Monocytic Differentiation of HL-60 Cells Is Characterized by the Nuclear Translocation of Phosphatidylinositol 3-Kinase and of Definite Phosphatidylinositol-Specific Phospholipase C Isoforms

Abstract

Immunochemical and immunocytochemical data indicate that nuclei of HL-60 cells contain different enzymes involved in the phosphoinositide cycle, such as PI 3-K and the phosphatidylinositol-specific PLC isoforms β3, γ1 and γ2. These enzymes translocate differently to the nuclear fraction when HL-60 cells are treated with differentiating doses of vitamin D3: PI 3-K translocated progressively to the nucleus in parallel with full differentiation until 96 hours. PLC β3 increased until 72 hours of treatment and then lowered its intranuclear amount and PLC γ1 was unchanged at all the examined times. PLC γ2 nuclear translocation increased progressively until 96 hours of vitamin D3 administration. A fourth PLC isozyme, β2, present in the cytoplasm of untreated cells, translocates to the cytoplasm after vitamin D3 addition and reaches the highest concentration at the end of monocytic differentiation. Terminal monocytic differentiation was characterized at the nuclear level by high levels of PI 3-K and PLC γ2 and by the novel expression of PLC β2. We then observed that the ξ isoform of PKC, constitutively present in nuclei of HL-60 cells, translocated to the nucleus when cells were induced to differentiate along the monocytic lineage, but the nuclear translocation of PKC ξ was blocked as a consequence of PI 3-K inhibition by Wortmannin. These findings indicate that the main components of the noncanonical and canonical inositol lipid signal transduction pathways, including PI 3-K, PLC β2 and β3, PLC γ2, undergo nuclear translocation and may therefore play a relevant role during monocytic differentiation at the nuclear level. Furthermore, PKC ξ nuclear translocation appears to be related to PI 3-K activity.