Genome instability is a hallmark of cancer. Replication stress (RS) results in genome instability by interfering with fork progression during DNA replication and thus is a potent inducer of a variety of hereditary and non- hereditary diseases including cancer. Therefore, the knowledge of the cellular responses to RS and the accurate elucidation of the mechanisms that stabilize the genome under RS are crucial for understanding cancer development and choosing the most efficient cancer therapy. While many proteins have been identified as important players in protecting genome stability under RS, how they interact with each other to preserve fork stability and promote fork restart is unclear. In the last funding cycle, we have established that the human CTC1/STN1/TEN1 complex (the CST complex) is a new player in countering RS. We have published findings demonstrating that in response to RS, CST proteins form distinct foci that colocalize with RAD51. We have also determined that RS induces physical interaction between CST and RAD51, and that this interaction is regulated by ATR in a DNA-independent manner. In addition, CST assists in RAD51 recruitment to stalled forks, particularly those stalled at G-rich repetitive sequences. The Cancer Genomics Atlas database shows that CST genes are frequently altered in multiple types of cancers including melanoma, prostate, breast and uterine cancers, indicating a previously-unrecognized role of CST in cancer development. These significant findings, together with additional unpublished preliminary studies, support the central hypothesis proposed in this competitive renewal ? that CST antagonizes fork degradation and that its deficiency induces genome instabilities that promote tumorigenesis. We will test this hypothesis by characterizing the functional significance of the CST/RAD51 interaction in antagonizing nascent strand degradation (Aim 1), by determining how CST coordinates with BRCA2 to inhibit excessive nascent strand degradation at stalled forks (Aim 2), and by determining whether Stn1 deletion promotes RS-induced tumor formation (Aim 3). We will integrate contemporary technologies, including CRISPR/Cas9, the DNA fiber and iPOND assays, as well as ChIP-seq, to accomplish the goals of the proposed research. In addition, a new transgenic mouse model will be developed that will serve as a valuable tool for the scientific community to study the role of genome maintenance in disease development and treatment. It is expected that findings from the proposed research will reveal novel information regarding the rescue of stalled replication and the preservation of genome stability.

Public Health Relevance

to public health: Maintenance of genome stability is essential for preventing diseases including aging, cancer, and neurogenesis diseases. There is growing evidence that environmental agents perturb normal DNA duplication that results in DNA lesions and genome instability. This proposal aims to yield new insights into how perturbed replication leads to cancer development, which is expected to provide valuable insights into the tumorigenesis process as well as assist in designing effective anti-cancer therapies.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Cancer Etiology Study Section (CE)
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Reddy, Michael K
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Loyola University Chicago
Schools of Medicine
United States
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Jia, Pingping; Chai, Weihang (2018) The MLH1 ATPase domain is needed for suppressing aberrant formation of interstitial telomeric sequences. DNA Repair (Amst) 65:20-25
Wang, Yuan; Chai, Weihang (2018) Pathogenic CTC1 mutations cause global genome instabilities under replication stress. Nucleic Acids Res 46:3981-3992
Huang, Chenhui; Jia, Pingping; Chastain, Megan et al. (2017) The human CTC1/STN1/TEN1 complex regulates telomere maintenance in ALT cancer cells. Exp Cell Res 355:95-104
Chastain, Megan; Zhou, Qing; Shiva, Olga et al. (2016) Human CST Facilitates Genome-wide RAD51 Recruitment to GC-Rich Repetitive Sequences in Response to Replication Stress. Cell Rep 16:1300-1314
Zhou, Qing; Chai, Weihang (2016) Suppression of STN1 enhances the cytotoxicity of chemotherapeutic agents in cancer cells by elevating DNA damage. Oncol Lett 12:800-808
Jia, Pingping; Chastain, Megan; Zou, Ying et al. (2016) Human MLH1 suppresses the insertion of telomeric sequences at intra-chromosomal sites in telomerase-expressing cells. Nucleic Acids Res :
Jia, Pingping; Her, Chengtao; Chai, Weihang (2015) DNA excision repair at telomeres. DNA Repair (Amst) 36:137-45
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