engleski

Presence and activation of nuclear phosphoinositide 3-kinase C2beta during compensatory liver growth.

Highly purified liver nuclei incorporated radiolabeled phosphate into phosphatidylinositol 4-phosphate (PtdIns(4)P), PtdIns(4, 5)P(2), and PtdIns(3, 4, 5)P(3). When nuclei were depleted of their membrane, no radiolabeling of PtdIns(3, 4, 5)P(3) could be detected showing that within the intranuclear region there are no class I phosphoinositide 3-kinases (PI3K)s. In membrane- depleted nuclei harvested 20 h after partial hepatectomy, the incorporation of radiolabel into PtdIns(3)P was observed together with an increase in immunoprecipitable PI3K-C2beta activity, which is sensitive to wortmannin (10 nm) and shows strong preference for PtdIns over PtdIns(4)P as a substrate. On Western blots PI3K-C2beta revealed a single immunoreactive band of 180 kDa, whereas 20 h after partial hepatectomy gel shift of 18 kDa was noticed, suggesting that observed activation of enzyme is achieved by proteolysis. When intact membrane-depleted nuclei were subjected to short term (20 min) exposure to micro-calpain, similar gel shift together with an increase in PI3K-C2beta activity was observed, when compared with the nuclei harvested 20 h after partial hepatectomy. Moreover, the above-mentioned gel shift and increase in PI3K-C2beta activity could be prevented by the calpain inhibitor calpeptin. The data presented in this report show that, in the membrane-deplet nuclei during the compensatory liver growth, there is an increase in PtdIns(3)P formation as a result of PI3K-C2beta activation, which may be a calpain-mediated event.

compensatory liver growth ; liver nuclei ; phosphoinositide 3-kinase C2beta ; phosphatidylinositol 4-phosphate ; phosphatidylinositol 4 ; 5-bisphosphate ; phosphatidylinositol 3 ; 4 ; 5-trisphosphate

nije evidentirano