DNA polymerase eta protects human cells against DNA damage induced by the tumor chemotherapeutic temozolomide

Human DNA polymerases can bypass DNA lesions performing translesion synthesis (TLS), a mechanism of DNA damage tolerance. Tumor cells use this mechanism to survive lesions caused by specific chemotherapeutic agents, resulting in treatment relapse. Moreover, TLS polymerases are error-prone and, thus, can lead to mutagenesis, increasing the resistance potential of tumor cells. DNA polymerase eta (pol eta) - a key protein from this group - is responsible for protecting against sunlight-induced tumors. Xeroderma Pigmentosum Variant (XP-V) patients are deficient in pol eta activity, which leads to symptoms related to higher sensitivity and increased incidence of skin cancer. Temozolomide (TMZ) is a chemotherapeutic agent used in glioblastoma and melanoma treatment. TMZ damages cells' genomes, but little is known about the role of TLS in TMZ-induced DNA lesions. This work investigates the effects of TMZ treatment in human XP-V cells, which lack pol eta, and in its complemented counterpart (XP-V comp). Interestingly, TMZ reduces the viability of XP-V cells compared to TLS proficient control cells. Furthermore, XP-V cells treated with TMZ presented increased phosphorylation of H2AX, forming γH2AX, compared to control cells. However, cell cycle assays indicate that XP-V cells treated with TMZ replicate damaged DNA and pass-through S-phase, arresting in the G2/M-phase. DNA fiber assay also fails to show any specific effect of TMZ-induced DNA damage blocking DNA elongation in pol eta deficient cells. These results show that pol eta plays a role in protecting human cells from TMZ-induced DNA damage, but this can be different from its canonical TLS mechanism. The new role opens novel therapeutic possibilities of using pol eta as a target to improve the efficacy of TMZ-based therapies against cancer.