Genotoxic stress confers preferential and coordinate messenger RNA stability on the five gadd genes

The growth arrest and DNA damage-inducible (gadd) genes represent a group of five stress-inducible genes that are coordinately regulated at the transcriptional level. Posttranscriptional regulation of gadd153, gadd45, gadd34, gadd33, and gadd7 was studied after exposure to DNA-damaging agents or other growth arrest treatments in hamster cells. Relative transcript levels were measured following treatment with the transcriptional inhibitor actinomycin D. After exposure to methylmethane sulfonate or UV radiation, all five gadd messages demonstrated a coordinate increase in mRNA stability compared to untreated exponentially growing cells. This enhanced stability was not an universal response to genotoxic stress since other DNA damage-inducible genes, such as c-jun and c-fos, did not show an appreciable increase in mRNA half-life. In contrast, induction of growth arrest by media depletion (starvation) or by treatment with the growth inhibitor prostaglandin A2 did not induce such an increase in mRNA stability in all gadd genes. Comparison of overall RNA turnover by 3H labeling of total cellular RNA also indicated that the preferential stabilization of the gadd transcripts by DNA-damaging agents was not an artifactual response due to variations in overall RNA metabolism within each treatment group. However, DNA-damaging agents were ineffective in inducing stabilization of gadd153 mRNA in growth-arrested cells. This suggest that the signal(s) that give rise to gadd mRNA stability may also be affected by the state of cellular proliferation. Together, these results suggest that the global posttranscriptional response of the gadd genes to DNA-damaging agents is specific and unique to actively growing cells, and further implicates the role of the gadd genes in the DNA damage response of cycling cells.