High-LET radiation induces apoptosis in lymphoblastoid cell lines derived from ataxia-telangiectasia patients

Purpose: To investigate and compare the propensity of Epstein-Barr virus (E BV)-transformed lymphoblastoid cell lines (LCL), derived from ataxia-telang iectasia (A-T) patients and from unaffected healthy individuals (controls), to undergo apoptosis after exposure to high-linear energy transfer (LET) r adiation. Materials and methods: Four A-T (ARO, BMA, CSA and RJO) and two control (JA C and KKB3) LCL were exposed to doses of up to 4 Gy of accelerated nitrogen ions (32-45 MeV/u, 8-12 Gy/min). For comparative purposes X-ray irradiatio n (1.36 Gy/min) was also performed. The induction of apoptosis was studied 0-48 h after irradiation with the use of two methods: (1) monitoring of hig h molecular weight (HMW) DNA fragments by field inversion pulse gel electro phoresis (FIGE); and (2) morphological characterization of apoptotic cells after fluorescent staining. In parallel, cell-cycle distribution, monitored by DNA flow cytometry, as well as measurements of p53/p21(WAF1) protein le vels by Western blots, were investigated in these cells. Results: High-LET radiation-induced apoptosis and G2/M-arrest in both A-T a nd control LCL. No significant increase in the amount of p53/p21(WAF1) prot eins preceded apoptosis in control or in A-T LCL after high-LET irradiation . However, low-LET radiation did induce significant enhanced levels of p53 proteins in control but not in A-T LCL. Conclusions: LCL from both A-T homozygous and unaffected healthy individual s undergo apoptosis without accumulation of p53/p21(WAF1) proteins after ex posure to high-LET radiation. In contrast, low-LET radiation induces apopto sis and significantly increases levels of p53 protein in control but not in A-T LCL.