Deoxycytidine is salvaged not only into DNA but also into phospholipid precursors. II. Ara-C does not inhibit the later process in lymphoid cells

The neuroleptic chlorpromazine inhibits the cationic and stimulates the anionic phospholipid precursor synthesis in human lymphocytes

The widely used neuroleptic drug chlorpromazine (CPZ) influences membrane functions at the levels of ionic channels and receptors as shown. Here we show the effect of short term treatments by CPZ (30 microM), on the nucleotide-containing phospholipid precursors in human lymphocyte primary cultures. During 60 minutes incubation of the cells, the CDP-ethanolamine (CDP-EA) content was only slightly reduced (87 to 76 pmol/10(6) cells), the amount of CDP-choline (CDP-Ch) was inhibited totally (from 25 to 0 pmol) upon the treatment with 30 microM CPZ under the same conditions. It has been shown earlier, that dCTP can be used as well as CTP for biosynthesis of phospholipids. Thus, the separation of the corresponding ribo- and deoxyribo-liponucleotides was developed. CPZ almost completely inhibited the synthesis of both dCDP-EA and dCDP-Ch under the same conditions The synthesis of the activated liponucleotide precursors, can be measured by incorporation of extracellular 14C-dCyt into both dCDP-EA and dCDP-Ch, as shown earlier. While the cationic deoxyribo-liponucleotide content (dCDP-Ch, dCDP-EA) was decreased, the labelling of the anionic phospholipid precursor dCDP-diacylglycerol (dCDP-DAG) was enhanced several times, it could be labelled only in the presence of CPZ from 14C-dCyd. Thus, a principal disturbance of the membrane phospholipid synthesis is presented (i.e., inhibition of the cationic and enhancement of the anionic dCDP-DAG synthesis). This profound influence on the membrane phospholipids by chlorpromazine, might be the primary effect that contributes to the wide spectrum of CPZ effects on neuronal cells.

Synergic stimulation of arabinosylcytosine induced apoptosis in mouse thymocytes by cyclic AMP

Previous studies demonstrated that arabinosylcytosine (ara-C) induced internucleosomal DNA fragmentation and cell death in mouse thymocytes and that those were inhibited by 1-(5-iso-quinoline-sulfonyl)-2-methylpiperazine hydrochloride, an inhibitor of protein kinases. In the present study, we examined the relationship between the DNA fragmentation induced by ara-C and that by agents which activate intracellular signaling and induce apoptosis in mouse thymocytes. 12-O-tetradecanoyl 13-acetate, a phorbol ester capable of activating protein kinase C or A23187, a calcium ionophore, had no effect on ara-C induced DNA fragmentation. However, ara-C induced DNA fragmentation was synergistically enhanced by cAMP and cAMP receptor agonists. Ara-C inhibited the incorporation of choline into the acid soluble and lipid fractions, and cAMP enhanced this inhibition, suggesting that ara-C metabolites interfere with membrane phospholipid metabolism, partly evoking a certain cellular signaling for apoptosis and interacting with cAMP-evoked signaling.

Compartmentation of dCTP pools disappears after hydroxyurea or araC treatment in lymphocytes

The calculated rate of DNA synthesis using [5-3H]TdR was about 4 times higher than in the case of [5-3H]CdR labeling, even after correction for the specific radioactivities of the intracellular pools. These data show a compartmentation of dCTP pools in lymphocytes. Hydroxyurea increased the specific activities of both dTTP and dCTP pools so that the calculated rate of DNA synthesis became equal. The same effect was found for araC treatment, but not for fluorodeoxyuridine. dCTP was supplied from CTP which is the lowest ribonucleotide pool in lymphocytes. Different functions of the two dCTP pools are proposed: one serving DNA replication; the other one supplies phospholipid precursors and DNA repair.

Regulation of c-jun gene expression in HL-60 leukemia cells by 1-beta-D-arabinofuranosylcytosine. Potential involvement of a protein kinase C dependent mechanism

1-beta-D-Arabinofuranosylcytosine (ara-C) is an effective chemotherapeutic agent that incorporates into DNA and results in DNA fragmentation. Recent work has demonstrated that ara-C transiently induces expression of the c-jun immediate early response gene. The present studies in HL-60 myeloid leukemia cells extend these findings by demonstrating that the increase in c-jun mRNA levels at 6 h of ara-C treatment is regulated by a transcriptional mechanism. In contrast, the subsequent down-regulation of c-jun expression is controlled by a posttranscriptional decrease in the stability of the c-jun transcripts. Previous work in phorbol ester treated cells has indicated that c-jun expression is regulated by the activation of protein kinase C. The present results demonstrate that protein kinase C activity is increased in ara-C-treated cells. This increase was maximal at 60 min and remained detectable through 6 h of ara-C exposure. Moreover, the induction of c-jun transcripts by ara-C was inhibited by the isoquinolinesulfonamide derivative H7, but not by HA1004, suggesting that this effect is mediated by protein kinase C. Ara-C-induced c-jun expression was also inhibited by staurosporine, another inhibitor of protein kinase C. Taken together, these results indicate that the cellular response to ara-C includes the activation of protein kinase C and that ara-C potentially induces c-jun transcription by a protein kinase C dependent signaling mechanism.

Deoxycytidine is salvaged not only into DNA but also into phospholipid precursors. III. dCOP-diacylglycerol formation in tonsillar lymphocytes

In addition to the water-soluble deoxyliponucleotides (Spasokukotskaja et al. (1988), Biochem. Biophys. Res. Commun. 155, 923), a lipid compound was shown to be labeled from external 3H-deoxycytidine (5-3H-CdR) in infant tonsillar lymphocytes. Chlorpromazine enhanced the labeling of this compound, identified by TLC as 3H-dCDP-diacylglycerol (3H-dCOP-DAG). The deoxynucleotide salvage pathway seems to be the main source for dCDP-DAG synthesis, as hydroxyurea increased its labeling from CdR. myo-Inositol induced the disappearance of 5-3H-dCOP-DAG, suggesting its utilization for phosphatidylinositol synthesis. 3H-Arabinosyl-Cytosine (araC) is also incorporated into the lipidic fraction at a rate comparable to its incorporation into DNA, supporting the effect of araC on membrane functions.