Relationship between differentiation mechanisms involving cAMP-dependent protein kinase and protein kinase C in uninduced and differentiating HL-60 cells.

The influence of protein kinases on the differentiation of a human promyelocytic leukemia-cell line HL-60 to granulocytes was studied by using H8 and staurosporine as inhibitors of PKA and PKC respectively. In order to determine the significance of these protein kinases of uninduced and differentiating cells for the final differentiation, the cells were treated with the inhibitors before (-24 hours-0 hours) and after induction (0 hour-96 hours) of differentiation. To elucidate potential "cross-talking" between PKA and PKC of uninduced and differentiating HL-60 cells, the effects of H8 and staurosporine on differentiation were further examined by exposing the cells, pretreated with inhibitors for approximately one cell cycle time before induction, to the same or a different inhibitor. The results demonstrated that the effects of the inhibition of protein kinases of these cells on differentiation are protein kinase and inducer dependent. There is also inducer-dependent "cross-talk" between the differentiation mechanisms involving PKA and PKC activities in uninduced HL-60 cells and in cells induced to differentiate by dbcAMP or RA. However, the data also demonstrate that the PKC activity of uninduced cells involved in the differentiating mechanisms is not related to the PKC activity of dbcAMP-mediated differentiation and PKA is not related to PKC, respectively, in RA-mediated differentiation. The effects of the pretreatment of HL-60 cells with dbcAMP or RA for 24 hours on their subsequent differentiation induced by dbcAMP or RA are different. The pretreatment of cells with dbcAMP strongly potentiates RA-mediated differentiation, while the pretreatment with RA suppresses twofold dbcAMP-mediated differentiation.