EphB Receptors Coordinate Migration and Proliferation in the Intestinal Stem Cell Niche

SummaryMore than 1010 cells are generated every day in the human intestine. Wnt proteins are key regulators of proliferation and are known endogenous mitogens for intestinal progenitor cells. The positioning of cells within the stem cell niche in the intestinal epithelium is controlled by B subclass ephrins through their interaction with EphB receptors. We report that EphB receptors, in addition to directing cell migration, regulate proliferation in the intestine. EphB signaling promotes cell-cycle reentry of progenitor cells and accounts for approximately 50% of the mitogenic activity in the adult mouse small intestine and colon. These data establish EphB receptors as key coordinators of migration and proliferation in the intestinal stem cell niche

Dissociation of EphB2 Signaling Pathways Mediating Progenitor Cell Proliferation and Tumor Suppression

SummarySignaling proteins driving the proliferation of stem and progenitor cells are often encoded by proto-oncogenes. EphB receptors represent a rare exception; they promote cell proliferation in the intestinal epithelium and function as tumor suppressors by controlling cell migration and inhibiting invasive growth. We show that cell migration and proliferation are controlled independently by the receptor EphB2. EphB2 regulated cell positioning is kinase-independent and mediated via phosphatidylinositol 3-kinase, whereas EphB2 tyrosine kinase activity regulates cell proliferation through an Abl-cyclin D1 pathway. Cyclin D1 regulation becomes uncoupled from EphB signaling during the progression from adenoma to colon carcinoma in humans, allowing continued proliferation with invasive growth. The dissociation of EphB2 signaling pathways enables the selective inhibition of the mitogenic effect without affecting the tumor suppressor function and identifies a pharmacological strategy to suppress adenoma growth

No Guts, no Glory : EphB mediated signaling in intestinal stem and progenitor cells

The work presented in this thesis is focused on the intestinal stem cell niche, the crypts, and the Eph tyrosine kinase receptors together with their ligands that are expressed by the crypt epithelial progenitor cells. Two fundamental cellular processes, high turnover coupled to a rapid ordered migration of the newborn cells out from the crypt, characterize the normal intestine. Transformed epithelial cells mirror these processes, gaining an advantage over the untransformed cells by the capacity of going through seemingly endless rounds of division, as well as expanding spatially into surrounding tissues by increased motility. The B class Eph receptors are involved in regulating both proliferation and migration in normal as well as transformed intestinal epithelial cells. In Paper I, we show that EphB receptors, in addition to directing cell migration, regulate proliferation in the intestine. We use both loss and gain of function experiments to correlate the EphB forward signaling to the rate of progenitor cell proliferation. EphB signaling promotes cell cycle reentry of progenitor cells and accounts for up to half the mitogenic activity in the adult intestine. We suggest a model where the restricted Wnt source plays an important role in establishing the EphBephrin- B gradients, hence extending the proliferative domain beyond the region directly influenced by the Wnt proteins themselves. In Paper II we continue to investigate the dual role of EphB receptors. We show that cell migration and proliferation are controlled independently by the EphB2 receptor. EphB2 regulated cell positioning is kinase-independent and mediated via PI3-kinase, whereas EphB2 tyrosine kinase activity regulates cell proliferation through an Abl-cyclin D1 pathway. Cyclin D1 regulation becomes uncoupled from EphB signaling during the progression from adenoma to colon carcinoma, allowing continued proliferation with invasive growth. The dissociation of EphB2 signaling pathways enables the selective inhibition of the mitogenic signaling pathway without affecting the tumor suppressor function of EphB2. In Paper III we investigate the role of the two ligands expressed in the intestinal epithelium, ephrin-B1 and ephrin-B2 and show that, although both ligands can bind EphB2 and EphB3, they have distinct functional outcomes when activating the receptors. Ephrin-B1 selectively affects migration, without influencing proliferation, whereas ephrin-B2 affects proliferation, but not migration

An EphB-Abl signaling pathway is associated with intestinal tumor initiation and growth

EphB receptors regulate the proliferation and positioning of intestinal stem and progenitor cells. In addition, they can act as tumor promoters for adenoma development but suppress progression to invasive carcinoma. We used imatinib to abrogate Abl kinase activity in Apc(Min/+) mice and in mice with LGR5(+) stem cells that were genetically engineered to develop adenomatous polyposis coli. Imatinib treatment inhibited the tumor-promoting effects of EphB signaling without attenuating EphB-mediated tumor suppression, demonstrating a role for EphB signaling in the initiation of intestinal tumors. The imatinib treatment regimen extended the life span of Apc(Min/+) mice and reduced cell proliferation in cultured slices of adenomas from patients with familial adenomatous polyposis. These findings connect the EphB signaling pathway to the regulation of intestinal adenoma initiation via Abl kinase. Our findings may have clinical implications for pharmacological therapy against adenoma formation and cancer progression in patients predisposed to develop colorectal cancer

The Tumor Suppressor Activity of the Transmembrane Protein with Epidermal Growth Factor and Two Follistatin Motifs 2 (TMEFF2) Correlates with Its Ability to Modulate Sarcosine Levels*

The type I transmembrane protein with epidermal growth factor and two follistatin motifs 2 (TMEFF2) is expressed in brain and prostate and overexpressed in prostate cancer, but its role in this disease is unclear. Several studies have suggested that TMEFF2 plays a role in suppressing the growth and invasive potential of human cancer cells, whereas others suggest that the shed portion of TMEFF2, which lacks the cytoplasmic region, has a growth-promoting activity. Here we show that TMEFF2 has a dual mode of action. Ectopic expression of wild-type full-length TMEFF2 inhibits soft agar colony formation, cellular invasion, and migration and increases cellular sensitivity to apoptosis. However, expression of the ectodomain portion of TMEFF2 increases cell proliferation. Using affinity chromatography and mass spectrometry, we identify sarcosine dehydrogenase (SARDH), the enzyme that converts sarcosine to glycine, as a TMEFF2-interacting protein. Co-immunoprecipitation and immunofluorescence analysis confirms the interaction of SARDH with full-length TMEFF2. The ectodomain does not bind to SARDH. Moreover, expression of the full-length TMEFF2 but not the ectodomain results in a decreased level of sarcosine in the cells. These results suggest that the tumor suppressor activity of TMEFF2 requires the cytoplasmic/transmembrane portion of the protein and correlates with its ability to bind to SARDH and to modulate the level of sarcosine