Regulation of IRF and STAT gene expression by retinoic acid

RIG-I regulates myeloid differentiation by promoting TRIM25-mediated ISGylation

Retinoic acid-inducible gene I (RIG-I) is up-regulated during granulocytic differentiation of acute promyelocytic leukemia (APL) cells induced by all-trans retinoic acid (ATRA). It has been reported that RIG-I recognizes virus-specific 5'-ppp-double-stranded RNA (dsRNA) and activates the type I interferons signaling pathways in innate immunity. However, the functions of RIG-I in hematopoiesis remain unclear, especially regarding its possible interaction with endogenous RNAs and the associated pathways that could contribute to the cellular differentiation and maturation. Herein, we identified a number of RIG-I-binding endogenous RNAs in APL cells following ATRA treatment, including the tripartite motif-containing protein 25 (TRIM25) messenger RNA (mRNA). TRIM25 encodes the protein known as an E3 ligase for ubiquitin/interferon (IFN)-induced 15-kDa protein (ISG15) that is involved in RIG-I-mediated antiviral signaling. We show that RIG-I could bind TRIM25 mRNA via its helicase domain and C-terminal regulatory domain, enhancing the stability of TRIM25 transcripts. RIG-I could increase the transcriptional expression of TRIM25 by caspase recruitment domain (CARD) domain through an IFN-stimulated response element. In addition, RIG-I activated other key genes in the ISGylation pathway by activating signal transducer and activator of transcription 1 (STAT1), including the modifier ISG15 and several enzymes responsible for the conjugation of ISG15 to protein substrates. RIG-I cooperated with STAT1/2 and interferon regulatory factor 1 (IRF1) to promote the activation of the ISGylation pathway. The integrity of ISGylation in ATRA or RIG-I-induced cell differentiation was essential given that knockdown of TRIM25 or ISG15 resulted in significant inhibition of this process. Our results provide insight into the role of the RIG-I-TRIM25-ISGylation axis in myeloid differentiation.

Understanding the Action of RARγ Agonists on Human Osteochondroma Explants

Osteochondromas are cartilage-capped growths located proximate to the physis that can cause skeletal deformities, pain, limited motion, and neurovascular impingement. Previous studies have demonstrated retinoic acid receptor gamma (RARγ) agonists to inhibit ectopic endochondral ossification, therefore we hypothesize that RARγ agonists can target on established osteochondromas. The purpose of this study was to examine the action of RARγ agonist in human osteochondromas. Osteochondroma specimens were obtained during surgery, subjected to explant culture and were treated with RARγ agonists or vehicles. Gene expression analysis confirmed the up-regulation of RARγ target genes in the explants treated with NRX 204647 and Palovarotene and revealed strong inhibition of cartilage matrix and increased extracellular matrix proteases gene expression. In addition, immunohistochemical staining for the neoepitope of protease-cleaved aggrecan indicated that RARγ agonist treatment stimulated cartilage matrix degradation. Interestingly, cell survival studies demonstrated that RARγ agonist treatment stimulated cell death. Moreover, RNA sequencing analysis indicates changes in multiple molecular pathways due to RARγ agonists treatment, showing similarly to human growth plate chondrocytes. Together, these findings suggest that RARγ agonist may exert anti-tumor function on osteochondromas by inhibiting matrix synthesis, promoting cartilage matrix degradation and stimulating cell death.

Regulation of Hepatitis C Virus Infection by Cellular Retinoic Acid Binding Proteins through the Modulation of Lipid Droplet Abundance

Retinoid (vitamin A) is an essential diet constituent that governs a broad range of biological processes. Its biologically active metabolite, all-trans retinoic acid (ATRA), exhibits a potent antiviral property by enhancing both innate and adaptive antiviral immunity against a variety of viral pathogens, such as, but not limited to, HIV, respiratory syncytial virus (RSV), herpes simplex virus (HSV), and measles. Even though the hepatocyte is highly enriched with retinoid and its metabolite ATRA, it supports the establishment of efficient hepatitis C virus (HCV) replication. Here, we demonstrate the hepatocyte-specific cell-intrinsic mechanism by which ATRA exerts either a proviral or antiviral effect, depending on how it engages cellular retinoic acid binding proteins (CRABPs). We found that the engagement of CRABP1 by ATRA potently supported viral infection by promoting the accumulation of lipid droplets (LDs), which robustly enhanced the formation of a replication complex on the LD-associated endoplasmic reticulum (ER) membrane. In contrast, ATRA binding to CRABP2 potently inhibited HCV via suppression of LD accumulation. However, this antiviral effect of CRABP2 was abrogated due to the functional and quantitative predominance of CRABP1 in the hepatocytes. In summary, our study demonstrates that CRABPs serve as an on-off switch that modulates the efficiency of the HCV life cycle and elucidates how HCV evades the antiviral properties of ATRA via the exploitation of CRABP1 functionality.IMPORTANCE ATRA, a biologically active metabolite of vitamin A, exerts pleiotropic biological effects, including the activation of both innate and adaptive immunity, thereby serving as a potent antimicrobial compound against numerous viral pathogens. Despite the enrichment of hepatocytes with vitamin A, HCV still establishes an efficient viral life cycle. Here, we discovered that the hepatocellular response to ATRA creates either a proviral or an antiviral environment depending on its engagement with CRABP1 or -2, respectively. CRABP1 supports the robust replication of HCV, while CRABP2 potently inhibits the efficiency of viral replication. Our biochemical, genetic, and microscopic analyses reveal that the pro- and antiviral effects of CRABPs are mediated by modulation of LD abundance, where HCV establishes the platform for viral replication and assembly on the LD-associated ER membrane. This study uncovered a cell-intrinsic mechanism by which HCV exploits the proviral function of CRABP1 to establish an efficient viral life cycle.

Induction of cellular and molecular immunomodulatory pathways by vitamin A and flavonoids

INTRODUCTION

A detailed study of reports on the immunomodulatory properties of vitamin A and select flavonoids may pave the way for using these natural compounds or compounds with similar structures in novel drug and vaccine designs against infectious and autoimmune diseases and cancers.

AREAS COVERED

Intracellular transduction pathways, cellular differentiation and functional immunomodulatory responses have been reviewed. The reported studies encompass in vitro, in vivo preclinical and clinical studies that address the role of vitamin A and select flavonoids in induction of innate and adaptive B- and T-cell responses, including TH1, TH2 and regulatory T cells (Treg).

EXPERT OPINION

While the immunomodulatory role of vitamin A, and related compounds, is well-established in many preclinical studies, its role in humans has begun to gain wider acceptance. In contrast, the role of flavonoids is mostly controversial in clinical trials, due to the diversity of the various classes of these compounds, and possibly due to the purity and the selected doses of the compounds. However, current preclinical and clinical studies warrant further detailed studies of these promising immunomodulatory compounds.

Mechanism of SB431542 in inhibiting mouse embryonic stem cell differentiation

SB431542 (SB) is an established small molecular inhibitor that specifically binds to the ATP binding domains of the activin receptor-like kinase receptors, ALK5, ALK4 and ALK7, and thus specifically inhibits Smad2/3 activation and blocks TGF-β signal transduction. SB maintains the undifferentiated state of mouse embryonic stem cells. However, the way of SB in maintaining the undifferentiated state of mouse embryonic stem cells remains unclear. Considering that SB could not maintain embryonic stem cells pluripotency when leukemia inhibitory factor was withdrawn, we sought to identify the mechanism of SB on pluripotent maintenance. Transcripts regulated by SB, including message RNAs and small non-coding RNAs were examined through microarray and deep-sequence experiments. After examination, Western blot analysis, and quantitative real-time PCR verification, we found that SB regulated the transcript expressions related to self-renewal and differentiation. SB mainly functioned by inhibiting differentiation. The key pluripotent factors expression were not significantly affected by SB, and intrinsic differentiation-related transcripts including fibroblast growth factor family members, were significantly down-regulated by SB. Moreover, SB could partially inhibit the retinoic acid response to neuronal differentiation of mouse embryonic stem cells.

Interferon regulatory factor-1 binds c-Cbl, enhances mitogen activated protein kinase signaling and promotes retinoic acid-induced differentiation of HL-60 human myelo-monoblastic leukemia cells

All-trans retinoic acid (RA) and interferons (IFNs) have efficacy in treating certain leukemias and lymphomas, respectively, motivating interest in their mechanism of action to improve therapy. Both RA and IFNs induce interferon regulatory factor-1 (IRF-1). We find that in HL-60 myeloblastic leukemia cells which undergo mitogen activated protien kinase (MAPK)-dependent myeloid differentiation in response to RA, IRF-1 propels differentiation. RA induces MAPK-dependent expression of IRF-1. IRF-1 binds c-Cbl, a MAPK related adaptor. Ectopic IRF-1 expression causes CD38 expression and activation of the Raf/MEK/ERK axis, and enhances RA-induced differentiation by augmenting CD38, CD11b, respiratory burst and G0 arrest. Ectopic IRF-1 expression also decreases the activity of aldehyde dehydrogenase 1, a stem cell marker, and enhances RA-induced ALDH1 down-regulation. Interestingly, expression of aryl hydrocarbon receptor (AhR), which is RA-induced and known to down-regulate Oct4 and drive RA-induced differentiation, also enhances IRF-1 expression. The data are consistent with a model whereby IRF-1 acts downstream of RA and AhR to enhance Raf/MEK/ERK activation and propel differentiation.

Antiproliferative effect of 13-cis-retinoic acid is associated with granulocyte differentiation and decrease in cyclin B1 and Bcl-2 protein levels in G0/G1 arrested HL-60 cells

Retinoic acid (RA), similar to specific growth factors, can induce differentiation of proliferating promyelocytic precursors into terminally differentiated granulocytes, although little is known about effects of its 13-cis isomer on promyelocytic leukemia (PML). In this study we demonstrate that 13-cis-RA has a dose and time-dependent antiproliferative effect on HL-60 PML cell line, that it induces cell accumulation in resting G0/G1 phase of the cell cycle followed by an increase in CD11b granulocyte differentiation antigen expression. The obtained increase in the percentage of HL-60 cells in G0/G1 phase and complementary decrease in S phase of the cell cycle are accompanied by a decrease in the expression of cell cycle regulatory molecule cyclin B1. We also show the induction of interferon regulatory factor-1 (IRF-1) transcription that can, also, to some extent contribute to the antiproliferative effect of 13-cis-RA. Furthermore, down-regulation of Bcl-2 protein expression in 13-cis-RA treated HL-60 cells may contribute to sensitivity to apoptosis of growth arrested HL-60 promyelocytic cells.

Cytodifferentiation by retinoids, a novel therapeutic option in oncology: rational combinations with other therapeutic agents

Retinoic acid (RA) and derivatives are promising antineoplastic agents endowed with both therapeutic and chemopreventive potential. Although the treatment of acute promyelocytic leukemia with all-trans retinoic acid is an outstanding example, the full potential of retinoids in oncology has not yet been explored and a more generalized use of these compounds is not yet a reality. One way to enhance the therapeutic and chemopreventive activity of RA and derivatives is to identify rational combinations between these compounds and other pharmacological agents. This is now possible given the information available on the biochemical and molecular mechanisms underlying the biological activity of retinoids. At the cellular level, the antileukemia and anticancer activity of retinoids is the result of three main actions, cytodifferentiation, growth inhibition, and apoptosis. Cytodifferentiation is a particularly attractive modality of treatment and differentiating agents promise to be less toxic and more specific than conventional chemotherapy. This is the result of the fact that cytotoxicity is not the primary aim of differentiation therapy. At the molecular level, retinoids act through the activation of nuclear retinoic acid receptor-dependent and -independent pathways. The cellular pathways and molecular networks relevant for retinoid activity are modulated by a panoply of other intracellular and extracellular pathways that may be targeted by known drugs and other experimental therapeutics. This chapter aims to summarize and critically discuss the available knowledge in the field.

Direct and indirect effects of retinoic acid on human Th2 cytokine and chemokine expression by human T lymphocytes

BACKGROUND

Vitamin A (VA) deficiency induces a type 1 cytokine response and exogenously provided retinoids can induce a type 2 cytokine response both in vitro and in vivo. The precise mechanism(s) involved in this phenotypic switch are inconsistent and have been poorly characterized in humans. In an effort to determine if retinoids are capable of inducing Th2 cytokine responses in human T cell cultures, we stimulated human PBMCs with immobilized anti-CD3 mAb in the presence or absence of all-trans retinoic acid (ATRA) or 9-cis-RA.

RESULTS

Stimulation of human PBMCs and purified T cells with ATRA and 9-cis-RA increased mRNA and protein levels of IL-4, IL-5, and IL-13 and decreased levels of IFN-gamma, IL-2, IL-12p70 and TNF-alpha upon activation with anti-CD3 and/or anti-CD28 mAbs. These effects were dose-dependent and evident as early as 12 hr post stimulation. Real time RT-PCR analysis revealed a dampened expression of the Th1-associated gene, T-bet, and a time-dependent increase in the mRNA for the Th2-associated genes, GATA-3, c-MAF and STAT6, upon treatment with ATRA. Besides Th1 and Th2 cytokines, a number of additional proinflammatory and regulatory cytokines including several chemokines were also differentially regulated by ATRA treatment.

CONCLUSION

These data provide strong evidence for multiple inductive roles for retinoids in the development of human type-2 cytokine responses.

Novel tumor antigens elicit anti-tumor humoral immune reactions in a subset of patients with polycythemia vera

We attempted to determine whether the immune reactions elicited by aberrantly expressed testis antigens contribute to the beneficial responses to interferon (IFN)-alpha therapy and other therapies in patients with polycythemia vera (PV). We screened a human testis cDNA library using SEREX (serological analysis of tumor antigens by screening an expression cDNA library with sera from three patients with PV who had undergone IFN-alpha-induced or other therapeutics-induced remission). We identified two novel PV associated tumor antigens, PV65 (eIF-2alpha) and PV13 (protamine 2). These 2 antigens elicited IgG antibody reactions in a subset of PV patients but not in healthy donors, suggesting that they are authentic tumor antigens. Increased phosphorylation of PV65 in response to stimulation of IFN-alpha, and upregulation of PV13 in tumor cells might enhance their abilities in elicitation of immune reactions in patients. These findings provide new insights into the mechanism underlying the regulation of the self-antigen repertoire in eliciting anti-tumor immune reactions in patients with polycythemia vera, and suggest their potential as the targets of novel immunotherapy.

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.

Differential regulation of tumor necrosis factor-alpha-converting enzyme and angiotensin-converting enzyme by type I and II interferons in human normal and leukemic myeloid cells

The transmembrane metalloproteases angiotensin-converting enzyme (ACE) and tumor necrosis factor-alpha (TNF-alpha)-converting enzyme (TACE/ADAM-17) have been associated with inflammation, cancer progression and angiogenesis. Few investigations into the regulation of these enzymes by physiological stimuli have been reported. In this study, we investigated the influence of interferons (IFNs) type I (alpha, beta) and II (gamma) on ACE and TACE expression of human leukemic NB4 cells and monocytes. We assessed the expression of proteases by reverse transcriptase-polymerase chain reaction, enzyme-linked immunosorbent assay and immunofluorescence analyses. IFNgamma, but not type I IFNs, upregulated membrane ACE in a dose- and time-dependency and this was reflected by the increase of ACE enzymatic activity and ACE mRNA. ACE upregulation was dependent on protein synthesis. Treatment of the interferon responsive factor 1 (IRF1)-unresponsive HepG2 cell line with IFNgamma did not affect ACE expression, thus suggesting the participation of the IRF1 signaling pathway in IFNgamma-mediated ACE upregulation in myeloid cells. In contrast, both types of IFNs, in a dose- and time-dependent manner, downregulated surface TACE without affecting TACE transcript. Soluble TACE was not detected in the medium of IFN-treated cells. IFNgamma-mediated decrease of surface TACE in NB4 cells was reversible, and correlated with an increase in intracellular TACE, suggesting that cell surface TACE was internalized in response to IFNs. These findings, showing the presence of IFN-dependent controlled mechanisms by which ACE and TACE levels are regulated in human normal and leukemic myeloid cells, may have implications in the context of current investigations on the therapeutic potential of IFNs.

All-trans retinoic acid induces XAF1 expression through an interferon regulatory factor-1 element in colon cancer

BACKGROUND & AIMS

X-linked inhibitor of apoptosis protein (XIAP)-associated factor 1 (XAF1) is a novel tumor suppressor and interferon (IFN)-stimulated gene. All-trans retinoic acid (ATRA) exerts an antiproliferative effect on tumor cells through up-regulation of IFN regulatory factor 1 (IRF-1) and the downstream IFN-stimulated genes. The aim of this study was to determine the effect and mechanism of ATRA on XAF1 expression and the role of XAF1 in ATRA-induced growth inhibition in colon cancer.

METHODS

Gene expression is detected by reverse-transcription polymerase chain reaction and immunoblotting. The transcription activity of XAF1 promoter is examined by luciferase reporter assay. The activity of IFN regulatory factor binding element (IRF-E) is assessed by electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Cell growth is evaluated by both in vitro and in vivo in nude mice xenografts.

RESULTS

IFN-alfa stimulates XAF1 promoter activity in the colon cancer cells Lovo and SW1116 dose-dependently. An IRF-1 binding element (IRF-E-XAF1) is found in the -30 to -38 nucleotide region upstream of the ATG initiator codon of the XAF1 gene. Site-directed mutagenesis of IRF-E-XAF1 abrogates native and IFN-induced promoter activity and binding capacity. ATRA induces XAF1 expression both in vitro and in vivo through interaction with IRF-E-XAF1. Overexpression of XAF1 increases cell susceptibility to ATRA-induced growth suppression both in vitro and in vivo. Furthermore, the effect of ATRA on XAF1 expression is independent of the promoter methylation and the subcellular distribution of XIAP.

CONCLUSIONS

XAF1 participates in ATRA-induced growth suppression through IRF-1-mediated transcriptional regulation.

New therapeutic target for CNS injury? The role of retinoic acid signaling after nerve lesions

Experiments with sciatic nerve lesions and spinal cord contusion injury demonstrate that the retinoic acid (RA) signaling cascade is activated by these traumatic events. In both cases the RA-synthesizing enzyme is RALDH-2. In the PNS, lesions cause RA-induced gene transcription, intracellular translocation of retinoid receptors, and increased transcription of CRBP-I, CRABP-II, and retinoid receptors. The activation of RARbeta appears to be responsible for neurotrophic and neuritogenic effects of RA on dorsal root ganglia and embryonic spinal cord. While the physiological role of RA in the injured nervous system is still under investigation three domains of functions are suggested: (1) neuroprotection and support of axonal growth, (2) modulation of the inflammatory reaction by microglia/macrophages, and (3) regulation of glial differentiation. Few studies have been performed to support nerve regeneration with RA signals in vivo, but a large number of experiments with neuronal and glial cell cultures and spinal cord explants point to beneficial effects of RA, so that future therapeutic approaches will likely focus on the activation of RA signaling.

N-Ras–Induced Growth Suppression of Myeloid Cells Is Mediated by IRF-1

Activating mutations in ras oncogenes occur at high frequency in human malignancies and expression of activated ras in immortalized cells lines is generally transforming. However, somewhat paradoxically, ectopic expression of ras in some myeloid cell lines has been shown to induce growth suppression associated with up-regulation of the cyclin-dependent kinase inhibitor p21CIP1/WAF1 in a p16INK4a, p15INK4b, and p53 independent fashion. We have used cDNA array technology to compare the expression profile induced by activated N-ras (N-rasG13R) in growth-suppressed myeloid cells with that induced in myeloid cells, which are transformed by N-rasG13R. The expression profile induced in growth suppressed cells was consistent with differentiation and included the up-regulation of the transcription factor IFN regulatory factor-1 (IRF-1), a known transcriptional activator of p21CIP/WAF1 expression and a target of oncogenic mutations associated with myeloid leukemia. Antisense suppression of IRF-1 prevented N-rasG13R–associated growth arrest and up-regulation of p21CIP1/WAF1. These results define a novel tumor suppressive response to oncogenic signaling and provide a mechanistic link between growth suppression and differentiation in myeloid cells.

The imidazoquinolines and their place in the therapy of cutaneous disease

The imidazoquinolines arose from efforts to develop a nucleoside analogue. Although molecularly similar to nucleosides, the imidazoquinolines did not have nucleoside-like activity. However, the imidazoquinolines induced immune modulatory cytokines, in part, because of their ability to activate toll receptors (TLR)s. Imiquimod, the first FDA-approved imidazoquinoline, has been marketed as a 5% cream, which is approved for the therapy of genital warts. The advantage of imiquimod therapy over other therapies for genital warts is the decrease in recurrence rate with the establishment of an adaptive immunological response or immunological memory/surveillance response. As tumours and viral infections are handled similarly by the immune system, there has been great interest in the use of topical imiquimod for the treatment of cutaneous neoplasms, particularly non-melanoma skin cancers. Future efforts in imidazoquinoline research is focused around the development of analogues with modifications in the immunological profiles, potency and penetration parameters that better focus these new analogues for the therapy of specific intracellular infections and neoplasms, as well as the development of imidazoquinolines for conditions related either directly or indirectly to patterns of immune dysregulation.

Signal transducer and activator of transcription proteins in leukemias

Signal transducer and activator of transcription (STAT) proteins are a 7-member family of cytoplasmic transcription factors that contribute to signal transduction by cytokines, hormones, and growth factors. STAT proteins control fundamental cellular processes, including survival, proliferation, and differentiation. Given the critical roles of STAT proteins, it was hypothesized that inappropriate or aberrant activation of STATs might contribute to cellular transformation and, in particular, leukemogenesis. Constitutive activation of mutated STAT3 has in fact been demonstrated to result in transformation. STAT activation has been extensively studied in leukemias, and mechanisms of STAT activation and the potential role of STAT signaling in leukemogenesis are the focus of this review. A better understanding of mechanisms of dysregulation of STAT signaling pathways may serve as a basis for designing novel therapeutic strategies that target these pathways in leukemia cells.

Molluscum contagiosum: recent advances in pathogenic mechanisms, and new therapies

Two poxviruses, Molluscum contagiosum virus (MCV) and Variola virus are specific to humans. MCV is present worldwide and is directly passed by direct skin to skin contact to produce cutaneous and, rarely, mucosal lesions. It occurs predominantly in preadolescent children, sexually active adults, participants in sports with skin to skin contact, and in individuals with impaired cellular immunity. MCV characteristically proliferates within the follicular epithelium, and with routine fixation produces an area of retraction artifact separating layers 1 to 3 of CD34+ stromal cells that immediately surround the follicle from the surrounding dermis. This feature may be obscured when the lesions are inflamed, usually after rupture into the surrounding dermis. MCV is a cytoplasmically replicating virus. MCV-infected cells grow in size, while internal organelles are dislocated and eventually obliterated by a large intracytoplasmic inclusion. Rupture and discharge of the virus-packed cells occurs in a process similar to membrane debris and MCV accumulate in the crater-like ostium; MCV infection is spread by contact with infectious debris. In HIV-1-positive patients the histologic features, as well as the clinical features, may be atypical in patients with MCV infections. Not only are the lesions often large, but they may be verrucous and markedly hyperkeratotic. Recent sequencing of the MCV genome has increased our understanding and investigations into its mechanisms for avoiding host defense mechanisms. These include regions which encode for homologues of cellular chemokines and chemokine-binding proteins, a homolog of MHC1 and a viral FLICE-like inhibitory protein. Treatment, until recently, has depended upon tissue destruction including curettage, cryotherapy, CO(2) laser, electrodesiccation, trichloracetic acid and cantharadin. Recently, topical immune modulators have been used with some success. Understanding of the MCV genome is providing the basis for the development of drugs for therapy and prevention of MCV infections.

Signaling revisited in acute promyelocytic leukemia

Although transcription factors are still the main focus to understanding leukemogenesis, recent results strongly suggest that alteration of a receptor and/or subsequent signaling plays a critical and co-operative role in the pathogenesis of acute myeloid leukemia (AML). The t(15;17) translocation, found in 95% of APL, encodes a PML-RARalpha fusion protein. A main model proposed for acute promyelocytic leukemia (APL) is that PML-RARalpha exerts its oncogenic effects by repressing retinoic acid-inducible genes critical to myeloid differentiation. Dysregulation of these genes may result in abnormal signaling, thereby freeing pre-leukemic cells from controls which normally induce the onset of differentiation. It is also likely that treatment of APL cells by retinoic acid induces de novo up-regulation of the same genes which are dominantly repressed by PML-RARalpha and whose expression is required for reactivation of the differentiation program. Identification of such genes together with the signaling pathways interrupted at the early stages of leukemia transformation and reactivated during retinoic acid-induced differentiation in APL cells will contribute to the development of new molecular targets for treatment of leukemia.

IRF regulation of HIV-1 long terminal repeat activity

Interferon (IFN) regulatory factors (IRF) constitute a family of transcriptional activators and repressors implicated in multiple biologic processes, including regulation of immune responses and host defense, cytokine signalling, cell growth regulation, and hematopoietic development. All members are characterized by well-conserved DNA binding domains at the N-terminal region that recognize similar DNA sequences termed IRF-binding element/IFN-stimulated response element (IRF-E/ISRE) present on the promoter of the IFN-alpha/beta genes and of some IFN-stimulated genes (ISG). Recently, a sequence homologous to the ISRE has been identified downstream of the 5' human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR). This sequence is a binding site for IRF-1 and IRF-2. Deletion of the LTR-ISRE results in impaired LTR promoter activity and decreased synthesis of viral RNA and proteins. Here, we briefly summarize characteristics of IRF-1 and IRF-2 binding to the HIV-1 LTR-ISRE and the data obtained to date on the functionality of this cis-element and on the role of IRF in the regulation of HIV-1 LTR transcriptional activity.

Ectopic expression of interferon regulatory factor-1 potentiates granulocytic differentiation

Numerous transcription factors allow haematopoietic cells to respond to lineage- and stage-specific cytokines and to act as their effectors. It is increasingly evident that the interferon regulatory factor-1 (IRF-1) transcription factor can selectively regulate different sets of genes depending on the cell type and/or the nature of cellular stimuli, evoking distinct responses in each. In the present study, we investigated mechanisms underlying the differentiation-inducing properties of granulocytic colony-stimulating factor (G-CSF) and whether IRF transcription factors are functionally relevant in myeloid differentiation. Both normal human progenitors and murine 32Dcl3 myeloblasts induced to differentiate along the granulocytic pathway showed an up-regulation of IRF-1 expression. Ectopic expression of IRF-1 did not abrogate the growth factor requirement of 32Dcl3 cells, although a small percentage of cells that survived cytokine deprivation differentiated fully to neutrophils. Moreover, in the presence of G-CSF, granulocytic differentiation of IRF-1-expressing cells was accelerated, as assessed by morphology and expression of specific differentiation markers. Down-modulation of c-Myb protein and direct stimulation of lysozyme promoter activity by IRF-1 were also observed. Conversely, constitutive expression of IRF-2, a repressor of IRF-1 transcriptional activity, completely abrogated the G-CSF-induced neutrophilic maturation. We conclude that IRF-1 exerts a pivotal role in granulocytic differentiation and that its induction by G-CSF represents a limiting step in the early events of differentiation.

Quantitation of interferon regulatory factor transcripts in patients with acute myeloid leukemia

Interferon regulatory factors IRF-1 and IRF-2, the two mutually antagonistic factors, fluctuate during the cell cycle and play an important role in normal and neoplastic growth processes. The relative levels of these two transcripts were analyzed in 5 normal and 43 acute myeloid leukemia (AML) bone marrow (BM) specimens by a semiquantitative RT-PCR method. IRF-1 and IRF-2 cDNA sequences were coamplified using primers that were designed to span regions of high homology between the genes. Each primer can anneal equally to both IRF-1 and IRF-2 sequences. Hence, the relative amount of amplified products from each cDNA species provides an estimation of proportional concentration of the RNA transcripts in the test sample. Results indicate expression of both the transcripts on all the leukemia and lymphoma cell lines tested, normal and AML BM. Significantly higher IRF-1:IRF-2 ratio was observed in normal as compared to AML BM (p = 0.007). There was no correlation with clinical factors such as FAB subtype. A single dose of amifostine or three daily doses of recombinant IL-4 were administered to 5 and 8 AML patients, respectively. The changes in the expression of these transcripts were studied prior to administration of the agent (d0) and after 3 days (d3). IL-4 treatment showed significant increase in the IRF-1:IRF-2 ratio in 4 of 8 patients (p = 0.05); amifostine treatment did not show any appreciable change.

Synergistic transcriptional activation of human Acyl-coenzyme A: cholesterol acyltransterase-1 gene by interferon-gamma and all-trans-retinoic acid THP-1 cells

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) is an intracellular enzyme involved in cellular cholesterol homeostasis and in atherosclerotic foam cell formation. Human ACAT-1 gene contains two promoters (P1 and P7), each located in a different chromosome (1 and 7) (Li, B. L., Li, X. L., Duan, Z. J., Lee, O., Lin, S., Ma, Z. M., Chang, C. C., Yang, X. Y., Park, J. P., Mohandas, T. K., Noll, W., Chan, L., and Chang, T. Y. (1999) J. Biol Chem. 274, 11060-11071). Interferon-gamma (IFN-gamma), a cytokine that exerts many pro-atherosclerotic effects in vivo, causes up-regulation of ACAT-1 mRNA in human blood monocyte-derived macrophages and macrophage-like cells but not in other cell types. To examine the molecular nature of this observation, we identified within the ACAT-1 P1 promoter a 159-base pair core region. This region contains 4 Sp1 elements and an IFN-gamma activated sequence (GAS) that overlaps with the second Sp1 element. In the monocytic cell line THP-1 cell, the combination of IFN-gamma and all-trans-retinoic acid (a known differentiation agent) enhances the ACAT-1 P1 promoter but not the P7 promoter. Additional experiments showed that all-trans-retinoic acid causes large induction of the transcription factor STAT1, while IFN-gamma causes activation of STAT1 such that it binds to the GAS/Sp1 site in the ACAT-1 P1 promoter. Our work provides a molecular mechanism to account for the effect of IFN-gamma in causing transcriptional activation of ACAT-1 in macrophage-like cells.

All-trans-retinoic acid and polyriboinosinoic:polyribocytidylic acid cooperate to elevate anti-tetanus immunoglobulin G and immunoglobulin M responses in vitamin A-deficient lewis rats and Balb/c mice

Vitamin A (VA) deficiency compromises antibody responses to T-cell-dependent antigens such as tetanus toxoid, but this effect can be reversed through administration of retinol or retinoic acid (RA). To test whether RA and polyriboinosinioc : polyribocytidylic acid (PIC), a known inducer of several forms of interferon (IFN), can cooperate to increase specific immunoglobulin (Ig)G and IgM production during VA deficiency, rats and mice were made VA-deficient, immunized with TT and treated with all-trans-RA, PIC or their combination. VA-deficient rats produced low primary and secondary anti-tetanus IgG responses (VA-deficient controls v. VA-sufficient controls P < 0.001), although total IgG was slightly elevated when compared with VA-sufficient control rats. Although RA administered alone elevated antibody production during VA deficiency to control levels, RA combined with PIC synergistically enhanced these responses (RA and PIC group v. all other groups P < 0.0001). In contrast, Balb/c mice maintained on a VA-deficient diet and immunized in a similar fashion showed no impairment in antigen-specific IgG levels, but treatment with a combination of RA and PIC still evoked an additive enhancement in antigen-specific antibody production. Additionally, RA and PIC administration to VA-sufficient mice resulted in elevated antibody responses, suggesting that this combination should be evaluated further for its immuno-stimulatory effects.

Interferon-alpha and the pathogenesis of myeloproliferative disorders

Interferon-alpha (IFN-alpha), a molecule with multiple biological actions, is widely used in the treatment of chronic myelogenous leukemia (CML) and the other myeloproliferative disorders. This glycoprotein belonging to the type I subfamily of interferons has been recombinantly manufactured and has been approved for the biotherapy of CML, now becoming the first line of treatment for CML patients in chronic phase who are not candidates for allogeneic hematopoietic stem cell or bone marrowtransplantation. Interferon-alpha action involves binding to its cell membrane receptor and initiation of an intracellular signal transduction cascade. Two major pathways mediate the biologic actions of IFN-alpha. The JAK-STAT pathway leads to phosphorylation and activation of STAT 1 and STAT 2 molecules and transcription of genes like p21 and caspase-1 resulting in cycle arrest and apoptosis. The PKR (protein kinase dsRNA-induced) kinase phosphorylates and inhibits the eukaryotic initiator of translation eIF-2alpha leading again to apoptosis. The PKR kinase cascade also leads to activation of the transcription factor NF-kappaB. The relevance of this activation is unclearand it is possiblethat NF-kappaB has not had the opportunity to transcribe its target genes as it is a substrate of effector caspases and is maybe cleaved by them before exerting any transcription activity. Through the JAK-STAT and the PKR kinase pathways IFN-alpha is able to modify the proliferative and antiapoptotic actions of the constitutively activated kinase bcr-abl, the product of the t(9;22) translocation present in CML, and has therapeutic effects in this disease.

Phosphorylation-deficient Stat1 inhibits retinoic acid–induced differentiation and cell cycle arrest in U-937 monoblasts

All-trans retinoic acid (ATRA) is a potent inducer of terminal differentiation of immature leukemic cell lines in vitro and of acute promyelocytic leukemia (APL) cells in vivo. Recent reports have shown that ATRA induces the expression of several interferon-regulated genes, including signal transducer and activator of transcription (Stat)1. To investigate the role of Stat1 activation in ATRA signaling, sublines were established for the human monoblastic cell line U-937 constitutively expressing wild-type or phosphorylation-defective Stat1, mutated in the conserved tyrosine 701 required for dimerization and nuclear translocation. Results showed that ATRA induction leads to activation of Stat1 by the phosphorylation of tyrosine 701 and subsequent nuclear translocation. Consistent with a functional importance of this activation, ectopic expression of Stat1Y701F suppressed ATRA-induced morphologic differentiation and expression of the monocytic surface markers CD11c and the granulocyte colony-stimulating factor receptor. Moreover, ATRA-induced growth arrest in the G0/G1phase of the cell cycle was inhibited by phosphorylation-deficient Stat1. Taken together, these results indicate that Stat1 is a key mediator of ATRA-induced cell cycle arrest and differentiation of U-937 cells.

Phosphorylation-deficient Stat1 inhibits retinoic acid–induced differentiation and cell cycle arrest in U-937 monoblasts

All-trans retinoic acid (ATRA) is a potent inducer of terminal differentiation of immature leukemic cell lines in vitro and of acute promyelocytic leukemia (APL) cells in vivo. Recent reports have shown that ATRA induces the expression of several interferon-regulated genes, including signal transducer and activator of transcription (Stat)1. To investigate the role of Stat1 activation in ATRA signaling, sublines were established for the human monoblastic cell line U-937 constitutively expressing wild-type or phosphorylation-defective Stat1, mutated in the conserved tyrosine 701 required for dimerization and nuclear translocation. Results showed that ATRA induction leads to activation of Stat1 by the phosphorylation of tyrosine 701 and subsequent nuclear translocation. Consistent with a functional importance of this activation, ectopic expression of Stat1Y701F suppressed ATRA-induced morphologic differentiation and expression of the monocytic surface markers CD11c and the granulocyte colony-stimulating factor receptor. Moreover, ATRA-induced growth arrest in the G0/G1phase of the cell cycle was inhibited by phosphorylation-deficient Stat1. Taken together, these results indicate that Stat1 is a key mediator of ATRA-induced cell cycle arrest and differentiation of U-937 cells.

Retinoic acid and polyriboinosinic acid act synergistically to enhance the antibody response to tetanus toxoid during vitamin A deficiency: possible involvement of interleukin-2 receptor-beta, signal transducer and activator of transcription-1, and interferon regulatory factor-1

Antibody responses to T cell-dependent antigens are reduced during vitamin A (VA) deficiency and restored by retinoids. To test whether retinoic acid (RA) and polyinosinic:polycytidylic acid (PIC), an inducer of interferons, can increase specific antibody production, VA-deficient rats were treated with all-trans-RA, PIC, or both at the time of primary immunization with tetanus toxoid. VA-deficient rats produced low primary and secondary anti-tetanus IgG responses (P<.001 vs. VA-sufficient controls). Both responses were increased synergistically by RA plus PIC (P<.0001). In VA-deficient spleens, mRNAs were low for interleukin (IL)-2 receptor-beta, interferon regulatory factor-1, and signal transducer and activator of transcription 1. Each, however, was induced by RA plus PIC (P<.0001 vs. controls). Conversely, IL-12 and IL-10 mRNAs were elevated in VA deficiency and were induced by PIC and suppressed by RA. Thus, RA plus PIC appears to be a promising combination for stimulating antigen-specific immunity. Several molecular factors identified here may partially account for the observed enhancement.

Regulation of CD26/DPPIV gene expression by interferons and retinoic acid in tumor B cells

Interferons (IFNs alpha, beta and gamma) and all trans retinoic acid (RA) have the ability to activate genes with GAS sites. We have found that the promoter of CD26/dipeptidylpeptidase IV (DPPIV) contains a consensus GAS site TTCnnnGAA located at bp-35 to -27, and computer analysis confirmed this sequence to be a putative Stat binding site. Consistent with this finding, we show that IFNs and RA rapidly enhanced CD26 gene and protein expression in chronic B lymphocytic leukemia (B-CLL) cells. Immunoblot analyses revealed that unstimulated B-CLL cells expressed detectable levels of serine/tyrosine-phosphorylated Stat1alpha, and RA and IFN-gamma treatment led to increased levels of tyrosine phosphorylation of Stat1alpha and its nuclear accumulation. As shown by electrophoretic mobility shift assay, RA and IFN-gamma increased the binding of a nuclear protein to the GAS-CD26 element. Shift-Western blotting identified Stat1alpha as the GAS-CD26 binding factor. Augmented levels of CD26 protein in malignant B cells cultured with IFNs or RA coincided with the enhancement of DPPIV activity. Taken together, our results are in favor of the IFN-/RA-mediated upregulation of CD26/DPPIV in B-CLL through the signaling pathway involving Stat1alpha and the GAS response element of CD26 promoter.

Association of some potential hormone response elements in human genes with the Alu family repeats

Short interspersed repeats of the Alu family located in promoters of some human genes contain high-affinity binding sites for thyroid hormone receptor, retinoic acid receptor and estrogen receptor. The standard binding sites for the receptors represent variants of duplicated AGGTCA motif with different spacing and orientation (direct, DR, or inverted, IR), and Alu sequences were found to have functional DR-4, DR-2 or variant IR-3/IR-17 elements. In this study we analyzed distribution and abundance of the elements in a set of human genomic sequences from GenBank and their association with Alu repeats. Our results indicate that a major fraction of potentially active DR-4, DR-2 and variant IR-3/IR-17 elements in the genes is located within Alu repeats. Alu-associated DR-2 elements are conserved in primate evolution. However, very few Alu have potential DR-3 glucocorticoid-response elements. Gel-shift experiments with the probe (AUB) corresponding to the consensus Alu sequence just upstream of the RNA polymerase III promoter B-box and containing duplicated AGGTCA motif indicate that the probe interacts in a sequence-specific manner with human nuclear proteins which bind to standard IR-0, DR-1, DR-4 or DR-5 elements. The AUB sequence was also able to promote thyroid hormone-dependent trans-activation of a reporter gene. The results support the view that Alu retroposons played an important role in evolution of regulation of the primate gene expression by nuclear hormone receptors.

Inhibition of myeloma cell growth by all-trans retinoic acid is associated with upregulation of p21WAF1 and dephosphorylation of the retinoblastoma protein

Retinoic acid and dexamethasone, in combination, inhibit the growth of human myeloma cell lines in a synergistic manner. Previously, we observed that all-trans retinoic acid (ATRA) caused G1 arrest and inhibited clonogenic growth of the OPM-2 human myeloma cell line. This was associated with downregulation of the IL-6 receptor (IL-6R) gp80 protein, while autocrine IL-6 production and gp130 were not affected. Growth inhibition was not reversed by the addition of exogenous IL-6 or forced, constitutive expression of the IL-6 receptor gp80 protein, suggesting that the mechanism of action of ATRA may be due to effects on the post-receptor pathway. Therefore, in this study we have investigated whether growth arrest was associated with changes in the level of phosphorylation of the RB protein. ATRA decreased the level of phosphorylation of the RB protein at doses > 5 x 10(-9) M and also induced a five fold increase in p21WAF1, while levels of p27KIP1 and CDK2 were unchanged. The ATRA-mediated increase in p21 preceded the change in RB phosphorylation and G1 arrest and was not reversed by the addition of exogenous IL-6. The levels of CDK2 activity were inhibited approximately 60% in ATRA-treated cells, suggesting that the increased p21 levels were sufficient to inhibit CDK activity and cause RB hypophosphorylation. Increased levels of p21 have recently been observed in human myeloma cells exposed to dexamethasone, and we suggest that the common ability of these two agents to inhibit myeloma cell growth depends on their induction of p21.