miR-20b downregulates polymerases κ and θ in XP-V tumor cells.

XP-V is a subtype of Xeroderma pigmentosum diseases with typical pigmentation and cancers in sun-exposed regions. The present study investigated the role of microRNA-20b (miR-20b) in the imbalance of polymerase expression levels in XP-V tumor cells. Following software prediction results, certain miRNAs were chosen as candidate regulators for the observed imbalance in polymerases in XP-V tumor cells. Reverse transcription-quantitative polymerase chain reaction and western blot were used to test candidate miRNAs for their ability to reduce the expression of these polymerases. A luciferase reporter assay was used to further verify the western blot results. Polymerases κ and θ were expressed at lower levels in XP-V tumor cells compared to normal control cells. A positive correlation was demonstrated between miR-20b and polymerases κ and θ. It was also demonstrated that a proportion of miRNAs had no effect on polymerases κ and θ, despite the software predicting that these miRNAs would target these two polymerases. Therefore, miR-20b may be responsible for the low expression levels of polymerase κ and θ in XP-V tumor cells, which accelerated mismatch in DNA replication repairing.