Topoisomerase regulation in the interplay between DNA transcription and replication

During DNA-involving processes such as transcription and replication the double helix is subjected to torsional stress. The over- or under-winding that encompasses torsional stress can be resolved by enzymes called topoisomerases. These enzymes cleave either one (Topoisomerase 1) or both (Topoisomerase 2) of the DNA strands, which allows for DNA relaxation, before resealing the break. Topoisomerase activity can be regulated by transcription or replication factors to fine-tune the efficiency of the genomic processes in which they are involved. Because cancers cells heavily rely on topoisomerases, these enzymes are common targets in cancer treatment.

In this thesis, I have investigated topoisomerase regulation during transcription and replication, as well as new pharmacological strategies targeting the regulation of topoisomerase activity. The long-term goal of this thesis project is to develop approaches to selectively affect cancer cells viability. In paper 1, we focused on studying how the RNA polymerase 2 modulates Topoisomerase 1 during mitotic transcription. In paper 2, we investigated the mechanism of cellular adaptation to Topoisomerase 1 inhibitors. In paper 3, we developed a therapeutic approach that blocks the interaction between RNA polymerase 2 and Topoisomerase 1. We tested the strategy in preclinical models of pancreatic cancers. We showed that the treatment is effective and specific for the cancer cells and we have characterized the mechanism of cell killing.

The thesis work integrates genomics, molecular biology, and drug screen methodologies, as well as preclinical mouse work done in collaboration. This works identifies Topoisomerase 1 as an important player in ensuring correct recruitment of various factors needed for transcription elongation, splicing and termination. The findings increase our understanding of regulatory pathways controlled by Topoisomerase 1 to protect DNA integrity and provide the rationale for the development of new approaches that target Topoisomerase 1 for cancer treatment.

List of scientific papers

I. "Topoisomerase 1 activity during mitotic transcription favors the transition from mitosis to G1" - Anika Wiegard, Vladislav Kuzin, Donald P. Cameron, Jan Grosser, Michele Ceribelli, Rashid Mehmood, Roberto Ballarino, Francesco Valant, Radoslaw Grochowski, Ivana Karabogdan, Nicola Crosetto, Arne Lindqvist, Anna Helene Bizard, Fedor Kouzine, Toyoaki Natsume, and Laura Baranello; Molecular Cell 81, 5007-5024.
https://doi.org/10.1016/j.molcel.2021.10.015

II. "NEDDylated Cullin 3 mediates the adaptive response to topoisomerase 1 inhibitors" - Alice Meroni, Jan Grosser, Sumedha Agashe, Natasha Ramakrishnan, Jessica Jackson, Priyanka Verma, Laura Baranello, Alessandro Vindigni; Sci. Adv. 8, eabq0648 (2022).
https://doi.org/10.1126/sciadv.abq0648

III. "Coinhibition of topoisomerase 1 and BRD4-mediated pause release selectively kills pancreatic cancer via readthrough transcription" - Donald P. Cameron*, Jan Grosser*, Swetlana Ladigan*, Vladislav Kuzin, Evanthia Iliopoulou, Anika Wiegard, Hajar Benredjem, Kathryn Jackson, Sven T. Liffers, Smiths Lueong, Phyllis F. Cheung, Deepak Vangala, Michael Pohl, Richard Viebahn, Christian Teschendorf, Heiner Wolters, Selami Usta, Keyi Geng, Claudia Kutter, Marie Arsenian-Henriksson, Jens T. Siveke, Andrea Tannapfel, Wolff Schmiegel, Stephan A. Hahn, Laura Baranello; Sci. Adv. 9, eadg5109 (2023).
https://doi.org/10.1126/sciadv.adg5109