Investigating ATM regulation of the cohesin complex in the DNA damage response

Investigating ATM regulation of the cohesin complex in the DNA damage response

Mihir Patel

As part of Dr. Michael Kastan’s lab in the Department of Pharmacology and Cancer Biology, my project focused on elucidating the role of cohesin-associated proteins in DNA damage response functions. Cohesin is a ringlike structure that entraps DNA and helps maintain sister chromatid cohesion during cell division and regulates gene expression by facilitating three-dimensional chromatin structure. Cohesin is phosphorylated by ATM, an apical kinase that phosphorylates numerous proteins to instigate DNA repair pathways. Specifically, we identified that proteins that help load and unload cohesin from chromatin, such as NIPBL, WAPL, and PDS5A, are novel ATM substrates. We also found that PDS5A is phosphorylated by ATM at Ser1278, and that this is required for activation of the S-phase cell cycle checkpoint and efficient DNA repair via homologous recombination. These findings will inform future work exploring the etiology of genetic diseases like ataxia-telangiectasia. This work culminated in a thesis that received a Graduation with High Distinction honor. Having the opportunity to work on this project with guided mentorship has allowed me to grow as a critical thinker. I was able to not only learn new lab techniques, such as flow cytometry, kinase assays, and coimmunoprecipitations, but also engage critically with existing literature to formulate strategies to optimize these assays for our experiments and surmount roadblocks. I also learned to evaluate data and brainstorm potential implications better. For example, by engaging with the literature, I was able to explore what our findings meant for the residence time of cohesin on chromatin and devise assays to explore whether ATM phosphorylation of PDS5A influences its interactions with other cohesin-associated proteins. Working on this project has taught me the importance of asking specific research questions, formulating evidence-based hypotheses, and analyzing data with both intense scrutiny and open-mindedness. Equally important has been my growth as a scientific communicator through this project. By regularly presenting at lab meetings and taking part in the Visible Thinking poster showcase, I have learned how to present complex data more comprehensibly and tailor presentation style to audiences of varying degrees of familiarity with our research. Overall, this project has helped me engage holistically with and better appreciate the scientific process, from start to finish. In addition, it has helped me better engage with the field of DNA damage research and expand my understanding of how regulation of genome architecture intersects with disease phenotypes. I am grateful to Dr. Michael Kastan for the opportunity to be part of the lab and for his guidance throughout the project; additionally, I am grateful to my mentor, Dr. Thomas Bass, for his supportive mentorship. I also thank the URS office for providing funding and enabling this work via the Deans’ Summer Research Fellowship.