Neutrophil maturation and the role of retinoic acid

The Effect of Retinoic Acid on Neutrophil Innate Immune Interactions With Cutaneous Bacterial Pathogens

Vitamin A and its biologically active derivative, retinoic acid (RA), are important for many immune processes. RA, in particular, is essential for the development of immune cells, including neutrophils, which serve as a front-line defense against infection. While vitamin A deficiency has been linked to higher susceptibility to infections, the precise role of vitamin A/RA in host-pathogen interactions remains poorly understood. Here, we provided evidence that RA boosts neutrophil killing of methicillin-resistant Staphylococcus aureus (MRSA). RA treatment stimulated primary human neutrophils to produce reactive oxygen species, neutrophil extracellular traps, and the antimicrobial peptide cathelicidin (LL-37). Because RA treatment was insufficient to reduce MRSA burden in an in vivo murine model of skin infection, we expanded our analysis to other infectious agents. RA did not affect the growth of a number of common bacterial pathogens, including MRSA, Escherichia coli K1 and Pseudomonas aeruginosa; however, RA directly inhibited the growth of group A Streptococcus (GAS). This antimicrobial effect, likely in combination with RA-mediated neutrophil boosting, resulted in substantial GAS killing in neutrophil killing assays conducted in the presence of RA. Furthermore, in a murine model of GAS skin infection, topical RA treatment showed therapeutic potential by reducing both skin lesion size and bacterial burden. These findings suggest that RA may hold promise as a therapeutic agent against GAS and perhaps other clinically significant human pathogens.

Single-cell transcriptional landscape of temporal neutrophil response to burn wound in larval zebrafish

Neutrophils accumulate early in tissue injury. However, the cellular and functional heterogeneity of neutrophils during homeostasis and in response to tissue damage remains unclear. Here, we use larval zebrafish to understand neutrophil responses to thermal injury. Single-cell transcriptional mapping of myeloid cells during a 3-day time course in burn and control larvae revealed distinct neutrophil subsets and their cell-cell interactions with macrophages across time and conditions. The trajectory formed by three zebrafish neutrophil subsets resembles human neutrophil maturation, with varying transition patterns between conditions. Through ligand-receptor cell-cell interaction analysis, we found neutrophils communicate more in burns in a pathway and temporal manner. Finally, we identified the correlation between zebrafish myeloid signatures and human burn severity, establishing GPR84+ neutrophils as a potential marker of early innate immune response in burns. This work builds the molecular foundation and a comparative single-cell genomic framework to identify neutrophil markers of tissue damage using model organisms.

Extirpating the cancer stem cell hydra: Differentiation therapy and Hyperthermia therapy for targeting the cancer stem cell hierarchy

Ever since the discovery of cancer stem cells (CSCs), they have progressively attracted more attention as a therapeutic target. Like the mythical hydra, this subpopulation of cells seems to contribute to cancer immortality, spawning more cells each time that some components of the cancer cell hierarchy are destroyed. Traditional modalities focusing on cancer treatment have emphasized apoptosis as a route to eliminate the tumor burden. A major problem is that cancer cells are often in varying degrees of dedifferentiation contributing to what is known as the CSCs hierarchy and cells which are known to be resistant to conventional therapy. Differentiation therapy is an experimental therapeutic modality aimed at the conversion of malignant phenotype to a more benign one. Hyperthermia therapy (HT) is a modality exploiting the changes induced in cells by the application of heat produced to aid in cancer therapy. While differentiation therapy has been successfully employed in the treatment of acute myeloid leukemia, it has not been hugely successful for other cancer types. Mounting evidence suggests that hyperthermia therapy may greatly augment the effects of differentiation therapy while simultaneously overcoming many of the hard-to-treat facets of recurrent tumors. This review summarizes the progress made so far in integrating hyperthermia therapy with existing modules of differentiation therapy. The focus is on studies related to the successful application of both hyperthermia and differentiation therapy when used alone or in conjunction for hard-to-treat cancer cell niche with emphasis on combined approaches to target the CSCs hierarchy.

Targeting DCs for Tolerance Induction: Don't Lose Sight of the Neutrophils

Chronic inflammatory disorders (CID), such as autoimmune diseases, are characterized by overactivation of the immune system and loss of immune tolerance. T helper 17 (Th17) cells are strongly associated with the pathogenesis of multiple CID, including psoriasis, rheumatoid arthritis, and inflammatory bowel disease. In line with the increasingly recognized contribution of innate immune cells to the modulation of dendritic cell (DC) function and DC-driven adaptive immune responses, we recently showed that neutrophils are required for DC-driven Th17 cell differentiation from human naive T cells. Consequently, recruitment of neutrophils to inflamed tissues and lymph nodes likely creates a highly inflammatory loop through the induction of Th17 cells that should be intercepted to attenuate disease progression. Tolerogenic therapy via DCs, the central orchestrators of the adaptive immune response, is a promising strategy for the treatment of CID. Tolerogenic DCs could restore immune tolerance by driving the development of regulatory T cells (Tregs) in the periphery. In this review, we discuss the effects of the tolerogenic adjuvants vitamin D3 (VD3), corticosteroids (CS), and retinoic acid (RA) on both DCs and neutrophils and their potential interplay. We briefly summarize how neutrophils shape DC-driven T-cell development in general. We propose that, for optimization of tolerogenic DC therapy for the treatment of CID, both DCs for tolerance induction and the neutrophil inflammatory loop should be targeted while preserving the potential Treg-enhancing effects of neutrophils.

Effect of Different Combinations of Dietary Vitamin A, Protein Levels, and Monensin on Inflammatory Markers and Metabolites, Retinol-Binding Protein, and Retinoid Status in Periparturient Dairy Cows

The objective of this study was to determine the effect of feeding different combinations of dietary vitamin A supplementation (0 or 110 IU/kg body weight), protein (10.3% or 12.2%), and an ionophore (monensin at 0 or 400 mg/day) on retinoid metabolism and immune function of dairy cows. Eighty multiparous Holstein dairy cows were studied from d -35 to +21 relative to expected parturition in a complete randomized block design with a 2 × 2 × 2 factorial arrangement of treatments. The significance of treatments was declared at p ≤ 0.05. Dairy cows receiving high crude protein (CP) diets with monensin had a greater retinol-binding protein serum concentration than cows receiving high CP diets without monensin (p = 0.04). Animals supplemented with vitamin A showed lower SCC (p = 0.04) and a higher thiobarbituric acid reactive substances concentration (p = 0.06) than cows non-supplemented. Moreover, cows receiving low crude protein diets had a greater haptoglobin concentration (p = 0.01). In addition, cows fed a high crude protein diet had a greater TNF-α expression in peripheral blood mononuclear cells (p = 0.04). Animals fed diets without monensin had a greater serum haptoglobin on day 3 postpartum than those fed monensin (p = 0.01). Moreover, dietary vitamin A increased serum 13-cis retinoic acid postpartum. We conclude that vitamin A, crude protein levels, and monensin fed during the close-up period affect milk somatic cell count, some vitamin statuses, and inflammatory markers during early lactation.

Transcriptomic and Epigenomic Profiling of Histone Deacetylase Inhibitor Treatment Reveals Distinct Gene Regulation Profiles Leading to Impaired Neutrophil Development

Supplemental Digital Content is available in the text

The clinical use of histone deacetylase inhibitors (HDACi) for the treatment of bone marrow failure and hematopoietic malignancies has increased dramatically over the last decades. Nonetheless, their effects on normal myelopoiesis remain poorly evaluated. Here, we treated cord blood derived CD34+ progenitor cells with two chemically distinct HDACi inhibitors MS-275 or SAHA and analyzed their effects on the transcriptome (RNA-seq), epigenome (H3K27ac ChIP-seq) and functional and morphological characteristics during neutrophil development. MS-275 (entinostat) selectively inhibits class I HDACs, with a preference for HDAC1, while SAHA (vorinostat) is a non-selective class I/II HDACi. Treatment with individual HDACi resulted in both overlapping and distinct effects on both transcriptome and epigenome, whereas functional effects were relatively similar. Both HDACi resulted in reduced expansion and increased apoptosis in neutrophil progenitor cells. Morphologically, HDACi disrupted normal neutrophil differentiation what was illustrated by decreased percentages of mature neutrophils. In addition, while SAHA treatment clearly showed a block at the promyelocytic stage, MS-275 treatment was characterized by dysplastic features and skewing towards the monocytic lineage. These effects could be mimicked using shRNA-mediated knockdown of HDAC1. Taken together, our data provide novel insights into the effects of HDAC inhibition on normal hematopoietic cells during neutrophil differentiation. These findings should be taken into account when considering the clinical use of MS-275 and SAHA, and can be potentially utilized to tailor more specific, hematopoietic-directed HDACi in the future.

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.

Filomicelles Deliver a Chemo-Differentiation Combination of Paclitaxel and Retinoic Acid That Durably Represses Carcinomas in Liver to Prolong Survival

Drug resistance and relapse is common in cancer treatments with chemotherapeutics, and while drug combinations with naturally occurring, differentiation-inducing retinoic acid (RA) provide remission-free cures for one type of liquid tumor, solid tumors present major problems for delivery. Here, inspired by filoviruses that can be microns in length, flexible filomicelles that self-assemble from an amphiphilic block copolymer (PEG-PCL) are shown to effectively deliver RA and paclitaxel (TAX) to several solid tumor models, particularly in the liver. These hydrophobic compounds synergistically load into the cores of the elongated micelles, and the coloaded micelles prove most effective at causing cell death, ploidy, and durable regression of tumors compared to free drugs or to separately loaded drugs. RA-TAX filomicelles also reduce mortality of human lung or liver derived cancers engrafted at liver, intraperitoneal, and subcutaneous sites in immunodeficient mice. In vitro studies show that the dual drug micelles effectively suppress proliferation while upregulating a generic differentiation marker. The results highlight the potency of dual-loaded filomicelles in killing cancer cells or else driving their differentiation away from growth.

Effects of exogenous vitamins A, C, and E and NADH supplementation on proliferation, cytokines release, and cell redox status of lymphocytes from healthy aged subjects

Aging is an inevitable biological event that is associated with immune alterations. These alterations are related to increased cellular oxidative stress and micronutrient deficiency. Antioxidant supplementation could improve these age-related abnormalities. The aim of this study was to determine in vitro effects of vitamin A, vitamin C, vitamin E, and nicotinamide adenine dinucleotide (NADH) on T cell proliferation, cytokine release, and cell redox status in the elderly compared with young adults. Peripheral blood lymphocytes were isolated using a density gradient of Histopaque. They were cultured in vitro and stimulated with concanavalin A in the presence or absence of vitamins. Cell proliferation was determined by conducting MTT assays, and based on interleukin-2 and interleukin-4 secretions. Cell oxidant/antioxidant balance was assessed by assaying reduced glutathione (GSH), malondialdehyde, carbonyl protein levels, and catalase activity. The present study demonstrated that T-lymphocyte proliferation was decreased with aging and was associated with cytokine secretion alterations, GSH depletion, and intracellular oxidative stress. In the elderly, vitamin C, vitamin E, and NADH significantly improved lymphocyte proliferation and mitigated cellular oxidative stress, whereas vitamin A did not affect cell proliferation or cell redox status. In conclusion, vitamin C, vitamin E, and NADH supplementation improved T-lymphocytes response in the elderly, and could contribute to the prevention of age-related immune alterations. Consumption of food items containing these vitamins is recommended, and further investigation is necessary to evaluate the effect of vitamin supplementation in vivo.

Retinoic acid induces hypersegmentation and enhances cytotoxicity of neutrophils against cancer cells

Hypersegmentation of nuclei is considered a distinct characteristic of the antitumoral phenotype of neutrophils. Retinoic acid, a metabolite of retinol, reorganizes and induces segmentation of the nucleus during the differentiation of neutrophils. However, the role of retinoic acid in the phenotype polarization of neutrophils has not been fully established. Here, we investigated the effect of retinoic acid on phenotype polarization of neutrophils. Retinoic acid-induced the hypersegmentation of human neutrophils via retinoic acid receptors and mTOR pathways. Retinoic acid-induced hypersegmented neutrophils enhanced neutrophil extracellular traps (NETs) formation in response to phorbol-12-myristate 13-acetate (PMA) and fMLP (N-Formylmethionine-leucyl-phenylalanine) stimulation, and increased cytotoxicity against various tumor cells. Moreover, retinoic acid treatment attenuated tumor growth in a murine model of tumor. Taken together, these results suggests that retinoic acid induces the phenotype polarization of neutrophils to exert antitumor effects.

The Histone Deacetylase Inhibitor BML-210 Influences Gene and Protein Expression in Human Promyelocytic Leukemia NB4 Cells via Epigenetic Reprogramming

Today, cancer is understood as an epigenetic as well as genetic disease. The main epigenetic hallmarks of the cancer cell are DNA methylation and histone modifications. Proteins such as histone deacetylases (HDACs) that cause modifications of histones and other proteins can be targets for novel anticancer agents. Recently, interest in compounds that can inhibit HDACs increased, and now there are many HDACs inhibitors (HDACIs) available with different chemical structures, biological and biochemical properties; hopefully some of them will succeed, probably in combination with other agents, in cancer therapies. In our study we focused on the novel HDACI-BML-210. We found that BML-210 (N-phenyl-N'-(2-Aminophenyl)hexamethylenediamide) inhibits the growth of NB4 cells in dose- and time-dependent manner. In this study we also examined how expression and activity of HDACs are affected after leukemia cell treatment with BML-210. Using a mass spectrometry method we identified proteins that changed expression after treatment with BML-210. We prepared RT-PCR analysis of these genes and the results correlated with proteomic data. Based on these and other findings from our group, we suggest that HDACIs, like BML-210, can be promising anticancer agents in promyelocytic leukemia treatment.

SPLUNC1 is associated with nasopharyngeal carcinoma prognosis and plays an important role in all-trans-retinoic acid-induced growth inhibition and differentiation in nasopharyngeal cancer cells

Human SPLUNC1 can suppress nasopharyngeal carcinoma (NPC) tumor formation; however, the correlation between SPLUNC1expression and NPC patient prognosis has not been reported. In the present study, we used a large-scale sample of 1015 tissue cores to detect SPLUNC1 expression and its association with patient prognosis. SPLUNC1 expression was reduced in NPC samples compared to nontumor nasopharyngeal epithelium tissues. Positive expression of SPLUNC1 in NPC predicted a better prognosis (disease-free survival, P = 0.034; overall survival, P = 0.048). Cox's proportional hazards model revealed that SPLUNC1 could be a significant prognostic factor affecting disease-free survival (P = 0.027). A cDNA micro-array analyzed by significant analysis of micro-array (SAM) and ingenuity pathway analysis (IPA) revealed that an indirect interaction existed between SPLUNC1 and retinoic acid (RA) in the cancer regulatory network. To further investigate the molecular mechanisms involved, we utilized several bioinformatics tools and identified 12 retinoid X receptors heterodimer binding sites in the promoter region of the SPLUNC1 gene. The transcriptional activity of the SPLUNC1 promoter was up-regulated significantly by all-trans-retinoic acid (ATRA). SPLUNC1 and retinoic acid receptor expression were induced significantly by ATRA, and removal of ATRA led to a progressive loss of SPLUNC1 and retinoic acid receptor expression. ATRA inhibited proliferation and induced the differentiation of NPC cells. Interestingly, over-expression of SPLUNC1 sensitized NPC cells to ATRA, whereas knockdown of SPLUNC1 in HNE1 cells increased cell viability. Under SPLUNC1 knockdown conditions, differentiation was reversed by ATRA treatment. We concluded that SPLUNC1 could potentially predict prognosis for NPC patients and play an important role in ATRA-induced growth inhibition and differentiation in NPC cells.

Retinoid levels influence enterohemorrhagic Escherichia coli infection and Shiga toxin 2 susceptibility in mice

Enterohemorrhagic Escherichia coli (EHEC) is a food-borne pathogen that produces Shiga toxin (Stx) and causes hemorrhagic colitis. Under some circumstances, Stx produced within the intestinal tract enters the bloodstream, leading to systemic complications that may cause the potentially fatal hemolytic-uremic syndrome. Although retinoids like vitamin A (VA) and retinoic acid (RA) are beneficial to gut integrity and the immune system, the effect of VA supplementation on gastrointestinal infections of different etiologies has been controversial. Thus, the aim of this work was to study the influence of different VA status on the outcome of an EHEC intestinal infection in mice. We report that VA deficiency worsened the intestinal damage during EHEC infection but simultaneously improved survival. Since death is associated mainly with Stx toxicity, Stx was intravenously inoculated to analyze whether retinoid levels affect Stx susceptibility. Interestingly, while VA-deficient (VA-D) mice were resistant to a lethal dose of Stx2, RA-supplemented mice were more susceptible to it. Given that peripheral blood polymorphonuclear cells (PMNs) are known to potentiate Stx2 toxicity, we studied the influence of retinoid levels on the absolute number and function of PMNs. We found that VA-D mice had decreased PMN numbers and a diminished capacity to produce reactive oxygen species, while RA supplementation had the opposite effect. These results are in line with the well-known function of retinoids in maintaining the homeostasis of the gut but support the idea that they have a proinflammatory effect by acting, in part, on the PMN population.

Serum amyloid A is a retinol binding protein that transports retinol during bacterial infection

Retinol plays a vital role in the immune response to infection, yet proteins that mediate retinol transport during infection have not been identified. Serum amyloid A (SAA) proteins are strongly induced in the liver by systemic infection and in the intestine by bacterial colonization, but their exact functions remain unclear. Here we show that mouse and human SAAs are retinol binding proteins. Mouse and human SAAs bound retinol with nanomolar affinity, were associated with retinol in vivo, and limited the bacterial burden in tissues after acute infection. We determined the crystal structure of mouse SAA3 at a resolution of 2 Å, finding that it forms a tetramer with a hydrophobic binding pocket that can accommodate retinol. Our results thus identify SAAs as a family of microbe-inducible retinol binding proteins, reveal a unique protein architecture involved in retinol binding, and suggest how retinol is circulated during infection.

DOI:http://dx.doi.org/10.7554/eLife.03206.001

Vitamins are nutrients that organisms require in order to survive and grow. If an organism is unable to synthesize a vitamin in sufficient quantities, it is essential that it obtain the vitamin through its diet instead.

Vitamin A is found in foods such as eggs, animal liver and carrots, and a diet that is lacking in this vitamin can cause blindness and an increased risk of microbial infections. Vitamin A is not a single compound, but rather a collection of compounds with similar molecular structures. One of these is retinol, which plays a vital role in the body's response to microbial infection. Retinol must bind to specific proteins to be able to move through the bloodstream and be transported around the body.

Serum retinol binding protein transports ingested retinol from the intestine to the liver and other tissues. However, during microbial infection—when retinol transport is particularly important—the amount of this protein dramatically decreases; as such it is unclear how retinol is transported when the body is under attack from pathogens.

It had been suggested that Serum Amyloid A (SAA) proteins, a family of proteins made by some liver and intestinal cells, could be involved in the response to infection, because these proteins' levels increase during infection. However, their exact functions were unknown. Derebe, Zlatkov et al. found that mice fed a diet poor in vitamin A produced fewer SAA proteins in their liver and intestinal cells. However, treating the cells with retinol or the molecule it is broken down into—called retinoic acid—caused more SAAs to be made. Derebe, Zlatkov et al. also discovered that SAAs are associated with retinol in blood samples taken from mice infected with salmonella; and that both mouse and human SAAs bind tightly to retinol. Combined, this evidence suggests that SAAs are the retinol binding proteins that transport retinol during infections.

Derebe, Zlatkov et al. went on to solve the crystal structure of a mouse SAA protein, and showed that four SAA molecules bind together to form a ‘pocket’ that can hold a retinol molecule. Future work will focus on understanding exactly how the transport of retinol by SAAs affects the development of immunity to infections.

DOI:http://dx.doi.org/10.7554/eLife.03206.002

Reduced serum retinol-binding protein levels in patients with de novo acute myeloid leukaemia

Retinol-binding protein (RBP) has been used as a nutritional index for children with acute myeloid leukaemia (AML) in previous studies. However, no studies have yet examined RBP levels in AML patients from all age groups. In this study, AML patients presented with lower RBP concentrations than healthy control subjects and patients with benign haematopathies. A negative association was observed between serum RBP level and peripheral white blood cell count in M4 and M5 AML patients. Moreover, patients carrying the FLT3-ITD mutation and young patients had lower RBP levels than those lacking this mutation and elderly patients. In conclusion, these observations suggest that aberrant retinol levels may be associated with AML.

Role of Fat-Soluble Vitamins A and D in the Pathogenesis of Influenza: A New Perspective

Reduced exposure to solar radiation, leading to a deficiency of vitamin D and hence impaired innate immunity, has been suggested as a trigger for influenza viral replication and as an explanation of seasonal influenza. Although this hypothesis accounts for many unexplained facts about the epidemiology of influenza, gaps remain in understanding the pathogenesis and manifestations of the disease. Several observations suggest a role for vitamin A compounds (retinoids) in the disease. This paper presents a new model of the etiopathogenesis of influenza, suggesting that host resistance and susceptibility depend importantly on the ratio of vitamin D to vitamin A activity. Retinoid concentrations within normal physiological limits appear to inhibit influenza pathogenesis whereas higher background concentrations (i.e., very low vitamin D : A ratios) increase the risk of severe complications of the disease. There is also evidence that influenza-induced or preexisting liver disease, diabetes, and obesity worsen the severity of infection, possibly via liver dysfunction and alterations in retinoid metabolism. The model could be tested by determining the presence of retinoids in the secretions of patients with influenza and by studies of retinoid profiles in patients and controls. Potential strategies for prevention and treatment are discussed.

Feeding the immune system

A well-functioning immune system is key to providing good defence against pathogenic organisms and to providing tolerance to non-threatening organisms, to food components and to self. The immune system works by providing an exclusion barrier, by identifying and eliminating pathogens and by identifying and tolerating non-threatening sources of antigens, and by maintaining a memory of immunological encounters. The immune system is complex involving many different cell types distributed throughout the body and many different chemical mediators some of which are involved directly in defence while others have a regulatory role. Babies are born with an immature immune system that fully develops in the first few years of life. Immune competence can decline with ageing. The sub-optimal immune competence that occurs early and late in life increases susceptibility to infection. Undernutrition decreases immune defences, making an individual more susceptible to infection. However, the immune response to an infection can itself impair nutritional status and alter body composition. Practically all forms of immunity are affected by protein-energy malnutrition, but non-specific defences and cell-mediated immunity are most severely affected. Micronutrient deficiencies impair immune function. Here, vitamins A, D and E, and Zn, Fe and Se are discussed. The gut-associated lymphoid tissue is especially important in health and well-being because of its close proximity to a large and diverse population of organisms in the gastrointestinal tract and its exposure to food constituents. Certain probiotic bacteria which modify the gut microbiota enhance immune function in laboratory animals and may do so in human subjects.

Hemidesmus indicus induces apoptosis as well as differentiation in a human promyelocytic leukemic cell line

ETHNOPHARMACOLOGICAL RELEVANCE

The decoction of the roots of Hemidesmus indicus is widely used in the Indian traditional medicine for the treatment of blood diseases, dyspepsia, loss of taste, dyspnea, cough, poison, menorrhagia, fever, and diarrhea. Poly-herbal preparations containing Hemidesmus are often used by traditional medical practitioners for the treatment of cancer. The aim of this study was to investigate the cytodifferentiative, cytostatic and cytotoxic potential of a decoction of Hemidesmus indicus's roots (0.31-3 mg/mL) on a human promyelocytic leukemia cell line (HL-60).

MATERIALS AND METHODS

The decoction of Hemidesmus indicus was characterized by HPLC to quantify its main phytomarkers. Induction of apoptosis, cell-cycle analysis, levels of specific membrane differentiation markers were evaluated by flow cytometry. The analysis of cell differentiation by nitroblue tetrazolium (NBT) reducing activity, adherence to the plastic substrate, α-napthyl acetate esterase activity and morphological analysis was performed through light microscopy (LM) and transmission electron microscopy (TEM).

RESULTS

Starting from the concentration of 0.31 mg/ml, Hemidesmus indicus induced cytotoxicity and altered cell-cycle progression, through a block in the G0/G1 phase. The decoction caused differentiation of HL-60 cells as shown by NBT reducing activity, adherence to the plastic substrate, α-naphtyl acetate esterase activity, and increasing expression of CD14 and CD15. The morphological analysis by LM and TEM clearly showed the presence of granulocytes and macrophages after Hemidesmus indicus treatment.

CONCLUSIONS

The cytodifferentiating, cytotoxic and cytostatic activities of Hemidesmus indicus offers a scientific basis for its use in traditional medicine. Its potent antileukemic activity provides a pre-clinical evidence for its traditional use in anticancer pharmacology. Further experiments are worthwhile to determine the in vivo anticancer potential of this plant decoction and its components.

Retinoic acid inhibits CD25+ dendritic cell expansion and γδ T-cell activation in experimental autoimmune uveitis

PURPOSE

We determined the mechanism by which all-trans retinoic acid (ATRA) inhibits experimental autoimmune uveitis (EAU) and determined the role of γδ T cells in this autoimmune disease.

METHODS

C57BL/6 (B6) mice were immunized with the uveitogenic, interphotoreceptor retinoid-binding protein1-20 peptide (IRBP1-20) in complete Freund's adjuvant (CFA), with or without a preceding ATRA treatment. Responses and pathogenic activity of Th1- and Th17-autoreactive T cells were compared, and the effects of ATRA on γδ T cells and CD25(+) dendritic cell (DC) subset were determined. Interactions among uveitogenic T cells, DC subsets, and γδ T cells were investigated.

RESULTS

Administration of ATRA to B6 mice in which EAU was induced suppressed the response of Th17 autoreactive T cells, which was associated with decreased generation of the CD25(+) DC subset and suppressed activation of γδ T cells. Adoptively transferred γδ T cells isolated from ATRA-treated mice showed a diminished ability to promote the activation of Th17 autoreactive T cells in vitro and in vivo compared to γδ T cells from untreated donors.

CONCLUSIONS

ATRA inhibits the expansion of CD25(+) DCs and γδ T-cell activation, thereby restraining the Th17 autoreactive T-cell response.

Retinoids: novel immunomodulators and tumour-suppressive agents?

Retinoids play important roles in the transcriptional activity of normal, degenerative and tumour cells. Retinoid analogues may be promising therapeutic agents for the treatment of immune disorders as different as type I diabetes and systemic lupus erythematosus. In addition, the use of retinoids in cancer treatment has progressed significantly in the last two decades; thus, numerous retinoid compounds have been synthesized and tested. In this paper, the actual or potential use of retinoids as immunomodulators or tumour-suppressive agents is discussed.

Essential role for retinoic acid in the promotion of CD4(+) T cell effector responses via retinoic acid receptor alpha

Vitamin A and its metabolite, retinoic acid (RA) are implicated in the regulation of immune homeostasis via the peripheral induction of regulatory T cells. Here we showed RA was also required to elicit proinflammatory CD4(+) helper T cell responses to infection and mucosal vaccination. Retinoic acid receptor alpha (RARα) was the critical mediator of these effects. Antagonism of RAR signaling and deficiency in RARα (Rara(-/-)) resulted in a cell-autonomous CD4(+) T cell activation defect, which impaired intermediate signaling events, including calcium mobilization. Altogether, these findings reveal a fundamental role for the RA-RARα axis in the development of both regulatory and inflammatory arms of adaptive immunity and establish nutritional status as a broad regulator of adaptive T cell responses.

The effects of all-trans retinoic acid on leukocytes in rat's embryo

This study was planned to determine the effects of All-Trans Retinoic Acid (ATRA) on the progenitors of White Blood Cells (WBC) and survey their outcomes in rat's embryo during both late-yolk sac and fetal liver stages of hematopoiesis. Single oral dose (100 mg kg(-1)) of ATRA was administered to rat on Gestation Day (GD) 10 and fetuses were observed on GD 18. The fetus's blood (from experimental group and control each, n = 24) were obtained directly from heart, as placental and mother circulation was continued and subsequently processed for Giemsa staining and followed by WBC counting and measuring. Statistical analysis was made by student t-test. A p-value <0.05 was considered significant. In the experimental embryos on GD 18, the mean number of WBC (29.2%), neutrophil, lymphocyte and monocyte were increased. There was a significant difference in WBC (p<0.0001) and neutrophil (p<0.001) between the groups in this regard. The mean diameter of neutrophil, lymphocyte and monocyte were compared in two groups. The results showed no significant change on experimental and control groups. We concluded that ATRA may have positive effects on proliferation, differentiation and maturation of neutrophil without having any significant effects on the diameter of cells throughout normal granulocyte differentiation in embryo during both late-yolk sac and fetal liver stages of hematopoiesis.

ROS-inhibitory activity of YopE is required for full virulence of Yersinia in mice

YopE, a type III secreted effector of Yersinia, is a GTPase Activating Protein for Rac1 and RhoA whose catalytic activity is critical for virulence. We found that YopE also inhibited reactive oxygen species (ROS) production and inactivated Rac2. How YopE distinguishes among its targets and which specific targets are critical for Yersinia survival in different tissues are unknown. A screen identifying YopE mutants in Yersinia pseudotuberculosis that interact with different Rho GTPases showed that YopE residues at positions 102, 106, 109 and 156 discern among switch I and II regions of Rac1, Rac2 and RhoA. Two mutants, which expressed YopE alleles with different antiphagocytic, ROS-inhibitory and cell-rounding activities, YptbL109A and YptbESptP, were studied in animal infections. Inhibition of both phagocytosis and ROS production were required for splenic colonization, whereas fewer YopE activities were required for Peyer's patch colonization. This study shows that Y. pseudotuberculosis encounters multiple host defences in different tissues and uses distinct YopE activities to disable them.

Transforming growth-interacting factor (TGIF) regulates proliferation and differentiation of human myeloid leukemia cells

Transforming growth-interacting factor (TGIF) is a homeobox transcriptional repressor that has been implicated in holoprosencephaly and various types of cancer. TGIF is expressed in hematopoietic stem cells and modulates TGF-beta and retinoic acid (RA) signaling, both of which play an important role in hematopoiesis. We recently reported that TGIF's levels correlate inversely with survival in patients with acute myelogenous leukemia. Here we present the first direct evidence of a role for TGIF in myelopoiesis. We used short hairpin RNA interference to define the effects of TGIF knockdown on proliferation and differentiation of myeloid leukemia-derived cell lines. Decreased TGIF expression resulted in reduced proliferation and differentiation and lower expression of CEBPbeta, CEBPepsilon, PU.1 and RUNX1, key myeloid transcription factors. Furthermore, TGF-beta signaling was increased and RA signaling was decreased. Further insights into the molecular basis of TGIF's effects were provided by a genome-wide chromatin immunoprecipitation-based elucidation of TGIF target genes. Together, these data suggest that TGIF has an important role myelopoiesis and may regulate the balance between proliferation and differentiation. Reduced TGIF expression could tip the balance toward quiescence thus providing progenitor as well as hematopoietic stem cells protection from anti-cycle agents.

The preferentially expressed antigen in melanoma (PRAME) inhibits myeloid differentiation in normal hematopoietic and leukemic progenitor cells

The preferentially expressed antigen in melanoma (PRAME) is expressed in several hematologic malignancies, but either is not expressed or is expressed at only low levels in normal hematopoietic cells, making it a target for cancer therapy. PRAME is a tumor-associated antigen and has been described as a corepressor of retinoic acid signaling in solid tumor cells, but its function in hematopoietic cells is unknown. PRAME mRNA expression increased with chronic myeloid leukemia (CML) disease progression and its detection in late chronic-phase CML patients before tyrosine kinase inhibitor therapy was associated with poorer therapeutic responses and ABL tyrosine kinase domain point mutations. In leukemia cell lines, PRAME protein expression inhibited granulocytic differentiation only in cell lines that differentiate along this lineage after all-trans retinoic acid (ATRA) exposure. Forced PRAME expression in normal hematopoietic progenitors, however, inhibited myeloid differentiation both in the presence and absence of ATRA, and this phenotype was reversed when PRAME was silenced in primary CML progenitors. These observations suggest that PRAME inhibits myeloid differentiation in certain myeloid leukemias, and that its function in these cells is lineage and phenotype dependent. Lastly, these observations suggest that PRAME is a target for both prognostic and therapeutic applications.

A myelopoiesis-associated regulatory intergenic noncoding RNA transcript within the human HOXA cluster

We have identified an intergenic transcriptional activity that is located between the human HOXA1 and HOXA2 genes, shows myeloid-specific expression, and is up-regulated during granulocytic differentiation. The novel gene, termed HOTAIRM1 (HOX antisense intergenic RNA myeloid 1), is transcribed antisense to the HOXA genes and originates from the same CpG island that embeds the start site of HOXA1. The transcript appears to be a noncoding RNA containing no long open-reading frame; sucrose gradient analysis shows no association with polyribosomal fractions. HOTAIRM1 is the most prominent intergenic transcript expressed and up-regulated during induced granulocytic differentiation of NB4 promyelocytic leukemia and normal human hematopoietic cells; its expression is specific to the myeloid lineage. Its induction during retinoic acid (RA)-driven granulocytic differentiation is through RA receptor and may depend on the expression of myeloid cell development factors targeted by RA signaling. Knockdown of HOTAIRM1 quantitatively blunted RA-induced expression of HOXA1 and HOXA4 during the myeloid differentiation of NB4 cells, and selectively attenuated induction of transcripts for the myeloid differentiation genes CD11b and CD18, but did not noticeably impact the more distal HOXA genes. These findings suggest that HOTAIRM1 plays a role in the myelopoiesis through modulation of gene expression in the HOXA cluster.

Drug-induced Sweet's syndrome

OBJECTIVE

To systematically review the pertinent literature on drug-induced Sweet's syndrome (SS).

DATA SOURCES

MEDLINE (1966-December 2006), International Pharmaceutical Abstracts (1970-December 2006), Science Citation Index (1945-December 2006), and EMBASE (1980-December 2006) were searched using the key terms Sweet's syndrome, drug-induced, and acute neutrophilic dermatitis.

STUDY SELECTION AND DATA EXTRACTION

All case reports of drug-induced SS located using the above databases were collected for causality assessment. In addition, relevant articles regarding the various causes and presentations of SS were selected to provide background information. Bibliographies of all relevant articles were reviewed for additional citations.

DATA SYNTHESIS

All case reports of drug-induced SS were evaluated against an expanded Naranjo scale with specific criteria for SS. Tables were developed listing key criteria for evaluating the case reports for causality. Data were evaluated by quantity and quality of evidence, and an assessment was made as to whether there was a feasible pharmacologic mechanism to explain causality.

CONCLUSIONS

Granulocyte colony-stimulating factor (G-CSF), all-trans retinoic acid (ATRA), and vaccines met 2 of 3 criteria for an association with SS. There are sufficient data and a plausible pharmacologic mechanism for G-CSF and ATRA. Vaccines meet the qualitative criteria and also have a plausible pharmacologic mechanism. The evidence regarding minocycline is of high quality; however, the quantity of evidence and a reasonable pharmacologic mechanism are lacking. A host of miscellaneous drugs have also been implicated in causing the disorder, all without sufficient evidence.

Heterochromatic gene repression of the retinoic acid pathway in acute myeloid leukemia

Alteration of lineage-specific transcriptional programs for hematopoiesis causes differentiation block and promotes leukemia development. Here, we show that AML1/ETO, the most common translocation fusion product in acute myeloid leukemia (AML), counteracts the activity of retinoic acid (RA), a transcriptional regulator of myelopoiesis. AML1/ETO participates in a protein complex with the RA receptor alpha (RARalpha) at RA regulatory regions on RARbeta2, which is a key RA target gene mediating RA activity/resistance in cells. At these sites, AML1/ETO recruits histone deacetylase, DNA methyltransferase, and DNA-methyl-CpG binding activities that promote a repressed chromatin conformation. The link among AML1/ETO, heterochromatic RARbeta2 repression, RA resistance, and myeloid differentiation block is indicated by the ability of either siRNA-AML1/ETO or the DNA methylation inhibitor 5-azacytidine to revert these epigenetic alterations and to restore RA differentiation response in AML1/ETO blasts. Finally, RARbeta2 is commonly silenced by hypermethylation in primary AML blasts but not in normal hematopoietic precursors, thus suggesting a role for the epigenetic repression of the RA signaling pathway in myeloid leukemogenesis.

Normal hematopoiesis after conditional targeting of RXRalpha in murine hematopoietic stem/progenitor cells

Because of the retinoic acid receptor-alpha (RARalpha) gene's involvement in acute promyelocytic leukemia, the important role of RARs in hematopoiesis is now well established. However, relatively few studies of hematopoiesis have focused on the role of the retinoid X receptors (RXRs), the obligate heterodimeric partners of the RARs. We sought to establish whether conditional targeting of RXRalpha in early hematopoietic progenitors, ideally to the level of the hematopoietic stem cell (HSC), would compromise hematopoiesis. For hematopoietic targeting of RXRalpha, we characterized IFN-inducible MxCre mice for use in studying the role of RXRalpha in hematopoiesis. We established that MxCre executes recombination of loxP-flanked RXRalpha in hematopoietic progenitors immunophenotypically enriched for HSC, leading to widespread and sustained targeting of RXRalpha in hematopoietic cells. However, we found no evidence of hematologic compromise in mice lacking RXRalpha, suggesting that RXRalpha is dispensable for normal murine hematopoiesis. Nonetheless, RXRalpha null bone marrow cells cultured in methylcellulose form colonies more efficiently than bone marrow cells obtained from control mice. This result suggests that although RXRalpha is not required for murine hematopoiesis, there may be hematopoietic signaling pathways that respond selectively to RXRalpha or settings in which combined expression of RXR (alpha, beta, and gamma) is limiting.

All-trans retinoic acid inhibits vascular endothelial growth factor expression in a cell model of neutrophil activation

Infiltrating neutrophil granulocytes are a particularly rich source of vascular endothelial growth factor (VEGF) in the endometrium and may contribute to the angiogenesis of endometriosis lesions. The objective of this study is to evaluate the expression and regulation of VEGF in endometrial neutrophils and in a model of neutrophil differentiation relevant to endometriosis. Immunohistochemistry was performed on endometriosis patient biopsies and cultured neutrophil-like HL-60 cells were assessed. The study was set in a reproductive biology division within an academic medical center. Endometrial biopsies were performed on women with endometriosis and HL-60 cells were treated with all-trans retinoic acid (atRA) and dimethyl sulfoxide in vitro. Immunofluorescence histochemistry, VEGF mRNA and protein quantification, and transfection studies of VEGF gene promoter-luciferase constructs were all main outcome measures. Immunofluorescence studies verified the presence of neutrophils in eutopic endometrium from women with endometriosis. Examination of the regulation of VEGF using differentiated HL-60 cells as a model, revealed that atRA induced a dose- and time-dependent suppression of VEGF mRNA and protein. Transient transfection, truncation, EMSA, and site-directed mutagenesis of human VEGF promoter-luciferase constructs in HL-60 cells indicated that atRA repressed VEGF gene transcription via a direct repeat 1 element located between -443 and -431 bp relative to the transcription initiation site. Because retinoic acid is synthesized de novo in endometrial cells under the influence of progesterone, our findings suggest that the up-regulated VEGF and angiogenesis in tissue from women with endometriosis may reflect failure of neutrophil differentiation in these cases, and provide a rationale for retinoid therapy in this condition.

Response to genistein: Assaying the activation status and chemotaxis efficacy of isolated neutrophils

Neutrophil (PMN) activation and chemotaxis toward inflammatory stimuli play critical roles in host defense and tissue inflammation. To determine the molecular mechanisms that regulate PMN function, many studies currently employ in vitro PMN activation and transmigration assays using freshly isolated peripheral PMN or PMN isolated from bone marrow. However, due to the highly sensitive nature of PMN, cell activation or priming can occur during isolation, which demands assay(s) that ensure the consistency of isolated PMN prior to using them in subsequent experiments. Here, we introduce a simple screening assay based on the observation that in transmigration assays, isolated PMN differentially respond to the tyrosine kinase inhibitor genistein and this is related to their activation status. As shown, we observed that isolated PMN for which early migration is enhanced by genistein have an overall high transmigration efficacy and that over 80% of applied PMN migrate across collagen-coated filters in a 2 h time period. Conversely, the inhibitory/non-enhancement effect of genistein is accompanied by a poor PMN transmigration, with less than 25% of applied PMN transmigrating across. Further analysis of PMN spontaneous adhesion, degranulation and cell surface CD11b/CD18 expression suggests that reduced migration of PMN is associated with PMN activation/priming that happens, in most cases, during the in vitro cell isolation procedure regardless of the blood donor. Thus, based on these observations, we developed a "genistein assay" to directly predict PMN status after each isolation. From our experience, this assay has not only revealed new insights into the mechanisms of PMN activation and assisted in functional assays, but it has also provided a method that can be mastered by both inexperienced and experienced researchers to assay isolated PMN and thus avoid using inconsistent cells (e.g. pre-activated PMN) in their experiments.

Retinoids and myelomonocytic growth factors cooperatively activate RARΑ and induce human myeloid leukemia cell differentiation via MAP kinase pathways

Use of all-trans-retinoic acid (ATRA) in combinatorial differentiation therapy of acute promyelocytic leukemia (APL) results in exceptional cure rates. However, potent cell differentiation effects of ATRA are so far largely restricted to this disease and long-term survival rates in non-APL acute myelogeneous leukemia (AML) remain unacceptably poor, requiring development of novel therapeutic strategies. We demonstrate here that myelomonocytic growth factors (granulocyte colony-stimulating factor [G-CSF] and/or granulocyte macrophage colony-stimulating factor [GM-CSF]) potentiate differentiation effects of ATRA in different AML cell lines and primary cells from patients with myeloid leukemia. The ligand-dependent activities of endogenous and transiently expressed retinoic acid receptor alpha (RARα) isoforms can be potentiated by G/GM-CSF in U-937 cells and correlate with increased expression of ATRA-inducible RARα2 isoform. Specific inhibitors of mitogen mitogen-activated protein kinase (MAPK) (MEK)-1/-2 or p38 extracellular signal-related kinase (ERK) kinase diminish the ATRA as well as ATRA and G/GM-CSF-induced activation of the RARα proteins and decreased the differentiation-induced decline in cell numbers. Our data demonstrate that acting, at least in part, via the MAP kinase pathways, myelomonocytic growth factors enhance ATRA-dependent activation of the RARα isoforms and maturation of myeloid leukemia cells. These results suggest that combinatorial use of these agents may be effective in differentiation therapy of AML. (Blood. 2005;105:341-349)

Retinoid-induced apoptosis in HL-60 cells is associated with nucleolin down-regulation and destabilization of Bcl-2 mRNA

All-trans retinoic acid (ATRA) induces differentiation of promyelocytic leukemia cells, but the mechanisms by which cellular differentiation leads to apoptosis are not well understood. Studies were done to address the question whether ATRA-induced apoptosis is a consequence of destabilization of bcl-2 mRNA and decreased cellular levels of the anti-apoptotic protein, bcl-2. ATRA induced differentiation of HL-60 cells along the granulocytic pathway within 48 h. The half-lives of bcl-2 mRNA in HL-60 cells incubated with ATRA for 48 or 72 h were reduced to 39 and 7% of the corresponding untreated control values, respectively. Cellular differentiation was accompanied by down-regulation of the cytoplasmic levels of nucleolin, a bcl-2 mRNA-stabilizing protein. Binding of a bcl-2 mRNA instability element (AU-rich element-1) to nucleolin in S100 extracts from ATRA-treated cells was decreased to 15% of control within 72 h. The decay of 5' capped, polyadenylated bcl-2 mRNA transcripts containing ARE-1 was more rapid in S100 extracts from ATRA-treated cells compared with untreated cells. However, when recombinant nucleolin was added to extracts of ATRA-treated cells, the rate of bcl-2 mRNA decay was similar to the rate in extracts of untreated cells. These results provide evidence that ATRA-induced apoptosis is a consequence of cellular differentiation, which leads to nucleolin down-regulation and bcl-2 mRNA instability.

Cytoskeletal influences on nuclear shape in granulocytic HL-60 cells

BACKGROUND

During granulopoiesis in the bone marrow, the nucleus differentiates from ovoid to lobulated shape. Addition of retinoic acid (RA) to leukemic HL-60 cells induces development of lobulated nuclei, furnishing a convenient model system for nuclear differentiation during granulopoiesis. Previous studies from our laboratory have implicated nuclear envelope composition as playing important roles in nuclear shape changes. Specifically noted were: 1) a paucity of lamins A/C and B1 in the undifferentiated and RA treated cell forms; 2) an elevation of lamin B receptor (LBR) during induced granulopoiesis.

RESULTS

The present study demonstrates that perturbation of cytoskeletal elements influences nuclear differentiation of HL-60 cells. Because of cytotoxicity from prolonged exposure to cytoskeleton-modifying drugs, most studies were performed with a Bcl-2 overexpressing HL-60 subline. We have found that: 1) nocodazole prevents RA induction of lobulation; 2) taxol induces lobulation and micronuclear formation, even in the absence of RA; 3) cytochalasin D does not inhibit RA induced nuclear lobulation, and prolonged exposure induces nuclear shape changes in the absence of RA.

CONCLUSIONS

The present results, in the context of earlier data and models, suggest a mechanism for granulocytic nuclear lobulation. Our current hypothesis is that the nuclear shape change involves factors that increase the flexibility of the nuclear envelope (reduced lamin content), augment connections to the underlying heterochromatin (increased levels of LBR) and promote distortions imposed by the cytoskeleton (microtubule motors creating tension in the nuclear envelope).

Divergent interactions of Ehrlichia chaffeensis- and Anaplasma phagocytophilum-infected leukocytes with endothelial cell barriers

Human anaplasmosis (formerly human granulocytic ehrlichiosis) and human monocytic ehrlichiosis (HME) are emerging tick-borne infections caused by obligate intracellular bacteria in the family Anaplasmataceae. Clinical findings include fever, headache, myalgia, leukopenia, thrombocytopenia, and hepatic inflammatory injury. Whereas Ehrlichia chaffeensis (HME) often causes meningoencephalitis, this is rare with Anaplasma phagocytophilum infection. The abilities of infected primary host monocytes and neutrophils and of infected HL-60 cells to cross human umbilical vein endothelial cell-derived EA.hy926 cell barriers and human brain microvascular cells (BMEC), a human blood-brain barrier model, were studied. Uninfected monocyte/macrophages crossed endothelial cell barriers six times more efficiently than neutrophils. More E. chaffeensis-infected monocytes transmigrated than uninfected monocytes, whereas A. phagocytophilum suppressed neutrophil transmigration. Differences were not due to barrier dysfunction, as transendothelial cell resistivities were the same for uninfected cell controls. Similar results were obtained for HL-60 cells used as hosts for E. chaffeensis and A. phagocytophilum. Differential transmigration of E. chaffeensis- and A. phagocytophilum-infected leukocytes and HL-60 cells confirmed a role for the pathogen in modifying cell migratory capacity. These results support the hypothesis that Anaplasmataceae intracellular infections lead to unique pathogen-specific host cell functional alterations that are likely important for pathogen survival, pathogenesis, and disease induction.

Exploring the functional complexity of cellular proteins by protein knockout

Comprehensive dissection of protein functions entails more complicated manipulations than simply eliminating the protein of interest. Established knockdown technologies, such as RNA interference, antisense oligodeoxynucleotides, or ribozymes, are limited for specific applications such as modulating protein levels or specific targeting of a posttranslationally modified subpopulation. Here we show that the engineered Skp1, Cullin 1, and F-box-containing betaTrCP substrate receptor ubiquitin-proteolytic system, designated protein knockout, could achieve not only total elimination but also rapid and systematic reduction of a given cellular protein. Stable expression of a single engineered betaTrCP demonstrated simultaneous and sustained degradation of the entire retinoblastoma family proteins. Furthermore, the engineered betaTrCP was capable of selecting hypo- but not hyperphosphorylated forms of retinoblastoma for degradation. The engineered betaTrCP has been extensively modified to increase its specificity in substrate selection. This optimized protein-knockout system offers a powerful and versatile proteomic tool to dissect diverse functional properties of cellular proteins in somatic cells.

3-Deazauridine triggers dose-dependent apoptosis in myeloid leukemia cells and enhances retinoic acid-induced granulocytic differentiation of HL-60 cells

Therapeutic nucleoside analogue 3-deazauridine (DU) exerts cytotoxic activity against cancer cells by disruption of DNA synthesis resulting in cell death. The present study evaluates whether DU alone at doses 2.5-15 microM or in combination with all trans retinoic acid (RA) or dibutyryl cAMP (dbcAMP) is effective against myelogenous leukemia. The data of this study indicate that DU induces dose-dependent cell death by apoptosis in myeloid leukemia cell lines HL-60, NB4, HEL and K562 as demonstrated by cell staining or flow cytometry and agarose gel electrophoresis. 24h-treatment with DU produced dose-dependent HL-60 cell growth inhibition and dose-independent S phase arrest that was not reversed upon removal of higher doses of DU (10-15 microM). Exposition to nontoxic dose of DU (2.5 microM) for 24h followed by RA or dbcAMP and 96 h-cotreatment with DU significantly enhanced RA- but not dbcAMP-mediated granulocytic differentiation. Cell maturation was paralleled with an increase in the proportion of cells in G1 or G2+M phase. We conclude that, depending on the dose or the sequence of administration with RA, an inhibitor of DNA replication, DU triggers a process of either differentiation or apoptosis in myeloid leukemia cells.

Molecular pathogenesis of acute promyelocytic leukaemia and APL variants

It has been 12 years since the simultaneous discovery of the unique sensitivity of acute promyelocytic leukaemia (APL) to differentiation therapy with all-trans retinoic acid (ATRA) and the discovery that the retinoic acid receptor alpha (RARalpha) gene was rearranged in APL. Nearly 98% of cases of APL are associated with t(15;17) chromosomal translocation and fusion of the PML gene to that encoding RARalpha to yield an abnormal receptor with the capability of de-regulating gene expression in the haematopoietic cell, causing differentiation block and eventually the development of leukaemia. Since this original discovery, four other translocations were described in APL. In each of these the RARalpha gene is fused to different partner genes, all yielding aberrant nuclear receptors. These fusion proteins share in common the ability to repress rather than activate retinoic acid targets, one so strongly that the result is an ATRA-resistant form of the disease. In addition each of the partner proteins is important for normal cell growth and development. In this chapter we explore the biology of the RARalpha, the fusion proteins created in APL and the normal forms of the partner proteins. Through continued study of this disease it is hoped that novel treatments, potentially more applicable to other forms of leukaemia, may arise.

Identification and genetic analysis of human and mouse activated Cdc42 interacting protein-4 isoforms

By yeast two-hybrid screening with the Src kinase Lyn as bait, we identified a novel gene product with features of a scaffolding protein. Reported as Felic ( es-related, with homology to Ezrin, Lyn interactor with Cdc42), it is related to the CIP4 (Cdc42 Interacting Protein-4) gene. Southern blotting for CIP4/Felic of genomic DNA shows a single band, suggesting no gene duplication. Felic differs from CIP4 because of a 29 nucleotide sequence derived from the end of intron 13. Consequently, there is an out-of-frame translation that destroys an SH3 domain. Analysis of various tissues shows that the original CIP4 is the predominant transcript. Therefore, we propose to call that, CIP4a and Felic, CIP4b. During screening of the colorectal CaCo2 cell line, clones corresponding to a third CIP4-related transcript (CIP4c) were identified. CIP4c encodes a premature stop codon, resulting in the loss of the SH3 domain. A fourth, relatively abundant transcript (CIP4h) was isolated from heart, lung, and trachea tissue. CIP4h retains the SH3 domain. CIP4 levels are modified by all-trans-retinoic acid. The presence of alternative splice transcripts, with or without SH3 domains, suggests that CIP4 regulates cytoskeletal organization through structural-functional differences in a tissue-specific manner.

Vitamin A, infection, and immune function

In populations where vitamin A availability from food is low, infectious diseases can precipitate vitamin A deficiency by decreasing intake, decreasing absorption, and increasing excretion. Infectious diseases that induce the acute-phase response also impair the assessment of vitamin A status by transiently depressing serum retinol concentrations. Vitamin A deficiency impairs innate immunity by impeding normal regeneration of mucosal barriers damaged by infection, and by diminishing the function of neutrophils, macrophages, and natural killer cells. Vitamin A is also required for adaptive immunity and plays a role in the development of T both-helper (Th) cells and B-cells. In particular, vitamin A deficiency diminishes antibody-mediated responses directed by Th2 cells, although some aspects of Th1-mediated immunity are also diminished. These changes in mucosal epithelial regeneration and immune function presumably account for the increased mortality seen in vitamin A-deficient infants, young children, and pregnant women in many areas of the world today.

Function of RARalpha during the maturation of neutrophils

The retinoic acid receptor alpha gene is the target of chromosomal rearrangements in all cases of acute promyelocytic leukemia (APL). This recurrent involvement of RARalpha in the pathogenesis of APL is likely to reflect an important role played by this receptor during the differentiation of immature myeloid cells to neutrophils. RARalpha is a negative regulator of promyelocyte differentiation when not complexed with RA, and stimulates this differentiation when bound to RA. Since RARs are dispensable for the generation of mature neutrophils, their role thus appears to be to modulatory, rather than obligatory, for the control of neutrophil differentiation. In vitro, retinoic acid is also a potent inducer of neutrophil cell fate, suggesting that it might play a role in the commitment of pluripotent hematopoietic progenitors to the neutrophil lineage. Thus, the APL translocations target an important regulator of myeloid cell differentiation.

Transcriptional regulation in acute promyelocytic leukemia

It has been 10 years since the seminal discovery that a mutant form of a retinoid acid receptor (RARalpha) is associated with acute promyelocytic leukemia (APL). This finding, coupled with the remarkable success of retinoic acid (RA), the natural ligand of RARalpha, in the treatment of APL, has made APL a unique model system in the study of oncogenic conversion of transcription factors in hematological malignancies. Indeed, subsequent basic and clinical studies showed that chromosomal translocation involving the RARalpha gene is the cytogenetic hallmark of APL and that these mutant forms of RARs are the oncogenes in APL that interfere with the proliferation and differentiation pathways controlled by both RAR and their fusion partners. However, it was not until recently that the role of aberrant transcriptional regulation in the pathogenesis of APL was revealed. In this review, we summarize the biochemical and biological mechanisms of transcriptional regulation by mutant RARs and their corresponding wild-type fusion partner PML and PLZF. These studies have been instrumental in our understanding of the process of leukemogenesis in general and have laid the scientific foundation for the novel concept of transcription therapy in the treatment of human cancer.

Genomic and proteomic analysis of the myeloid differentiation program

Although the mature neutrophil is one of the better characterized mammalian cell types, the mechanisms of myeloid differentiation are incompletely understood at the molecular level. A mouse promyelocytic cell line (MPRO), derived from murine bone marrow cells and arrested developmentally by a dominant-negative retinoic acid receptor, morphologically differentiates to mature neutrophils in the presence of 10 microM retinoic acid. An extensive catalog was prepared of the gene expression changes that occur during morphologic maturation. To do this, 3'-end differential display, oligonucleotide chip array hybridization, and 2-dimensional protein electrophoresis were used. A large number of genes whose mRNA levels are modulated during differentiation of MPRO cells were identified. The results suggest the involvement of several transcription regulatory factors not previously implicated in this process, but they also emphasize the importance of events other than the production of new transcription factors. Furthermore, gene expression patterns were compared at the level of mRNA and protein, and the correlation between 2 parameters was studied. (Blood. 2001;98:513-524)

Positive and negative regulation of granulopoiesis by endogenous RARalpha

Acute promyelocytic leukemia (APL) is always associated with chromosomal translocations that disrupt the retinoic acid receptor alpha (RARalpha) gene. Whether these translocations relate to a role for endogenous RARalpha in normal granulopoiesis remains uncertain because most studies addressing this question have used non-physiological overexpression systems. Granulocyte differentiation in cells derived from RARalpha-deficient (RARalpha(-/-)) mice was studied and evaluated in the context of agonist-bound and ligand-free RARalpha. Our results demonstrate that RARalpha is dispensable for granulopoiesis, as RARalpha(-/-) mice have a normal granulocyte population despite an impaired ability to respond to retinoids. However, although it is not absolutely required, RARalpha can bidirectionally modulate granulopoiesis. RARalpha stimulates differentiation in response to exogenous retinoic acid. Furthermore, endogenous retinoids control granulopoiesis in vivo, as either vitamin A-deficient mice or animals treated with an RAR antagonist accumulate more immature granulocytes in their bone marrow. Conversely, RARalpha acts to limit differentiation in the absence of ligand because granulocyte precursors from RARalpha(-/-) mice differentiate earlier in culture. Thus, the block in granulopoiesis exerted by RARalpha fusion proteins expressed in APL cells may correspond to an amplification of a normal function of unliganded RARalpha.

Transcription factors that regulate growth and differentiation of myeloid cells

Recently much progress has been made in our understanding of how myeloid progenitor cells undergo commitment and become mature granulocytes or monocytes/macrophages. Studies of normal and leukemic myeloid cells as well as those of cells derived from mice with targeted disruption showed that a series of transcription factors play a major role in both commitment and maturation of myeloid cells. This is primarily because these transcription factors direct an ordered pattern of gene expression according to a well-defined developmental program. PU.1, an Ets family member, is one of the master transcription factors identified to regulate development of both granulocytes and monocytes/macrophages. Further, C/EBPalpha and C/EBPvarepsilon of the bZip family have important roles in directing granulocytic maturation. A number of additional transcription factors such as AML1, RARalpha, MZF-1, Hox and STAT families of transcription factors, Egr-1 and c-myb etc are shown to play roles in myeloid cell differentiation. Our laboratory has recently obtained evidence that ICSBP, a member of the IRF family, is involved in lineage commitment during myeloid cell differentiation and stimulates maturation of functional macrophages. Future elucidation of pathways and networks through which these transcription factors act in various stages of development would provide a more definitive picture of myeloid cell commitment and maturation.

A functionally active RARalpha nuclear receptor is expressed in retinoic acid non responsive early myeloblastic cell lines

Although all-trans retinoic acid (ATRA) can restore the differentiation capacity of leukemic promyelocytes, early leukemic myeloblasts are conversely not responsive to ATRA induced granulocytic differentiation. To assess whether this resistance to ATRA is related to an impaired function of the Retinoic Acid Receptor alpha (RARalpha), we performed an analysis of RARalpha expression and transactivation activity, in several myeloid leukemic cell lines, representative of different types of spontaneous acute myeloid leukemias. Our results indicate that a functionally active RARalpha nuclear receptor is expressed in all the analyzed cell lines, regardless of their differentiation capacity following exposure to ATRA. The observation that ATRA treatment is able to induce the expression of retinoic acid target genes, in late- but not in early-myeloblastic leukemic cells, raises the possibility that the differentiation block of these cells is achieved through a chromatin mediated mechanism. Acetylation is apparently not involved in this process, since the histone deacetylase inhibitor trichostatin A, is not able to restore the differentiation capacity of early leukemic myeloblasts. Further investigation is needed to clarify whether myeloid transcription factors, distinct to RARalpha, play a role in the resistance of these cells to ATRA treatment.

Retinoic acid receptor alpha (RAralpha) Mutations in Human Leukemia

The retinoic acid receptor alpha (RARalpha) plays a central role in the biology of the myeloid cellular compartment. Chromosomal translocations involving the RARalpha locus probably represent the malignant initiating events in acute promyelocytic leukemia (APL). Recent studies that identify novel interactions between RARalpha and the nuclear receptor co-activators and co-repressors, new functions of the oncogenic RARalpha fusion proteins and their catabolism in retinoic acid-induced differentiation, and the availability of new transgenic mice models have provided important insights into our understanding of the mechanisms by which mutant forms of RARalpha can be implicated in the development of leukemia. Novel alterations of the RARalpha gene identified in hematopoietic malignant disorders other than APL, such as myelodysplastic syndromes, non-APL acute myeloid leukemias and B-chronic lymphocytic leukemias, suggest that disruption of the RARalpha gene might predispose to myeloid and lymphoid disorders.

Regulation of cathelicidin gene expression: induction by lipopolysaccharide, interleukin-6, retinoic acid, and Salmonella enterica serovar typhimurium infection

Cathelicidins are a family of antimicrobial peptides prominent in the host defense mechanisms of several mammalian species. In addition to their antimicrobial activities, these peptides have been implicated in wound healing, angiogenesis, and other innate immune mechanisms. To investigate the regulatory mechanisms of cathelicidin gene expression, we conducted in vitro experiments evaluating the bone marrow cell expression of two porcine cathelicidins, PR-39 and protegrin, and cloned and evaluated the promoter sequence of PR-39. In addition, we evaluated in vivo kinetics of cathelicidin gene expression in pigs during an infection with Salmonella enterica serovar Typhimurium. Lipopolysaccharide (LPS) increased PR-39 and protegrin mRNA expression, which was ameliorated by polymyxin B. Concentrations of PR-39 in supernatants from bone marrow cell cultures were increased 10-fold after LPS stimulation. Similarly, interleukin-6 (IL-6) and all-trans retinoic acid (RA) markedly induced cathelicidin gene expression. To verify the transcriptional activation of the PR-39 gene by these agents, we made a PR-39 promoter-luciferase construct containing the full-length PR-39 promoter driving luciferase gene expression and transiently transfected PK-15 epithelial cells. RA and IL-6 increased luciferase activity in PK-15 cells transfected with the PR-39 promoter-luciferase reporter. Similarly, Salmonella-challenged pigs showed increased expression of PR-39 and protegrin mRNA in bone marrow cells at 6 and 24 h postchallenge. Taken together, these findings show that bacterial products (LPS), IL-6, RA, and Salmonella infection enhance the expression of the cathelicidins, PR-39 and protegrin, in bone marrow progenitor cells, and we suggest that extrinsic modulation of this innate host defense mechanism may be possible.