Involvement of Human Small Fragment Nuclease in the Resistance of Human Cells to UV‐C‐induced Cell Death^¶

Abstract

Human small fragment nuclease (Sfn) is one of the cellular proteins that were reported to degrade small, single‐stranded DNA and RNA. However, the biological role of Sfn in cellular response to various stressors such as UV‐C (mainly 254 nm wavelength ultraviolet ray) remains unclear. We have examined whether modulation of human SFN gene expression affects cell survival capacity against UV‐C‐induced cell death, analyzing colony survival ability in UV‐C‐sensitive human RSa cells treated with short double‐stranded RNA (siRNA) specific for SFN messenger RNA (mRNA). The expression levels of SFN mRNA in the siRNA‐treated RSa cells decreased to about 15% compared with those in the control siRNA‐treated cells. The siRNA‐treated RSa cells showed lower colony survival and higher activity of caspase‐3 after UV‐C irradiation than the control siRNA‐treated RSa cells. Furthermore, the removal capacity of cyclobutane pyrimidine dimers (CPD) in the siRNA‐treated RSa cells decreased compared with the control siRNA‐treated RSa cells. There was no difference in the colony survival and CPD removal capacity after UV‐C irradiation between the control siRNA‐treated RSa cells and mock‐treated RSa cells. These results suggest that SFN expression is involved in resistance of RSa cells to UV‐C‐induced cell death through the roles it plays in the DNA repair process.