Nuclei Of HL-60 Cells Research Articles

Development and application of a rapid and sensitive liquid chromatography-mass spectrometry method for simultaneous analysis of cytarabine, cytarabine monophosphate, cytarabine diphosphate and cytarabine triphosphate in the cytosol and nucleus

In this study, a sensitive and rapid ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was developed for the simultaneous analysis of cytarabine (ara-C), cytarabine monophosphate (ara-CMP), cytarabine diphosphate (ara-CDP) and cytarabine triphosphate (ara-CTP) in the cytosol and nucleus. The separation of analytes and endogenous interferents was achieved in 8 min on a hypercarb column (2.1 mm × 100 mm, 3 µm) by using a gradient elution with 95% acetonitrile and aqueous 5 mM hexylamine with 0.4% (v/v) diethylamine adjusted to pH 10. The analytes were detected with both negative and positive electrospray ionization in multiple reaction monitoring (MRM) mode. The calibration curve demonstrated good linearity ranging from 5 to 750 nM for ara-C, 50–7500 nM for ara-CMP, 20–3000 nM for ara-CDP and 1–150 nM for ara-CTP in the cytosol. In the nucleus, good linearity was achieved over a concentration range of 1–100 nM for ara-C, 5–500 nM for ara-CMP, 2.5–250 nM for ara-CDP and 0.5–50 nM for ara-CTP. Intra- and interbatch accuracies and precisions met the standards of validation. The matrix effect, recovery and stability were also within acceptable ranges. After incubation with 10 μM ara-C for 3 h, the levels of ara-C, ara-CMP, ara-CDP and ara-CTP in the cytosol and nucleus of HL-60 cells and HL-60/ara-C cells were determined. Most of the metabolites were found within the quantitation range. The results showed that the nuclear ara-CTP level was significantly different than the intracellular ara-CTP level between HL-60 and HL-60/ara-C cells.

Protein kinase A activation by retinoic acid in the nuclei of HL60 cells

BackgroundActivation of protein kinase A (PKA) occurs during retinoic acid (RA)-induced granulocytic differentiation of human promyelocytic leukemia HL60 cells. It is known that the RIIα regulatory subunit of PKA, is modified by RA (retinoylated) in the early stages of differentiation. We have investigated the effects of RA on PKA during cell differentiation in order to understand the potential significance of this process in the retinoylation of RIIα subunits. MethodsImmunoblotting, immunoprecipitation, confocal microscopy, PCR, and PKA activity assays were employed for characterizing the effects of RA on PKA. ResultsWe found that RA induces intracellular mobility of RIIα and the activation of PKA in HL60 cells. Increases in RIIα levels were observed in RA-treated HL60 cells. RA treatment altered intracellular localization of the PKA subunits, RIIα and Cα, and increased their protein levels in the nuclei as detected by both immunoblotting and immunostaining analyses. Coincident with the increase in nuclear Cα, RA-treated HL60 cells showed increases in both the protein phosphorylation activity of PKA and the levels of phosphorylated proteins in nuclear fractions as compared to control cells. In addition, RIIα protein was stabilized in RA-treated HL60 cells as compared to control cells. ConclusionsThese results suggest that RA stabilizes RIIα protein and activates PKA in the nucleus, with a resultant increase in the phosphorylation of nuclear proteins. General significanceOur evidence suggests that retinoylation of PKA might contribute to its stabilization and activation and that this could potentially participate in RA's ability to induce granulocytic differentiation of HL60 cells.

Generation of phosphorylated histone H2AX by benzene metabolites

Benzene is a well known environmental carcinogen which causes myeloid leukemia. DNA damage induced by benzene metabolites such as hydroquinone (HQ) and p-benzoquinone (BQ) is one reason for the leukemogenesis. In this study, we showed that treatment with HQ and BQ quickly and clearly generated phosphorylated histone H2AX (gamma-H2AX) which has been recently considered an index of the production of double strand breaks (DSBs). HQ and BQ produced discrete foci of gamma-H2AX within the nucleus of HL-60 cells in a dose-dependent manner. gamma-H2AX appeared after the treatment with HQ and BQ for 2h, and increased time-dependently up to 4-8h. HQ and BQ increased intracellular oxidation, and an antioxidant, N-acetylcysteine, clearly inhibited the phosphorylation, suggesting that reactive oxygen species produced from HQ and BQ contributed to the generation. gamma-H2AX was sensitively detected after treatment with low concentrations of HQ and BQ, compared with the direct detection of DSBs by biased sinusoidal field gel electrophoresis and with the assessment of cytotoxicity based on cell survival. DSBs are the most serious form of DNA damage and are associated with genomic instability leading to myeloid leukemia. gamma-H2AX may be a useful tool for judging the genotoxicity of benzene metabolites sensitively.

Drug-Resistant AML Cells and Primary AML Specimens Are Killed by 111In-Anti-CD33 Monoclonal Antibodies Modified with Nuclear Localizing Peptide Sequences

Multidrug resistance (MDR) is a major challenge to the successful treatment of acute myeloid leukemia (AML). Our purpose was to determine whether (111)In-HuM195 anti-CD33 antibodies modified with peptides harboring nuclear localizing sequences (NLS) could kill drug-resistant AML cell lines and primary AML patient specimens expressing MDR transporters through the emission of Auger electrons. HuM195, M195, and irrelevant mouse IgG (mIgG) were conjugated to 10+/-3 NLS peptides and then labeled with (111)In by diethylenetriaminepentaacetic acid substitution to a specific activity of 1-8 MBq/microg. The binding affinity of HuM195 and M195 was determined for HL-60 and mitoxantrone-resistant HL-60-MX-1 cells. Nuclear localization of (111)In-NLS-HuM195, (111)In-NLS-M195, (111)In-HuM195, and (111)In-M195 was measured by subcellular fractionation. The antiproliferative effects of (111)In-NLS-HuM195, (111)In-NLS-M195, (111)In-HuM195, and (111)In-M195 (2.5-250 kBq/well) on HL-60 and HL-60-MX-1 were studied using the WST-1 assay. Clonogenic survival of HL-60 and HL-60-MX-1 leukemic cells and 10 primary AML specimens with MDR phenotype (assessed by flow cytometry) was determined after exposure for 3 h at 37 degrees C to 2.5-250 mBq/cell of (111)In-NLS-HuM195, (111)In-HuM195, or (111)In-NLS-mIgG. Clonogenic survival versus the amount of radioactivity incubated with the cells (mBq/cell) was plotted, and the mean lethal amount of radioactivity and the lower asymptote of the curve (plateau) were determined. The (111)In-labeled anti-CD33 monoclonal antibodies HuM195 and M195 modified with NLS were efficiently routed to the nucleus of HL-60 cells and their mitoxantrone-resistant clone after CD33-mediated internalization. The following are the principal findings of our study: (111)In-NLS-HuM195 was more effective at killing HL-60 and HL-60-MX-1 cells than was (111)In-HuM195, a strong correlation between the specific activity of the (111)In-labeled radioimmunoconjugates and their cytotoxicity toward AML cells existed, and leukemic cells from patients were killed by (111)In-NLS-M195 or (111)In-M195, but the cytotoxic response among specimens was heterogeneous. NLS conjugation enhanced the nuclear uptake and cytotoxicity of (111)In-HuM195 and (111)In-M195 toward drug-resistant AML cell lines as well as patient specimens expressing a diversity of MDR phenotypes, including Pgp-170, BCRP1, or MRP1 transporters. Targeted Auger electron radioimmunotherapy using (111)In-labeled anti-CD33 monoclonal antibodies modified with NLS may be able to overcome MDR and provide a means of treating chemotherapy-resistant myeloid leukemias in patients.

Regulatory properties and cellular redistribution of zinc during macrophage differentiation of human leukemia cells

Many proteins require the binding of trace metals such as Ca, Fe, Cu, or Zn, which may modulate their structure, function, or activity. To determine if there were any overall changes in metalloprotein distribution or metal concentration during the process of macrophage differentiation we induced human myeloid HL-60 leukemia cells with phorbol 12-myristate 13-acetate (PMA) and quantitatively mapped their metal content using hard X-ray fluorescence micro-analysis. We found a transient increase in the zinc content of HL-60 cell nuclei during the early stages of differentiation induction. This finding was confirmed by spectrofluorometry in HL-60 cells and extended to U-937 leukemia cells. A role for protein kinase C-β (PKC-β) in this process was established by examining zinc content in an HL-60 variant, HL-525, which is PKC-β deficient, and in HL-525 cells in which PKC-β was restored by stable overexpression. Chemical chelation of both Cu and Zn served to inhibit macrophage differentiation in HL-60 cells, indicating a requirement for these metals during this process. Finally, we demonstrate that growth of HL-60 cells in a low-zinc environment removes their susceptibility to PMA-induced differentiation, and that this capacity can be partially restored by the addition of exogenous zinc.

Nuclear phospholipase C-β 1b activation during G 2/M and late G 1 phase in nocodazole-synchronized HL-60 cells

In this study, the activity of nuclear phosphatidylinositol-specific phosholipase C (PI-PLC) was investigated in HL-60 cells blocked at G 2/M phase by the addition of nocodazole, and released into medium as synchronously progressing cells. Two peaks of an increase in the nuclear PI-PLC activities were detected; an early peak reached a maximum at 1 h after release from the nocodazole block, and a second increase was detected at 8.5 h after the release. Immunoprecipitation studies indicated that the increase in the activity was due to the activation of the nuclear PI-PLC-β 1. Western blot analysis demonstrated no changes in the level of both a and b splicing variants of PI-PLC-β 1 in the nuclei of cells isolated at either 1 h or 8.5 h after the block. However, an increase in the serine-phosphorylation of PI-PLC-β 1b was detected in the nuclei of HL-60 cells isolated at 1 and 8.5 h after the block, and the presence of MEK-inhibitor PD98059 completely inhibited both the serine phosphorylation and the increase in the PI-PLC activities in vitro. The presence of PI-PLC inhibitor prevented the progression of HL-60 cells through the G 1 into S phase of the cell cycle. These results demonstrate that two peaks of nuclear PI-PLC activities, which are due to a PD98059-sensitive phosphorylation of nuclear PLC-β 1b on serine, occur at the G 2/M and late G 1 phase and are necessary for the progression of the cells through the cell cycle.

Nuclear CD38 in retinoic acid-induced HL-60 cells

The cell surface antigen, CD38, is a 45-kDa transmembrane protein which is predominantly expressed on hematopoietic cells during differentiation. As a bifunctional ectoenzyme, it catalyzes the synthesis of cyclic ADP-ribose (cADPR) from NAD + and hydrolysis of either NAD + or cADPR to ADP-ribose. All- trans-retinoic acid (RA) is a potent and specific inducer of CD38 in myeloid cells. In this report, we demonstrate that the nuclei of RA-treated human HL-60 myeloblastic cells reveal enzymatic activities inherent to CD38. Thus, GDP-ribosyl cyclase and NAD + glycohydrolase activities in the nuclear fraction increased very significantly in response to incubation with RA. With Western blotting, we detected in the nuclear protein fraction from RA-treated cells a ∼43-kDa protein band which was reactive with the CD38-specific monoclonal antibody OKT10. The expression of CD38 in HL-60 nuclei was also shown with FACScan analysis. RA treatment gave rise to an increase in in vitro ADP ribosylation of the ∼43-kDa nuclear protein. Moreover, nuclei isolated from RA-treated HL-60 cells revealed calcium release in response to cADPR, whereas a similar response was not observed in control nuclei. These results suggest that CD38 is expressed in HL-60 cell nuclei during RA-induced differentiation.

Fluorescence and ultrastructural localization of actin distribution patterns in the nucleus of HL-60 and K-562 cell lines treated with cytostatic drugs

Actin has been studied extensively for decades, but so far its well-defined role has been found localized to the cytoplasm. The present study characterizes the distribution pattern of actin in the nucleus of HL-60 and K-562 cell lines treated with etoposide and doxorubicin. F-actin labeled with TRITC-phalloidin was found in the nucleus in both cell lines independently of the cytostatic drugs used. Using confocal microscopy F-actin is seen in the center of the nucleus showed labeling of the nucleoli by phalloidin. There are also distinct tracts of F-actin seen from nucleoli to the nuclear envelope in some sections. HL-60 cells treated with 200 micro M etoposide and 5, 10 micro M doxorubicin showed cells with characteristic features of apoptosis at the ultrastructural level. Intense immunogold labeling for actin was seen in nucleus of HL-60 cells with compaction and margination of chromatin. In K-562 cells more intense labeling was often found in the cytoplasm of the cells. Positive labeling for actin was not found after control incubations. F-actin is present in the nucleus and there is labeling of nucleoli by phalloidin. The observation at the ultrastructural level suggests that actin can be involved in chromatin reorganization during the process of apoptosis. Increase of labeling at the ultrastructural level in the nucleus of HL-60 cells in relation with compaction and margination of nuclear chromatin might also suggest translocation of actin from cytoplasm to the nucleus in connection with chromatin reorganization.

Induction of apoptosis by lupeol isolated from mokumen (Gossampinus malabarica L. Merr) in human promyelotic leukemia HL-60 cells

We have investigated the effect of lupeol (lup-20(29)-ene-3beta-ene-3-ol) isolated from mokumen (Gossampinus malabarica L. Merr) on DNA of human promyelotic HL-60 leukemia cells. Induction of apoptosis by lupeol was observed in human leukemia HL-60 cells. Morphological change showing apoptotic bodies was observed in the HL-60 cells treated with lupeol. The fragmentation of DNA by lupeol to oligonucleosomal-sized fragments that is a characteristic of apoptosis was observed to be concentration- and time-dependent in the HL-60 cells. Flow cytometric analysis showed that the hypodiploid nuclei of HL-60 cells were increased to 28.5, 42.0 and 70.9% after a 3-day treatment with 75, 100 and 150 micro M lupeol, respectively. The data of the present study show that the suppression by lupeol of growth of the HL-60 cells results from the induction of apoptosis by this compound.

Hot water soluble sesquiterpenes [anhydroperoxy-costunolide and 3-oxoeudesma-1,4(15),11(13)triene-12,6α-olide] isolated from laurel (Laurus nobilis L.) induce cell death and morphological change indicative of apoptotic chromatin condensation in leukemia cells

Hot water soluble (HWS)-sesquiterpenes [anhydroperoxycostunolide and 3-oxo-eudesma-1,4(15),11(13)triene-12,6alpha-olide] were purified from Laurel (Laurus nobilis L.) and identified by Mass, and 1H- and 13C-NMR. These HWS-sesquiterpenes displayed strong growth inhibitory effect against human promyelotic leukemia HL-60 cells. Apoptotic morphological changes of the nucleus, including chromatin condensation were induced in the HL-60 cells treated with the sesquiterpenes. Flow cytometric analysis showed that the hypodiploid nuclei of HL-60 cells were increased to 10.5, 46.5, and 91.3% after a 3 day-treatment with 2.5, 5 and 10 micromoles anhydroperoxycostunolide, respectively. And the same analysis showed that the hypodiploid nuclei of HL-60 cells were increased to 9.8, 39.2 and 89.6% after a 3 day-treatment with 5, 10 and 20 micromoles 3-oxo-eudesma-1,4(15),11(13)triene-12,6alpha-olide, respectively. These findings suggest that growth inhibition by anhydroperoxycostunolide and 3-oxo-eudesma-1,4(15),11(13)triene-12,6alpha-olide of HL-60 cells results from the induction of chromatin condensation in the HL-60 cells. On the other hand, fragmentations by these compounds of DNA to oligonucleosomal-sized fragments were not observed in the HL-60 cells.

Sesquiterpenes (costunolide and zaluzanin D) isolated from laurel (Laurus nobilis L.) induce cell death and morphological change indicative of apoptotic chromatin condensation in leukemia HL-60 cells

Sesquiterpenes (costunolide and zaluzanin D) were purified from laurel (Laurus nobilis L.) and identified by Mass, and 1H- and 13C-NMR. These sesquiterpenes displayed strong growth inhibitory effect against human promyelotic leukemia HL-60 cells. Apoptotic morphological changes of the nucleus, including chromatin condensation were induced in the HL-60 cells treated with the sesquiterpenes. Flow cytometric analysis showed that the hypodiploid nuclei of HL-60 cells were increased to 11.4, 47.0, and 92.5% after a 3-day-treatment with 5, 10 and 15 micro M costunolide, respectively. The same analysis showed that the hypodiploid nuclei of HL 60 cells were increased to 12.4, 28.9 and 76.7% after a 3-day-treatment with 10, 15 and 20 micro M zaluzanin D, respectively. These findings suggest that growth inhibition by costunolide and zaluzanin D of HL-60 cells results from the induction of chromatin condensation in the HL-60 cells. On the other hand, fragmentations by these compounds of DNA to oligonucleosomal-sized fragments were not observed in the HL-60 cells.

Protodioscin isolated from fenugreek (Trigonella foenumgraecum L.) induces cell death and morphological change indicative of apoptosis in leukemic cell line H-60, but not in gastric cancer cell line KATO III

Protodioscin (PD) was purified from fenugreek (Trigonella foenumgraecum L.) and identified by Mass, and 1H- and 13C-NMR. The effects of PD on cell viability in human leukemia HL-60 and human stomach cancer KATO III cells were investigated. PD displayed strong growth inhibitory effect against HL-60 cells, but weak growth inhibitory effect on KATO III cells. Morphological change showing apoptotic bodies was observed in the HL-60 cells treated with PD, but not in KATO III cells treated with PD. Flow cytometric analysis showed that the hypodiploid nuclei of HL-60 cells were increased to 75.2, 96.3, and 100% after a 3-day treatment with 2.5, 5, and 10 microM PD, respectively. The fragmentation by PD of DNA to oligonucleosomal-sized fragments, that is a characteristic of apoptosis, was observed to be both concentration- and time-dependent in the HL-60 cells. These findings suggest that growth inhibition by PD of HL-60 cells results from the induction of apoptosis by this compound in HL-60 cells.

3D-computer based reconstructions of apoptotic nuclei.

We present a 3D-model of apoptotic nuclei of HL-60 cells treated with 10 g/ml Etoposide (topoisomerase II inhibitor) for 24 hours. The static model was generated from a series of optical sections obtained through a confocal microscope by freeware and shareware graphical programs available in the Internet. Its animation was done by 3D Studio Max. We demonstrate the appearance of typical fragmentation and condensation of chromatin accompanied by its aggregation to the inner side of the nuclear membrane.

3D-computer based reconstructions of apoptotic nuclei

We present a 3D-model of apoptotic nuclei of HL-60 cells treated with 10 g/ml Etoposide (topoisomerase II inhibitor) for 24 hours. The static model was generated from a series of optical sections obtained through a confocal microscope by freeware and shareware graphical programs available in the Internet. Its animation was done by 3D Studio Max. We demonstrate the appearance of typical fragmentation and condensation of chromatin accompanied by its aggregation to the inner side of the nuclear membrane.

Induction of apoptosis by esculetin in human leukemia cells

Esculetin, a coumarin compound, has been shown to exhibit antioxidant and anti-inflammatory effects. In the present study, esculetin was found to inhibit the survival of human promyelocytic leukemia HL-60 cells in a concentration-dependent and time-dependent manner. HL-60 cells underwent internucleosomal DNA fragmentation and morphological changes characteristic of apoptosis after a 24-h treatment with esculetin (100 μM). Flow cytometric analysis showed that the hypodiploid nuclei of HL-60 cells were increased to 40.93% after a 36-h treatment with esculetin (100 μM). Further investigation showed that esculetin induced the release of cytochrome c from mitochondria into cytosol in a time-dependent and concentration-dependent manner. Moreover, esculetin application reduced Bcl-2 protein expression to 58% after 9 h as compared with that time at 0. Cysteine protease 32 kDa proenzyme (CPP32), a caspase 3, was activated and its substrate, poly (adenosine diphosphate-ribose) polymerase, was cleaved after a 24-h treatment of HL-60 cells with esculetin. These data suggest that esculetin induces apoptosis in human leukemia cells by increasing cytosolic translocation of cytochrome c and activation of CPP32.

Poly(ADP-ribose) Polymerase Is a B-MYB Coactivator

B-MYB is implicated in cell growth control, differentiation, and cancer and belongs to the MYB family of nuclear transcription factors. Evidence exists that cellular proteins bind directly to B-MYB, and it has been hypothesized that B-MYB transcriptional activity may be modulated by specific cofactors. In an attempt to isolate proteins that interact with the B-MYB DNA-binding domain, a modular domain that has the potential to mediate protein-protein interaction, we performed pull-down experiments with a glutathione S-transferase-B-MYB protein and mammalian protein extracts. We isolated a 110-kDa protein associated endogenously with B-MYB in the nuclei of HL60 cells. Microsequence analysis and immunoprecipitation experiments determined that the bound protein was poly(ADP-ribose) polymerase (PARP). Transient transfection assays showed that PARP enhanced B-MYB transactivation and that PARP enzymatic activity is not required for B-MYB-dependent transactivation. These results suggest that PARP, as a transcriptional cofactor of a potentially oncogenic protein, may play a role in growth control and cancer.

Glycosylated nuclear lectin CBP70 also associated with endoplasmic reticulum and the Golgi apparatus: does the "classic pathway" of glycosylation also apply to nuclear glycoproteins?

The subcellular plurilocalization of some lectins (galectin-1, galectin-3, galectin-10, calreticulin, etc.) is an intriguing problem, implying different partners according to their localization, and involvement in a variety of cellular activities. For example, the well-known lectin, galectin-3, a lactose-binding protein, can act inside the nucleus in splicing events, and at the plasma membrane in adhesion, and it was demonstrated that galectin-3 interacts in the cytoplasm with Bcl-2, an antiapoptotic protein. Some years ago, our group isolated a nuclear lectin CBP70, capable of recognizing N-acetylglucosamine residues. This lectin, first isolated from the nucleus of HL60 cells, was also localized in the cytoplasm. It has been demonstrated that CBP70 is a glycosylated lectin, with different types of glycosylation, comparing cytoplasmic and nuclear forms. In this article, we have studied the localization of CBP70 in undifferentiated HL60 cells by electron microscopy, immunofluorescence analysis, and subcellular fractionation. The results obtained clearly demonstrated that CBP70 is a plurilocalized lectin that is found in the nucleus, at the endoplasmic reticulum, the Golgi apparatus, and mitochondria, but not at the plasma membrane. Because CBP70, a nuclear glycoprotein, was found to be associated also with the endoplasmic reticulum and the Golgi apparatus where the glycosylation take place, it raised the question: where does the glycosylation of nuclear proteins occur?

Cleavage of Automodified Poly(ADP-ribose) Polymerase during Apoptosis: EVIDENCE FOR INVOLVEMENT OF CASPASE-7

The abundant nuclear enzyme poly(ADP-ribose) polymerase (PARP) synthesizes poly(ADP-ribose) in response to DNA strand breaks. During almost all forms of apoptosis, PARP is cleaved by caspases, suggesting the crucial role of its inactivation. A few studies have also reported a stimulation of PARP during apoptosis. However, the role of PARP stimulation and cleavage during this cell death process remains poorly understood. Here, we measured the stimulation of endogenous poly(ADP-ribose) synthesis during VP-16-induced apoptosis in HL60 cells and found that PARP was cleaved by caspases at the time of its poly(ADP-ribosyl)ation. In vitro experiments showed that PARP cleavage by caspase-7, but not by caspase-3, was stimulated by its automodification by long and branched poly(ADP-ribose). Consistently, caspase-7 exhibited an affinity for poly(ADP-ribose), whereas caspase-3 did not. In addition, caspase-7 was activated and accumulated in the nucleus of HL60 cells in response to the VP-16 treatment. Furthermore, caspase-7 activation was concommitant with PARP cleavage in the caspase-3-deficient cell line MCF-7 in response to staurosporine treatment. These results strongly suggest that, in vivo, it is caspase-7 that is responsible for PARP cleavage and that poly(ADP-ribosyl)ation of PARP accelerates its proteolysis. Cleavage of the active form of caspase substrates could be a general feature of the apoptotic process, ensuring the rapid inactivation of stress signaling proteins.

Monocytic Differentiation of HL-60 Cells Is Characterized by the Nuclear Translocation of Phosphatidylinositol 3-Kinase and of Definite Phosphatidylinositol-Specific Phospholipase C Isoforms

Immunochemical and immunocytochemical data indicate that nuclei of HL-60 cells contain different enzymes involved in the phosphoinositide cycle, such as PI 3-K and the phosphatidylinositol-specific PLC isoforms β3, γ1 and γ2. These enzymes translocate differently to the nuclear fraction when HL-60 cells are treated with differentiating doses of vitamin D3: PI 3-K translocated progressively to the nucleus in parallel with full differentiation until 96 hours. PLC β3 increased until 72 hours of treatment and then lowered its intranuclear amount and PLC γ1 was unchanged at all the examined times. PLC γ2 nuclear translocation increased progressively until 96 hours of vitamin D3 administration. A fourth PLC isozyme, β2, present in the cytoplasm of untreated cells, translocates to the cytoplasm after vitamin D3 addition and reaches the highest concentration at the end of monocytic differentiation. Terminal monocytic differentiation was characterized at the nuclear level by high levels of PI 3-K and PLC γ2 and by the novel expression of PLC β2. We then observed that the ξ isoform of PKC, constitutively present in nuclei of HL-60 cells, translocated to the nucleus when cells were induced to differentiate along the monocytic lineage, but the nuclear translocation of PKC ξ was blocked as a consequence of PI 3-K inhibition by Wortmannin. These findings indicate that the main components of the noncanonical and canonical inositol lipid signal transduction pathways, including PI 3-K, PLC β2 and β3, PLC γ2, undergo nuclear translocation and may therefore play a relevant role during monocytic differentiation at the nuclear level. Furthermore, PKC ξ nuclear translocation appears to be related to PI 3-K activity.

Co-localization of mitochondrial and double minute DNA in the nuclei of HL-60 cells but not normal cells

In an attempt to isolate genes located on double minute (Dmin) DNA in HL-60 cells, we prepared DNA probe from purified micronuclei. Micronucleation was induced in HL-60 cells by treatment with hydroxyurea. Screening of a cDNA library unexpectedly produced a number of clones containing mitochondrial DNA (mtDNA) sequences. Here, we show that amplified mtDNA sequences were localized in nuclei and micronuclei of HL-60 and COLO 320DM cells, but not in nuclei of WI-38 normal human fibroblasts or peripheral blood T-cells. To unequivocally demonstrate the presence of mtDNA inside of nuclei and micronuclei, we obtained tomographic fluorescence in situ hybridization (FISH) images of mtDNA by confocal microscopy of consecutive sections of paraformaldehyde (PFA)-fixed material. We also located mtDNA in nuclear buds and purified micronuclei. Dmin DNA and mtDNA were always located at similar sites. The mechanisms of nuclear retention of mtDNA and Dmin DNA and the resulting influence on tumorigenesis are discussed.