The Control of Breast Cancer Cell Death

Institution: Stanford University
Investigator(s): Daria Mochly-Rosen, Ph.D. -
Award Cycle: 2000 (Cycle VI) Grant #: 6JB-0056 Award: $306,149
Award Type: IDEAS II
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease



Initial Award Abstract (2000)
The conversion of normal breast cells to those capable of forming malignant tumors involves alterations in multiple cellular processes, including pathways controlling the delicate balance between growth and cell death. In order to eliminate cells, the body can ‘trigger’ them to commit suicide using a process termed apoptosis. However, cancer cells have developed mechanisms to ignore the signals that should trigger them to die. This is particularly true in breast cancer patients that have failed chemotherapy treatments, and suffer recurrence of the disease. Thus, new information and drugs are needed to increase the sensitivity of cancer cells to death signals. The protein kinase C (PKC) family of enzymes participates in signaling pathways controlling both growth and apoptosis, both in normal and in cancerous cells. However, the specific PKC family members contributing to the abnormal survival of breast cancer cells have not yet been determined. We propose to identify the PKC family members that render the cancer cells resistant to apoptosis.

We have developed tools which will allow us to determine which member or members of the PKC family allow cancer cells to live and form tumors, particularly in those settings when the cells should die. These tools were developed during the course of our work on the functions of PKC family members in heart physiology. PKCs must be located at appropriate sites within the cell to be effective enzymes, and we have identified proteins, termed RACKs, which are the ‘anchors’ responsible for PKC localization. Next, we then identified inhibitors that prevent the interactions of PKCs with RACKs, and prevent PKCs from carrying out their functions. These inhibitors are unusual, because unlike other inhibitors available, they are specific for individual PKC family members. This BCRP-funded project will allow us to extend the potential use these inhibitors to breast cancer. From preliminary data, we predict that inhibition of a PKC family member, called delta-PKC, will allow breast cancer cells to undergo apoptotic death, and will prevent tumor formation. Our experiments are performed both using breast cancer cell lines and by establishing PKC-modified cell lines to be studied for the capacity to form tumors and metastasize in mice.

If confirmed, then manipulation of specific PKC family members may be part of a more effective treatment regimen for breast cancer.


Final Report (2002)
The formation of tumors in the body occurs when cancer cells overcome the restraints designed to keep them from growing inappropriately. There are two levels of restraints. First, there are control mechanisms that keep cells from dividing. Secondly, other controls will cause cells to commit suicide, in a process called "apoptosis." The protein kinase C (PKC) family of enzymes participates in signaling pathways controlling both cell division and suicide, in normal and cancerous cells. However, the specific PKC family members contributing to the abnormal growth and survival of breast cancer cells have not yet been determined. Our goal is to identify the PKC family members that allow breast cells to form tumors.

During the course of our work on the functions of PKC family members in heart physiology, we developed tools that have allowed us to ask which member(s) of the PKC family regulate cancer cell survival. PKCs must be located at appropriate sites within the cell to be effective enzymes, and we have identified proteins, termed RACKs, which are the anchors responsible for PKC localization. We then identified inhibitors that prevent the interactions of PKCs with RACKs, and prevent PKCs from carrying out their functions. These tools include specific inhibitors of the PKC family members, delta ( d), and epsilon ( e), which have been implicated in growth control in several types of cells.

We have used two approaches to determine the roles of d-and e-PKCs in human breast cancer. First, we have engineered human breast cancer cells, called MCF7 cells, to make d- and e-PKCs inhibitors themselves. When d-PKC is inhibited in this way, the cells are prevented from death by apoptosis under certain conditions. Second, we have grown tumors from MCF7 cells in mice, and have implanted pumps to deliver the inhibitors during the period of tumor growth. Inhibiting d-PKC in this way resulted in the tumors being larger. These results suggest roles for d-PKC in the regulation of apoptosis and growth in human breast cancer cells.

The converse implied by our findings, is that activation of d-PKC may result in inhibition of tumor cell growth, and in induction of apoptosis, both desirable anti-tumor therapies. Therefore, d-PKC may be an effective target for therapeutic intervention in human breast cancer. Our laboratory has recently developed an activator of d-PKC, and future studies will address the possibility that this activator can be used as a drug as part of a multi-pronged therapeutic regimen.