Retinoic Acid-induced Cell Cycle Arrest of Human Myeloid Cell Lines

Retinoic acid induced specific changes in the phosphoproteome of C17.2 neural stem cells

Retinoic acid (RA), a vitamin A derivative, is an effective cell differentiating factor which plays critical roles in neuronal differentiation induction and the production of neurotransmitters in neurons. However, the specific changes in phosphorylation levels and downstream signalling pathways associated with RA remain unclear. This study employed qualitative and quantitative phosphoproteomics approaches based on mass spectrometry to investigate the phosphorylation changes induced by RA in C17.2 neural stem cells (NSCs). Dimethyl labelling, in conjunction with TiO2 phosphopeptide enrichment, was utilized to profile the phosphoproteome of self-renewing and RA-induced differentiated cells in C17.2 NSCs. The results of our study revealed that, qualitatively, 230 and 14 phosphoproteins were exclusively identified in the self-renewal and RA-induced groups respectively. Quantitatively, we successfully identified and quantified 177 unique phosphoproteins, among which 70 exhibited differential phosphorylation levels. Analysis of conserved phosphorylation motifs demonstrated enrichment of motifs corresponding to cyclin-dependent kinase and MAPK in the RA-induced group. Additionally, through a comprehensive literature and database survey, we found that the differentially expressed proteins were associated with the Wnt/β-catenin and Hippo signalling pathways. This work sheds light on the changes in phosphorylation levels induced by RA in C17.2 NSCs, thereby expanding our understanding of the molecular mechanisms underlying RA-induced neuronal differentiation.

The synergistic effect of eucalyptus oil and retinoic acid on human esophagus cancer cell line SK-GT-4

Background

In order to improve cancer patients' chances of survival, scientists have prioritized finding alternatives to chemotherapy, focusing their efforts on natural sources. The current study investigates the anti-cancer action of retinoic acid and Eucalyptus oil in esophageal cancer and studies their combined effect as well as the cellular pathways that each trigger as part of ongoing research in this field. As a model of esophageal cancer, the SK-GT-4 cancer cell line was treated with a series of concentrations of both materials.

Results

The concentrations of Eucalyptus oil (10, 100, 1000, and 1500 g/mL) and Retinoic acid (5, 100, 150, and 200 M/mL) were used for treatment of cells. The MTT test was used to assess the anti-cancer activity of Eucalyptus oil and Retinoic acid, and qPCR was used to determine cellular pathways. Our findings show that both Eucalyptus oil and Retinoic acid inhibit cancer cell growth significantly. Our findings revealed that the IC50 values for eucalyptus oil were 63 g/mL and 111.3 M l/mL for retinoic acid. Furthermore, the impact was at the level that causes apoptosis. The findings suggested that any herbal substance could act as an inducer of the caspase-9-dependent pathway. The caspase-8-dependent pathway, on the other hand, was restricted to retinoic acid.

Conclusion

Our research discovered that the two chemicals worked together to create a synergistic effect. This synergistic effect could be attributed to a close connection between external and internal apoptotic pathways, which inhibits SK-GT-4 cell growth.

Graphical Abstract

Mechanistic aspects of carotenoid health benefits - where are we now?

Dietary intake and tissue levels of carotenoids have been associated with a reduced risk of several chronic diseases, including cardiovascular diseases, type 2 diabetes, obesity, brain-related diseases and some types of cancer. However, intervention trials with isolated carotenoid supplements have mostly failed to confirm the postulated health benefits. It has thereby been speculated that dosing, matrix and synergistic effects, as well as underlying health and the individual nutritional status plus genetic background do play a role. It appears that our knowledge on carotenoid-mediated health benefits may still be incomplete, as the underlying mechanisms of action are poorly understood in relation to human relevance. Antioxidant mechanisms - direct or via transcription factors such as NRF2 and NF-κB - and activation of nuclear hormone receptor pathways such as of RAR, RXR or also PPARs, via carotenoid metabolites, are the basic principles which we try to connect with carotenoid-transmitted health benefits as exemplified with described common diseases including obesity/diabetes and cancer. Depending on the targeted diseases, single or multiple mechanisms of actions may play a role. In this review and position paper, we try to highlight our present knowledge on carotenoid metabolism and mechanisms translatable into health benefits related to several chronic diseases.

All-Trans Retinoic Acid Stimulates Viral Mimicry, Interferon Responses and Antigen Presentation in Breast-Cancer Cells

All-trans retinoic acid (ATRA), a recognized differentiating agent, has significant potential in the personalized/stratified treatment of breast cancer. The present study reports on the molecular mechanisms underlying the anti-tumor activity of ATRA in breast cancer. The work is based on transcriptomic experiments performed on ATRA-treated breast cancer cell-lines, short-term tissue cultures of patient-derived mammary-tumors and a xenograft model. ATRA upregulates gene networks involved in interferon-responses, immune-modulation and antigen-presentation in retinoid-sensitive cells and tumors characterized by poor immunogenicity. ATRA-dependent upregulation of these gene networks is caused by a viral mimicry process, involving the activation of endogenous retroviruses. ATRA induces a non-canonical type of viral mimicry, which results in increased expression of the IRF1 (Interferon Responsive Factor 1) transcription factor and the DTX3L (Deltex-E3-Ubiquitin-Ligase-3L) downstream effector. Functional knockdown studies indicate that IRF1 and DTX3L are part of a negative feedback loop controlling ATRA-dependent growth inhibition of breast cancer cells. The study is of relevance from a clinical/therapeutic perspective. In fact, ATRA stimulates processes controlling the sensitivity to immuno-modulatory drugs, such as immune-checkpoint-inhibitors. This suggests that ATRA and immunotherapeutic agents represent rational combinations for the personalized treatment of breast cancer. Remarkably, ATRA-sensitivity seems to be relatively high in immune-cold mammary tumors, which are generally resistant to immunotherapy.

Long non-coding RNA zinc finger antisense 1 functions as an oncogene in acute promyelocytic leukemia cells

Despite progress in the diagnosis and treatment of acute promyelocytic leukemia (APL), its prognosis remains poor. Multiple studies have shown that long non-coding RNAs (lncRNAs) are involved in carcinogenesis and metastasis. The present study assessed the function of the lncRNA zinc finger antisense 1 (ZFAS1) in APL. In a cohort of 33 patients, ZFAS1 was significantly overexpressed compared with the level in healthy controls. To investigate the specific mechanisms of this upregulation, in vitro studies showed that silencing of ZFAS1 by small interfering RNA significantly inhibited cell proliferation in APL cells. Moreover, downregulation of ZFAS1 increased cellular apoptosis, decreased expression of B-cell lymphoma-2 and of induced myeloid leukemia cell differentiation protein Mcl-1, increased the expression of apoptosis regulator BAX and promoted the release of cytochrome c and Diablo homolog mitochondrial into the cytoplasm. In conclusion, these data indicate that ZFAS1 may serve as an oncogene in APL and may thus be a useful target for future clinical management.

Strategies to generate functionally normal neutrophils to reduce infection and infection-related mortality in cancer chemotherapy

Neutrophils form an essential part of innate immunity against infection. Cancer chemotherapy-induced neutropenia (CCIN) is a condition in which the number of neutrophils in a patient's bloodstream is decreased, leading to increased susceptibility to infection. Granulocyte colony-stimulating factor (GCSF) has been the only approved treatment for CCIN over two decades. To date, CCIN-related infection and mortality remain a significant concern, as neutrophils generated in response to administered GCSF are functionally immature and cannot effectively fight infection. This review summarizes the molecular regulatory mechanisms of neutrophil granulocytic differentiation and innate immunity development, dissects the biology of GCSF in myeloid expansion, highlights the shortcomings of GCSF in CCIN treatment, updates the recent advance of a selective retinoid agonist that promotes neutrophil granulocytic differentiation, and evaluates the benefits of developing GCSF biosimilars to increase access to GCSF biologics versus seeking a new mode to fundamentally advance GCSF therapy for treatment of CCIN.

Retinoic acid signalling is a candidate regulator of the expression of pituitary-specific transcription factor Prop1 in the developing rodent pituitary

Development of the anterior pituitary proceeds via spatiotemporal patterning of transcription factors and signalling molecules. Among them, retinoic acid (RA) functions as an important signalling molecule for vertebrate organogenesis in many tissues. However, little is known regarding the target genes in the developing pituitary. The present study aimed to clarify the relationship between endogenous RA signalling and mRNA expression of the pituitary-specific transcription factor Prop1 in the pituitary primordium of Rathke's pouch. Gene expression analysis and in situ hybridisation demonstrated that retinaldehyde dehydrogenases (Raldhs) and all types of RA receptors (Rars) are expressed at the level of transcription in the rat Rathke's pouch. Ex vivo organ culture using Rathke's pouch and an in vitro reporter assay demonstrated that RA signalling increases the expression level of Prop1 via RARα. Moreover, a reporter assay using serial truncated constructs of the 5'-upstream region of mouse Prop1 revealed a predicted cis-regulatory element of RARα. This is the first report of a relationship between RA signalling and Prop1-expression during early pituitary development.

Regulation of Active DNA Demethylation through RAR-Mediated Recruitment of a TET/TDG Complex

Retinoic acid (RA) plays important roles in development, growth, and homeostasis through regulation of the nuclear receptors for RA (RARs). Herein, we identify Hypermethylated in Cancer 1 (Hic1) as an RA-inducible gene. HIC1 encodes a tumor suppressor, which is often silenced by promoter hypermethylation in cancer. Treatment of cells with an RAR agonist causes a rapid recruitment of an RAR/RXR complex consisting of TDG, the lysine acetyltransferase CBP, and TET 1/2 to the Hic1 promoter. Complex binding coincides with a transient accumulation of 5fC/5caC and concomitant upregulation of Hic1 expression, both of which are TDG dependent. Furthermore, conditional deletion of Tdg in vivo is associated with Hic1 silencing and DNA hypermethylation of the Hic1 promoter. These findings suggest that the catalytic and scaffolding activities of TDG are essential for RA-dependent gene expression and provide important insights into the mechanisms underlying targeting of TET-TDG complexes.

Nardostachys chinensis induces granulocytic differentiation with the suppression of cell growth through p27(Kip1) protein-related G0/G1 phase arrest in human promyelocytic leukemic cells

CONTEXT

Nardostachys chinensis Batalin (Valerianaceae) has been used in Korean traditional medicine to elicit stomachic and sedative effects. However, the anti-leukemic activities of N. chinensis have not been well examined.

OBJECTIVE

To investigate the effect of N. chinensis on differentiation and proliferation in the human promyelocytic leukemic HL-60 cells.

MATERIALS AND METHODS

The dried roots and stems of N. chiensis are extracted using hot water and then freeze-dried. The yield of extract was 12.82% (w/w). The HL-60 cells were treated with 25-200 μg/ml of N. chinensis for 72 h or 100 μg/ml of N. chinensis for 24-72 h.

RESULTS

Nardostachys chinensis significantly inhibited cell viability dose dependently with an IC50 of 100 μg/ml in HL-60 cells. Nardostachys chinensis induced differentiation of the cells as measured by reduction activity of NBT and expression of CD11b but not of CD14 as analyzed by flow cytometry, which indicates a differentiation toward the granulocytic lineage. Nardostachys chinensis also induced growth inhibition through G0/G1 phase arrest in the cell cycle of HL-60 cells. Among the G0/G1 phase in the cell cycle-related protein, the expression of cyclin-dependent kinase (CDK) inhibitor p27(Kip1) was increased in N. chinensis-treated HL-60 cells, whereas the expression levels of CDK2, CDK4, CDK6, cyclin D1, cyclin D3, cyclin E, and cyclin A were decreased. Interestingly, N. chinensis markedly enhanced the binding of p27(Kip1) with CDK2 and CDK6.

DISCUSSION AND CONCLUSION

This study demonstrated that N. chinensis is capable of inducing cellular differentiation and growth inhibition through p27(Kip1) protein-related G0/G1 phase arrest in HL-60 cells.

Long intergenic non-coding RNA HOTAIRM1 regulates cell cycle progression during myeloid maturation in NB4 human promyelocytic leukemia cells

HOTAIRM1 is a long intergenic non-coding RNA encoded in the human HOXA gene cluster, with gene expression highly specific for maturing myeloid cells. Knockdown of HOTAIRM1 in the NB4 acute promyelocytic leukemia cell line retarded all-trans retinoid acid (ATRA)-induced granulocytic differentiation, resulting in a significantly larger population of immature and proliferating cells that maintained cell cycle progression from G1 to S phases. Correspondingly, HOTAIRM1 knockdown resulted in retained expression of many otherwise ATRA-suppressed cell cycle and DNA replication genes, and abated ATRA induction of cell surface leukocyte activation, defense response, and other maturation-related genes. Resistance to ATRA-induced cell cycle arrest at the G1/S phase transition in knockdown cells was accompanied by retained expression of ITGA4 (CD49d) and decreased induction of ITGAX (CD11c). The coupling of cell cycle progression with temporal dynamics in the expression patterns of these integrin genes suggests a regulated switch to control the transit from the proliferative phase to granulocytic maturation. Furthermore, ITGAX was among a small number of genes showing perturbation in transcript levels upon HOTAIRM1 knockdown even without ATRA treatment, suggesting a direct pathway of regulation. These results indicate that HOTAIRM1 provides a regulatory link in myeloid maturation by modulating integrin-controlled cell cycle progression at the gene expression level.

AKN-028 induces cell cycle arrest, downregulation of Myc associated genes and dose dependent reduction of tyrosine kinase activity in acute myeloid leukemia

AKN-028 is a novel tyrosine kinase inhibitor with preclinical activity in acute myeloid leukemia (AML), presently undergoing investigation in a phase I/II study. It is a potent inhibitor of the FMS-like kinase 3 (FLT3) but shows in vitro activity in a wide range of AML samples. In the present study, we have characterized the effects of AKN-028 on AML cells in more detail. AKN-028 induced a dose-dependent G0/1 arrest in AML cell line MV4-11. Treatment with AKN-028 caused significantly altered gene expression in all AML cell types tested (430 downregulated, 280 upregulated transcripts). Subsequent gene set enrichment analysis revealed enrichment of genes associated with the proto-oncogene and cell cycle regulator c-Myc among the downregulated genes in both AKN-028 and midostaurin treated cells. Kinase activity profiling in AML cell lines and primary AML samples showed that tyrosine kinase activity, but not serine/threonine kinase activity, was inhibited by AKN-028 in a dose dependent manner in all samples tested, reaching approximately the same level of kinase activity. Cells sensitive to AKN-028 showed a higher overall tyrosine kinase activity than more resistant ones, whereas serine/threonine kinase activity was similar for all primary AML samples. In summary, AKN-028 induces cell cycle arrest in AML cells, downregulates Myc-associated genes and affect several signaling pathways. AML cells with high global tyrosine kinase activity seem to be more sensitive to the cytotoxic effect of AKN-028 in vitro.

CDK1 interacts with RARγ and plays an important role in treatment response of acute myeloid leukemia

Alterations in cell cycle pathways and retinoic acid signaling are implicated in leukemogenesis. However, little is known about the roles of cyclin-dependent kinases (CDKs) in treatment response of leukemia. In this study, we observed that CDK1 expression was significantly higher in bone marrow from 42 patients with acute myeloid leukemia (AML) at recurrence than that at first diagnosis (p = 0.04). AML patients had higher level of nuclear CDK1 in their leukemic blasts tended to have poorer clinical outcome compared with those with lower levels. We showed that CDK1 function is required for all-trans retinoic acid (ATRA) to achieve the optimal effect in U-937 human leukemic cells. CDK1 modulates the levels of P27(kip) and AKT phosphorylation in response to ATRA treatment. Further, we show, for the first time, that RARγ in concert with ATRA regulates protein levels of CDK1 and its subcellular localization. The regulation of the subcellular content of CDK1 and RARγ by ATRA is an important process for achieving an effective response in treatment of leukemia. RARγ and CDK1 form a reciprocal regulatory circuit in the nucleus and influence the function and protein stability of each other and the level of P27(kip) protein. In addition, expression of wee1 kinase and Cdc25A/C phosphatases also coincide with CDK1 expression and its subcellular localization in response to ATRA treatment. Our study reveals a novel mechanism by which CDK1 and RARγ coordinate with ATRA to influence cell cycle progression and cellular differentiation.

Reversal by RARα agonist Am580 of c-Myc-induced imbalance in RARα/RARγ expression during MMTV-Myc tumorigenesis

INTRODUCTION

Retinoic acid signaling plays key roles in embryonic development and in maintaining the differentiated status of adult tissues. Recently, the nuclear retinoic acid receptor (RAR) isotypes α, β and γ were found to play specific functions in the expansion and differentiation of the stem compartments of various tissues. For instance, RARγ appears to be involved in stem cell compartment expansion, while RARα and RARβ are implicated in the subsequent cell differentiation. We found that over-expressing c-Myc in normal mouse mammary epithelium and in a c-Myc-driven transgenic model of mammary cancer, disrupts the balance between RARγ and RARα/β in favor of RARγ.

METHODS

The effects of c-Myc on RAR isotype expression were evaluated in normal mouse mammary epithelium, mammary tumor cells obtained from the MMTV-Myc transgenic mouse model as well as human normal immortalized breast epithelial and breast cancer cell lines. The in vivo effect of the RARα-selective agonist 4-[(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)carboxamido]benzoic acid (Am580) was examined in the MMTV-Myc mouse model of mammary tumorigenesis.

RESULTS

Modulation of the RARα/β to RARγ expression in mammary glands of normal mice, oncomice, and human mammary cell lines through the alteration of RAR-target gene expression affected cell proliferation, survival and tumor growth. Treatment of MMTV-Myc mice with the RARα-selective agonist Am580 led to significant inhibition of mammary tumor growth (~90%, P<0.001), lung metastasis (P<0.01) and extended tumor latency in 63% of mice. Immunocytochemical analysis showed that in these mice, RARα responsive genes such as Cyp26A1, E-cadherin, cellular retinol-binding protein 1 (CRBP1) and p27, were up-regulated. In contrast, the mammary gland tumors of mice that responded poorly to Am580 treatment (37%) expressed significantly higher levels of RARγ. In vitro experiments indicated that the rise in RARγ was functionally linked to promotion of tumor growth and inhibition of differentiation. Thus, activation of the RARα pathway is linked to tumor growth inhibition, differentiation and cell death.

CONCLUSIONS

The functional consequence of the interplay between c-Myc oncogene expression and the RARγ to RARα/β balance suggests that prevalence of RARγ over-RARα/β expression levels in breast cancer accompanied by c-Myc amplification or over-expression in breast cancer should be predictive of response to treatment with RARα-isotype-specific agonists and warrant monitoring during clinical trials.

Retinoids, retinoic acid receptors, and cancer

Retinoids (i.e., vitamin A, all-trans retinoic acid, and related signaling molecules) induce the differentiation of various types of stem cells. Nuclear retinoic acid receptors mediate most but not all of the effects of retinoids. Retinoid signaling is often compromised early in carcinogenesis, which suggests that a reduction in retinoid signaling may be required for tumor development. Retinoids interact with other signaling pathways, including estrogen signaling in breast cancer. Retinoids are used to treat cancer, in part because of their ability to induce differentiation and arrest proliferation. Delivery of retinoids to patients is challenging because of the rapid metabolism of some retinoids and because epigenetic changes can render cells retinoid resistant. Successful cancer therapy with retinoids is likely to require combination therapy with drugs that regulate the epigenome, such as DNA methyltransferase and histone deacetylase inhibitors, as well as classical chemotherapeutic agents. Thus, retinoid research benefits both cancer prevention and cancer treatment.

Ganoderma lucidum Polysaccharides Induce Macrophage-Like Differentiation in Human Leukemia THP-1 Cells via Caspase and p53 Activation

Differentiation therapy by induction of tumor cells is an important method in the treatment of hematological cancers such as leukemia. Tumor cell differentiation ends cancer cells' immortality, thus stopping cell growth and proliferation. In our previous study, we found that fucose-containing polysaccharide fraction F3 extracted from Ganoderma lucidum can bring about cytokine secretion and cell death in human leukemia THP-1 cells. This prompted us to further investigate on how F3 induces the differentiation in human leukemia cells. We integrated time-course microarray analysis and network modeling to study the F3-induced effects on THP-1 cells. In addition, we determined the differentiation effect using Liu's staining, nitroblue tetrazolium (NBT) reduction assay, flow cytometer, western blotting and Q-PCR. We also examined the modulation and regulation by F3 during the differentiation process. Dynamic gene expression profiles showed that cell differentiation was induced in F3-treated THP-1 cells. Furthermore, F3-treated THP-1 cells exhibited enhanced macrophage differentiation, as demonstrated by changes in cell adherence, cell cycle arrest, NBT reduction and expression of differentiation markers including CD11b, CD14, CD68, matrix metalloproteinase-9 and myeloperoxidase. In addition, caspase cleavage and p53 activation were found to be significantly enhanced in F3-treated THP-1 cells. We unraveled the role of caspases and p53 in F3-induced THP-1 cells differentiation into macrophages. Our results provide a molecular explanation for the differentiation effect of F3 on human leukemia THP-1 cells and offer a prospect for a potential leukemia differentiation therapy.

Effects of retinoic acid isomers on apoptosis and enzymatic antioxidant system in human breast cancer cells

Retinoic acids (RAs) modulate growth, differentiation, and apoptosis in normal, pre-malignant & malignant cells. In the present study, the effects of RA isomers (all-trans RA, 13-cis RA, and 9-cis RA) on the cell signal transduction of human breast cancer cells have been studied. The relationship between RAs and an enzymatic antioxidant system was also determined. Estrogen-receptor (ER) positive MCF-7 and ER-negative MDA-MB-231 human breast cancer cells were treated with different doses of each RA isomers, all-trans RA, 13-cis RA, or 9-cis RA. Treatment of RA isomers inhibited cell viability and induced apoptosis of MCF-7 cells as a result of increased caspase activity in cytoplasm and cytochrome C released from mitochondria. All-trans RA was the most effective RA isomer in both cell growth inhibition and induction of apoptosis in MCF-7 cells. However, no significant effect of RA isomers was observed on the cell growth or apoptosis in ER-negative MDA-MB-231 cells. In addition, activities of antioxidant enzymes such as catalase and glutathione peroxidase were decreased effectively after treatment of RA in MCF-7 cells, whereas SOD activity was rarely affected. Thus, the present data suggest that all-trans RA is the most potential inducer of apoptosis and modulator of antioxidant enzymes among RA isomers in MCF-7 human breast cancer cells.

Diverse actions of retinoid receptors in cancer prevention and treatment

Retinoids (retinol [vitamin A] and its biologically active metabolites) are essential signaling molecules that control various developmental pathways and influence the proliferation and differentiation of a variety of cell types. The physiological actions of retinoids are mediated primarily by the retinoic acid receptors alpha, beta, and gamma (RARs) and rexinoid receptors alpha, beta, and gamma. Although mutations in RARalpha, via the PML-RARalpha fusion proteins, result in acute promyelocytic leukemia, RARs have generally not been reported to be mutated or part of fusion proteins in carcinomas. However, the retinoid signaling pathway is often compromised in carcinomas. Altered retinol metabolism, including low levels of lecithin:retinol acyl trasferase and retinaldehyde dehydrogenase 2, and higher levels of CYP26A1, has been observed in various tumors. RARbeta(2) expression is also reduced or is absent in many types of cancer. A greater understanding of the molecular mechanisms by which retinoids induce cell differentiation, and in particular stem cell differentiation, is required in order to solve the issue of retinoid resistance in tumors, and thereby to utilize RA and synthetic retinoids more effectively in combination therapies for human cancer.

Involvement of apoptotic cell death and cell cycle perturbation in retinoic acid-induced cleft palate in mice

Retinoic acid (RA), a metabolite of vitamin A, plays a key role in a variety of biological processes and is essential for normal embryonic development. On the other hand, exogenous RA could cause cleft palate in offspring when it is given to pregnant animals at either the early or late phases of palatogenesis, but the pathogenetic mechanism of cleft palate caused by excess RA remains not fully elucidated. The aim of the present study was to investigate the effects of excess of RA on early palatogenesis in mouse fetuses and analyze the teratogenic mechanism, especially at the stage prior to palatal shelf elevation. We gave all-trans RA (100 mg/kg) orally to E11.5 ICR pregnant mice and observed the changes occurring in the palatal shelves of their fetuses. It was found that apoptotic cell death increased not only in the epithelium of the palatal shelves but also in the tongue primordium, which might affect tongue withdrawal movement during palatogenesis and impair the horizontal elevation of palatal shelves. In addition, RA was found to prevent the G(1)/S progression of palatal mesenchymal cells through upregulation of p21(Cip1), leading to Rb hypophospholylation. Thus, RA appears to cause G(1) arrest in palatal mesenchymal cells in a similar manner as in various cancer and embryonic cells. It is likely that apoptotic cell death and cell cycle disruption are involved in cleft palate formation induced by RA.

Effects of all-trans-retinoic on human gastric cancer cells BGC-823

OBJECTIVE

To determine the inhibitory effects of all-trans-retinoic acid (ATRA) on cell growth, cell cycle and vascular endothelial growth factor (VEGF) expression in the human gastric cancer cell line BGC-823 in vitro.

METHODS

Human gastric cancer BGC-823 cells were treated with various concentrations of ATRA and the cell growth was then determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide viability assay. The cell cycle distribution was analyzed using a flow cytometer. The VEGF mRNA and protein expression were analyzed by semi-quantitative RT-PCR and Western blotting, respectively.

RESULTS

ATRA at concentrations of 0.1-10 micromol/L inhibited the growth of BGC-823 cells grown in culture; a time- and dose-dependent inhibitory influence was found. ATRA arrested BGC-823 cells at the G0/G1 phase in a dose-dependent way. Both VEGF mRNA and protein were decreased by ATRA in a dose-dependent way.

CONCLUSION

The anti-tumor effects of ATRA on human gastric cancer cells are associated with G0/G1 phase arrest and decreased VEGF expression.

All-trans-retinoic acid inhibits collapsin response mediator protein-2 transcriptional activity during SH-SY5Y neuroblastoma cell differentiation

Neurons are highly polarized cells composed of two structurally and functionally distinct parts, the axon and the dendrite. The establishment of this asymmetric structure is a tightly regulated process. In fact, alterations in the proteins involved in the configuration of the microtubule lattice are frequent in neuro-oncologic diseases. One of these cytoplasmic mediators is the protein known as collapsin response mediator protein-2, which interacts with and promotes tubulin polymerization. In this study, we investigated collapsin response mediator protein-2 transcriptional regulation during all-trans-retinoic acid-induced differentiation of SH-SY5Y neuroblastoma cells. All-trans-retinoic acid is considered to be a potential preventive and therapeutic agent, and has been extensively used to differentiate neuroblastoma cells in vitro. Therefore, we first demonstrated that collapsin response mediator protein-2 mRNA levels are downregulated during the differentiation process. After completion of deletion construct analysis and mutagenesis and mobility shift assays, we concluded that collapsin response mediator protein-2 basal promoter activity is regulated by the transcription factors AP-2 and Pax-3, whereas E2F, Sp1 and NeuroD1 seem not to participate in its regulation. Furthermore, we finally established that reduced expression of collapsin response mediator protein-2 after all-trans-retinoic acid exposure is associated with impaired Pax-3 and AP-2 binding to their consensus sequences in the collapsin response mediator protein-2 promoter. Decreased attachment of AP-2 is a consequence of its accumulation in the cytoplasm. On the other hand, Pax-3 shows lower binding due to all-trans-retinoic acid-mediated transcriptional repression. Unraveling the molecular mechanisms behind the action of all-trans-retinoic acid on neuroblastoma cells may well offer new perspectives for its clinical application.

Inhibition of Monocytic Differentiation by Phosphorylation-deficient Stat1 is Associated with Impaired Expression of Stat2, ICSBP/IRF8 and C/EBPɛ

Monocytic differentiation is coordinated through the ordered activation of multiple signalling pathways, controlling transcription of specific subsets of genes that regulate the development of the mature phenotype. To identify key transcription factors involved in this process, we used the human monoblastic U-937 cell line as a model of monocytic differentiation. U-937 cells can be differentiated by treatment with all-trans retinoic acid (ATRA) and 1,25alpha-dihydroxycholecalciferol (VitD3), resulting in G(0)/G(1)-arrested cells expressing monocytic surface markers. We have previously shown that ATRA-induced differentiation and cell cycle arrest specifically requires Stat1 activation, through phosphorylation of tyrosine 701 and serine 727. In this report, we used U-937 cells expressing phosphorylation-deficient mutants of Stat1 (Stat1Y701F and Stat1S727A) to determine myeloid-specific transcription factors that are activated downstream of Stat1 during induced monocytic differentiation. We demonstrate that ATRA-induced upregulation of Stat2, ICSBP/IRF8 and C/EBPepsilon, key transcription factors linked to myelomonocytic differentiation, is selectively impaired in cells expressing mutant Stat1. In contrast, ATRA-induced expression of PU.1, C/EBPalpha, C/EBPbeta and IRF-1 was unaffected. Taken together, our data suggest that ATRA-induced regulation of Stat2, ICSBP and C/EBPepsilon is dependent on active Stat1, and that a failure to correctly regulate these transcription factors is associated with the inhibition of monocytic differentiation.

Increased p21 expression and complex formation with cyclin E/CDK2 in retinoid-induced pre-B lymphoma cell apoptosis

Cip/Kip family protein p21, a cyclin-dependent kinase (CDK) inhibitor, is directly transactivated by retinoic acid receptor alpha (RARalpha) upon retinoic acid (RA):RARalpha binding. Yet the role of p21 upregulation by RA in lymphoma cells remains unknown. Here, we show that, in human pre-B lymphoma Nalm6 cells, RA-induced proliferation inhibition results from massive cell death characterized by apoptosis. Upregulated p21 by RA accompanies caspase-3 activation and precedes the occurrence of apoptosis. p21 induction leads to increased p21 complex formation with cyclin E/CDK2, which occurs when cyclin E and CDK2 levels remain constant. CDK2 can alternatively promote apoptosis, but the mechanisms remain unknown. Data presented here suggest a novel RA-signaling, by which RA-induced p21 induction and complex formation with cyclin E/CDK2 diverts CDK2 function from normally driving proliferation to alternatively promoting apoptosis.

Transforming growth factor-β1 inhibits all-trans retinoic acid-induced apoptosis

The interaction between retinoids and transforming growth factor-beta1 (TGF-beta1) leading to regulation of proliferation, differentiation and apoptosis is not still fully understood. In this study, we demonstrated that a combination treatment with all-trans retinoic acid (ATRA) and TGF-beta1 led to the enhancement of ATRA-induced suppression of cell proliferation, which is accompanied by inhibition of ATRA-induced apoptosis in human leukemia HL-60 cells. This effect was preceded by the arrest of cells in G0/G1 cell cycle phase linked with pRb protein dephosphorylation, continuous accumulation of p21 and transiently increased level of p27, inhibitors of cyclin-dependent kinases. Inhibition of ATRA-induced apoptosis by TGF-beta1 was associated with an increased level of Mcl-1 protein, an anti-apoptotic member of Bcl-2 family, but not with inhibition of mitochondrial membrane depolarization. Levels of other Bcl-2 family proteins (Bcl-2, Bcl-X(L), Bad, Bak, Bax) were unaffected by simultaneous ATRA and TGF-beta1 treatment, when compared to ATRA alone. Upregulation of c-FLIP(L) protein, an inhibitor of apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), correspond with inhibition of ATRA-induced (autocrine TRAIL-mediated) caspase-8 activation and apoptosis. These results suggest that apoptosis inhibition associated with proliferation block could depend on modulation of the TRAIL apoptotic pathway and regulation of the Mcl-1 protein level. In summary, we demonstrate that the balance of processes leading to regulation of proliferation and differentiation of myeloid cells can modulate cell sensitivity to apoptosis-inducing stimuli.

All-trans retinoic acid inhibits proliferation of intestinal epithelial cells by inhibiting expression of the gene encoding Kruppel-like factor 5

Retinoids are known inhibitors of epithelial cell proliferation. Previous studies indicate that Kruppel-like factor 5 (KLF5) is a pro-proliferative transcription factor. Here, we examined the effect of all-trans retinoid acid (ATRA) on proliferation of the intestinal epithelial cell line, IEC6. Treatment of IEC6 cells with ATRA inhibited their proliferation due to G1 cell cycle arrest. This inhibition was correlated with a decrease in the levels of KLF5 mRNA and promoter activity. In contrast, constitutive expression of KLF5 in stably transfected IEC6 cells with a KLF5-expressing plasmid driven by a viral promoter abrogated the growth inhibitory effect of ATRA. Moreover, ATRA inhibited proliferation of several human colon cancer cell lines with high levels of KLF5 expression but not those with low levels of KLF5 expression. Our results indicate that KLF5 is a potential mediator for the inhibitory effect of ATRA on intestinal epithelial cell proliferation.

β-Carotene stimulates chemotaxis of human endothelial progenitor cells

Angiogenesis is a crucial process in tissue remodeling during growth, both in the embryo and the adult. In our study we concentrated on the direct effect of β-carotene on human umbilical cord originating from endothelial progenitor cells (EPCs). β-Carotene uptake by EPCs was measured using a HPLC method. The determination of cell surface antigens was performed by flow cytometry. The effect on cell proliferation was estimated by measuring bromo-deoxyuridine incorporation. The influence on the formation of a tubular-like structure was investigated in a 3D assay in matrigel. Quantitative gene expression was estimated using real-time PCR. We demonstrated that β-carotene in the physiological range of concentrations found in human blood is a potent activator of EPC chemotaxis, which is accompanied by a change in the expression of genes mediating cell adhesion and homing, but does not activate the final markers of endothelial differentiation. This study points to the prochemotactic and homing activity of β-carotene in undifferentiated endothelial cell progenitors for the first time, which may suggest a potential role of this carotenoid in progenitor cell therapy aimed at angiogenesis and tissue repair.