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Biomedical subjects

A Yen

Publications and source records attributed to A Yen.

At least 109 records · Page 6Linked to original sources
PubMed1990

Dual effects of protoporphyrin and long wave ultraviolet light on histamine release from rat peritoneal and cutaneous mast cells.

In this study we investigated the effects of long wave ultraviolet light (UVA) and various doses of protoporphyrin (PP) on the release of histamine from rat peritoneal and cutaneous mast cells. We also correlated these results with morphologic characteristics and viability of the cells. PP at a dose of 30 ng/ml plus UVA-induced negligible histamine release from rat peritoneal mast cells (RPMC), but was able to suppress the ability of the cells to release histamine in response to subsequent exposure to the calcium ionophore A23187, compound 48/80, or the combination of Ag and IgE. This functional change was associated with an increase in cell size, and cell lysis that gradually occurred during 24 h in culture. PP at a dose of 3 ng/ml plus UVA also significantly inhibited secretogogue-induced histamine release from rat peritoneal mast cells, but this dose was not associated with significant changes in morphology or viability. These various effects of PP plus UVA were also observed with mast cell preparations obtained by the enzymatic dispersion of rat skin. The suppression of secretogogue-induced histamine release in rat peritoneal mast cells treated with PP (3 ng/ml) and UVA could not be reversed by culturing the cells in the dark for 24 h in the absence of PP. Unlike the direct cytotoxic histamine releasing action of high doses of PP plus UVA, the suppressive effect of low PP doses could not be inhibited by catalase, but could be reduced by the absence of calcium. Our results indicate that PP plus UVA has dual effects on mast cells, apparently involving distinct mechanisms. This implies the possibility that PP and UVA at appropriate doses could be used in photochemotherapy of mast cell-mediated skin diseases.

Animals↗
PubMed1990

c-myc down regulation and precommitment in HL-60 cells due to bromodeoxyuridine.

HL-60 human nonlymphocytic leukemia cells undergo terminal differentiation along either the myeloid or monocytic pathway in a process previously shown to involve two sequential steps, early events leading to a precommitment state and late events leading to onset of terminal differentiation. The present report shows that bromodeoxyuridine induces the early events leading to precommitment. In this course bromodeoxyuridine causes the rapid down regulation of the c-myc protooncogene. The course is similar to other common inducers of HL-60 differentiation including retinoic acid, dimethyl sulfoxide, 1,25-dihydroxyvitamin D3, and sodium butyrate. HL-60 cells which were initially exponentially proliferating were exposed to 10 microM bromodeoxyuridine for 24 h, a period corresponding to one division cycle in these cells. When the cells were subsequently exposed to either retinoic acid or 1,25-dihydroxyvitamin D3, onset of G1/0 specific growth arrest and display of the differentiated phenotype occurred within 24 h. This is in contrast to the 48-h exposure needed for onset of terminal differentiation if either inducer is used singly during continuous exposure, as has been reported previously. Thus bromodeoxyuridine consummated the early events, including the rapid down regulation of c-myc message levels, which occur during the first division cycle of the induced cellular metabolic cascade leading to onset of terminal differentiation. The ability of bromodeoxyuridine to drive events in the metabolic cascade leading to onset of terminal differentiation was specific for early events, inasmuch as it was relatively ineffective at driving late events. Down regulation of c-myc was not in itself sufficient to result in subsequent terminal differentiation, since pulse exposure to bromodeoxyuridine followed by culture in inducer free medium resulted in little G1/0 specific growth arrest or phenotypic differentiation. Continuous exposure to bromodeoxyuridine, in contrast, resulted in significant G1/0 specific growth arrest but little phenotypic differentiation, indicating that the regulation of cell cycle transit and differentiation are separable.

Bromodeoxyuridine↗
PubMed1990

Ethanol causes accelerated G1 arrest in differentiating HL-60 cells.

The effects of clinically relevant ethanol concentrations on myeloid differentiation in the HL-60 cell promyelocytic leukemia line have been studied. The exposure of noninduced stem cells to 60 mM ethanol results in an increase in G1 cells, but there is no increase in superoxide production or expression of the Mo1 antigen. When HL-60 cells are induced to differentiate along the myeloid line with dimethylsulfoxide (DMSO) or retinoic acid (RA), there is a shift to smaller cell size, an increase in G1 cells and acquisition of the ability to produce superoxide as reported previously by several authors. When ethanol is present during differentiation, there are further increases in G1 cells, and increases in the percentage of cells which produce superoxide and express Mo1, and decreases in mean cell size and total growth during the incubation period. Regrowth experiments after periods of differentiation indicate that the increased G1 arrest seen in the presence of ethanol represents terminal commitment if inducer is present, but in the absence of inducer the increased G1 percentage is readily reversible. Examination of RNA content by flow cytometry reveals a decrease in both the peak and mean G1 RNA content during DMSO or RA induced differentiation. These decreases are accentuated by the presence of ethanol, resulting in a higher G1A/G1B ratio than in nonexposed cells. These findings indicate that ethanol enhances G1 growth arrest in HL-60 cells exposed to myeloid inducers. Partial differentiation occurs during this process, resulting in terminally arrested cells, some of which have undergone fewer postinduction cell divisions than normal and may not be fully competent.

Cell Differentiation↗
PubMed1990

Ethanol induced growth inhibition and growth adaptation in vitro. Cell cycle delay in late G1.

We have characterized the growth responses of HTC rat hepatoma sublines after exposure to clinically relevant concentrations of ethanol. These experiments demonstrate growth inhibition by ethanol, and both adaptive and non-adaptive growth responses after chronic exposure. Examination of the cell cycle compartmentation of HTC lines shows that a rapid accumulation of G0/G1 cells is induced by ethanol. Estimates of cellular G1 RNA content by flow cytometry reveal increases in mean G1 RNA and in late G1 cells in the line which growth adapts, and decreases in these parameters in a line which does not adapt to ethanol. Both the growth responses and the timing of cell cycle restriction by ethanol in the adapting line suggest parallels with the reported data for regenerating rat liver. Ethanol induced late G1 restriction appears to be of significant interest in the study of cellular mechanisms which are disturbed by ethanol in proliferating tissues.

Animals↗
PubMed1989

Cell cycle-dependent regulation of phosphorylation of the human retinoblastoma gene product.

The human retinoblastoma gene (RB1) encodes a protein (Rb) of 105 kilodaltons that can be phosphorylated. Analysis of Rb metabolism has shown that the protein has a half-life of more than 10 hours and is synthesized at all phases of the cell cycle. Newly synthesized Rb is not extensively phosphorylated (it is "underphosphorylated") in cells in the G0 and G1 phases but is phosphorylated at multiple sites at the G1/S boundary and in S phase. HL-60 cells that were induced to terminally differentiate by various chemicals lost their ability to phosphorylate newly synthesized Rb at multiple sites when cell growth was arrested. These findings suggest that underphosphorylated Rb may restrict cell proliferation.

Cell Cycle↗
PubMed1988

Retinoic-acid-induced modulation of c-myc not dependent on its continued presence: possible role in pre-commitment for HL-60 cells.

Induced differentiation of HL-60 human promyelocytic cells along the myeloid or monocytic lineages has been previously shown to involve an intermediate regulatory state, the pre-commitment state. Pre-commitment cells have completed the early events in the processes leading ultimately to terminal differentiation and require only an abbreviated subsequent exposure to inducer for onset of terminal differentiation. The pre-commitment state has 2 properties relevant to the present communication: (1) when induced by retinoic acid (RA), it has a characteristic duration following removal of the RA; and (2) it can also be induced by a pulse exposure to hydroxyurea. In the present studies, it was observed that after exposure of HL-60 human promyelocytic leukemia cells to RA for 24 hr (ca. one division cycle) their levels of c-myc RNA were elevated. The c-myc RNA level then remained elevated for several subsequent division cycles despite the removal of retinoic acid. Thus, retinoic acid induced a change in HL-60 c-myc RNA levels which was sustained regardless of the continued presence or absence of RA. The elevation, decreasing to control levels 3 division cycles after termination of the pulse exposure, paralleled the known duration of the pre-commitment memory state. Furthermore, a pulse exposure of HL-60 cells to a subcytotoxic dose of hydroxyurea, which is also known to induce a pre-commitment state, also induced an elevation of c-myc RNA levels. The observed changes in c-myc levels were not common to all oncogenes. C-fos responded differently to the retinoic acid treatment. Furthermore, although hydroxyurea affected c-myc levels, it did not alter c-fos levels. Most significantly, the present results suggest a cellular function for the c-myc gene product, which is derivation of the pre-commitment state.

Cell Differentiation↗
PubMed1988

Induction of HL-60 monocytic cell differentiation promoted by a perturbation of DNA synthesis: hydroxyurea promotes action of TPA.

Control of terminal cell differentiation was studied using the human promyelocytic leukemia cell line, HL-60. HL-60 cells are known to undergo terminal monocytic differentiation when continuously exposed to 1.6 nM tetradecanoylphorbol acetate (TPA). The dose-response relationship between TPA concentration and induced differentiation is relatively steep. TPA (1.1 nM) induces little G1/0 specific growth inhibition or phenotypic differentiation. In contrast, pretreating the cells with a pulse exposure to hydroxyurea promotes their capability to terminally differentiate in response to TPA. Initially exponentially proliferating cells exposed for 20 h, approximately one doubling time, to 0.3 mM hydroxyurea, a subcytotoxic dose, underwent rapid G1/0 specific growth arrest and cell differentiation in response to subsequent exposure to 1.1 nM TPA. The extent of terminal differentiation was comparable to that induced by 1.6 nM TPA. The results support the hypothesis that early events in induction of terminal HL-60 cell differentiation depend on an S phase-specific process which may involve gene amplification.

Cell Differentiation↗
PubMed1987

Control of HL-60 cell differentiation lineage specificity, a late event occurring after precommitment.

Terminal cell differentiation of HL-60 promyelocytic leukemia cells results when they are continuously exposed to retinoic acid. This process involves an intermediate regulatory state, the precommitment memory state, which occurs before onset of differentiation or growth arrest in G0. The cellular processes occurring prior to onset of terminal differentiation can be resolved into early events anteceding development of the precommitment memory state and late events subsequent to it. While it has been suggested that retinoic acid induced early events regulate G1/0 specific growth arrest associated with terminal differentiation, the significance of induced late events is not known. Exploiting the capability of HL-60 cells to undergo either myeloid or monocytic differentiation in response to different inducers, the present studies examine the response of HL-60 cells to the sequential application of myeloid and monocytic inducers prior to onset of terminal differentiation. The results indicate that the precommitment state induced by retinoic acid is not differentiation lineage specific. Sequential application first of retinoic acid, a myeloid inducer, and then of 1,25-dihydroxyvitamin D3, a monocytic inducer, and vice versa, show that cellular choice of a specific differentiation lineage is regulated by late inducer driven events. The data support a two-step model for induction of terminal differentiation where early events anteceding precommitment regulate growth arrest and late events subsequent to precommitment regulate choice of a specific differentiation lineage. The results are of potential significance to the use of differentiation-inducing agents in chemotherapy. The potential toxicity of prolonged exposure to a single inducer might thus be mitigated by sequential brief exposures to different inducers.

Calcitriol↗
PubMed1987

Precommitment states induced during HL-60 myeloid differentiation: possible similarities of retinoic acid- and DMSO-induced early events.

The possible relationship of the pathways by which two inducers, retinoic acid and DMSO, cause myeloid differentiation of HL-60 promyelocytic leukemia cells was studied. HL-60 cells were first exposed to retinoic acid and then washed free of it. As reported previously, this brief exposure results in no subsequent G0 growth arrest or phenotypic differentiation. When these cells were subsequently exposed to DMSO, onset of G1/0 growth arrest but not phenotypic differentiation occurred within 24 h. Since in these cells retinoic acid or DMSO normally requires 48 h of continuous exposure for onset of significant G0 growth arrest and phenotypic differentiation, it appears that retinoic acid and DMSO induce similar early cellular events needed for subsequent G0 growth arrest but not for phenotypic differentiation. While onset of growth arrest and differentiation occur together when the cells are exposed for 48 h to retinoic acid, the present results indicate that their occurrence can be uncoupled by this split dosage to inducers. The results are discussed in terms of a previously hypothesized model of cellular response to the inducers.

Cell Cycle↗
PubMed1987

Control of HL-60 monocytic differentiation. Different pathways and uncoupled expression of differentiation markers.

Control of expression of the terminally differentiated phenotype was studied using the human promyelocytic leukemia cell line HL-60. Three known inducers of HL-60 monocytic differentiation were compared: 1,25-dihydroxy vitamin D3, tetradecanoylphorbol acetate (TPA), and sodium butyrate. At concentrations where all three inducers resulted in similar courses of G1/0-specific growth arrest, the kinetics of appearance of certain differentiation markers typically characteristic of mature monocytic cells was determined. The markers were inducible oxidative metabolism, non-specific esterase activity, and the cell surface determinants Mo1, My4, and Mo2. The results indicate that: Regulation of the expression of these markers during induced monocytic differentiation is not controlled in common. The three monocytic inducers do not induce the same metabolic cascade leading to differentiation. Similar states of differentiation could thus be reached by different pathways apparently due to the fact that control of expression of different differentiation markers was not tightly coupled.

Antigens, Surface↗
PubMed1987

Hydroxyurea indices precommitment during retinoic induced HL-60 terminal myeloid differentiation: possible involvement of gene amplification.

Control of terminal cell differentiation was studied in the HL-60 human promyeloctyic leukemia cell line. Retinoic acid is known to induce myeloid differentiation associated with GO arrest in these cells. In this case, onset of terminal differentiation occurs after an exposure period corresponding to two division cycles. This is preceded by acquisition of a precommitment memory state occurring by one division cycle. Cells in precommitment undergo accelerated onset of terminal differentiation upon reexposure to inducer. The present report shows that the precommitment state can be induced by a pulse exposure to hydroxyurea. While the hydroxyurea exposure does not itself induce terminal differentiation, the treated cells undergo accelerated onset of phenotypic differentiation and GO arrest upon exposure to retinoic acid. Thus a perturbation of S-phase specific cellular metabolism induces the early precommitment regulatory state in the course of induced HL-60 terminal myeloid differentiation. The results support a model in which initiation of a cellular program of terminal differentiation depends on an S-phase specific event associated with replication of cellular DNA and possibly involving gene amplification. Significantly, the results indicate that a conventional chemotherapeutic agent such as hydroxyurea can synergistically interact with a differentiation inducing agent such as retinoic acid. This indicates the significance of investigating the interaction between conventional S-phase specific chemotherapeutic agents and differentiation inducing agents as a potential treatment modality.

Cell Differentiation↗
PubMed1986

Cell cycle dependence of calmodulin levels during HL-60 proliferation and myeloid differentiation. No changes during pre-commitment.

The putative role of Ca2+ and calmodulin in regulating cell proliferation and differentiation was tested in HL-60 human promyelocytic leukemia cells. The dependence of retinoic acid (RA)-induced terminal myeloid differentiation of HL-60 promyelocytic leukemia cells on calmodulin levels and calcium ion flux was ascertained. RA-treated and untreated control cells were stained for cellular DNA with a Hoechst dye. Populations of G1/0, S and G2 + M phase cells were isolated by fluorescence activated cell sorting (FACS). Cytosolic calmodulin levels were then measured as a function of cell cycle phase for RA-treated and untreated cells using a radioimmunoassay. RA-treated cells were measured at early times, corresponding to the pre-commitment state, and late times, when significant cell differentiation had occurred. Cellular calmodulin levels increased with progression through the cell cycle. In contrast, no difference in calmodulin levels was observed between RA-untreated or -treated cells in the same cell cycle phases at early or late times. RA-induced HL-60 terminal myeloid differentiation was thus apparently not regulated by cellular cytosolic calmodulin levels. These conclusions were supported by the effects of calmodulin antagonists and calcium flux inhibitors. The calmodulin antagonists trifluoperazine and compound 48/80 both retarded cell growth in a concentration-dependent manner. But at concentrations where cellular effect was evidenced by slight growth inhibition, neither antagonist inhibited RA-induced cell differentiation or G1/0 growth arrest. The same was true of the gated calcium channel inhibitors, verapamil and nitrendipene, and the passive calcium flux inhibitor, CoCl2. RA-induced HL-60 cell differentiation and arrest in G0 was thus apparently not strongly dependent on cellular calmodulin levels or calcium flux. This is in strong contrast to murine erythroleukemia cells. The results argue against a central regulatory role for calmodulin or calcium flux in control of HL-60 growth arrest or differentiation.

Calmodulin↗
PubMed1986

Retinoic acid induced HL-60 myeloid differentiation: dependence of early and late events on isomeric structure.

The capability of HL-60 cells to undergo G1/0 specific growth arrest and myeloid differentiation in response to isomers of retinoic acid (RA) having an altered alkyl chain was determined. At a concentration where beta-all trans RA induces myeloid differentiation and G1/0 specific growth arrest, 11,13-dicis and 9,13-dicis isomers failed to induce significant phenotypic differentiation, assayed by the inducible superoxide production characteristic of mature myeloid cells, but could induce moderate G1/0 specific growth arrest. The 9-cis and 11-cis isomers induced both phenotypic differentiation and G1/0 specific growth arrest. The occurrence of G1/0 specific growth arrest without phenotypic differentiation indicates that the induced cellular programs leading to phenotypic differentiation and G1/0 specific growth arrest are not tightly coupled. Within the 48-h period usually required by beta-all trans RA to induce onset of phenotypic differentiation and G1/0 specific growth arrest, all isomers could complete early events in the cellular programs leading to G1/0 specific growth arrest and phenotypic differentiation, but the dicis isomers could not complete late events in the phenotypic differentiation program. The capability of dicis isomers to drive late events in the G1/0 specific growth arrest program was also compromised. Characteristic early and late changes in Ca2+ binding cytosolic proteins induced by RA and its isomers were consistent with their early and late capabilities. Failure of the dicis isomers to induce differentiation was thus due to a failure in late events associated with aberrations in cytosolic, Ca2+ binding proteins. The results suggest a model in which RA presents two signals to induce HL-60 terminal differentiation.

Calcium-Binding Proteins↗
PubMed1986

Differential reduction by caffeine of adriamycin induced cell killing and cell cycle delays in Chinese hamster V79 cells.

Exponentially growing Chinese-hamster V79-cells were treated with various doses of adriamycin (ADR) for 1 hr in the presence or absence of 2 mM caffeine and were subsequently incubated for 24 hr in fresh medium with or without caffeine (2 mM) before plating to assay for survival. The results indicated a reduction in killing when caffeine was present during treatment with ADR (e.g., reduction in killing from 0.03 to 0.3 after exposure to 0.5 microgram/ml ADR). This reduction in killing was even more pronounced after a 24 hr treatment with ADR in the presence of caffeine (e.g., reduction from 0.005 to 0.5 after exposure to 0.08 microgram/ml ADR). Incubation with caffeine after ADR treatment (1 hr) caused only a comparably small increase in cell survival. Presence of caffeine either simultaneously or after treatment with ADR caused a reduction of the inhibition of growth and mean-cell-volume increase, and a reduction of the accumulation of cells in G2-phase. Qualitatively similar results were also obtained after continuous treatment with ADR in the presence or absence of caffeine. Reduction in growth inhibition and accumulation of cells in G2-phase was observed under conditions only slightly affecting cell survival, thus suggesting that caffeine may affect these two phenomena by independent mechanisms. Flow cytometry measurement of the intracellular ADR content indicated a reduction in the presence of caffeine. Furthermore, post-treatment incubation with caffeine was found to increase the rate of decay of ADR-related fluorescence. Quantitative comparison between the effect of caffeine in the intracellular ADR accumulation and cell survival suggested that the observed reduction in killing could be attributed to a decrease in the intracellular drug levels. The reduction by caffeine of the ADR-induced cell cycle delays is attributed to either the decrease in the intracellular ADR dose in the presence of caffeine, or to an effect of caffeine similar to that exerted after exposure of cells to ionizing radiation. Trifluoperazine, which had only a small effect on cell survival of cells treated with ADR alone, potentiated killing when cells were treated with ADR in the presence of caffeine. This effect can be partly attributed to the observed modification in the intracellular ADR content under these conditions but, as a quantitative comparison suggests, other effects might also be involved.

Animals↗
PubMed1986

Increased c-myc RNA levels associated with the precommitment state during HL-60 myeloid differentiation.

The dynamics in levels of HL-60 (a human promyelocytic leukemia cell line) c-myc RNA due to retinoic acid-induced myeloid differentiation were measured. An increase in levels of c-myc RNA occurred early in this process when the cells are known to be in a precommitment early regulatory state. The increased levels of c-myc RNA occurred before any G1-0-specific growth arrest or phenotypic differentiation. Cells in G1 and S had similar levels of c-myc RNA during this process. Onset of growth arrest and phenotypic differentiation preceded an apparent decline of c-myc RNA levels. Levels of c-myc RNA decreased only in advanced cultures with growth arrest and differentiation essentially completed. The kinetics and cell cycle dependence of the early increase in c-myc levels paralleled previously reported nuclear structural changes characteristic of the precommitment state. Since c-myc encodes a putative nuclear matrix protein, the results suggest a regulatory role for increased c-myc expression in mediating the nuclear structural change characteristic of precommitment early in the retinoic acid-induced process of HL-60 terminal myeloid differentiation. The results argue against a change in c-myc RNA levels as a requirement for G1 to S transit or for G1-0-specific growth arrest during terminal differentiation. In contrast, the results argue for a putative regulatory role for c-myc in induction of the precommitment early regulatory state. C-myc may thus act in a homeotic regulatory capacity during HL-60 terminal myeloid differentiation.

Cell Cycle↗
PubMed1986

Modulation of adriamycin and N-trifluoroacetyladriamycin-14-valerate induced effects on cell cycle traverse and cytotoxicity in P388 mouse leukemia cells by caffeine and the calmodulin inhibitor trifluoperazine.

1,3,7-Trimethylxanthine "caffeine" (CAF) is reported to induce a differential effect on the cytotoxicity of the DNA intercalators actinomycin-D versus Adriamycin (ADR). In the present study the effect of caffeine and/or trifluoperazine in modulating cell cycle traverse, drug accumulation, and cytotoxicity of anthracyclines was evaluated. The survival in soft agar of P388 mouse leukemia cells treated with ADR (0.05-0.25 micrograms/ml) alone for 1 h was 1.2- to 3-fold lower when the cells were incubated for 24 h in drug-free medium versus medium supplemented with 2 mM CAF. In contrast, for P388 cells treated with ADR in the presence of 2 mM CAF for 1 h and subsequently incubated for 24 h in the absence or presence of 2 mM CAF, cell killed based on colony formation in soft agar was 2- to 20-fold lower than in ADR-treated cells never exposed to 2 mM CAF. In cells treated continuously for 24 h with ADR (0.01-0.05 micrograms/ml) or the DNA nonbinding ADR analogue N-trifluoro-acetyladriamycin-14-valerate (AD32) (0.05 and 0.1 micrograms/ml) the survival in soft agar was 3- to 20-fold higher in the presence versus the absence of 2 mM CAF. The decreased cytotoxicity in cells treated with ADR or AD32 in the presence of CAF was accompanied by a significant reduction in the accumulation of cells in G2. However, in cells treated with ADR or AD32 in the presence of 2 mM CAF plus 5 microM trifluoperazine the decreased G2 accumulation was not accompanied by a reduction in anthracycline cytotoxicity. The modulation by CAF of ADR and AD32 cytotoxicity did not correlate with decreased cellular ADR and AD32 accumulation. Results from this study indicate that CAF markedly reduces the cytotoxicity of ADR or AD32 and trifluoperazine circumvents the effects of CAF.

Animals↗