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-depleted 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.
Department of Physiology and Croatian Institute for Brain Research, School of Medicine, University of Zagreb, Salata 3, Zagreb 10,000, Croatia.
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Sindić
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Aleksandrova
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Volinia
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Banfić
D000818:Animals; D002467:Cell Nucleus / Q000201:enzymology; D004789:Enzyme Activation; D008115:Liver Regeneration; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction
D019869:Phosphatidylinositol 3-Kinases