Role of Gamma-catenin in a Breast Cancer Mouse Model

Institution: The Burnham Institute for Medical Research
Investigator(s): John Reed, M.D., Ph.D. -
Award Cycle: 1998 (Cycle IV) Grant #: 4JB-0061 Award: $290,363
Award Type: IDEAS II
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease

Initial Award Abstract (1998)
Breast cancer is associated with numerous genetic alterations that lead to disregulated cellular functions. Our current interest is in the mechanism of defective cell adhesion signaling in breast cancer cells. Specifically, there are surface proteins called cadherins, which are located in cell-cell interaction sites. In normal epithelium, the interaction of cadherin proteins on adjacent cells signals the cells to stop dividing and form a normally functioning epithelial layer. This signaling becomes defective in cancer cells. There can be both a reduction in the amounts of the cadherins present, and in the intracellular signaling mechanism that arrest cell growth. The key signaling molecules linked to cadherins are called catenins. We are interested in two catenins, b-catenin and g-catenin (also called plakoglobin). Our hypothesis is that g-catenin acts like a tumor suppressor. Thus, we would expect that mutations that result in loss of g-catenin expression would be associated with the tumor phenotype, and overexpression or restoration of g-catenin would suppress tumor function. As supporting evidence for our hypothesis, it has been reported that chromosomal losses occur in breast cancer for the region where g-catenin is found and possible g-catenin loss-of-function mutations occur in breast cancer patient samples.

Our approach is to generate mice that overexpress g-catenin. For these experiments the gene for g-catenin is linked to a mammary virus gene regulation system and is introduced into mouse eggs. The resulting animals will overexpress g-catenin in the mammary glands. We will use molecular and biochemical methods to confirm the expression of our gene in the mammary gland of the mice. In addition, we will examine the structure of the mammary gland cells. One specific area of interest is the structure of the cell-cell epithelial junctions (desmosomes), which are formed through actions of the cell surface of cadherin receptors. There is evidence the g-catenin regulates the function of this key receptor in maintaining normal mammary epithelial structure. An additional experimental focus will be to look at the effects of the carcinogenic drug, ENU, in inducing cancer in the g-catenin overexpressing mice and whether any observed effects are associated with changes in the cellular mechanisms for programmed cell death (apoptosis).

Our study is designed to generate key information on how the mammary epithelial layer is organized, and what key genes are involved in sensitizing the cells to carcinogenic agents and causing cell death. These types of studies can only be performed in whole animals where the genes of interest can be manipulated in a known manner. This information would provide a rationale for further study of g-catenin in patients and strategies for breast cancer prevention and treatment.

Final Report (2000)
In normal organs, including the breast, cells recognize their neighbor cells through cell adhesion molecules. The recognition system permits the cells to grow, divide, and attach to each other in organized arrays. They receive signals from their neighboring cells to stop growing through cell adhesion molecules. In cancer, including breast cancer, cells have lost the ability to "talk" to their neighbors to receive these signals and consequently, they grow in a disorganized mariner. Intracellular proteins, called catenins, bind to adhesion molecules and act like a "switchboard" for the incoming messages. Mutations in catenin genes have been found in cancers, implicating them in the malignancy process. For example, mutations in the gene that encodes g-catenin have been found in many women with breast cancers. The catenins, such as g-catenin and b-catenin, attach to APC (ademomatous polyposis gene- a tumor suppressing gene first found in colon cancers).

Recently we discovered another protein that binds APC, called Siah. The Siah protein collaborates with APC to induce degradation of b-catenin, which suppresses tumor cell growth. We discovered a network of protein interactions, thus revealing the molecular mechanism by which Siah induces degradation of g-catenin, and thereby suppresses tumor cell growth. Furthermore, we discovered that this pathway is induced when tumor cells are treated with anti-cancer drugs, thus explaining (in part) how these drugs suppress the growth of malignant cells (including human breast cancer cells maintained in laboratory conditions). Efforts were initiated to extend these observations, which were made by studying human cancer cells propagated in the laboratory, into mouse models, thus more closely mimicking the situation in the human body.

The foundation of knowledge laid by these studies defines a novel pathway for suppressing cancer development and sheds light into the biochemical mechanisms that go astray when tumor cells become resistant to current chemotherapy.

p21-Activated Kinase 1 Phosphorylates the Death Agonist Bad and Protects Cells from Apoptosis
Periodical:Molecular Biology of the Cell
Index Medicus: Mol Biol Cell
Authors: Schurmann A, Mooney AF, Sanders LC, Sells MA, Wang HG, Reed JC, Bokoch GM
Yr: 2000 Vol: 20 Nbr: 2 Abs: Pg:453-461

Identification of novel human F-box proteins
Periodical:Proceedings of the American Association for Cancer Research
Index Medicus: Proc Am Assoc Cancer Res
Authors: Matsuzawa S, Reed JC
Yr: 2000 Vol: 41 Nbr: Abs: Pg:3586

p53 Suppressed the c-Myb-induced Activation of heat Shock Transcription Factor 3
Periodical:Journal of Biological Chemistry
Index Medicus: J Biol Chem
Authors: Tanikawa J, Ichikawa-Iwata E, et al.
Yr: 2000 Vol: 275 Nbr: 20 Abs: Pg:15578-15585

Siah, SIP, and Ebi collaborate in a novel pathway for b-catenin degradation linked to p53 responses
Periodical:Molecular Cell
Index Medicus: Mol Cell
Authors: Matsuzawa SI, Reed JC
Yr: 2001 Vol: 7 Nbr: 5 Abs: Pg:915-26

SIP: a protein that bridges Siah-family E3 ubiquitin ligases to the SCF complex component Skp1.
Periodical:Proceedings of the American Association for Cancer Research
Index Medicus: Proc Am Assoc Cancer Res
Authors: Matsuzawa S, and Reed JC
Yr: 2000 Vol: 41 Nbr: Abs: Pg:3587