Selective activation of specific PKC isoforms dictating the fate of CD14⁺ monocytes towards differentiation or apoptosis

In this study, phorbol-12-myristate-13-acetate (PMA) at low concentrations (+ monocytes into monocyte-derived macrophages (MDMs) while PMA at high concentrations (>100-nM; H-PMA) causes the apoptosis of these cells. The pre-treatment with Go6976 (a PKC-α/β₁ selective inhibitor), not anilinemonoindolylmaleimide [a PKC-β inhibitor (PKC-β inh.)], significantly (P-+ monocytes. On the other hand, either of the above two PKC inhibitors is capable of suppressing the H-PMA-induced apoptosis of CD14⁺ monocytes. However, only the inclusion of PKC-β inh., not Go6976, prevents the cells from serum deprivation-induced cell apoptosis. Although the membrane translocation of conventional PKC-α, β₁, and β₂ isoforms was observed in the H-PMA-treated CD14⁺ monocytes, only PKC-β₂ exhibits a mitochondrial translocation activity among those PKCs responsive to H-PMA treatment. Moreover, the activation of DEVD-dependent caspases (DEVDase) was also detected in the H-PMA-treated CD14⁺ monocytes, indicating the involvement of a caspase-dependent signaling pathway in the H-PMA-induced cell apoptosis of CD14⁺ monocytes. Together with our previous findings that the selective activation of PKC-α or PKC-β₁ induces the differentiation of CD14⁺ monocytes into MDMs or dendritic cells (MoDCs), respectively, the results in this study further demonstrate that PKC-β₂ activation is responsible for relaying the apoptotic signal to intrinsic mitochondria-dependent caspase signaling cascades in the CD14⁺ monocytes. It is likely that the selective activation of specific PKC isoforms provides a new strategy to manipulate the differential cell fate commitment of multipotent CD14⁺ monocytes towards apoptosis or differentiation into MDMs, MoDCs, and other cell types.