Transcriptional and post‐transcriptional regulation of granulocyte‐macrophage colony‐stimulating factor production in human growth factor dependent M‐07e cells

Summary. To elucidate the regulatory mechanisms of granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) production in human myeloid leukaemic cells we studied GM‐CSF gene transcription, mRNA expression and GM‐CSF secretion in human growth factor dependent M‐07e cells. GM‐CSF transcript was detected in cells cultured in the presence of interleukin‐3 (IL‐3), GM‐CSF or mast cell growth factor (MGF), whereas it was undetectable in growth factor deprived cells. Growth factor re‐addition induced, within 2 h, the appearance of GM‐CSF mRNA. Nuclear run‐on experiments demonstrated that the increase of GM‐CSF mRNA levels depends on GM‐CSF gene transcription. The simultaneous addition, to deprived cells, of the growth factor, and of cycloheximide (CHX) for 2h inhibited GM‐CSF mRNA expression, suggesting the requirement for newly made proteins for GM‐CSF gene transcription. By means of the M‐07e bioassay, which allows the detection of GM‐CSF, IL‐3 and MGF activities, and neutralizing antibodies to each of these factors, GM‐CSF activity was detected in the cell‐free extract of both IL‐3‐ and MGF‐sustained cells and of cells deprived for 24 h. This finding demonstrates that M‐07e cells produce and store biologically active GM‐CSF in response to both IL‐3 and MGF. In contrast, analysis of the growth stimulatory activity present in the culture supernatants revealed that MGF, unlike IL‐3, is able to induce the secretion of consistent amounts of GM‐CSF. Taken together, our results suggest that, in M‐07e cells, GM‐CSF gene transcription and GM‐CSF production are mediated, unlike its secretion, by mechanisms shared by IL‐3 and MGF.