Granulocyte colony-stimulating factor promotes the translocation of protein kinase Cι in neutrophilic differentiation cells

Previously, we suggested that the phosphatidylinositol 3-kinase (PI3K)-p70 S6 kinase (p70 S6K) pathway plays an important role in granulocyte colony-stimulating factor (G-CSF)-dependent enhancement of the neutrophilic differentiation and proliferation of HL-60 cells. While atypical protein kinase C (PKC) has been reported to be a regulator of p70 S6K, abundant expression of PKCι was observed in myeloid and lymphoid cells. Therefore, we analyzed the participation of PKCι in G-CSF-dependent proliferation. The maximum stimulation of PKCι was observed from 15 to 30 min after the addition of G-CSF. From 5 to 15 min into this lag time, PKCι was found to translocate from the nucleus to the membrane. At 30 min it re-translocated to the cytosol. This dynamic translocation of PKCι was also observed in G-CSF-stimulated myeloperoxidase-positive cells differentiated from cord blood cells. Small interfering RNA for PKCι inhibited G-CSF-induced proliferation and the promotion of neutrophilic differentiation of HL-60 cells. These data indicate that the G-CSF-induced dynamic translocation and activation processes of PKCι are important to neutrophilic proliferation. J. Cell. Physiol. 211: 189–196, 2007. © 2006 Wiley-Liss, Inc.