A role for Id in the regulation of TGF-β-induced epithelial–mesenchymal transdifferentiation

Abstract

Epithelial-mesenchymal transdifferentiation (EMT) is a critical morphogenic event that occurs during embryonic development and during the progression of various epithelial tumors. EMT can be induced by transforming growth factor (TGF)-b in mouse NMuMG mammary epithelial cells. Here, we demonstrate a central role of helix-loop-helix factors, E2A and inhibitor of differentiation (Id) proteins, in TGF-b-induced EMT. Epithelial cells ectopically expressing E2A adopt a fibroblastic phenotype and acquire migratory/invasive properties, concomitant with the suppression of E-cadherin expression. Id proteins interacted with E2A proteins and antagonized E2A-dependent suppression of the E-cadherin promoter. Levels of Id proteins were dramatically decreased by TGF-b. Moreover, NMuMG cells overexpressed Id2 showed partial resistance to TGF-b-induced EMT. Id proteins thus inhibit the action of E2A proteins on the expression of E-cadherin, but after TGF-b stimulation, E2A proteins are present in molar excess of the Id proteins, thus over-riding their inhibitory function and leading to EMT.

Differential Regulation of Epithelial and Mesenchymal Markers by δEF1 Proteins in Epithelial–Mesenchymal Transition Induced by TGF-β

“…TGF-␤ has been reported to induce EMT in NMuMG cells (Miettinen et al, 1994;Piek et al, 1999;Kondo et al, 2004). As previously reported, treatment with TGF-␤ dramatically altered the morphological phenotypes of NMuMG cells from cobblestone-like to spindle shapes ( Figure 1A).…”

“…Expression of Twist could not be detected, whereas that of E12/E47 was not altered after TGF-␤ treatment (data not shown and Kondo et al, 2004). Expression of mRNA for Id2, a negative regulator of TGF-␤-induced EMT (Kondo et al, 2004;Kowanetz et al, 2004), decreased rapidly by 4 h after treatment with TGF-␤ ( Figure 1D). These findings demonstrated that, among these factors, increases in SIP1 and ␦EF1 by TGF-␤ appear to strongly correlate with the reduction in E-cadherin in NMuMG cells.…”

“…Mouse E-cadherin promoters with point mutations in E-boxes (termed E1, E2, E3, E21, E13, E23, and E213) were constructed using PCR-based mutagenesis on the mouse E-cadherin promoter (Ϫ178 to ϩ 92 base pairs) in pGL2 (Kondo et al, 2004). Human ␦EF1 promoter (Ϫ1107 to ϩ 55 base pairs from the translation start site) was cloned using PCR from genomic DNA of human keratinocyte HaCaT cells isolated by DNeasy (QIAGEN, Chatsworth, CA).…”

“…Through constitutive association with bHLH E12/E47 proteins, Id proteins maintain epithelial phenotypes by repressing the function of E12/E47, which acts as a repressor of E-cadherin. Down-regulation of Id2 by TGF-␤ thus relieves this inhibition, permitting conversion of epithelial cells to cells with mesenchymal phenotypes (Kondo et al, 2004;Kowanetz et al, 2004).In the present study, we investigated the regulatory mechanisms by which TGF-␤ elicits EMT in NMuMG cells. We show that the ␦EF1 family proteins, SIP1 and ␦EF1, are required for TGF-␤-induced E-cadherin repression, but not for the expression of mesenchymal markers.…”

Transcriptional regulation of cell polarity in EMT and cancer

“…Although still preliminary, the evidence available suggests that components of the PAR polarity complex are not direct targets of EMT transcriptional regulators, but rather they can be modulated in response to different oncogenes, tumour suppressors or EMT regulatory signals (reviewed by Lee and Vasioukhin, 2008). TGF-b is one of the more robust cues inducing EMT in different model systems (reviewed by Zavadil and Bottinger, 2005), leading to the upregulation of several EMT inducers, including SNAI1/SNAI2, ZEB1, Twist and the Id factors through Smad-dependent and Smad-independent pathways (Peinado et al, 2003;Kondo et al, 2004;Thuault et al, 2006;Moustakas and Heldin, 2007). Recent insights into the regulation of cell polarity by TGF-b during EMT have converged on the PAR complex.…”