Synthesis of polyphosphoinositides in nuclei of Friend cells. Evidence for polyphosphoinositide metabolism inside the nucleus which changes with cell differentiation

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Abstract
Previous work demonstrated the existence of phosphatidylinositol kinase and phosphatidylinositol phosphate kinase in rat liver nuclei, with the suggestion that these activities are in the nuclear membrane [Smith & Wells (1983) J. Biol. Chem. 258, 9368-9373]. Here we show that highly purified nuclei from Friend cells, washed free of nuclear membrane by Triton, can incorporate radiolabel from [gamma-32P]ATP into phosphatidic acid, phosphatidylinositol phosphate and phosphatidylinositol 4,5-bisphosphate. The degree of radiolabelling of phosphatidylinositol bisphosphate is highly dependent on the state of differentiation of the cells, being barely detectable in growing cells and much greater after dimethyl sulphoxide-induced differentiation; this difference is mostly due to different amounts of phosphatidylinositol phosphate in the isolated nuclei. We suggest that polyphosphoinositides are made inside the nucleus and that they have a role in chromatin function; either the phospholipids themselves play a role, or there is a possibility of intranuclear signalling by inositide-derived molecules.

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