The Role of Podosomes in Breast Cancer Metastasis

Institution: The Burnham Institute for Medical Research
Investigator(s): Barbara Blouw, Ph.D. -
Award Cycle: 2006 (Cycle 12) Grant #: 12FB-0076 Award: $134,618
Award Type: Postdoctoral Fellowship
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease



Initial Award Abstract (2006)

One of the mechanisms cancer cells use to invade other tissues is by forming special structures on the cellular membrane called podosomes, which are dynamic, actin-rich adhesion structures in a variety of cell types. Because podosomes are found mainly in motile cells and control the activity of matrix metalloproteases, they are thought to contribute to tissue invasion. My mentorís lab (Dr. Sara Courtneidge) recently identified a key molecule in podosomes, called Tks5, and showed that when the expression of Tks5 is reduced, it will inhibit cellular movement and invasion. Even though it was shown that Tks5 expression correlated with the invasiveness of breast cancer cell lines and tumor biopsies, it is still unclear how Tks5 contributes to breast cancer progression, especially in advanced tumor models.

My first goal is to characterize the primary tumors and lung metastasis of the PyMT mouse for Tks5 expression and test whether Tks5 expression in these tumors correlates with invasiveness and tumor progression. The PyMT mouse model consistently develops mammary tumors with associated lung metastases. I will also test the function of Tks5 in different cell types that are present in the tumor. Next, I will study how deletion of Tks5 in tumor cells and different cell types in the tumor-supporting stroma will affect tumor growth and metastasis. We will use immunohistochemstry to analyze tumor sections (primary and metastasis) of the PyMT mice for Tks5 expression. Next, I will use siRNA technology to reduce Tks5 expression in different cell cultures (epithelial cells, fibroblasts, myeloid cells and endothelial cells) obtained from both primary and lung metastasis of the PyMT mouse. Altered Tks5 levels in cells will be correlated with podosome function using cell invasion assays. In order to study differences between tumor formation and metastasis, I will reduce the expression of Tks5 in carcinoma cell lines derived from the PyMT tumors (primary and lung metastasis) using short hairpin RNA technology and either implant these cells in the fat pad or inject cells in the tail vein of mice. Finally, I will create transgenic mice of the PyMT model in which Tks5 is deleted in specific tissues using the CreLoxP mouse model system.

This research will clarify how Tks5 and podosome formation contributes to tumor progression in breast cancer.




Final Report (2009)

In recent years, improvements in the early detection of breast cancer have greatly reduced the mortality of breast cancer. However, once the primary tumor has metastasized through the body and colonized a distant organ, treatment options are limited. Therefore it is crucial to understand the mechanisms cancer cells use to metastasize, in order to be able to find new targets for the development of novel drugs. Mounting evidence suggest that one of the methods cancer cells use to invade the surrounding tissue is by means of specialized structures called podosomes. These are located on the ventral side of the cellular membrane, are actin rich and are composed of a number of different proteins, including a Src-scaffold protein named Tks5. Tks5 was shown to be essential for podosome formation in various cell lines and its expression in human breast cancer samples correlates with tumor progression. These data led me to hypothesize that Tks5 and podosomes might play a role in breast cancer tumor growth and progression.

To answer this question I used a mouse model of breast cancer. First, I found that Tks5 is also expressed the cancer cells of the tumors and metastasis in the commonly used PyMT mouse model of breast cancer. Tks5 is also expressed in the human breast cancer cell line MDA-231. When inoculated in the fat pad of immunocompromised mice, this cell line will recapitulate human breast cancer tumor progression with metastasis to the lung and lymph nodes. Therefore, I chose to use this cell line to ask whether Tks5 and podosomes are required for primary tumor growth and metastasis. Preliminary data suggests that upon a reduced expression of Tks5 in these cells, primary tumor growth is decreased. These experiments are currently being verified and will be further analyzed for the role of Tks5 and podosomes in metastasis.

Publications:
The Invadopodia Scaffold Protein Tks5 Is Required for the Growth of Human Breast Cancer Cells



A role for the podosome/invadopodia scaffold protein Tks5 in tumor growth in vivo.
Periodical:European Journal of Cell Biology
Index Medicus: Eur J Cell Biol
Authors: Blouw B, Seals DF, Pass I, Diaz B, Courtneidge SA
Yr: 2008 Vol: Nbr: Abs: Pg:Apr 14 (E-Pub)