The translesion synthesis (TLS) pathway is the primary mechanism through which proliferating cells can tolerate DNA damage during replication. While playing a central role in normal cell survival after DNA damage, TLS also allows cancers to survive genotoxic chemotherapy. Furthermore, TLS increases the rate of mutation in tumors leading to rapid emergence of drug-resistant cells. Therefore, it has also been implicated as a driving force responsible for the onset of resistance to platinum-based therapy. Inhibition of TLS has demonstrated the ability to sensitize cancer cells to platinating agents and reduce mutagenesis in tumors, suggesting that combination therapy with an inhibitor of TLS could reduce both the dose of platinating agents and the associated toxic side effects, as well as help avert chemoresistance. As such, small molecule inhibitors of TLS are emerging as a promising new class of adjuvant agents for first-line cancer chemotherapy.
The replicative bypass of bulky DNA adducts caused by platinating agents is mediated by a set of specialized low-fidelity TLS DNA polymerases that can copy over DNA lesions while temporarily leaving them unrepaired. Multi-protein complexes that act in this process are comprised of the Y-family DNA polymerases Rev1, polη, polι and/or polκ and the B-family polymerase polζ assembled on a DNA-sliding clamp PCNA. Most importantly, Rev1 plays a key structural role in this Rev1/polζ-dependent TLS by serving as a scaffold that controls fine-tuned assembly of active TLS DNA polymerase complexes. Rev1 protein-protein interactions (PPIs) with all other TLS enzymes are mediated by its C-terminal (Rev1-CT) domain that can bind Rev1-interacting regions (RIR) from polκ, polι and polη and, at the same time, interact with the accessory Rev7 subunit of polζ. Cells deficient in Rev1 exhibit increased sensitivity to DNA damage and a significantly reduced mutation rate. Deletion of the Rev1-CT domain confers a similar phenotype, suggesting that this domain is critical for the cellular function of the TLS pathway. Finally, suppressing Rev1 activity in vitro and in vivo sensitizes cancers to genotoxic chemotherapy and prevents the onset of drug resistance by decreasing tumor mutation rate.
In collaboration with Dmitry Korzhnev at the University of Connecticut Health Center, we are developing, optimizing, and implementing high-throughput screening assays to identify small molecules that inhibit TLS by disrupting Rev1-CT PPIs.