IDENTIFICATION OF PI-PLC BETA-1, GAMMA-1, AND DELTA-1 IN RAT-LIVER - SUBCELLULAR-DISTRIBUTION AND RELATIONSHIP TO INOSITOL LIPID NUCLEAR SIGNALING

The subcellular distribution of PI-PLC beta 1, gamma 1, and delta 1 ha s been investigated in rat liver by western blot and immunohistochemic al analysis with a panel of isoform-specific antibodies. The data obta ined in situ on cryo-sectioned tissue indicate that PI-PLC beta 1 is p redominantly nuclear, while gamma 1 is largely cytoplasmic and delta 1 is sharply restricted to the cytoplasm. In fractionation experiments, the Western blot analysis indicated that the recovery of the nuclear isoforms beta 1 and gamma 1 was not affected by the removal of the nuc lear membrane, and that the two enzymes persisted in nuclear matrix an d lamina, obtained after nuclease digestion and extraction with high s alt and detergent. The assay of the phosphodiesterase activity in diff erent cell fractions correlates with the observed relative abundance o f the enzymes, and specific inhibition with neutralizing anti-beta 1 a nd -gamma 1 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 dis crete intracellular distribution, and suggest that PI-PLC beta 1 and g amma 1 play a central role in modulating the nuclear phosphoinositide cycle.