title: Initiation of apoptosis in cells exposed to medium from the progeny of irradiated cells: a possible mechanism for bystander-induced genomic instability?
abstract: Genomic instability and bystander effects have recently been linked experimentally both in vivo and in vitro. The aim of the present study was to determine if medium from irradiated cells several passages distant from the original exposure could initiate apoptosis in unirradiated cells. Human keratinocytes (from the HPV-G cell line) were irradiated with 0.5 Gy or 5 Gy gamma rays. Medium was harvested at each passage up to the 7th passage (approximately 35 population doublings) postirradiation and transferred to unirradiated keratinocytes. Intracellular calcium levels, mitochondrial membrane potential, and the level of reactive oxygen species were all monitored for 24 h after medium transfer. Rapid calcium fluxes (within 30 s), loss of mitochondrial membrane potential, and increases in reactive oxygen species (from 6 h after medium transfer) were observed in the recipient cells. There was no significant difference between medium conditioned by cells irradiated with 0.5 or 5 Gy. The effect of medium from progeny was the same as the initial effect reported previously and did not diminish with increasing passage number. The data suggest that initiating events in the cascade that leads to apoptosis are induced in unirradiated cells by a signal produced by irradiated cells and that this signal can still be produced by the progeny of irradiated cells for several generations.
authors.affiliation: Radiation and Environmental Science Centre, Dublin Institute of Technology, Fitzwilliam House, 30 Upper Pembroke Street, Dublin 2, Ireland. fiona.lyng@dit.ie
authors.forename: F M
authors.initials: FM
authors.lastname: Lyng
authors.forename: C B
authors.initials: CB
authors.lastname: Seymour
authors.forename: C
authors.initials: C
authors.lastname: Mothersill
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D024201:Bystander Effect / Q000528:radiation effects*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D017077:Culture Media, Conditioned / Q000494:pharmacology*; D004249:DNA Damage / Q000235:genetics / Q000528:radiation effects*; D005453:Fluorescence; D007424:Intracellular Fluid / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D008564:Membrane Potentials / Q000187:drug effects / Q000528:radiation effects; D008928:Mitochondria / Q000187:drug effects / Q000528:radiation effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D020112:Rhodamine 123 / Q000378:metabolism
chemical_list: D017077:Culture Media, Conditioned; D017382:Reactive Oxygen Species; D020112:Rhodamine 123; D002118:Calcium