Postdoctoral fellow, UCSD - Moores Cancer Center
Increased stiffness drives breast tumor invasion and metastasis via mechanoregulation of Twist1.
Mechanical forces were recently recognized as potent regulatory signals of cellular behavior in various biological contexts. Matrix stiffness is controlled by deposition and modification of the extracellular matrix. Breast tumors are often detected due to their apparent “hardness” compared to normal tissues, and we and others have previously shown that increasing matrix stiffness correlates with disease progression and poor survival. These observations raise the question of how mechanical forces generated by the microenvironment impact tumor progression and metastasis. Mammary epithelial cells form normal ductal acini with stable adherens junctions and intact basement membrane mimicking normal mammary ducts in the compliant matrix stiffness whereas they present weaker junctions and invade through basement membrane in the rigid stiffness similar to breast tumors. These cell morphological changes in response to increasing mechanical forces resemble the Epithelial-Mesenchymal Transition (EMT) program. Here we show that the transcription factor Twist1 is an essential mechano-mediator that promotes EMT in response to increasing extracellular matrix (ECM) stiffness. High ECM stiffness promotes nuclear translocation of Twist1 by releasing Twist1 from its novel cytoplasmic binding partner G3BP2. We identified the kinase responsible for phosphorylating Twist1 within the G3BP2-binding motif. Inhibition (pharmacological inhibition and shRNA-mediated downregulation) of the identified kinase blocks ECM stiffness-induced EMT and restores the interaction between Twist1 and G3BP2. Loss of G3BP2 in mammary epithelial cells leads to constitutive Twist1 nuclear localization and synergizes with increasing matrix stiffness to induce EMT, local invasion, and metastatic dissemination to the lungs in breast tumor xenografts. In human breast tumors, collagen fiber alignment, a marker of increasing matrix stiffness, and reduced expression of G3BP2 together predict poor survival. In summary, our study identifies a novel mechanotransduction pathway that regulates the subcellular localization of the EMT transcription factor Twist1 to drive EMT and invasion during breast tumor progression. Our ongoing study aims to uncover the upstream sensors and transmitters that convert mechanical signals from the microenvironment to regulate the interaction between Twist1 and G3BP2 in response to increasing ECM stiffness.
Abstract: Matrix stiffness potently regulates cellular behaviour in various biological contexts. In breast tumours, the presence of dense clusters of collagen fibrils indicates increased matrix stiffness and correlates with poor survival. It is unclear how mechanical inputs are transduced into transcriptional outputs to drive tumour progression. Here we report that TWIST1 is an essential mechanomediator that promotes epithelial-mesenchymal transition (EMT) in response to increasing matrix stiffness. High matrix stiffness promotes nuclear translocation of TWIST1 by releasing TWIST1 from its cytoplasmic binding partner G3BP2. Loss of G3BP2 leads to constitutive TWIST1 nuclear localization and synergizes with increasing matrix stiffness to induce EMT and promote tumour invasion and metastasis. In human breast tumours, collagen fibre alignment, a marker of increasing matrix stiffness, and reduced expression of G3BP2 together predict poor survival. Our findings reveal a TWIST1-G3BP2 mechanotransduction pathway that responds to biomechanical signals from the tumour microenvironment to drive EMT, invasion and metastasis.
Pub.: 22 Apr '15, Pinned: 15 Jun '17