GRANULOCYTE-COLONY-STIMULATING FACTOR-STIMULATED PROLIFERATION OF MYELOID CELLS - MODE OF CELL-CYCLE CONTROL BY A RANGE OF INHIBITORS

The myeloid cell line, NFS-60, is dependent on granulocyte colony-stim ulating factor (G-CSF) or interleukin-3 (IL-3) for survival and growth , Long-term G-CSF-dependent proliferation was found to be completely i nhibited by interferon-gamma (IFN-gamma), cyclic AMP, and dimethylamil oride and partially inhibited by IFN-alpha and lipopolysaccharide. Wit h the exception of IFN-gamma, these agents exhibited a corresponding p attern of inhibition of DNA synthesis in quiescent NFS-60 cells stimul ated with G-CSF, IFN-gamma was only a weak inhibitor of DNA synthesis, suggesting that it may act at a later stage to block proliferation, T he addition of G-CSF to NFS-60 cells resulted in phosphorylation of th e retinoblastoma protein (pRB) and activation of E2F DNA binding activ ity, The inhibitors were found to suppress the phosphorylation of pRB, lead to the production of higher order E2F complexes, and suppress th e expression of c-myc and proliferating cell nuclear antigen (PCNA) to an extent that correlated with their ability to block DNA synthesis, These findings are consistent with the notion that the ratio of free/b ound E2F binding activity is critical in controlling cell cycle progre ssion through G(1) to S-phase in these cells.