Modulation of ornithine decarboxylase gene transcript levels by differentiation inducers in human promyelocytic leukemia HL60 cells

12-O-Tetradecanoylphorbol-13-acetate May Both Potentiate and Decrease the Generation of Apoptosis by the Antileukemic Agent Arsenic Trioxide in Human Promonocytic Cells

Arsenic trioxide (As(2)O(3)) caused apoptosis in U-937 human promonocytic cells. This effect was potentiated by the simultaneous addition of the glutathione (GSH) synthesis inhibitor DL-buthionine-(R,S)-sulfoximine or the protein kinase C activators 12-O-tetradecanoylphorbol-13-acetate (TPA) and bryostatin 1. In addition TPA decreased the intracellular GSH content, caused ERK activation, and potentiated the As(2)O(3)-provoked activation of p38 and JNK. The addition of N-acetyl-L-cysteine, the PKC inhibitor GF109203X, and the MEK/ERK inhibitors PD98059 and U0126 attenuated both apoptosis induction and GSH decrease, whereas the p38 inhibitor SB203580 and the JNK inhibitor SP600125 were ineffective. TPA also potentiated ERK activation and GSH depletion when added simultaneously to cadmium chloride (CdCl(2)) and doxorubicin. However, TPA only enhanced apoptosis in the case of CdCl(2), which is a GSH-sensitive agent, whereas it reduced the toxicity of doxorubicin and other DNA-specific drugs. Finally, preincubation for 14-24 h with TPA did not potentiate but, instead, attenuated the As(2)O(3)- and CdCl(2)-provoked apoptosis. The same result was obtained by preincubation with bryostatin 1 and other differentiation inducers. It is concluded that TPA increases the apoptotic action of As(2)O(3), an effect mediated by ERK activation and GSH depletion. However, the increase in apoptosis is only effective in non-differentiated cells.

Cloning and characterization of DIP1, a novel protein that is related to the Id family of proteins

Using human cyclin D1 as the "bait" in a yeast two-hybrid system, together with a HL60 cDNA library, we identified a novel human nuclear protein designated DIP1. This protein is expressed in a variety of cell types, and in fibroblasts its level remains constant throughout the cell cycle. However, the level of this protein increases severalfold during the differentiation of HL60 cells. The DIP1 protein can be phosphorylated in vitro by a cellular kinase and this activity reaches its maximum in extracts obtained from cells in the G1 phase of the cell cycle. DIP1 contains a helix-loop-helix motif but lacks an adjacent basic DNA-binding domain, thus resembling the Id family of proteins. The dip1 gene is located on human chromosome 16p11.2-12, a locus that is amplified in several types of human cancer. These results suggest that DIP1 may be involved in the control of gene expression and differentiation, but its precise function remains to be determined.

Etoposide stimulates 1,25-dihydroxyvitamin D3 differentiation activity, hormone binding and hormone receptor expression in HL-60 human promyelocytic cells

The simultaneous administration of the DNA topoisomerase II inhibitor etoposide (0.15 mM) and 1,25-dihydroxyvitamin D3 (VD3) (10 nM) synergistically induced the differentiation of HL-60 human promyelocytic leukemia cells. Similar results were obtained using U-937 human promonocytic cells, or the topoisomerase II inhibitors doxorubicin (15 nM) and mitoxantrone (2.5 nM). When sequential treatments were used, pre-incubation with VD3 had little effect on the subsequent action of etoposide, while pre-incubation with etoposide greatly potentiated the subsequent action of VD3. In addition, etoposide treatment stimulated VD3 binding activity and increased VD3 receptor mRNA and protein levels. The increase in hormone receptor expression may explain, at least in part, the capacity of topoisomerase inhibitors to potentiate the differentiation inducing activity of VD3.

Effect of dexamethasone on insulin receptor mRNA levels, RNA stability and isotype RNA pattern in U-937 human promonocytic cells

The administration of 5 x 10(-6) mol/l dexamethasone transiently increased insulin receptor (IR) mRNA levels in U-937 human promonocytic cells, which reached the maximum level at 15 h of treatment. Dexamethasone treatment did not affect the IR mRNA half-life (approximately 4 h), suggesting that the increase is regulated at the transcriptional level. The stimulatory action of dexamethasone was not prevented by the simultaneous presence of the protein synthesis inhibitor cycloheximide, indicating that the induction of IR gene transcription occurs as a direct response to the action of the synthetic glucocorticoid. Finally, the A isoform (lacking exon 11) was found to be the only IR isoform present in both untreated and dexamethasone treated-U-937 cells.

Modulation of HSP70 and HSP27 gene expression by the differentiation inducer sodium butyrate in U-937 human promonocytic leukemia cells

The treatment of U-937 human promonocytic cells with the differentiation inducer sodium butyrate (0.75 mM) transiently increased heat-shock protein 70 (HSP70) mRNA levels between 3 and 6 h, and heat-shock protein 27 (HSP27) mRNA levels between 12 and 24 h, as indicated by northern blot assays. Gel retardation assays indicated that butyrate also stimulated heat-shock factor (HSF) binding activity between 3 and 6 h, suggesting that the activation of HSP70 gene expression was mediated by the heat-shock factor DNA response element (HSE). In addition, the treatment provoked a biphasic alteration of the c-fos mRNA level, consisting of a slight increase between 0.5 and 3 h followed by a greater increase between 12 and 48 h, while it caused a single increase between 12 and 48 h in c-jun mRNA level. The possible involvement of the heat-shock protein genes in the butyrate-induced differentiation of U-937 cells is discussed.

Unassembled (soluble) vimentin in human myeloid leukemia cell line HL60

The intermediate filament proteins which include vimentin, desmin, and the keratins are one of three major classes of cytoskeletal proteins in eukaryotic cells. In this study we found that most of the vimentin of undifferentiated HL60 and cells induced to differentiate either along the monocytoid pathway by 12-O-tetradecanoylphorbol-13-acetate (TPA) or along the granulocytic pathway by retinoic acid was soluble in a buffer containing 1% Triton X-100/0.6 mol/l KCl in which the intermediate filament proteins usually are not soluble. HL60 vimentin separated on polyacrylamide gel electrophoresis into two proteins of Mr 55,000 and 54,000 that we detected by immunoblotting. The Mr 55,000 species was the major form in undifferentiated HL60 cells and cells induced by retinoic acid. The distribution of both forms of vimentin changed during induction of differentiation by TPA and after 24 h the Mr 54,000 species was predominant. After an additional 24 h exposure to TPA the relative levels of the two forms of vimentin approached equivalence and a high level of vimentin degradation products was seen. These results suggest that TPA may increase vimentin degradation along a pathway that has a Mr 54,000 intermediate. In addition, the high levels of soluble vimentin in HL60 cells suggests that these cells may be a good model for studying components involved in vimentin assembly.

The action of the DNA intercalating agents 4'-(9-acridinylamino) methanesulphon-m-anisidide and 1,4-bis(butylamino) benzo[g]phthalazine in U-937 human promonocytic cells: relationship between cell cycle and differentiation

The action of two structurally related DNA intercalating agents has been studied and compared, namely 4'-(9-acridinylamino) methanesulphon-m-anisidide (amsacrine, mAMSA) and 1,4-bis(butylamino)benzo[g]phthalazine (ABP) on the cell cycle and differentiation of U-937 human promonocytic leukemia cells. mAMSA (0.1 microM) and ABP (4 microM) reduced the proliferation activity to a similar extent and caused little cell mortality. At these subcytotoxic concentrations mAMSA induced the cells to accumulate at the G2 phase of the cycle, while cycle inhibition provoked by ABP was not phase specific. In addition, mAMSA caused an increase in the cell mass while ABP provoked cell shrinkage. This was consistent with the fact that ABP considerably inhibited protein synthesis, while mAMSA did not significantly affect this activity. SDS/K+DNA precipitation assays indicated that mAMSA, but not ABP, stimulated protein-DNA covalent complex formation. Finally, it was found that mAMSA, but not ABP, elicited the expression of differentiation markers, namely nitroblue tetrazolium reduction, activation of vimentin and leukocyte integrin (CD11b/CD18 and CD11c/CD18) expression, and downregulation of c-myc expression. The DNA intercalators doxorubicin and mitoxantrone, which like mAMSA induced the cells to accumulate at the G2 phase and increased the cell mass, induced the expression of differentiation markers. In contrast, the intercalators aclarubicin and caffeine and the non-intercalator novobiocin, which produced minor alterations on cell-cycle distribution and caused cell shrinkage, did not significantly elicit differentiation. These results support the conclusion that differentiation of myeloid leukemia cells by cytostatic drugs depends on the perturbations of the cell cycle, leading to disproportionate increases in cell mass.

Growth-regulated expression of vimentin in hamster fibroblasts is a result of increased transcription

We have previously shown that vimentin is a growth-regulated gene whose mRNA levels increase after serum stimulation of quiescent hamster fibroblasts. In this study, the control of the growth-regulated expression of vimentin was determined in ts13 cells induced to proliferate by serum. Both transcriptional and post-transcriptional mechanisms of regulation were examined by determining transcriptional rates, cytoplasmic transcript abundance, transcript stability, and protein abundance. We observed a fourfold increase in vimentin transcripts in the cytoplasm of serum-stimulated ts13 cells. Since transcripts are stable in both quiescent and stimulated cells, this induction of vimentin expression is a result of a fivefold increase in vimentin-specific transcriptional activity. As a result of this increased transcript availability, the abundance of polymerized vimentin protein increased following serum stimulation of quiescent fibroblasts. Overall, the induction of vimentin expression in fibroblasts by serum is a consequence of increased vimentin-specific transcriptional activity. The significance of this with regard to cytoskeletal organization and cell division is discussed.

Phorbol esters induce differentiation of U-937 human promonocytic cells in the absence of LFA-1/ICAM-1-mediated intercellular adhesion

Intercellular adhesions which occur during the mononuclear phagocyte differentiation are predominantly mediated by the lymphocyte-function-associated antigen-1 (LFA-1) family and the intercellular-adhesion molecule-1 (ICAM-1) which is a ligand for LFA-1. Thus, differentiation of U-937 promonocytic cells induced by phorbol esters occurs concomitantly with intercellular LFA-1/ICAM-1-dependent cluster formation. Since these homotypic adhesions can be inhibited by monoclonal antibodies (mAb) directed to either LFA-1 or ICAM-1, we have analyzed whether the lack of cell-cell adhesions impairs the differentiation process. Treatment of U-937 cells with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate in the presence of mAb to LFA-1 or ICAM-1 antigens yielded cells free from homotypic adhesions but differentiated as evidenced by their decreased proliferation and enhanced capacity for generation of superoxide anion. In addition, expression of the CD11c antigen was increased, whereas the transferrin receptor disappeared from the cell surface. Vimentin gene transcription was also greatly augmented as opposed to a clear diminution in the levels of c-myc and ornithine decarboxylase transcripts. These results clearly demonstrate that phorbol esters can induce differentiation of monocytic cells independently of cell-cell adhesion.

The induction of vimentin gene expression by sodium butyrate in human promonocytic leukemia U937 cells

The administration of 1 mM sodium butyrate induced the phenotypic differentiation of human promonocytic leukemia U937 cells, as judged by the expression of cD11b and cD11c antigens, two differentiation-specific surface markers. At the same time, butyrate greatly induced the expression at the mRNA level of the vimentin gene. The increase in the level of this RNA started at 6 h of treatment and reached the maximum at Hour 24. Such an increase was caused at least in part by a stimulation in the rate of gene transcription, as suggested by transcription assays in isolated nuclei. Experiments in the presence of cycloheximide suggested that vimentin induction is probably a direct response to the action of butyrate, not mediated by the prior induction of other gene products. Unlike the case of vimentin, the levels of other RNAs, namely beta-actin, ornithine decarboxylase, and c-myc, were not enhanced, but they decreased at different times of treatment with butyrate. Finally, we observed that butyrate induced also the differentiation of HL60 cells, another human myeloid cell type. Nevertheless, the drug failed to stimulate the expression of vimentin in this cell line.