Biology of the Normal Breast: The Starting Point
Research Conclusions
Research in Progress
Breast Development
Other Processes in Breast Biology
Breast Cell Aging and Death
Research Initiated in 2000
Breast Development
Other Processes in Breast Biology
As any woman who performs her monthly breast self-examinations knows, the normal breast is a constantly changing organ. The breast's normal changes can obscure the more ominous changes associated with cancer. Researchers have worked hard to determine what constitutes a cancerous change in the breast, but the lack of a thorough understanding of the normal breast makes this work more difficult. Because a relatively small amount of research is being done in this area, the California Breast Cancer Research Program earmarks funds especially for it. In 2000, we funded researchers who are studying the development, structure, hormonal regulation and genetic control of the normal breast. Our hope is that these studies will provide a strong foundation for distinguishing the difference between benign and malignant breast changes.
Research Conclusions
Cancer and Complexity: Questions for a New Millennium
Mary Helen Barcellos-Hoff, Ph.D., Mina Bissell, Ph.D., and G. Shyamala, Ph.D., of the Lawrence Berkeley National Laboratory, Berkeley hosted a highly successful conference on March 31, 2000 in Berkeley. It brought together industry researchers, academic researchers and health care professionals from two different scientific disciplines: breast biology and computational science. They discussed how to develop dynamic computer models of cell behavior in the breast. In the first session, "Dynamic Interactions in Carcinogenesis," Drs. Don Coffey, Allan Balmain and Harry Rubin discussed the paradoxes of human cancer and the complexity of genetic progression in cancer development. In the second session, "Heterogeneity of Target Genes and Target Cells" Drs. G. Shyamala, Satyabrata Nandi and Robert Cardiff described what is known about breast pathology and the role of hormones in breast biology and breast cancer. Drs. Mina Bissell, James Baish and Stuart Newman in the "Cell and Tissue Interactions" session talked about breast structure. They outlined how new techniques can play a role in understanding the interactions and functions of different cell types.
These techniques include informatics, which uses computer technology to process and make sense of large amounts of information with many variables, and analytical tools, such as complex mathematical equations called fractals. In the final session, "Integration of Complex Processes: Tools for a New Millennium," Drs. Ed Liu, Sylvia Spengler, Adam Arkin, and Joe Gray described informatics-based tools that can be used for deciphering breast cell function and the cells' relationship to their environment. The conference generated lively discussion. Hopefully, it will lead to collaborative research projects between breast biologists and computational scientists.
Research in Progress
Breast Development
Epithelial Cells Several studies in this section deal with epithelial cells. In the bodies of humans and animals, epithelial cells cover most syrfaces, form lands and line most cavities. The breast (or the mammary gland in mice, rats and other mammals) is composed of several types of epithelial cells that are responsible for producing milk and delivering it to the nipple. these cells are also the source of most breast cancers. |
The breast changes at the structural and cellular level as a woman goes through puberty, pregnancy, breast-feeding, and weaning. A better understanding of the factors that control breast development through these different stages can provide clues to how tumors develop.
Hox Genes in Normal Breast Development and Breast Cancer. Carmen Hagios, Ph.D., at the Lawrence Berkeley National Laboratory, Berkeley is finding that when a developmental gene called HoxA1 is deactivated in tumor cells, they behave more like normal cells.
Hormonal Regulation of TGF-β during Mammary Development. The reproductive organs of female mice go through the estrus cycle, where periods when pregnancy is possible alternate with periods when it isn't. Levels of the hormones estrogen and progesterone rise and fall in a pattern during the mouse estrus cycle, as they do during the human menstrual cycle. Mary Helen Barcellos-Hoff, Ph.D., at the Lawrence Berkeley National Laboratory, Berkeley genetically engineered a mouse that lacks the growth factor TGF-β1. Growth factors are proteins that stimulate the cell from outside to cause the cell to divide, mature or go through some other growth process. Dr. Barcellos-Hoff examined mammary glands in normal mice and mice lacking TGF-β1 during various stages of the estrus cycle. She found that estrogen and progesterone each have a different influence on TGF-β1's ability to regulate epithelial cell growth and death. This study is discussed in Breast Cancer Research (2000;2:92-99).
Two investigators are studying factors that make the breast and cells within it mature (differentiate). Identification of Pregnancy-Associated Breast Cancer Genes. Satyabrata Nandi, Ph.D., from the University of California, Berkeley is continuing a project to identify and study breast cancer-related genes associated with pregnancy. A full-term pregnancy reduces a young woman's lifetime risk of breast cancer by about 30%. Dr. Nandi has identified a novel gene, called RMT1, which appears to be turned on at high levels in the breast cells of virgin rats. This gene also appears to be turned on at higher levels than normal in breast cancer in rats. Dr. Nandi is exploring the type of breast cell where RMT1 is found, along with its gene sequence and hormonal regulation. The rationale and background for this project has been published in the Proceedings of the National Academy of Sciences, USA (1999;96(5):2520-5).
Identification of Novel Id-1 Regulated Genes in Breast Cells. Id-1 is a gene that keeps cells from maturing. It also allows cells to multiply and move into the bloodstream through blood vessel walls. Jarnail Singh, Ph.D., at the California Pacific Medical Center, San Francisco is finding genes that Id-1 regulates. Dr. Singh has found that Id-1 causes a protein called clusterin to decrease. Clusterin protein tends to be high in cells that are producing milk in culture and in animals.
Other Processes in Breast Biology
Mechanisms of Fluid Transport in Human Mammary Epithelium. Sheldon Miller, Ph.D., at the University of California, Berkeley is investigating how epithelial cells regulate the movement of fluid into the ducts of the breast. The regulation process is critical for milk production; deregulation leads to breast cystic disease. Dr. Miller has identified the proteins that regulate the movement of fluids and ions (electrically charged molecules) across mammary cell membranes in mice. In the coming year, he will determine whether the same proteins are at work in human cells.
Regulation of Breast Epithelial Cell Motility by Proteases. Breast epithelial cells are surrounded by a complex structure containing support components (the extracellular matrix) and other types of cells. The interaction between epithelial cells and other cell types in their surrounding environment plays an important part in dictating how epithelial cells behave. This interaction can be regulated by hormonal interaction between cells or by their physical relationship to one another. These factors also tend to be activated when a tumor achieves the ability to move from the breast to a distant organ. The structural components of the breast include proteins called laminin. To move around and reorganize (or in the case of cancer, spread to other parts of the body), the epithelial cells need to digest the structural proteins supporting them. Vito Quaranta, Ph.D., at The Scripps Research Institute, La Jolla is investigating how an enzyme, MT1-MMP, digests a laminin protein, Ln-5, and is determining the physiological result of this process. He has found the section (site) of Ln-5 that allows MT1-MMP to digest it. Over the next year, he will use genetically altered mice to determine the physiological consequence of having breast cells that are missing Ln-5 or not able to bind Ln-5.
The Role of Nitric Oxide and Arginine in the Breast. Exposure to molecules containing oxygen (oxidation) has ramifications for both normal and tumor breast cells. Arginine is an amino acid that can be converted to nitric oxide. Carol MacLeod, Ph.D., at the University of California, San Diego has found a molecule, CAT2, which can transport arginine into cells and increase their production of nitric oxide. She is finding that genetically altered mice that are deficient in CAT2 are less likely to develop hyperplasias and dysplasias, which are abnormal tissue structures that are more likely than normal tissues to later become cancer. CAT2-deficient mice also have a lower tumor burden than mice with normal CAT2.
Genetic Repair of Oxidative Damage: Effect of Estrogen. Nicholas Rampino, Ph.D., of The Burnham Institute, La Jolla is also studying oxygenation in cells. He exposed cells that are sensitive to the hormone estrogen to molecules containing oxygen. Then, he exposed the cells to the drugs raloxifene and tamoxifen, and also to pure estrogen inhibitor IC 182,780. The cells exposed to raloxifene had lower mutation rates than cells exposed to the other two substances. This indicates that raloxifene may be a superior agent for preventing breast cancer.
Breast Cell Aging and Death
Breast Cancer Chemoprevention by Retinoids. Xiaokun Zhang, Ph.D., at The Burnham Institute, La Jolla is also exploring the effect of agents that have the potential to prevent breast cancer. He is investigating how Vitamin A (retinoic acid) inhibits breast cell growth. Dr. Zhang has identified a new mechanism through which Vitamin A acts within breast cells. The protein in cells that takes in Vitamin A acts through a part of the cell called the mitochondria. This discovery provides a new basis for potentially developing a breast cancer-preventive drug based on Vitamin A. Results from this study have been published in Molecular and Cell Biology (2000;20:957-970); Cancer Research (2000;60(12):3271-3280); and Science (2000;289(5482):1159-1164).
Cloning of Senescence Genes in Mammary Epithelial Cells. Investigators have made progress in understanding how normal cells age and eventually stop reproducing (senesce). Hong Zhang, Ph.D., at Stanford University, Palo Alto is using a technique (random homozygous knock-out, or RHKO) to generate immortal clones from normal human breast epithelial cells. Using these cells, he is trying to find the senescence genes that cause normal cell aging. In the first year he made an RHKO human breast epithelial cell library of about 25,000 independent sections of genes, and started to search for the gene(s) that cause cells to age normally.
The Role of PAK2 in Breast Cancer Cell Death. Gary Bokoch, Ph.D. at The Scripps Research Institute, La Jolla has found that an enzyme, p21-activated kinase (PAK), removes the protein that triggers cell death, BAD, from action. PAK stops BAD's action by attaching a phosphate molecule to it. By identifying the regulators of this process, investigators are hoping to find the keys to how tumor cells, which often gain the capacity to grow continually, circumvent it.
Research Initiated in 2000
Breast Development
Pregnancy and Breast Cancer: an Immunological Connection? A full term pregnancy at an early age protects a woman against developing breast cancer. But what changes occur in the breast to explain it? Many theories concentrate on hormones. Michael Campbell, Ph.D., of the University of California, San Francisco will investigate whether the immune system plays a part. Dr. Campbell will examine the sera (a part of blood) from women who have had multiple pregnancies. He is looking for antibodies that specifically recognize breast tumors. At the end of the study, he hopes to have a panel of antibodies and antigens that are normally present and can protect against tumor development.
Other Processes in Breast Biology
The Role of NCo-R During Normal Mammary Gland Development. The relationship between hormones such as estrogen and breast development has been firmly established, however the mechanism for this regulation is still unclear. Sung Hee Baek, Ph.D., of the University of California, San Diego will look at the role of a protein, N-CoR , in the growth and development of the normal mammary gland. N-CoR is a molecule inside the nucleus that is involved in estrogen regulation of cell growth. Using mice with cloned genes transferred into their DNA, she is analyzing the mammary gland growth patterns when N-CoR is either absent or present at elevated levels.
A Vascular Restriction of Mammary Tumor Progression. Robert Oshima, Ph.D., of The Burnham Institute, La Jolla will investigate the influence of pregnancy on the normal organization of breast blood vessels. He will also investigate how that blood vessel organization is influenced when breasts produce milk and when breasts go through the changes that come when they stop producing milk. He will also determine whether altered levels of the blood vessel growth factors (proteins from outside cells that trigger division, maturing or other growth processes) can make mammary gland tumors more or less likely to develop or grow.
Genetic Changes in Normal Epithelium of the Cancerous Breast. Shanaz Dairkee, Ph.D., of the California Pacific Medical Center Research Institute, San Francisco will investigate genetic changes that occur in normal-appearing breast cells to identify changes that indicate a propensity to become cancer.
Method for Measuring Breast Epithelial Turnover in Humans. A reliable measure of the rate of epithelial cell division is important to understanding how cancer develops and to test how cancer preventive agents work. Marc Hellerstein, Ph.D., of the University of California, Berkeley will use a technique his laboratory recently developed for measuring the rate at which T cells in AIDS patients divide. He will attempt to measure breast epithelial cell division in animals and people accurately, without using radioactivity or toxic metabolites. A second goal in this project is to use the test to determine how genistein affects breast cell division. Genistein is found in soybeans and is a potent cancer preventative agent in rats. In addition, Dr. Hellerstein will establish normal rates of breast cell division in humans and see how these rates are affected by factors that are associated with higher or lower levels of breast cancer risk among women, such as age, weight, ethnicity and diet.
