Tumor cell apoptosis by irradiation-induced nitric oxide production in vascular endothelium.
We examined the effects of X-ray irradiation on endothelial nitric oxide (NO) production in bovine aortic endothelial cells (BAECs). Single irradiation of up to 60 Gy did not affect the expression of endothelial NO synthase (eNOS) mRNA, as assessed by reverse transcription-PCR, in BAECs. The basal level of intracellular Ca(2+) concentration and Ca(2+) mobilization induced by thapsigargin and ATP were also not affected by single irradiation. However, eNOS-mediated, Ca(2+)-dependent constitutional NO production could not be examined directly because irradiated BAECs showed continuous NO production, as measured by diaminofluorescein-2 fluorescence, without agonist stimulation. Expression of inducible NO synthase (iNOS) mRNA and protein was markedly increased by 2 Gy of irradiation, thereby indicating that the basal and continuous NO production in irradiated BAECs was due to the expression of iNOS. Hepatoma HepG2 cells cocultured with irradiated BAECs showed apoptosis in the presence of L-arginine, and the apoptosis was prevented by L-NAME (N(omega)-nitro-L-arginine methyl ester). These results indicate that single irradiation does not affect Ca(2+) mobilization and eNOS expression but induces the expression of iNOS in BAECs, and the latter property would be beneficial to induce apoptosis in the adjacent tumor cells.
Hirakawa
Masakazu
M
Department of Pharmacology, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan.
Oike
Masahiro
M
Masuda
Kouji
K
Ito
Yushi
Y
D000818:Animals; D017209:Apoptosis; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D004730:Endothelium, Vascular / Q000378:metabolism / Q000528:radiation effects*; D009369:Neoplasms / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D009569:Nitric Oxide / Q000096:biosynthesis*; D019001:Nitric Oxide Synthase / Q000235:genetics; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III
D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D002118:Calcium