The Role of Twist1 in Epithelial-mesenchymal Transition

Institution: University of California, San Diego
Investigator(s): Jeff Tsai, Ph.D. -
Award Cycle: 2010 (Cycle 16) Grant #: 16FB-0009 Award: $90,000
Award Type: Postdoctoral Fellowship
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease

Initial Award Abstract (2010)

Metastasis is a multi-step process that requires epithelial tumor cells to invade through surrounding extracellular matrix, migrate to distant sites, and form a secondary tumor. Tumor cells have been shown to activate a cellular program called Epithelial-Mesenchymal Transition (EMT) to break away from neighboring cells and migrate to distant tissues. EMT is characterized by epithelial cells losing polarity and adhesion, and gaining a more migratory morphology. Studies from our lab demonstrated that Twist1, a transcription factor that induces EMT during development, is essential for the ability of breast tumor cells to metastasize from the mammary gland to the lung in mice. These results suggest that carcinoma cells activate the EMT program to gain motility, invade, and metastasize.

Despite evidence supporting the role of EMT in tumor metastasis, this process remains controversial due to the limited observation of human carcinoma transitioning from an epithelial to mesenchymal morphology in clinical samples. One model explaining this observation hypothesizes that primary epithelial tumors undergo EMT to disseminate to distant sites; afterwards they undergo a reverse process, called Mesenchymal-Epithelial Transition (MET), to establish secondary tumors in distant organs. However, the role of this reversible EMT process in tumor metastasis in vivo has not been demonstrated.

To better understand how Twist1 regulates the EMT/MET process during breast tumor progression, we plan the following studies:
1) Establish a 3-dimensional mammary “organoid culture system” to visualize and study EMT.
2) Determine the mechanism for Twist1-induced EMT in 3D mammary organoids.
3) Determine the role of Twist1 on EMT and metastasis during breast tumor progression.

Using the organoid culture system, we can study how Twist1 influences cell polarity and basement membrane integrity, both important processes during tumor progression. For our breast tumor studies, we will use a mouse breast tumor model that mimics human breast tumors with Her2 amplification, an ideal model to study the role of Twist1 and EMT on tumor metastasis. Understanding the regulation of the EMT/MET process in animal models is critical for discerning how tumor cells spread to distant sites in human disease pathogenesis. This project will develop and use novel preclinical models to better dissect the EMT program to identify biomarkers as potential targets for therapy.

Final Report (2012)

Formation of metastatic tumors is the hallmark of late stage breast cancer and is commonly associated with poor survival rates. Despite the importance of this, little is known about how tumor cells spread throughout the body. I hypothesize that tumor cells can undergo a process called epithelial-to-mesenchymal transition (EMT) to travel from one site to another. EMT is characterized by epithelial cells, which are tightly clustered and relatively immobile, undergoing cellular changes to become more like mesenchymal cells, which are scattered and highly motile. This can occur through the regulation of Twist1, a gene that has been shown to regulate EMT during development and cancer.

Previous studies have implicated a role for Twist1 in breast cancer metastasis. However, there is a lack of relevant models to study Twist1 activation and EMT in mammals and provide convincing evidence for how Twist1 regulates EMT during tumor progression. In order to study how Twist1 regulates EMT during cancer progression in mammals, our lab generated mice in which we can turn on and off Twist1 (inducible Twist1 mice). Using these mice, I have established a convenient and effective system to analyze the effect of Twist1 and other EMT factors on mammary epithelial cells. This system will allow us to better dissect the pathways involved in EMT and possibly design inhibitors of these pathways to control the EMT process in animals. In addition, one of the major findings using these inducible Twist1 mice is that the duration and location of Twist1 expression strongly affects the ability of tumor cells to metastasize. Specifically, Twist1 expression at the primary tumor site induces EMT to promote tumor cells to invade the local surrounding tissue and enter into the blood vessel. Once the tumor cells reach a distant site and exit the blood vessel, tumor cells lose Twist1 expression, reverse EMT, and grow into a secondary tumor. This reversal of EMT is essential for tumor cells to effectively establish metastatic tumors.

As a follow up to these studies, I hope to better understand how EMT is regulated in animals. Specifically, I plan on using the mammary 3D culture system to identify downstream targets of Twist1 and determine whether inhibition of these targets will prevent EMT. I hope these studies will provide important insights as to how tumors are able to spread to distant locations. And understanding this may lead to generation of novel treatments to prevent tumor metastasis.

Spatiotemporal Regulation of Epithelial-Mesenchymal Transition Is Essential for Squamous Cell Carcinoma Metastasis
Periodical:Cancer Cell
Index Medicus:
Authors: Tsai JH, Donaher JL, Murphy DA, Chau S, Yang J.
Yr: 2012 Vol: 22 Nbr: 6 Abs: Pg:725-736