The ratio of retinoblastoma (RB) to fos and RB to myc expression during the cell cycle

The putative transregulatory activity of the RB (retinoblastoma tumor suppressor) gene product on the expression of the c-myc and c-fos proteins during the cell cycle was assessed in HL-60 promyelocytic leukemia cells. Multiparameter flow cytometry was used to simultaneously measure nuclear DNA content, RB protein, and MYC or FOS protein per cell. The amount of RB protein per cell increased with progression through the cell cycle. As the amount of RB protein increased, the ratio of RB to MYC or to FOS protein could be determined per cell as a function of cell cycle phase. Although the amount of RB protein per cell increased with progression through successive cell cycle phases, during S phase the relative rate of increase was not as rapid as that of nuclear DNA. The amount of MYC and FOS per cell also increased throughout the cell cycle, but also more slowly than DNA during S. The ratio of the amount of RB protein to MYC protein remained constant throughout the cell cycle, consistent with putative co-regulation suggested by previous studies of promoter structure. In contrast, the ratio of RB protein to FOS protein increased with progression through the phases of the cell cycle, consistent with a putative negative effect of RB on FOS which was found in previous studies with transgenes and reporters. There was no significant change in these ratios with myelo-monocytic differentiation. Although MYC and FOS have both been implicated as growth-promoting oncogenes putatively transregulated by RB, their behavior during the cell cycle relative to RB is thus distinguishable. Interestingly, in the case of all three of these putative cell cycle regulatory proteins, their cell cycle phase-specific expression levels are consistent with a minimum amount per cell that is necessary but not sufficient for progression to the next cell cycle phase.

Herpesvirus-like DNA sequences in classic Kaposi's sarcomas

Kaposi's sarcoma (KS) accounts for more than 15% of AIDS-related malignancies. The etiology of KS is unresolved but is postulated to be multifactorial, involving viruses and overexpression of cellular growth factors and/or oncogenes. Recently, herpesvirus-like sequences (KSHV) were identified with high prevalence in AIDS-KS (AKS), endemic KS, and in classic KS biopsies (CKS). To confirm the presence and the prevalence of the KSHV sequences, 18 CKS and 13 AKS samples were tested using polymerase chain reaction (PCR) analysis. To our knowledge this is the highest number of CKS samples that has ever been included in a single study, and it is also important that the biopsies were obtained from different institutions and geographical locations. KSHV sequences were detected in 100% of the AKS samples and 72% of the CKS biopsies using PCR analysis. The presence of the unique KSHV sequences was confirmed by direct sequencing of representative PCR products obtained from AKS and CKS samples. Reverse transcriptase (RT)-PCR experiments showed that the KSHV sequences were transcribed to mRNA in both AKS and CKS samples. Our results confirm that the putative new herpesvirus-like agent is associated with both AKS and CKS and may have an etiological role in the pathogenesis of this malignancy.

Elastoderma

Elastoderma is an exceedingly rare condition that is characterized clinically as an acquired localized laxity of skin resembling cutis laxa and histologically as an excessive accumulation of pleomorphic elastic structures within the dermis. We report the case of a 27-year-old white man with a 2-year history of lax, extensible, wrinkled skin with areas of protrusion and ulceration localized to the anterior aspect and back of the neck. Histologic examination of specimens from the affected area revealed increased masses of intertwined thin, elastic fibers without calcification in the papillary and upper reticular dermis. Transmission and scanning electron microscopy demonstrated irregular deposition of elastic material at the periphery of elastic tissue fibers, with grapelike globular structures. To our knowledge, this is the second reported case of elastoderma.

RB phosphorylation in sodium butyrate-resistant HL-60 cells: cross-resistance to retinoic acid but not vitamin D3

To examine the potential coupling between inducible cellular changes in RB (retinoblastoma) tumor suppressor protein phosphorylation and ability to G0 growth arrest and differentiate, HL-60 promyelocytic leukemia cells were cultured in incremental sodium butyrate (NaB) concentrations and thereby made resistant to the growth inhibitory effects of sodium butyrate, which normally induces G0 arrest and monocytic differentiation in wild type HL-60 cells. The resistant cells were also unable to differentiate in response to NaB, indicating that a regulatory function controlling both G0 growth arrest and differentiation had been affected. The induced resistance was not genetic in origin since the cells regained the ability to G0 arrest and differentiate after being recultured in medium free of sodium butyrate for only three days. The resistant cells had similar cell cycle phase durations as the original wild type cells. The resistant cells retained the ability to both G0 arrest and differentiate in response to 1,25-dihydroxy vitamin D3 (VD3), normally an inducer of G0 arrest and monocytic differentiation in wild type cells. However, they were cross-resistant to retinoic acid (RA), another ligand for the same steroid thyroid hormone receptor family, which induces G0 arrest and myeloid differentiation in wild type cells. The ability to G0 arrest and phenotypically differentiate in response to RA were both grossly impaired. Unlike wild type cells which undergo early down-regulation and then hypophosphorylation of the RB protein when induced to differentiate, in resistant cells, hypophosphorylation of RB in response to NaB was grossly retarded. These changes in RB protein occurred faster when the cells were treated with VD3. In contrast, the changes in RB phosphorylation occurred significantly slower when the cells were treated with RA. The results suggest a coupling between the ability to G0 growth arrest and phenotypically convert and the ability to hypophosphorylate RB.

Herpesvirus-like DNA sequences in non-Kaposi's sarcoma skin lesions of transplant patients

Herpesvirus-like DNA sequences (KSHV) have been reported to be associated with various forms of Kaposi's sarcoma (KS). To determine if KSHV was associated with other proliferative skin lesions from non-AIDS immunocompromised patients, 33 skin lesions (basal cell carcinomas, squamous cell carcinomas, actinic keratoses, verruca vulgaris, atypical squamous proliferations, and seborrhoeic keratosis) from 4 organ-transplant patients receiving immunosuppressive therapy were tested for KSHV by PCR. KSHV sequences were detected in 82% of these skin lesions. Our results suggest that KSHV is associated with lesions other than KS in non-AIDS immunocompromised patients, and may also be involved in the pathogenesis of the various forms of proliferative skin lesions from organ-transplant patients.

Development, characterization, and initial evaluations of S1. A new chromogenic cephalosporin for beta-lactamase detection

A novel, chromogenic cephalosporin reagent (S1) for beta-lactamase testing was produced that shares physicochemical characteristics with nitrocefin (formerly 87/312). S1 and nitrocefin in a disk-testing format for beta-lactamase performed at 100% agreement for detecting enzyme-producing isolates of Bacteroides fragilis group, Haemophilus influenzae, Moraxella catarrhalis, Neisseria gonorrhoeae, Staphylococcus aureus, and selected Enterobacteriaceae. The time required to achieve an initial color change or a strong positive reaction was comparable for both chromogenic reagents for all organisms except the Gram-positive species. S1 reaction times were approximately 50% faster than nitrocefin for beta-lactamase-positive enterococci and S. aureus. These results from the developmental studies and a commercially prepared disk lot indicate that S1 is a promising beta-lactamase disk test reagent with the ability to detect all significant enzyme-producing species strains, some significantly earlier than the nitrocefin disk method.

Characterization of a vitamin D3-resistant human chronic myelogenous leukemia cell line

A variant of the chronic myelogenous leukemia cell line, RWLeu-4, that is resistant to the antiproliferative effects of vitamin D3 was established. Although RWLeu-4 proliferation is inhibited by 1 nmol/L vitamin D3, the resistant cells (JMRD3) continue to proliferate in the presence of 100 nmol/L vitamin D3. Both cells express similar patterns of differentiation-specific antigens after treatment with vitamin D3, and both express the retinoblastoma gene product (p110Rb). Vitamin D3 treatment of the sensitive RWLeu-4 cells decreased the level of the p110Rb protein, as well as its phosphorylation. In contrast, vitamin D3 treatment of JMRD3 had no effect on p110Rb expression or phosphorylation. Both RWLeu-4 and JMRD3 express similar vitamin D3 receptors and vitamin D3-inducible enzyme activities. Differences were detected in the DNA binding characteristics of the vitamin D3 receptors as determined by electrophoretic mobility shift studies. However, sequence analysis of the DNA-binding domain and immunoblot analysis showed no differences in the receptors. We conclude that some process subsequent to vitamin D3 receptor activation is altered in JMRD3 that partially separates vitamin D3-induced inhibition of proliferation from the induction of differentiation.

Inhibition of human peripheral blood lymphocyte function by protoporphyrin and longwave ultraviolet light

Modulation of immunologic effector cells by exogenous photoactive substances has been advanced as an underlying mechanism for the efficacy of various photochemotherapeutic regimens. It is also possible that endogenous photosensitizers, such as protoporphyrin, could similarly modify the function of immune cell types. We examined the effects of protoporphyrin plus longwave UV light on the ability of human PBL to proliferate in response to mitogens. Noncytotoxic dosages of protoporphyrin plus UV light suppressed PHA-stimulated proliferation of both PBMC and enriched T cells. CD8+ cells were more sensitive to this inhibitory effect than CD4+ cells. The inhibitory effect was also observed when proliferation was induced by the combination of a phorbol ester and ionomycin. Inhibition of PBMC proliferation was associated with inhibition of IL-2 secretion but proliferation was not restored with exogenous IL-2. Instead, the effect of protoporphyrin plus UV light may be on IL-2R. Cells treated with protoporphyrin and UV light did not display the increase in CD25 and the beta-chain of the IL-2R induced by PHA in control cells. In contrast to the effects of protoporphyrin and UV light on IL-2 and IL-2R alpha-chain protein expression, the accumulation of mRNA for these proteins induced by PHA was unaffected. None of the effects of protoporphyrin plus UV light on lymphocytes were observed in control experiments where cells were treated with either protoporphyrin or UV light alone. We conclude that biologically relevant dosages of protoporphyrin and UV light modify the function of circulating lymphocytes.

Inhibition of human peripheral blood lymphocyte function by protoporphyrin and longwave ultraviolet light

Modulation of immunologic effector cells by exogenous photoactive substances has been advanced as an underlying mechanism for the efficacy of various photochemotherapeutic regimens. It is also possible that endogenous photosensitizers, such as protoporphyrin, could similarly modify the function of immune cell types. We examined the effects of protoporphyrin plus longwave UV light on the ability of human PBL to proliferate in response to mitogens. Noncytotoxic dosages of protoporphyrin plus UV light suppressed PHA-stimulated proliferation of both PBMC and enriched T cells. CD8+ cells were more sensitive to this inhibitory effect than CD4+ cells. The inhibitory effect was also observed when proliferation was induced by the combination of a phorbol ester and ionomycin. Inhibition of PBMC proliferation was associated with inhibition of IL-2 secretion but proliferation was not restored with exogenous IL-2. Instead, the effect of protoporphyrin plus UV light may be on IL-2R. Cells treated with protoporphyrin and UV light did not display the increase in CD25 and the beta-chain of the IL-2R induced by PHA in control cells. In contrast to the effects of protoporphyrin and UV light on IL-2 and IL-2R alpha-chain protein expression, the accumulation of mRNA for these proteins induced by PHA was unaffected. None of the effects of protoporphyrin plus UV light on lymphocytes were observed in control experiments where cells were treated with either protoporphyrin or UV light alone. We conclude that biologically relevant dosages of protoporphyrin and UV light modify the function of circulating lymphocytes.

Expression of activated RAF accelerates cell differentiation and RB protein down-regulation but not hypophosphorylation

Expression of an activated raf transgene accelerated the terminal myeloid differentiation of HL-60 human promyelocytic leukemia cells induced by retinoic acid. A similar result was obtained when 1,25-dihydroxyvitamin D3 was used to induce monocytic differentiation. The stable transfectants were derived by transfecting HL-60 cells with DNA encoding an N-terminal truncated raf-1 protein. In normal HL-60 cells retinoic acid is known to induce a colony-stimulating factor-1 (CSF-1)-dependent metabolic cascade culminating in G0 arrest and phenotypic conversion. Early in this cascade, expression of the RB tumor suppressor gene product is down-regulated. A progressive redistribution of the form of the protein from largely hyperphosphorylated protein to the hypophosphorylated form begins later with G0 arrest and differentiation. In the activated raf-transfected cells, RB down regulation occurred more rapidly, consistent with accelerated differentiation. But the conversion to the hypophosphorylated form was not accelerated and occurred after G0 arrest and phenotypic conversion to myeloid differentiated cells. Thus raf activation appears to be a component of the induced metabolic cascade culminating in terminal differentiation. In this cascade raf activation promotes RB down-regulation. The data are consistent with a model in which raf is an effector of the CSF-1-dependent metabolic cascade which culminates in terminal cell differentiation, and RB downregulation is one of the downstream consequences of RAF action. Furthermore, they indicate that RB down-regulation may be an essential component of the cellular processes causing G0 arrest and differentiation, but RB hypophosphorylation is more likely a consequence thereof and not a cause.

Late dephosphorylation of the RB protein in G2 during the process of induced cell differentiation

The cell cycle phase-specific phosphorylation status of the RB protein (retinoblastoma tumor suppressor gene product) during an elicited cellular program of G0 arrest and cell differentiation was characterized. The RB protein phosphorylation state is presumed to be an important determinant of cell proliferation or arrest. The cell cycle phase specificity of RB protein phosphorylation and dephosphorylation during HL-60 human leukemia cell proliferation and differentiation was determined using DNA-based fluorescence-activated cell sorting and Western analysis. The RB protein in proliferating G1 cells was phosphorylated, but at a relatively low level. The extent of phosphorylation increased in S phase cells and was maximum in G2 + M cells. After the cells were treated with retinoic acid or 1,25-dihydroxy vitamin D3, they began to accumulate in G1/0 and phenotypically convert. Significant unphosphorylated RB protein did not appear until after the first cells had arrested and differentiated. Dephosphorylation of the RB protein was first apparent at the beginning of G2 in the remaining cycling cells after onset of arrest and differentiation had already occurred. By the time the remaining cycling cells had divided and arrested, resulting in G0 cells, a majority of RB protein was dephosphorylated, but some remained phosphorylated. The data indicate that dephosphorylation of RB does not determine residence in G1/0. Rather dephosphorylation appears as one relatively late-occurring component of the metabolic cascade culminating in G0-arrested, phenotypically differentiated cells. Dephosphorylated RB appears as a feature of differentiated cells. The data are consistent with a role for hypophosphorylated RB not so much in deriving, but in possibly sustaining the differentiated state.

Enhanced cell differentiation when RB is hypophosphorylated and down-regulated by radicicol, a SRC-kinase inhibitor

Radicicol, an inhibitor of src or src-like kinases, causes hypophosphorylation and down-regulation of the RB retinoblastoma tumor suppressor protein in HL-60 human promyelocytic leukemia cells. Both of these changes in the RB protein typically are associated with myeloid or monocytic differentiation of these cells induced by retinoic acid or 1,25-dihydroxy vitamin D3. When added with either inducer, radicicol caused the typically induced myeloid or monocytic differentiation of these cells to be accelerated. By itself radicicol caused a transient inhibition of G1 to S transit, but did not cause phenotypic conversion. The down-regulation and dephosphorylation of RB by radicicol may thus facilitate cell differentiation.

Effect of dietary omega-3 and omega-6 fatty acid sources on PUVA-induced cutaneous toxicity and tumorigenesis in the hairless mouse

Because of concern about psoralen-induced phototoxicity and photocarcinogenesis, we investigated the effects of dietary lipids in a mouse model in which 8-methoxypsoralen (8-MOP) and UVA (PUVA) therapy has been shown to be carcinogenic. SKH-Hr-1 hairless albino mice were fed diets containing either omega-3 or omega-6 fatty-acid sources (menhaden oil and corn oil, respectively). After 2 weeks on the diets, the mice were treated topically with 8-MOP and then exposed to UVA (5 J/cm2). Mice receiving the omega-3 fatty-acid source exhibited a marked decrease in inflammatory response and a more rapid repair, as expressed both grossly and microscopically. In support of the latter response, i.e. repair, ornithine decarboxylase activity was about 20% greater in animals receiving the omega-3 fatty-acid source. The effects of the dietary fatty acid sources on PUVA tumorigenesis were examined in long-term studies in which animals were treated topically with 0.01% 8-MOP thrice weekly after which they were exposed to UVA (1 J/cm2). These studies indicated that a dietary lipid rich in omega-3 fatty acid and known to exhibit anti-inflammatory properties can markedly ameliorate the course of PUVA toxicity but does not impede the course of PUVA tumorigenesis.

Predesquamin extends maturation of cultured keratinocytes

Predesquamin is a glycoprotein that we have isolated from human epidermis. Its monospecific polyclonal antibody immunolocalizes to the lower stratum corneum. We have previously found that it is not expressed ordinarily in primary keratinocyte cultures, but that it is expressed in a serum-containing medium that is supplemented with interferon-gamma. Under these conditions, we observed larger outer squames and a more mature pattern of desquamation. We now demonstrate, by adding predesquamin directly to the culture medium without the cytokine, that the morphological changes are caused by predesquamin (and the role of IFN-gamma in the previous experiment was to stimulate the expression of predesquamin).

Character of shed blood in cardiac and thoracic surgery patients: implications for reinfusion

OBJECTIVE

To determine whether the independently observed increase in the levels of cardiac enzymes in peripheral blood can be accounted for by elevations from postoperative shed-blood reinfusion in patients who have undergone cardiac or thoracic operations.

DESIGN

Prospective, case-controlled study.

SETTING

A cardiothoracic surgery unit at a university referral centre.

PATIENTS

Thirty-four consecutive patients who underwent cardiac or thoracic surgery within a 3-week period.

INTERVENTIONS

Coronary artery revascularization (23 patients), cardiac valve replacement or repair (4) and lung resection (7).

MAIN OUTCOME MEASURES

Determination of levels of cardiac enzymes and isoenzymes in samples of peripheral and shed blood. Statistical comparison was by paired t-tests within groups and by unpaired t-tests between groups.

RESULTS

Serum levels of creatine kinase, lactic dehydrogenase and aspartate aminotransferase were significantly (p < 0.001) elevated in samples of shed blood compared with peripheral blood in all groups. The elevations were found to be related to skeletal muscle injury and were not of cardiac origin. In the absence of myocardial infarction, cardiac isoenzyme levels were significantly (p < 0.001) elevated in the peripheral blood of cardiac surgery patients compared with that of thoracic surgery patients.

CONCLUSION

Reinfusion of shed blood will result in elevated levels of cardiac enzymes in peripheral blood but will not increase the percentage of isoenzymes.

Inhibition of mast cell mediator secretion induced by protoporphyrin plus long-wave ultraviolet light: a morphometric and ultrastructural analysis

It has been shown that treatment of rat peritoneal mast cells with protoporphyrin plus long-wave ultraviolet light (UVA) irradiation can suppress mediator secretion. In this study we conducted a morphometric and ultrastructural analysis of rat peritoneal mast cells to investigate possible alterations produced by this treatment before or after stimulation with calcium ionophore. Protoporphyrin plus UVA, at doses causing inhibition of mediator release, had no effect on either cell size or viability but increased cellular sphericity. There was a 43% reduction of the cell surface area, and qualitative inspection of the cells revealed that this change was associated with a reduction in microfolds on the cell surface. After 1 minute of incubation with calcium ionophore A23187 (1 mumol/L), both cells that were pretreated with protoporphyrin plus UVA and control cells showed dramatic changes in granule structure. Although treated cells had an unchanged tendency to have granules that closely approached the plasma membrane, there was an inhibition of granule extrusion in response to ionophore stimulation. These observations may be relevant to the inhibitory effect of protoporphyrin plus UVA on the generation and release of mast cell mediators.

C-FMS dependent HL-60 cell differentiation and regulation of RB gene expression

The dependence of induced myelomonocytic cell differentiation, and regulation of the RB tumor suppressor gene during this process, on the c-fms gene product, the CSF-1 lymphokine receptor, was determined in HL-60 promyelocytic leukemia cells. Adding a monoclonal antibody with specificity for the c-fms gene product to cells treated with various inducers of myelomonocytic or macrophage differentiation, including retinoic acid and 1,25-dihydroxy vitamin D3, inhibited the rate of differentiation. During the period of inducer treatment usually preceding onset of differentiation, longer periods of antibody exposure caused greater inhibition of differentiation. In a stable HL-60 transfectant overexpressing the CSF-1 receptor at the cell surface due to a constitutively driven c-fms trans gene, the rate of differentiation was enhanced compared to the wild type cell, consistent with a positive regulatory role for the CSF-1 receptor. The anti-fms antibody caused much less inhibition of differentiation in the transfectants than in wild type cells, consistent with a larger number of receptors causing reduced sensitivity. During the induced metabolic cascade leading to differentiation, the typical early down regulation of RB gene expression was inhibited by the antibody. The antibody itself caused an increase in RB expression per cell, which offset the decrease normally caused by differentiation inducers (1,25-dihydroxy vitamin D3 and retinoic acid). The changes in RB expression preceded changes in the RB protein to the hypophosphorylated state. Most of the RB protein in proliferating cells was phosphorylated and no significant accumulation of hypophosphorylated RB protein occurred until after onset of G0 arrest. Thus the metabolic cascade leading to myelomonocytic differentiation of HL-60 cells appears to be driven by a function of the c-fms protein. Inhibiting that process by attacking this receptor impedes differentiation and also compromises the early down regulation of RB tumor suppressor gene expression which normally precedes differentiation. These findings provide additional support for a potential role for down regulating RB expression in promoting cell differentiation, and suggest the possibility that RB may be either a target or intermediate mediator of CSF-1 actions.

Alterations in Fc epsilon RI induced by protoporphyrin plus long-wavelength ultraviolet light in mouse bone marrow-derived mast cells

As previously reported, protoporphyrin plus long-wavelength UV light (PP/UVA) inhibits IgE-mediated degranulation of mouse bone marrow-derived mast cells, as assessed by measurement of the release of beta-hexosaminidase. This inhibitory effect was seen with cells sensitized with IgE either before or after PP/UVA treatment (57.8 and 55.3% inhibition, respectively). PP/UVA did not dissociate IgE already bound to cells as assessed either by measuring release of bound 125I-IgE or by flow cytometric analysis. Results from immunoadsorption followed by SDS-PAGE analysis suggested that PP/UVA treatment may cause stable conjugation of IgE to its receptor. In unsensitized cells, PP/UVA did not cause conjugation of the unoccupied Fc epsilon RI to other proteins in the plasma membrane. Nevertheless, Scatchard analysis revealed that PP/UVA decreased the number of Fc epsilon RI per cell by 37% (0.95 x 10(5) vs 1.51 x 10(5)/cell), whereas affinity of the receptor for IgE was comparable between PP/UVA-treated and untreated cells (3.40 nM vs 3.27 nM). Flow cytometric analysis also confirmed the decrease in Fc epsilon RI number in PP/UVA-treated unsensitized mouse bone marrow-derived mast cells. Although 84% of PP/UVA-treated and 82% of untreated cells expressed positive fluorescence when stained with FITC-conjugated IgE, fluorescence intensity was reduced by 40% after PP/UVA treatment. We conclude that PP/UVA alters the conformational structure and/or number of Fc epsilon RI expressed on the mast cell surface. This effect could potentially explain the ability of PP/UVA to inhibit mast cell secretory function and may be related to an ability of PP/UVA to alter the properties of the plasma membrane.

Alterations in Fc epsilon RI induced by protoporphyrin plus long-wavelength ultraviolet light in mouse bone marrow-derived mast cells

As previously reported, protoporphyrin plus long-wavelength UV light (PP/UVA) inhibits IgE-mediated degranulation of mouse bone marrow-derived mast cells, as assessed by measurement of the release of beta-hexosaminidase. This inhibitory effect was seen with cells sensitized with IgE either before or after PP/UVA treatment (57.8 and 55.3% inhibition, respectively). PP/UVA did not dissociate IgE already bound to cells as assessed either by measuring release of bound 125I-IgE or by flow cytometric analysis. Results from immunoadsorption followed by SDS-PAGE analysis suggested that PP/UVA treatment may cause stable conjugation of IgE to its receptor. In unsensitized cells, PP/UVA did not cause conjugation of the unoccupied Fc epsilon RI to other proteins in the plasma membrane. Nevertheless, Scatchard analysis revealed that PP/UVA decreased the number of Fc epsilon RI per cell by 37% (0.95 x 10(5) vs 1.51 x 10(5)/cell), whereas affinity of the receptor for IgE was comparable between PP/UVA-treated and untreated cells (3.40 nM vs 3.27 nM). Flow cytometric analysis also confirmed the decrease in Fc epsilon RI number in PP/UVA-treated unsensitized mouse bone marrow-derived mast cells. Although 84% of PP/UVA-treated and 82% of untreated cells expressed positive fluorescence when stained with FITC-conjugated IgE, fluorescence intensity was reduced by 40% after PP/UVA treatment. We conclude that PP/UVA alters the conformational structure and/or number of Fc epsilon RI expressed on the mast cell surface. This effect could potentially explain the ability of PP/UVA to inhibit mast cell secretory function and may be related to an ability of PP/UVA to alter the properties of the plasma membrane.

1,25-Dihydroxy vitamin D3 and 12-O-tetradecanoyl phorbol-13-acetate synergistically induce monocytic cell differentiation: FOS and RB expression

1,25-dihydroxy vitamin D3 and 12-O-tetradecanoyl phorbol-13-acetate (TPA) interact synergistically to induce monocytic differentiation of U937 histiocytic lymphoma cells. Addition of TPA causes an otherwise ineffective dose of 1,25-dihydroxy vitamin D3 to induce differentiation. The induced differentiation depends on the simultaneous (vs. sequential) presence of both agents. The kinetics of induced differentiation are consistent with a G1 specific cellular response to initiate the metabolic cascade culminating in cell differentiation. The induced differentiation occurs with down-regulation of c-fos protein and an accompanying up-regulation of RB protein expression, consistent with a possible need for up-regulated RB expression to maintain a given differentiated phenotype and suppress transcriptional activators that might typically be associated with proliferation.

12-O-tetradecanoylphorbol-13-acetate and staurosporine induce increased retinoblastoma tumor suppressor gene expression with megakaryocytic differentiation of leukemic cells

The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), induced increased expression of the retinoblastoma (RB) tumor suppressor gene product in the course of megakaryocytic differentiation of the K562 human leukemia cell line, a differentiatively multipotent hematopoietic precursor cell. The induced increase in RB protein per cell occurred early, by 8 h of treatment, preceding any significant phenotypic differentiation evidenced by cellular expression of the CD41 differentiation-specific megakaryocytic cell surface marker, but not inhibition of cell cycle transit, leading to a cell population arrested with 2 n, 4 n, and 8 n DNA content. The increase in RB protein per cell occurred for cells in all cell cycle phases. Staurosporine (STSP) was found to induce a similar course of cell cycle arrest and differentiation. Furthermore, STSP caused an up-regulation of RB expression similar to that caused by TPA. Almost all of the RB protein is phosphorylated in untreated cells, but TPA and STSP both caused the late appearance of hypophosphorylated RB protein following cell cycle arrest. The STSP-caused hypophosphorylation was much later than the TPA effect. Hypophosphorylation of RB is, thus, not necessarily a prerequisite for cell cycle arrest but may be a consequence of G0. Given that TPA can be an activator and STSP an inhibitor of protein kinase C, it appears that the induced processes of tumor suppressor gene regulation and growth and differentiation control are not necessarily protein kinase C dependent in K562 cells. Furthermore, the findings that these two presumably divergent inducing agents caused a similar increase in RB gene expression suggests that the up-regulation of RB associated with differentiation is not a coincidence of just one specific inducer but may be a common essential feature of the induced differentiation. The amount of RB protein per cell increased within hours of exposure to TPA or STSP and may have a role in the induced metabolic cascade producing the new phenotype.

Calcifying panniculitis and systemic calciphylaxis in an end-stage renal patient

A patient with a history of end-stage renal failure who had been receiving hemodialysis for approximately six months experienced painful plaques bilaterally on the medial aspects of her thighs. A biopsy specimen of the affected subcutaneous tissue demonstrated calcification in the subcutaneous tissue. In this case of calcifying panniculitis, the conditions for systemic calciphylaxis appear to have been present.

IgE and adenosine 5' triphosphate receptors on immature murine mast cells are functionally linked to signal transduction mechanisms

Calcium mobilization in response to IgE-receptor cross-linking by antigen was assessed in immature murine mast cells cultured from bone marrow to determine whether the early expression of IgE receptors on such cells may be of functional significance. IgE receptors were expressed by approximately 30% of cells after 1 week in culture and by an increased proportion at 2 and 3 weeks. The ability of a non-IgE-dependent stimulus, adenosine 5' triphosphate (ATP), to increase intracellular calcium in these cells was also tested. Calcium mobilization in large numbers of individual cells was monitored with use of a fluorimetric reagent and flow cytometry. Both antigen and ATP had significant effects on intracellular calcium in cells cultured for as little as 1 week with interleukin-3, when few cells exhibited morphologic or functional characteristics of mast cells. Longer times in culture were associated with an increase in the proportion of cells responding to these stimuli with calcium mobilization, but not with a change in the magnitude of the response. We conclude that the early expression of IgE receptors during mast cell development may be functionally significant, since these receptors appear to be linked to cellular signal transduction mechanisms. The data additionally imply a possible role for ATP in mast cell development.

Biliary concentrations of fluconazole in a patient with candidal cholecystitis: case report

A patient with acute cholecystitis due to Candida albicans and Candida parapsilosis was treated with a percutaneous cholecystostomy and daily intravenous fluconazole. Fluconazole levels in serum and bile were measured by gas chromatography. Fluconazole levels in the bile were equal to those in the blood for the first 8 hours after a dose and were slightly higher than serum levels after that. Bile levels after an oral dose of fluconazole were 15% higher than levels achieved after intravenous administration of the drug. The infection was cured after 2 weeks of treatment. This experience suggests that sufficient fluconazole is excreted in the bile to be effective for treatment of biliary infections due to susceptible yeasts.

Regulation of cell proliferation: late down-regulation of c-myb preceding myelo-monocytic cell differentiation

Expression of the c-myb nuclear oncogene during the cell proliferation and differentiation of HL-60 human promyelocytic leukemia cells was characterized and compared to the expression of c-fos, another nuclear oncogene with transcriptional regulatory activity. During progression through the cell cycle, the amount of c-myb protein increased. The increase was commensurate with total cell size, thus preserving the relative abundance of c-myb protein present at the onset of the cell cycle. In HL-60 cells, the induced metabolic cascade leading to terminal myeloid or monocytic differentiation segregates into two steps occurring over two division cycles. Expression of c-myb did not diverge from the control until late in this metabolic cascade when it declined prior to onset of terminal differentiation. This course of expression was similar for both the retinoic acid induced myeloid or the 1,25-dihydroxy vitamin D2 induced monocytic terminal differentiation of the cells. Bromodeoxyuridine, which induces proliferative arrest but not phenotypic differentiation of these cells, induced the same course of c-myb expression as the inducers of terminal differentiation. The same course of c-myb expression with growth arrest induced by these three different means is consistent with a potential proliferation regulatory role for c-myb in late but not early events leading to terminal differentiation. The dynamics of c-myb expression during this process were qualitatively, but not quantitatively, similar to the course of c-fos expression. Thus, taken with previous results, then amongst the nuclear oncogenes or tumor suppressor genes, c-myc, RB, c-fos, and c-myb, only c-myc and RB expression exhibit early regulation during induced HL-60 cell differentiation.

RB tumor suppressor gene expression responds to DNA synthesis inhibitors

Expression of the RB tumor suppressor gene, whose function is putatively in controlling cell growth, may be regulated by S-phase specific inhibitors of DNA synthesis that are commonly used in cell synchronization and cancer chemotherapy. Relatively low concentrations of the agents, cytosine arabinoside, bromodeoxyuridine, 5-fluorouracil, hydroxyurea, methotrexate and retinoic acid, were tested. At low concentrations still permitting submaximal cell growth, these drugs all changed RB gene expression, causing either up or down regulation of RB expression to varying degrees. Despite their potential similarity as a class, the nucleotide analogues elicited differential effects. The drug-induced up or down regulation of RB expression did not correlate with changes in c-myc expression indicating that the changes are not a manifestation of general metabolic changes potentially associated with altered proliferation. Amongst the agents considered, retinoic acid was the only one that caused a significant parallel reduction in RB and c-myc expression in the HL-60 human promyelocytic leukemia cells tested. The results thus show that even low concentrations of DNA synthesis inhibitors can have unpredictable affects on expression of growth regulatory genes.

Modulation, in vivo and in vitro, of surface expression of CD18 by bovine neutrophils

A series of experiments was designed to elucidate some of the factors that may influence surface expression of CD18 by bovine neutrophils. Expression of CD18 was determined by immunofluorescence flow cytometry. Neutrophils recovered from the uterus of cows (n = 9) after intrauterine administration of sterile oyster glycogen solution expressed (mean +/- SD) 123 +/- 21% more CD18 than did circulating neutrophils recovered simultaneously from the same cows (P = 0.003). In 8 cows given 20 mg of dexamethasone IM daily for 3 days, expression of CD18 on blood neutrophils was 29.6 +/- 8% less after treatment than before treatment (P = 0.0078). Neutrophils from 12 cows or bulls exposed to phorbol myristate acetate in vitro increased expression of CD18 by 137 +/- 37% (P = 0.0035). Likewise, exposure of neutrophils from 8 cattle to zymosan-activated bovine plasma increased CD18 exposure by 10.6 +/- 3.8% (P = 0.029). These findings indicate that expression of CD18 by bovine neutrophils is a dynamic system, capable of responding to inflammatory stimuli. Inadvertent activation of neutrophils may be responsible for some of the variance in expression observed when examining large groups of cattle for CD18 expression by neutrophils. The ability of bovine neutrophils to respond rapidly to various stimuli by increasing surface expression of CD18 indicates that a pool of intracellular CD18 may be available for inclusion in the plasmalemma, as has been reported for human neutrophils.

Achromatic holographic configuration for 100-nm-period lithography

For the fabrication of large-area, spatially coherent gratings with periods of 100 nm or less, a grating interferometer is preferred over a conventional holographic configuration because of the limited coherence of available sources. Using a configuration that employs two matched fused silica phase gratings and an ArF excimer laser, we obtain high-quality 100-nm gratings in polymethyl methacrylate. We analyze the conditions for achieving high-contrast fringes with such an achromatic holographic configuration and show that the depth of focus depends only on the spatial coherence of the source. We also describe a highly accurate method for calculating the diffraction efficiency of the phase gratings as a function of polarization, incidence angle, and grating structure.

Protoporphyrin and long-wave ultraviolet light modulate metabolic events in rat peritoneal mast cells

We have previously shown that protoporphyrin (PP) plus long-wave ultraviolet light (UVA) has an inhibitory effect on the release of histamine from rat peritoneal mast cells in response to various stimuli, without compromising cell viability. In the present study, we observed that protoporphyrin at a noncytolytic dose (3 ng/ml) plus UVA irradiation (0.038 J/cm2) is also able to suppress prostaglandin D2 generation by rat peritoneal mast cells in response to calcium ionophore A23187, compound 48/80, or anti-IgE antibody by 64%, 92%, and 100%, respectively. Because of the participation of protein kinase C in stimulus-secretion coupling in mast cells, we also investigated the effect of PP plus UVA on the release of histamine induced by the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA). PP plus UVA inhibited histamine release induced by PMA. The release of histamine induced by the synergistic combination of PMA (50 nM) and a low dose of calcium ionophore A23187 (0.1 microM) was also inhibited. PP plus UVA inhibited the release of histamine induced by the non-fluorescent calcium ionophore, 4-Br-A23187, by 47.8%, but had essentially no effect on changes in intracellular calcium induced by this stimulus. In contrast, both the release of histamine and changes in intracellular calcium stimulated by compound 48/80 were inhibited. We conclude from these results that PP plus UVA may affect both early and late biochemical events involved in mast cell mediator release.

Coupled down-regulation of the RB retinoblastoma and c-myc genes antecedes cell differentiation: possible role of RB as a "status quo" gene

The ability of the well known morphogen, retinoic acid (RA), as well as 1,25-dihydroxy-vitamin D3 (VD), whose receptor complex binds a DNA consensus sequence related to that of the retinoic acid receptor, to regulate expression of the retinoblastoma (RB) tumor suppressor gene in a context of induced cell differentiation was characterized. HL-60 human promyelocytic leukemia cells were induced to undergo myeloid or monocytic terminal cell differentiation by these agents. To investigate the potential coupling between down-regulation of RB and c-myc oncogene expression with cell differentiation, dose response relationships for the induced down-regulation of RB and c-myc expression were compared with each other and with induced cell differentiation. The total amount of RB protein per cell increased as cells advanced through the cell cycle, but the amount of RB protein relative to the total cell mass remained approximately constant. Treated with RA or VD, an early progressive decrease in cellular content of the RB protein occurred in all cell cycle phases well before any cell cycle modulation or phenotypic differentiation. For a differentiation-defective variant HL-60 cell line, failure to differentiate was preceded by a failure to down-regulate cellular levels of the RB protein. In dose response experiments, progressively increasing RA or VD concentrations caused progressively greater reductions in RB as well as c-myc expression with an increasing fraction of cells terminally differentiating. For both RA and VD, the dose response relationships for reductions in RB and c-myc expression were similar suggesting that their down-regulation may be coupled. These observations are consistent with a model whereby RB expression acts as a cellular brake to sustain a developmentally ordained state of differentiation (i.e., preserve the "status quo"); and the down-regulation of heterogeneously distributed RB protein per cell below a threshold is part of the metabolic cascade culminating in terminal cell differentiation. Thus, RB may have a role in this developmental context.

Inducers of leukemic cell differentiation cause down-regulation of RB gene expression

Expression of the retinoblastoma (RB) tumor suppressor gene during cell differentiation induced by dimethyl sulfoxide or sodium butyrate was studied in HL-60 human promyelocytic leukemia cells. As cells progressed through the cell cycle, the amount of RB protein per cell increased with homeostasis maintained, so that the amount of RB protein relative to the total cell mass remained almost constant. Dimethyl sulfoxide was used to induce these promyelocytic leukemia cells to undergo terminal differentiation into mature myeloid cells. There was an early reduction in the RB protein expressed per cell. The reduction in expression was similar for cells in all cell cycle phases. There was also progressively reduced expression at later times as cells terminally differentiated. This was compared to the case in which sodium butyrate was used to induce the differentiation of HL-60 cells into mature monocytic cells. An early reduction in RB protein expression per cell also occurred. It occurred for cells in all cell cycle phases as well. Thus, the induced differentiation of HL-60 cells along either the myeloid or the monocytic differentiation lineage involves an early reduction in RB expression, which is common to both pathways. The reduction anteceded proliferative arrest or differentiation. In both cases, the final, resulting G0-differentiated cells had less RB protein per cell than the proliferating, immature, leukemic precursor cells.

Modulation of human cutaneous mast cell responsiveness by a single, low-dose, PUVA treatment

The present study was conducted to investigate whether a single administration of a relatively low dose of 8-methoxypsoralen (8-MP) with long-wave ultraviolet A (UVA) irradiation alters human skin test responses to a mast cell secretagogue, codeine, and to a vasodilator, histamine. Administration of 8-MP at a dose of 10 mg followed by UVA irradiation (1 joule/cm2) suppressed the skin flare-and-wheal response to codeine and decreased the number of visible degranulated mast cells in biopsy specimens examined histologically. UVA irradiation alone enhanced the skin wheal-and-flare response to either codeine or histamine. The inhibitory effect of 8-MP plus UVA irradiation on both wheal-and-flare responses to codeine tended to decrease, and an increasing enhancement of the skin response to histamine could be observed as the dose of 8-MP was increased from 10 to 30 mg. We postulate that (1) a single 8-MP plus UVA irradiation treatment at appropriate doses could be a potential approach to modulate the mediator-releasing properties of mast cells resident in the skin and (2) the underlying mechanisms of this inhibition is complex, probably reflecting a balance between the inhibitory effect of 8-MP plus UVA irradiation on mast cell-mediator release, enhancement of the vascular response to histamine, and direct photoactivation of resident mast cells.

Regulated expression of the RB "tumor suppressor gene" in normal lymphocyte mitogenesis: elevated expression in transformed leukocytes and role as a "status quo" gene

Expression of the RB retinoblastoma tumor suppressor gene product is regulated early during the stimulation of normal human peripheral blood lymphocytes, suggesting a regulatory role for the amount of this protein in mitogenesis of normal cells. When normal human peripheral blood lymphocytes were mitogenically stimulated with pokeweed mitogen, bivariate flow cytometric measurements of cellular DNA and RB protein content showed an early decrease in the amount of RB protein per cell, anteceding onset of S phase. A subsequent increase in the amount of RB protein per cell occurred with cell proliferation. Thus the amount of RB protein relative to the total cell mass underwent a biphasic response with mitogenesis. The resulting proliferating cells had a slightly elevated level of RB protein per cell compared to the unstimulated cells. Comparison of other proliferating leukocytes to normal lymphocytes showed that both EBV virally transformed lymphocytes and human promyelocytic leukemia cells (HL-60) had elevated levels of RB protein per cell compared to normal peripheral blood lymphocytes. Mitogenic stimulation or transformation by other means thus is associated with regulation of the amount of RB protein per cell, suggesting a regulatory role for the RB protein in normal cell growth control.

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.

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.

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.

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.

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.

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.

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.