Nuclear localization and signalling activity of phosphoinositidase Cβ in Swiss 3T3 cells

Abstract

The hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) is a widespread receptor-coupled signalling system at the plasma membrane of most eukaryotic cells. The existence of an entirely separate nuclear phosphoinositide signalling system is suggested from evidence that purified nuclei synthesize PtdInsP2 and phosphatidylinositol 4-phosphate (PtdInsP) in vitro and that a transient decrease in the mass of these lipids occurs when Swiss 3T3 cells are cultured in the presence of insulin-like growth factor-1 (IGF-1). These IGF-1-dependent changes in inositol lipids coincide with an increase in nuclear diacyglycerol and precede translocation to the nucleus and activation of protein kinase C (refs 5, 6). Circumstantial evidence that links these changes with mitosis comes from the isolation of a 3T3 clone that expresses the type-1 IGF receptor and binds IGF-1 peptide but does not respond mitogenically or show transient mass changes in nuclear inositol lipids. A key question is how IGF-1 initiates the rapid breakdown of PtdInsP and PtdInsP2 in the nucleus. Here we present evidence that nuclei of 3T3 cells contain the beta-isozyme of phosphoinositidase C, whereas the gamma-isozyme is confined to the cytoplasm and that IGF-1 treatment stimulates exclusively the activity of nuclear phosphoinositidase C.

Cytoplasmic and Nuclear Phospholipase C-β1 Relocation: Role in Resumption of Meiosis in the Mouse Oocyte

“…It has been proposed that phosphatidylinositol-transfer proteins deliver phosphatidylinositol to lipid kinases to yield phosphatidylinositol 4,5-biphosphate (PIP2) as a substrate for PLC-␤ (Thomas et al, 1993). It has also been shown that the enzymes responsible for the metabolism of inositol lipids and present in the nuclei of several cell types are the ␤1-and ␤2-isoforms of PLC (Martelli et al, 1992;Divecha et al, 1993b;Zini et al, 1993Zini et al, , 1994Bertagnolo et al, 1997). PLC-␤1 has been demonstrated in mouse oocytes by using polymerase chain reaction (Dupont et al, 1996).…”

Terminal deoxynucleotidil transferase is a nuclear PKC substrate

“…SDS-polyacrylamide gel electrophoresis followed by autoradiography revealed a major labeled band of 58 kDa corresponding, as observed in vitro phosphorylation, to the high molecular weight form of TdT (Fig. 3, [31,32] and can be downregulated in KM-3 cells after 24 h of PMA treatment (pers. data).…”

“…Since TdT and PKC colocalize in the interchromatin domains ( [12,15,23,[29][30][31][32][33] and pers. data), we tested TdT as a substrate for PKC.…”

Nuclear phospholipid signaling: phosphatidylinositol-specific phospholipase C and phosphoinositide 3-kinase

“…2. 3.1. Nuclear phospholipase C-β 1 IGF-mediated PtdIns(4,5)P 2 hydrolysis and DAG generation in membrane-depleted nuclei of Swiss 3T3 cells pointed to the possible involvement of phospholipase C (20), and the activation of the nuclear PI-PLC-β 1 in response to IGF-I was later confirmed (46,47). In vivo model of regenerating rat liver showed the similar increase in the level of the nuclear DAG 20 hours after partial hepatectomy (5).…”

“…IGF-mediated increase in the level of nuclear DAG and the activity of PI-PLC that was described 15 years ago (20,46) When aphidicolin-synchronized HL-60 cells were released from the block and allowed to progress synchronously through the cell cycle, a PI-PLC inhibitor-sensitive increase in the level of DAG was observed in nuclei 8 h after release from the block that corresponded to G 2 /M phase of the cell cycle (68). In addition, the presence of the PI-PLC inhibitor delayed the progression of the cells through G 2 /M phase and correlated with translocation of PKC-βΙΙ that was previously shown to phosphorylate lamins (29,68,71).…”