Role of iNOS in bystander signaling between macrophages and lymphoma cells.

PURPOSE: The present report describes the bystander effects of radiation between similar and dissimilar cells and the role of iNOS in such communication.

MATERIALS AND METHODS: EL-4 and RAW 264.7 cells were exposed to 5 Gy gamma-irradiation. The medium from irradiated cells was transferred to unirradiated cells.

RESULTS: Irradiated EL-4 cells as well as those cultured in the presence of medium from gamma-irradiated EL-4 cells showed an upregulation of NF-kappaB, iNOS, p53, and p21/waf1 genes. The directly irradiated and the bystander EL-4 cells showed an increase in DNA damage, apoptosis, and NO production. Bystander signaling was also found to exist between RAW 264.7 (macrophage) and EL-4 (lymphoma) cells. Unstimulated or irradiated RAW 264.7 cells did not induce bystander effect in unirradiated EL-4 cells, but LPS stimulated and irradiated RAW 264.7 cells induced an upregulation of NF-kappaB and iNOS genes and increased the DNA damage in bystander EL-4 cells. Treatment of EL-4 or RAW 264.7 cells with L-NAME significantly reduced the induction of gene expression and DNA damage in the bystander EL-4 cells, whereas treatment with cPTIO only partially reduced the induction of gene expression and DNA damage in the bystander EL-4 cells.

CONCLUSIONS: It was concluded that active iNOS in the irradiated cells was essential for bystander response.