A Role for Nuclear Phosphatidylinositol-specific Phospholipase C in the G2/M Phase Transition

Abstract

. Our data are consistent with the hypothesis that nuclear PI-PLC generates DAG to activate nuclear ␤ II PKC, whose activity is required for mitosis.The PKC 1 family of enzymes is involved in the transduction of external signals from many growth factors, cytokines, and hormones (reviewed in Refs. 1-3). Many of the details of the receptor-mediated signaling pathways that lead to PKC activation have been elucidated (2, 3). A common feature of these pathways is receptor-mediated activation of lipid-metabolizing enzymes that generate DAG. DAG in turn activates PKC family members. The best characterized of these pathways involves the activation of phosphatidylinositol-specific phospholipase C (PI-PLC) activity (4). Two major classes of cellular receptor utilize the PI-PLC/PKC activation pathway. Growth factor receptors containing intrinsic tyrosine kinase activity activate PI-PLC ␥ isoforms through direct tyrosine phosphorylation and activation of the enzyme (4). Many G-protein-coupled receptors activate PI-PLC␤ isoforms through direct interaction with heterotrimeric G-proteins of the G q class (4). Activation of PI-PLC enzymes leads to generation of inositol trisphosphate and DAG, two metabolites of phosphatidylinositol 4,5-bisphosphate that stimulate intracellular calcium release and activate PKC isozymes, respectively. Extracellular ligands can also stimulate activation of phosphatidylcholine-specific phospholipase C (PC-PLC) and/or phospholipase D (PLD) activities (5). These phospholipases can give rise to increased cellular DAG levels and PKC activation, including the novel, calcium-independent isozymes (3). More recently, it has been demonstrated that phosphatidylinositol 3,4,5-trisphosphate, a product of growth factor receptor-activated PI3 kinase, can directly and selectively activate the atypical PKC isozymes (6 -10). Elucidation of these pathways has enhanced our understanding of how lipid metabolism and PKC activation are coupled to acute growth factor and hormone actions, including mitogenesis.In addition to its well established role in acute mitogenic signaling, PKC has also been implicated in intrinsic signaling pathways, including those involved in cell cycle control (1). We recently demonstrated that activation of the ␤ II PKC isoform at the nucleus is both cell cycle-regulated and necessary for entry of cells into mitosis (11-16). At the nucleus, ␤ II PKC directly phosphorylates the nuclear envelope polypeptide lamin B at sites involved in mitotic nuclear lamina disassembly (12,16). Inhibition of nuclear PKC activity leads to cell cycle arrest in the G 2 phase, indicating the importance of nuclear PKC in mitotic events (16). Although it is clear that nuclear PKC activity is cell cycle-regulated, the basis for this regulation is not clear. In the present study, we report that nuclear DAG levels fluctuate during cell cycle and that changes in nuclear DAG levels correlate with cell cycle progression through the G 2 /M phase. Furthermore, a nuclear PI-PLC activity has been identified that is active durin...

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

“…Like nuclear PLC-␤1, the cytoplasmic enzyme appears to be involved in the resumption of meiosis. This is in agreement with the role of nuclear phospholipase C in mitosis in leukemic cells (Sun et al, 1997) and during meiosis in Xenopus oocytes (Carnero and Lacal, 1993). However, the activation of PLC by G-protein ␣q subunit is not an absolute requirement for maturation of Xenopus oocytes (Guttridge et al, 1995).…”

Mammalian phospholipid homeostasis: Homeoviscous adaptation deconstructed by lipidomic data driven modelling

“…However, the coincidence of elevated PI species with the G2/M phase suggests they are associated with the PI-PLC cycle, cellular division (Sun et al, 1997) and nuclear signalling, detailed data driven modelling studies of the lipid composition of the nuclear envelope will be needed to further investigate this possibility.…”

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

“…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). Therefore, a certain physiological role of G 2 /M-associated nuclear PI-PLC activation was suggested as the phosphorylation of lamins is known to precede nuclear envelope breakdown at the beginning 11 of the mitosis.…”

“…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).…”

“…The majority of PI-PLC-β 1 is probably not located in the nuclear envelope as the activity of PI-PLC-β 1 is present in both whole nuclei (21,40) and nuclei treated with different concentrations of detergents in order to remove the nuclear membrane (21,25,48,68,75,77). In rat liver nuclei, fractionation experiments indicated that both PI-PLC-β 1 and PI-PLC-γ 1 persisted in nuclear matrix and lamina, obtained after nuclease digestion and extraction with high salt and detergent (6).…”