Changes in the components of a nuclear inositide cycle during differentiation in murine erythroleukaemia cells.

Differentiation of murine erythroleukaemia cells with the chemical agent DMSO leads to a cessation of proliferation and the production of a number of erythrocyte markers such as haemoglobin. We have previously demonstrated that activation of proliferation leads to an increase in the production of nuclear diacylglycerol (DAG). Here we demonstrate that differentiation leads to a decrease in the levels of nuclear DAG and the activity of the nuclear-associated phosphoinositidase C (PIC). The change in activity appears to be due to a decrease in the mass levels of the beta 1 isoform, as demonstrated by the use of isoform-specific antibodies. Moreover, the changes correlate with the cessation of proliferation and an increase in the number of cells in G1 phase of the cell cycle, rather than with the number of cells which have differentiated. Indeed, although treatment of the cells with phorbol 12-myristate 13-acetate (PMA) inhibits the differentiation programme as assessed by haemoglobin staining, it does not inhibit the number of cells blocking in G1 of the cell cycle or the changes in nuclear DAG or PIC activity. The possible involvement of this nuclear inositide cycle during progression through the cell cycle is discussed.