Myeloid differentiation (MyD) primary response genes in hematopoiesis

Spatially resolved deconvolution of the fibrotic niche in lung fibrosis

A defining pathological feature of human lung fibrosis is localized tissue heterogeneity, which challenges the interpretation of transcriptomic studies that typically lose spatial information. Here we investigate spatial gene expression in diagnostic tissue using digital profiling technology. We identify distinct, region-specific gene expression signatures as well as shared gene signatures. By integration with single-cell data, we spatially map the cellular composition within and distant from the fibrotic niche, demonstrating discrete changes in homeostatic and pathologic cell populations even in morphologically preserved lung, while through ligand-receptor analysis, we investigate cellular cross-talk within the fibrotic niche. We confirm findings through bioinformatic, tissue, and in vitro analyses, identifying that loss of NFKB inhibitor zeta in alveolar epithelial cells dysregulates the TGFβ/IL-6 signaling axis, which may impair homeostatic responses to environmental stress. Thus, spatially resolved deconvolution advances understanding of cell composition and microenvironment in human lung fibrogenesis.

Deciphering molecular heterogeneity in pediatric AML using a cancer vs. normal transcriptomic approach

BACKGROUND

Still 30-40% of pediatric acute myeloid leukemia (pedAML) patients relapse. Delineation of the transcriptomic profile of leukemic subpopulations could aid in a better understanding of molecular biology and provide novel biomarkers.

METHODS

Using microarray profiling and quantitative PCR validation, transcript expression was measured in leukemic stem cells (LSC, n = 24) and leukemic blasts (L-blast, n = 25) from pedAML patients in comparison to hematopoietic stem cells (HSCs, n = 19) and control myeloblasts (C-blast, n = 20) sorted from healthy subjects. Gene set enrichment analysis was performed to identify relevant gene set enrichment signatures, and functional protein associations were identified by STRING analysis.

RESULTS

Highly significantly overexpressed genes in LSC and L-blast were identified with a vast majority not studied in AML. CDKN1A, CFP, and CFD (LSC) and HOMER3, CTSA, and GADD45B (L-blast) represent potentially interesting biomarkers and therapeutic targets. Eleven LSC downregulated targets were identified that potentially qualify as tumor suppressor genes, with MYCT1, PBX1, and PTPRD of highest interest. Inflammatory and immune dysregulation appeared to be perturbed biological networks in LSC, whereas dysregulated metabolic profiles were observed in L-blast.

CONCLUSION

Our study illustrates the power of taking into account cell population heterogeneity and reveals novel targets eligible for functional evaluation and therapy in pedAML.

IMPACT

Novel transcriptional targets were discovered showing a significant differential expression in LSCs and blasts from pedAML patients compared to their normal counterparts from healthy controls. Deregulated pathways, including immune and metabolic dysregulation, were addressed for the first time in children, offering a deeper understanding of the molecular pathogenesis. These novel targets have the potential of acting as biomarkers for risk stratification, follow-up, and targeted therapy. Multiple LSC-downregulated targets endow tumor suppressor roles in other cancer entities, and further investigation whether hypomethylating therapy could result into LSC eradication in pedAML is warranted.

Activator protein-1 transactivation of the major immediate early locus is a determinant of cytomegalovirus reactivation from latency

Human cytomegalovirus (HCMV) is a ubiquitous pathogen that latently infects hematopoietic cells and has the ability to reactivate when triggered by immunological stress. This reactivation causes significant morbidity and mortality in immune-deficient patients, who are unable to control viral dissemination. While a competent immune system helps prevent clinically detectable viremia, a portrait of the factors that induce reactivation following the proper cues remains incomplete. Our understanding of the complex molecular mechanisms underlying latency and reactivation continues to evolve. We previously showed the HCMV-encoded G protein-coupled receptor US28 is expressed during latency and facilitates latent infection by attenuating the activator protein-1 (AP-1) transcription factor subunit, c-fos, expression and activity. We now show AP-1 is a critical component for HCMV reactivation. Pharmacological inhibition of c-fos significantly attenuates viral reactivation. In agreement, infection with a virus in which we disrupted the proximal AP-1 binding site in the major immediate early (MIE) enhancer results in inefficient reactivation compared to WT. Concomitantly, AP-1 recruitment to the MIE enhancer is significantly decreased following reactivation of the mutant virus. Furthermore, AP-1 is critical for derepression of MIE-driven transcripts and downstream early and late genes, while immediate early genes from other loci remain unaffected. Our data also reveal MIE transcripts driven from the MIE promoter, the distal promoter, and the internal promoter, iP2, are dependent upon AP-1 recruitment, while iP1-driven transcripts are AP-1-independent. Collectively, our data demonstrate AP-1 binding to and activation of the MIE enhancer is a key molecular process controlling reactivation from latency.

Gadd45β promotes regeneration after injury through TGFβ-dependent restitution in experimental colitis

Dysregulated immune responses and impaired function in intestinal epithelial cells contribute to the pathogenesis of inflammatory bowel disease (IBD). Growth arrest and DNA damage-inducible 45 beta (Gadd45β) has been implicated in the pathogenesis of various inflammatory symptoms. However, the role of Gadd45β in IBD is completely unknown. This study aimed to evaluate the role of Gadd45β in IBD. Gadd45β-KO mice exhibited drastically greater susceptibility to dextran sulfate sodium (DSS)-induced colitis and mortality than C57BL/6J mice. Bone marrow transplantation experiments revealed that Gadd45β functions predominantly in the intestinal epithelium and is critical during the recovery phase. Gadd45β regulates the TGF-β signaling pathway in colon tissue and epithelial cells by inhibiting Smurf-mediated degradation of TGF-β receptor type 1 via competitive binding to the N-terminal domain of Smad7. Furthermore, these results indicate that the Gadd45β-regulated TGF-β signaling pathway is involved in wound healing by enhancing epithelial restitution. These results expand the current understanding of the function of Gadd45β and its therapeutic potential in ulcerative colitis.

A signaling molecule that prevents inflammatory damage in an animal model of ulcerative colitis offers a promising therapeutic target. The molecular drivers of this form of inflammatory bowel disease remain poorly understood, but the associated damage to the intestinal epithelium is primarily due to uncontrolled immune cell activity. Jung Hwan Hwang of the Korea Research Institute of Bioscience and Biotechnology, Daejeon, and coworkers have now demonstrated that a protein called Gadd45β helps to reduce inflammatory damage to the epithelial barrier. They showed that a mouse model of chemically induced ulcerative colitis exhibited more severe disease symptoms and higher mortality when these animals also lacked Gadd45β. This protein is generally known to modulate immune cell activity response, but in this disease model, the authors primarily observed activity within intestinal epithelial cells, where it appears to facilitate wound healing.

MyD88 is an essential component of retinoic acid-induced differentiation in human pluripotent embryonal carcinoma cells

We have previously reported that myeloid differentiation primary response gene 88 (MyD88) is downregulated during all-trans retinoic acid (RA)-induced differentiation of pluripotent NTera2 human embryonal carcinoma cells (hECCs), whereas its maintained expression is associated with RA differentiation resistance in nullipotent 2102Ep hECCs. MyD88 is the main adapter for toll-like receptor (TLR) signalling, where it determines the secretion of chemokines and cytokines in response to pathogens. In this study, we report that loss of MyD88 is essential for RA-facilitated differentiation of hECCs. Functional analysis using a specific MyD88 peptide inhibitor (PepInh) demonstrated that high MyD88 expression in the self-renewal state inhibits the expression of a specific set of HOX genes. In NTera2 cells, MyD88 is downregulated during RA-induced differentiation, a mechanism that could be broadly replicated by MyD88 PepInh treatment of 2102Ep cells. Notably, MyD88 inhibition transitioned 2102Ep cells into a stable, self-renewing state that appears to be primed for differentiation upon addition of RA. At a molecular level, MyD88 inhibition combined with RA treatment upregulated HOX, RA signalling and TLR signalling genes. These events permit differentiation through a standard downregulation of Oct4-Sox2-Nanog mechanism. In line with its role in regulating secretion of specific proteins, conditioned media experiments demonstrated that differentiated (MyD88 low) NTera2 cell media was sufficient to differentiate NTera2 cells. Protein array analysis indicated that this was owing to secretion of factors known to regulate angiogenesis, neurogenesis and all three branches of TGF-β Superfamily signalling. Collectively, these data offer new insights into RA controlled differentiation of pluripotent cells, with notable parallels to the ground state model of embryonic stem cell self-renewal. These data may provide insights to facilitate improved differentiation protocols for regenerative medicine and differentiation-therapies in cancer treatment.

Kaposi's Sarcoma-Associated Herpesvirus MicroRNAs Target GADD45B To Protect Infected Cells from Cell Cycle Arrest and Apoptosis

Kaposi's sarcoma is one of the most common malignancies in HIV-infected individuals. The responsible agent, Kaposi's sarcoma-associated herpesvirus (KSHV; HHV8), expresses multiple microRNAs (miRNAs), but the targets and functions of these miRNAs are not completely understood. After infection in primary endothelial cells with KSHV, growth arrest DNA damage-inducible gene 45 beta (GADD45B) is one of the most repressed genes using genomic expression profiling. GADD45B was also repressed in mRNA expression profiling experiments when KSHV miRNAs were introduced to uninfected cells. We hypothesized that KSHV miRNAs target human GADD45B to protect cells from consequences of DNA damage, which can be triggered by viral infection. Expression of GADD45B protein is induced by the p53 activator, Nutlin-3, and KSHV miRNA-K9 inhibits this induction. In addition, Nutlin-3 increased apoptosis and cell cycle arrest based on flow cytometry assays. KSHV miR-K9 protected primary endothelial cells from apoptosis and cell cycle arrest following Nutlin-3 treatment. Similar protective phenotypes were seen for targeting GADD45B with short interfering RNAs (siRNAs), as with miR-K9. KSHV miR-K9 also decreased the protein levels of cleaved caspase-3, cleaved caspase-7, and cleaved poly(ADP-ribose) polymerase (PARP). In B lymphocytes latently infected with KSHV, specific inhibitors of KSHV miR-K9 led to increased GADD45B expression and apoptosis, indicating that miR-K9 is important for reducing apoptosis in infected cells. Furthermore, ectopic expression of GADD45B in KSHV-infected cells promoted apoptosis. Together, these results identify a new miRNA target and demonstrate that KSHV miRNAs are important for protecting infected cells from DNA damage responses.

IMPORTANCE

Kaposi's sarcoma-associated herpesvirus is a leading cause of cancers in individuals with AIDS. Promoting survival of infected cells is essential for maintaining viral infections. A virus needs to combat various cellular defense mechanisms designed to eradicate the viral infection. One such response can include DNA damage response factors, which can promote an arrest in cell growth and trigger cell death. We used a new approach to search for human genes repressed by small nucleic acids (microRNAs) expressed by a gammaherpesvirus (KSHV), which identified a gene called GADD45B as a target of microRNAs. Repression of GADD45B, which is expressed in response to DNA damage, benefited survival of infected cells in response to a DNA damage response. This information could be used to design new treatments for herpesvirus infections.

Differential DNA Methylation Analysis without a Reference Genome

Genome-wide DNA methylation mapping uncovers epigenetic changes associated with animal development, environmental adaptation, and species evolution. To address the lack of high-throughput methods for DNA methylation analysis in non-model organisms, we developed an integrated approach for studying DNA methylation differences independent of a reference genome. Experimentally, our method relies on an optimized 96-well protocol for reduced representation bisulfite sequencing (RRBS), which we have validated in nine species (human, mouse, rat, cow, dog, chicken, carp, sea bass, and zebrafish). Bioinformatically, we developed the RefFreeDMA software to deduce ad hoc genomes directly from RRBS reads and to pinpoint differentially methylated regions between samples or groups of individuals (http://RefFreeDMA.computational-epigenetics.org). The identified regions are interpreted using motif enrichment analysis and/or cross-mapping to annotated genomes. We validated our method by reference-free analysis of cell-type-specific DNA methylation in the blood of human, cow, and carp. In summary, we present a cost-effective method for epigenome analysis in ecology and evolution, which enables epigenome-wide association studies in natural populations and species without a reference genome.

Phosphorylation of Atg5 by the Gadd45β-MEKK4-p38 pathway inhibits autophagy

Autophagy is a lysosomal degradation pathway important for cellular homeostasis, mammalian development, cancer and immunity. Many molecular components of autophagy have been identified, but little is known about regulatory mechanisms controlling their effector functions. Here, we show that, in contrast to other p38 MAP kinase activators, the growth arrest and DNA damage 45 beta (Gadd45β)-MAPK/ERK kinase kinase 4 (MEKK4) pathway specifically directs p38 to autophagosomes. This process results in an accumulation of autophagosomes through p38-mediated inhibition of lysosome fusion. Conversely, autophagic flux is increased in p38-deficient fibroblasts and Gadd45β-deficient cells. We further identified the underlying mechanism and demonstrate that phosphorylation of the autophagy regulator autophagy-related (Atg)5 at threonine 75 through p38 is responsible for inhibition of starvation-induced autophagy. Thus, we show for the first time that Atg5 activity is controlled by phosphorylation and, moreover, that the spatial regulation of p38 by Gadd45β/MEKK4 negatively regulates the autophagic process.

Batf promotes growth arrest and terminal differentiation of mouse myeloid leukemia cells

Batf is a basic leucine zipper transcription factor belonging to the activator protein-1 superfamily. Batf expression is regulated following stimulation of both lymphoid and myeloid cells. When treated with leukemia inhibitory factor, mouse M1 myeloid leukemia cells commit to a macrophage differentiation program that is dependent on Stat3 and involves the induction of Batf gene transcription via the binding of Stat3 to the Batf promoter. RNA interference was employed to block Batf induction in this system and the cells failed to growth arrest or to terminally differentiate. Restoring Batf expression not only reversed the differentiation-defective phenotype but also caused the cells to display signs of spontaneous differentiation in the absence of stimulation. Efforts to define genetic targets of the Batf transcription factor in M1 cells led to the identification of c-myb, a proto-oncogene known to promote blood cell proliferation and to inhibit the differentiation of M1 cells. These results provide strong evidence that Batf mediates the differentiation-inducing effects of Stat3 signaling in M1 cells and suggest that Batf may play a similar role in other blood cell lineages where alterations to the Jak-Stat pathway are hallmarks of disrupted development and disease.

Blood fluke exploitation of non-cognate CD4+ T cell help to facilitate parasite development

Schistosoma blood flukes, which infect over 200 million people globally, co-opt CD4⁺ T cell-dependent mechanisms to facilitate parasite development and egg excretion. The latter requires Th2 responses, while the mechanism underpinning the former has remained obscure. Using mice that are either defective in T cell receptor (TCR) signaling or that lack TCRs that can respond to schistosomes, we show that naïve CD4⁺ T cells facilitate schistosome development in the absence of T cell receptor signaling. Concurrently, the presence of naïve CD4⁺ T cells correlates with both steady-state changes in the expression of genes that are critical for the development of monocytes and macrophages and with significant changes in the composition of peripheral mononuclear phagocyte populations. Finally, we show that direct stimulation of the mononuclear phagocyte system restores blood fluke development in the absence of CD4⁺ T cells. Thus we conclude that schistosomes co-opt innate immune signals to facilitate their development and that the role of CD4⁺ T cells in this process may be limited to the provision of non-cognate help for mononuclear phagocyte function. Our findings have significance for understanding interactions between schistosomiasis and other co-infections, such as bacterial infections and human immunodeficiency virus infection, which potently stimulate innate responses or interfere with T cell help, respectively. An understanding of immunological factors that either promote or inhibit schistosome development may be valuable in guiding the development of efficacious new therapies and vaccines for schistosomiasis.

Schistosomes, or blood flukes, cause a debilitating illness in millions of people worldwide, which manifests when inflammation develops in response to parasite eggs that become trapped in the liver and other organs. Paradoxically, schistosomes require signals from the host's immune system in order to develop fully into egg-producing adults. Previously, we showed that CD4⁺ T cells facilitate schistosome development. Here, we show that the mere presence of CD4⁺ T cells is sufficient for schistosome development to proceed. There is no requirement for these cells to respond to the parasite, or to exhibit any typical “effector” response. Two pieces of data suggest this effect on parasite development is mediated by antigen-presenting cells of the innate immune system such as monocytes and macrophages, which interact with CD4⁺ T cells by expressing MHC class II molecules. First, the presence of naïve CD4⁺ T cells correlates with baseline changes in the development of monocyte/macrophage populations. Second, direct stimulation of the monocyte-macrophage system restores parasite development, bypassing the requirement for CD4⁺ T cells in schistosome development. Understanding the mechanisms that promote or inhibit blood fluke infection may facilitate the development of new treatments and vaccines for schistosomiasis.

Interferon regulatory factors in hematopoietic cell differentiation and immune regulation

Members of the interferon regulatory factor (IRF) family are transcription factors implicated in the regulation of a variety of biological processes. Originally identified as intracellular mediators of the induction and biological activities of interferons, their central role in host resistance to pathogens has recently been confirmed by the recognition of their involvement in the regulation of gene expression in responses triggered by Toll-like receptors and other pattern recognition receptors (PRRs). Their function in regulating the development as well as the activity of hematopoietic cells puts them at the interface between innate and adaptive immune responses. IRFs also regulate cell growth and apoptosis in several cell types, thereby affecting susceptibility to and the progression of cancer. In this review the role of some members of the family more deeply involved in the differentiation of hematopoietic cells and in immune regulation is addressed, with a specific focus on T cells and dendritic cells.

Lack of MyD88 protects the immunodeficient host against fatal lung inflammation triggered by the opportunistic bacteria Burkholderia cenocepacia

Burkholderia cenocepacia is an opportunistic pathogen of major concern for cystic fibrosis patients as well as immunocompromised cancer patients and transplant recipients. The mechanisms by which B. cenocepacia triggers a rapid health deterioration of the susceptible host have yet to be characterized. TLR and their key signaling intermediate MyD88 play a central role in the detection of microbial molecular patterns and in the initiation of an effective immune response. We performed a study to better understand the role of TLR-MyD88 signaling in B. cenocepacia-induced pathogenesis in the immunocompromised host, using an experimental murine model. The time-course of several dynamic parameters, including animal survival, bacterial load, and secretion of critical inflammatory mediators, was compared in infected and immunosuppressed wild-type and MyD88(-/-) mice. Notably, when compared with wild-type mice, infected MyD88(-/-) animals displayed significantly reduced levels of inflammatory mediators (including KC, TNF-alpha, IL-6, MIP-2, and G-CSF) in blood and lung airspaces. Moreover, despite a higher transient bacterial load in the lungs, immunosuppressed mice deficient in MyD88 had an unexpected survival advantage. Finally, we showed that this B. cenocepacia-induced life-threatening infection of wild-type mice involved the proinflammatory cytokine TNF-alpha and could be prevented by corticosteroids. Altogether, our findings demonstrate that a MyD88-dependent pathway can critically contribute to a detrimental host inflammatory response that leads to fatal pneumonia.

Association of loss of heterozygosity with cytogenetic abnormalities in acute myeloid leukemia and myelodysplastic syndrome

Deletions on chromosomes 5 and 7 are frequently seen in myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). It is assumed that these deletions indicate loss of tumor suppressor genes on these chromosomes and until these tumor suppressor genes are identified, the functional consequences of these deletions and the molecular basis of these myeloid disorders cannot be completely understood. We evaluated loss of heterozygosity (LOH) in 44 patients (18 MDS and 26 AML, diagnosed according to WHO classification criteria) at diagnosis, using a four-microsatellite marker panel: an intragenic marker on the 7th intron of gene IRF-1 of the 5q31.1 region and three markers located inside the 7q31.1 region and correlated the LOH with karyotype abnormalities. The microsatellites chosen corresponded to chromosome regions frequently deleted in MDS/AML. The samples with Q (peak area) less than or equal to 0.50 were indicative of LOH. The percent of informative samples (i.e., heterozygous) for the intragenic microsatellite in gene IRF-1 and in loci D7S486, D7S515 and D7S522 were 66.6, 73.7, 75.5, and 48.8%, respectively. Cytogenetic abnormalities by G-banding were found in 36% (16/44) of the patients (2 of 18 MDS and 14 of 26 AML patients). We found a significantly positive association of the occurrence of LOH with abnormal karyotype (P < 0.05; chi-square test) and there were cases with LOH but the karyotype was normal (by G-banding). These data indicate that LOH in different microsatellite markers is possibly an event previous to chromosomal abnormalities in these myeloid neoplasias.

Sildenafil augments early protective transcriptional changes after ischemia in mouse myocardium

Recently, targeting cyclic-GMP specific phosphodiesterase-5 (PDE5) has attracted much interest in several cardiopulmonary diseases, in particular myocardial ischemia (MI). Although multiple mechanisms were postulated for these beneficial effects at cellular level, early transcriptional changes were unknown. The aim of present study was to examine gene expression profiles in response to MI after 24 h of ischemia in murine model and compare transcriptional modulation by sildenafil, a popular phosphodiesterase 5 (PDE5) inhibitor. Mice were divided into four groups: Control sham (C), Sildenafil sham (S), Control MI (CMI) and Sildenafil MI (SMI). Sildenafil was given at a dose of 0.7 mg/kg intraperitoneally 30 min before LAD occlusion. cDNA microarray analysis of peri-infarct tissue was done using a custom cloneset and employing a looped dye swap design. Replicate signals were median averaged and normalized using LOWESS algorithm. R/MAANOVA analysis was used and false discovery rate corrected permutation p-values <0.005 were employed as significance thresholds. 156 genes were identified as significantly regulated demonstrating fold difference >1.5 in at least one of the four groups. 52 genes were significantly upregulated in SMI compared to CMI. For a randomly chosen subset of genes (9), microarray data were confirmed through real time RT-PCR. The differentially expressed genes could be classified into following groups based on their function: phosphorylation/dephosphorylation, apoptosis, differentiation, ATP binding. Our results suggest that sildenafil treatment might regulate early genetic reprogramming strategy for preservation of the ischemic myocardium.

Gadd45 beta is a pro-survival factor associated with stress-resistant tumors

Tumors that acquire resistance against death stimuli constitute a severe problem in the context of cancer therapy. To determine genetic alterations that favor the development of stress-resistant tumors in vivo, we took advantage of polyclonal tumors generated after retroviral infection of newborn Elambda-MYC mice, in which the retroviral integration acts as a mutagen to enhance tumor progression. Tumor cells were cultivated ex vivo and exposed to gamma-irradiation prior to their transplantation into syngenic recipients, thereby providing a strong selective pressure for pro-survival mutations. Secondary tumors developing from stress-resistant tumor stem cells were analysed for retroviral integration sites to reveal candidate genes whose dysregulation confer survival. In addition to the gene encoding the antiapoptotic Bcl-x(L) protein, we identified the gadd45b locus to be a novel common integration site in these tumors, leading to enhanced expression. In accord with a thus far undocumented role of Gadd45beta in tumorigenesis, we showed that NIH3T3 cells overexpressing Gadd45beta form tumors in NOD/SCID mice. Interestingly and differently to other known 'classical' antiapoptotic factors, high Gadd45beta levels did not protect against MYC-, UV- or gamma-irradiation-induced apoptosis, but conferred a strong and specific survival advantage to serum withdrawal.

Insights into the structural basis of the GADD45beta-mediated inactivation of the JNK kinase, MKK7/JNKK2

NF-kappaB/Rel factors control programmed cell death (PCD), and this control is crucial to oncogenesis, cancer chemoresistance, and antagonism of tumor necrosis factor (TNF) alpha-induced killing. With TNFalpha, NF-kappaB-mediated protection involves suppression of the c-Jun-N-terminal kinase (JNK) cascade, and we have identified Gadd45beta, a member of the Gadd45 family, as a pivotal effector of this activity of NF-kappaB. Inhibition of TNFalpha-induced JNK signaling by Gadd45beta depends on direct targeting of the JNK kinase, MKK7/JNKK2. The mechanism by which Gadd45beta blunts MKK7, however, is unknown. Here we show that Gadd45beta is a structured protein with a predicted four-stranded beta-sheet core, five alpha-helices, and two acidic loops. Association of Gadd45beta with MKK7 involves a network of interactions mediated by its putative helices alpha3 and alpha4 and loops 1 and 2. Whereas alpha3 appears to primarily mediate docking to MKK7, loop 1 and alpha4-loop 2 seemingly afford kinase inactivation by engaging the ATP-binding site and causing conformational changes that impede catalytic function. These data provide a basis for Gadd45beta-mediated blockade of MKK7, and ultimately, TNFalpha-induced PCD. They also have important implications for treatment of widespread diseases.

Early growth response transcriptional regulators are dispensable for macrophage differentiation

Early growth response (Egr) proteins comprise a family of transcriptional regulators (Egr1-4) that modulate gene expression involved in the growth and differentiation of many cell types. In particular, Egr1 is widely believed to have an essential role in regulating monocyte/macrophage differentiation. However, Egr1-deficient mice have normal numbers of functional macrophages, an observation that has led to the hypothesis that other Egr proteins may compensate for Egr1 function in vivo. We examined whether other Egr transcription factors have a functionally redundant role in monocyte/macrophage differentiation. Egr1 and Egr3 expression was found to be induced in myeloid cells when they were differentiated into macrophages by treatment with M-CSF, whereas Egr2 was minimally induced and Egr4 was not detected. In either Egr1/Egr3 or Egr1/Egr2 double homozygous mutant mice, macrophage differentiation and function remained unimpaired. Additionally, the expression of molecules that broadly inhibit Egr function failed to block commitment to the monocytic lineage or inhibit the maturation of monocyte precursors. Finally, several hemopoietic growth factors were found to induce Egr gene expression, indicating that Egr gene expression is not cell lineage specific. Taken together, these results demonstrate that Egr transcription factors are neither essential for nor specific to monocyte/macrophage differentiation.

Oncolytic viruses and DNA-repair machinery: overcoming chemoresistance of gliomas

The current standard of care for malignant gliomas is surgical resection and radiotherapy followed by extended adjuvant treatment with the alkylating agent temozolomide. Temozolomide causes DNA damage, which induces cell death. Through changes in the DNA-repair machinery, glioma cells develop resistance to temozolomide, compromising the therapeutic effect of the drug. Oncolytic viruses, such as herpes simplex viruses and adenoviruses, are being introduced into clinical trials as a new treatment for this malignancy. Biological studies have revealed that these viruses use mechanisms to either inactivate (adenovirus) or take advantage of (herpes simplex virus) the cellular DNA-repair machinery to achieve productive replication. Adenoviruses express proteins from the early genes to either downregulate the damage-repair enzyme, O(6)-methylguanine-DNA methyltransferase, or degrade poly (ADP-ribose) polymerase or the Mre11-Rad50-NBS1 complex, which detects DNA strand breaks. Temozolomide enhances herpes simplex virus oncolysis by upregulating the DNA repair-related genes growth arrest DNA damage 34 and ribonucleotide reductase. The interactions between viruses and the DNA-repair machinery suggest that a combined temozolomide and viral therapy will overcome the limitations of a single therapy by diminishing chemoresistance or enhancing oncolysis. This hypothesis has been supported by promising findings from preclinical and clinical studies.

Effects of expression of p53 and Gadd45 on osmotic tolerance of renal inner medullary cells

The response of renal inner medullary (IM) collecting duct cells (mIMCD3) to high NaCl involves increased expression of Gadd45 and p53, both of which have important effects on growth and survival of the cells. However, mIMCD3 cells, being immortalized by SV40, proliferate rapidly, which is known to sensitize cells to high NaCl, whereas IM cells in situ proliferate very slowly and survive much higher levels of NaCl. In the present studies, we have examined the importance of Gadd45 and p53 for survival of normal IM cells in their usual high-NaCl environment by using more slowly proliferating second-passage mouse inner medullary epithelial (p2mIME) cells and comparing cells from wild-type and gene knockout mice. Acutely elevating NaCl (and/or urea) reduces Gadd45a, but increases Gadd45b and Gadd45g mRNA, depending on the mix of NaCl and urea and the rate of increase of osmolality. Nevertheless, p2mIME cells from Gadd45b−/−, Gadd45g−/−, and Gadd45bg−/− mice survive elevation of NaCl (or urea) essentially the same as do wild-type cells. p53−/− Cells do not tolerate as high a concentration of NaCl (or urea) as p53+/+ cells, but urinary concentrating ability of p53−/− mice is normal, as is the histology of inner medullas from p53−/− and Gadd45abg−/− mice. Thus although Gadd45 and p53 may play roles in osmotically stressed mIMCD3 cells, we do not find that their expression makes an important difference, either for Gadd45 in slower proliferating p2mIME cells or for Gadd45 or p53 in normal inner medullary epithelial cells in situ.

GADD45alpha is highly expressed in pancreatic ductal adenocarcinoma cells and required for tumor cell viability

Pancreatic ductal adenocarcinoma is one of the most common causes of cancer death in the western civilization. Recently, NF-kappaB has been shown to be activated in pancreatic ductal adenocarcinoma through constitutive activation of IkappaB kinase (IKK). Inhibition of NF-kappaB by a super-inhibitor of NF-kappaB--delta-N-IkappaBalpha--resulted in impaired proliferation and induction of apoptosis, suggesting an important role of NF-kappaB in pancreatic tumorigenesis. Downstream target genes of IkappaBalpha have not been elucidated in pancreatic ductal adenocarcinoma in detail. Using expression profiling by cDNA array analysis of pancreatic ductal adenocarcinoma cell lines stably transfected with super-IkappaBalpha, we identified GADD45alpha as a significant regulated gene. GADD45alpha is overexpressed in pancreatic ductal adenocarcinoma at the mRNA and protein level. Using RNAi we show that downregulation of GADD45alpha reduces proliferation and induces apoptosis in pancreatic cancer cells. These findings provide evidence that GADD45alpha contributes to pancreatic cancer cell proliferation and viability.

Trans-Repressive Effect of NUP98-PMX1 on PMX1-Regulated c-FOSGene through Recruitment of Histone Deacetylase 1 by FG Repeats

The formation of fusion genes between NUP98 and members of the HOX family represents a critical factor for the genesis of acute leukemia or acute transformation of chronic myeloid leukemia (CML). To gain insights into the molecular mechanisms underlying the leukemogenesis of NUP98-HOX fusion products, we cloned NUP98-PMX1 from a CML-blast crisis patient with t(1;11) as a secondary chromosomal translocation, and functionally studied the fusion products in detail through various molecular and protein biochemical assays. In addition to many interesting features, we have found that the NUP98-PMX1 fusion protein exerts a repressive effect on PMX1 or serum response factor-mediated c-FOS activation, probably through the recruitment of a common corepressor histone deacetylase 1 by FG domains of the NUP98-PMX1 fusion protein. Moreover, we have provided evidence that the FG domains of NUP98-PMX1 and two other NUP98-containing fusion proteins, i.e., NUP98-HOXA9 and NUP98-HOXC11, all exhibit dual binding ability to both CREB binding protein, a coactivator, and histone deacetylase 1, a corepressor. Accordingly, we have hypothesized that this dual binding activity is shared by most, if not all, NUP98-HOX-involved fusion proteins, enabling these fusion proteins to act as both trans-activators and trans-repressors, and contributing to the genesis of acute leukemia or acute transformation of CML.

Deletion of the genes encoding the type III secretion system and cytotoxic enterotoxin alters host responses to Aeromonas hydrophila infection

In our previous study, we deleted the gene encoding Aeromonas outer membrane protein B (AopB), a structural component of the type III secretion system (T3SS) from a cytotoxic enterotoxin gene (act)-minus diarrheal isolate SSU of Aeromonas hydrophila. Our laboratory also molecularly characterized the cytotoxic enterotoxin (Act), which is secreted by the bacterium utilizing the type II secretion system (T2SS). The act/aopB mutant exhibited significantly reduced cytotoxicity to cultured cells (e.g. RAW 264.7 murine macrophages and HT-29 human colonic epithelial cells) and was avirulent in mice. In this study, we developed additional A. hydrophila mutants in which T3SS-associated ascV and acrV genes were deleted, either individually or in combination with that of the act gene, to examine host-pathogen interactions. A significant reduction in the induction of inflammatory cytokines and chemokines was noted in the sera of mice infected with these mutants when compared to animals infected with wild-type (WT) A. hydrophila. After infection with the WT and act/aopB mutant, we performed microarray analyses on RNA from the above-mentioned murine macrophages and human colonic epithelial cells to examine global cellular transcriptional responses. Based on three independent experiments, WT A. hydrophila altered the expression of 434 genes in RAW 264.7 cells and 80 genes in HT-29 cells. Alteration in the expression of 209 macrophage and 32 epithelial cell genes was reduced when the act/aopB mutant was used, compared to when cells were infected with the WT bacterium, indicating the involvement of Act and/or AopB in transcriptional regulation of these genes. We verified up-regulation of 15 genes by real-time reverse transcriptase-polymerase chain reaction and confirmed A. hydrophila WT-versus mutant-induced production of cytokines/chemokines in supernatants from RAW 264.7 and HT-29 cells. This is the first description of host cell transcriptional responses to A. hydrophila infection.

The NF-κB-mediated control of the JNK cascade in the antagonism of programmed cell death in health and disease

NF-kappaB/Rel transcription factors have recently emerged as crucial regulators of cell survival. Activation of NF-kappaB antagonizes programmed cell death (PCD) induced by tumor necrosis factor-receptors (TNF-Rs) and several other triggers. This prosurvival activity of NF-kappaB participates in a wide range of biological processes, including immunity, lymphopoiesis and development. It is also crucial for pathogenesis of various cancers, chronic inflammation and certain hereditary disorders. This participation of NF-kappaB in survival signaling often involves an antagonism of PCD triggered by TNF-R-family receptors, and is mediated through a suppression of the formation of reactive oxygen species (ROS) and a control of sustained activation of the Jun-N-terminal kinase (JNK) cascade. Effectors of this antagonistic activity of NF-kappaB on this ROS/JNK pathway have been recently identified. Indeed, further delineating the mechanisms by which NF-kappaB promotes cell survival might hold the key to developing new highly effective therapies for treatment of widespread human diseases.

In the Crosshairs: NF-κB Targets the JNK Signaling Cascade

NF-κB/Rel transcription factors are well-known for their roles in the regulation of inflammation and immunity. NF-κB also blocks programmed cell death (PCD) or apoptosis triggered by proinflammatory cytokine, tumor necrosis factor (TNF)α. Through transcriptional induction of distinct subsets of cyto-protective target genes, NF-κB inhibits the execution of apoptosis activated by this cytokine. This protective action is mediated, in part, by factors (such as A20, GADD45β, and XIAP) that downregulate the pro-apoptotic c-Jun-N-terminal (JNK) pathway. A suppression of reactive oxygen species (ROS), which are themselves major cell death-inducing elements activated by TNFα, is an additional protective function recently ascribed to NF-κB. This function of NF-κB involves an induction of mitochondrial anti-oxidant enzyme, manganese superoxide dismutase (Mn-SOD), and a control of cellular iron availability through upregulation of Ferritin heavy chain - one of two subunits of Ferritin, the major iron storage protein complex of the cell. An emerging view of NF-κB is that, while integrated, its actions in immunity and in promoting cell survival are executed through upregulation of distinct subsets of target genes. Thus, these inducible blockers of apoptosis may provide potential new targets to inhibit specific functions of NF-κB. In the future, this might allow for a better treatment of complex human diseases involving dysregulated NF-κB activity, including chronic inflammatory conditions and cancer.

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.

Glucocorticoids inhibit osteocalcin transcription in osteoblasts by suppressing Egr2/Krox20-binding enhancer

OBJECTIVE

Glucocorticoids are widely used for the management of rheumatoid arthritis. Osteoporosis is a major side effect of glucocorticoid therapy and is attributable to inhibition of bone formation. We developed an osteoblast culture system in which glucocorticoids strongly inhibit development of the osteoblast phenotype, including expression of the bone-specific osteocalcin (OC) gene. Using this gene as a model, the goal of this study was to discover glucocorticoid-sensitive transcriptional mechanisms in osteoblasts.

METHODS

Dexamethasone (DEX; 1 microM) was administered to murine MC3T3-E1 osteoblastic cultures under conditions that inhibit mineralized extracellular matrix formation and OC messenger RNA levels by >10-fold. Because standard (short-term) transient transfection assays with OC promoter-reporter constructs did not recapitulate the strong DEX-mediated repression, mapping of OC negative glucocorticoid response elements (GREs) was performed initially by stable transfection and then with long-term transient transfection assays. Transcription factor binding to the OC negative GRE was studied by electrophoretic mobility shift assays.

RESULTS

Several-fold repression of OC-luciferase constructs was recapitulated in stable and long-term transient transfection assays, in which the transfected cells were allowed to progress to a sufficiently advanced developmental stage. Analysis of a 5' promoter deletion series mapped an OC negative GRE to a 15-bp G/C-rich motif (-161/-147) located just upstream of the binding site for the osteoblast master transcription factor Runx2. Oligonucleotides encompassing this element and MC3T3-E1 cell extracts formed a protein-DNA complex that contained an Egr/Krox family member(s). Complex formation was competed by either an oligonucleotide containing 2 consensus Egr motifs or by anti-Egr2/Krox20 antibodies. Three copies of this Krox-binding element conferred 20-fold transcriptional activation on the 147-bp basal OC promoter in osteoblasts, and the enhancer activity was inhibited by DEX. Enhancer activity was not observed in 10T1/2 fibroblasts unless these cells were cotransfected with Runx2.

CONCLUSION

An Egr2/Krox20-binding site located immediately upstream of the Runx2 site of the mouse OC promoter was identified as an enhancer in osteoblasts, whose activity is repressed by glucocorticoids. Sequence similarity suggests that such a mechanism is likely operative in both murine and human cells. Because glucocorticoids inhibit Egr2/Krox20 expression in osteoblasts, and because trabecular bone formation is arrested in Egr2/Krox20-knockout mice, the inhibition of Egr2/Krox20 activity likely contributes to glucocorticoid-induced osteoporosis.

An Essential Role for IFN-α in the Overexpression of Fas Ligand on MRL/lpr Lymphocytes and on Their Spontaneous Fas-Mediated Cytotoxic Potential

Lymphocytes from aged autoimmune MRL/lpr mice overexpress Fas ligand (FasL), and are cytotoxic against Fas+ target cells. This cytotoxic potential is only partly due to FasL, as wild-type MRL+/+ lymphocytes are not able to kill Fas+ targets after induction of FasL. In addition, serum levels of interferon-alpha (IFN-alpha) increase in parallel with the Fas-dependent cytotoxic potential of lymphocytes from MRL/lpr mice as they age. To understand the mechanisms underlying these observations, combined suppression subtractive hybridization (SSH) and RT-PCR were used to study differential gene expression in splenocytes from MRL/lpr mice compared with splenocytes from MRL+/+ mice. Twenty-two genes were upregulated transcriptionally in MRL/lpr splenocytes compared with their MRL+/+ counterparts. Furthermore, 9 of these genes were also upregulated after treatment of MRL/lpr splenocytes with IFN-alpha, and 4 were strongly downregulated. MRL/lpr lymphocytes were also found to be hyperresponsive to IFN-alpha. Thus, MRL/lpr lymphocytes overexpressed mRNA for the IFN-alpha receptor (IFNAR-1 and IFNAR-2) chains of the IFN-alpha/beta receptor and exhibited high endogenous levels of both Stat1 and phosphorylated Stat1 proteins. Lymphocytes from young MRL/lpr mice, with low Fas-dependent cytotoxic activity, were found to become highly cytotoxic against Fas+ targets after treatment with IFN-alpha. These data suggest that IFN-alpha plays an important role in the physiopathology of the systemic lupus erythematosus (SLE)-like syndrome that occurs in MRL/lpr mice.

Microarray analysis of Aeromonas hydrophila cytotoxic enterotoxin-treated murine primary macrophages

We performed microarray analyses of murine peritoneal macrophages to examine cellular transcriptional responses to a cytotoxic enterotoxin of Aeromonas hydrophila. While 66% of altered genes were common to both primary macrophages and the murine macrophage cell line RAW 264.7, Act caused expression changes of 28 genes specifically in murine peritoneal macrophages.

Impaired myelopoiesis in mice devoid of interferon regulatory factor 1

Interferon regulatory factor (IRF)-1 is a transcription factor controlling the expression of several genes, which are differentially induced depending on the cell type and signal. IRF-1 modulates multiple functions, including regulation of immune responses and host defence, cell growth, cytokine signalling and hematopoietic development. Here, we investigated the role of IRF-1 in granulocytic differentiation in mice with a null mutation in the IRF-1 gene. We show that IRF-1(-/-) bone marrow cells exhibit an increased number of immature granulocytic precursors, associated with a decreased number of mature granulocytic elements as compared to normal mice, suggestive of a defective maturation process. Clonogenetic analyses revealed a reduced number of CFU-G, CFU-M and CFU-GM colonies in IRF-1(-/-) mice, while the number of BFU-E/CFU-E colonies was unchanged. At the molecular level, the expression of CAAT-enhancer-binding protein (C/EBP)-epsilon, -alpha and PU.1 was substantially lower in the CD11b(+) cells from the bone marrow of IRF-1(-/-) mice as compared to cells from wild-type mice. These results, together with the fact that IRF-1 is markedly induced early during granulo-monocytic differentiation of CD34+ cells, highlight the pivotal role of IRF-1 in the early phases of myelopoiesis.

Cigarette smoke condensate-induced transformation of normal human breast epithelial cells in vitro

In the present study, we showed that a single-dose treatment of normal breast epithelial cell line, MCF10A, for 72 h with cigarette smoke condensate (CSC) resulted in a transformed phenotype. The anchorage-dependent growth of these cells was decreased due to increased cell cycle arrest in S-G2/M phase; however, the surviving cells developed resistance due to an increased Bcl-xL to Bax ratio. Levels of PCNA and gadd45 proteins--involved in DNA repair in response to genomic damage--were increased, suggesting that the cells were responding to CSC-induced genomic damage. The transformation of MCF10A cells was determined by their colony-forming efficiency in soft-agar in an anchorage-independent manner. CSC-treated MCF10A cells efficiently formed colonies in soft-agar. We then re-established cell lines from the soft-agar colonies and further examined the persistence of their transforming characteristics. The re-established cell lines, when plated after 17 passages without CSC treatment, still formed colonies in the soft-agar. An increased staining of neuropilin-1 (NRP-1) further showed a transformation characteristic of MCF10A cells treated with CSC. In summary, our results suggest that CSC is capable of transforming the MCF10A cells in vitro, supporting the role of cigarette smoking and increased risk for breast cancer.

Fos modulates myeloid cell survival and differentiation and partially abrogates the c-Myc block in terminal myeloid differentiation

Previously, we have shown that Fos/Jun transcription factor complexes function as positive modulators of myeloid differentiation. Fos, which is stably induced during normal myeloid differentiation, is not induced upon differentiation of M1 myeloblastic leukemia cells. Establishing M1 cells that express a β-estradiol-conditional FosER chimera, we show that in the absence of the differentiation inducer interleukin-6 (IL-6), Fos expression in M1 myeloblasts promoted apoptotic cell death, entailing cytochrome c release and caspase-9 activation. In contrast, in the presence of IL-6, Fos-mediated apoptosis was abrogated, and Fos promoted terminal differentiation, increasing the sensitivity of M1 cells to be induced for differentiation by IL-6. Fos-mediated apoptosis was accelerated by deregulated c-Myc. Furthermore, restoring Fos expression in M1 partially abrogated the block imparted by deregulated c-Myc on the myeloid differentiation program, increased the sensitivity of the cells to be induced for differentiation, and curtailed their leukemic phenotype. These data provide evidence that Fos/Jun transcription factor complexes play a role in modulating both myeloid cell survival and differentiation and suggest that genetic lesions that alter Fos expression may cooperate with deregulated c-Myc in leukemogenesis. (Blood. 2004;103:4259-4267)

Mechanisms involved in the induced differentiation of leukemia cells

Despite the remarkable progress achieved in the treatment of leukemias over the last several years, many problems (multidrug resistance [MDR], cellular heterogeneity, heterogeneous molecular abnormalities, karyotypic instability, and lack of selective action of antineoplastic agents) still remain. The recent progress in tumor molecular biology has revealed that leukemias are likely to arise from disruption of differentiation of early hematopoietic progenitors that fail to give birth to cell lineage restricted phenotypes. Evidence supporting such mechanisms has been derived from studying bone marrow leukemiogenesis and analyzing differentiation of leukemic cell lines in culture that serve as models of erythroleukemic (murine erythroleukemia [MEL] and human leukemia [K562] cells) and myeloid (human promyelocytic leukemia [HL-60] cells) cell maturation. This paper reviews the current concepts of differentiation, the chemical/pharmacological inducing agents developed thus far, and the mechanisms involved in initiation of leukemic cell differentiation. Emphasis was given on commitment and the cell lineage transcriptional factors as key regulators of terminal differentiation as well as on membrane-mediated events and signaling pathways involved in hematopoietic cell differentiation. The developmental program of MEL cells was presented in considerable depth. It is quite remarkable that the erythrocytic maturation of these cells is orchestrated into specific subprograms and gene expression patterns, suggesting that leukemic cell differentiation represents a highly coordinated set of events that lead to irreversible growth arrest and expression of cell lineage restricted phenotypes. In MEL and other leukemic cells, differentiation appears to be accompanied by differentiation-dependent apoptosis (DDA), an event that can be exploited chemotherapeutically. The mechanisms by which the chemical inducers promote differentiation of leukemic cells have been discussed.

GADD34-PP1c recruited by Smad7 dephosphorylates TGFbeta type I receptor

The cascade of phosphorylation is a pivotal event in transforming growth factor β (TGFβ) signaling. Reversible phosphorylation regulates fundamental aspects of cell activity. TGFβ-induced Smad7 binds to type I receptor (TGFβ type I receptor; TβRI) functioning as a receptor kinase antagonist. We found Smad7 interacts with growth arrest and DNA damage protein, GADD34, a regulatory subunit of the protein phosphatase 1 (PP1) holoenzyme, which subsequently recruits catalytic subunit of PP1 (PP1c) to dephosphorylate TβRI. Blocking Smad7 expression by RNA interference inhibits association of GADD34–PP1c complex with TβRI, indicating Smad7 acts as an adaptor protein in the formation of the PP1 holoenzyme that targets TβRI for dephosphorylation. SARA (Smad anchor for receptor activation) enhances the recruitment PP1c to the Smad7–GADD34 complex by controlling the specific subcellular localization of PP1c. Importantly, GADD34–PP1c recruited by Smad7 inhibits TGFβ-induced cell cycle arrest and mediates TGFβ resistance in responding to UV light irradiation. The dephosphorylation of TβRI mediated by Smad7 is an effective mechanism for governing negative feedback in TGFβ signaling.

Gadd45beta is important for perpetuating cognate and inflammatory signals in T cells

Gadd45beta (growth arrest and DNA damage-inducible, beta) is involved in cell cycle arrest, apoptosis, signal transduction and cell survival. In T cells, Gadd45b was rapidly induced by T cell receptor (TCR) and inflammatory signals. Deficiency of Gadd45beta in CD4+ T cells impaired their responses to TCR stimulation or inflammatory cytokines. ERK, p38 and JNK activation were all substantially suppressed in Gadd45beta-deficient CD4+ T cells. Cytokine production by Gadd45beta-deficient CD4+ T cells was also impaired. Furthermore, Gadd45beta mediated inflammatory cytokine production by dendritic cells, and Gadd45beta-deficient mice showed an impaired T helper type 1 response during Listeria monocytogenes infection. Gadd45beta is therefore a critical feedback regulator that perpetuates both cognate and inflammatory signals.

Identification of Aeromonas hydrophila cytotoxic enterotoxin-induced genes in macrophages using microarrays

A cytotoxic enterotoxin (Act) of Aeromonas hydrophila possesses several biological activities, and it induces an inflammatory response in the host. In this study, we used microarrays to gain a global and molecular view of the cellular transcriptional responses to Act and to identify important genes up-regulated by this toxin. Total RNA was isolated at 0, 2, and 12 h from Act-treated macrophages and applied to Affymetrix MGU74 arrays, and the data were processed using a multi-analysis approach to identify genes that might be critical in the inflammatory process evoked by Act. Seventy-six genes were significantly and consistently up-regulated. Many of these genes were immune-related, and several were transcription factors, adhesion molecules, and cytokines. Additionally, we identified several apoptosis-associated genes that were significantly up-regulated in Act-treated macrophages. Act-induced apoptosis of macrophages was confirmed by annexin V staining and DNA laddering. Quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay were used to verify increased expression of some inflammatory and apoptosis-associated genes identified by the microarray analysis. To further confirm Act-induced increases in gene expression, real-time RT-PCR was also used for selected genes. Taken together, the array data provided for the first time a global view of Act-mediated signal transduction and clearly demonstrated an inflammatory response and apoptosis mediated by this toxin in host cells at the molecular level.

Regulation of the growth arrest and DNA damage-inducible gene 45 (GADD45) by peroxisome proliferator-activated receptor gamma in vascular smooth muscle cells

Peroxisome proliferator-activated receptor (PPAR) gamma is activated by thiazolidinediones (TZDs), widely used as insulin-sensitizing agents for the treatment of type 2 diabetes. TZDs have been shown to induce apoptosis in a variety of mammalian cells. In vascular smooth muscle cells (VSMCs), proliferation and apoptosis may be competing processes during the formation of restenotic and atherosclerotic lesions. The precise molecular mechanisms by which TZDs induce apoptosis in VSMCs, however, remain unclear. In the present study, we demonstrate that the TZDs rosiglitazone (RSG), troglitazone (TRO), and a novel non-TZD partial PPARgamma agonist (nTZDpa) induce caspase-mediated apoptosis of human coronary VSMCs. Induction of VSMC apoptosis correlated closely with an upregulation of growth arrest and DNA damage-inducible gene 45 (GADD45) mRNA expression and transcription, a well-recognized modulator of cell cycle arrest and apoptosis. Using adenoviral-mediated overexpression of a constitutively active PPARgamma mutant and the irreversible PPARgamma antagonist GW9662, we provide evidence that PPARgamma ligands induce caspase-mediated apoptosis and GADD45 expression through a receptor-dependent pathway. Deletion analysis of the GADD45 promoter revealed that a 153-bp region between -234 and -81 bp proximal to the transcription start site, containing an Oct-1 element, was crucial for the PPARgamma ligand-mediated induction of the GADD45 promoter. PPARgamma activation induced Oct-1 protein expression and DNA binding and stimulated activity of a reporter plasmid driven by multiple Oct-1 elements. These findings suggest that activation of PPARgamma can lead to apoptosis and growth arrest in VSMCs, at least in part, by inducing Oct-1-mediated transcription of GADD45. The full text of this article is available online at http://www.circresaha.org.

Hematopoietic stem cells and hematopoiesis

BACKGROUND

The highly orchestrated process of blood cell development and homeostasis is termed "hematopoiesis." Understanding the biology of hematopoietic stem cells as well as hematopoiesis is important to developing improved treatments for hematologic malignancies, congenital disorders, chemotherapy-related cytopenias, and blood and marrow transplants.

METHODS

The author reviews the current state of the art regarding hematopoietic stem cells and hematopoiesis.

RESULTS

Several new concepts, including stem cell plasticity, suggest the possibility that stem cells may have the ability to differentiate into other tissues in addition to blood cells.

CONCLUSIONS

While much is known about hematopoietic stem cells and hematopoiesis, much remains to be clarified about the environmental and genetic processes that govern the growth and development of the blood system. In addition, careful studies remain to be conducted to determine whether hematopoietic stem cells can differentiate into extra-hematopoietic tissues.