Identification of PI-PLC β1, γ1, and δ1 in rat liver: Subcellular distribution and relationship to inositol lipid nuclear signalling

Abstract

The subcellular distribution of PI-PLC β1, γ1, and δ1 has been investigated in rat liver by western blot and immunohistochemical analysis with a panel of isoform-specific antibodies. The data obtained in situ on cryo-sectioned tissue indicate that PI-PLC β1 is predominantly nuclear, while γ1 is largely cytoplasmic and δ1 is sharply restricted to the cytoplasm. In fractionation experiments, the Western blot analysis indicated that the recovery of the nuclear isoforms β1 and γ1 was not affected by the removal of the nuclear membrane, and that the two enzymes persisted in nuclear matrix and lamina, obtained after nuclease digestion and extraction with high salt and detergent. The assay of the phosphodiesterase activity in different cell fractions correlates with the observed relative abundance of the enzymes, and specific inhibition with neutralizing anti-β1 and -γ1 isoforms confirms that these are the enzymes active at the nuclear level. These results demonstrate that in rat liver cells, as in other cell types, different members of the PI-PLC family show a discrete intracellular distribution, and suggest that PI-PLC β1 and γ1 play a central role in modulating the nuclear phosphoinositide cycle.