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.

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.

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.

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.

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.

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.

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 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.

Clinical pharmacology of polyethylene glycol-L-asparaginase

Polyethylene glycol (PEG)-L-asparaginase, at doses ranging from 500 to 8000 units/m2, was infused iv over 60 min in 31 patients of whom 27 were evaluable pharmacokinetically. The plasma disappearance of PEG-L-asparaginase is described by a monophasic curve with a mean half-life of 357 +/- 243 hr which is much longer than that of the unconjugated enzyme (half-life of approximately 20 hr). The rate of total clearance (128 +/- 74 ml/m2 X day) is much slower than that of L-asparaginase (2196 +/- 1098 ml/m2 X day). The volume of distribution is 2093 +/- 643 ml/m2, which is similar to that of L-asparaginase, indicating that PEG-L-asparaginase is mainly localized in the plasma. No enzyme could be measured in urine samples taken from nine patients for a period of up to 4 days. Additionally, no enzyme was measurable in one patient's pleural fluid obtained at the end of infusion and 6 days after infusion of a 1000-unit/m2 dose; the corresponding concentrations in plasma were 0.64 and 0.62 units/ml, respectively. In general, the plasma enzyme concentrations at the end of the 1-hr infusion and at 14 days after drug administration were proportional to the dose given. However, in two patients, a sudden disappearance of enzyme levels occurred which preceded anaphylactic reactions during subsequent treatment. A third patient developed severe bronchospasm 30 min after the first dose, but his enzyme levels were within the normal range.

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.

Myeloid differentiation-inducing factors produced by pokeweed mitogen-treated normal G1/0 lymphocytes but not chronic lymphocytic leukemia cells

HL-60 human promyelocytic leukemia cells undergo myeloid differentiation and G1/0 specific growth arrest in response to an activity produced by pokeweed mitogen stimulated peripheral blood mononuclear cells. Elaboration of this myeloid differentiation inducing activity does not require lymphocytic proliferation or pokeweed mitogen induced B-lymphocyte differentiation. The activity is a product of initially stimulated G1/0 lymphocytes. It is not produced by proliferating lymphocytes. The activity is not elaborated by G1/0 peripheral blood lymphocytes of patients with chronic lymphocytic leukemia, cells which are proliferatively refractory to pokeweed mitogen stimulation.

Control of HL-60 myeloid differentiation. Evidence of uncoupled growth and differentiation control, S-phase specificity, and two-step regulation

Myeloid differentiation of HL-60 human promyelocytic leukemia cells was studied during DMSO-induced differentiation. G 1/0-specific growth arrest could occur without the usual associated subsequent phenotypic differentiation into mature myeloid cells, suggesting that growth arrest and phenotypic differentiation are separately regulated. In the course of differentiating, the cells achieved a semi-stable intermediate state where they had a labile, pre-commitment memory of exposure to inducer, but were not yet committed to differentiation. This state was associated with a nuclear structural change previously found to be associated with the precommitment memory state. The process of differentiation could thus be resolved into two steps, early events up through development of pre-commitment memory and late events subsequents to pre-commitment memory. The kinetics of terminal cell differentiation indicated that the cellular regulatory event initiating a program of differentiation in response to inducer was S phase-specific. A comparison of the present results for DSMO to previous results for retinoic acid (RA)-induced HL-60 myeloid differentiation showed that the two inducers effect different cellular pathways for differentiation of HL-60 cells to mature myeloid cells, but with certain common features including the above S-phase specificity and pre-commitment memory.

Control of cell differentiation during proliferation. II. Myeloid differentiation and cell cycle arrest of HL-60 promyelocytes preceded by nuclear structural changes

The time-dependent dynamics of nuclear structure, cell cycle transit and arrest, and cellular differentiation were studied using the human promyelocytic leukemia cell line HL-60. Myeloid differentiation of HL-60 cells was induced by 10(-6) M beta, all trans, retinoic acid (RA). During exponential growth the cells had G1, S, G2 and M durations of 9, 11, 0.5 and 0.5 h respectively. Significant growth arrest in the G1/0 phase of the cell cycle was apparent after 48 h of RA exposure or after two division cycles. Thereafter, cells arrested in G1/0 with wide dispersion in times of arrest which extended over several cell cycle generation times. The kinetics of phenotypic differentiation, detected by phorbol myristate acetate inducible superoxide production, paralleled those of G1/0 growth arrest with similar lag and dispersion. These kinetics are consistent with a model hypothesizing the existence of an S-phase differentiation control (DC) point regulating both terminal proliferation and differentiation. Before any cell differentiation or termination of cell proliferation occurred, the nuclei of RA-treated cells underwent a structural change detected by narrow-angle light scatter measured with flow cytometry. Narrow-angle light scatter was transiently reduced, reaching a nadir at 24-48 h and returning to control values at 96 h. This change was independent of cell cycle phase or total nuclear protein content. It was associated with a morphological change of the nuclear membrane from a smooth to dimpled or pitted structure. These findings focus attention on the potential significance of nuclear structural reorganization as an early event during cell differentiation.

Endothelial cell cycle kinetics. Changes in culture and correlation with endothelial properties

Endothelial cells in culture have emerged as a model system for evaluation of endothelial properties. Culture conditions may affect expression of these endothelial properties or growth characteristics. Therefore, we evaluated cell cycle kinetics, prostacyclin release, and angiotensin-converting enzyme activity in primary and subcultured cells from bovine pulmonary and systemic vessels. Prostacyclin release was highly variable during passage in culture. However, release following stimulation with ionophore A23187 declined with serial passage. Angiotensin-converting enzyme activity also declined with repeated subculturing. Greater than 10% of primary confluent bovine endothelial cells were cycling compared to 2 to 8% of human umbilical vein endothelial cells. With passage in culture, 25% of bovine endothelial cells were cycling at confluence. Occasional strains of subcultured bovine endothelium arrested in G2 but would reenter G1 upon subculturing. Exposure to trypsin did not appear to contribute to this phenomenon. These studies have demonstrated variability in endothelial cell properties and growth characteristics during in vitro propagation. The existence of this variability must be considered when studying properties or responses of subcultured endothelium.

Evidence for cell cycle phase-specific initiation of a program of HL-60 cell myeloid differentiation mediated by inducer uptake

The question of whether the initial regulatory event, which directs an uncommitted precursor cell toward terminal differentiation, is cell cycle phase specific was examined using the human promyelocytic leukemia cell line, HL-60. While the HL-60 system does not reflect all of the features of normal hematopoiesis, it does provide a relatively well-defined in vitro experimental system which can be useful for examining aspects of the differentiation process. HL-60 cells were induced to undergo myeloid differentiation by retinoic acid. The subsequent differentiation kinetics of HL-60 populations initially enriched in different cell cycle phases was measured. This was compared to the cellular uptake of retinoic acid as a function of cell cycle position. If the initial differentiation-regulating event were cell cycle phase independent, then the kinetics of differentiation would be independent of the cell cycle status of the initial population. Flow cytometric cell sorting, based on cellular narrow angle and orthogonal light scatter intensity spectra, was used to select G1-enriched and S + G2 + M-enriched cell populations without pharmacological perturbation. These two populations were each induced to undergo myeloid differentiation with 10(-6) M beta-all-trans-retinoic acid. The kinetics of G1/0 arrest associated with terminal cell differentiation, as well as phenotypic differentiation, assayed by development of oxidative metabolism, was measured for both populations. The kinetics of differentiation differed for the two populations, indicating that the initial differentiation-regulating event was cell cycle phase specific. For both of the initial cell populations, significant phenotypic differentiation followed approximately 24 hr after enrichment in the relative number of S-phase cells. When exponentially proliferating HL-60 cells were exposed to a 1-hr pulse of 10(-5) M [3H]retinoic acid and then flow cytometrically sorted by DNA content, cells in late S + G2 + M had an approximately 10-fold higher uptake than cells in G1 or early S. The results indicate that cellular regulation of myeloid differentiation first becomes responsive to the inducer, retinoic acid, in S phase when uptake is enhanced.

Membrane origin for a signal eliciting a program of cell differentiation

Evidence is presented to indicate that the retiNOic acid (RA)-induced program of myeloid differentiation and growth arrest by HL-60 human promyelocytic leukemia cells was initiated by a signal originating at the cell membrane. Free RA and RA covalently immobilized on a solid substrate elicited similar kinetics of differentiation and G1/0-specific growth arrest. No evidence of cell-induced RA detachment from the solid substrate was found. The data explain why HL-60 cells which are deficient in cellular RA-binding protein (CRABP) nevertheless respond to RA.

Dependence of HL-60 myeloid cell differentiation on continuous and split retinoic acid exposures: precommitment memory associated with altered nuclear structure

The cell differentiation of HL-60 human leukemic promyelocytes along the myeloid pathway due to various continuous and distributed exposures to retinoic acid was studied. HL-60 myeloid differentiation was a continuously driven process; significant terminal cell differentiation occurred only after a minimum exposure to inducer of two division cycles. Cells so committed to differentiation retained a heritable, finite memory of differentiation commitment over a further division cycle. Prior to becoming committed, cells acquired precommitment memory of exposure to inducer. Precommitment memory abbreviated the subsequent exposure to inducer needed for commitment to differentiation. Precommitment memory was semistable. It was heritable, but was lost after four division cycles. The acquisition and loss of precommitment memory correlated with alterations in nuclear architecture detected by narrow angle light scatter using flow cytometry. The altered nuclear architecture first occurred before any overt cell differentiation or growth arrest. It was thus an early event in the induced program of terminal cell differentiation. Alterations in relative abundances of cytoplasmic proteins also occurred prior to overt cell differentiation or growth arrest. One of these was a 17 kdalton, anionic, probably Ca2+ binding, protein. Retinoic acid thus induced early cellular changes, including cytoplasmic and nuclear alterations, within one cell cycle when cell differentiation was not yet apparent.

Control of cell differentiation during proliferation. I. Monocytic differentiation of HL-60 promyelocytes

The cell proliferation relating an uncommitted precursor cell to a differentiated terminal cell has been quantitated. HL-60 promyelocytes, a bipotent precursor cell capable of differentiating along either the myeloid or monocytic pathway, were induced by a human lymphocyte-conditioned medium (CM) to differentiate into macrophage-like cells. The promyelocytes had a generation time of approx. 42 h. Most promyelocytes which differentiated became macrophage-like cells after only one cell division. Some, a minority, underwent more than one division. The time between induction of differentiation and expression of differentiated characteristics could thus be very short. Labelled S-phase promyelocytes could differentiate after traversing S. G2 and undergoing mitosis. Some, approx. 21%, required a subsequent complete cell cycle before differentiating. The data suggest a model in which cells must undergo a S-phase-specific differentiation control event in the presence of CM in order to differentiate in the subsequent G1 phase. This model proposes that a discrete time in S phase exists when cells are susceptible to exogenous regulation directing them to yield differentiated daughter cells.

Serum-free media for a human lymphocyte cell line and for pwm-stimulated peripheral blood lymphocytes: requirements for insulin, transferrin and albumin

Two simple chemically defined media are reported to support cell proliferation of a human lymphocyte cell line and of mitogenically (PWM) stimulated peripheral blood lymphocytes. The medium in the former instance is Ham's F12 supplemented with insulin, transferrin, albumin and cholesterol. In the latter case, RPMI 1640 supplemented with insulin, transferrin and albumin was found to support cell proliferation as well as fetal calf serum. There was no apparent cell cycle specificity observed for the mode of action of insulin and transferrin. A comparison of the two defined media showed that the one for the cell line was more enriched for lipids and lipid precursors.

Interferon inhibits PWM induced B cell differentiation but not onset of proliferation

The dependence of B lymphocyte differentiation into plasmacytes on anteceding B and T cell proliferation was studied using interferon as a probe. Possible correlations of the effect of interferon on PWM induced T and B cell proliferation and B cell differentiation into either kappa or lambda light chain immunoglobulin synthesizing plasmacytes have been investigated. The hypothesis that the observed inhibition of the PWM induced formation of plasmacytes by interferon is due to putative enhanced suppressor cell activity resulting from increased T cell proliferation is tested. Human, peripheral blood lymphocytes were exposed to PWM in the presence or absence of human leukocyte interferon. Proliferation was assayed by pulse cytophotometric analysis of cell kinetics, as well as [3H]TdR labelling of S-phase cells. Incidence of plasmacytes was detected by immunofluorescence using kappa or lambda light chain specific antibody. During continuous [3H]TdR labelling of stimulated cells, interferon inhibited incorporation of precipitable label by 40% at 96 and 144 h, indicating reduced net DNA synthesis by interferon treated cells. The relative fraction of cells in S-phase as well as G1- and G2 + M- was similar for treated and untreated cells. The fraction of cells rosetting SRBC remained stable for both treated and untreated cells. The size of the interferon treated population was persistently smaller once proliferation began. The time of initiation of proliferation was comparable for treated and untreated cells. Consistent with the findings of others using cell lines, interferon apparently induces a dilation of all cell cycle phases, thereby reducing the rate of proliferation. The same reduction occurred for both T and B cells. Time of initiation of DNA synthesis was, in contrast, not delayed by interferon, suggesting it is specific for events during the proliferative cell cycle. The occurrence of both kappa and lambda light chain immunoglobulin secreting plasmacytes was inhibited by interferon. The degree of inhibition was comparable for both kinds of plasmacytes detected. While not delaying the onset of DNA synthesis, interferon apparently retards subsequent cell proliferation and inhibits the differentiation of B cells to plasmacytes. The data indicate that active cellular proliferation and B cell differentiation require interferon sensitive events which cells initially recruited from quiescence by PWM do not. The inhibition of the incidence of plasmacytes cannot be attributed to an imbalance of T cell proliferation relative to non-T cells.

Inaccuracy of estimations of s phase fraction by reduction in cloning efficiency with hydroxyurea or tritiated thymidine

The current hypothesis, that the fractional reduction of cloning efficiency in semi-solid culture systems induced by pretreatment of the cells with hydroxyurea (HU) or [3H]TdR equals the fraction of cells initially in S phase, is tested. A lymphoblastoid cell line, SK-L7, with known cell cycle kinetics was exposed to cytotoxic concentrations of HU or suicidal doses of [3H]TdR and then initiated in semi-solid and liquid culture. Although approximately 0.6 of the initial population was in S, 1-hr exposures of HU at concentrations of up to 10(-2) M failed to reduce subsequent cloning efficiency. The 1-hr exposure to HU did not reduce either the immediate cell number or the gross population doubling rate over 24 hr. A 24-hr exposure to 10(-3) M HU reduced the cloning efficiency by approximately 98%, confirming the drug's cytotoxic capability. [3H]TdR at doses of 100 microCi/ml for 20--40 min reduced the cloning efficiency by approximately 60 and 70%, respectively. Although no cytotoxicity immediately after exposure was observed in either case, gross population doubling rate in liquid culture was reduced. While HU failed to reduce subsequent cloning efficiency, [3H]TdR reduced cloning efficiency by approximately the fraction of initial cells in S. The above hypothesis, therefore, cannot be applied naïvely as a technique for quantitating the fraction of a clonogenic cell population in S phase.

Human megakaryocyte stimulation of proliferation of bone marrow fibroblasts

Human marrow cells were processed sequentially by density centrifugation and by velocity sedimentation in serum-free Percoll gradients in order to purify megakaryocytes and to determine if these cells are the source of the growth factor derived from platelets. Cell homogenates were made from the resulting fractions and tested for growth-promoting activity(ies) in 3T3 cells and in well characterized human marrow fibroblasts. Growth was evaluated by 3H-TdR incorporation and changes in DNA cell content, as measured by flow microfluorometry. The highest mitogenic activity was derived from homogenates of low density (less than 1.050 g/cu cm), rapidly sedimenting cells. This fraction contained the highest percentage of megakaryocytes. The assessment of growth-promoting activity(ies) derived from various megakaryocyte-enriched marrow cell homogenates containing different proportions of megakaryocytes demonstrated a positive correlation between the number of megakaryocytes and their stimulatory capacity as determined by 3H-TdR uptake. The growth-promoting activities elicited from homogenates of platelets and marrow fractions enriched for megakaryocytes were similar. The dose--response curves for both were parallel, and they were both temperature resistant and trypsin sensitive. These findings implicate megakaryocytes as a source of the growth factor derived from platelets and suggest that megakaryocytes may play a role in the pathogenesis of the marrow fibrosis observed in myeloproliferative disorders by stimulating fibroblast proliferation and collagen secretion.

Cloning of fresh lymphoma cells

We attempted to induce in vivo clonal growth of neoplastic lymphoid cells from fresh specimens of involved tissue from 22 patients with no-Hodgkin lymphoma (NHL). Conditioned media derived from two human B-lymphocyte tissue culture lines were tested for their ability to promote colony growth. In addition, we compared the incidence of colony induction to the flash-3H-thymidine labeling index (LI) of the cells in the tissues cultured. Successful colony induction occurred in three-tenths of the cases of diffuse histiocytic lymphoma and one-half of the cases of nodular lymphoma. Cloning efficiencies were low, ranging from 0.0003 to 0.04%. There was no apparent relationship between successful instances of cloning and LI. We have confirmed the observations of Jones et al that lymphoid tumor cells can be cloned from tissues involved by NHL using a soft agar system. The possibility of using such systems for clinical predictive assays of chemotherapeutic drug toxicity toward tumor cells of NHL is discussed. We conclude that further refinements of the assays are desirable before they can be applied to widespread clinical use.

Role of nuclear size in cell growth initiation

Swiss 3T3 cells arrested in B0 (quiescent state) by reducing serum content of the medium all contain the same amount of DNA but vary in nuclear volume over approximately a twofold range. By use of flow microfluorimetry, scatterplots of nuclear volume versus DNA content were obtained in intervals after serum stimulation. The earliest cells to enter DNA synthesis were those with the largest nuclei, whereas cells with the smallest nuclei were among the latest. Regulation of cellular transit from G0 to the S phase was therefore, at least in part, deterministic, since all G0 cells did not have equal probabilities of entry into S at a given moment. All cells having the same nuclear volume did not initiate DNA synthesis at the same moment; therefore, factors other than nuclear volume must also influence this timing. Nuclear volume correlated with the maximum rate at which cells could enter S. The kinetic model of the cell cycle postulating a probabilistic event as solely responsible for entry into S thus appears too simple.

Ultrastructure of the capillary loops in the dermal papillae of psoriasis

Electron microscopy was used to define the ultrastructure of the capillary loops in the dermal papillae of psoriatic lesions. Pustular psoriasis of von Zumbusch and psoriasis vulgaris were studied before and after treatment with the Goeckerman regimen. Capillary loops were reconstructed from 1-mum plastic-embedded sections. Ultrathin sections were taken at intervals for correlation with the 1-mum sections. There were no ultrastructural differences between the capillary loops in psoriasis vulgaris and pustular psoriasis. The intrapapillary portion of the loop was predominantly a venous capillary. Four basic ultrastructural loop patterns were recognized which can serve as markers in studying the responses of psoriatic loops in various experimental situations. Following 3 weeks of Goeckerman therapy, the morphology of psoriatic capillary loops changed from venous capillaries to arterial capillaries which are found in the papillae of normal skin. This transformation was observed to begin 48 to 72 hr after the initiation of therapy.

Ultrastructure of the human dermal microcirculation. II. The capillary loops of the dermal papillae

Electron microscopy was used to define the ultrastructure of the capillary loops in the dermal papillae of normal, eczematous, and psoriatic skin. Capillary loops were reconstructed from 1-mum plastic-embedded sections. Ultrathin sections were taken at 4- to 6-mum intervals for correlation with the thick sections. The capillary loops of normal forearm and elbow skin could be divided into two segments: an intrapapillary and extrapapillary portion. The intrapapillary portion had the ultrastructural characteristics of an arterial capillary--homogeneous-appearing basement membrane without bridged fenestrations. The ascending limb in the extrapapillary portion was also an arterial capillary and the descending limb in the same portion had venous characteristics--multilayered basement membrane. The intrapapillary arterial loop developed venous characteristics abruptly after the vessel left the dermal papilla proper. The capillary loops in acute nummular eczema were identical in ultrastructure to those of normal skin. Bridged fenestrations were found in one capillary loop in eczema but not in normal skin. By contrast, the intrapapillary capillary loops in psoriasis were venous capillaries which were characterized by bridge fenestrations and multilayered basement membrane. The ultrastructural features of the capillary loops and those of the microcirculatory segments in the horizontal dermal plexus should provide sufficient criteria for one to evaluate the nature of vascular abnormalities that occur in the upper dermis.

Ultrastructure of the human dermal microcirculation: the horizontal plexus of the papillary dermis

Electron microscopy was used to define the ultrastructure of the various segments of the human cutaneous microcirculation in normal forearem skin. The organization of the vessels in the horizontal plexus of the papillary dermis was reconstructed from 1-mum plasticembedded sections. Ultrathin sections were taken at 10- to 20-mum intervals over a distance of 450 mum. Arterioles were followed through the capillary bed to their venous connections. Terminal arterioles, arterial and venous capillaries, and postcapillary venules were identified on the basis of size, cellular composition of their walls, and their relationship to the other segments of the microvascular bed. The arterial segments were characterized by a homogeneous basement membrane and the venous segments by a multilaminated basement membrane. The elastic lamina in the arterioles was a discontinuous layer which gradually disappeared from the arteriolar wall to form an external sheath just before the arteriole connected with the arterial capillary segment. The vascular walls varied from 1 to 5 mum in all of the segments of the microvascular bed. Criteria are proposed for identifying the various segments of the microcirculation so that their roles in dermatoses and vascular malformations can be evaluated.

Demonstration of immune complexes in spontaneous and histamine-induced lesions and in normal skin of patients with leukocytoclastic angitis

Clinical and laboratory observations have strongly suggested that leukocytoclastic angitis is an immune complex disease. Since immune complexes can be visualized as electron-dense deposits by electron microscopy (EM), this method was used in conjunction with direct immunofluorescence (IF) to determine whether complexes could be demonstrated in spontaneous lesions, and in uninvolved skin in which the vessels were made permeable by the local injection of histamine. Histamine-induced wheals were produced in the uninvolved skin of patients with active angitis. In the resulting wheal, EM studies revealed electron-dense deposits characteristic of immune complexes in postcapillary venules and direct IF studies demonstrated complement and immunoglobulins in the vessel walls. Neutrophils in varying stages of disintegration were present thereby reproducing the histopathologic changes of spontaneous lesions. EM and IF studies of nonmanipulated uninvolved skin also revealed electron-dense deposits and immune reactants in the vessel walls. Neutrophils were not present, however. This observation indicates that immune complexes are deposited in vessels before tissue damage ensues. Study of spontaneous lesions older than 24 hr revealed only fibrin by EM and no immune reactants by direct IF. In spontaneous lesions less than 24 hr old, electron-dense deposits and fibrin were seen by EM, and complement and immunoglobulins by IF. Histamine-induced wheals should be a useful device to investigate patients with disorders that have an immune complex pathogenesis.