DIFFERENTIATION-LINKED CHANGES IN GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR-RECEPTOR MEDIATED SIGNALING IN THE HL-60 PROMYELOCYTIC CELL-LINE

Granulocyte-macrophage colony-stimulating factor (GM-CSF) induces the proliferation and maturation of immature myeloid progenitor cells and primes mature cell function in phagocytes. To investigate whether the biochemical events following the binding of GM-CSF to its receptor are differentiation dependent we analysed GM-CSF mediated activation of t he JAK 2-STAT 5 and MAP kinase pathways in undifferentiated HL-60 cell s and HL-60 cells induced to differentiate with dimethyl sulphoxide (D MSO) or retinoic acid (RA). GM-CSF stimulated MAP kinase activation in both the undifferentiated and differentiated HL-60 cells. Activation of MAP kinase (expressed as a proportion of total cellular MAP kinase) was maximal at 5 min and of similar magnitude in both cell types. The re was, however, a marked difference in the later kinetics of activati on, with the response being transient in the undifferentiated cells an d disappearing within 15 min, whereas it was prolonged and persisted f or at least 60 min in the differentiated cells. GMCSF mediated activat ion of STAT 5 was markedly increased (15-20-fold) after differentiatio n of HL-60 cells but the kinetics of activation did not change, The in crease in STAT 5 activation was not due to a change in total cellular STAT 5 expression but correlated with increased JAK-2 protein levels. These data show that in the HL-60 cell model, differentiation modulate s the activation of signalling molecules downstream of the GM-CSF rece ptor.