Tumor Suppression by Dystrogylcan in Breast Epithelial Cells

Institution: Lawrence Berkeley National Laboratory
Investigator(s): John Muschler, Ph.D. -
Award Cycle: 2000 (Cycle VI) Grant #: 6KB-0130 Award: $181,347
Award Type: New Investigator Awards
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease



Initial Award Abstract (2000)
Normal breast epithelial cells are organized as a single layer of cells with one side of the cell attached to a basement membrane. The cellular attachment to proteins present in the basement membrane is critical to breast cell physiology. This cell-basement membrane interaction helps prevent uncontrolled cell growth. In fact, normal breast epithelial cells will usually die, if this attachment process is disrupted. The situation is quite different when cells become cancerous. In breast cancer the cells grow as disorganized masses and growth is unregulated. In the very early stages of breast cancer, there is considerable evidence that restoring critical attachment functions will serve to reverse the disease. Specific molecular information on breast cell attachment is one potential key to controlling disease progression, and even for finding ways to prevent breast cancer.

Our interest is in the interaction of breast cells with a specific basement membrane protein, called laminin. One counterpart protein present on the surface of breast cells that allows this interaction is called dystroglycan. When we have studied breast tumor cells, it appears that dystroglycan is absent or non-functional. We find that introducing dystroglycan into breast cancer cells will restore many normal properties. We plan to use this BCRP funding to study, (i) how dystroglycan acts as in normal breast cells as a tumor suppressor, and (ii) why dystroglycan function is compromised in breast cancer cells. The experimental approaches are, first, to analyze the complex signaling pathways emanating from dystroglycan which regulate gene expression and growth control. Our second approach is to make genetic mutants in normal breast cells to effectively remove dystroglycan. Analysis of the mutant cells will permit us to learn how dystroglycan is involved in breast structure and physiology. In addition, we plan experiments to re-introduce variant forms of dystroglycan into the mutant cells to learn where the functional regions of dystroglycan are located that confer its tumor suppressor properties.

This research will shed light on a novel and important growth-regulatory mechanism within mammary epithelial cells, and potentially reveal some root causes of tumor cell behavior. But most importantly, the studies presented here can reveal strategies to restore critical aspects of dystroglycan function in tumor cells, giving us new methods to fight cancer cell proliferation and spreading.


Final Report (2001)
Note: The project ended on 12/31/01. The PI was awarded another CBCRP New Investigator award, such that the duration of the present and new award was within the 3-yr duration the CBCRP allows for New Investigators. The new CBCRP award, funded in 2001/Cycle 7, will continue the current project.

Normal breast epithelial cells are organized as a single layer of cells with one side of the cell attached to a basement membrane. The cellular attachment to proteins present in the basement membrane is critical to breast cell physiology. This cell-basement membrane interaction helps prevent uncontrolled cell growth. In fact, normal breast epithelial cells will usually die, if this attachment process is disrupted. In the very early stages of breast cancer, there is considerable evidence that restoring critical attachment functions will serve to reverse the disease. Our interest is in the interaction of breast cells with a specific basement membrane protein, called laminin. One counterpart protein present on the surface of breast cells that allows this interaction is called dystroglycan (DG). When we have studied breast tumor cells, it appears that DG is absent or non-functional. In addition to interacting with laminin, DG 'works' by sending information into the cell, telling it to adopt a particular structure and to stop growing.

With support from the CBCRP we have begun to dissect how DG transmits information into the cell, and why it does not function correctly in many tumor cells. We have analyzed multiple breast carcinoma cell lines and found that DG is produced in all cell lines examined, but that an important portion of the molecule (called alpha-DG) is often detached from the cell surface and is no longer functional. Therefore, DG function is missing in many tumor cells, in part, as the result of specific protein structural changes, and not as a result of genetic mutation. Other experiments have indicated that DG function can also be compromised by low levels of DG gene expression and by competitive signals from molecules that induce cell growth. Some of our findings show that breast tumor cells vary considerable in the relative ratios of the two forms of DG, DG and DG . We find that DG is the most critical for establishing key properties of normal cell polarity. The presence of DG strongly influences specific cell signaling pathways inside of tumor cells. And, DG is caused to be shed from cells, it appears, by certain metalloproteinases (MPs), that are present on breast tumor cell lines. Thus, an important aspect of cell adhesion to laminin through DG appears both to involve the post-translational processing and shedding process.

The goal is to find ways to restore DG function in tumor cells as a means to reduce or eliminate their tumorigenic properties. An important tool that we will use for future studies will be transgenic mice.