Effect of nuclear Ca2+ uptake inhibitors on Ca(2+)-activated DNA fragmentation in rat liver nuclei

Functional role of phospholipids in the nuclear events

This review presents the structural and functional role of phospholipids in chromatin and nuclear matrix as well as the difference in composition and turnover compared to those present in the nuclear membrane. Nuclei have a very active lipid metabolism which seems to play an important role in the transduction of the signals to the genome in response to agonists acting at the plasma membrane level. The evidence on the presence of phospholipid-calcium-dependent protein kinase C (PKC) in nuclei and enzymes of phospholipids turnover is given. Protein kinase C interacts with nuclear phosphoinositol and sphingomyelin cycles products. This fact evidences about possibility that signal transduction events could also occur at the nuclear level during induction of cell proliferation, differentiation and apoptosis.

Nuclear calcium release by InsP3-receptor channels plays a role in meiosis reinitiation in the mouse oocyte

Our purpose was to investigate the presence of nuclear specific elements of the phosphoinositide pathway, and the link between nuclear calcium events and the first step of meiosis resumption, i.e. germinal vesicle breakdown (GVB) in mouse immature oocytes. Using confocal laser scanning microscopy, we analyzed the effects of nuclear microinjection of inositol 1,4,5-trisphosphate (InsP3), heparin and anti-InsP3 receptor monoclonal antibodies on both spontaneous nuclear and cytoplasmic calcium oscillations, as well as the effects of these components on the GVB. First we observed that nuclear Ca2+ events were dependent upon both nucleoplasmic and cytoplasmic InsP3 levels, highlighting a cross-talk between the GV and the cytoplasm concerning the Ca2+/InsP3 pathway. We demonstrated also that: 1) type 1 InsP3 receptors were localized at the nuclear membrane level while type 3 were absent from the nucleus; 2) calcium release from nuclear stores was mediated by type 1 rather than type 3 InsP3 receptor associated channels; 3) the anti-InsP3 R-1 mAB microinjected into the nucleus inhibited the GVB. These results demonstrate that reinitiation of meiosis requires an increase in nuclear phosphoinositide dependent Ca2+. Thus, the role of nuclear Ca2+ homeostasis is discussed with particular emphasis on nuclear envelope dynamics.

Presence of zinc and calcium permeant channels in the inner membrane of the nuclear envelope

The nuclear envelope possesses specific ion channels that regulate the ionic traffic between the cytoplasm or the perinuclear space and the nucleoplasm. Using the patch-clamp technique to isolated rat nuclei exhibiting only the inner membrane of the nuclear envelope, we report the existence of calcium and zinc permeant channels. These channels displayed similar characteristics (conductance : 8 and 11 pS respectively, open time constant (3.5 ms and 3.7 ms) and close time constant (5.1 ms and 4.8 ms)) and were insensitive to different types of calcium channels blockers and to calcium concentration in the bathing solution. The exact role of these channels remains to define, but they may contribute to the regulation of intranuclear Ca++ or Zn++ dependent processes as important as cell proliferation or programmed cell death. Moreover, this work demonstrates that our nuclei preparation provides a way to study the inner membrane of the nuclear envelope.

Effect of apoptosis-related compounds on Ca2+ transport system in isolated rat liver nuclei

The effect of various inhibitors of DNA topoisomerase II, which has been shown to induce apoptotic cell death, on Ca2+ transport in isolated rat liver nuclei was investigated. Ca2+ uptake and release were determined with a Ca2+ electrode. The presence of aurintricarboxylic acid (ATA; 10(-6) to 10(-4) M), etoposide (10(-4) M), genistein (10(-5) and 10(-4) M) or amsacrine (10(-4) M) in the reaction mixture caused a significant increase in Ca2+ release from the nuclei. Also, these compounds (10(-4) M) significantly inhibited Ca2+ uptake by the nuclei. However, the presence of ATA (10(-5) and 10(-4) M) in the enzyme reaction mixture did not significantly inhibit Ca2+-ATPase activity, which is involved in the nuclear Ca2+ uptake, in the liver nuclei, while etoposide (10(-4) M), genistein (10(-4) M) and amsacrine (10(-4) M) appreciably decreased the enzyme activity. Meanwhile, addition of Ca2+ clearly activated DNA fragmentation in the liver nuclei. The Ca2+ activated DNA fragmentation was significantly prevented by the presence of etoposide, genistein and amsacrine with the concentrations of 10(-5) and 10(-4) M in the reaction mixture, although ATA (10(-5) and 10(-4) M) had no effect. The present study demonstrates that some apoptosis inducible compounds used can influence on Ca2+ transport system in isolated rat liver nuclei, suggesting a decrease of nuclear Ca2+ level involved in nuclear functions.