Activation of phosphoinositide 3-kinase C2β in the nuclear matrix during compensatory liver growth

In the nuclear matrix harvested 20 h after partial hepatectomy, an increase in immunoprecipitable PI3K-C2β activity is observed, which is sensitive to wortmannin (10 Mm) and shows strong preference for PtdIns over PtdIns(4)P as a substrate. On western blots PI3K-C2β revealed a single immunoreactive band of 180 kD, whereas 20 h after partial hepatectomy gel shift of 18 kDa was noticed in the nuclear matrix, suggesting that observed activation of enzyme is achieved by proteolysis. As it is know that PI3K-C2α is associated with nuclear speckles [Didichenko SA, Thelen M. Phosphatidylinositol 3-kinase C2α contains a nuclear localization sequence and associates with nuclear speckles. J Biol Chem 2001;276:48135-42.], the data presented in this report show that in the nuclear matrix PI3K-C2β is activated during the compensatory liver growth, which clearly demonstrates that different class II PI3K enzymes have different subnuclear localization and therefore might have different intranuclear functions.