Twist Activation in Breast Cancer Metastasis

Institution: University of California, San Diego
Investigator(s): Jing Yang, Ph.D. -
Award Cycle: 2006 (Cycle 12) Grant #: 12IB-0065 Award: $150,000
Award Type: IDEA
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease



Initial Award Abstract (2006)
Almost all breast cancer deaths are caused by metastatic growths from disseminated tumor cells in distant organs. Metastasis is a multi-step process by which tumor cells spread from a primary site to distant organs and establish secondary tumors. During tumor metastasis, tumor cells need to obtain the ability to break away from their neighbor cells and migrate. Our previous studies showed that tumor cells activate the transcription factor Twist to gain motility, invade and metastasize. Twist can promote a developmental program termed epithelial-mesenchymal transition (EMT) to allow tumor cell dissemination. The role of EMT in tumor metastasis is still highly debated due to clinical observations showing that the majority of human breast carcinoma metastases maintain their epithelial morphology, not switching to mesenchymal phenotype. This discrepancy, we think, is due to the interpretation of EMT as a permanent, non-reversible step during tumor metastasis. We propose a reversible EMT model to describe the dynamic changes that tumor cells experience during tumor metastasis. In this model, breast cancer cells activate Twist and undergo EMT to break away from their neighbors and spread into distant organs. Once reaching those organs, these tumor cells switch off Twist and the EMT program, colonize and grow in distant organs.

We will test whether a transient reversible EMT induced by Twist could promote tumor invasion and metastasis in both mouse mammary tumor models and in human breast cancer cell xenografts in mice. For these studies, we: (1) have established mouse breast cancer models to allow transient activation of the Twist-induced EMT program to test its role in promoting breast tumor metastasis, and (2) will determine how transient activation of the Twist-induced EMT promotes human breast cancer cell metastasis.

Not only does this project address the molecular basis of tumor metastasis, it also has implications for breast cancer prognosis and treatment. Presently, we do not have a reliable means to classify early stage breast cancer patients with respect to potential risk for metastasis. Since activation of Twist and EMT is an early event to allow carcinoma cell dissemination, genes and pathways involved in EMT holds promise to be useful prognostic markers for metastatic disease. Furthermore, the EMT program is mainly activated to induce cellular movement during development, and many such genes are silent in adult tissues. Thus, EMT-specific genes might provide excellent targets for anti-tumor drugs with minimal side effects.


Final Report (2007)
Our research aims to address how breast tumor cells spread from a primary site to distant organs and establish secondary tumors. Our previous studies showed that cancer cells activate a gene named Twist to gain motility, invade, enter the blood circulation, and then metastasize to distant organs. Twist can promote a developmental program termed epithelial-mesenchymal transition (EMT), during which cells lose cell-cell contact and thus can spread as single cells into distant organs. Twist is associated with cell migration in an embryonic developmental setting, so it is logical to investigate this gene as a potential regulator of tumor cell migration and metastasis.

The aim of this project was to address how activation of Twist promotes breast tumor cells to spread to distant organs. Our first approach is to utilize genetically engineered mice that enable us to “turn on” Twist at specific ages and determine the effect on the mammary gland. . We found that Twist expression promotes an EMT-like phenotype in the mouse mammary gland. This alters mammary morphology resulting in fewer ducts and changes in the ductal structure associated with altered cell polarity. We are continuing these studies by generating new mouse strains where Twist can be selectively expressed in only the mammary gland. Secondly, using tumor cell lines (HMLE, human mammary epithelial cells) we demonstrated that Twist induction appears to facilitate metastasis, but continued Twist expression also appears to inhibit proliferation at metastatic sites (e.g., lung and liver).

Our results showed that activation of Twist was sufficient to promote certain human breast cancer cells to reachdistant organs, such as the lung. Further work may establish Twist as an important prognostic marker and a potential drug target for metastatic breast cancers.


Symposium Abstract (2007)
In breast cancer patients, almost all deaths are caused by the spreading and growth of breast tumor lesions in distant organs, including lung, liver, bone and brain. The process by which tumor cells spread from a primary site to distant organs and establish secondary tumors is termed “metastasis.” During tumor metastasis, tumor cells need to obtain the ability to break away from their neighbor cells and migrate. Our previous studies showed that tumor cells activate a gene named Twist to gain motility, invade and metastasize. Twist can promote a developmental program termed epithelial-mesenchymal transition (EMT), during which cells lose cell-to-cell contact and thus can invade as single cells.

However, the role of EMT in tumor metastasis is still highly debated due to the difficulty in capturing single tumor cells that have turned on the EMT program to metastasize in human breast tumors. We propose a reversible EMT model to describe the dynamic changes that tumor cells experience during tumor metastasis. In this model, breast cancer cells activate Twist and undergo EMT to break away from their neighbors and spread into distant organs. Once reaching those organs, these tumor cells “switch off” Twist and the EMT program, colonize and grow in distant organs. To test this hypothesis, we have established an inducible Twist mouse model. In this model, when the mice develop primary breast tumors, we can switch on/off Twist and the EMT program, and test its contribution to breast cancer metastasis. We are in the process of examining the effect of Twist activation on mammary gland structure and breast cancer progression. We believe that these experiments will demonstrate the in vivo roles of Twist and EMT in breast tumor invasion and metastasis.

In early stage breast cancer patients, studies showed that 70-80% of patients receiving chemotherapy would have survived well without it upon removal of their primary tumors. Unfortunately, due to the lack of reliable means to identify metastasis high-risk patients, all patients face the decision on whether the stressful and costly chemotherapy is necessary for them. Since an EMT is likely an early event to allow carcinoma cell spreading, genes in EMT hold promise to be useful prognostic markers for metastatic breast tumors. The signaling pathways controlling EMT are also excellent candidates for cancer therapeutics.