The accurate bypass of pyrimidine dimers by DNA polymerase eta contributes to ultraviolet-induced mutagenesis

Human xeroderma pigmentosum variant (XP-V) patients are mutated in the POLH gene, responsible for encoding the translesion synthesis (TLS) DNA polymerase eta (Pol eta). These patients suffer from a high frequency of skin tumors. Despite several decades of research, studies on Pol eta still offer an intriguing paradox: How does this error-prone polymerase suppress mutations? This review examines recent evidence suggesting that cyclobutane pyrimidine dimers (CPDs) are instructional for Pol eta. Consequently, it can accurately replicate these lesions, and the mutagenic effects induced by UV radiation stem from the deamination of C-containing CPDs. In this model, the deamination of C (forming a U) within CPDs leads to the correct insertion of an A opposite to the deaminated C (or U)-containing dimers. This intricate process results in C>T transitions, which represent the most prevalent mutations detected in skin cancers. Finally, the delayed replication in XP-V cells amplifies the process of C-deamination in CPDs and increases the burden of C>T mutations prevalent in XP-V tumors through the activity of backup TLS polymerases.

Automated summary

Studies have shown that xeroderma pigmentosum variant (XP-V) patients have mutations in the POLH gene, resulting in a high frequency of skin tumors. However, it is paradoxical that the translesion synthesis DNA polymerase eta (Pol η) in these patients can actually suppress mutations, and the mechanism behind this is still unclear. Recent evidence suggests that cyclobutane pyrimidine dimers (CPDs) play an instructional role for Pol η, enabling accurate replication of these lesions, and the mutagenic effects induced by UV radiation are caused by the deamination of C-containing CPDs. This process leads to C>T transitions, which are the most common mutations in skin cancers. The delayed replication in XP-V cells amplifies the deamination of C in CPDs and increases the burden of C>T mutations through the activity of backup TLS polymerases.