Monocytic differentiation of HL-60 cells is characterized by the nuclear translocation of phosphatidylinositol 3-kinase and of definite phosphatidylinositol-specific phospholipase C isoforms

Immunochemical and immunocytochemical data indicate that nuclei of HL-60 ce lls contain different enzymes involved in the phosphoinositide cycle, such as PI 3-H and the phosphatidylinositol-specific PLC isoforms beta 3, gamma 1 and gamma 2, These enzymes translocate differently to the nuclear fractio n when HL-60 cells are treated with differentiating doses of vitamin D3: PI 3-K translocated progressively to the nucleus in parallel with full differ entiation until 96 hours. PLC beta 3 increased until 72 hours of treatment and then lowered its intranuclear amount and PLC gamma 1 was unchanged at a ll the examined times. PLC gamma 2 nuclear translocation increased progress ively until 96 hours of vitamin D3 administration. A fourth PLC isozyme, be ta 2, present in the cytoplasm of untreated cells, translocates to the cyto plasm after vitamin D3 addition and reaches the highest concentration at th e end of monocytic differentiation. Terminal monocytic differentiation was characterized at the nuclear level by high levels of PI 3-K and PLC gamma 2 and by the novel expression of PLC beta 2, We then observed that the xi is oform. of PKC, constitutively present in nuclei of HL-60 cells, translocate d to the nucleus when cells were induced to differentiate along the monocyt ic lineage, but the nuclear translocation of PKC xi was blocked as a conseq uence of PI 3-K inhibition by Wortmannin. These findings indicate that the main components of the noncanonical and canonical inositol lipid signal tra nsduction pathways, including PI 3-K, PLC beta 2 and beta 3, PLC gamma 2, u ndergo nuclear translocation and may therefore play a relevant role during monocytic differentiation at the nuclear level. Furthermore, PKC xi nuclear translocation appears to be related to PI 3-K activity. (C) 1999 Academic Press.