Interplay Between Tissue Architecture and Nuclear Organization in the DNA Damage

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7. Project Summary Double-strand DNA breaks (DSBs) constitute a constant threat for genome integrity. In absence of accurate repair, they lead to mutations and chromosomal translocations promoting cancer progression. In addition, anticancer therapies largely rely on genotoxic treatments generating DSBs in cancer cells. How normal tissues and cancer cells cope with DSBs has therefore major implications for cancer prevention and control. Cells have evolved elaborate DNA damage response (DDR) mechanisms to sense DSBs, activate repair pathways, and control cell cycle progression to prevent the propagation of genomic instability. A great challenge is to understand the DDR in the context of tissues and to define the influence of the tissue architecture (i.e., the organized assembly of multicellular structures) on the DDR. Basoapical polarity is an essential aspect of epithelial architecture that is lost during cancer development. Our preliminary data indicate that the DDR is enhanced in polarized tissues by basement membrane (BM) signaling through hemidesmosomal integrins. This effect is observed both for non-neoplastic and malignant cells in 3D culture, but not in flat cell monolayers, indicating dependency on tissue morphogenesis. Nuclear organization is interconnected with tissue morphogenesis and carcinogenesis. In polarized cells, the nuclear mitotic apparatus (NuMA) protein redistributes in the nucleus after DSB induction. NuMA is rapidly phosphorylated upon DNA damage, is necessary for the maintenance of H2AX phosphorylation (a chromatin mark at DSBs), and interacts with the WICH chromatin remodeling complex that functions in the DDR. These observations led us to propose a model in which tissue polarity and the nuclear structural protein NuMA cooperate to maintain genome integrity. The proposed research will test this model from two angles: the cell nucleus and the cell-BM interphase. Aim 1 will be to characterize the role of NuMA in the DDR. NuMA may serve as a molecular scaffold facilitating the targeting and anchorage of repair factors and chromatin remodelers at DNA lesions and/or preventing free diffusion of broken DNA in the nucleus. NuMA phosphorylation by ATM may confer spatial and temporal resolution within the scaffold. During the mentored K99 phase, protein interactions involving NuMA and DDR factors will be analyzed. During the independent R00 phase, the effect of NuMA disruption on genomic translocation frequencies and DSB mobility will be determined to test the hypothesis that NuMA anchors DNA breaks. The function of NuMA phosphorylation (P- NuMA) in the DDR will be addressed by identifying P-NuMA interaction partners, localizing, and disrupting P- NuMA. Aim 2 will be to define the mechanism by which tissue architecture controls DSB repair. Mechanotransduction or biochemical signaling via hemidesmosomal integrins may convey extracellular cues to the cell nucleus, leading to changes in nuclear organization affecting the DDR. Experiments in the K99 phase will examine the influence of basal polarity on DSB repair and nuclear organization in breast tissue samples. In the R00 phase, the mechanotransduction hypothesis will be tested with engineered hydrogels of defined stiffness, interference with the cytoskeleton dynamics, and uncoupling integrins from the cytoskeleton. The possibility that biochemical BM signals mediate the effect of basal polarity on DSB repair and NuMA distribution will be addressed by inhibiting integrin signaling cascades. A 3D culture model of ductal carcinoma in situ will be used to test if altering mechanical or biochemical BM signaling leads to decreased DSB repair in cancer cell. I am fascinated by the organization of the cell nucleus and by the mechanisms that maintain genome integrity. My career goal is to expand my current mentored project on DNA repair, initiated three years ago, as an academic principal investigator and to develop innovative strategies to fight the cancer burden. Before embracing a career in cancer research, I have built a solid background in molecular and cellular biology and acquired extensive expertise in fluorescence techniques that will be applied to this project. The K99 mechanism would offer me a unique opportunity of career development by allowing me to initiate a translational aspect of research on DNA repair (collaboration with Drs. S. Badve and K. Hodges at the IU School of Medicine). It would also provide me training in proteomics and micromechanics that I could directly apply to my project. Importantly, I will seek advice from my Mentor (Dr. S. Lelièvre) and co-mentors (Drs. T. Misteli and J. Irudayaraj) whose combined expertise include breast cancer biology, 3D tissue models, nuclear organization, DNA repair, and the application of new technology to cell biology. This mentoring team will assess my progress in research and chaperone my transition to independence. Purdue University has a very strong focus on cancer research and offers excellent training in breast cancer detection, treatment, and prevention with seminars, courses, journal club, and retreats organized within the NCI-designated Purdue Center for Cancer Research. Purdue is a unique environment for multidisciplinary endeavors between biologists, engineers, and clinicians. This milieu and my developing scientific network will drive technical advances and foster conceptual development.