1,25-dihydroxyvitamin D3 modulates effects of ionizing radiation (IR) on human keratinocytes: in vitro analysis of cell viability/proliferation, DNA-damage and -repair.

We investigated the capacity of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) to protect spontaneously immortalized human keratinocytes (HaCaT) and cutaneous squamous cell carcinoma cells (SCL-1) against the hazardous effects of ionizing radiation (IR). We pretreated HaCaT and SCL-1 cells in vitro with 1,25(OH)2D3 (10(-7) M) over 48 h and then irradiated them once with IR (1 Gy, 2 Gy, and 5 Gy). Using WST-1-assay and crystal violet (CV) assay, we compared viability/proliferation in 1,25(OH)2D3-pretreated cells with controls that were pretreated with the carrier substance ethanol alone. Additionally, we analyzed the effects of 1,25(OH)2D3 on the presence of IR-induced DNA-damage by immunocytochemical detection of gamma-H2AX-foci in HaCaT-keratinocytes. We demonstrate that 1,25(OH)2D3 (10(-7) M) inhibits proliferation of human keratinocytes and that IR (1-5 Gy) has no significant effect on proliferation and viability of HaCaT-keratinocytes and SCL-1 cells. Moreover, we show that IR modulates dose-dependently the number of gammaH2AX-foci in HaCaT-keratinocytes. Pretreatment of the cells with 1,25(OH)2D3 reduces the number of IR-induced gammaH2AX-foci after irradiation with 1 Gy and 2 Gy and increases it after irradiation with 5 Gy. To put it in a nutshell, our data support the hypothesis that 1,25(OH)2D3 modulates the effects of low-dose IR (1-5 Gy) on cultured human keratinocytes.