UV radiation is known as one of the apoptosis inducers. UVA (320-400 nm) radiation induce immediate apoptosis of cells related to membrane damages, whereas UVB (290-320 nm) and UVC (190-290 nm) radiation cause DNA damage and delayed apoptosis of cells. According to the literature data endothelial cells are less sensitive to apoptotic cell death after UV irradiation. It is related to the formation of nitric oxide (NO) by cytokine-inducible isoenzyme of nitric oxide synthase (iNOS). NO takes part in quenching free radicals’ reactions leading to DNA damage and membrane disruption induced by lipid peroxidation. The decreased sensitivity of endothelial cells to apoptosis following exposure to UVC light is also connected with the modulation of the Bcl-2 family proteins expression.

On the other hand, cancer cells are known to be sensitive to UV radiation. Immortalized EA.hy926 cells are derived from the fusion of human umbilical vein endothelial cells (HUVEC) with A549 lung carcinoma cells. It was reported that these cells exhibit several endothelial properties. It was interesting if they retain a lowered sensitivity to UVC light characteristic for endothelial cells.

The aim of this study was to compare the time-course of apoptosis triggered by UVC irradiation between immortalized EA.hy926 cells and human promyelocytic leukaemia HL60 cells. The apoptotic hallmarks following exposure to UVC irradiation were assessed by flow cytometry (the appearance of sub-G₁ region in DNA content histograms) as well as agarose gel electrophoresis (occurrence of apoptosis-related DNA fragments; “DNA-laddering”). It was found that 2 hours after irradiation (using the dose of 0.07 J/cm²), there was ca. 40% of apoptotic HL60 cells whereas EA.hy926 cells seemed to be intact. After increasing the UVC dose to 0.3 J/cm² we have observed ca. 8% and ca. 19% of apoptotic EA.hy926 cells after 24 and 72 hours of post-incubation, respectively.

In conclusion: presented data show that immortalized hybrid endothelial-cancer cells EA.hy926 cells retain the lowered sensitivity to UVC radiation characteristic for endothelial cells.

This study was supported by the State Committee for Scientific Research, Warsaw, Poland (Grant no. PBZ-KBN-101/T09/2003).

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