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 of the differentiation of a human pro myelocytic leukemia cell line HL-60 to granulocytes was studied by usi ng H8 and staurosporine as inhibitors of PKA and PKC respectively. In order to determine the significance of these protein kinases of unindu ced and differentiating cells for the final differentiation, the cells were treated with the inhibitors before (-24 hours - 0 hour) and afte r induction (0 hour - 96 hours) of differentiation. To elucidate poten tial ''cross-talking'' between PKA and PKC of uninduced and differenti ating HL-60 cells, pretreated with inhibitors for approximately one ce ll 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 indu cer dependent. There is also inducer-dependent ''cross-talk'' between the differentiation mechanisms involving PKA and PKC activities in uni nduced HL-60 cells and in cells induced to differentiate by dbcAMP or RA. However, the data also demonstrate that the PKC activity of unindu ced cells involved in the differentiating mechanisms is not related to the PKC activity of dbcAMP-mediated differentiation and PKA is not re lated to PKC, respectively, in RA-mediated differentiation. The effect s of the pretreatment of HL-60 cells with dbcAMP or RA for 24 hours on their subsequent differentiation induced by dbcAMP and RA are differe nt. The pretreatment of cells with dbcAMP strongly potentiates RA-medi ated differentiation, while the pretreatment with RA suppresses twofol d dbcAMP-meidated differentiation.