Modulation of apoptosis of proliferating and differentiating HL-60 cells by protein kinase inhibitors: suppression of PKC or PKA differently affects cell differentiation and apoptosis

The relationship between RA- or dbcaMP-mediated differentiation and subsequ ent apoptosis in HL-60 cells was assessed by modulating the levels of diffe rentiation suppressing the activity of PKC and PKA with calphostin C or GF 109203X and H89, respectively. Results demonstrated that (1) RA and dbcAMP caused a dose-dependent increase in apoptosis concomitant with progressive differentiation; (2) the suppression of PKC activity resulted in an increas e of apoptosis unrelated to the modulated levels of differentiation; (3) th e inhibition of PKA decreased granulocytic differentiation, but did not sig nificantly affect apoptosis; (4) the pretreatment of cells with dbcAMP stro ngly potentiated RA-mediated differentiation without apparent changes in ap optosis; (5) cell differentiation and apoptosis were associated with cell c ycle arrest in G1 phase and G2/M phases, respectively. Our findings indicat e that the functional maturity of differentiating cells is not directly rel ated to the apoptotic programme, and suggest that induction of cell differe ntiation and apoptosis are regulated by separate mechanisms in which PKC an d PKA are involved.