Figure 4.

Differential involvement of PKC in HL-60 cell differentiation induced by ATRA and sesquiterpene lactone compounds. (a) HL-60 cells were treated for 40 min with various concentrations of PKC inhibitors (GF 109203X or H 7), followed by incubation for 72 h with 50 nM ATRA alone, or in combination with 1 μM helenalin (HT) or 10 μM of costunolide (CT), parthenolide (PT) or sclareolide (SC). Cell differentiation was assessed by the NBT reduction assay. Each value represents the mean±s.e.mean (n=3). (b) HL-60 cells were treated with 50 nM ATRA alone or in combination with 1 μM HN, or 10 μM of CT, PT or SC and total PKC activity in the treated cells was measured. (c) The levels of conventional PKC isoforms were determined by western blot analysis. The experiment was repeated at least two times with similar results. (d) Densitometric analysis of the protein band intensities in immunoblots shown in panel c. The data are expressed as a relative density of the bands representing the ATRA+sesquiterpene lactone combination groups to that of the corresponding ATRA alone treatment groups. The values are presented as the means±s.e.mean (n=3). ^*P<0.05, relative to a group treated with ATRA alone.