Irradiation increases levels of GM-CSF through RNA stabilization which requires an AU-rich region in cancer cells.

Granulocyte/macrophage colony stimulating factor (GM-CSF) is a hematopoietic growth factor that stimulates a wide range of myeloid hematopoietic cells; RNAs coding for many oncogenes and cytokines including GM-CSF have a very short half-life. The motif of AUUUA is a highly conserved sequence in the 3'untranslated regions (3'UTR) of these transcripts and is repeated a number of times in these short-lived cytokines and oncogenes. These sequences play a major role in controlling stability of these transcripts. Human cancer cells were transfected with a chimeric rabbit beta-globin gene linked to either a 58 bp sequence of the AT-rich region from GM-CSF or a control sequence. We have found that irradiation stimulates accumulation of GM-CSF, interleukin-6 (IL-6), and IL-1 beta RNAs. In addition, this accumulation of GM-CSF was at least, in part, a result of increased stabilization of GM-CSF transcripts. Further experiments showed that irradiation increased levels of the chimeric beta-globin transcripts containing AUUUA sequences from GM-CSF, but not those containing the control sequences. Our results suggest that irradiation increases expression of GM-CSF RNA and that posttranscriptional stabilization requiring AUUUA sequences probably is in part one of the mechanisms producing the increased levels of GM-CSF RNA by irradiation.