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    Research Grants Awarded

    Chromosome Instability (CIN) In Breast Cancer Cells

    Study Section:
    Tumor Cell Biology V

    Scientific Abstract:
    Background : Most breast cancer cells, especially at later disease stages, exhibit aneuploidy, due to chromosome instability (CIN). Reports have suggested a link between CIN and a defective spindle checkpoint, which monitors kinetochore-microtubule attachment. The relationship between the spindle checkpoint and apoptosis has been unclear; apoptosis induced by the loss of spindle checkpoint activity is thought to occur at the subsequent G1 phase. We found that kinetochore defects can be caused by the HSP90 inhibitor 17-AAG, a new anticancer drug whose use in preclinical models, especially breast cancer models, has been well validated. In studies of 17-AAG, we discovered a novel programmed cell–death mechanism called caspase-independent mitotic apoptosis (CIMA) controlled by BUB1 but not by MAD2 (both are spindle checkpoint components). Our finding suggests that CIMA prevents aneuploid cell survival. However, further analysis is required to characterize this death pathway. Objective/Hypothesis : We hypothesize that CIMA protects cells from aneuploidy by killing those that, because of a spindle checkpoint defect, are prone to chromosome missegregation. Therefore, we will further investigate CIMA. Specific Aims: We seek to determine the molecular mechanism of aneuploidy in breast cancer cells and the role of CIMA in preventing such aneuploidy. Therefore, our aims are 1) to determine the molecular mechanism of CIMA and 2) to characterize the role of CIMA in breast cancer development. Study Design: We will accomplish Aim 1 by assessing phenotypes of cells in which siRNA has knocked down expression of spindle checkpoint components other than BUB1, known BUB1 interactors, and BUB1 interactors that we will discover by immunoprecipitation–mass spectrometry. We will also determine whether BUB1 kinase activity is involved in CIMA. To accomplish Aim 2, we will examine whether CIMA occurs in breast CIN tumors, test BUB1 activity in breast CIN tumors, and characterize the status of BUB1 interactors/substrates in breast CIN tumors. Potential Outcomes and Benefits of the Research: This work will uncover the spindle checkpoint’s role in protecting breast cells from aneuploidy, which is relevant to the current understanding of cancer. Investigation of proteins involved in this checkpoint and CIMA will elucidate the mechanism of aneuploidy in breast cancer cells. By identifying factors required for protecting cells from aneuploidy, our project will also contribute to the understanding of CIN development in breast cancer. Factors that we will discover will be possible targets of future cancer therapies.

    Lay Abstract:
    Background: Breast cancer cells often have an abnormal number of chromosomes (aneuploidy) due to chromosome instability (CIN). Reports have suggested a link between CIN in breast cancer and defects in the cells’ spindle checkpoint, which monitors kinetochore-microtubule attachment (microtubules move chromosomes to daughter cells equally.). Our studies showed kinetochore defects can be caused by 17-AAG, a new drug whose effectiveness in preclinical models of breast cancer has been well validated. In the same studies, we discovered a programmed cell–death mechanism called caspase-independent mitotic apoptosis (CIMA) induced by 17-AAG and depletion of a spindle-checkpoint component (BUB1) but not by another (MAD2). This finding and others suggest that CIMA prevents the survival of cells with aneuploidy. Objective/Hypothesis: We hypothesize that CIMA protects cells from aneuploidy by killing spindle checkpoint–defective cells, which are prone to chromosome missegregation. Therefore, we will investigate CIMA. Specific Aims: Our goal is to determine how aneuploidy occurs in breast cancer cells. Therefore, our aims are 1) to determine the molecular mechanism of CIMA and 2) to characterize the role of CIMA in breast cancer development. Study Design: To accomplish Aim 1 , we will first characterize traits of cells with a significantly reduced amount of the following: spindle checkpoint components other than BUB1, proteins known to interact with BUB1, or BUB1-interacting proteins we will discover by immunoprecipitation–mass spectrometry. Reduction of proteins involved in CIMA is expected to result in that type of death; thus, we will identify CIMA participants. We will also examine whether CIMA involves BUB1’s ability to activate other proteins by adding phosphate groups. To achieve Aim 2 , we will determine whether CIMA occurs in breast cancer cells with CIN, test BUB1 activity in breast cancer cells with CIN, and characterize BUB1 interactors/substrates in breast cancer cells with CIN. Potential Outcomes and Benefits of the Research: We will uncover the role of the spindle checkpoint in aneuploidy, which is relevant to understanding CIN-associated breast cancer. Investigation of participants in this checkpoint and CIMA will show how aneuploidy occurs in breast cancer cells. Characterizing factors that protect against aneuploidy will contribute to the understanding of CIN in breast cancer. Factors that we will discover will be possible targets of future cancer therapies.