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

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.

Luminol and diazoluminomelanin as indicators of HL-60 cell differentiation

This paper describes use of a novel substituted melanin which is useful in detection of differentiating leukemia cells and their membranes. Comparisons of luminol-(5-amino-2,3-dihydro-1,4-phthalazinedione) and diazoluminomelanin (DALM)-mediated chemiluminescence (CL) were made with various types of differentiated and undifferentiated HL-60 whole cells, cell lysates, and membrane fractions. Luminol had a greater CL response than DALM with HL-60 promyelocytic stem cells and differentiated macrophage-like or neutrophil-like whole cell and cell lysate preparations. However, DALM showed markedly greater CL than luminol for membrane fractions derived from each cell type. The greatest luminol-dependent CL was observed for cell types high in myeloperoxidase (MPO). The greatest DALM-mediated CL was seen with cell types that are high in MPO or strong producers of superoxide (O2-) anions. In some cases, significant differences in CL could also be distinguished on the basis of inducing agent used [i.e. dimethylsulfoxide, all-trans retinoic acid or 12-o-tetradecanoylphorbol-13-acetate]. Both luminol- and DALM-dependent CL were strongly inhibited by preincubation of cellular preparations with 3-amino-L-tyrosine (a component of DALM). Taken together, these data suggest that the reaction mechanism of luminol favors interaction with cytoplasmic MPO whereas that of DALM favors membrane interactions. Thus, both reagents may be of use in assays to detect differentiating leukocytes or their cellular components.

Expression of intermediate filament proteins in TPA-induced MPC-11 and HL-60 cells

Under normal culture conditions, the tumor cell lines MPC-11 and HL-60 exhibit high rates of proliferation and show a peculiar expression of intermediate filament proteins as they appear to synthesize only lamin B. A 48-h exposure of murine plasmacytomas MPC-11 to the phorbol ester TPA reduces their growth and induces vimentin synthesis without affecting the composition of their nuclear lamina. When applied to human leukemic promyelocytes HL-60, such treatment promotes their maturation into macrophage-like cells: their proliferative ability is suppressed, a differentiated phenotype is developed, and their content in intermediate filament proteins now includes vimentin and a full complement of lamins A, B, and C. In the present study, a kinetic analysis of vimentin and lamin A/C expression in relation to proliferation and differentiation has been performed in these two cellular systems. Proliferation rates of MPC-11 and HL-60 populations were evaluated by monitoring cell growth and measuring thymidine incorporation. Maturation of HL-60 cells was assessed by Giemsa staining and percentage of adherent cells. Expression of vimentin and lamins A/C was analyzed using immunofluorescence and immunoblotting techniques. Our data show that there is a relationship between the level of vimentin expression and the extent of growth inhibition in both systems. They also suggest that the expression of lamins A/C during the TPA-induced maturation of HL-60 promyelocytes might be part of the processes which lock these cells into the macrophage pathway.

Relationship of eukaryotic DNA replication to committed gene expression: general theory for gene control

The historic arguments for the participation of eukaryotic DNA replication in the control of gene expression are reconsidered along with more recent evidence. An earlier view in which gene commitment was achieved with stable chromatin structures which required DNA replication to reset expression potential (D. D. Brown, Cell 37:359-365, 1984) is further considered. The participation of nonspecific stable repressor of gene activity (histones and other chromatin proteins), as previously proposed, is reexamined. The possible function of positive trans-acting factors is now further developed by considering evidence from DNA virus models. It is proposed that these positive factors act to control the initiation of replicon-specific DNA synthesis in the S phase (early or late replication timing). Stable chromatin assembles during replication into potentially active (early S) or inactive (late S) states with prevailing trans-acting factors (early) or repressing factors (late) and may asymmetrically commit daughter templates. This suggests logical schemes for programming differentiation based on replicons and trans-acting initiators. This proposal requires that DNA replication precede major changes in gene commitment. Prior evidence against a role for DNA replication during terminal differentiation is reexamined along with other results from terminal differentiation of lower eukaryotes. This leads to a proposal that DNA replication may yet underlie terminal gene commitment, but that for it to do so there must exist two distinct modes of replication control. In one mode (mitotic replication) replicon initiation is tightly linked to the cell cycle, whereas the other mode (terminal replication) initiation is not cell cycle restricted, is replicon specific, and can lead to a terminally differentiated state. Aberrant control of mitotic and terminal modes of DNA replication may underlie the transformed state. Implications of a replicon basis for chromatin structure-function and the evolution of metazoan organisms are considered.

Improved coupling between proliferation-arrest and differentiation-induction in ML-1 human myeloblastic leukemia cells

Proliferation and differentiation are coupled in normal cells and are aberrant in leukemia cells. The studies reported here were aimed at more effectively coupling proliferation-arrest and differentiation-induction in a human myeloblastic leukemia cell line (ML-1). This was accomplished by using reduced serum conditions in conjunction with a differentiation-inducing agent: cells were first incubated in reduced serum [0.3% fetal bovine serum (FBS)] instead of standard conditions (7.5% FBS) and, second, exposed to 12-O-tetradecanoylphorbol-13-acetate (TPA). The effects of this protocol were as follows: first, cell proliferation was slowed and cells accumulated in G0/G1 phase of the cell cycle; this occurred with only a minimal decrease in viability [to approximately 88-92% (0.3% FBS) from greater than or equal to 96% (7.5% FBS)]. Second, the induction of differentiation was accelerated; this allowed the time of exposure to TPA to be decreased. Acceleration of induction was very pronounced when cells were maintained in 0.3% FBS both before and during exposure to TPA, with TPA at concentrations above the minimum sufficient for induction but below those causing significant cytotoxicity; as little as 1 hour of TPA exposure resulted in near-maximal induction (approximately 80%) with this protocol, compared to the greater than or equal to 1 day required with previous standard protocols. In sum, conditions that slow ML-1 cell proliferation (0.3% FBS) enhance TPA-induced differentiation, substantially narrowing the time frame of induction; these conditions should be useful for studying the molecular mechanisms that underlie the induction process.

S-phase inhibitors induce vimentin expression in human promonocytic U-937 cells

The administration of hydroxyurea (3 x 10(-4) M) and cytosine arabinoside (10(-7) M) greatly induces the expression of the vimentin gene in human promonocytic leukemia U-937 cells. The induction takes place at both the mRNA and protein levels, as demonstrated by Northern blot, immunoblot and immunofluorescence assays. On the contrary, the drugs inhibit the expression of c-myc and ornithine decarboxylase, and do not modify significantly the expression of beta-actin. Since hydroxyurea and cytosine arabinoside trigger the phenotypic differentiation of U-937 cells, as demonstrated by the induction of the differentiation-specific CD11b and CD11c antigens, it is concluded that vimentin expression might be implicated in the maturation of these cells.

Antiproliferative mechanism of anti-class II monoclonal antibodies

The function of Class II molecules in proliferation was explored by treating human cell lines with three distinct anti-DR monoclonal antibodies (MABs). Dose-dependent, specific inhibition of eight DR+ cell lines of different origin and lineage was found. Inhibition was durable (i.e., cells did not become resistant to the anti-DR MABs despite prolonged treatment) yet reversible. The mechanism of inhibition was not due to differentiation or killing but was cytostatic. Inhibition was temporally associated with decreases in nuclear size and irregularity and appeared to be due to a non-phase-specific cell cycle arrest.