Protein kinase C isoforms in normal and leukemic neutrophils: altered levels in leukemic neutrophils and changes during myeloid maturation in chronic myeloid leukemia

Abstract

Protein kinase C (PKC) is reported to play a role in maturation of the myeloid cell and functions of the mature neutrophil. The neutrophils in chronic myeloid leukemia (CML) exhibit defects in several functions. As a step towards understanding the role of PKC in the defects in function of the leukemic cells, this study investigates the expression of PKC isoforms, their subcellular distribution, levels and kinase activity in the normal and leukemic neutrophils. It also investigates changes in representative PKC isoforms during myeloid maturation. This study confirms the presence of PKC α, β and δ and shows, for the first time, the presence of non conventional PKC isoform θ, atypical PKC isoform λ/ι and PKC isoform μ in normal human neutrophils. In unstimulated cells all the detected PKC isoforms showed a predominantly cytosolic localisation in normal and CML neutrophils. Cytosol-membrane distribution of PKC α and δ were significantly altered in leukemic neutrophils as compared to normal cells. Cytosolic levels of all PKC isoforms were reduced in CML neutrophils with PKC α, β, I, θ, and μ showing a significant decrease. Cytosolic levels of PKC δ contrary to the trend observed for other PKC isoforms showed a slight increase in CML cells, while its membrane levels were significantly reduced in CML neutrophils. Total PKC kinase activity in CML neutrophil cytosol was significantly reduced, while specific kinase activity of two representative isoforms, PKC α and δ, from normal and CML neutrophils were similar, thereby increasing the significance of the altered levels of PKC isoforms in CML, and highlighting their role in the defects in function exhibited by the leukemic neutrophils. The levels of PKC δ and ι increased and decreased respectively as the leukemic myeloid cell matured from the blast to the neutrophil, while the levels of PKC α and β were not altered. This suggests a role for PKC δ and ι in the maturation of the leukemic myeloid cell.