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J. Biol. Chem., Vol. 276, Issue 21, 17754-17761, May 25, 2001
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From the Highly purified liver nuclei incorporated
radiolabeled phosphate into phosphatidylinositol 4-phosphate
(PtdIns(4)P), PtdIns(4,5)P2, and
PtdIns(3,4,5)P3. When nuclei were depleted of their
membrane, no radiolabeling of PtdIns(3,4,5)P3 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-C2
Presence and Activation of Nuclear Phosphoinositide 3-Kinase
C2
during Compensatory Liver Growth*
i
§,
§,
, and
**
Department of Physiology and Croatian
Institute for Brain Research, School of Medicine, University of Zagreb,
Salata 3, Zagreb 10,000, Croatia, the ¶ Sealy Center for
Cancer Cell Biology, University of Texas Medical Branch, Galveston,
Texas 77555-1048, and the
Dip. di Morfologia ed Embriologia,
Universita degli Studi, Via Fossato di Mortara 64/b, Ferrara 44100, Italy
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-C2
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 µ-calpain, similar gel shift together with an increase in
PI3K-C2
activity was observed, when compared with the nuclei
harvested 20 h after partial hepatectomy. Moreover, the
above-mentioned gel shift and increase in PI3K-C2
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-C2
activation, which may be a calpain-mediated event.
*
This work was supported by the Ministry of Science of the
Republic of Croatia (to H. B.), by a Fogarty International Research Collaboration Award (to A. P. F. and H. B.), and by the AIRC
(to S. V.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
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