Disabled-2 (Dab2) Is Required for Transforming Growth Factor β-induced Epithelial to Mesenchymal Transition (EMT)

Abstract

Transforming growth factor ␤ (TGF␤) induces an epithelial to mesenchymal transition (EMT) during both physiological and pathological processes; however, the mechanism underlying this transition is not fully eluci- Epithelial to mesenchymal transition (EMT)1 is a fundamental multistep process that occurs during both physiological and pathological states (1, 2). By allowing cells to detach from the epithelial tissue where they originate and to migrate, such transitions are necessary for proper embryonic development. However, they also provide a way for epithelium-derived tumors from a benign stage to become invasive and metastasize throughout the body. It has been demonstrated that there is commonality in the signaling pathways regulating EMT during both embryonic development and tumor progression, suggesting that similar molecular mechanisms underlie these processes and raising the possibility that tumor metastasis might simply be considered as a reactivation of some aspects of the embryonic program of EMT.The process of EMT requires loss of cell-cell interaction and acquisition of fibroblastic morphology with increased expression of mesenchymal markers, such as N-cadherin (3). Among growth factors that can promote this structural conversion, transforming growth factor ␤ (TGF␤) has been well characterized as an important inducer of EMT during development as well as during cancerogenesis (4). Indeed, although TGF␤ is considered a tumor suppressor during the first stage of tumorigenesis, principally through its ability to cause growth arrest and apoptosis in many non-transformed epithelial cell types, numerous reports show that TGF␤ can also promote tumor progression, particularly through its ability to promote EMT (4, 5). Moreover, it has been shown that blocking TGF␤ signaling in transgenic mice that develop multifocal metastatic mammary tumors reduces mammary tumor intravasation and lung metastasis and increases mammary tumor cell apoptosis (6).TGF␤ exerts its biological effects by inducing the formation of a heteromeric complex composed of type I and type II serine/ threonine kinases receptors. The activated receptor complex, in turn, phosphorylates and activates the receptor-regulated

The inhibitory effects of Disabled-2 (Dab2) on Wnt signaling are mediated through Axin

“…We next examined whether the effects of Dab2 on Axin expression and on b-catenin signaling were specific to F9 cells. We previously demonstrated in a TGFbinduced epithelial to mesenchymal transdifferentiation model in mouse mammary epithelial cells (NMuMG) that Dab2 expression is induced and required for transdifferentiation (Prunier and Howe, 2005). As previously demonstrated, TGFb induces Dab2 expression levels in these cells following a 24-h treatment (Figure 6a, a-Dab2 panel).…”

“…RA-induced Dab2 and Sparc levels were unaffected by Wnt treatment and in siDab2/F9 cells, Dab2 and Sparc are not induced and Wnt treatment has no effect. The differentiation marker GATA-4 is not induced in Dab2-ablated cells (Prunier and Howe, 2005) and by cDNA array analysis villin and collagen type IV are also not induced (data not shown).…”

“…Since Dab2 expression in these cells is induced during differentiation (Smith et al, 2001;Prunier and Howe, 2005) and Dab2 is a negative regulator of Wnt signaling (Hocevar et al, 2003), we used this model to examine the role of Dab2 in Wnt-mediated signaling. Figure 1a demonstrates that RA (100 nM) significantly increases Dab2, with a concomitant increase in the expression of the visceral endoderm marker GATA binding protein 4 (GATA-4) (Smith et al, 2001).…”

“…We next investigated whether F9 cells displayed differentiation state-dependent responsiveness to Wnt and whether Dab2 played any regulatory role in the transitional response of these cells to Wnt. We took advantage of an F9 cell line, which we have established in which Dab2 expression is ablated by stable expression of small interfering RNA (si-RNA) (siDab2/F9 cells) (Prunier and Howe, 2005). As shown in Figures 1b and c, Wnt stimulation for either short term (0-3 h) or long term (0-72 h) has no effect either on Dab2 or on the differentiation marker Sparc (Wiles, 1988).…”

Cell and molecular regulation of the mouse blastocyst

“…Cells labeled with PE markers are found scattered in the middle of the ICM (Yang et al, 2002). Dab2 is a PTB domain containing adaptor protein that modulates cellular adhesiveness during megakaryocytic differentiation of the human chronic myeloid leukemic cell line K562 (Tseng et al, 2003) and transiently interacts with Integrin ␤1 to regulate its activation during induced epithelial to mesenchymal transition in normal murine mammary gland cells (Prunier and Howe, 2005). Moreover, mutation of LamC1 and Integrin␤1, genes known to modulate cell adhesiveness, causes similar phenotypes (Stephens et al, 1995;Smyth et al, 1999).…”