Related Experiment Video
Updated: Nov 12, 2025

Comparing the Affinity of GTPase-binding Proteins using Competition Assays
Published on: October 8, 2015
TGF-β-induced cell motility requires downregulation of ARHGAPs to sustain Rac1 activity
Mitsuyoshi Motizuki1, Daizo Koinuma2, Takashi Yokoyama1
1Department of Biochemistry, Graduate School of Medicine, University of Yamanashi, Yamanashi, Japan.
Abstract:
Transforming growth factor-β (TGF-β) signaling promotes cancer progression. In particular, the epithelial-mesenchymal transition (EMT) induced by TGF-β is considered crucial to the malignant phenotype of cancer cells. Here, we report that the EMT-associated cellular responses induced by TGF-β are mediated by distinct signaling pathways that diverge at Smad3. By expressing chimeric Smad1/Smad3 proteins in SMAD3 knockout A549 cells, we found that the β4 region in the Smad3 MH1 domain is essential for TGF-β-induced cell motility, but is not essential for other EMT-associated responses including epithelial marker downregulation. TGF-β was previously reported to enhance cell motility by activating Rac1 via phosphoinositide 3-kinase. Intriguingly, TGF-β-dependent signaling mediated by Smad3's β4 region causes the downregulation of multiple mRNAs that encode GTPase activating proteins that target Rac1 (ARHGAPs), thereby attenuating Rac1 inactivation. Therefore, two independent pathways downstream of TGF-β type I receptor contribute cooperatively to sustained Rac1 activation, thereby leading to enhanced cell motility.
Related Concept Videos
Small GTPases - Ras and Rho
Three regulatory proteins control their activity:
Cell Polarization by Rho Proteins
Mechanism of Lamellipodia Formation
TGF - β Signaling Pathway
Intracellular Signaling Affects Focal Adhesions
Some...
Rab Cascades

