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

Area of Science:

• Molecular Biology
• Genetics
• Dermatology

Background:

• Xeroderma pigmentosum variant (XP-V) is linked to mutations in the POLH gene, encoding translesion synthesis (TLS) DNA polymerase eta (Pol eta).
• XP-V patients exhibit a high incidence of skin tumors, yet the precise role of Pol eta in mutation suppression remains paradoxical.
• Understanding Pol eta's function is critical for explaining UV-induced mutagenesis and skin cancer development.

Purpose of the Study:

• To review recent evidence on how DNA polymerase eta (Pol eta) suppresses mutations despite its error-prone nature.
• To elucidate the mechanism by which UV radiation leads to C>T transitions, the predominant mutations in skin cancers.
• To explain the increased C>T mutation burden in XP-V tumors.

Main Methods:

• Review of existing scientific literature and research findings on Pol eta function.
• Analysis of the proposed model involving cyclobutane pyrimidine dimers (CPDs) and DNA polymerase activity.
• Examination of the role of deamination and backup TLS polymerases in XP-V cells.

Main Results:

• Cyclobutane pyrimidine dimers (CPDs) act as instructional templates for Pol eta, enabling accurate lesion replication.
• UV-induced mutagenic effects originate from the deamination of cytosine (C) within CPDs, leading to C>T transitions.
• Delayed replication in XP-V cells enhances C-deamination and C>T mutations via backup TLS polymerases.

Conclusions:

• Pol eta's accurate replication of CPDs contributes to mutation suppression, challenging the notion of it being solely error-prone.
• Cytosine deamination within CPDs is a key driver of C>T mutations in UV-exposed skin, particularly in XP-V.
• The interplay between Pol eta, deamination, and backup TLS polymerases dictates the mutation spectrum in XP-V and skin cancer.