Phosphoinositide signaling in nuclei of friend cells: Tiazofurin down-regulates phospholipase C β₁

Previous investigations have demonstrated the presence of conventional lipid kinases and phospholipase C (PLC) activities in nuclei of Friend erythroleukemia cells. Moreover, when Friend erythroleukemia cells are treated for 96 h with the antitumor drug tiazofurin, the induction of erythroid differentiation is accompanied by changes in amounts of both phosphatidylinositol and phosphatidylinositol 4,5-bisphosphate due to the inhibition of an uncharacterized nuclear PLC activity. Here, we show that the nuclear PLC β₁ isoform is down-regulated by tiazofurin (5 μM) treatment of Friend erythroleukemia cells as shown by both Western blot and Northern blot analyses for PLC β₁ message. This indicates that PLC β₁ down-regulation is tightly linked with erythroid differentiation of Friend erythroleukemia cells and that the autonomous nuclear signaling via inositol lipid cycle can be controlled by the antitumor drug tiazofurin.