The Regulation of SATB1 in Metastatic Breast Cancer

Institution: Lawrence Berkeley National Laboratory
Investigator(s): Laurie Friesenhahn, Ph.D. -
Award Cycle: 2009 (Cycle 15) Grant #: 15FB-0097 Award: $36,379
Award Type: Postdoctoral Fellowship
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease



Initial Award Abstract (2009)

Metastasis occurs when tumor cells travel to distal organs and create new tumors in the body. There is strong evidence to suggest that a protein in the cell, SATB1 (Special AT Sequence Binding Protein 1), regulates the tumor-initiating and metastatic potential of breast cancer cells. Adding this protein (SATB1) to non-aggressive breast cancer cell lines causes these cells to now have the ability to form tumors and metastasize. Depleting this protein from highly aggressive breast cancer cell lines reduces the metastatic potential and tumor-initiating ability of these cells. Additionally, the presence of SATB1 in primary breast tumors is strongly associated with an aggressive cancer phenotype and a poor prognosis, independent of the lymph-node status. Tumors are comprised of many different types of cells, and only a small percentage of these cells (i.e., cancer stem cells) have the ability to initiate new tumors and metastasize. Not every cancer cell in a primary tumor has the SATB1 protein, but these experiments provide evidence to support the hypothesis that cells with SATB1 are an aggressive, metastatic, sub-population of tumor-initiating cells.

There are three aims for this project: (1) screen for cytokines, chemokines, and growth factors that are involved in the activation and expression of SATB1 in metastatic breast cancer, (2) screen for transcription factors and signaling pathways that are involved in the activation and expression of SATB1 in metastatic breast cancer, and (3) study the relationship between SATB1 expression and progenitor breast cancer cells. A main approach will be non-biased, genome-wide RNAi screening to discover candidate genes that activate or maintain SATB1 expression in cancer cells. To define the relationship between SATB1 expression and cancer stem cells, I will use FACS analysis to characterize SATB1-expressing cells relative to cancer stem cell markers and employ mice models of breast cancer to determine the metastatic potential of different stem cell-containing populations.

These experiments will establish whether SATB1 expression is necessary and sufficient to convert a non-aggressive breast cancer cell to a metastatic cancer stem cell. If we can learn what molecules and pathways are important for the generation and/or persistence of cancer stem cells, we can effectively target these processes and develop more effective cancer therapies. This research is necessary to learn whether SATB1 will be an effective therapeutic target.




Final Report (2010)

Metastasis is a hallmark of malignant cancer, and it greatly decreases a cancer patient's chances for survival. Metastasis occurs when tumor cells travel to distal organs and create new tumors in the body. Recent research reports suggest that a protein called SATB1 (Special AT Sequence Binding Protein 1) promotes breast cancer metastasis and growth. Adding this protein (SATB1) to non-aggressive breast cancer cell lines causes these cells to now have the ability to form tumors and metastasize. Depleting this protein from highly aggressive breast cancer cell lines reduces the metastatic potential and tumor-initiating ability of these cells. The presence of SATB1 in primary breast tumors is strongly associated with an aggressive cancer phenotype and poor prognosis, independent of the lymph-node status. Tumors are comprised of many different types of cells, and only a small percentage of these cells have the ability to initiate new tumors and metastasize. Not every cancer cell in a primary tumor has the SATB1 protein, but these experiments provide evidence to support the hypothesis that cells with SATB1 are an aggressive, metastatic sub-population of tumor-initiating cells.

New experiments show that cells expressing SATB1 are resistant to the chemotherapy drug, Fluorouracil. SATB1 was transduced into a breast cancer cell line called SKBR3 cells, and single cell clones were isolated. Five of these clones and the parental cell line not expressing SATB1 were treated with different concentrations of Fluorouracil. All the single cell clones transduced with SATB1 expressing SATB1 showed a significant increase in viability compared to the parent cell line with no SATB1 expression. This significant finding supports the hypothesis that cells expressing SATB1 represent a population of cells in the tumor that pose a great risk of relapse to the cancer patient. Current therapies may focus on targeting and eliminating the bulk of the tumor mass, but, if therapies are not effective in eliminating this small population of tumor-initiating cells, these cells will re-grow the tumor and metastasize after therapy has ended.

We will continue to investigate the link between SATB1 expressing cells and chemo-resistance. This will be done with different chemotherapy drugs and different breast cancer cell lines. Additionally, experiments that investigate how cells initiate and sustain SATB1 expression in cells will also be done. If we can discover the mechanism of how SATB1 is activated in breast cancer, more effective therapies can be developed to target the expression of SATB1.




Symposium Abstract (2010)

Ellen Ordinario*, Hye-Jung Han*, Laurie B. Friesenhahn, Francis Rodier, Judith Campisi, Debopriya Das, Joe W. Gray, Y oshinori Kohwi and Terumi Kohwi-Shigematsu

Life Sciences Division, Lawrence Berkeley National Laboratory, University of California,

SATB1 acts as a genome organizer by tethering a large number of genomic loci onto the SATB1 regulatory network via specialized DNA sequences called base unpairing regions (BURs). Genes that are bound to SATB1 are assembled with chromatin-remodeling enzymes and transcription factors which SATB1 recruits. We have previously shown that SATB1 has critical roles in promoting both tumor growth and metastasis of breast tumors by reprogramming the chromatin organization and transcription profiles of breast cancer cells. This was determined by examining the effects of SATB1 knockdown or ectopic expression in human breast cancer cell lines (MDA-MB-231, Hs578T, BT549, and SKBR3) in nude mice. We have followed up on our studies by examining the effects of SATB1 expression in non-tumorigenic, immortalized MCF10A cells. We found that at least in one MCF10A cell line, SATB1 expression promoted the epithelial-mesenchymal transition in vitro. These SATB1-expressing MCF10A cells also promoted tumor growth and metastasis in nude mice, indicating an oncogenic activity of SATB1. SATB1 expression does not promote tumorigenesis in all MCF10A cell lines, however. This indicates that the oncogenic activity of SATB1 requires certain conditions to be met in MCF10A cells. Although comparative genomic hybridization array patterns did not show any major changes between these cell lines, we found that, in those MCF10A cells that have a potential to form tumors in mice when SATB1 is expressed, the G2 checkpoint fails. We also show data on the drug resistance of breast cancer cells when SATB1 is expressed. These data are consistent with our previous observation that SATB1 does have an important function in promoting breast cancer progression.