Growth of single HL60 cells in liquid culture: analysis of the influences of differentiative agents

CXCR4 blockade induces atherosclerosis by affecting neutrophil function

AIMS

The SDF-1α/CXCR4 dyad was previously shown by us and others to be instrumental in intimal hyperplasia as well as early stage atherosclerosis. We here sought to investigate its impact on clinically relevant stages of atherosclerosis in mouse and man.

METHODS AND RESULTS

Immunohistochemical analysis of CXCR4 expression in human atherosclerotic lesions revealed a progressive accumulation of CXCR4(+) cells during plaque progression. To address causal involvement of CXCR4 in advanced stages of atherosclerosis we reconstituted LDLr(-/-) mice with autologous bone marrow infected with lentivirus encoding SDF-1α antagonist or CXCR4 degrakine, which effects proteasomal degradation of CXCR4. Functional CXCR4 blockade led to progressive plaque expansion with disease progression, while also promoting intraplaque haemorrhage. Moreover, CXCR4 knockdown was seen to augment endothelial adhesion of neutrophils. Concordant with this finding, inhibition of CXCR4 function increased adhesive capacity and reduced apoptosis of neutrophils and resulted in hyperactivation of circulating neutrophils. Compatible with a role of the neutrophil CXCR4 in end-stage atherosclerosis, CXCR4 expression by circulating neutrophils was lowered in patients with acute cardiovascular syndromes.

CONCLUSION

In conclusion, CXCR4 contributes to later stages of plaque progression by perturbing neutrophil function.

Antagonists of retinoic acid receptors (RARs) are potent growth inhibitors of prostate carcinoma cells

Novel synthetic antagonists of retinoic acid receptors (RARs) have been developed. To avoid interference by serum retinoids when testing these compounds, we established serum-free grown sub-lines (>3 years) of the prostate carcinoma lines LNCaP, PC3 and DU145. A high affinity pan-RAR antagonist (AGN194310, K(d) for binding to RARs = 2-5 nM) inhibited colony formation (by 50%) by all three lines at 16-34 nM, and led to a transient accumulation of flask-cultured cells in G1 followed by apoptosis. AGN194310 is 12-22 fold more potent than all-trans retinoic acid (ATRA) against cell lines and also more potent in inhibiting the growth of primary prostate carcinoma cells. PC3 and DU145 cells do not express RARbeta, and an antagonist with predominant activity at RARbeta and RARgamma (AGN194431) inhibited colony formation at concentrations (approximately 100 nM) commensurate with a K(d)value of 70 nM at RARgamma. An RARalpha antagonist (AGN194301) was less potent (IC(50) approximately 200 nM), but was more active than specific agonists of RARalpha and of betagamma. A component(s) of serum and of LNCaP-conditioned medium diminishes the activity of antagonists: this factor is not the most likely candidates IGF-1 and EGF. In vitro studies of RAR antagonists together with data from RAR-null mice lead to the hypothesis that RARgamma-regulated gene transcription is necessary for the survival and maintenance of prostate epithelium. The increased potencies of RAR antagonists, as compared with agonists, suggest that antagonists may be useful in the treatment of prostate carcinoma.

Cell proliferation and CD11b expression are controlled independently during HL60 cell differentiation initiated by 1,25 alpha-dihydroxyvitamin D(3) or all-trans-retinoic acid

When 1 alpha,25-dihydroxyvitamin D(3) (D(3)) induces HL60 cells to differentiate to monocytes, a burst of approximately three shortened cell cycles ("maturation divisions") precedes exit from cell cycle and completion of maturation. Here we show that similar maturation divisions occur during neutrophil differentiation induced by all-trans-retinoic acid (ATRA), but without shortening of the cell cycle. Both ATRA and D(3) initiate these maturation divisions as cells pass through a "window of sensitivity" during early G1. We also investigated whether the initiation of maturation divisions and of the expression of CD11b, an early-expressed maturation marker, are linked. Cells treated with D(3) or ATRA start to express CD11b after 9--14 h, before completing the first maturation division. Elutriation was used to isolate small HL60 cells (almost all in G1) and larger cells (in G1 and S phases) from unsynchronized populations. When these were cultured with D(3) or ATRA, most reentered cycle synchronously, multiplied, and differentiated. Following D(3) treatment, the G1-enriched small cells expressed CD11b slightly faster than unsynchronized cultures or fractions dominated by late G1 cells and/or S phase cells. D(3)-induced CD11b expression occurred at a similar rate even in G1 cells that were held at the G1/S boundary by thymidine. In conclusion, changes in the control of the cell cycle that characterize the onset of monocytic and neutrophil differentiation are only triggered in early G1, but CD11b expression can be initiated from most points in the cell cycle. Differentiating agents must therefore regulate the proliferation and the maturation of differentiating myeloid cells by mechanisms that are at least partly independent.

Monocytically differentiating HL60 cells proliferate rapidly before they mature

1alpha,25-Dihydroxyvitamin D(3) (D(3)) provokes growth arrest and monocytic differentiation in myeloid cells. Although it is usually assumed that the cellular events leading to growth arrest start within one cell cycle of D(3) addition, there is also evidence that D(3) provokes the expression of proliferation-related genes and accelerates cell division. Herein we clarify the relationship between proliferation and maturation in differentiating HL60 cells. Cells were cultured singly, D(3) was added at various stages of the cell cycle, the progeny were counted, and the proportions of mature monocytes were determined. Initially, the D(3)-treated cells proliferated at an accelerated rate, and they matured only later. If cells encountered D(3) early in G1 they divided two to four times before maturing, and if they encountered D(3) later in the cell cycle they underwent an extra division. Indomethacin slows HL60 cell multiplication by prolonging G1, and when these slower-growing cells were exposed to D(3), they matured after the usual period but underwent one division less than indomethacin-free cells. Contrary to common assumptions, we conclude that promyeloid cells do not initiate growth arrest or monocytic maturation immediately after exposure to D(3). Instead, an encounter with D(3) early in G1 sets in train a complex differentiation program. This consists of 2-3 days of rapid proliferation-probably employing cell cycles with a shortened G1 phase-that is followed by growth arrest and maturation. As a result, a single D(3)-treated promyeloid cell gives rise to 10 or more mature monocytes. These observations not only explain why "differentiating" cells express proliferation-related characteristics soon after D(3) addition, but they also show that the process of D(3)-induced monocytic differentiation is much more complex than has previously been realized.

Metabolism of 1alpha,25(OH)2D3 and its 20-epi analog integrates clonal expansion, maturation and apoptosis during HL-60 cell differentiation

Induction of growth arrest and monocyte differentiation of HL-60 leukemia cells by 1alpha,25 dihydroxyvitamin D3 (1alpha,25(OH)2D3) is well established. By contrast, we have observed, that 1alpha,25(OH)2D3 and its metabolites play separate roles in clonal expansion and survival of differentiating HL-60 cells. Cells that had differentiated by 48 h (CD14 positive) grew slower than control cells, whereas CD14 negative cells were growing faster at this time point. Inhibiting 1alpha,25(OH)2D3 or 1alpha,25(OH)2-20-epi-D3 metabolism, by the 25(OH)D3-24-hydroxylase inhibitor ketoconazole, abolished hyperproliferation of CD14 negative cells. Instead, both the onset of differentiation and subsequent apoptosis were enhanced. These events were associated with immediate up-regulation of the cyclin-dependent kinase inhibitor p21(waf1) and a lack of sustained expression, respectively. Stimulation and inhibition of growth by vitamin D3-related compounds was observed to be concentration and metabolite specific. Low amounts of 1alpha,25(OH)2-20-epi-D3 and 1alpha,24,25(OH)3-20-epi-D3 stimulated HL-60 cell growth. At higher concentrations, 1alpha,25(OH)2-20-epi-D3 was a more potent inducer than 1alpha,24,25(OH)3-20-epi-D3 of HL-60 differentiation; 1alpha,25(OH)2-20-epi-24-oxo-D3 was exclusively pro-differentiative at all concentrations. 1alpha,25(OH)2-20-epi-D3 and 1alpha,24,25(OH)3-20-epi-D3 stimulated proliferation of KG-1a leukemia cells, but neither of these compounds nor 1alpha,25(OH)3-20-epi-24-oxo-D3 exerted pro-differentiative effects on these cells. These findings shed new light on the pro- and anti-proliferative effects of 1alpha,25(OH)2D3 and lead to the postulate that metabolism of 1alpha,25(OH)2D3 and its 20-epi analog regulates different subsets of genes so as to co-ordinate population expansion and the differentiation process. Furthermore, 1alpha,25(OH)2D3 metabolism and/or sensitivity to the effects of metabolites may be altered in transformed cells to derive a clonal advantage.

Identification of transcription factors expressed during ATRA-induced neutrophil differentiation of HL60 cells

A recent clinical therapeutic initiative has been the use of chemical agents which induce the leukaemic cells to overcome their block in differentiation. In order to understand this block the cascade of molecular events needs to be characterized. Haemopoietic differentiation is ultimately controlled at the level of gene transcription which is mediated by an array of transcription factors. Many transcription factors contain similar structural protein sequences, and we have used an RT-PCR-based approach to isolate sequences, from transcription factor gene families which share similar domains. Degenerate primers corresponding to the TFIIIA zinc-finger consensus amino acid sequences and to the POU-homeodomain and POU-specific domain were used to amplify genes on the basis that they contained similarities in structural motifs shared within these families of transcription factors. A serum-independent HL60 cell line was induced towards the neutrophil lineage by treatment with all-trans retinoic acid (ATRA) for 24 h. CD38+ cells committed towards this lineage were enriched and a population of these cells treated with dihydroxyvitamin D3 to induce neutrophil maturation. RNA extracted from uninduced, ATRA-induced CD38+ cells, and vitamin D3 treated maturing cell cultures were amplified using the degenerate primers. PCR fragments were cloned, sequenced, clustered into homologous groups, and the group sequences searched on the GenBank database. The Oct 1 transcription factor, and a very close homologue, KIAA0144, was identified using the POU family primers. The zinc-finger primers identified three zinc-finger genes. The pattern of gene expression was suggested from the number of clones in each group at neutrophil commitment and maturation. The differential expression of the genes in the zinc finger and POU families will lead to a better understanding of the cascade of gene expression which occurs following ATRA-induced differentiation.