Membrane origin for a signal eliciting a program of cell differentiation

[Prevention and Treatment of Cancer with Vitamin A and Its Derivatives: Cell Differentiation and Proliferation]

Normal differentiation and proliferation of cells are essential for maintaining homeostasis. Following the successful completion of whole genome sequencing, protein modification has been attracted increasing attention in order to understand the roles of protein diversification in protein function and to elucidate molecular targets in mechanisms of signal transduction. Vitamin A is an essential nutrient for health maintenance. It is present as β-carotene in green and yellow vegetables and retinyl ester in animal products and absorbed into the body from the intestines. After ingestion, it is converted to retinol and oxidized in target cells to retinal, which plays critical roles in vision. It is then further oxidized to retinoic acid (RA), which exhibits a number of effects prior to being metabolized by cytochrome P450 and excreted from the body. Since RA exhibits cell differentiation-inducing actions, it is used as a therapeutic agent for patients with acute promyelocytic leukemia. The current paper describes: (1) HL60 cell differentiation and cell differentiation induction therapy by RA; (2) roles played by RA and retinal and their mechanisms of action; (3) retinoylation, post-translational protein-modified by RA, a novel non-genomic RA mechanism of action without RA receptor; (4) new actions of β-carotene and retinol in vivo and (5) potent anticancer effects of p-dodecylaminophenol (p-DDAP), a novel vitamin A derivative created from the RA derivative fenretinide. We propose that nutritional management of vitamin A can be effective at preventing and treating diseases, and that p-DDAP is a promising anticancer drug.

Vitamin A in health care: Suppression of growth and induction of differentiation in cancer cells by vitamin A and its derivatives and their mechanisms of action

Vitamin A is an important micro-essential nutrient, whose primary dietary source is retinyl esters. In addition, β-carotene (pro-vitamin A) is a precursor of vitamin A contained in green and yellow vegetables that is converted to retinol in the body after ingestion. Retinol is oxidized to produce visual retinal, which is further oxidized to retinoic acid (RA), which is used as a therapeutic agent for patients with promyelocytic leukemia. Thus, the effects of retinal and RA are well known. In this paper, we will introduce (1) vitamin A circulation in the body, (2) the actions and mechanisms of retinal and RA, (3) retinoylation: another RA mechanism not depending on RA receptors, (4) the relationship between cancer and actions of retinol or β-carotene, whose roles in vivo are still unknown, and (5) anti-cancer actions of vitamin A derivatives derived from fenretinide (4-HPR). We propose that vitamin A nutritional management is effective in the prevention of cancer.

The Influence of Amphotericin B on Differentiation Induced by Dimethylsulfoxide and Actinomycin D in HL60 and Friend Cell Lines

We use murine erythroid Friend cells and human promyelocytic HL60 cells to investigate the influence of a transmembrane signal in triggering myeloid or erythroid cell differentiation. Combined treatments were given with dimethylsulfoxide, actinomycin D and amphotericin B, a substance which resembles a deviant membrane lipid and which seems to influence exclusively membrane activity. Our results suggest that a membrane modification alone is sufficient for in vitro HL60 cell differentiation, whereas both a transmembrane and a nuclear signal are necessary for Friend cell differentiation.

Using cell fate attractors to uncover transcriptional regulation of HL60 neutrophil differentiation

BACKGROUND

The process of cellular differentiation is governed by complex dynamical biomolecular networks consisting of a multitude of genes and their products acting in concert to determine a particular cell fate. Thus, a systems level view is necessary for understanding how a cell coordinates this process and for developing effective therapeutic strategies to treat diseases, such as cancer, in which differentiation plays a significant role. Theoretical considerations and recent experimental evidence support the view that cell fates are high dimensional attractor states of the underlying molecular networks. The temporal behavior of the network states progressing toward different cell fate attractors has the potential to elucidate the underlying molecular mechanisms governing differentiation.

RESULTS

Using the HL60 multipotent promyelocytic leukemia cell line, we performed experiments that ultimately led to two different cell fate attractors by two treatments of varying dosage and duration of the differentiation agent all-trans-retinoic acid (ATRA). The dosage and duration combinations of the two treatments were chosen by means of flow cytometric measurements of CD11b, a well-known early differentiation marker, such that they generated two intermediate populations that were poised at the apparently same stage of differentiation. However, the population of one treatment proceeded toward the terminally differentiated neutrophil attractor while that of the other treatment reverted back toward the undifferentiated promyelocytic attractor. We monitored the gene expression changes in the two populations after their respective treatments over a period of five days and identified a set of genes that diverged in their expression, a subset of which promotes neutrophil differentiation while the other represses cell cycle progression. By employing promoter based transcription factor binding site analysis, we found enrichment in the set of divergent genes, of transcription factors functionally linked to tumor progression, cell cycle, and development.

CONCLUSION

Since many of the transcription factors identified by this approach are also known to be implicated in hematopoietic differentiation and leukemia, this study points to the utility of incorporating a dynamical systems level view into a computational analysis framework for elucidating transcriptional mechanisms regulating differentiation.

Differential Cellular Distribution of Retinoic Acid during Staurosporine Potentiation of Retinoic Acid-Induced Granulocytic Differentiation in Human Leukemia HL-60 Cells

Pretreatment of cells with staurosporine, a protein kinase C (PKC) inhibitor, was found to potentiate the granulocytic differentiation induced by a brief (2 h) retinoic acid treatment. By cell cycle analysis, staurosporine was found to have little effect on the cell cycle. Retinoic acid was distributed equally in the nuclei (40%) and in the plasma membrane (40%) of staurosporine-pretreated cells while less than 20% of retinoic acid was found in the membrane of control non-staurosporine-pretreated cells during the retinoic acid-induced differentiation. These results indicate that the enhancing effect of staurosporine may be somehow associated with the localization of retinoic acid in the plasma membrane of the cell. Copyright 1995 S. Karger AG, Basel

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

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

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.

Intracellular actions of vitamin A

Because the effects of vitamin A vary with tissue type and often with the form of vitamin A itself, a complete understanding of the mechanism(s) of action still has not been attained. The action of vitamin A may be at the level of genomic expression, at the membrane level, or both. Intercellular and intracellular transport of vitamin A are facilitated by specific binding proteins but probably not in the cellular uptake of vitamin A. Subcellularly, vitamin A may exert a direct effect on transit through the Golgi apparatus, as observed from both biochemical and morphological studies. In my laboratory, recent work using cell-free systems has shown that retinol stimulates transition vesicle formation from endoplasmic reticulum in a GTP-requiring step.

A dominant negative mutation of the alpha retinoic acid receptor gene in a retinoic acid-nonresponsive embryonal carcinoma cell

Pluripotential embryonal carcinoma cells such as those of the P19 line differentiate when exposed to retinoic acid (RA). The RAC65 cell line is a mutant clone of P19 cells selected to be RA nonresponsive. RAC65 cells carry a rearrangement affecting one of the genes encoding a nuclear retinoic acid receptor (RAR alpha). The mutant gene encodes a protein, RAR alpha', that has lost its 70 C-terminal amino acids, thus truncating the RA-binding domain. The RAR alpha' was found to be a dominant repressor of transcription from an RA-responsive target gene; however, expression of RAR alpha' was insufficient to confer RA nonresponsiveness, suggesting that RAC65 cells carry an additional mutation(s) affecting RA-induced genes.

Synergistic effect of retinoic acid and 1,25-dihydroxyvitamin D3 on the differentiation of the human monocytic cell line U937

The human-derived leukemia cell lines HL-60 and U937 are known to differentiate into more mature phagocytic cells in the presence of retinoic acid or 1,25-dihydroxyvitamin D3. We studied the effects of combinations of these two agents on cell growth and differentiation. These treatments were found to increase inhibition of cell proliferation. A dramatic enhancement of functional properties was observed in U937, but not HL-60 cells exposed to combinations of the two inducers. We investigated the conditions required to obtain the highest synergistic effects on the differentiation of U937 cells. These effects were found to be highly dose-dependent. We found that synergism required the simultaneous presence of both inducers and did not occur upon sequential exposure to each agent used separately.

A dominant negative mutation of the alpha retinoic acid receptor gene in a retinoic acid-nonresponsive embryonal carcinoma cell

Pluripotential embryonal carcinoma cells such as those of the P19 line differentiate when exposed to retinoic acid (RA). The RAC65 cell line is a mutant clone of P19 cells selected to be RA nonresponsive. RAC65 cells carry a rearrangement affecting one of the genes encoding a nuclear retinoic acid receptor (RAR alpha). The mutant gene encodes a protein, RAR alpha', that has lost its 70 C-terminal amino acids, thus truncating the RA-binding domain. The RAR alpha' was found to be a dominant repressor of transcription from an RA-responsive target gene; however, expression of RAR alpha' was insufficient to confer RA nonresponsiveness, suggesting that RAC65 cells carry an additional mutation(s) affecting RA-induced genes.

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.

Effect of butylated hydroxytoluene on bilineage differentiation of the human HL-60 myeloblastic leukemia cell

Butylated hydroxytoluene (BHT), which has both antioxidant and membrane active properties, has been reported to affect cellular differentiation. We studied its effect on the bipotent lineage differentiation of the important HL-60 human myeloblastic leukemia cell line using reduction of nitroblue tetrazolium, cell cycle analysis, population growth rate, monoclonal antibodies, and morphology. BHT markedly accelerated retinoic acid-induced myelocytic differentiation and dihydroxyvitamin D3-induced monocytic differentiation in a concentration and time-dependent manner. Butylated hydroxyanisole (BHA) had a comparable effect. Preincubation with the compounds was not necessary to evoke the acceleration Other antioxidants and inhibitors of eicosanoid synthesis were inactive. We conclude that the important food preservatives BHT and BHA accelerate the kinetics of terminal differentiation of human leukemia and that this effect is likely due at least in part to their membrane active properties.

Cell density and cell cycle effects on retinoic acid-induced embryonal carcinoma cell differentiation

P19 embryonal carcinoma cells can be induced to differentiate with a pulse of only 4 hr in retinoic acid (RA). The efficiency of RA-induced differentiation is independent of the position of P19 cells in the cell cycle but is critically dependent on the ratio between the number of cells and the number of moles of RA in the culture medium. P19 cultures at lower cell density are more efficiently induced to differentiate than cultures containing cells at higher cell densities. This effect is not mediated by cell-to-cell contact but may be related to the rapid metabolism of RA by the cells. Individual clones of differentiating P19 cells can develop into at least three different cell types suggesting that each cell in the population of embryonal carcinoma cells retains pluripotency.

Effect of retinoic acid on the phosphorylation of endogenous proteins in HL-60 cells

HL-60 cells were incubated with [32P]-Pi in order to label endogenous phosphoproteins in situ. These were then resolved via two-dimensional electrophoresis and autoradiograms were made from the gels. A comparison of autoradiograms made from retinoic-acid-differentiated cells with those made from control cells revealed a small number of phosphoproteins whose labeling was enhanced in differentiated cells. Incubating HL-60 cells with [35S]-methionine revealed that RA induced the synthesis of one of these proteins, (53 kDa, pl 4.8) although not to a degree sufficient to account for the increased phosphate labeling observed in differentiated cells. Difluoromethylornithine (DFMO), which arrests HL-60 cell proliferation without inducing differentiation, had no effect on endogenous protein phosphorylation. Treatment of DFMO-arrested cells with retinoic acid, however, increased the phosphorylation of the proteins and resulted in differentiation of the cells. Densitometric analysis of autoradiograms made from two-dimensional gels revealed that the phosphorylation of the 53-kDa, pl 4.8 protein was significantly elevated in cells exposed to RA for as little as 12 hours, i.e., before the cells were committed to differentiate and before a significant increase in the number of phenotypically mature cells was observed. It therefore appears that this protein may be an intermediate in the retinoic-acid-induced differentiation process.

Comparison of the uptake and metabolism of retinol delivered to primary mouse keratinocytes either free or bound to rat serum retinol-binding protein

Serum retinol-binding protein (RBP) is believed to be responsible for the transport of retinol from its storage site in the liver to vitamin A requiring target cells such as keratinocytes. We have used primary mouse keratinocytes as a model system to compare the uptake and metabolism of [3H] retinol delivered to them either free in solution or bound to RBP. RBP was purified from rat serum, loaded with [3H]retinol, and the [3H]retinol-RBP complex purified by affinity chromatography on human transthyretin-Sepharose. Keratinocytes incubated with either free [3H]retinol or [3H]retinol-RBP complex accumulated [3H]retinol in a time and temperature dependent manner. However, cells incubated with free [3H]retinol acquired 15- to 20-fold more ligand than if the retinol was delivered via RBP. The uptake of free [3H]retinol or [3H]retinol from RBP was not inhibited by excess unlabeled free retinol. The uptake of [3H]retinol from RBP was inhibited by high concentrations of holo-RBP, with half maximal inhibition occurring at 3 microM holo-RBP. However, no specific binding of 125I-labeled RBP to monolayers of keratinocytes or membranes prepared from them was found indicating the absence of a high affinity RBP receptor on keratinocytes. Surprisingly, 50% of the [3H]retinol delivered to the keratinocytes during a 30-min uptake period was released from them within 30-min irrespective of whether or not it was initially delivered to them as free [3H]retinol or bound to RBP. The remaining 50% was lost at a much slower rate, but only 20% remained 24-h after delivery. Studies on retinol metabolism demonstrated that 7%-12% of the total cell-associated [3H]retinol delivered during a 90-min uptake period was esterified (mostly as retinyl palmitate) whether or not it was given free in solution or bound to RBP. Additionally, [3H]retinol taken up by the keratinocytes during the initial 90-min incubation was not chased into a stable retinyl ester pool in a subsequent 9.5-h incubation, but instead, retinyl ester was lost from the cells with kinetics similar to those of total cell-associated radioactivity. These results suggest that a function of RBP is to protect cells from a rapid accumulation of the vitamin which occurs when it is delivered free in solution. However, the cellular fate and metabolism of retinol appears to be the same whether the vitamin is delivered free in solution or bound to RBP.

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.

Transformation with SV40 virus prevents retinoic acid inhibition of plasma membrane NADH diferric transferrin reductase in rat liver cells

Retinoic acid inhibits the reduction of diferric transferrin through the transplasma membrane electron transport system on fetal rat liver cells infected with a temperature-sensitive SV40 virus when the cells are in the nontransformed state cultured at 40 degrees C. When the cells are in the transformed state (grown at the permissive 33 degrees C temperature), retinoic acid does not inhibit the diferric transferrin reduction. Inhibition of activity of nontransformed cells is specific for retinoic acid with only slight inhibition by retinol and retinyl acetate at higher concentrations. Isolated rat liver plasma membrane NADH diferric transferrin reductase is also inhibited by retinoic acid. The effect of transformation with SV40 virus to decrease susceptibility to retinoic acid inhibition stands in contrast to much greater adriamycin inhibition of diferric transferrin reduction in the transformed cells than in nontransformed cells.

Retinoic acid (RA): an inhibitor of 5 alpha-reductase in human prostatic cancer cells

The effect of retinoic acid (RA) on testosterone metabolism was examined in a prostatic cancer cell line of human origin, PC-3. In cells growing as monolayers as well as in cell homogenates RA causes a dose-dependent inhibition of the 5 alpha-reductase activity, thus preventing the conversion of testosterone into its hormonally active metabolite, dihydrotestosterone. Fifty per cent inhibition of the enzyme activity occurred at an RA concentration of 2 x 10(-5)M. The pattern of inhibition was that of a non-competitive inhibitor. However, when incubations were performed in the presence of varying amounts of NADPH, it turned out that RA exerts its effect by competitive inhibition of the cofactor action. Although the severe toxicity of RA precludes its systemic use as a 5 alpha-reductase inhibitory drug in humans, the possible anti-androgenic effect of other, less toxic, retinoids should be investigated.

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.

Retinoic acid inhibition of transplasmalemma diferric transferrin reductase

All trans retinoic acid inhibited diferric transferrin reduction by HeLa cells. The NADH diferric transferrin reductase activity of isolated liver plasma membranes was also inhibited by retinoic acid. Retinol and retinyl acetate had very little effect. Transplasma membrane ferricyanide reduction by HeLa cells and NADH ferricyanide reductase of liver plasma membrane was also inhibited by retinoic acid, therefore the inhibition was in the electron transport system and not at the transferrin receptor. Since the transmembrane electron transport has been shown to stimulate cell growth, the growth inhibition by retinoic acid thus may be based on inhibition of the NADH diferric transferrin reductase.

Dog tracheal epithelial cells in culture synthesize sulfated macromolecular glycoconjugates and release them from the cell surface upon exposure to extracellular proteinases

To determine whether glycoconjugates can be released into airways by surface epithelial cells that do not contain secretory granules and, if so, whether extracellular proteinases can affect this release, we studied dog tracheal epithelial cells after 8-10 days in culture. Ultrastructurally, these cells showed an extensive cell surface coat and no secretory granules. Cells were pulse labeled with radioactive sulfate (Na2 35SO4, 50 microCi/ml/24 h) and washed free of the unbound label. Release of sulfated products was then measured at 20-min intervals under basal conditions and again after 20 min of incubation with various extracellular proteinase. We found that these cells synthesized sulfated products and released them spontaneously and continuously into the medium. In addition, trypsin, Pseudomonas aeruginosa elastase, thermolysin, Staphylococcus aureus proteinase, mast cell chymase, plasmin, and kallikrein (each at 10(-7) M except plasmin, at 5 X 10(-6) M) increased the release of sulfated products to 77-667% over baseline release (p less than 0.01, n = 5 dogs for each); preliminary results showed that human neutrophil elastase was also very potent. The sulfated products released by trypsin had an apparent molecular weight of greater than or equal to 10(6) da as determined by gel filtration on Sepharose Cl-4B. Over 50% of these 35S-labeled products were digested to low-molecular-weight products (500-2000 da) upon incubation with endo-beta-galactosidase or with keratanase, suggesting that they are glycoconjugates containing poly(N-acetyllactosamine)-type carbohydrate chains. Decrease in cell staining by lectins specific for poly(N-acetyllactosamine), which accompanied the release of glycoconjugates, indicates that these sulfated glycoconjugates were released by proteinases from the apical cell surface. We conclude that cultured tracheal epithelial cells synthesize and transport sulfated macromolecular glycoconjugates to apical cell surfaces. These glycoconjugates are released from cell surfaces when exposed to extracellular proteinases. We therefore suggest that macromolecular glycoconjugates in airway secretions can originate not only from secretory granules but also from epithelial cell surfaces during airway inflammation.

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.

Retinoic-acid-induced differentiation of HL-60 cells is associated with biphasic activation of the Na+-K+ pump

The human promyelocytic leukemia cell line, HL-60, can be induced to differentiate into granulocyte-like cells when cultured in the presence of 10(-6) M retinoic acid (RA) for several days. Following the addition of RA two kinds of changes occur. First, there are early changes that comprise an increase in the intracellular concentration of sodium ions [Na]i, which reaches its maximum after 6 h, and an increase in the activity of the Na+-pump, which is reflected by an ouabain-sensitive K+ influx that peaks at 8 h (170% of the control value) and that occurs without any change in the number of pump molecules, as measured by the binding of 3H-ouabain. Second, beginning after 12 h of culture with RA, a decrease in the number of ouabain-binding sites occurs, this being accompanied by an increase in the number of K+ ions actively transported by each site. The effect of modulation of Na+-pump activity on the RA-induced differentiation of HL-60 cells was studied using low, noncytotoxic concentrations of ouabain which, although alone having no differentiating effect, accelerated and potentiated the effect of RA on differentiation. When added in combination, these drugs induced rapid stimulation of the Na+-pump, which reached its peak after 2 h. These results indicate that a concomitant increase in the level of [Na+]i and in the activity of the Na+-pump constitute primary events in the interaction between RA and HL-60 cells, and that cation fluxes may play a role in the initiation of the process of differentiation.

Ability of oncogenically transformed cells to grow without anchorage correlates with phosphorylation of a group of cell surface membrane proteins

Anchorage-independent growth in vitro is strongly correlated with cellular malignancy in vivo and it has been shown that retinoic acid (RA; a vitamin A analog) inhibits anchorage-independent growth of a wide variety of oncogenically transformed cells (RA-sensitive cells). We report here that decreased or lack of phosphorylation of a group of low molecular weight (20-30 kD) cell surface membrane proteins, particularly one of Mr 28 kD, correlates strongly with RA-induced loss of anchorage-independent growth of RA-sensitive cells. Our studies also show that this group of proteins are not phosphorylated in non-transformed cells which do not grow in an anchorage-independent manner. Analysis of [35S]methionine-labeled proteins revealed that these polypeptides are present in both RA-treated and untreated cell surface membranes. This suggests that modulation of phosphorylation rather than lack of synthesis of these proteins is correlated with anchorage regulation of cells. V8 protease mapping of the 28 kD phosphoprotein from transformed cells, irrespective of their origin or of transforming agents, revealed complete fragment homology. Furthermore, the 28 kD phosphoprotein was found to be phosphorylated exclusively at threonine residues. The data obtained from this study suggest that the ability of cells to grow without anchorage is correlated with the phosphorylation of a group of cell surface membrane proteins and RA inhibits anchorage-independent growth by interfering with the phosphorylation rather than synthesis of these proteins.

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.

Structure-activity relationships of aromatic retinoids on the differentiation of the human histiocytic lymphoma cell line U-937

The differentiation-inducer activity of a series of derivatives modified on the terminal ring, the polyene side-chain or the polar end group of the retinoic acid molecule was tested on the human histiocytic lymphoma cell line U-937 and compared with that of all-trans-retinoic acid. Only retinoids with both an unsaturated terminal end ring and a free carboxyl polar end group were found to be active in this system. Introduction of an aromatic ring in place of the first double bond of the side chain increased highly the activity whereas cyclisation of the last two double bonds decreased it. Replacement of the unsaturated terminal ring by an aromatic ring abolished the activity as did the esterification of the carboxyl end group or its replacement by a sodium sulfinate, sodium sulfonate or ethyl sulfone end group. All but only the active retinoids induced the same morphological and biochemical changes on U-937 cells, suggesting that they have the same route of action. However, biologically inactive retinoids were shown to be able to inhibit the differentiation of U-937 cells, induced by active ones, indicating that they can compete for a common "receptor".

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.

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.