ShcA Protects against Epithelial–Mesenchymal Transition through Compartmentalized Inhibition of TGF-β-Induced Smad Activation

Abstract

Epithelial–mesenchymal transition (EMT) is a normal cell differentiation event during development and contributes pathologically to carcinoma and fibrosis progression. EMT often associates with increased transforming growth factor-β (TGF-β) signaling, and TGF-β drives EMT, in part through Smad-mediated reprogramming of gene expression. TGF-β also activates the Erk MAPK pathway through recruitment and Tyr phosphorylation of the adaptor protein ShcA by the activated TGF-β type I receptor. We found that ShcA protects the epithelial integrity of nontransformed cells against EMT by repressing TGF-β-induced, Smad-mediated gene expression. p52ShcA competed with Smad3 for TGF-β receptor binding, and down-regulation of ShcA expression enhanced autocrine TGF-β/Smad signaling and target gene expression, whereas increased p52ShcA expression resulted in decreased Smad3 binding to the TGF-β receptor, decreased Smad3 activation, and increased Erk MAPK and Akt signaling. Furthermore, p52ShcA sequestered TGF-β receptor complexes to caveolin-associated membrane compartments, and reducing ShcA expression enhanced the receptor localization in clathrin-associated membrane compartments that enable Smad activation. Consequently, silencing ShcA expression induced EMT, with increased cell migration, invasion, and dissemination, and increased stem cell generation and mammosphere formation, dependent upon autocrine TGF-β signaling. These findings position ShcA as a determinant of the epithelial phenotype by repressing TGF-β-induced Smad activation through differential partitioning of receptor complexes at the cell surface.

Comprehensive transcriptome analysis of fluid shear stress altered gene expression in renal epithelial cells

“…We also noticed an increase in gene expression of several integrins during shear stress, including integrin α v ( Itgav ) . In addition, there are several connections between TGF‐β and MAPK signaling (Hough et al, ; Kretzschmar et al, ; Lee et al, ; Muthusamy et al, ), thereby modulating the response to shear. Our data show that the shear stress response of a subset of genes is attenuated upon MEK1/2 inhibition, while other genes showed an enhanced response.…”

TGF-β Signaling from Receptors to Smads

“…Dab2 also interacts with TβRI, enhances its clathrin-mediated endocytosis, and inhibits TGF-β-induced JNK (c-Jun amino-terminal kinase) activation (Shapira et al 2014). In contrast, the adaptor protein ShcA (also known as Shc1) can sequester TβRI in caveolin-1-positive compartments and promote Erk and Akt signaling while attenuating Smad3 signaling (Muthusamy et al 2015). These results are consistent with the requirement of lipid raft localization of TGF-β receptors for TGF-β-mediated MAPK activation (Zuo and Chen 2009).…”

Intracellular trafficking of transforming growth factor β receptors

“…The GPIanchored protein CD109, a TGFβ co-receptor and a negative regulator of TGFβ signaling, associates with caveolin-1 and promotes localization of the TGFβ receptors into the caveolar compartment in the presence of ligand [39]. The adaptor protein p52ShcA competes with Smad3 for binding to TβRI and stabilizes the association of the receptor with caveolin-1 [40].…”

“…Silencing of caveolin-1 expression in primary hepatocytes results in repression of TGFβ-induced Akt activation [47]. The adaptor protein p52ShcA facilitates TGFβ-induced Erk MAPK and Akt activation in epithelial cells by stabilizing the association of TβRI with caveolin-1 and promoting caveolar localization of TGFβ receptor complexes [40].…”