Understanding the Role of GATA3 in Breast Cancer

Institution: University of California, San Francisco
Investigator(s): Jonathan Chou, B.S. -
Award Cycle: 2009 (Cycle 15) Grant #: 15GB-0012 Award: $38,000
Award Type: Dissertation Award
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease



Initial Award Abstract (2009)

Despite recent advances in our understanding of the mechanisms underlying the initiation and progression of breast cancer, patients who develop metastatic disease have poor prognoses. The focus of this project is to understand how GATA3, a transcription factor that is lost in breast cancer progression, functions at the molecular and cellular level. Decreased expression of GATA3 has been associated as a strong negative prognostic indicator. The Werb lab at UCSF has shown that in the normal mouse mammary gland, GATA3 maintains luminal epithelial cell differentiation, and deletion of GATA3 results in proliferation and detachment of the luminal epithelial cells from the basement membrane. In the pathologic situation, breast tumors may suppress GATA3 to promote proliferation and metastasis, but the molecular effects of losing GATA3 are not well understood. One possibility is that GATA3 regulates the expression of microRNAs (miRNAs), which are small, non-coding RNAs that serve to modulate gene expression by either inhibiting translation or causing degradation of the target mRNAs. Indeed, abnormal expression of miRNAs has been implicated in cancer biology as a general mechanism underlying many tumor-specific processes.

In this dissertation project, the aims are to identify the miRNA targets controlled by GATA3 and determine the relationship of GATA3 and miRNA expression in tumor samples from mice and humans. These experiments are designed to determine whether expression of these miRNAs in GATA3-negative tumor cells is sufficient to prevent tumor spread. We plan to use a bioinformatics approach (i.e., the application of information technology to the field of molecular biology) to identify the mRNA targets of these miRNAs and validate these targets using in vitro assays. Our methods include PCR-based microRNA arrays to identify differentially expressed miRNA targets controlled by GATA3 and in mouse models of breast cancer. Next, actual tumor samples from both mice and humans will also be analyzed by immunohistochemistry and in situ hybridization to understand the relationship between GATA3 and miRNAs. Finally, we plan to conduct studies in mice using “knockdown” and over-expression approaches. Metastasis will be monitored in real-time by bioluminescent whole-animal imaging, and also by recovering and analyzing the tumors from mice at selected time points.

The underlying rationale for this project is the general appreciation that breast cancer cells may “hijack” normal, developmental regulatory pathways to promote proliferation and metastasis. Because loss of GATA3 correlates strongly with poor prognosis in humans, understanding the mechanisms by which GATA3 controls biological processes is critical to our understanding of breast cancer. In addition, because miRNAs also have the potential to be translated into therapeutics, investigating the link between GATA3 and miRNAs may provide valuable insight into both the basic biology underlying breast cancer and offer novel therapeutic strategies.




Final Report (2010)

Note: the PI resigned the CBCRP grant after one year to accept another fellowship.

Despite recent advances in our understanding of breast cancer, patients who do not respond to treatment or who develop metastatic disease have poor prognoses. Mortality from breast cancer is often secondary to metastasis, a process by which cells from the primary tumor spread to distant sites such as the lung, brain, and bone. This multi-stage process includes recruitment of new blood vessels, entry and exit from the circulatory system, and survival at a distant site to form a tumor. The molecular basis of metastasis, however, is largely unknown. Thus, the focus of my project is to investigate the molecular and cellular events that lead to metastasis and identify mechanisms that may suppress this deadly process.

We have previously shown that GATA3 is a master regulatory transcription factor that specifies mammary cell differentiation. This gene is important for maintaining epithelial cell fate, and is lost during breast cancer progression. Interestingly, re-expression of GATA3 in mouse mammary tumor cells suppresses metastasis to the lung in a mouse model of breast cancer. To understand how GATA3 prevents metastasis, we have conducted a microRNA (miRNA) screen to identify downstream GATA3-regulated miRNAs (Specific Aim 1). miRNAs modulate global gene expression post-transcriptionally, and have recently been shown to be important during tumor development and metastasis. Our results indicate that GATA3 induces the expression of miR29b, a miRNA that has recently been shown to be a tumor suppressor. We show that miR29 family members regulate key factors involved in blood vessel recruitment and permeability, including vascular endothelial growth factor (VEGF) (Specific Aim 3). In addition, we show that miR29b is lost during tumor progression in a mouse model of breast cancer, concomitant with the loss of GATA3. Preliminary studies suggest that restoration of miR29b in breast tumor cells also prevents lung metastasis in vivo (Specific Aim 2).

Future studies are being conducted to test whether miR29b targets are important regulators of tumor metastasis, and whether miR29b expression promotes mammary cell differentiation. These findings reveal a novel mechanism by which miRNAs regulate metastasis, and may help add to arsenal of agents currently used to treat breast cancer.




Symposium Abstract (2010)

Despite recent advances in our understanding of breast cancer, patients who develop metastatic disease often have poor prognoses. Mortality from breast cancer is often due to metastasis, a process by which malignant cells from the primary tumor spread to distant sites such as the lung, brain, and bone. To do so, tumor cells must first enter the circulatory system by recruiting new blood vessels (known as angiogenesis), exit from the circulatory system, and survive at a distant site to form a secondary tumor. Although this emphasizes the key role that angiogenesis plays in promoting metastasis, the molecular basis of this process is largely unknown. Thus, the focus of my project is to investigate the molecular and cellular events that lead to metastasis and identify mechanisms that may suppress this deadly process. We have previously shown that GATA3 is a master regulatory transcription factor that specifies mammary luminal cell fate, and is lost during breast cancer progression. Interestingly, re-expression of GATA3 in tumor cells transplanted orthotopically suppresses metastasis to the lung in vivo.

To understand how GATA3 prevents metastasis, we have conducted a screen to identify microRNAs (miRNAs) regulated by GATA3. miRNAs modulate global gene expression post-transcriptionally, and have recently been implicated to be important during tumor development and metastasis. Our results indicate that GATA3 induces the expression of microRNAs, including miR29b, that regulate genes involved in blood vessel recruitment and permeability, including vascular endothelial growth factor (VEGF). When cultured in low oxygen conditions, cells expressing these miRNAs suppress the induction of VEGF. In addition, we found that miR29b is lost during mammary tumor progression, concomitant with the loss of GATA3. Current studies are being conducted to determine if miRNA restoration in breast tumor cells may also prevent metastasis in vivo.

These findings suggest a novel mechanism by which miRNAs regulate angiogenesis, and may serve as a basis to develop new anti-angiogenic agents to treat breast cancer.



GATA3 in development and cancer differentiation: cells GATA have it!
Periodical:Journal of Cellular Physiology
Index Medicus: J Cell Physiol
Authors: Chou J, Provot S, Werb Z
Yr: 2010 Vol: 222 Nbr: 1 Abs: Pg:42-9