Expression of cytoskeletal elements in proliferating cells following radiation exposure

Previous work has demonstrated that radiation exposure modulates the expression of a series of genes, including those that encode cytoskeletal elements. The experiments reported here were designed to examine (1) the comparative effects of neutrons administered at high versus low dose-rates, (2) the comparative effects of neutrons on cycling versus resting cells and (3) the comparative effects of neutrons versus γrays on β and γactin mRNA accumulation in Syrian hamster embryo (SHE) cells 1 and 3 h post-irradiation. JANUS fission-spectrum neutrons from Argonne National Laboratory's JANUS reactor administered at high (12 cGy/min) dose-rates had little effect on resting cells, but at very low dose-rates (0.1 cGy/min) had a repressive effect on γactin mRNA accumulation. Increased accumulation of βactin mRNA was detected following the exposure of cells to neutrons administered at high dose-rates, but repression of βactin mRNA was observed when neutrons were administered at low dose-rates. Cycling cells (unexposed and neutron irradiated) in all cases expressed higher levels of all actin-specific mRNAs than resting cells; βactin mRNA (but not γactin mRNA) was induced to a greater extent in cycling cells than in resting cells during the first hour following neutron exposure. In resting cells, however, low dose-rate neutrons were more effective than low dose-rate γrays at repressing both γ and βactin mRNA accumulation. These results demonstrate the differential effects of radiation quality (neutrons versus γrays) and cell-cycle state on the modulation of actin isotype-specific gene expression.