities in Intestinal Tumorigenesis

Abstract

Colorectal cancer is the second cause of cancer-related death in the western world, and although the genetic and molecular mechanisms involved in the initiation and progression of these tumors are among the best characterized, there are significant gaps in our understanding of this disease. The role of EPHB signaling in colorectal cancer has only recently been realized. Here, we use animal models to investigate the role of EphB4 in intestinal tumorigenesis. Modulation of EPHB4 levels in colon cancer cell lines resulted in significant differences in tumor growth in a xenograft model, with low levels of EPHB4 associated with faster growth. In addition, using a genetic model of intestinal tumorigenesis where adenomatous polyposis coli (Apc) mutations lead to initiation of the tumorigenic process (Apc min mice), we show that inactivation of a single allele of EphB4 results in higher proliferation in both the normal epithelium and intestinal tumors, significantly larger tumors in the small intestine, and a 10-fold increase in the number of tumors in the large intestine. This was associated with a 25% reduction in the lifespan of Apc min mice (P < 0.0001). Gene expression analysis showed that EphB4 mutations result in a profound transcriptional reprogramming, affecting genes involved in cell proliferation, remodeling of the extracellular matrix, and cell attachment to the basement membrane among other functional groups of genes. Importantly, in agreement with the expression profiling experiments, using an in vitro assay, we show that loss of EPHB4 in colon cancer cells results in a significantly increased potential to invade through a complex extracellular matrix. Collectively, these results indicate that EphB4 has tumor suppressor activities and that regulation of cell proliferation, extracellular matrix remodeling, and invasive potential are important mechanisms of tumor suppression. [Cancer Res 2009;69(18):7430-8]

Eph/ephrin molecules—a hub for signaling and endocytosis

“…Later in colorectal cancer progression, the expression of receptors like EphB2 and EphB4 is lost despite constitutive b-catenin activation (Batlle et al 2005). Lack of EphB3 or EphB4 or overexpression of a dominant-negative EphB2 receptor in Apc Min mice causes accelerated colorectal tumorigenesis and the formation of aggressive adenocarcinomas, which suggests that EphBs act as tumor suppressors (Batlle et al 2005;Dopeso et al 2009). Remarkably, distinct EphB2 downstream signaling activities control cell positioning and cell cycle regulation in the intestine (Genander et al 2009).…”

Eph-dependent cell-cell adhesion and segregation in development and cancer

“…Thus, in contrast to roles of EphA2 in tumour promotion, EphA2 knock-out mice show increased susceptibility to carcinogen-induced skin tumours and their invasive malignant progression [181]. Similarly, EphB4 can elicit promotion or suppression of tumour growth [164,176,[182][183][184]: while it is found up-regulated in colon and endometrial cancers [185,186], its loss is correlated with more invasive cancers of both colon [182] and breast [187]. One possible explanation for this dichotomy is that an initial increase in Eph receptor expression and function is followed by epigenetic silencing or modulation of function as the tumour progresses [6].…”

“…Mechanistically, EphB signalling may suppress cancer progression at this stage by regulating adherens junction formation and promoting compartmentalisation of colon carcinoma cells [197], although in parallel contributing to adenoma growth via Abl-cyclin D1 proliferative signalling [198]. Loss of EphB receptor expression or activity during CRC progression leads to uncoupling of EphB function from cyclin D1 signalling and results in increased tumour invasion while maintaining a high proliferation rate [182,183,197,198]. Recent evidence now also suggests that EphB2 marks tumour-initiating intestinal stem cells in aggressive CRCs potentially contributing to disease relapse [199].…”

Preponderance of cells with stem cell characteristics in metastasising mouse mammary tumours induced by deregulated EphB4 and ephrin-B2 expression

“…Despite these observations, the role(s) of EphB4 and ephrin-B2 in carcinogenesis are still unclear. Whereas EphB4 has been described as a survival factor in breast cancer (32), head and neck squamous carcinoma (33) and colorectal cancer (34,35), others have presented evidence that EphB4 can serve as a tumour suppressor in breast (30) and colorectal cancer (36).…”