Targeted cytoplasmic irradiation with alpha particles induces mutations in mammalian cells

Abstract

Ever since x-rays were shown to induce mutation in Drosophila more than 70 years ago, prevailing dogma considered the genotoxic effects of ionizing radiation, such as mutations and carcinogenesis, as being due mostly to direct damage to the nucleus. Although there was indication that alpha particle traversal through cellular cytoplasm was innocuous, the full impact remained unknown. The availability of the microbeam at the Radiological Research Accelerator Facility of Columbia University made it possible to target and irradiate the cytoplasm of individual cells in a highly localized spatial region. By using dual f luorochrome dyes (Hoechst and Nile Red) to locate nucleus and cellular cytoplasm, respectively, thereby avoiding inadvertent traversal of nuclei, we show here that cytoplasmic irradiation is mutagenic at the CD59 (S1) locus of human-hamster hybrid (A L ) cells, while inf licting minimal cytotoxicity. The principal class of mutations induced are similar to those of spontaneous origin and are entirely different from those of nuclear irradiation. Furthermore, experiments with radical scavenger and inhibitor of intracellular glutathione indicated that the mutagenicity of cytoplasmic irradiation depends on generation of reactive oxygen species. These findings suggest that cytoplasm is an important target for genotoxic effects of ionizing radiation, particularly radon, the second leading cause of lung cancer in the United States. In addition, cytoplasmic traversal by alpha particles may be more dangerous than nuclear traversal, because the mutagenicity is accomplished by little or no killing of the target cells.

Production of a signal by irradiated cells which leads to a response in unirradiated cells characteristic of initiation of apoptosis

“…They proposed that the de novo production of new aberrations in the descendants of irradiated cells was due to oxidative damage but had no explanation for why the oxygen radical generation was persistently elevated. Recent data from several laboratories Lorimore et al, 1998;Azzam et al, 1999;Wu et al, 1999) have shown that all the endpoints which characterize 'genomic instability', can in fact be induced in cells that were never directly exposed to irradiation. Wu et al (1999) and Azzam et al (1999) showed mutations in cells that were not traversed by a radiation track.…”

“…Recent data from several laboratories Lorimore et al, 1998;Azzam et al, 1999;Wu et al, 1999) have shown that all the endpoints which characterize 'genomic instability', can in fact be induced in cells that were never directly exposed to irradiation. Wu et al (1999) and Azzam et al (1999) showed mutations in cells that were not traversed by a radiation track. Lorimore et al (1998) showed that persistent chromosomal aberrations following alpha particle irradiation were found in the parts of the culture which were not ever hit by a particle.…”

“…The data show that effects of single cell irradiation are not limited to the exposed cell but affect other cells in the vicinity. Mutation, chromosome aberration and protein induction, have all been shown in cells distant from the target cell (Prise et al, 1998;Belyakov et al, 1999;Wu et al, 1999). The mechanism is unclear as is the nature of the substance or signal.…”

DNA-PKcs and ATM influence generation of ionizing radiation-induced bystander signals

“…Such a damage response may initiate as yet undefined pathways that ultimately lead to the generation of a BSE in non-irradiated cells, and hints at a tissue-level response to radiation injury moderated by some of the same proteins that orchestrate the intracellular response to DNA damage. Although an intracellular IR-induced signaling response has been demonstrated (Wu et al, 1999), it has also been shown that ATM and DNA-PKcs signaling activates NF-kB through the p53-independent MEK/ERK/p90rsk/IKK signaling pathway in an antiapoptotic response to DNA damage (Panta et al, 2004). In addition, DNA-PKcs is required for the activation of the stress kinases SAPK/JNK (Fritz and Kaina, 2006).…”

New challenges in radiobiology research with microbeams

“…This soon made possible the direct study of effects of single traversals through the cell nucleus (Miller et al 1999) or cytoplasm (Wu et al 1999) and evidence for the bystander effect (Zhou et al 2000). However, several other applications were soon introduced and technologies rapidly improved.…”