Global Gene Regulation by SATB1 in Metastatic Breast Cancer

Institution: Lawrence Berkeley National Laboratory
Investigator(s): Terumi Kohwi-Shigematsu, Ph.D. -
Award Cycle: 2002 (Cycle VIII) Grant #: 8IB-0183 Award: $161,176
Award Type: IDEA
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease



Initial Award Abstract (2002)
The chromosomal DNA double-stranded fiber, the genetic material of all living organisms, is tightly folded in an organized manner to fit into the cells' small nuclei. There are specific proteins that form complexes with DNA and play important roles in such DNA packaging. An important element of DNA packaging involves folding into loop domains, which are separated from each other by the periodic attachment of specialized DNA sequences (matrix attachment region or MARs) onto the nuclear matrix. We study how proteins that specifically bind to MARs regulate genomic DNA organization and cell functions such as transcription and replication. We previously identified a MAR-binding protein, SATB1, which is a cell-type specific MAR-binding protein. SATB1 actively folds chromosomal DNA and regulates hundreds of genes so that certain proteins are produced at the right time and place.

The importance of MAR-binding proteins in cancer is that alterations in their activity could impact multiple genes and re-program them simultaneously. Although SATB1 is not found in normal breast epithelial cells, our recent data show an unexpected link of SATB1 to breast carcinomas. SATB1 is expressed in metastatic, but not in non-metastatic breast cancer cell lines that we have tested. We hypothesize that SATB 1 may be a good "marker" for cells that have high potential for metastasis. We will use antibody against SATB1 to screen a number of human breast biopsy specimens at different stages of the disease and with known 5-year follow-up records. During this one year funding period, we will also study the role of SATB1 in metastatic cancer cell lines by identifying some of the target genes of SATB1 and determine whether expression of these genes are altered in metastatic breast carcinomas compared to that in non-metastatic breast carcinomas. Taken together, these experiments will provide important information regarding the biological function of SATB1 in breast metastasis. It is true that single genes, such as BRCA1 and p53, might have a capability of affecting the initial risk for breast cancer. But, in advanced disease how the changes in chromosomal structure and gene expression are brought about is not well understood. Thus, the global gene regulator, SATB1, and its presence in cancer progression might make it an attractive target for clinical evaluation and future therapy of breast cancer.


Final Report (2004)
The chromosomal DNA double-stranded fiber, the genetic material of all living organisms, is tightly folded in an organized manner to fit into the cells' small nuclei. There are specific proteins that form complexes with DNA and play important roles in such DNA packaging. We previously identified a nuclear protein called SATB1, which is expressed in precursor/progenitor cells of restricted cell types. SATB1 actively folds chromosomal DNA into loop domains and regulates hundreds of genes. The proteins that have the activity to organize DNA in cancer are important because alterations in their activity could impact multiple genes and re-program each of them simultaneously. Although SATB1 is not found in normal breast epithelial cells, our recent data show an unexpected link of SATB1 to breast carcinomas. SATB1 is expressed in metastatic, but not in non-metastatic breast cancer cell lines, that we have tested. We hypothesize that SATB 1 may be a good "marker' for cells that have high potential for metastasis. In this CBCRP-funded project, we used an antibody against SATB1 to screen a total of 77 human breast biopsy specimens. In most cases, we found SATB1 expression for the invasive ductal and lobular carcinomas, and in some restricted cases for ductal carcinoma in situ and morphologically benign lesions. Unexpectedly, we observed SATB1 located also in the cytoplasm, in addition to its normal nuclear location in most of the invasive carcinoma specimens. To date, we have not found a strict correlation between SATB1 expression, or its localation, with any of the known breast cancer markers. To further evaluate this, we need to set up a larger-scale analysis. Under another project aim, we identified in vivo "target genes" of SATB1 in metastatic cancer cell lines. Using a modified chromatin immunoprecipitation assay, we identified the Abelson (ABL1) and Neu (Her-2) proto-oncogenes in MDA-MB231 cells. By the RNAi method, we reduced the level of SATB1 in these cells and found that normal levels of SATB1 serves to up-regulate these two proto-oncogenes. Furthermore, we tested the effect of SATB1 on metastasis-suppressor genes highly relevant to breast carcinogenesis. In these experiments we found that SATB1 down-regulates the KISS-1, nm23, and BRMS1 genes, which suggests that SATB1 expression promotes breast cancer spread.

At the "physical level", the SATB1 network regulates the three-dimensional chromatin organization in cancer cells, and changes in the amount or function of SATB has intriguing links to breast cancer via the genes described above. These studies lead us towards several important lines of research in the future. In breast cancer cells in culture, SATB1 is located exclusively in nuclei. We need to investigate the mechanism of translocation of SATB1 to the cytoplasm in human breast carcinomas tumor samples to uncover new SATB1 functions. Next, we need to investigate the potential of SATB1 expression as a biomarker for prognosis/diagnosis. Finally, because SATB1 regulates multiple genes important for breast carcinogenesis, SATB1 might be an attractive target for future therapy for breast cancer.