Production of Delayed Death and Neoplastic Transformation in CGL1 Cells by Radiation-Induced Bystander Effects

Abstract

Other investigators have demonstrated by transfer of medium from irradiated cells and by irradiation with low-fluence alpha particles or microbeams that cells do not have to be directly exposed to ionizing radiation to be detrimentally affected, i.e. bystander effects. In this study, we demonstrate by transfer of medium from X-irradiated human CGL1 hybrid cells that the killing of bystander cells reduces the plating efficiency of the nonirradiated CGL1 cells by 33 +/- 6%. In addition, we show that the amount of cell death induced by bystander effects is not dependent on X-ray dose, and that the induction of apoptosis does not appear to be responsible for the cell death. Furthermore, we found that the reduction in plating efficiency in bystander cells is evident for over 18 days, or 22 cell population doublings, after medium transfer, despite repeated refeeding of the cell cultures. Finally, we report the novel observation that bystander effects induced by the transfer of medium from irradiated cells can induce neoplastic transformation. Exposing unirradiated CGL1 cells to medium from cells irradiated with 5 or 7 Gy increased the frequency of neoplastic transformation significantly from 6.3 x 10(-6) in unirradiated controls to 2.3 x 10(-5) (a factor of nearly four). We conclude that the bystander effect induces persistent, long-term, transmissible changes in the progeny of CGL1 cells that result in delayed death and neoplastic transformation. The data suggest that neoplastic transformation in bystander cells may play a significant role in radiation-induced neoplastic transformation at lower doses of X rays.

Mechanism of radiation-induced bystander effect: Role of the cyclooxygenase-2 signaling pathway

“…These results suggested that irradiated cells secreted a cytotoxic factor into the culture medium, which was capable of killing nonirradiated cells. Furthermore, transferring media from low linear energy transfer-irradiated cultures to nonirradiated cells lead to increased levels of various bystander effects, such as cell killing (18)(19)(20), neoplastic transformation (21), and genomic instability (22). In contrast, in feeder layer culture, metabolic cooperation between cells of similar or different types increases the clonogenic survival of the nonirradiated cells by providing growth factors and matrix support and is considered a positive aspect of the bystander phenomenon.…”

Changes in the ornithine cycle following ionising radiation cause a cytotoxic conditioning of the culture medium of H35 hepatoma cells

“…Cytotoxic and clastogenic effects were detected on nonirradiated cells in contact with irradiated cells or exchanged via the culture medium (Hallahan et al, 1989;Mothersill and Seymour, 1997;Bishayee et al, 2001; Lewis et al, 2001;Sawant et al, 2002). The contribution of such bystander effects to radiation-induced cell death can be significant.…”

Constitutive nitric oxide acting as a possible intercellular signaling molecule in the initiation of radiation-induced DNA double strand breaks in non-irradiated bystander cells

“…Mothersill and Seymour (1997) first demonstrated a highly significant reduction in cloning efficiency in both non-irradiated normal as well as malignant epithelial cell lines that had received media from 60 Co-g-ray-irradiated human epithelial cell cultures. Further studies found that transferring media from low or high linear energy transfer-irradiated cultures to non-irradiated cells led to increased levels of various bystander effects, such as cell killing (Mothersill and Seymour, 1998;Lyng et al, 2000;Nagar et al, 2003), neoplastic transformation (Lewis et al, 2001), proliferation (Iyer and Lehnert, 2000) and genomic instability . These studies suggested that irradiated cells secreted a cytotoxic factor such as reactive oxygen species (ROS), transforming growth factor-b1 (TGF-b1) or interleukin-8 (IL-8 Nitric oxide as a signal in bystander effects W Han et al into the culture medium which was capable of causing damage in non-irradiated cells.…”