Abstract IA24: Forcing through tumor metastasis: Regulation of epithelial-mesenchymal plasticity by matrix stiffness

Abstract

Abstract In cancer, the presence of dense clusters of collagen fibrils indicates increased matrix stiffness and correlates with poor survival. Previous studies have identified a functional role for matrix stiffness in driving tumor progression, but it is unclear how mechanical inputs are transduced into transcriptional outputs to drive tumor metastasis. To investigate mechanisms of tumor cell mechanotransduction, we utilized a 3D Matrigel culture of murine (Eph4Ras) or human (MCF10A, MCF10DCIS, Bt-549) mammary epithelial cells coupled with a polyacrylamide hydrogel base with calibrated elastic moduli ranging between ~150Pa of normal mammary gland and ~5700Pa of breast tumor tissues. This approach allows for the interrogation of the effects of changes in matrix stiffness independent of other biochemical variables in extracellular matrix (ECM). Using this system, we show that increasing matrix stiffness induced morphological changes resembling the Epithelial-Mesenchymal Transition (EMT) program. Therefore, we hypothesized that increasing matrix stiffness could directly signal through EMT-inducing transcription factors to induce EMT and promote invasion. Using a combination of bioengineering, cell biollogy, proteomic, imaging, and murine tumor modeling approaches, we found that the EMT-inducing transcription factor TWIST1 is an essential mechanomediator that promotes EMT in response to increasing matrix stiffness. Loss of Twist1 prevents matrix stiffness-induced EMT and tumor cell invasion. TGF-beta signaling, a major EMT-inducing biochemical signal, acts synergistically with increasing matrix stiffness, the mechanical cure to induce a complete EMT program in a Twist1-dependent manner. At the compliant matrix stiffness, TWIST1 is sequestered in the cytoplasm by its cytoplasmic binding partner G3BP2, thus preventing TWIST1 from accessing DNA to drive EMT. High matrix stiffness promotes nuclear translocation of TWIST1 by releasing TWIST1 from G3BP2. Loss of G3BP2 leads to constitutive TWIST1 nuclear localization and synergizes with increasing matrix stiffness to induce EMT and invasion in a Twist1-dependent manner. In MCF10DCIS breast tumor xenografts, loss of G3BP2 promotes local invasion and distant metastasis in the lung. In human stage-3 breast tumors, collagen fiber alignment, a marker of increasing matrix stiffness, and reduced expression of G3BP2 together predict poor survival. Together, our findings reveal a TWIST1-G3BP2 mechanotransduction pathway that responds to biomechanical signals from the tumor microenvironment to drive EMT, invasion and metastasis. Citation Format: Jing Yang. Forcing through tumor metastasis: Regulation of epithelial-mesenchymal plasticity by matrix stiffness. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr IA24.