Novel Ways to Control the Growth of Mammary Epithelial Cells

Institution: Scripps Research Institute
Investigator(s): Susanne Koch, Ph.D. -
Award Cycle: 1996 (Cycle II) Grant #: 2FB-0090 Award: $35,256
Award Type: Postdoctoral Fellowship
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease

Initial Award Abstract (1996)
Each organ in our body is made up of cells which work together as a team to perform a specific function. To make an organ, the cells must increase in number (i.e., proliferate) and change their behavior (i.e., differentiate), acquiring the skills and teamwork necessary for proper tissue function. Cell proliferation and differentiation are controlled by special proteins, called growth factors or growth hormones. When you are cut, for example, growth factors are made which activate the growth and differentiation of new skin cells to heal the wound. When the wound heals, the growth factors are no longer made. Infrequently, this exquisite regulation breaks down when a single cellís genetic makeup gets changed by a process called "mutation." Consequently, this cell may alter its behavior and begin to proliferate in an uncontrolled manner. This process can lead to breast cancer when certain cells of the breast, the breast epithelial cells, grow uncontrollably. The growing mass of cells that stay in the breast forms a lump. Other cancer cells, especially those that are no longer differentiated and have "forgotten" they are breast cells, move away to form tumors elsewhere in the body. These undifferentiated cells are the most dangerous.

Growth factors bind to and activate proteins that sit on the cellís membrane. Activated growth factor receptors send signals into the cell to trigger cell proliferation and/or differentiation. These signals have to be tightly controlled to prevent unlimited cell proliferation. Growth signals can be stopped when the activated receptors and their bound growth factors are internalized and degraded. Our laboratory studies this process of receptor internalization, called "endocytosis." We have recently discovered that taking activated growth factor receptors into the cell can also change the messages they transmit, tipping the balance between triggering cell proliferation and differentiation.

The overall goal of my research is to understand the role of endocytosis in controlling the cellís response to growth factors. Conceivably, we can find a way to tip the balance toward differentiation and away from proliferation. To accomplish this, I propose to analyze how endocytosis affects the balance between differentiation and proliferative signals in breast epithelial cells engineered so that we can experimentally turn endocytosis on or off. Results from these studies will provide insight into novel ways to control breast cancer proliferation.

Progress Report 1 (1997)
The generation and deletion of cells in the body is a process under tight regulation. Only very rarely, this careful regulation is disturbed when a single cellís genetic material mutates. This alteration in the genetic make up often simply leads to the premature death of the cell, but alternatively it can lead to the acquisition of a new trait such as the ability to loosen the control over its division rate. The resulting uncontrolled division can eventually lead to a tumor.

The regulation of cell growth in normal cells is often mediated by soluble factors. Membrane receptors "fish" out the soluble factors and shuttle them to the inside of the cell. Receiving the "signal" of the incoming molecule, the cell proliferates in response. This proliferative program has to be tightly regulated in order to achieve net proliferation (growth), net death (decrease), or a balance of growth and death of the cell numbers. The uptake of the soluble factor (ligand) also serves the purpose to attenuate the signal because, once internalized, the ligand gets destroyed. This ensures that the signal is an event that is limited to last only a short period of time.

Our research involves the analysis of the uptake mechanism that forms the membrane invaginations forming a vesicle. One of these proteins on the inner side of the membrane is called dynamin. I have been trying to find possible partner proteins that a) might regulate quantity, b) might determine its location and c) might aid in vesicle formation. Using anti dynamin antibodies I can generate a kind of "molecular Velcro". Cellular extracts are then passed over to bind putative partner proteins and in turn to analyze and identify them.

In a related project, I have started to develop an assay that involves cell membranes (broken cells) where I can vary the conditions to identify the optimal conditions under which dynamin relocates from a soluble pool of proteins to the membrane. Once partner proteins are identified, one can study their involvement in the binding of dynamin to the membrane using this assay.

If a cell were unable to remove receptor/ligand from the surface, one would expect that proliferative signals continue unchecked, generating "offspring" cells that develop into a tumor. It is crucial to understand how these uptake and regulation mechanisms function and with this knowledge one can expect to change normal breast cells into cancerous cells in the culture dish by preventing receptor uptake.