Telomere Dynamics during Breast Development

Institution: Lawrence Berkeley National Laboratory
Investigator(s): Sahn-Ho Kim, Ph.D. -
Award Cycle: 2001 (Cycle VII) Grant #: 7KB-0151 Award: $157,189
Award Type: New Investigator Awards
Research Priorities
Biology of the Breast Cell>Biology of the Normal Breast: the starting point

Initial Award Abstract (2001)
Currently, little is known about the regulatory mechanisms controlling normal growth and development in breast cells. We found that there is a relationship between telomeres and the development of breast cells. Telomeres are DNA-protein structures that cap the ends of linear chromosomes and they are believed to be critical regulators for preventing cancer and aging.

We found that a novel mechanism that involves forming telomere clusters controls the development of breast cells. The ability of telomeres to cluster depends on both their length and the proteins that are associated with them. The identification of proteins that modulate telomere clustering provides important tools for understanding breast cell development. I identified a novel telomere-associated protein, called TIN2. By causing human breast cells to make TIN2 and performing biochemical analysis of them, TIN2 has been shown to be an important regulator of telomere clustering. Taken together, TIN2 might be involved in the development of breast cells.

In this project, I will systematically analyze the relationship between telomere clustering and TIN2 during breast development. I will make breast cells that have green telomeres and visualize telomere movement during breast development in order to understand how introduction of TIN2 into breast cells affects breast development and telomere clustering. Then, I will confirm the role of TIN2 during mouse breast development using mouse model system.

Our studies will provide a better understanding of how modulation of telomere structure by TIN2 regulates breast development. These results will provide insights into the mechanisms responsible for breast disorders, such as cancer.

Final Report (2003)
Background: Unlike most other cells, breast cells undergo coordinated changes during breast development, at puberty, and throughout most of adulthood, with striking changes occurring during pregnancy and lactation. Telomeres are located at the ends of chromosomes and are important for protecting the chromosomes from destruction or rearrangement. Little is known about how the development of breast cells is influenced by telomere-associated proteins and possibly telomeres.

Hypothesis: TIN2 is a novel human telomere-associated protein. Cells having a mutant form of TIN2, TIN2-13, have increased telomere length. Our preliminary results suggested that TIN2 could regulate telomere length by changing telomere structure. Also, mutant TIN2-13 disrupted the development of breast cells in cell culture. Taken together, our results suggested that TIN2 or telomere structure might be involved in the development of breast cells.

Objectives/Aims: This proposal was funded for 1 year as a New Investigator Award. We modified and adjusted the proposed specific aims (1, 2, 3). We modified specific aim 1 to complement specific aim 2 and focused on specific aim 2. To determine how TIN2 alters the development of breast cells, we studied the detailed function of TIN2 using breast cells and other cells. To determine the role of TIN2 in breast development, we created transgenic mice (genetically modified mice) that express the mutant TIN2-13 only in breast cells.

Progress: We found that TIN2 is critical for proper assembly of the telomere complex. Removal of TIN2 from cells caused cell death, suggesting that TIN2 and telomeres are essential for cell survival. Some mutant forms of TIN2 might be good candidates killing breast tumor cells. We also observed TIN2 clustering in breast cells that stopped dividing in culture. This clustering was specific to TIN2 and is not accompanied by telomere clustering. Although there is a parallel between the presence of TIN2 clusters and growth arrest, we do not yet know if these clusters are a consequence of growth-arrest or if they are indeed actively involved in the mechanism of growth-arrest. We generated transgenic mice expressing the TIN2-13 mutant in only the breast. We found that breast cells of these mice were indistinguishable from control mice during breast development, suggesting that mTIN2-13 had no influence on the breast development. However, other mutants of TIN2 might be effective in altering the differentiation of mammary epithelial cells. However, we could not test mTIN2-15 in mice due to the short period in this proposal.

Relevance to breast cancer: Our studies will provide a better understanding of how telomere structure controls the development of breast cells. The results can make an important contribution to understanding why and how breast cells lose their developmental capacity when breast cells become tumorigenic and will provide a rational basis for developing strategies to treat breast cancer based on telomere-mediated processes.

Telomeres, aging and cancer: in search of a happy ending
Index Medicus: Oncogene
Authors: Kim S-H, Kaminker P, Campisi J
Yr: 2002 Vol: 21 Nbr: 4 Abs: Pg:503-11

Reversible manipulation of telomerase expression and telomere length. Implications for the ionizing radiation response and replicative senescence of human cells
Periodical:Journal of Biological Chemistry
Index Medicus: J Biol Chem
Authors: Rubio MA, Kim SH, Campisi J
Yr: 2002 Vol: 277 Nbr: 32 Abs: Pg:28609-17