Sphinganine potentiation of dimethyl sulfoxide-induced granulocyte differentiation, increase of alkaline phosphatase activity and decrease of protein kinase C activity in a human leukemia cell line (HL-60)

The differentiation of HL-60 promyelocytic cells toward mature granulocytic cells induced by dimethyl sulfoxide (DMSO) was accompanied by a quantitative similar increase in alkaline phosphatase (ALP) activity and decrease in protein kinase C (PKC) activity. The combination of DMSO and sphinganine (SP), a potent inhibitor of PKC, increased in parallel the percentage of mature cells and the ALP activity. The enhancement of DMSO-induced differentiation and the potentiation of the decrease of PKC activity by SP also seemed to correlate with each other. Our results indicate that both ALP and PKC may play a role in the DMSO-induced granulocytic differentiation.

Differential regulation of protein kinase C isoenzymes during sphinganine potentiation of retinoic acid-induced granulocytic differentiation in human leukemia HL-60 cells

Differential changes in the expression of PKC isoenzymes in the RA-induced differentiation were noted. As measured by Western blot analysis, our results indicated the expressions of PKC-alpha, and -beta isoenzymes decreased in the cell membrane but increased in the cytosol during the RA-induced granulocytic differentiation. The amounts of PKC-gamma, on the other hand, decreased in the cell membrane while there was no significant changes in the cytosol. Similarly, the expression of PKC-delta was not altered in the cytosol, but was slightly reduced during the SP enhancement of RA-induced differentiation. In contrast, there were virtually little changes in the expression of PKC-epsilon and -zeta in the cell membrane or in the cytosol during the RA-induced differentiation in the absence or presence of SP. Concomitant with the decreased total PKC activity, there was a decline in the generation of sn-1,2-diacylglycerol (DAG) during the RA-induced differentiation. SP, enhancing the RA-induced differentiation, also potentiated the decrease of DAG content.

Cell cycle phase-dependent effect of retinoic acid on the induction of granulocytic differentiation in HL-60 promyelocytic leukemia cells. Evidence for sphinganine potentiation of retinoic acid-induced differentiation

The efficiency of retinoic acid (RA)-induced differentiation was dependent on the position of HL-60 cells in the cell cycle. Our results demonstrated that cells at the G1/S border were more efficiently induced to differentiate by short exposure to RA than cells at other phases of the cell cycle. Synchronization of cells in G1/S phase by aphidicolin (APH) or mimosine (MIMO) increased the sensitivity of cells to RA short exposure treatment. Pretreatment with sphinganine (SP), a protein kinase C (PKC) inhibitor, potentiated RA-induced cell differentiation. By cell cycle analysis, SP was found to block the cell progression through the G1/S phase. Consequently, cells accumulated in the G1/S phase of the cell cycle. The present data therefore suggest a possible mechanism of action of SP to enhance RA-induced differentiation.

Alkaline phosphatase activity during sphinganine potentiation of retinoic acid-induced differentiation of human promyelocytic leukemia cell line, HL-60

Sphinganine (SP) pre-treatment potentiated the retinoic acid (RA)-induced (4-96h exposures) differentiation and increase of alkaline phosphatase (ALP) activity. A higher percentage of SP pre-treated cells in RA exposures resembled mature myelocytes or granulocytes; greater increase in ALP activity was observed. In cells exposed to RA alone for only a period of 24h, the ALP activity could still increase and reach a similar maximum ALP activity (8.5-10.0 units/mg protein) at 48h as it was under continuous RA treatment. In all cells with longer exposures (24-96h) to RA, SP pre-treatment increased ALP activity to more or less the same higher maximum (14.0-15.5 units/mg protein). SP, added 24h before or concomitantly, but not 24 nor 48h after the addition of RA, could potentiate the RA-induced differentiation and increase of ALP activity.

Phosphoprotein B23 translocation and modulation of actinomycin D and doxorubicin cytotoxicity by dipyridamole in HeLa cells

During continuous exposure, cells were more responsive to doxorubicin (DOX) in the presence of dipyridamole (DPM). Translocation of nucleolar phosphoprotein B23 and inhibition of cell growth occurred with a lower dose of DOX and in a shorter incubation time in the presence of DPM. DPM did not change translocation induced by actinomycin D (Act-D). Short exposure of HeLa cells to Act-D induced "reversible" translocation of protein B23 as well as "reversible" inhibition of cell growth. DPM included in the cell culture after removal of Act-D inhibited the recovery of cell growth as well as the corresponding relocalization of protein B23 from the nucleoplasm to nucleoli. DPM administered in the fresh medium after 30 min exposure to DOX had little effect on the potentiation of the induced translocation of protein B23 and inhibition of cell growth. Our results indicated that "B23 translocation" is closely associated with states of cell growth. The potentiation of the inhibition of cell growth by DPM is associated with the extent of enhanced protein B23 translocation. "B23 translocation" may therefore be a simple and rapid method for assessing the inhibition of cell growth and for determining the efficacy of combination cancer chemotherapy.

Schedule-dependent effects of two consecutive, divided, low doses of actinomycin D on translocation of protein B23, inhibition of cell growth and RNA synthesis in HeLa cells

The effects of 2 consecutive, divided, low doses of actinomycin-D (Act-D) on cellular localization of protein B23, inhibition of cell growth, RNA synthesis and colony formation were studied in HeLa cells. The second dose of Act-D was administered at various times after removal of the first dose. One short exposure of HeLa cells to Act-D had previously been shown to induce "reversible" translocation of protein B23, inhibition of cell growth, and RNA synthesis. Relocalization of protein B23 from the nucleoplasm to nucleoli as well as "reversible" inhibition of cell growth and RNA synthesis were still observed in cells that had been treated with a second dose of Act-D administered as early as 0-2 hr or as late as 30 hr after removal of the first dose of Act-D. In contrast, no relocalization of protein B23 from the nucleoplasm to nucleoli was observed in cells that had been treated with a second dose of Act-D administered 9 hr after removal of the first dose. A second exposure to Act-D, administered 9 hr after removal of the first dose, caused irreversible inhibition of cell growth and RNA synthesis; a significant inhibitory effect on colony formation was also observed. RNA synthesis in HeLa cells after 2 sequential exposures to Act-D was further analyzed by 1% agarose gel electrophoresis. There were higher-molecular-weight bands above 28S RNA, which may be the 45S and 32S RNA, observed in the controls and in the cells that had been exposed to Act-D treatment once or in the cells that underwent Act-D exposure twice, in which the second dose was administered as early as 0-2 hr or as late as 30 hr after removal of the first dose. These high-molecular-weight bands were not observed in the cells that underwent Act-D exposure twice, in which the second dose was administered 9 hr after removal of the first. These results indicated that cells at different stages of inhibition or that have recovered from the first exposure to Act-D respond differently to the second short Act-D exposure.

Interaction of antileukemia agents adriamycin and daunomycin with sphinganine on the differentiation of human leukemia cell line HL-60

A slight induction of granulocytic differentiation of HL-60 cells occurred after treatment with antileukemia chemotherapeutic agents Adriamycin (ADM) and daunomycin (DM). Addition of an inhibitor (sphinganine, SP) of protein kinase C (PKC) enhanced 2-4-fold the ADM or DM-induced differentiation. This phenomenon was accompanied by a slightly augmented antiproliferative effect. The enhancement of differentiation induction in these treatments seemed to be absolute, since the combination treatment (ADM-SP or DM-SP) showed about 2.5-3.6 times as many differentiated cells as the treatment with the anticancer drugs ADM or DM alone. Further characterization of the interaction of ADM and DM with SP on differentiation of HL-60 cells was carried out. Whereas the addition of SP in the fresh medium after the removal of ADM or DM (0.5 h treatment) enhanced the induction of differentiation, a pretreatment (24 h) of the cells with SP followed by continuous exposure to ADM or DM did not show such enhancement effect. The addition of SP at as late as 48 h after the administration of ADM or DM potentiated the induction of differentiation to the same extent as in the simultaneous combination of ADM-SP or DM-SP. Similar results were obtained in the experiments with another PKC inhibitor, staurosporine. These results indicated that inhibition of PKC activities may play an important role in the later events during the induction of differentiation elicited by ADM or DM. The use of the antileukemia drugs ADM and DM in combination with an inhibition of PKC activity results in enhancement of induction of differentiation and suggests a new strategy and a promising approach to the treatment of leukemia.

Schedule-dependent sphinganine potentiation of retinoic acid-induced differentiation, cell growth inhibition, and nucleophosmin translocation in a human leukemia cell line (HL-60)

Induction of differentiation, inhibition of cell growth, and localization of nucleophosmin in HL-60 cells under the treatment of retinoic acid (RA) were studied. Bright nucleolar fluorescence was observed in control promyelocytic growing cells. The addition of RA in the culture system resulted in time- and dose-dependent induction of differentiation, cell growth inhibition, and nucleophosmin translocation from nucleoli to nucleoplasm. Unlike the control cells, many fewer nucleophosmin-associated preribosomal ribonucleoprotein particles (pre-rRNPs) could be obtained from nucleoli of RA-treated cells. Addition of sphinganine, an inhibitor of protein kinase C, facilitated the RA-induced differentiation, nucleophosmin translocation, and cell growth inhibition. Cells treated with sphinganine were more responsive to RA. Differentiation, translocation of nucleophosmin, and inhibition of cell growth occurred with lesser doses of RA or in shorter incubation times in the presence of sphinganine. Significant numbers of HL-60 cells could be rescued from the effects of RA upon the removal of RA after 2-h drug exposure. Pretreatment but not posttreatment of HL-60 cells with sphinganine, however, modulated the reversibility of the effects induced by short-exposure RA treatment. These results indicated that RA therapy can be improved by the pretreatment or the concurrent use of a modulator of protein kinase C activity. Nucleophosmin translocation as observed by immunofluorescence may be a simple and rapid method for assessing inhibition of cellular growth in response to differentiation inducers such as RA in cancer chemotherapy.

Identification of high-density lipoprotein in serum to determine anti-cancer efficacy of doxorubicin in HeLa cells

The cytotoxic effects of doxorubicin (DOX) and daunorubicin (DAU) on HeLa cells cultured under different serum conditions were analyzed by the "nucleophosmin translocation" assay using immunofluorescence. Bright nucleolar fluorescence was observed in untreated cells. A shift from nucleolar to nuclear fluorescence was observed with increasing doses of DOX or DAU, with longer incubation times. A lesser degree of nucleophosmin translocation from nucleoli to nucleoplasm was observed in serum-deprived cells under the same DOX or DAU treatment. These results correlated well with those of cell-growth-reversibility and colony-formation studies, showing decreased inhibitory effects of growth on cells cultured in medium without serum. Furthermore, cells cultured in medium supplemented with the lipoprotein-free serum responded to DOX in a similar way to cells cultured without serum. High-density lipoprotein (HDL) and low-density lipoprotein (LDL) were then added to the lipoprotein-free serum. Cells cultured in medium with the HDL-supplemented, serum showed increased sensitivity to DOX. Inhibition of cell growth and colony formation was observed in such HDL-supplemented cells upon DOX treatment (30 min). LDL, on the other hand, did not show an increase in the anti-cancer response. These results suggested that the variation in response of cells to DOX anti-cancer treatment under different growth conditions may be due to their varied concentrations of HDL. "Nucleophosmin translocation", which is useful for monitoring and ensuring the efficacy of the drug during anti-cancer treatment, provides an improved potential for successful chemotherapy.

Alkaline phosphatase activity during differentiation of the human promyelocytic leukemia cell line, HL-60

The differentiation of HL-60 promyelocytic cells toward mature myelocytic cells induced by retinoic acid (RA) was accompanied by a quantitative similar increase in alkaline phosphatase (ALP) activity. The potentiation of RA-induced differentiation and the enhancement of ALP activity by sphinganine seemed to correlate with each other. The combination of RA and sphinganine increased in parallel the percentage of mature cells and the ALP activities. Short exposures (4-8h) of HL-60 cells to RA promoted differentiation and ALP activity to a fraction (about 50%) of their maximums which were achieved in cells after 24h or longer RA exposure. Our results indicate that the key step for the induction of ALP activity and the differentiation by RA probably takes place within 24h of incubation.

Protein kinase C activity during sphinganine potentiation of retinoic acid-induced differentiation in a human leukemia cell line (HL-60)

The differentiation of HL-60 promyelocytic cells toward mature granulocytic cells induced by retinoic acid (RA) was accompanied by a decrease in protein kinase C (PKC) activity. The enhancement of RA-induced differentiation and the potentiation of the decrease of PKC activity by sphinganine (SP) seemed to correlate with each other. Kinetically, PKC activity during RA-induced differentiation without SP decreased to its lowest (75% of the control) after 48h; about 50% of the reduction was observed at 24h. In the presence of SP, PKC activity decreased more rapidly to its lowest (60% of the control) within 24h of incubation of RA. SP, added 24h before or concomitantly with the addition of RA, could potentiate the RA-induced differentiation and the reduction of PKC activity. Our results indicate that the effect of SP and the role of PKC during RA-induced differentiation may be critical at the early stages of induction of differentiation (within 24h of RA exposure).

Protein B23 (M.W./pI = 37 kD/5.1) is the only major protein extracted from HeLa nucleoli with 3M urea

HeLa nucleoli were isolated using the NP-40 method and subsequently extracted with 3M urea. The extract was incubated at 60 degrees C for 30 min, and precipitated proteins were removed by centrifugation. The supernatant was analyzed by one- and two-dimensional SDS polyacrylamide gel electrophoresis (PAGE). Protein B23 was the only major protein extracted from HeLa nucleoli by this procedure. Using this procedure, 1 mg of protein B23 was obtained from 2 g of HeLa cells. The purity of the extracted protein B23 was 98%, as measured by one- and two-dimensional gel electrophoresis.

Modulation of the reversibility of actinomycin D cytotoxicity in HeLa cells by verapamil

Actinomycin D treatment (0.001-0.005 micrograms/ml; 0.5-24 h) induced a dose and time response shifting of nucleolar to nuclear fluorescence. In the presence of verapamil, cells were more responsive to actinomycin D. Translocation of protein B23 occurred with lower doses of actinomycin D and in shorter incubation times in the presence of verapamil. Short exposure (0.5 h) of HeLa cells to actinomycin D (0.05-0.25 micrograms/ml) induced 'reversible' translocation of protein B23 as well as 'reversible' inhibition of cell growth and RNA synthesis. Verapamil (5 microM) included in the cell culture after removal of actinomycin D inhibited the recoveries of cell growth, RNA synthesis as well as the corresponding relocalization of protein B23 from the nucleoplasm to nucleoli. These results indicate that verapamil can potentiate the antiproliferating activity of actinomycin D by inhibiting reversibility of its cytotoxicity and suggest clinical application.

Dipyridamole enhancement of doxorubicin-induced translocation of nucleophosmin and inhibition of cell growth in HL-60 cells

Dipyridamole (DPM) enhanced sensitivity to doxorubicin (DOX) in a human leukemia cell line that was already relatively sensitive to this agent. Using an immunofluorescence technique, we determined the localization of nucleophosmin (protein B23) in HL-60 cells after incubation with DOX in the absence and presence of DPM. Bright nucleolar fluorescence was observed in control HL-60 cells. The addition of DOX (0.1-0.25 micrograms/ml) in the culture system resulted in time- and dose-dependent induction of nucleophosmin translocation from the nucleolus to nucleoplasm and inhibition of cell growth. DPM (5 microM) alone had no effect on nucleophosmin translocation and inhibition of cell growth. However, the addition of DPM to the cells enhanced DOX-stimulated translocation of nucleophosmin. There was a good correlation between the DPM enhancement of DOX-induced nucleophosmin translocation and the increased inhibition of cell growth. The cell number decreased to a greater extent within a shorter time period under treatment with DOX in the presence of DPM. Short exposure (0.5 hr) of HL-60 cells to DOX induced dose-response nucleophosmin translocation and cell growth inhibition. Such effects of a short exposure to DOX were also enhanced by DPM (5 microM) included in the fresh medium after removal of DOX. This was in agreement with the observation that DPM could increase the cellular DOX by inhibiting the drug efflux from the cells. These results demonstrate that DPM, being able to increase and retain the intracellular levels of DOX, can markedly enhance the cytotoxicity of DOX, and suggest possible clinical application. "Nucleophosmin translocation", as observed by immunofluorescence, could be useful in determining the efficacy of combinations of DOX and DPM in cancer chemotherapy.

Nucleolar protein B23 translocation after deferoxamine treatment in a human leukemia cell line

Localization of nucleolar protein B23 in HL-60 cells under the treatment by iron chelator deferoxamine (DSF) was studied using indirect immunofluorescence. Bright nucleolar fluorescence was observed in exponentially growing control cells. The addition of DSF in the culture system resulted in time- and dose-dependent induction of protein B23 translocation from nucleoli to nucleoplasm, inhibition of cell growth, DNA and RNA synthesis. The addition of FeCl3 at culture initiation completely reversed the effects of DSF. Furthermore, significant numbers of HL-60 cells could be rescued from the effects of DSF when iron was added back as late as 24 hr after exposure to DSF. Cells resumed their abilities to grow and to synthesize DNA and RNA upon the iron rescue. Protein B23, accordingly, relocated from nucleoplasm to nucleoli. These results indicate the importance of iron for proliferation of leukemic cells and localization of protein B23 in nucleoli. Preribosomal ribonucleoprotein particles (pre-rRNPs) were extracted from isolated nucleoli of HL-60 cells and fractionated on sucrose density gradients. Protein B23 was found to be co-localized with the pre-rRNPs as determined by ELISA assays. No such B23-associated pre-rRNPs or other pre-rRNP fractions were obtained from nucleoli of DSF-treated cells. These results suggest that one of the effects of the anti-proliferative action of DSF is the inhibition of rRNA synthesis in nucleoli. Due to the lack of new synthesis of rRNA in nucleoli, protein B23 loses its binding target and translocates into the nucleoplasm. B23 translocation, as observed by immunofluorescence, may be a simple and rapid method for assessing inhibition of cell growth in response to anti-proliferative drugs such as deferoxamine in cancer chemotherapy.

Short exposure to actinomycin D induces "reversible" translocation of protein B23 as well as "reversible" inhibition of cell growth and RNA synthesis in HeLa cells

HeLa cells were grown in medium containing various amounts of actinomycin D for various times. Cellular localization of protein B23 was detected using an immunofluorescence technique. Bright nucleolar fluorescence was observed in untreated cells. A shifting of nucleolar to nuclear fluorescence was observed with increasing doses of actinomycin D and longer incubation times. The degree of translocation of protein B23 from nucleoli to nucleoplasm is dependent on the amount of the drug used and the duration of incubation. Short exposure (0.5 h) of HeLa cells to actinomycin D (0.01-0.25 microgram/ml) induced "reversible" translocation of protein B23, inhibition of cell growth, and RNA synthesis. A majority of cells (greater than 75%) treated with actinomycin D (0.01-0.25 microgram/ml) for 0.5 h still retained bright nucleolar fluorescence. A shifting of nucleolar to nuclear fluorescence as well as inhibition of cell growth and RNA synthesis were observed within 6 h after the removal of the drug. However, at the extended periods (greater than 24 h) after drug removal, RNA synthesis and cell growth resumed at the normal rate, and protein B23 relocated from nucleoplasm to nucleoli. This is in contrast to the results obtained from the experiments using higher doses (1 microgram/ml; 0.5 h) or longer (0.25 microgram/ml; 2 h) exposure of HeLa cells to actinomycin D, which induced irreversible B23 translocation as well as irreversible inhibition of cell growth and RNA synthesis. These results indicated that actinomycin D can be a reversible inhibitor depending on the drug extracellular concentrations and exposure times. Our results also indicated that "B23 translocation" is closely associated with states of cell growth and inhibition of RNA synthesis. "B23 translocation" may therefore be a simple and rapid method for assessing the inhibition of cell growth in response to antitumor therapy.

Immunolocalization of phosphoprotein B23 in proliferating and non-proliferating HeLa cells

Localization of protein B23 in HeLa cells under different growth conditions was studied using indirect immunofluorescence. Bright nucleolar fluorescence was observed in exponentially growing cells. After 3 to 4 days, the initial cell inocula entered a phase of stationary growth as defined by no increments in cell number. The nucleolar fluorescence was then diminished and a general nuclear immunofluorescence was observed. This change in localization of fluorescence indicated that protein B23 had migrated out of the nucleoli during the suboptimal growth conditions. Relocation of protein B23 in nucleoli was observed in cells of stationary growth after treatment with adriamycin or daunomycin at their subtoxic concentrations (10(-10) M). Adriamycin and daunomycin, at their toxic concentrations (greater than 5.0 x 10(-7) M), on the other hand, inhibited cell growth and induced B23 translocation from nucleoli to nucleoplasm in growing cells. These results indicate that both adriamycin and daunomycin exhibit biphasic effects on the proliferation of cells by either stimulation or inhibition depending on the drug concentrations and the growth conditions. B23 translocation, as observed by immunofluorescence may be a simple and rapid method for assessing inhibition-stimulation growth response to anti-tumor therapy.

Fate of the DnaA initiator protein in replication at the origin of the Escherichia coli chromosome in vitro

The dnaA initiator protein binds specific sequences in the 245-base pair Escherichia coli origin (oriC) to form a series of complexes which eventually are opened enough to admit dnaB helicase into a prepriming complex (Bramhill, D., and Kornberg, A. (1988) Cell 52, 743-755). ATP bound to a high-affinity site on dnaA protein is the preferred form for one or more of the early stages, but an elevated level of ATP is needed for a later stage; further evidence for a low-affinity site has now been obtained. We find that at limiting levels of dnaA protein only the ATP form produces an active initial complex; neither the ADP nor the non-nucleotide forms are effective. Augmentation of the activity of a limiting level of the ATP form of dnaA protein by the otherwise inert ADP form implies that at some stage of initiation both forms are active. The dnaA protein is essential up to the stage of forming the prepriming complex; upon salt dissociation from an oriC complex, the protein can be recycled to function at a fresh origin. Distinctive conformational states of the ATP form are implied by interactions with oriC DNA, by the influence of phospholipids on accelerating nucleotide exchange, and by the susceptibility to proteolytic cleavage.

The dnaA initiator protein binds separate domains in the replication origin of Escherichia coli

After binding to its four 9-mer boxes in the 245-base pair Escherichia coli replication origin (oriC), dnaA protein effects the formation of an "open complex" in an adjacent region made up of three 13-mers (Bramhill, D., and Kornberg, A. (1988) Cell 52, 743-755). This open complex formation requires the ATP form of dnaA protein assisted by HU protein (Sekimizu, K., Bramhill, D., and Kornberg, A. (1987) Cell 50, 259-265). We now provide direct evidence that dnaA protein binds the 13-mers, sequences that bear no resemblance to the 9-mer box. The evidence is (i) displacement of dnaA protein from the open complex by oriC or by a synthetic oligonucleotide containing the 13-mers, but not by a mutant of oriC lacking the 13-mers; (ii) filter binding of the synthetic (13-mer) oligonucleotide by dnaA protein; and (iii) requirement for the ATP form of dnaA protein assisted by HU protein for temperature-dependent binding to the 13-mer region. Controlled proteolysis of dnaA protein results in a prompt loss of oriC binding; an NH2-terminal 30-kDa peptide contains the domain that binds ATP and phospholipids known to destabilize the tightly bound ATP.

Membrane attachment activates dnaA protein, the initiation protein of chromosome replication in Escherichia coli

ADP and ATP are tightly bound to dnaA protein and are crucial to its function in DNA replication; the exchange of these nucleotides is effected specifically by the acidic phospholipids (cardiolipin and phosphatidylglycerol) present in Escherichia coli membranes [Sekimizu, K. & Kornberg, A. (1988) J. Biol. Chem. 263, 7131-7135]. We now find that phospholipids derived from membranes lacking an unsaturated fatty acid (e.g., oleic acid) are unable to promote the exchange. This observation correlates strikingly with the long-known effect of 3-decynoyl-N-acetylcysteamine, a "suicide analog" that prevents initiation of a cycle of replication in E. coli by inhibiting the synthesis of oleic acid, an inhibition that can be overcome by providing the cells with oleic acid. Profound influences on the specific binding of dnaA protein to phospholipids by temperature, the content of unsaturated fatty acids, and the inclusion of cholesterol can be explained by the need for the phospholipids to be in fluid-phase vesicles. These findings suggest that membrane attachment of dnaA protein is vital for its function in the initiation of chromosome replication in E. coli.

The dnaA protein of Escherichia coli. Abundance, improved purification, and membrane binding

Immunoassays of dnaA protein in extracts from five strains showed a rather constant abundance relative to cell mass, with a variation of 800-2100 molecules/cell; overproducing cells contained 100-fold that number. About half of the dnaA protein in wild type cells was solubilized by a lysis procedure. Within the insoluble fractions, dnaA protein was identified by its characteristic high-affinity binding of ATP. An improved, rapid procedure for purifying dnaA protein from overproducing cells appears to depend on its coprecipitation with phospholipids and depends on solubilization by guanidine HCl. The procedure, with a 5-fold increased yield, also eliminates a potent ATPase contaminant. Purified dnaA protein, unlike dnaB and dnaC proteins, binds to phospholipid vesicles as judged by analysis on sucrose gradient centrifugation.

Identification and characterization of a hexameric form of nucleolar phosphoprotein B23

Under native purification conditions, an oligomeric form (Mr = 230,000) and monomeric form (37,000) of protein B23 were purified by affinity chromatography. Both forms were identified by Western blot immunoassay and ELISA. The molecular weight of the oligomeric form of protein B23 was estimated to be 230,000 with a Stoke's radius and a sedimentation coefficient of 51 A and 10 S, respectively. The oligomer (230 kDa) of protein B23 was dissociated into monomers (37 kDa) by treatment with 7 M urea. Quantitation of the monomer by gel scanning densitometry indicated that the oligomeric form of protein B23 is a hexamer containing four alpha and two beta monomers (37 kDa). A trace amount of nucleic acids (amounting to less than 3% of the total mass) was detected in the affinity-purified oligomers of protein B23. Protein B23 may be a structural element which is involved in ribosome transport or assembly in the nucleus.

Nucleolar protein B23 translocation after doxorubicin treatment in murine tumor cells

Rats bearing Novikoff hepatoma ascites cells were given i.p. injections of actinomycin D, doxorubicin, or daunorubicin. Four hours after injection, tumor cells were removed from the ascites fluid and analyzed for protein B23 translocation using an immunofluorescence technique. Bright nucleolar fluorescence was observed in untreated cells. Treatment with actinomycin D (1.25 mg/kg), doxorubicin (25 mg/kg), or daunorubicin (12.5 mg/kg) produced a uniform nucleoplasmic fluorescence. This change in immunofluorescence distribution indicated that protein B23 translocated from the nucleolus to the nucleoplasm after drug treatment. These results are an extension of previous studies with HeLa cells (Yung et al., Cancer Res. 46: 922-925, 1986). Doxorubicin-resistant and -sensitive mouse leukemia cells (P388) were cultured in medium containing various doses of doxorubicin for 4 h, and the responsive levels of the cells to doxorubicin were compared. At 50 micrograms/ml doxorubicin, 86% of the doxorubicin-sensitive cells showed uniform nucleoplasmic fluorescence, and less than 2% of the cells retained nucleolar fluorescence. At this same dose, only 9% of the resistant cells showed nucleoplasmic fluorescence, and 75% of the cells retained nucleolar fluorescence. At 100 micrograms/ml, about 26% of the resistant cells showed translocation, in contrast to 100% of the sensitive cells that showed B23 translocation. About 57% of the resistant cells showed an intermediate effect, and about 17% of the resistant cells maintained bright nucleolar fluorescence at this dose. The resistant cells also showed less responsiveness to actinomycin D. These results suggest that identification of "B23 translocation" may be used to detect drug-resistant cells and to study the efficacy of certain antitumor agents.

Amino acid sequence of a specific antigenic peptide of protein B23

A specific antigenic peptide was obtained from protein B23 (Mr/pI = 37,000/5.1) after 30 min of digestion with staphylococcal V8 protease (10 micrograms/ml/mg protein B23). The antigenic peptide was purified by DEAE-cellulose chromatography and high pressure liquid chromatography on a reverse-phase C18 column. The antigenic peptide contains 14.7 and 18.7 mol% of glutamic acid and lysine, respectively. Amino acid sequence analysis showed that the peptide has 68 amino acids and is located on the carboxyl-terminal sequence of protein B23. The sequence is Ser-Phe-Lys-Lys-Gln-Glu-Lys-Thr-Pro-Lys-Thr-Pro- Lys-Gly-Pro-Ser-Ser-Val-Glu-Asp-Ile-Lys-Ala-Lys-Met-Gln-Ala-Ser-Ile-Glu- Lys-Gly- Gly-Ser-Leu-Pro-Lys-Val-Glu-Ala-Lys-Phe-Ile-Asn-Tyr-Val-Lys-Asn-Cys-Phe- Arg-Met- Thr-Asp-Gln-Glu-Ala-Ile-Gln-Asp-Leu-Trp-Gln-Trp-Arg-Lys-Ser-Leu-Cooh. Extensive digestion of the antigenic peptide with V8 protease, trypsin, or chymotrypsin results in loss of the antigenic activity. Three cloned cDNAs (hpB1, hpB2, and hpB7) which code for the 82 amino acids at the COOH terminus of protein B23 and the 3' non-translating sequence were identified and characterized. All three clones have identical nucleotide sequences coding for the antigenic portion of the protein (68 amino acids at the COOH terminus), the stop codon, and the 3' non-translated region. However, mutation of 6 nucleotide bases of one clone (hpB2) caused changes in 4 amino acids in the sequence just preceding the immunoreactive region. The result suggests the presence of at least 2 immunologically similar but distinct proteins which are both recognized by the anti-B23 antibody.